Biology PDF - Cell Theory & Structure

TOPIC 1 Cell theory - Living organisms are composed by cells (Or cell products) - The cell is the smallest unit of life - Cells exist due to pre-existing cells Cases that may not seem like but follow the cell theory: - Striated muscles are composed by multinucleated fused cel...

TOPIC 1 Cell theory - Living organisms are composed by cells (Or cell products) - The cell is the smallest unit of life - Cells exist due to pre-existing cells Cases that may not seem like but follow the cell theory: - Striated muscles are composed by multinucleated fused cells - Giant algae is a huge unicellular organism of a large size - Aseptate hyphae has a continuous cytoplasm and lacks partitioning Functions of life. Unicellular organisms can still perform: Metabolism Reproduction Sensitivity Homeostasis Excretion Nutrition Growth Cell size Surface area over volume ratio is important in the limitation of cell size in order to perform efficient material exchange - Small SA/volume ratio increases metabolic rate but decreases material exchange = less survival chances - Large SA/volume ratio decreases metabolic rate and increases material exchange = more survival chances Magnification (MIA) Actual size (AIM) 𝐼𝑚𝑎𝑔𝑒 𝑠𝑖𝑧𝑒 𝐼𝑚𝑎𝑔𝑒 𝑠𝑖𝑧𝑒 𝑀𝑎𝑔𝑛𝑖𝑓𝑖𝑐𝑎𝑡𝑖𝑜𝑛 = 𝐴𝑐𝑡𝑢𝑎𝑙 𝑠𝑖𝑧𝑒 𝐴𝑐𝑡𝑢𝑎𝑙 𝑠𝑖𝑧𝑒 = 𝑀𝑎𝑔𝑛𝑖𝑓𝑖𝑐𝑎𝑡𝑖𝑜𝑛 Percentage Change (𝑓𝑖𝑛𝑎𝑙 𝑚𝑎𝑠𝑠 − 𝑖𝑛𝑖𝑡𝑖𝑎𝑙 𝑚𝑎𝑠𝑠) % 𝑚𝑎𝑠𝑠 𝑐ℎ𝑎𝑛𝑔𝑒 = 𝑖𝑛𝑖𝑡𝑖𝑎𝑙 𝑚𝑎𝑠𝑠 𝑥 100% Microscopes Light microscopes: - Bend light - View living specimens in their natural color - Lower magnification and resolution Electromagnetic microscopes: - Focus on electrons - Only view dead specimens in monochrome - Higher magnification and resolution Cellular organization Cell → Tissue → Organ – System Emergent properties are present in multicellular organisms but not in the individual cells Arise from the interaction of individual cells to produce an aggregate function. For example, antibiotic resistance. Cell specialization Stem cells are unspecialized. 1. Self renewal: continuously divide and replicate 2. Potency: can be differentiated In human development they can be: Totipotent: can form any cell type, and also extraembryonic tissue. EMBRYONIC STEM CELLS Pluripotent: can form any cell type. EMBRYONIC STEM CELLS and FETAL.  Multipotent: can differentiate into closely related cell types. FETAL STEM CELLS and ADULT STEM CELLS. Unipotent: cannot differentiate but are capable of self renewal. Stem cell therapy: they can replace damaged or disease cells with healthy ones. We must take into account: - Harvest from appropriate sources - Suppressing the host immune system to prevent rejection - Monitoring new cells to prevent them from being cancerous Example Condition Treatment Stargardt’s disease Macular degeneration Replace defective retinal cells Parkinson’s disease Death of nerve tissue Replace damaged nerve cells Leukemia Cancer of the blood Replacement of bone marrow Source Growth Tumour risk Harvesting Disadvantages potential Embryo High High Regenerated Destruction of (pluripotent) artificially embryo Umbilical cord Low Low Easily obtained Cells must be blood (multipotent) and stored stored from birth at cost ($$$) Adult tissue Low Low Invasive to Restricted (multipotent) extract availability Differentiation: though all calls of an organism contain an identical genome, it involves the expression of some genes and not others in the cell’s genome. By activation of different genes within a given cell, it will differentiate from others. Gene packaging  - Heterochromatin are inactive and dark - Euchromatin are active and light colored. Prokaryotic structure ALL PROKARYOTES: - Lack nucleus - Have a singular and circular DNA molecule (genophore) - Peptidoglycan cell wall - 70s Ribosomes SOME MAY CONTAIN: - Pili: attachment or bacterial conjugation - Flagella: movement - Plasmids: autonomous DNA molecules Prokaryotic vs Eukaryotic: DORA Prokaryote Eukaryote DNA naked, circular bound to proteins, linear  Organelle no nucleus; 70s ribosomes nucleus; 80s ribosomes Reproduction binary fission; single mitosis/meiosis; paired chromosome chromosomes Average size smaller larger Bacterial cell division Prokaryotes divide through a type of asexual reproduction called binary fission. 1. Circular DNA is copies 2. DNA loops attach to the membrane 3. Cell elongates, which separates the loops 4. Cytokinesis occurs to form two cells. Eukaryotic cells Organelles: compartmentalized structures for specific purposes - 80s ribosomes: protein synthesis (translation) - nucleus: storage of genetic information (transcription) - Mitochondria: aerobic respiration (ATP production) - Endoplasmic reticulum: transports materials between organelles - Golgi apparatus: sorts, stores, modifies and exports secretory products - Centrosomes: involved in meiosis and mitosis  Animal cells Plant cells No chloroplast Chloroplast for photosynthesis Lysosome for breaking down No lysosome macromolecules No cell wall Cell wall (cellulose) No plasmodesmata Plasmodesmata Temporary vacuoles Large central vacuoles Cholesterol present in the cell membrane No cholesterol present in the cell membrane Glucose → Glycogen Glucose → Starch Membrane structure Phospholipid bilayer - Polar head and two nonpolar tails - Amphiphatic = hydrophilic + hydrophobic parts Arrangement in Membranes: - Spontaneous arrangement of phospholipids into the bilayer - Polar head faces out into the surrounding solution, nonpolar tail faces inwards and are shielded from polar fluids. Properties of the phospholipid bilayer: - Held together by weak hydrophobic interactions between the tails - Individual phospholipids can move within the bilayer (flexibility) - Semipermeable Cholesterol: fundamental component of animal cell membranes  - Not needed in plant cells because their cell wall is already rigid - Reduces membrane fluidity and permeability to solutes - Anchors peripheral proteins and prevents crystallization Membrane proteins’ functions: Junctions Enzymes Transport Recognition Anchorage Transduction Fluid Mosaic Models Cell membranes are represented as: – Fluid: membrane components can move positions – Mosaic: phospholipid bilayer is embedded with protein This model falsifies the DD model Membrane models When shown in an electron microscope, the membrane shows three distinct layers. DD proposed a model whereby a phospholipid bilayer was flanked by two protein layers. This model was falsified based on: - Fluorescent tagging which showed protein mobility - Protein ratio - Freeze fracturing identified transmembrane proteins Membrane transport Properties: - Semipermeable: only certain things can cross - Selective: membranes regulate material passage Types of membrane transport - Passive: with transportation gradient, no ATP required - Active: against transportation gradient, ATP required Passive transport - Simple diffusion: high to low concentration until equilibrium is reached. Involves small molecules. - Facilitated diffusion: movement of molecules across a cell membrane with a little help of membrane proteins. Involves large and charged molecules. - Osmosis: net of movement of water molecules across a semipermeable membrane from low solute to high solute concentration. Osmolarity: measure of solute concentration - Hypertonic: high solute concentration (Gains water) - Hypotonic: low solute concentration (Loses water) - Isotonic: same solute concentration (No net movement) Active transport: uses ATP to move molecules against a concentration gradient 1. Molecule binds to a transmembrane protein pump 2. Hydrolysis of ATP causes a conformational change, translocating the molecule across the membrane Sometimes we have co-transports: molecules passively coupled to an actively transported molecule - Symport: both molecules move the same direction - Antiport: molecules move in an opposite direction Vesicular transport: requires ATP for the plasma membrane to break and reform around materials - Exocytosis: materials are released from a cell via vesicles - Endocytosis: materials internalized within the vesicle Origin of cells Abiogenesis: formation of living cells from nonliving material 1. Nonliving synthesis of simple organic molecules 2. Assembly of organic molecules into complex polymers 3. Formation of polymers that can self-replicate 4. Packaging of molecules into membranes to create an internal chemistry different from surroundings. The Miller-Urey experiment replicated the conditions of a pre-biotic Earth to synthesize organic molecules. Biogenesis: requires specific conditions to proceed - Reducing atmosphere (no Oxygen) - High temperatures or electrical discharges As these conditions no longer commonly exist on Earth, cells can only be formed by the division of preexisting cells. Thanks to Louis Pasteur we can model: 1. Heat: broth boiled to kill organisms - No growth: condensation seals the flask - Growth: break to expose contamination. THIS HAPPENED. Conclusion: cells only arise from preexisting cells Endosimbiosis: eukaryotic cells are believed to have evolved from aerobic prokaryotes that were engulfed by endocytosis. The engulfed cell remained undigested and contributed new functionality to the engulfing cell (like becoming an organelle). Prokaryote → Endosymbiosis → Eukaryote. Chloroplast and mitochondria arose vía endosymbiosis. Oxygenation of Earth: due to the appearance of photosynthetic organisms.  - Oceans: originally, earth;s oceans had high levels of dissolved iron. Oxygen chemically interacted with the iron to form an insoluble precipitate. - Rock deposition: insoluble iron formed banded iron formations. These deposits are not commonly found in round rocks. Here is when you can identify photosynthetic organisms that first evolved. - Atmosphere: when dissolved iron was completely consumed, oxygen started accumulating in the anoxic atmosphere. Cell division Cell cycle 1. Interphase: active phase where may metabolic reactions occur - G1: Growth and metabolism - S: Replication of DNA - G2: Growth and preparation 2. M Phase: division - Mitosis (P, M, A, T) and cytokinesis Interphase: as normal metabolism cannot occur during M phase, the following events must occur for cell division to occur: DNA replication (during S phase) Organelle reproduction Cell growth Transcription or translation Obtaining nutrients Respiration (at a cellular level) Supercoiling: during mitosis, chromatin condenses via supercoiling to become tightly packed chromosomes. Due to replication (S phase), chromosomes consist of identical sister chromatids joined at a centromere. Mitosis: division of a diploid nucleus into two genetically identical diploid nuclei. This process is necessary for: Tissue repair Organism growth Asexual reproduction Development of embryos Cytokinesis: cytoplasm division. Cell splits in tow. - Occurs in telophase Animals: - Microtubules form a concentric ring and contract towards the center (centripetal). Animals: - Vesicles form at the cell's center and fuse outwards to form a cell plate (centrifugal). Mitotic index: measures the proliferation of a cell population 𝐶𝑒𝑙𝑙𝑠 𝑖𝑛 𝑚𝑖𝑡𝑜𝑠𝑖𝑠 𝑀𝑖𝑡𝑜𝑡𝑖𝑐 𝐼𝑛𝑑𝑒𝑥 = 𝑇𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑐𝑒𝑙𝑙𝑠 Stages of Mitosis Interphase (2n) - DNA is condensed into chromatin - DNA is replicated (S phase) to form genetically identical sister chromatids - Cell grows in size and organelles are duplicated (G1 and G2) Prophase (2n) - DNA super coils and condenses (visible chromosomes) - Nuclear membrane dissolves - Centrosomes move to poles and begin to produce spindle fibers Metaphase (2n) - Centrosome spindle fibers attach to the centromere of each chromosome - Spindle fibers contract and move the chromosomes toward the cell center - Chromosomes form a line among the middle of the cell Anaphase (2n → 4n) - Spindle fibers continue to contract - Sister chromatids separate and move to opposite sides of the cell - Sister chromatids are now regarded as two separate chromosomes Telophase (4n) - Chromosomes decondense (DNA forms chromatin) - Nuclear membrane form around the two identical chromosome sets - Cytokinesis occurs concurrently Cytokinesis (2n x 2) - Cytoplasmic division occurs to divide the cell into two daughter cells - Each daughter cell contains one copy of each identical sister chromatid - Daughter cells are genetically identical Cell cycle regulation Checkpoints  G1: - monitors potential growth conditions - assessed level of DNA damage G2: - monitors state of pre-mitotic cell - identifies and repairs DNA replication errors Metaphase - ensures proper alignment Cyclings: proteins that control progression of the cell cycle - Bind to CDKs - Involved in a specific cell cycle event - After the event has occurred, the cyclin is degraded and the CDK is rendered inactive Cáncer: diseases caused by uncontrolled cell division. The resulting abnormal growth is a tumor. Tumor cells may remain in their original location (bening) or spread eventually and invade neighboring cells (malignant). Metastasis is the spread of cancer from an original site to a new body location (which forms the secondary tumor). Cancer development Mutagens: agents that change the genetic material of cells - Physical, chemical or biological in origin - Classified as carcinogens Genetics - Proto-oncogenes: stimulate cell growth and proliferation. Create cancer-causing oncogenes. - Tumor suppressor genes: repress cell cycle progression Cell death - Necrosis: uncontrolled “cell homicide” 1. Cell loses functional control due to injury, toxins, etc 2. Desensibilization of membranes, leading to swelling 3. Cell bursts and releases its content (causes inflammation) - Apoptosis: programmed “cell suicide” 1. Triggered by mitochondrial proteins 2. Cell contents are packaged in membranous protrusions 3. The cell fragments into apoptotic bodies which are recycled Smoking: positive correlation between the frequency of smoking and the incidence of cancer. Not causation. TOPIC 2 Molecular Biology Organic compounds Contains molecules that are only found in living organisms, with the exceptions of carbonates and oxides of carbon. - Carbon atoms form the basis of organic life due to their capacity to form covalent bonds. - Allows diversity of stable compounds to exist. Biomacromolecules - Carbs, lipids, proteins and nucleic acids. CLASS MONOMER POLYMER Carb Monosaccharide Polysaccharide  Protein Amino Acid Polypeptide Nucleic Acid Nucleotide DNA / RNA - Lipids are not composed of repeating monomers, but may contain smaller subunits. CLASS SUBUNIT Triglyceride Glycerol + 3 Fatty acids Anabolism CONSTRUYE - Simpler molecule join into complex molecules - Involves condensation reactions (water is produced) - F.E: photosynthesis Catabolism DESTRUYE - Complex molecules into simpler molecules - Hydrolysis reactions (water is consumed) - F.E: cellular respiration Vitalism: living organisms were thought to possess a “vital force” that was required to manufacture organic molecules. Doctrine that dictated that organic molecules could only be synthesized by living systems by a ‘vital force’. Falsification (1828) by Woehler. Artificially synthesized an organic molecule: - Heated an inorganic salt under laboratory conditions and produced urea (organic) Water Structure Made up of two hydrogen atoms COVALENTLY BONDED to one oxygen atom. Oxygen on top, hydrogens down. This is because Oxygen is more electronegative, which attracts the shared electrons and enhances polarity. Hydrogen bonding As water molecules are polar, they can form polar associations with other charged molecules (Polar or ionic). Can also form hydrogen bonds with other water molecules. Cohesive properties: form associations with molecules that share common properties - Cohesion: form hydrogen bonds with other water molecules. Results in high surface tension, can resist low level external forces. WATER ATTRACTED TO WATER. - Adhesion: form polar associations with charged molecules. Allows for potential capillary action (transpiration in plants). WATER ATTRACTED TO OTHER MOLECULES. Solvent properties Water is the universal solvent due to its capacity to dissolve a large number of substances as long as they are ionic or polar, they are hydrophilic. If they cannot dissolve in water, they are hydrophobic. Thermal properties Water can absorb large amounts of heat energy before changing in state. - High specific heat capacity. - Effective coolant - Evaporation of sweat requires absorption of water Other properties - Water is transparent, so light can get through during photosynthesis and vision - Water expands when frozen, so it's less dense. Therefore, ice floats and the oceans underneath don't freeze automatically. Water vs Methane Carbohydrates - Monosaccharides like glucose and ribose are used for short term energy storage - Polysaccharides can: - Be used for short term energy storage (glycogen) - Structural components (cellulose) - Recognition (glycoproteins) Types of polysaccharides Cellulose: component of plant cell wall - Linear molecule made of beta glucose subunits - Subunits bound in a 1-4 arrangement Starch: energy storage in plants - alpha glucose subunits. Can be in the form of - Amylose: linear 1-4 arrangement - Amylopectin: branched both 1-4 and 1-6 Energy storage Storage: lipids used for long term, carbs for short term Osmotic pressure: lipid is easier to store, carbs more difficult Digestion: carbs are easier to use, lipids more difficult ATP yield: lipids require more energy Solubility: lipids insoluble and harder to transport Body Mass Index (BMI) 2 𝐵𝑀𝐼 = 𝑀𝑎𝑠𝑠 (𝑘𝑔) % 𝐻𝑒𝑖𝑔ℎ𝑡 (𝑚) Lipids - Nonpolar organic molecules Storage of energy (triglycerides) Hormonal role (steroids) Insulation (thermal) Protection of organs Structural roles (cholesterol) Triglycerides: long term energy storage Fatty acids: hydrocarbon chains found in certain lipids - Saturated: no double bonds in the hydrocarbon chain Generally solid at room temperature - Unsaturated: double bonds Generally liquid at room temperature - Cis: H atoms on same side Generally good for health Natural  - Trans H atoms on different sides Generally bad for health Processed food Health risks As fats and cholesterol cannot be dissolved in the blood, they are packaged in proteins for transport. - BAD: low density lipoproteins transport cholesterol from liver → body - GOD: high density lipoproteins clean excessive cholesterol and return in to the liver for disposal Cis fats raise levels of high density lipoproteins and decreases cholesterol Saturated fats raise levels of low density lipoprotein and increase cholesterol Trans fats raise levels of low density lipoprotein and lowers density of high density lipoprotein High levels of cholesterol can cause atherosclerosis and lead to health issues like coronary heart disease. Proteins Peptide bonds Amino acids (monomers) are covalently joined by peptide bonds = peptide chain thanks to condensation reaction in the ribosome. Structure Primary - Order of amino acid sequence - Formed by covalent peptide bonds Secondary - Folding into repeat patterns - By hydrogen bonding between amine and carboxyl group Tertiary - Three-dimensional arrangement of polypeptide - Determined by the interactions of the variable side chains Quaternary - Presence of multiple polypeptides Functions Structure (collagen) Hormone (insulin) Immunity Transport (hemoglobin) Sensation Movement Enzymatic (rubisco) Denaturation: Loss of biological properties of a protein - Temperature: heat breaks structural bonds - pH: alter protein charge → changes solubility and shape Enzymes - Speed up chemical reactions by lowering the activation energy - Are not consumed by the reaction and can be reused Enzymes react with the substrate, a molecule that binds to an active site. Specificity Lock and Key model - Enzyme and substrate compliment each other precisely - The active site and the substrate will share specificity - This model is flawed Induced fit Model - Active site is not rigid fit for the substrate and changes its conformation to better accommodate the substrate - This stresses the substrate bonds and induces catalysis Factors affecting the enzyme activity Temperature - Increases enzyme activity; more kinetic energy, more energy - Peak at an optimum temperature - Higher temperatures decreases activity which cause denaturation pH - Enzyme activity is highest at an optimal pH range - Activity decreases outside of this range due to denaturation Substrate concentration  - Increases enzyme activity; more particles, more collisions - Plateau reaches due to saturation of active sites Industrial Enzymes - Fixed to a static surface to prevent enzyme loss - This improves separation of product and purity of yield Lactose (Lactase) → Galactose Lactase is fixed to an inert surface Milk is passed over this surface to become lactose free Benefits of lactose free milk: Provides a source of dairy for lactose-intolerant people Increases sweetness of milk (less need for sweeteners) Reduction of crystallization and production time for cheese Nucleic acids The monomer is a nucleotide Nitrogenous base: can be made of Adenine, Guanine, Cytosine, Thymine, Uracil Formation Nucleotides are joined together into a single strand via condensation reactions (5’-phosphate and a 3’-hydroxyl group) DNA structure Two complementary strands lined up in an opposite direction with the bases facing inwards and connected by hydrogen bonds (G C and A T) The double helix allows a more stable energy configuration. RNA structure Single stranded but may fold upon itself to form double stranded motifs. DNA RNA Deoxyribose Ribose Has T Has U Double stranded Single stranded The structure of DNA was elucidated by Watson and Crick. Their model demonstrated: - Double helix structure composed of antiparallel DNA strands - Bases with complementary strands (A T; C G) DNA Replication - Semiconservative: one strand is from an original template molecule and the other is newly synthesized - Each base will only pair with its complementary partner Helicase: - Unwinds and separates the double stranded DNA - Breaks the hydrogen bonds between the base pairs DNA Polymerase III - Free nucleotides line up opposite complementary partners - DNA Pol III covalently joins free nucleotides together Meselson-Stahl Experiment There used to be three theories 1) Conservative: new copy 2) Dispersive 3) Semiconservative Experiment: - Worked with heave 15N 1. Centrifugation separates the DNA according to weight 2. First division: the lighter 14N was in the sample now, and the N were in the middle. This discarded the conservative theory, which would have predicted that one light had been all light, and the other all heavy. 3. Second division: the new model was either half heavy and half light or entirely light. This contradicts the dispersion theory, as it would have predicted that there would be a mixture of heavy and light dna 4. This agrees with the semiconservative dna model. PCR: used to rapidly copy sequences 1. Denaturation: DNA head in order to separate strands 2. Annealing: primers attach to ends of a target sequence when temperature decreases 3. Elongation: heat-tolerant conditions allow a polymerase to copy strands. Transcription and translation Transcription: genetic code is turned into RNA in the nucleus - Mediated by RNA polymerase Separates the DNA strands Covalently joins free complementary RNA nucleotides together After transcription, RNA is released to the cytoplasm (for translation) and the DNA remains within the nucleus and reforms a double helix Types of RNA - mRNA: Transcript used to make proteins - tRNA: Transports amino acids to ribosome - rRNA: Catalytic component of ribosomes Genetic code: set of rules by which information encoded in mRNA sequences is converted into a polypeptide sequence. Codons: triplets of bases which correspond to a particular amino acid. - Starts with AUG - Ends with STOP codon It is universal and degenerate (multiple codons may code for the same amino acid. Translation: process where RNA is used to produce proteins 1. mRNA is transported to the ribosome 2. A ribosome leads an mRNA sequence in codons 3. tRNA transports amino acids 4. tRNA aligns opposite to a codon via a complementary anticodon 5. The ribosome moves along the mRNA sequence (5’ → 3’) and joins amino acids together with peptide bonds 6. The synthesis of a polypeptide is initiated at a start codon (AUG) and is completed at the STOP codon From gene to protein Gene: sequence of DNA which encodes a polypeptide sequence. However… - Genes may be alternatively spliced (one gene = many polypeptides) - Genes encoding tRNA or rRNA are transcribed but not translated - Genes may be mutated to alter original polypeptide product Cell respiration - Controlled process of releasing energy in order to produce ATP - ATP is an immediate source of energy that can be hydrolyzed into ADP Glycolysis: breaking down glucose as the first step of cell respiration  1. Glucose is transformed into pyruvate (2x) 2. There is a small net yield of ATP (2 ATP gained) 3. NAD+ is reduced to NADH Anaerobic vs Aerobic Pyruvate can follow either anaerobic or aerobic Anaerobic respiration - Does not require oxygen and takes place in the cytosol - Results in a small net yield of ATP - Forms lactic acid or ethanol and CO2 - Reversible fermentation Aerobic respiration - Requires oxygen and happens in the mitochondria - Large energy yield - Produces CO2 and water - Hydrogen carries ATP Fermentation: allows ATP production in the absence of oxygen It is reversible because it restores NAD+ stocks (used in glycolysis) to ensure a continuous production of ATP (for glycolysis) In animals, lactic acid is produced to maximize muscle contraction when oxygen is limited Ethanol and CO2 can be used for yeast fermentation, yogurt, alcohol, etc Respirometry: measures an organism’s rate by carbon dioxide production or oxygen uptake, usually in invertebrates. 1. Organism is sealed in a container with a CO2 absorbent 2. Oxygen uptake creates pressure which displaces the fluid in the nanometer Photosynthesis Takes light energy from the inorganic molecules to synthesize organic compounds Spectrum: violet has the shortest wavelength, red the longest Light absorption Pigments are needed for the conversion of light energy into chemical energy Chlorophyll is the most common photosynthetic pigment, which absorbs blue and red but reflects green, which is why we see plants that color. Light dependent reactions: take place in the thylakoids. Thylakoids are small vesicles that contain pigment and as they are piled up forming Granum they increase the surface area over volume to make photosynthesis more efficient. 1. LIght is captured. Water, which is a reactant in the photosynthesis equation, is divided into protons, electrons and oxygen. This means that oxygen is also a product of the light dependent reaction. 2. Light dependent reactions also produce ATP and NADPH. Both will be needed for the independent reaction Light independent reaction: anabolic. also happens in the chloroplast. However, specifically in the Stroma, a fluid outside of the thylakoids. 1. CO2 It is taken in from pores, stomata, which can open and close. CO2 will enter the stomata and will be fixed. O2 enters with the aid of RUBISCO, the most abundant enzyme and will take its inorganic form to a more useful one, organic. 2. The ATP from the light dependent reaction works as a currency of energy while the NADPH will supply reducing power, meaning it adds high energy electrons to the process CACTUS: involving adaptation of photosynthetic process As they live in hot conditions, if they open their stomata for CO2 intake, they can lose more water than ideal as it can escape faster. So, they perform CAM Photosynthesis. This means they open their stomata at night, when it is not so hot, they can capture CO2 and chemically store it and use it the next day with their stomata closed. Chromatography: the separation of pigments according to their size - Pigments are absorbed by a fluid - The fluid is passed through a static material Rf = distance of pigment ÷ distance of solvent Limiting factors - Light intensity: required for chlorophyll photoactivation - Temperature: affects enzyme activity - CO2: core substrate Genes - Heritable factor made up of a sequence of DNA and influences a specific trait - The genes is found in the locus TOPIC 3 Alleles - Alternate forms of a gene which code variations of a specific trait - New alleles may be formed due to a mutation Genome - Totality of genetic information: includes all genes and noncoding sequences Human Genome Project (2003): mapped the entire base sequence of human genes - Human cells typically have 46 chromosomes Mutations: a change in the base sequence of the DNA which codes a specific trait. - Somatic: happens in a body cell which affects the tissue - Germline: occurs in the gamete and affects offspring Mutation may include: Substitution: silent, missense or nonsense Insertion Deletion The last two change the whole reading of the Frameshift. Genome size has nothing to do with the complexity of chromosomes. Homozygous An organism has two identical alleles for a trait. AA (homozygous dominant) or aa (homozygous recessive) Heterozygous An organism has two different alleles for a trait. Example: Aa Dominant Alleles These alleles express their trait even when only one copy is present. Example: In the case of Aa, "A" is the dominant allele, so the dominant trait is expressed. Recessive Alleles These alleles only express their trait when two copies are present (homozygous). In aa, "a" is the recessive allele, so the recessive trait is expressed. Codominant Alleles Both alleles are expressed equally in the phenotype when present together (heterozygous). In the case of blood types, if one allele is for type A and the other for type B (AB), both traits are expressed, resulting in type AB blood. Sickle Cell Anemia - Substitution in the codon - Codominant trait and heterozygous individuals demonstrate an increased resistant to malaria* - Alters hemoglobin structure, makes it insoluble - Due to this change in the structure, it cannot transport oxygen effectively - Forms clots and are destroyed at a higher rate (which causes anemia) *Anemic people often have altered red blood cells that can make it harder for the malaria parasite to survive and reproduce. The changes in their blood cells can limit the parasite's ability to invade and thrive. Autoradiography: measures the size of DNA when uncoiled  1. Radioactive thymine is inserted into the DNA 2. Chromosomes were fixed in a photographic surface and treated with silver bromide 3. Radiation converts silver ions into soluble grains 4. Once the film is developed, it can be seen in an electron microscope - Diploid: two sets of chromosomes - Haploid: one set of chromosomes Homologous Chromosomes: those passed by the mother and father in sexually reproducing animals. - Same locus - May express a different allele Sex determination - Humans have 23 pairs of chromosomes (diploid 2n= 46) - 22/23 pairs are autosomes Each pair is in the same loci Alleles may vary (as one is parental and the other maternal) - 1/23 pairs are sex chromosomes Females XX Males XY The Y chromosome is responsible for the male characteristics; therefore, the father is determinant of the sex of the offspring. Karyotyping: identifies the number and type of chromosome in an organism - Can potentially diagnose an abnormality or the sex during pregnancy - Cells are collected at the amniotic fluid of the womb: Amniocentesis - Cells are collected in the placental fluid: Chorionic Villi Sample Meiosis - Reduces diploid cell into four haploid cells (Gametes) that are genetically distinct 1. Meiosis I: separates homologous chromosomes 2. Meiosis II: separates sister chromatids DISCO PUG Mitosis Meiosis  División One Two Independent Assortment No Yes (Metaphase I) Synapsis No Yes Crossing over No Yes (Prophase I) Outcome Two cells Four cells Ploidy Diploid → Diploid Diploid → Haploid Use Body cells Sex cells Genetic Identical (clones) Genetic variation* * Genetic variation Crossing over - Via synapsis in prophase I - Homologous chromosomes form bivalents (or tetrads) - Chiasmata is where the genetic information has been exchanged between the homologous pair. - The nonsister chromatids that have exchanged information are now recombinant Random assortment - During metaphase I the chromosomes align randomly - This means there is an equal chance of containing either maternal or paternal chromosomes Sexual Life Cycle - Source for genetic variation - Sperm + Egg = Zygote Nondisjunction: failure of separation, which results in missing or extra chromosomes in the genome in Anaphase or Anaphase I If a normal gamete fuses with an extra chromosome, it will have three copies (Down syndrome) Older parents have a higher chance of nondisjunction offspring Models of Inheritance Gregor Mendel crossed large numbers of pea plants - Organisms have heritable traits - Parents contribute equally by supplying one version of each - Gametes are haploid - Fusion of gametes are diploid - Happens via Meiosis Genotype is the allele combination of a specific trait Phenotype is evidenced in the physique Genetic Disease Autosomal Recessive - Cystic fibrosis is caused by a mutation in the CFTR gene - Produces thick mucus that interferes with the airways and causes respiratory tissue Autosomal Dominant - Huntington’s disease is caused by a mutation - An amplification of CAG causes neurodegeneration Autosomal Codominant - Anemia (ya está más arriba) Radiation exposure Increase mutation rates and cause genetic diseases. Long-term consequences: - Increased incidence of cancer - Reduces immunity - Congenital abnormalities - A variety of organ-specific health effects Monohybrid Crosses: determines allele combinations for potential offspring for one gene only with a punnet grid. Sex linkage (on the beach): a gene is on a sex chromosome Y is short X is large Sex linked Traits - Males have a higher rate of X linked recessive conditions as they cannot mask the recessive allele - Females can be carriers for X linked recessive conditions but not express it X linked conditions: Recessive: Affected mothers must have sons Dominant: Affected fathers must have daughters Examples of X linked recessive: - Hemophilia - Colour blindness Genetic Modification Gel Electrophoresis: separates DNA fragments according to size - Smaller samples move faster through the gel - DNA is negatively charged and samples move towards a positive terminus - Proteins are treated with anionic detergent to impart a uniform negative charge on all molecules DNA Profiling: individuals can be identified by their genetic sequence - Segments of different lengths of particular DNA are amplified by PCR and separated by gel electrophoresis - Used for forensic investigation or paternity tests Gene transfer: universal 1. DNA Extraction: the gene of interest is isolated and amplified by PCR with a plasmid 2. Digestion and Ligation: plasmid and gene cut with a specific restriction enzyme and the gene is spliced into plasmid vector by DNA ligase  3. Transformation and Expression: recombinant plasmid is inserted into a host cell. Antibiotic selection may be used to select for successful transgenic cell as long as the plasmid has the antibiotic resistance gene. GMO Debate Examples: - Bt corn: reduces an insecticide. May be impacting survival of monarch butterflies. In lab conditions, butterfly mortality is higher when fed plants dusted with Bt pollen. Benefits of GM Crops: - Could be used to improve nutritional standards - Can grow a wide range of environments - Could reduce farming costs and associated deforestation - Could reduce spoilage Risks of GM Crops: - Trigger unexpected health issues - Patent protections could restrict access - Possible cross-pollination with weeds - Could compete with native plants Cloning Animal Cloning Binary Fission - The parental organisms divides equally into two - Happens in flatworms Budding - Cells divide off from parent and generate smaller clones - Occurs in hydra Fragmentation - New organisms grow from separated fragment of parent - Common to starfish Parthenogenesis  - Embryos formed from an unfertilised ovary - Occurs in fish or amphibians Human Cloning - Identical twins (monozygotic) are created when fertilized eggs split in two, forming two identical embryos. Plant Cloning - Totipotent tissue capable of cellular differentiation - Stem cut used to regrow a new clone via vegetative propagation Artificial Cloning - Separating the embryonic cells into groups - As embryonic stem cells are pluripotent, each cell can potentially form a cloned offspring - It is not possible to control the genetic features of potential clones Adult Cloning - Adults can be cloned by SCNT - The nucleus is removed from an adult body cell (diploid) and fused with an enucleated egg cell - An electric shock stimulates the division of the egg cell and the growing embryo is implanted into a surrogate TOPIC 4 Ecological Organization - Species: a group of organisms that can interbreed and produce viable offspring - Population: group of organisms of the same species, living in the same area at the same time  - Community: group of different populations living together and interacting in an area - Habitat: environment in which a species lives - Ecosystem: a community and its environment (biotic and abiotic) NUTRIENT CYCLING: Autotrophs: convert inorganic nutrients into organic (produce their own food) - Light (photoautotrophs) - Oxidation reactions (chemoautotrophs) Heterotrophs: ingest organic molecules and may release inorganic byproducts Saprotrophs: break down nutrients in dead organisms and return them to soil. SPECIES ASSOCIATIONS: Positive Association: ○ Predator/Prey ○ Symbiotic interaction (mutualisms, commensalism, parasitism) Negative Association: ○ Competition MESOCOSM: Enclosed environments with controlled conditions used to study sustainability. They need: - Energy Availability (light) - Nutrient Availability (decomposers) - Waste Recycling (detoxifying bacteria) QUADRAT SAMPLING The presence of a species in a given area can be determined via quadrat sampling. It is done by placing a square frame (quadrat) of known dimensions into random locations, there, researchers count the species of organisms within each quadrat and extrapolate the results to estimate the population for the entire area. Chi Test Can be applied into quadrat sampling data to determine statistical significance Step 1: Identify expected frequencies Null hypothesis (H0) - There is no association Alternative hypothesis (H1) - There is association Expected Frequency = (Row total x Column Total) / Grand Total Observed Frequency Degree of freedom = (num rows - 1) x (num of columns - 1) Step 2: Apply Chi-Squared Formula  2 2 (𝑂−𝐸) 𝑋 =∑ 𝐸 Step 3: Determine Significance p Capillaries > Veins Circulation of the blood Cardiac cycle: - Blood flows from higher to lower pressure - Contraction increases the pressure - Valves open/close according to pressure gradients Valves open when atrial pressures are higher > ventricular pressures Valves close when atrial pressure is lower < ventricular pressures Sinoatrial (SA) node: There is a group of cells in the right atrium that depolarize, they emit electrical impulses all the time and initiate the heartbeat. This is why it does not need the nervous system to pump. The SA node is a natural pacemaker of the heart. Blood flows Blood flows to AV valves SL valves from Diastole Vein Atria Open Closed (relaxation) Atrial Systole Atria Ventricles Open Closed Ventricular Ventricles Arteries Closed Open Systole Contraction of the heart are myogenic (muscle) Both atria contract. After a 0.1 delay*, the signal gets from the SA to the atrioventricular (AV) node and is sent down through the septum, (bundles of His or bundle branches)after to the Heart Apex (bottom left of the heart) and then up to the sides of the ventricles (Purkinje fibers) cruising both ventricles to contract. *The delay allows contraction and pumping of ventricles. The stethoscope is used to listen to the heart’s sound. They are called: Lub: first sound, the closing of ATRIOVENTRICULAR valves Dub: second sound, closing of SINOATRIAL valves Changing the heart rate At rest, the nervous system is not involved in the heart rate. However, when exercising, it increases the rate to keep up with the muscular cells. There are two nerves from the Medulla in the brain that are involved in changing the heart rate: 1. Sympathetic nerve (increases HR) 2. Vagus nerve (decreases HR) Cells in the cardiovascular center of the brain serve signals: If low blood pressure, low O2 and low pH (acidic) → sympathetic nerve will increase HR. If high blood pressure, high O2 and high pH → Vagus nerve will decrease HR pH of blood is a reflection of level of CO2 because it forms carbonic acid: CO2 + H2O → Carbonic Acid (H2CO3) and the pH decreases. Adrenaline: hormone Epinephrine (in humans) that is released in the Adrenal (kidney) glands. It increases the HR to prepare the Fight or Flight response. Muscles receive O2 and glucose to produce energy and be ready to react. p.300 Pressure changes during cardiac cycle, and it can be seen in the Atrium, Ventricle (either left or right) and Artery. Defibrillator: Ventricular fibrillation: The ventricle is contracting and relaxing regardless of the other ventricle and the atrium. This is a life threatening situation. However, it can be saved by using a Defibrillator. The defibrillator is made of two paddles placed diagonally on the chest, with the heart in the middle. The machine indicates the steps. First, it checks whether the person is actually fibrillating and if so, it sends an electrical current that will “restart” the heart rate and the ventricular movement. It advises you not to be touching the fibrillated person because it will electrocute you as well. Hypertension (p. 690) Sphygmomanometer: device used to measure the blood pressure 1. A cuff is inserted to prevent blood flow of the artery of the (left) arm. 2. The air will start being reduced so that blood will be able to flow through the cuff. 3. As there is a stethoscope below the device, the doctor will be able to hear the heartbeat (which is blood pumping in the walls of the artery). Types of muscle: - Cardiac: involuntary - Skeletal: voluntary  - Smooth: involuntary Cardiac muscle cells: - Striated and have one nucleus. - They have abundant mitochondria to produce ATP for muscle contraction - Between neighboring cells there are Intercalated discs, where we find abundant gap junctions. They allow the passage of ions from the cytoplasm of one cell to another. - Cells are branched (in a Y shape) allowing propagation of impulse that allows the passage. Functions of the liver - It has a dual blood supply: there are two blood vessels that give blood to the liver: 1. Hepatic arteries bring oxygenated blood (from the heart) to the liver. 2. Hepatic portal vein carries blood (from the intestine) rich in nutrients but poor in oxygen These blood vessels branch until they form thin blood vessels called Sinusoids, which are surrounded by hepatocytes (cells of the liver). Sinusoids are not the same as Capillaries. Though both are very thin (capillaries are the thinnest), in sinusoids (they are more leaky) there are gaps between the cells so blood (liquid) can get more in contact with the Hepatocytes. Functions of the liver: Processing and storage of nutrients: - Carbs: the liver stores glucose in the form of glycogen (excess of glucose). This will happen in response to insulin (hormone released by the pancreas). When blood  glucose levels are low, the pancreas releases the hormone glucagon, which triggers the hydrolysis of glycogen in the liver into glucose molecules that will get to the blood. - Proteins: cannot be stored so they are broken down into amino acids. Excess of amino acids are broken down in the liver producing urea, a toxic compound that will be excreted in the kidneys. - Lipids: some lipids are synthesized in the liver (like cholesterol and very low density lipoproteins, VLDP) and some are processed in the liver (chylomicrons coming from the small intestine). Excess in iron (Fe), vitamin A, and vitamin D are stored in the liver and released when there is a deficit of them in the blood. Recycling of red blood cells: sacks full of hemoglobin. Since they don't have a nucleus, they have a limited blood spawn (120 days approximately). So, when they are old, they are broken down and their components are recycled. - Old RBC are engulfed (phagocytosis) by kupffer cells in the sinusoids of the liver. - Hemoglobin is broken down into: * Heme: which is broken down into iron (carried to the bone marrow to make new RBC or stored in the liver if found in excess) and bilirubin (yellow pigment used to make bile) * Globin: broken down into amino acids and then recycled to make proteins. Jaundice Caused by high levels of bilirubin in the liver, which can lead to hepatitis or liver cancer. Happens quite often in newborns because there is a high number of red blood cells and the process of recycling is more frequent. To solve this, they are placed under the UV light (risk-benefit). Conversion of cholesterol into bile salts (stored in the gallbladder and later to the duodenum) Cholesterol is produced by hepatocytes. It is needed for plasma membrane, production of vitamin D, steroid hormones (Testosterone) and bile. Excess saturated fat in the diet increases cholesterol production (may lead to plaque formation and obstruction of blood vessels). Excess cholesterol is used to make bile (together with bilirubin and other components). Production of plasma (liquid part of the blood) proteins 1. Albumin : carrier protein (to transport things in the blood like minerals) and is also used to regulate/maintain the osmotic pressure 2. Fibrinogen: has a role in blood clotting. Hepatocytes have a very developed Rough ER and Gogli. Because there are proteins that will be secreted out of the blood. Detoxification of blood The liver takes up toxic substances from the blood and converts it into less toxic ones. The liver takes a hydrophobic substance (like alcohol) and turns it hydrophilic so its easier to excrete. Examples: - Alcohol detoxification (with enzyme alcohol dehydrogenase) - Ammonia produced from amino acid breakdown is turned into urea Ventilation system - Ventilation (breathing) - Gas exchange - Respiration: metabolic process that produces ATP from organic compounds (cell respiration, level) It is more efficient that air goes through the nasal cavity rather than the mouth because the hairs of the nose filter the air (dust particles, pathogens) and when the air goes through the nose, it gets to the lungs warmer, which is better. Air will get through the Trachea, a tube that is open by rings of cartilage. It then branches into two bronchi (one bronchus). It then keeps branching into bronchioles (which are much thinner). They end up at the Alveoli (one alveolus), where gas exchanges. The Diaphragm is the muscle right below the lungs. Lungs are in the Thoracic Cavity. The purpose of ventilation is maintaining the concentration gradient in the Alveoli. We need O2 to go from the alveolus to the blood, we need a high concentration of oxygen in the alveolus, and low concentration of oxygen in the blood. The O2 concentration in the alveoli is not as high as in fresh air that is inhaled because as soon as O2 reaches the alveoli, it rapidly diffuses in the blood. Structure function relation in the alveoli Function: gas exchange Structure: millions of microscopic alveoli in each lung which increases the surface area over volume ratio for gas exchange to access The alveolar walls are made of one layer of flat cells called Type I pneumocytes so the distance for diffusion is shorter. Each alveolus is surrounded by a heavy network of capillaries in close proximity, so the diffusion process is more efficient. Type II pneumocytes secrete a liquid called surfactant that prevents the collapse of the alveolar walls (it reduces the surface area tension). In addition, gasses diffuse better when dissolved in liquid. Ventilation mechanism Air flows from high pressure to low pressure There is an intense reaction between volume and pressure There are two pairs of antagonistic muscles involved in ventilation: - Diaphragm and abdominal muscles - External and internal intercostal muscles - Pleura is a tissue that attaches the lungs to the ribcage Whatever changes happen to the ribcage, the lungs will respond accordingly. p. 316 Inspiration When the diaphragm contracts, it flattens: The rib cage will go up and to the side. This is because the intercostal muscles contract, bringing ribcage up and to the sides. Expiration The diaphragm relaxes and becomes dome-shaped. Internal intercostal muscles relax, bringing ribcage down. The volume decreases, pressure increases and air goes down. Spirometer Common way to measure the volume of air that gets in and out of the lungs Emphysema - Dangerous because there is less surface area over volume ratio for efficiency. - The walls are thicker (more difficult for oxygen to get to the lungs through diffusion, larger distance). What could cause it: - Phagocytes: inside the alveoli, these cells do phagocytosis to threatening cells. When they engulf (Protect us), they produce an enzyme called elastase, which kills the bacteria or waste. If exposed to smoke, more elastase is produced to combat them, but this accumulative process can damage the cell walls. Unit 6.5 Neurons and synapses I find it hard to decide which system is more incredible, the immune or the nervous. ☺ We will study only the tip of the iceberg of what is known about the nervous system, but I think it will be enough for you to understand how amazing it is. We should not forget that neurobiology is a branch of biology that is developing fast, and a lot is yet to be learnt about how the nervous system, especially the brain, functions. Watch the videos and answer the questions: The Nervous System, Part 1: Crash Course Anatomy & Physiology: https://www.youtube.com/watch?v=qPix_X-9t7E This video contains more information than you need to know for the IB, but I think you will find the extra information interesting. Questions related to this video: What are the three main functions of the nervous system? Describe them briefly. - Sensory input: Sensor stimulus. All the information is gathered by neurons, (gila) and synapses. - Integration: Decides what should be done with the information. - Motor output: Response due to the activation of certain parts of your body What structures compose the central and the peripheral nervous systems (CNS and PNS)? Central nervous system (CNS): brain and spinal cord. Decides and makes the decision. Processing center. Peripheral nervous system (PNS): made up by all the nerves that branch off both the brain and spinal cord. They account for the communication from the CNS to the rest of the body. It is divided into two: - Sensory division (afferent): picks up sensory stimuli, and slings that information to the brain. - Motor division (efferent): sends information from the brain to the muscles and glands. Motor division is divided into: Somatic (voluntary) Nervous System: rules the skeletal and muscle movement. It connects CNS with organs and striated muscles in order to perform daily functions. Autonomic (involuntary) Nervous System: regulates physiological processes, such as keeping heart beating, the stomach churning and lungs breathing. ANS can be divided into: - Sympathetic division: activates fight-or-flight response. As we have seen before, we have the SYMPATHETIC NERVE. When blood pressure, oxygen levels, and ph levels are low, the sympathetic nerve increases the heartbeat. - Parasympathetic division: networks of nerves that relax the body after a period of stress or danger. MOTOR NEURON STRUCTURE: What are neurons? They are a paramount type of cells that respond to stimuli and transmit signals. a. Label the numbered structures. 1. Dendrites: Branched-like projections. Receive and convey information to… 2. Soma: cell body. Has the neuron’s life support. Has nucleus and mitochondria, ribosome, and cytoplasm. 3. Myelin Sheath: protects the axon and speeds up the transmission of electrical impulses. 4. Node of Ranvier: allows the diffusion of ions. 5. Axon 6. End of Axon: carries information. Emit electrical impulses away from the cell to the rest of the cells. b. From where to where is a nervous impulse propagated? Neurons transmit electrical impulses from one edge to the other. Therefore, the pathways of impulse is propagated all the way from the dendrites to the axon terminal.  TYPES OF NEURONS: Complete the function of each type of neuron c. Sensory neurons: carries information about external or internal changes in the environment from sensory receptors to the CNS. d. Relay or interconnecting neurons: make use of chemical and electrical signals to transmit information to the organisms rapidly. From CNS to… e. Motor neurons: allow the voluntary and involuntary movement from the CNS to effectors (muscles or glands, do the response). The Nervous System, Part 2 - Action! Potential!: Crash Course Anatomy & Physiology: https://www.youtube.com/watch?v=OZG8M_ldA1M In this video you will learn how a nervous (electrical) impulse is propagated. I’m not going to lie, it can get tricky… take your time. But hey! At least you already know how the sodium potassium pump works! ☺ Questions related to this video: MEMBRANE POTENTIAL: f. What is it? The membrane potential is the difference of electrical charge between the inside and outside of the axon, which produces a voltage (Vm) that affects the cell’s function. g. What is the (conceptual) difference between the resting and the action potentials? Resting potentials are more negative from the inside and are stable, relaxed, when the neuron is not actively responding. Action potentials are rapid signals sent temporarily when the neuron sends a signal to change to the resting potential.  h. What is the value (voltage) of the resting potential? Negative (- 70 mV). i. The resting potential is determined (not only but mostly) by the action of the good old sodium potassium pump (Na/K pump). Look at the image and try to determine: why is the potential across the membrane more negative on the cytoplasmic side? (We say that the membrane is “polarized”.) The potential across the membrane is more negative on the cytoplasmic side (Inside) because of the pumping of sodium ions outside the cell and potassium ions inside the cell. As a result, there is a higher concentration of positive ions outside the cell compared to inside, resulting in a negative charge inside the cell. As the plasma membrane is more permeable to potassium ions, which lead to increasing the negative charge in the cytoplasmic side. j. The action potential happens when, for a brief moment, the potential of the membrane becomes more positive on the cytoplasmic side. (This is called “depolarization”.) Which membrane channels open leading to depolarization of the membrane? What leads to the opening of these channels? What type of transport mechanism is this? Page 321, Figure 5: Voltage-gated Sodium channels: open when there is a voltage of -50 mV. This is known as the Threshold potential, which causes the opening of the voltage-gated Sodium channels. Therefore, the sodium ions will enter the cell through facilitated diffusion. As the inside becomes more positive, the cell depolarizes, it is the beginning of the action potential. k. At one point, the membrane becomes re-polarized again. The opening of what channels is responsible for this? As sodium enters the membrane, it becomes more positive, until it reaches to +35 mV. The Sodium channels close, but the Voltage-gated Potassium channels open. Therefore, potassium will leave the cell through facilitated diffusion. l. The refractory period is a period of time when the membrane cannot become depolarized again. Which protein is working during this period? The sodium potassium pump will work in order to restore the resting potential again. m. What does it mean that the action potential is an “all or none” event? What is the threshold potential? Because if you reach the threshold potential, the action potential will occur (“All” the changes in membrane potential during nervous impulse). Otherwise, it fails and action potential does not happen (“None”). Changes in membrane potential during a nervous impulse. Can you label the letters on the diagram? (Look at the time scale!!!) In myelinated neurons, the nerve impulses travel very fast, in what is called: saltatory conduction. n. What is the function of the myelin sheath surrounding the axon of a neuron? Myelin sheath is an insulating layer that surrounds (some) axons. It is produced by schwann cells. The schwann cell surrounds the axon many times; this many layers of schwann cells are plasma membranes made up of phospholipids, which is why ions cannot pass through. o. What are the nodes of Ranvier? Gaps on the neuron axon that are not insulated by myelin sheath. p. What is saltatory conduction? Action potential travels down the axon by “jumping” from one node to another, which makes the impulse propagation 100x faster. The synapse is the connection between two neurons. The presynaptic (sending) and postsynaptic (receiving) neurons. They communicate through neurotransmitters, chemical transmissions that allow communication between neurons. The action potential travels along the axon until it reaches the axon terminal of the presynaptic neuron. Once it reaches the axon terminal, calcium channels open, calcium enters. The vesicles with neurotransmitters will fuse to the membrane because of the calcium, so neurotransmitters are released to the synaptic cleft (through exocytosis). Calcium triggers exocytosis. The neurotransmitter will diffuse across the synaptic cleft (high concentration to low concentration) and binds for the neurotransmitter (it is specific for the neurotransmitter). This will cause the opening of sodium channels, for example, so the potential of the membrane will change → depolarization of the postsynaptic neuron and action potential will pass to the next neuron. As (I hope) you understood by now, the propagation of an impulse along a neuron occurs using electrical transmission. However, when a neuron communicates with another, this mostly happens via chemical communication. Neurotransmitters pass from one neuron to another across a synapse. The Nervous System, Part 3 - Synapses!: Crash Course Anatomy & Physiology https://www.youtube.com/watch?v=VitFvNvRIIY Again, more than required by the IB, but super interesting and totally worth the time. The steps leading to synaptic transmission are summarized in your book on page 325 and Figure 14. Label as many letters as you can on the following diagram (including X and Y!). Applying the knowledge on synaptic communication: Acetylcholine and neonicotinoids. (pages 326 and 327) Acetylcholine: causes muscle contraction (like peristalsis or heart contractions). Works in a neuro-musuclar junction. Acetylcholine will bind to a receptor in the muscle and cause its contraction. AChE is an enzyme that destroys acetylcholine once the muscle should stop contracting. Why are we focusing on this? There is an incesticide called Neonicotinoids, with a structure very similar to Acetylcholine, which means it can bind to its receptor, lead to muscle contraction, but the enzyme AChE cannot destroy it. Muscle contraction does not stop. This is damaging in case of killing unintended insects, which causes an imbalance in the food web. Last video: IB teacher summarizing the highlights of this unit: https://www.youtube.com/watch?v=cWtBfRezE-8 Hormone: released into the blood. Travels in the plasma until the target cell. It knows it has reached the target cell because there is a receptor for the hormone on the cell membrane. A signal travels to the cell and responds accordingly. This type of communication is slower. Homeostasis means keeping internal conditions within tolerable limits, and it is one of the basic functions of life. Homeostasis does not mean that conditions are always static, only that when there is a deviation from a set point mechanisms are activated to correct those imbalances. Both the nervous and endocrine systems work together to maintain homeostasis, usually in a negative feedback loop. Negative feedback loop is when the system responds opposite to the signal. For example, when temperature increases, the body temperature will decrease. Positive feedback: the response is amplified to make it occur more rapidly. As one increases, the following does as well. For example, GH gasses. The pancreas has an endocrine part. There are a group of cells called islets of langerhans which can be: - Alpha cells: release glucagon - Beta calls: release insulin High blood sugar levels inhibit the release of insulin. Insulin will decrease the levels of blood glucose by two ways: 1) Stimulating glucose uptake from blood into the cells. Cells need glucose for cell respiration 2) Promoting the formation of glycogen in the liver This is a negative feedback that decreases the levels of blood sugar. Diabetes mellitus is a metabolic disorder that results from a high blood glucose concentration over a prolonged period. THere are two major types of diabetes: I (insulin dependent) and II (Non-insulin dependent). Cells cannot produce energy, so they may end up dying.  Type I: INSULIN DEPENDENT Type II: NON-INSULIN DEPENDENT Usually occurs during childhood Usually occurs during adulthood Pancreas does not produce sufficient Body does not respond to insulin insulin production Caused by destruction of beta calls Caused by the down-regulated of insulin receptors Requires insulin injections to regulate Controlled by managing and lifestyle blood glucose It used to be a deadly disease until it was discovered that the juice of the pancreas could treat diabetes. Thyroxin: secreted by the thyroid gland - It increases the metabolic rate. Metabolism produces heat, if the thyroid gland is not working properly, you will feel cold as there is no or little release of thyroxine. - Almost all cells are target of thyroxin - It requires the production of iodine atoms - Hypothyroidism symptoms: Lack of energy or feeling tired all the time Weight gain despite of loss of appetite Feeling cold Constipation Leptin : released by the adipose tissue, controls appetite. Increases the feeling of satiety. Mice that cannot release leptin are obese, if they are injected with leptin their appetite declines. Melatonin: helps you sleep. Regulates the 24 hour cycle Melatonin is released by the pineal gland in response to darkness, playing a crucial role in regulating circadian rhythms. The process begins when light diminishes, signaling the retina, which sends information to the suprachiasmatic nucleus (SCN) in the hypothalamus. The SCN then communicates with the sympathetic nervous system, which inhibits the production of melatonin during the day and promotes its synthesis at night. In the pineal gland, serotonin is converted into melatonin by the enzyme acetylserotonin O-methyltransferase, primarily during the dark hours. This release of melatonin helps signal to the body that it is time to sleep, thereby regulating sleep-wake cycles and other biological rhythms. - Jet lag is a psychological effect related to melatonin  Human reproduction Hormones related to sexual reproduction are steroid hormones that require cholesterol. - Testosterone - Estrogen - Progesteron Hormones that are NOT steroid, but control the menstrual cycle: - LH - FSH Determination of gender - Females have XX and males XY - The gene SRY in the Y chromosome codes for the DNA binding protein TDF - The presence of SRY gene promotes the development of testes (male gonads) in embryonic development - Testes secrete the hormone testosterone which causes male genitalia to develop during embryonic development - The secretion of testosterone increases during puberty. The function of testosterone is: Stimulation of sperm production in the testes Development of male secondary sexual characteristics such as enlargement of penis, growth of pubic hair and deepening the voice due to growth of larynx The absence of a Y chromosome leads to the development of female gonad (ovaries) during embryonic development The hormones estrogen and progesterone are released during pregnancy, leading to the development of female reproductive organs During puberty the secretion of estrogen and progesterone increases, causing the development of females secondary seXual characteristics such as enlargement of breasts, widening of the hips and growth of pubic hair. Menstrual cycle Endometrium: inner lining of uterus Follicle: fluid-filled sac inside which an egg cell develops Corpus Luteum: structure produced from the remaining follicle cells after an egg has passed into the oviduct (ovulation). Menstrual cycle: a hormonal cycle that lasts on average of 28 days (from puberty to menopause). The aim is to release an egg for a possible fertilization and implantation into endometrium. The endometrium is highly vascularized for implantation of an embryo to occur. If there i s no implantation, menstrual bleeding occurs. Regulated by Estrogen, progesterone, LH and FSH. STAGES: 1. A group of follicles is stimulated to grow. Meanwhile, the endometrium is thickening 2. One follicle (the most developed one) breaks open and releases an egg in the oviduct (ovulation) 3. Endometrium continues to develop, preparing for the implantation of an embryo. 4. The rest of the follicles degenerate and the one that released the egg becomes corpus luteum. 5. If fertilization does not occur, the corpus luteum breaks down and so doesn the thickening of the endometrium, to be shed during menstruation. Follicular phase → Ovulation → Luteal phase