Cell & Molecular Biology PDF

1 1 2 DAT Booster | Booster Prep™ Biochemistry 1 2.1 Basic Chemical Context of Life Van der Waals Interactions: weak, temporary attractio...

1 1 2 DAT Booster | Booster Prep™ Biochemistry 1 2.1 Basic Chemical Context of Life Van der Waals Interactions: weak, temporary attraction between atoms or molecules in close proximity. Occurs due Matter is composed of atoms linked 1 together by bonds. to the transient, uneven distributions of electrons in a Atoms are made up of neutrons, protons, and electrons. molecule at any given time. Weak attraction individually, Molecules are groups of 2 or more atoms held together by but can add up to a powerful force. chemical bonds. Chemical bonds form due to electron interactions between atoms. Electronegativity describes 2.2 Water the ability of an atom to attract shared electrons within a bond (high electronegativity = atom pulls the electrons Water is a highly polar molecule capable of hydrogen closer to itself). bonding with several exceptional properties. Bond Types: Excellent solvent: dipoles of H2O can interact with Ionic Bond: complete transfer of electrons from one opposite charges in polar or ionic molecules, atom to another (between atoms with very different surrounding them with a hydration shell (like dissolves electronegativities). Ionic bonds exist between ions 2 like). (charged atoms or molecules). - Nonpolar hydrophobic substances lack permanent dipoles or charges, are not attracted by water, and Covalent Bond: electrons are shared between atoms do not dissolve easily. with similar electronegativities – can be single, double, triple bonds. High Heat Capacity: amount of heat needed to raise - Nonpolar Bond: equal sharing of electrons (highly the temperature of water is high (makes water very similar electronegativity). temperature stable). - Polar Bond: unequal sharing of electrons (slightly different electronegativity and formation of a dipole). Density: water is denser as a liquid than as a solid, ‣ Dipoles are differences in charge between two allowing ice to float. parts of a molecule. - In ice H-bonds become rigid and form a crystal structure that keeps molecules separated further Hydrogen Bond (H-Bond): weak bond between apart than they are in the liquid form, allowing ice to molecules that meet two conditions. float in water. 1. Molecule must have a hydrogen covalently bonded to a highly electronegative atom (F, O, N). Cohesion: attraction between like molecules, such as 2. That same hydrogen atom is attracted to another molecules of H2O; water has high cohesion due to H- highly electronegative atom (F, O, N). bonds; H2O molecules have strong cohesion which ‣ Hydrogen bonds can be within a molecule produces a high surface tension. (intramolecular) or between molecules - Allows small organisms like insects to walk on water. (intermolecular). Adhesion: attraction between unlike substances such as water and non-water substances. - E.g. using a wet finger to flip a page. - Adhesion and cohesion collectively explain capillary action: ability of liquid to flow without external forces (e.g. against gravity). Helps water to flow upward through plants during transpiration. DAT Booster | Booster Prep™  2 2.3 Micromolecules 2.5 Carbohydrates Essential nutrients that the body cannot produce in Functions: energy storage and structural molecules. sufficient quantities; must be obtained from the diet. Monomer: monosaccharide. 1 Polymer: polysaccharide. Minerals: inorganic ions (e.g. Calcium, Potassium) Linkage type: glycosidic bonds. Can be alpha (α) or beta found intracellularly and extracellularly. (β) - Function in bone development, establishing electrochemical gradients for muscles and nerves, and in hemoglobin. Vitamins: organic micromolecules that are classified as either water-soluble or fat-soluble. - Fat Soluble: excess deposited in body fat; overconsumption can lead to toxicity. ‣ Vitamin A: visual pigment and epithelial maintenance. ‣ Vitamin D: regulates calcium levels by promoting absorption from the intestine; synthesized when alpha (α) glycosidic bond UV light strikes the skin. ‣ Vitamin E: antioxidant (neutralizes free radicals that can damage cells). ‣ Vitamin K: important for blood clotting. - Water Soluble: excess not stored in the body and are excreted in urine. ‣ Vitamin B: coenzymes or precursors to coenzymes; there are 8 different B-group vitamins. ‣ Vitamin C: important for collagen synthesis; beta (β) glycosidic bond deficiency leads to scurvy. Classes of Carbohydrates 2.4 Macromolecules Monosaccharides: single sugar molecule (e.g. glucose, All organic molecules contain carbon atoms. Large organic fructose, galactose). mo ecules are called macromolecules, composed of Disaccharides: two monosaccharides joined by a monomers (single subunits) that link together to form glycosidic linkage (e.g. glucose + fructose = sucrose, polymers (series of repeating monomers). There are four glucose + galactose = lactose, glucose + glucose = major biological macromolcules: Carbohydrates, Lipids, maltose). Proteins, and Nucleotides. Polysaccharides: series of connected monosaccharides that form long chains. Dehydration Synthesis: Process by which monomers - α-glucose polymers with branched structure. combine to form polymers, producing an H2O ‣ Starch: stores energy in plants. molecule. ‣ Glycogen: stores energy in animals. Hydrolysis: Process by which an H2O molecule is used - β-glucose polymers with no branching (linear to break polymer linkages. polysaccharides). ‣ Cellulose: structural molecule in plant cell walls. DAT Booster | Booster Prep™ l­  3 ‣ Chitin: structural molecule in fungi cells walls and Porphyrins: 4 joined pyrrole rings with a central metal arthropod exoskeletons. Chitin contains nitrogen atom. atoms. - Examples: Chlorophyll (central Mg absorbs light) and hemoglobin (central Fe transports oxygen). *Note: humans cannot cleave beta1 glycosidic linkages; some animals (e.g. cows) can cleave these linkages because Cold temperatures: cells add cholesterol and unsaturated of bacteria in their gut. fatty acids to the cell membrane to prevent excess membrane stiffness. 2.6 Lipids Hot temperatures: cells add cholesterol and saturated Nonpolar, hydrophobic molecules. fatty acids to the cell membrane to prevent excess membrane fluidity. Functions: insulation, energy storage, cell structure, Note*: cholesterol prevents excess membrane fluidity and endocrine molecules, and membrane structure. rigidity. Monomer: hydrocarbons (note: hydrocarbons are not true 2.7 Proteins monomers). Polymer: hydrocarbon chains (note: lipids are not true Functions: structural molecules, storage, transport, polymers because they lack repeating monomer units). immunity, 2 hormones, enzymes, signaling, motor functions, Linkage type: covalent carbon-carbon bonds. fluid balance, channels, and pumps. Types of Lipids Monomer: amino acid. Triglycerides: three non-polar fatty acid chains Polymer: peptide. attached to a glycerol backbone. Glycerol is a 3-carbon Linkage type: peptide bonds. molecule. Fatty acids are long carbon chains which can be saturated or unsaturated. - Saturated: no double bonds (forms straight chains). ‣ Stack densely and form fat plaques  Less healthy - Unsaturated: contains double bonds (branched structure). ‣ Stack loosely and do not form fat plaques  More healthy Phospholipid: two fatty acids and a phosphate group attached to a glycerol backbone. - Contain a polar (phosphate) head and nonpolar (fatty acid) tail, giving phospholipids hydrophilic and hydrophobic properties (amphipathic). - Major component of cell membranes. Phospholipids Protein structure: form a bilayer in water: the polar heads face the 1. Primary structure - linear sequence of amino acids aqueous environments inside and outside the cell, connected by peptide bonds; determined by the while the fatty acids face each other, forming a sequence of translated mRNA codons. hydrophobic region. 2. Secondary structure - 3D shape resulting from hydrogen bonding between amino and carboxyl Steroids: four joined hydrocarbon rings. groups of adjacent amino acids. - Steroids form steroid hormones, cholesterol (a cell a. Includes alpha helix and beta sheet. membrane component), vitamin D, and bile acids. DAT Booster | Booster Prep™  4 3. Tertiary structure - 3D structure due to interactions DNA (deoxyribonucleic acid): Double-stranded between amino acid R groups. polymer containing the deoxyribose sugar group. Two a. Interactions include: H-bonds, ionic bonds, strands of nucleic acid are intertwined to form a double hydrophobic effect, disulfide bonds, Van der helix. Nucleotides on the same strand are connected by Waals forces. 1 phosphodiester bonds (the phosphate group of one 4. Quaternary structure - 3D structure that arises from nucleotide is covalently linked to the sugar group of multiple protein subunits joining together. the next nucleotide, in a 5’  3’ direction, forming a sugar-phosphate backbone). The two strands are *Note: Proteins are the only macromolecules with disulfide connected by hydrogen bonds between the nitrogen bonds (and sulfur atoms in general). bases of nucleotides on opposite strands. - Directionality: DNA is antiparallel. Each strand runs Protein Denaturation: Loss of 3D structure (protein retains 5’  3’ in opposite directions. only primary structure); leads to loss of protein function, - Complementarity: DNA is complementary. Nitrogen which is dependent on 3D shape. bases on one strand bind to their complementary Denaturation agents: temperature, pH, change in salt base on the opposing strand (forming a base pair). concentration, UV light, and chemicals. Adenine binds to Thymine (AT base pair), whereas Guanine binds to Cytosine (GC base pair). 2 ‣ AT base pairs are held together by 2 H-bonds, 2.8 Nucleic Acids while GC base pairs are held together by 3 H- bonds. Nucleic acids with more GC base pairs Functions: store, transmit, and express the genetic material are held together by more hydrogen bonds; of cells. higher temperatures are required to separate Monomer: nucleotide. these strands. Polymer: nucleic acids (DNA and RNA). - Chargaff’s Rule: number of purines is always equal Linkage type: phosphodiester bond. to the number of pyrimidines. In other words, A + G = T + C (Implied: A = T and C = G). E.g. If a DNA molecule is 20% Adenine, it must also be 20% Thymine. RNA (ribonucleic acid): polymer of nucleotides containing the ribose sugar group. Ribose has an extra OH group compared to the deoxyribose sugar group (found in DNA), which makes RNA more reactive than DNA. - Unlike DNA, RNA is usually single stranded. - RNA does not contain the nucleotide thymine. Instead, it has the nucleotide uracil, which basepairs with adenine. Nucleotide: nitrogen base (A, C, G, T, U) + five carbon sugar (deoxyribose in DNA, ribose in RNA) + Pro-Tip: To keep track of which nucleotides belong to phosphate group. which category, remember the mnemonic CUT the PYE - Purines: nucleotides with double ring nitrogen bases (the Pyrimidines are Cytosine, Uracil, and Thymine). (adenine, guanine). - Pyrimidines: nucleotides with single ring nitrogen bases (cytosine, uracil, thymine). DAT Booster | Booster Prep™ Cells and Organelles 5 3.1 Cell Theory Each phospholipid is amphipathic and consists of 2 fatty acid tails (hydrophobic) and a phosphate head Cells: the basic functional units in 1biology; smallest unit of (hydrophilic). The fatty acid tails point inward, away organization that can perform all activities required for life. from water, while the phosphate heads face the Cells are too small to be seen by the naked eye. aqueous environment of the cell’s interior and exterior. Polar head Cell Theory: 1. All organisms are composed of 1 or more cells 2. The cell is the basic unit of structure and organization in organisms 3. All cells come from pre-existing cells Hydrophobic region 4. The activity of an organism depends on the total Fatty acid tail activity of independent cells 5. Cells have a functional metabolism (energy flow occurs within cells) 2 6. Cells carry and pass on hereditary information Hydrophilic region (DNA) when a cell divides or an organism has offspring The cell membrane is a barrier that separates the outside 7. All cells of similar species have the same basic and inside of a cell, allows for communication with other chemical composition (e.g.: animal cells use cells, provides structural support and protection, and is carbohydrates as a source of energy, phospholipids selectively permeable to allow for the movement of as a part of the cell membrane, proteins to perform substances in/out of the cell. enzymatic activities, etc.) Selective permeability: only certain substances can Some organisms are single cells (e.g. bacteria, amoeba) cross the membrane without assistance from while others are multicellular (e.g. humans). Multicellular membrane transport proteins organisms contain groups of cells (tissues) which work Molecule Type Permeability Examples together to accomplish specialized tasks. Can cross Steroids, CO2, O2, Small, nonpolar All cells contain: membrane on its (hydrophobic) N2 Plasma membrane: selective barrier that separates and own protects cell contents from the outer environment Can cross DNA: the source of genetic information Small, uncharged, H2O,Glycerol, Urea, membrane on its Ribosomes: synthesize functional proteins from DNA polar Ethanol own Two cell types exist: prokaryotes (less complex; no Large, uncharged Unable to cross on nucleus or membrane bound organelles) & eukaryotes Glucose, Sucrose polar its own (more complex, have nucleus and organelles) Unable to cross on Ion Na+, H+, Ca2+ its own 3.2 Cell Membrane and Permeability The cell membrane is described as a uid mosaic: fluid Cell membranes are made of a phospholipid bilayer. The because the phospholipids can freely move around, and “phospholipid bilayer” is 2 layers of phospholipids (outer mosaic because different components (e.g. proteins) are and inner layer). embedded within it. DAT Booster | Booster Prep™ fl  6 3.3 Organelles and Cell Structures Endoplasmic reticulum (ER): network of interconnected membranes with flattened areas (cisternae). Organelles are membrane bound structures within cells that Rough ER (RER): Synthesizes proteins for modification carry out specialized functions. and export. Close to the nucleus and studded with 1 ribosomes. Nucleus: contains the cell’s DNA. Controls gene - The rough ER is capable of post-translational expression. The structure of the nucleus includes: modifications of protein (e.g.: attaching 1. Nuclear envelope: double membrane (two carbohydrates to make glycoproteins) phospholipid bilayers) with pores allowing molecules to enter and exit Smooth ER (SER): Synthesizes lipids and steroid 2. Nuclear lamina: protein network that maintains the hormones for export. Has no ribosomes. shape of the nucleus - In liver cells, SER functions in breakdown of toxins, 3. Nucleolus: region inside the nucleus where drugs, and toxic by-products. ribosomal RNA (rRNA) is made - Muscle cells have a specialized SER called the a. Ribosomal proteins are imported from the sarcoplasmic reticulum that stores and releases Ca2+ cytoplasm to the nucleolus and combined with ions. rRNA to form ribosomal subunits. The subunits are exported to the cytoplasm for final Golgi Apparatus: a directional (cis/trans faces) series of 2 assembly into complete ribosome flattened membrane sacs (cisternae) that sort, modify, and Most cells have one nucleus, but some can have transport proteins after synthesis. Also produce lysosomes multiple (osteoclasts and skeletal muscle cells), or none and transports lipids. (red blood cells and platelets). The golgi has a cis end (accepts incoming vesicles) and DNA is long and must be condensed to fit in the a trans end (exports vesicles) nucleus. A continuous strand of DNA is wrapped around repeating units of histone proteins to reduce size. Chromatin is the condensed form of DNA. - Nucleosome: a bundle of 8 histones with DNA Nucleolus coiled around them - Chromosome: tightly condensed chromatin which is visible when the cell is ready to divide Cytosol/cytoplasm: aqueous substance inside the cell that the organelles are suspended in. Ribosomes: non-membrane bound organelles found in both prokaryotes and eukaryotes. Responsible for protein synthesis (translation). The test does consider ribosomes to Smooth ER be organelles! Ribosomes Rough ER Made of rRNA and protein. Composed of 2 subunits synthesized in the nucleolus but assembled in the cytoplasm. Pro-Tip: The Rough ER and Golgi are the two organelles - Eukaryotic subunits are larger than prokaryotic capable of post-translational protein modification subunits Ribosomes can be found free floating (make proteins that function inside the cell) or bound to the rough ER (make proteins exported out of the cell) DAT Booster | Booster Prep™  7 3.4 Cell Digestion and Assorted Structures 3. Microtubules: Hollow tubes made of polymers of the protein tubulin. Provide support and motility for Organelles involved in breaking down substances: cellular activities and intracellular transport. E.g. spindle apparatus in cell division, cilia and flagella, Lysosomes: digestive enzyme-containing 1 membrane bound centrioles vesicles produced by the Golgi Functions include apoptosis (cell suicide), autophagy (breakdown of organelles), nutrient breakdown, and destruction of internal phagocytes) Peroxisomes: membrane bound organelles that break down toxic substances and fatty acid. Produce and breakdown hydrogen peroxide (H2O2) using the enzyme catalase Flagella are whip-like extensions from cells while cilia are Vacuoles: large vesicles that store and move materials. short, hair-like extensions from cells. Both can be used to Various types: allow the cell to move through the environment, or to Transport vacuoles: move materials between sweep 2 substances in the environment in a specific direction. organelles or to the plasma membrane Both are made of centrioles and are organized at their base Food vacuoles: temporary receptacles of nutrients from basal bodies. which merge with lysosomes for intracellular digestion Central vacuole: large vacuole for nutrient and water Microtubules organizing centers (MTOCs): arrange storage in plants. microtubule structures within the cell (e.g. centrioles and - Exerts turgor pressure when filled to maintain cell basal bodies) rigidity by pressing up against cell wall Contractile vacuoles: collect and pump excess water Centrosome: two perpendicularly arranged centrioles used out of the cells to prevent bursting. Found in organisms in the formation of spindle fibers during cell division living in hypotonic environments (e.g. protists) Centrioles are a 9x3 array of microtubules. Plant cells lack centrioles but do have MTOC’s (spindle pole Structures involved in cellular organization: bodies) Cytoskeleton: network of tubules and filaments in the Microvilli: tiny, finger-like projections of cell membrane with cytosol. Functions include maintaining cell shape/providing an actin core that emerge from the apical surface of a cell. mechanical support, movement of components within the Function to increase the surface area of a cell, allowing cell, cell motility, and anchoring membrane proteins cells in the digestive system to absorb nutrients more efficiently 3 main components of the cytoskeleton (ordered from smallest to largest diameter) 3.5 Energy Production and Endosymbiotic Theory 1. Micro laments: composed of two intertwined strands of actin that function in cell motility. E.g. Organelles Involved in energy production: skeletal muscle contraction, amoeba pseudopods, cleavage furrow during cell division Mitochondria: double membrane bound organelle that 2. Intermediate laments: composed of intertwined creates chemical energy (ATP) and breaks down fatty acids coiled proteins that provide support to maintain cell (beta-oxidation) shape. E.g. keratin found in the skin Inner membrane is highly folded (cristae) to increase surface area. Contained within the inner membrane is the mitochondrial matrix DAT Booster | Booster Prep™ fi fi  8 Cells that need more energy have more mitochondria 3.6 Membrane Proteins Types of membrane proteins: Chloroplasts: double membrane bound organelle that is Peripheral: attached to the membrane surface. the site of photosynthesis in plants and algae. Uses light Hydrophilic and held in place with hydrogen bonds and energy to produce sugar. 1 electrostatic interactions. Removable with high salt Absorb red and blue light, reflect green light concentration or extreme pH Evolved from photosynthetic cyanobacteria Integral: Extend into the membrane and have hydrophobic regions. Removable with a detergent Endosymbiotic Theory: certain organelles (mitochondria which destroys the membrane. and chloroplasts) in eukaryotic cells were once independent - Transmembrane proteins: integral proteins that prokaryotic organisms that later formed a symbiotic pass all the way through the membrane, connecting relationship with a larger cell, leading to their presence as the interior and exterior of the cell to allow organelles in eukaryotic cells today. Evidence for this theory substance flow. includes: Mitochondria and chloroplasts have their own circular DNA genome Similar in size to prokaryotic cells and divide by binary fission (prokaryotic method of cell division) 2 Contain prokaryotic structures (e.g.: smaller ribosomes) Membrane proteins can also be categorized by function: Transport Proteins: transport materials across the membrane. - Channel Proteins: hollow tubes substances can move through (e.g.: aquaporins allow for quick movement of water across the membrane) ‣ Ion Channels: allow the passage of ions across the membrane. Can be gated: Endosymbiotic Theory ❖ Voltage-gated: opens or closes in response to a difference in membrane potential Both plant and animal cells are eukaryotic and contain ❖ Mechanically-gated: opens in response to many of the same organelles, with some key differences: pressure, vibration, temperature, etc. ❖ Ligand-gated: a molecule binds to open the Plant cells have a cell wall, animal cells do not channel Animal cells use centrioles as their MTOC’s, plants use - Carrier Proteins: pass molecules across the spindle pole bodies membrane by changing shape Plant cells have several unique organelles that animal cells lack: Receptor Proteins: binding site for hormones and - Plastids: chloroplasts (site of photosynthesis), other signaling molecules that trigger changes inside leucoplasts (store nutrients) and chromoplasts (store the cell when activated pigments) - Storage Vacuoles: store nutrients, waste, water, etc. DAT Booster | Booster Prep™  9 Glycoproteins: proteins with carbohydrates attached. Important for cell-to-cell recognition, signaling, and adhesion - Immune cells check membrane glycoproteins to determine if a cell is foreign1 - Can act as receptors by binding to signaling molecules Enzymes: accelerate chemical reactions by helping to convert one substance to another Basement Membrane: part of the extracellular matrix Adhesion/Anchor Proteins: attach cells to adjacent that anchors and supports cells attached to it. cells and other extracellular or intracellular proteins/ filaments for stability and communication Cell orientation: the apical (top) surface points outward, lateral surfaces are on the side, and the basal Cell junctions are attachments between cells. surface forms the bottom of the cell. 1. Tight junctions: form a seal between adjacent cells, preventing the passage or leakage of material between them. Found in the digestive tract and blood brain barrier. 2. Adherens Junctions: Firmly attaches adjacent cells together, allowing organization into tissues (e.g. cells lining blood vessels). a. Further stabilized by attaching to actin filaments on the inside of the cell 3. Desmosomes: similar to adherens junctions, but a stronger connection between cells. Found in tissues prone to mechanical stress (e.g. cardiac muscle, epidermis) a. Attached to intermediate filaments (keratin) inside the cell for reinforcement 3.7 Cell Transport 4. Hemidesmosomes: attach cells to the extracellular matrix (at the basement membrane). Found in Passive Transport: movement of substances across a epidermis of skin. membrane from higher to lower concentration. Does a. Helps stabilize cells and hold them in place to not require energy. - Simple diffusion: substances move passively down underlying tissues 5. Gap Junctions: narrow tunnels between cells which their concentration gradient directly across the cell allow for cell-to-cell communication. Allow passage membrane, without any membrane proteins - Facilitated diffusion: substances move passively of ions and small molecules to flow directly from one cell to another down their concentration gradient, but use the a. Electrical signals can pass through smoothly; assistance of membrane proteins in the cell used to conduct electrical signals in cardiac membrane muscle cells Active Transport: movement of substances against their concentration gradient (from lower to higher concentration). Requires energy (ATP) and transport proteins. DAT Booster | Booster Prep™  10 - Primary active transport: ATP is directly used to move substances against the concentration gradient - Secondary active transport: energy from an established electrochemical gradient is used to move substances against their1 concentration gradient. The movement of one molecule provides energy to actively drive the transport of a different molecule ‣ Antiporters: move molecules in opposite directions ‣ Symporters: move molecules in the same Diffusion vs Osmosis: direction Diffusion: solute (particles dissolved in the solvent) moves from areas of higher concentration to lower Solute Movement Favorability Energy Required? concentration Hight to Low Energetically Osmosis: solvent (usually water) moves from areas of No Concentration Favorable lower concentration to higher concentration (i.e. balances out concentration) Low to High Energetically Yes 2 Concentration Unfavorable Cells will respond to the type of solution they are placed in: Hypotonic solution: solution has a lower solute Without energy input, solutes move down the concentration compared to the inside of the cell. Water concentration gradient (high to low) until equilibrium is enters the cell to achieve equilibrium. reached. If a solution is very hypotonic (e.g. distilled water), water will continue to rush into the cell until it bursts More advanced cellular transport mechanisms can be used (lysis) to transport substances out of or into cells. Isotonic solution: roughly equal concentration as inside Endocytosis: extracellular substance is brought into the the cell; no overall net movement of water. cell by the membrane folding around it Hypertonic solution: solution has a higher solute - Phagocytosis: substances outside the cell are concentration compared to the inside of the cell. Water engulfed into the cell membrane through exits the cell to achieve equilibrium. pseudopods (membrane extends outwards). - A cell placed in a hypertonic solution will shrivel Substance engulfed into a vesicle (plasmolysis) ‣ Common in the immune system: pathogens are brought into the cell to be destroyed via Plants cells can behave differently when placed in these lysosomes solutions: - Pinocytosis: “cell drinking.” The membrane pinches Hypotonic solution: plant cells are generally in inwards to non-selectively incorporate extracellular hypotonic environments and do not burst open due to fluid and substances dissolved in the liquid their cell wall. Instead, these cells become turgid due - Receptor-Mediated Endocytosis: endocytosis to their central vacuole swelling. triggered by extracellular molecules binding to Isotonic solution: plant cell is flaccid receptors on the cell membrane Hypertonic solution: plasmolysis occurs (plant cell ‣ Signals clathrin proteins to attach to the maintains its shape due to the cell wall, but is shriveled) membrane and pull inward *Note: hypertonic and hypotonic are relative terms that can Exocytosis: substances exit the cell via the membrane also be used to describe the inside of the cell rather than pinching outward. the solution DAT Booster | Booster Prep™  11 Lipopolysaccharide 3.8 Outer Cell and Intracellular Transport Extracellular Matrix (ECM): a network of fibrous structural proteins, adhesion proteins, and polysaccharides in the The cell wall is an additional layer outside of the plasma area between adjacent animal cells. 1 membrane for support and protection. Knowing what the Three main functions: structural support, cell adhesion/ cell wall is made of is critical for the test. anchoring, and cell signaling 5 Major Components: glycoproteins, proteoglycans, Cell Type Cell Wall Composition collagen, fibronectin, and integrin Plant Cellulose - Collagen is a particularly strong protein fiber 2 ‣ Most abundant protein in the human body (found Fungi Chitin in bones, muscles, and skin) Bacteria Peptidoglycan ‣ Has a triple helix structure in which every third amino acid is glycine Archea Polysacchardies Animal No Cell Wall Intracellular transport is accomplished by microtubules and motor proteins: Note that animal cells do not have a cell wall. Microtubules provide a network of “tracks” along which Bacteria cell walls can be further categorized as gram organelles and vesicles are transported using motor negative or gram positive. proteins. - The motor proteins kinesin and dynein move along Gram Negative: thin peptidoglycan layer sandwiched microtubules to transport substances in between an outer and inner membrane. Stains pink. ‣ Gram negative bacteria have Cyclosis: streaming movement of cytoplasm which is lipopolysaccharides (LPS) attached to their outer generated by contraction and relaxation of the membrane. When broken down, these LPS cytoskeleton molecules act as endotoxins that can trigger an immune response Gram Positive: thick peptidoglycan layer that surrounds an inner membrane. Stains purple Glycocalyx: a carbohydrate coat that covers the outer surface of some animal and bacterial cells. Can also be found on the inside of blood vessels to protect vascular walls. Acts as a barrier to chemical or physical damage, provides adhesive capabilities, and prevents pathogens from entering the cell molecules act as endotoxins that can trigger an immune response DAT Booster | Booster Prep™ Biothermodynamics 12 4.1 Introduction to Metabolism and ATP Bonds between the phosphate groups store energy which is released when the bonds are broken during Biothermodynamics: the transfer 1of energy between and ATP hydrolysis (very energetically favorable) within living organisms ATP Hydrolysis: ATP ➞ ADP + Pi (exergonic/ -∆G) ATP Reformation: ADP + Pi ➞ ATP (endergonic/ +∆G) Kinetic Energy: the energy of anything in motion (e.g. ATP harnesses the energy of highly exergonic flagella whipping back and forth) processes (like cellular respiration) to power endergonic reactions Potential Energy: stored energy, often in chemical bonds (e.g. glycogen stored in muscles) Cell Metabolism: the sum of all chemical reactions in a cell (metabolism= catabolism + anabolism + energy transfer) Types of chemical reactions: Catabolism: the breakdown of complex molecules into Exergonic: a spontaneous reaction that releases energy simpler molecules. Releases energy which can drive (energy level of products is lower than reactants) anabolic pathways Endergonic: a non-spontaneous that requires energy 2 Anabolism: the synthesis of complex molecules from (energy level of reactants is lower than products) simpler ones, using energy 3 Laws of thermodynamics: 1. Energy cannot be created or destroyed – only transferred and transformed 2. Entropy of closed systems tends to increase over time. a. Livings organisms are not closed systems, so they can become more ordered (decreased entropy) over time by increasing disorder in their surroundings 3. Entropy minimizes as a system approaches absolute Spontaneous reactions can occur on their own without the 0 Kelvin addition of energy 4.2 Enzymes Gibbs Free Energy formula: ∆G = ∆H - T∆S; H= enthalpy, S=entropy, T=temperature Catalysts are molecules that accelerate the rate of a ∆G < 0 = spontaneous/exergonic reaction reaction without being consumed themselves. They do so ∆G > 0 = nonspontaneous/endergonic reaction by lowering the activation energy of a reaction. Endergonic reactions can be driven forward by coupling Enzymes are biological catalysts (usually proteins). them with exergonic reactions. Endergonic reactions are Substrate: the molecule that an enzyme acts on often coupled to the highly exergonic breakdown of ATP Active site: the location on the enzyme where the (ATP hydrolysis substrate binds. The shape of the active site determines the enzyme’s substrate specificity (i.e. what Adenosine Triphosphate (ATP): chemical form of stored molecules it can interact with) energy DAT Booster | Booster Prep™  13 Enzyme binding follows the induced t model (the 4.3 Enzyme Ef ciency and Regulation enzyme’s active site molds itself to the substrate, forming a better fit between the two). The “lock and key” theory of Enzyme activity can be affected by factor such as pH & enzyme binding (active substrate and enzyme fit together temperature. 1 perfectly like a lock to a key) has since been disproved. Extreme pH or temperature change can cause protein denaturation. Cofactors: nonprotein structures that assist enzymes in - A denatured protein has lost all structure except its their function. Can bind permanently or reversibly. primary structure and is nonfunctional Organic cofactors (coenzymes): E.g. vitamins or heme groups - Prosthetic groups: organic cofactors which bind covalently (permanently) to enzymes - Cosubstrates: organic cofactors which bind reversibly to enzymes Inorganic cofactors: metal ions (e.g. Fe2+, Mg2+) Levels of enzyme regulation: Genetic Level: genes producing enzymes can be How enzymes work: 1. Substrate binds non-covalently to the active site of activated or disabled (e.g.: lac operon) 2 Physical Level: enzymes can be stored in vesicles and an enzyme 2. Enzyme catalyzes conversion of substrate into a only released as needed Enzyme Level: enzymes can be activated/disabled via product molecule 3. Product molecule is released from active site, chemical modification Negative Feedback/Feedback Inhibition: when the allowing a new substrate molecule to bind product of a reaction binds to and inhibits that reaction, preventing excess product production - Primary way the body maintains homeostasis 4.4 Enzyme Kinetics Enzyme Kinetics: how quickly an enzyme can convert substrates into products Key Terms: Vmax: maximum rate of a reaction - Vmax increases as the amount of substrate increases. Important enzyme facts: - Limited by enzyme saturation (increasing enzyme Not consumed in reaction concentration also increases Vmax) Highly specific ½ Vmax: half of the max rate Do not change ∆G, or the reaction equilibrium Km (Michaelis Constant): the concentration of substrate Are usually proteins (can be denatured in extreme at ½ Vmax. Inversely proportional to substrate binding conditions) except for ribozymes affinity (how well the enzyme binds to a substrate) - Small Km: high binding affinity; less substrate Ribozymes: RNA molecules with enzymatic function needed to saturate the enzyme - Large Km: low binding affinity; more substrate Zymogens (proenzymes): inactive precursor form of an needed to saturate the enzyme enzyme. Activated/cleaved by certain conditions or - Km is an intrinsic property and can only be changed molecules by inhibitors. Km is not affected by changing enzyme E.g. pepsinogen (zymogen) ➞ pepsin (active form) or substrate concentration when exposed to stomach acid DAT Booster | Booster Prep™ fi fi  14 1 Types of inhibitory regulation Competitive Inhibition: inhibitor reversibly binds to the active site. Can be overcome by increasing substrate concentration. - Vmax is unaffected, Km increases Non-Competitive Inhibition: the inhibitor binds to the enzyme at a location other than the active site. Cannot be overcome by increasing substrate concentration. - Vmax decreases, Km is unaffected Allosteric Inhibition: inhibitor binds to the allosterc site of enzyme and induces the enzyme’s inactive form. 2 Allosteric inhibition is a form of non-competitive inhibition. Some enzymes have multiple actives sites to bind multiple substrate molecules. In cooperativity, the binding of one substrate can affect the af nity of additional substrates to bind. Positive Cooperativity: each substrate that binds makes it easier for more substrates to bind. Can be seen in non-enzyme molecules as well (e.g. oxygen binding to hemoglobin) Negative Cooperativity: each substrate that binds makes it harder for more substrates to bind DAT Booster | Booster Prep™ fi Cellular Respiration 15 5.1 Mitochondria Anatomy 5.2 Glycolysis Glucose + 2 NAD+ + 2 ADP ➞ 2 Pyruvate + 2 ATP + 2 Cellular Respiration: combination1of aerobic and anaerobic NADH + 2 H2O catabolic pathways that cells use to breakdown organic compounds (e.g. glucose) into ATP Glycolysis is anaerobic (no O2 required) breakdown of glucose into two pyruvate molecules which occurs in the Aerobic Cellular Respiration of glucose: consists of 3 steps cytosol of all living cells (prokaryotic and eukaryotic). 1. Glycolysis (in cytosol of cell) Produces ATP via substrate level phosphorylation 2. Citric Acid/Krebs/Tricarboxylic Acid Cycle (in mitochondrial matrix) Important steps of Glycolysis: 3. Oxidative Phosphorylation/Electron Transport Chain Step 1: Hexokinase uses 1 ATP to convert glucose ➞ (across inner mitochondrial membrane) glucose 6-phosphate, providing a net negative charge and preventing diffusion out of the cell Mitochondria are critical to cellular respiration in eukaryotic Step 3: Phosphofructokinase (PFK) uses 1 ATP to cells as they are the site of aerobic cellular respiration to 2 convert fructose 6-phosphate ➞ fructose 1,6- synthesize ATP. bisphosphate, committing the molecule to glycolysis Cells which need more energy have more mitochondria (irreversible, key regulatory step) (e.g: muscle cells). - High ATP inhibits PFK, preventing glycolysis Have their own DNA (circular genome which replicates - Low ATP disinhibits PFK, encouraging glycolysis independently from cell) and their own ribosomes. All mitochondrial DNA is maternally inherited. Glycolysis has two distinct phases, creating a net production of 2 ATP, 2 pyruvate, 2 NADH: Mitochondria Anatomy 1. Energy investment phase (2 ATP invested) 2. Energy payoff phase (4 ATP and 2 NADH generated) NADH: electron carrier, useful later in cellular respiration NAD+ must be available for glycolysis to occur and create NADH Following glycolysis, pyruvate has two possible paths: 1. Respiratory path: oxygen is present (pyruvate will enter the Krebs cycle ➞ electron transport chain) Overall Reaction of Cellular Respiration: 2. Non-respiratory path: oxygen is absent C6H12O6 (glucose) + O2 ➞ 6CO2 + 6H2O + Energy (fermentation) Cellular respiration is oxidative (glucose loses electrons) and exergonic (spontaneous, energy released) Two ways to produce ATP: Substrate-level Phosphorylation: an enzyme directly transfers phosphate onto ADP to form ATP Oxidative Phosphorylation: ATP is produced using energy from electron flow of the electron transport chain DAT Booster | Booster Prep™  16 Cycle occurs twice per glucose molecule Each cycle produces 1 ATP 3 NADH, and 1 FADH2 - 2 CO2 are also produced per cycle. This is the CO2 exhaled during respiration *Note: One glucose molecule yields 6 NADH, 2FADH2, 2 ATP, and 4 CO2, from the CAC Electron carriers (NADH, FADH2): molecules that function as high energy electron carriers During glycolysis and CAC, glucose is stripped of high energy electrons and these carriers are reduced as they gain the electrons: NAD+ ➞ NADH 5.3 Citric Acid Cycle FAD ➞ FADH2 NADH and FADH2 then shuttle glucose’s electrons to the Pyruvate decarboxylation: if oxygen is present, pyruvate is ETC to create ATP 2 converted into acetyl CoA in the mitochondrial 1 matrix 2 Pyruvate ➞ 2 Acetyl CoA + 2 NADH + 2 CO2 5.4 Electron Transport Chain The Acetyl CoA molecules then enter the Citric Acid Cycle Electron Transport Chain (ETC): a series of proteins which (aka Krebs Cycle/Tricarboxylic Acid Cycle) pass high energy electrons to each other; embedded in the Citric Acid Cycle (CAC) produces ATP via substrate inner membrane of the mitochondria level phosphorylation (like glycolysis) and occurs in the mitochondrial matrix NADH and FADH2 are oxidized as they pass their high energy electrons to the proteins in the ETC NADH ➞ NAD+ FADH2 ➞ FAD NAD+ and FAD will re-enter glycolysis and the CAC to pick up more electrons As high energy electrons pass through the ETC , the energy from their redox reactions is used to pump protons (H+) from the mitochondrial matrix into the intermembrane space, across the inner mitochondrial membrane. H+ accumulates in intermembrane space, establishing an electrochemical gradient (a difference in concentration and charge across membrane) - Intermembrane space increases in H+ concentration Exergonic transfer of electrons through the ETC is coupled to endergonic pumping of protons against their concentration gradient CAC summarized: Acetyl CoA from pyruvate Final step of ETC: electrons are transferred to O2. The O2, decarboxylation merges with oxaloacetate to form citrate protons, and electrons combine to form water (H2O) ➞ citrate undergoes 7 more steps, forming different Note that oxygen is the final electron acceptor, forming intermediates ➞ oxaloacetate is reformed ➞ cycle repeats water in the process DAT Booster | Booster Prep™  17 ATP Synthase: makes ATP from ADP via oxidative phosphorylation, powered by the proton-motive force. Embedded in inner mitochondrial membrane. Proton-Motive force: gradient of protons (high [H+] in 1 intermembrane space, low [H+] in mitochondrial matrix) forming electrochemical gradient Chemiosmosis: movement of ions down a concentration gradient across a semipermeable membrane 5.5 Anaerobic Respiration Protons flow down their gradient (from the Anaerobic respiration and fermentation are two entirely intermembrane space into the mitochondrial matrix) different processes. through ATP synthase. ATP synthase uses the flow of H+ to make ATP from ADP Anaerobic respiration: cellular respiration (glycolysis ➞ CAC ➞ ETC) that occurs with molecules other than O2 as the final e- acceptor (e.g. SO42-, NO3-, S). Fermentation: 2 anaerobic recycling of NADH into NAD+ from pyruvate. Occurs in the cytoplasm of the cell and does not generate any ATP (only regenerates NAD+) During glycolysis, 2 NAD+ ➞ 2 NADH. In anaerobic conditions, NAD+ gets depleted, preventing further glycolysis. NADH must turn back into NAD+ to continue glycolysis Under anaerobic conditions, pyruvate enters the fermentation process instead of undergoing pyruvate decarboxylation Mitochondria’s highly folded inner membrane increases Types of fermentation: surface area for more electron transport chains, allowing Alcohol fermentation: occurs in yeast and some bacteria. more ATP production Two steps: In prokaryotes, the ETC is embedded in the cellular 1. Pyruvate ➞ Acetaldehyde + CO2 membrane instead of the inner mitochondrial 2. Acetaldehyde + NADH ➞ Ethanol + NAD+ membrane (no membrane-bound organelles) - NAD+ is replenished for glycolysis - Acetaldehyde acts as the final electron acceptor Lactic acid fermentation: takes place in human muscle cells, fungi and bacteria. One step: 1. Pyruvate + NADH ➞ Lactate + NAD 2. In muscles, lactate is transported to the liver and transformed back into glucose via the Cori Cycle - NAD+ is replenished for glycolysis 3. Occurs during intense exercise/physical exertion, when O2 availability is too low for aerobic respiration The ETC yields a total of approximately 34 ATP ETC produces by far the most ATP in cellular respiration DAT Booster | Booster Prep™  18 Cellular metabolism = all an organism’s chemical reactions. Involves both anabolic and catabolic reactions 1 5.7 Alternative Energy Sources (Carbohydrates) Carbohydrate Metabolism Pathways: 1. Glycogenesis: body stores extra glucose as glycogen by linking glucose molecules together. a. Glycogen is mostly stored in liver and skeletal muscles b. Energy cost: ATP is used to turn glucose into glucose-6-phosphate (G6P). G6P is the crossroad for many different carbohydrate metabolism pathways 2. Glycogenolysis: breakdown of stored glycogen into glucose for energy. Occurs when glucose 2 levels are low. 3. Gluconeogenesis: synthesis of glucose from non-carbohydrate molecules (proteins and lipids). Occurs in the liver and the kidney when glucose and glycogen levels are low. 4. Glycolysis: breakdown of glucose to make pyruvate and produce ATP. Carbohydrate metabolism is regulated by two important pancreatic hormones: 1. Insulin: endocrine hormone released when blood glucose is high. Effects of Insulin: a. Tells cells to uptake glucose b. Promotes glycogenesis and glycolysis 2. Glucagon: released when blood glucose is low. Effects of Glucagon: a. Triggers glycogenolysis b. Inhibits glycogenesis and glycolysis (preserves glucose for critical functions the brain) 5.8 Alternative Energy Sources (Lipids) 5.6 Intro to Alternative Energy Sources In lipolysis, triglycerides are broken down into glycerol Glucose is the cell’s preferred source of energy, but + 3 fatty acid chains other molecules (others carbohydrates, lipids, or Lipase splits glycerol and the fatty acids apart. proteins) can be used if glucose is not present. Glycerol is phosphorylated into G3P (a glycolysis Cellular respiration = catabolic process which intermediate) releases energy by breaking down organic Fatty acid chains are broken down via beta- molecules. Can use electrons from the break down oxidation (occurs in mitochondrial matrix) to towards the ETC, to make lots of ATP produce a lot of ATP DAT Booster | Booster Prep™  19 In beta oxidation, carbons are cut away from the fatty acid chain to produce acetyl CoA, NADH, and FADH2 Although fats provide more ATP per gram than carbohydrates, carbohydrates remain the preferred energy source because they 1are quicker for the body to access The brain prefers to use glucose for energy but when glucose is low, the brain uses ketones (produced from fatty acids) as a backup energy source. 5.9 Alternative Energy Sources (Proteins) Proteins are the least desirable source of energy (only used when carbs and fats are scarce). When necessary, amino acids are broken down into intermediates that enter the cellular respiration pathway. Oxidative deamination: removal of amino group from 2 amino acids in order to make other metabolic intermediates. Mostly occurs in the liver. Remaining ammonia molecule is toxic so the body converts it to urea for excretion Nucleic acids are not used to generate energy, but when DNA/RNA gets broken down, compounds produced can be salvaged to make new nucleotides. DAT Booster | Booster Prep™ Photosynthesis 20 6.1 Chloroplast Anatomy 6.2 Light Dependent Reactions Photosynthesis includes: Photosynthesis: biological process done by 1. Light Dependent Reactions (Light Reactions) photoautotrophs (plants, some bacteria and protists); a. Products: ATP, NADPH, O2 captures energy from sunlight and converts it to chemical energy stored in the form of glucose 2. Light Independent Reactions (Dark Reactions/ Takes place in the chloroplast Calvin Cycle) Overall Reaction: 6CO2 + 6H2O → C6H12O6 + 6O2 a. Convert CO2 → glucose Chloroplast: organelle that is only found in Light-Dependent Reactions: include cyclic and noncyclic photoautotrophs; contains chlorophyll (light absorbing photophosphorylation using chlorophyll found in pigment with a porphyrin ring that has an Mg atom in the photosystems center; similar structure to hemoglobin) Photosystems (PS): large chlorophyll containing proteins found in the thylakoid membrane. Chloroplast Structure (external to internal): Action 2 Spectrum: plots wavelengths of light that are 1. Outer membrane (smooth) most effective at causing photosynthesis 2. Intermembrane space Red/blue light: highest rate of photosynthesis 3. Inner membrane (smooth) Green light: lowest rate of photosynthesis (chlorophyll 4. Stroma (cytoplasm of chloroplast) reflects green wavelength of light instead of absorbing a. Stroma lamellae: connect thylakoids together it; this is why plants are green) b. Thylakoids: membrane bound flattened disks found in the stroma i. Thylakoid membrane: contain chlorophyll ii. Thylakoid lumen: space enclosed by thylakoid membrane iii. Granum: stack of thylakoids Stroma lamellae Thylakoid lumen Thylakoid membrane Outer membrane Intermembrane Noncyclic Photophosphorylation Steps: occurs in space thylakoid membrane, uses PS II and PS I Granum 1. Sunlight hits PS II → photons from light excite electrons (boosts electrons to higher energy level) Inner membrane 2. High energy electrons passed to primary electron acceptor 3. Primary electron acceptor passes electrons through the electron transport chain (ETC), pumps protons Thylakoid Stroma (H+) against concentration gradient from stroma ➞ thylakoid lumen (creates an electrochemical gradient) DAT Booster | Booster Prep™  21 4. Protons flow through ATP synthase down their 3 phases of the Calvin Cycle: concentration gradient, catalyzing the conversion of 1. Carbon xation: taking carbon from an inorganic ADP to ATP source (CO2 in atmosphere) and converting it to an a. This ATP is used to power photosynthesis. organic compound (glucose) Cellular respiration still1 occurs to produce a. Done by autotrophs (plants, photosynthetic energy in plants. organisms, chemoautotrophic prokaryotes) 5. Electrons (now low-energy) arrive at PS I ➞ photons 2. Reduction (steps that use up ATP and NADPH from from sunlight re-excite electrons to higher energy light reactions) level 3. Regeneration: intermediates are regenerated so 6. Electrons are passed to an electron acceptor and cycle can continue travel down another ETC 7. NADPH is formed by combining high energy Important Steps of Calvin Cycle: electrons with NADP+ 1. RuBisCo (most abundant enzyme on Earth) a. NADPH transports high energy electrons to the combines CO2 with RuBP, forming a 6 carbon Calvin cycle for glucose production intermediate (carbon fixation phase) 2. 6 carbon molecule is broken into two 3-carbon Photolysis: splitting of water by light that occurs in PS II. phosphoglycerate (PGA) molecules Water is split into: 3. PGA is phosphorylated to G3P (using ATP and 2 1. H+ (used in concentration gradients) NADPH during the reduction phase) 2. Electrons (stored in photosystems to be excited by 4. Most G3P is converted back to RuBP (requires ATP) sunlight) and remaining G3P is used to make glucose 3. Oxygen (released into atmosphere – source of (regeneration phase) oxygen we breathe) a. 1 molecule of glucose is produced with 6 turns of the cycle (1 cycle produces 2 G3P molecules, Cyclic Photophosphorylation Steps: occurs in the stroma so 6 cycles produce 12 G3P. 10 are used to lamellae; only involves PS I reform RuBP, and the remaining 2 are used to 1. Electrons in PS I get excited by sunlight to a high make glucose) energy state 2. Electrons get recycled passed back to the first ETC, allowing more pumping of H+ and making more ATP instead of NADPH (replenishes the ATP used in 6.3 Light Independent Reactions Light Independent Reactions (aka Dark Reactions/Calvin Cycle): do not directly use sunlight, but still need the ATP and NADPH formed by the light reactions. Occurs in the stroma of the chloroplast. Converts CO2 ➞ glucose DAT Booster | Booster Prep™ fi  22 6.4 Photorespiration and Photosynthesis Types CAM Photosynthesis Steps: 1. CO2 combines with PEP to form malic acid (stored Photorespiration: an undesirable process which reduces in plant vacuole) at night when there is no sunlight the efficiency of carbon fixation, forming useless to prevent water loss byproducts. Occurs when RuBisCo1 binds O2 instead of CO2 2. Malic acid is converted back into CO2 and the Oxygen is a competitive inhibitor of RuBisCo Calvin Cycle can occur when stomata are closed and there is sunlight Types of Photosynthesis: C2: photorespiration; product = useless 2 carbon molecule Takes place in all plants Some plants have no way to stop C2 and photosynthesize less efficiently C3: normal photosynthesis Takes place in all plants in the mesophyll cells C4: prevents photorespiration by physically separating light 2 and dark reactions Plant leaf anatomy (external to internal): mesophyll cells → bundle-sheath cells → vascular tissue - Oxygen can reach mesophyll cells, but not the deeper bundle-sheath cells C4 plants undergo the dark reactions in the bundle- sheath cells instead of the mesophyll cells C4 Photosynthesis Steps: 1. CO2 combines with PEP to form malate 2. Malate is moved to bundle sheath cells, and is converted to CO2 + pyruvate 3. Pyruvate shuttled to mesophyll cells and converted back to PEP + CO2 Note that plants can continue functioning at night despite 4. CO2 will enter Calvin Cycle (combine with RuBP via the lack of sunlight because they store extra glucose in the RuBisCo) to make glucose in the bundle-sheath cell form of starch which can be converted back to glucose to a. O2 can’t get to bundle sheath cells, minimizing power plant cell function when sunlight is unavailable. photorespiration CAM: minimizes water loss via temporal separation instead of spatial (common in plants in dry environments e.g. cactus) Stomata are pores found on bottom of leaves for gas exchange. In most plants, stomata are always open for continuous exchange of CO2 and O2, allowing water to escape easily in certain environments - CAM plants only open their stomata at night so that CO2 can enter and less water is lost. However, there is no sunlight at night, so there is no ATP/NADPH from the light reactions to power the Calvin Cycle DAT Booster | Booster Prep™ Cell Division 23 7.1 Intro to Cell Division Homologous Chromosomes are a set of a chromosomes (one from each parent) in a pair. Found in diploid cells. Cell division is how cells replicate to increase their number. Homologous chromosomes are similar in length, gene Most eukaryotic cell division starts with nuclear division position, and centromere position. They carry genetic followed by cytokinesis (division of cytoplasm). information for the same traits, but are not genetically Chromatin is a condensed form of DNA that is wrapped identical. around histones. DNA is stored as chromatin, but during Humans have 46 chromosomes (23 homologous pairs); cell division, it condenses even more into chromosomes. except in males, the XY sex chromosomes are Chromosomes: dense packaging of chromatin, existing technically not homologous. during mitosis and meiosis. Chromosomes can be in duplicated or unduplicated forms. - Chromatid: one half of a duplicated chromosome - Sister Chromatids: two duplicated chromatids that are completely identical to one another. They can connect at the centromere to form an X-shaped 2 chromosome - Centromere: region where two sister chromatids are connected; kinetochores attach here Centrosomes are the Microtubule Organizing Centers (MTOCs) of animal cells. A centrosome is composed of 2 centrioles perpendicular to each other. Spindle Fibers: microtubules that emerge from the centrosome. They allow chromosomes and chromatids to be separated during specific phases of cell division. Spindle fibers do not attach directly to chromosomes – Haploid vs Diploid Cell instead they attach to kinetochores (proteins that n = number of chromosomes in a set adhere to the centromere region of the chromosome) Haploid Human cells: n=23, but most cells are - Drugs that disrupt microtubule formation or diploid, so there are 46 total chromosomes breakdown will inhibit cell division Diploid Cells (2n) have 2 sets of chromosomes: one Plant cells do not have centrosomes – they use a from the mother and one from the father. The vast different MTOC majority of human cells are diploid. - Human cells: n=23, but most cells are diploid, so 7.2 Mitosis there are 46 total chromosomes Mitosis: nuclear division that creates a pair of diploid cells that are genetically identical to the original cell Occurs in somatic cells (cells not directly involved in producing gametes) Mitosis Overview: prophase → prometaphase → metaphase → anaphase → telophase and cytokinesis DAT Booster | Booster Prep™  24 Telophase Nucleoli redevelop Two nuclear envelopes develop Chromosomes decondense back into chromatin 1 Spindle fibers disappear Cytokinesis occurs during telophase - Mitosis: the nucleus duplicates - Cytokinesis: the rest of the cell duplicates Cytokinesis: physical division of the cytoplasm to form two Prophase cells. Cytokinesis is technically not part of mitosis; mitosis Chromatin condenses into chromosomes divides the nucleus, then cytokinesis divides the cytoplasm. Nucleolus disappears The two processes overlap and together create separate Mitotic spindle begins to form cells with separate nuclei. Cytokinesis typically begins Centrosomes begin to move towards opposite ends of during telophase. the cell Animal cells form a cleavage furrow (contractile ring formed by actin and myosin) forms; ring contracts to Prometaphase separating the dividing cells into two 2 Nucleus disassembles Plant cells form a cell plate that develops between the Chromosomes condense even further two nuclei; essentially a cell wall that fuses with the Each chromatid is attached to a kinetochore existing plant cell wall, separating the two ce