Biology Exam #2 Study Notes PDF

Lecture 6: Organic Chemistry Carbon Key component of macromolecules Can form covalent bonds with up to four different atoms Serves as a “backbone” for the macromolecules Has four electrons in the outer shell Forms four covalent bonds to fill the outer shell which allows it to achieve the “octet rule...

Lecture 6: Organic Chemistry Carbon Key component of macromolecules Can form covalent bonds with up to four different atoms Serves as a “backbone” for the macromolecules Has four electrons in the outer shell Forms four covalent bonds to fill the outer shell which allows it to achieve the “octet rule” Hydrocarbons Carbon + Hydrogen (Ex: Methane) Covalent bonds between atoms in hydrocarbons store energy, the energy gets released when the molecules get burned The energy released from these hydrocarbons heat our homes and power our cars Methane Binds to four hydrogens to satisfy the octet rule Has a tetrahedral geometry, with each of the four hydrogen atoms spaced 109.5° apart Hydrocarbon Chains AKA Aliphatic Hydrocarbons Carbon forms single bonds with other atoms – shape is tetrahedral Two carbon atoms form a double bond – shape is planar, or flat Single bonds, like those found in ethane, can rotate Double bonds, like those found in ethane cannot rotate, so the atoms on either side are locked in place Hydrocarbon Rings AKA Aromatic Hydrocarbons Carbon can form five and six membered rings (closed chain) Single or double bonds may correct the carbons in the ring Nitrogen may be substituted for carbon Benzene: an important hydrocarbon ring – used in some amino acids, cholesterol, and its derivatives Four major classes of macromolecules 1. Carbohydrates 2. Lipids 3. Proteins 4. Nucleic acids Organic molecules all contain carbon (may also contain hydrogen, oxygen, nitrogen, and some other minor elements) Monomers Individual subunits of macromolecules Polymers Monomers are linked together via covalent bonds into polymers Dehydration synthesis Two molecules of glucose are linked to form the disaccharide maltose A water molecule is formed as the two monosaccharides are linked by a covalent bond Hydrolysis Process of breaking polymers down into individual monomers, AKA dehydration reaction Water serves as a reactant; one monomer receives a H+ and the other monomer receives an OH- Enzymes Are biological molecules that catalyze or “speed up” reactions Chemical reactions involving macromolecules are catalyzed by enzymes Enzymes speed up hydrolysis and dehydration reactions Dehydration reactions form new bonds/require energy Hydrolysis reactions break bonds/release energy Specific enzymes exist for each macromolecule class Carbohydrates- broken down by amylase, sucrose, lactase, maltase Lipids - broken down by lipases Proteins - broken down by pepsin and peptidase Carbohydrates Found in grains, fruits, and vegetables Provide energy to body in form of glucose Represented by the general formula (CH2O)n Ratio of Carbon: Hydrogen: Oxygen is 1:2:1 Has 2 main subtypes: 1. Monosaccharides 2. Disaccharides 3. Polysaccharides Monosaccharides Usually have 3-7 carbons End with the suffix -ose Contains a carbonyl group C=O Aldoses: carbonyl group at the end of the carbon chain Ketoses: carbonyl group in the middle of the carbon chain Trioses: three carbons Pentoses: five carbons Hexoses: six carbons Three structural isomers of a hexose monosaccharide Structural isomers/formula (C6H12O6) 1. Glucose - important source of energy 2. Galactose - part of lactose/milk sugar 3. Fructose - part of sucrose/fruit Monosaccharides exist as linear chain or ring-shaped molecules o Five- and six-carbon monosaccharides exist in equilibrium between linear and ring forms o Ring forms and the side chains closes and is locked into an alpha or beta position o Fructose and ribose also form rings o They form five-member end rings as opposed to the six-membered ring of glucose Disaccharides Form when two monosaccharides are linked in a dehydration reaction Example: o Glucose + Fructose = sucrose (disaccharide) o Two monomers are joined by glycosidic bond o Water is also released o Carbon atoms in a monosaccharide are numbered from the terminal carbon closest to the carbonyl group o Glycosidic linkage is formed between carbon 1 in glucose and carbon 2 in fructose o Results in 1,2 glycosidic linkages Other common disaccharides Maltose (grain sugar) Lactose (milk sugar) Sucrose (table sugar) All are created via formation of covalent glycosidic linkages Polysaccharides Long chain of monosaccharides joined by glycosidic linkages May be branched or unbranched May consist of multiple layers of monosaccharides Molecular weight could be >10,000 Daltons Polysaccharides can be distinguished by their glycosidic linkages Starch is composed of Amylose and Amylopectin The monomers are joined in two linkage types: 1. α 1-4 glycosidic bonds 2. α 1-6 glycosidic bonds Amylose = unbranched glucose monomers in α 1-4 glycosidic bonds Amylopectin = branched glucose monomers in α 1-4 and α 1-6 glycosidic bonds Cellulose A polysaccharide found in the cell wall of plants Glucose monomers are linked in unbranched chained by β 1-4 glycosidic linkages Every glucose monomer is flipped relative to the next one resulting in a linear, fibrous structure Chitin The hard exoskeleton of arthropods is composed of the polysaccharide chitin Contains nitrogen Lipids Are a diverse group of non-polar hydrocarbons Non-polar hydrocarbons are hydrophobic Function of Lipids Long-term energy stores Provides insulation from environment for plants and animals Serve as building blocks for some hormones Important component of cellular membranes Types of Lipids Fats Oils Waxes Phospholipids Steroids Fats and oils Fats – contain two main components 1. Glycerol 2. Fatty Acids Triacylglycerol – formed by joining three fatty acids to a glycerol backbone The glycerol molecules are attached to the fatty acids via an ester linkage Three molecules of water are released in this reaction Saturated and Unsaturated Fatty Acids Stearic acid is a common saturated fatty acid This means it contains no carbon-carbon double bonds in the carbon backbone Pack tighly and exist as solids at room temperature (butter, fats in meats, etc) May be associated with cardiovascular disease – should be limited in your diet Oleic acid is a common unsaturated fatty acid Contains at least one carbon-carbon double bond in carbon chain backbone ▫ Monounsaturated fat = one double bond ▫ Polyunsaturated fat = more than one double bond Most unsaturated fats are lipids at room temperature – referred to as oils What’s the deal with Trans-Fats? Each double bond of an unsaturated fat may be in one of two positions  ▫ Cis configuration – hydrogens are on the same side of the chain ▫ Trans configuration – hydrogens are on the opposite side of the chain Cis-acids have a kink in the chain ▫ They cannot be packed tightly ▫ Liquid at room temperature Trans-acids – no kink ▫ Can be created through processing ▫ Foods with trans-fat may increase LDL cholesterol in humans (bad for the heart) Essential Fatty Acids Required but not synthesized by the body – must be part of diet ▫ Omega-3 fatty acid (found in salmon, trout, tuna) ▫ Omega-6 fatty acid These fats are heart healthy ▫ Reduce risk of heart attack, reduce triglycerides in blood, lower blood pressure Waxes Long fatty acid chains esterified to long chain alcohols Hydrophobic and prevent water from sticking to surface Found on the feathers of some aquatic birds and on the surface of leaves from certain plants Phospholipids Molecule with two fatty acids and a modified phosphate group attached to a glycerol backbone The phosphate may be modified by the addition of charged or polar chemical groups Two common chemical groups that attach to phosphate are choline and serine Phospholipids are major constituents of the plasma membrane The hydrophilic head groups of the phospholipids face the aqueous solution The hydrophobic tails are sequestered in the middle of the bilayer Phospholipids contribute to the dynamic nature of plasma membrane Steroids Have a closed ring structure ▫ Four linked carbon rings ▫ Many have a short tail Structure is different from that of other lipids They are hydrophobic They are insoluble in water Cholesterol is the most common steroid ▫ Synthesized in liver ▫ Precursor to other hormones such as testosterone and estradiol ▫ Precursor to vitamin D ▫ Precursor to bile salts 09/26/24 Lecture 9: Macromolecules II Proteins Most abundant organic molecule Has a diverse range of functions o Regulatory functions o Structural functions o Protective functions o Transport  o Enzymes o Toxins Enzymes catalysts in biochemical reactions Specific enzyme for specific substrate Types of enzymes Catabolic - breakdown substrate Anabolic - build more complex molecules Catalytic - affect the rate of reaction Types of proteins Digestive enzyme  Example: amylase, lipase, pepsin, trypsin  Function: helps in digestion of food by catabolizing nutrients into monomer if units Transport  Examples: hemoglobin, albumin  Function: carries substances in the blood or lymph throughout the body Structural  Examples: actin, tubulin, keratin  Function: construct different structures, like the cytoskeleton Hormones  Examples: insulin, thyroxine  Function: coordinate the activity of different body systems Defense  Example: immunoglobulins  Function: protect the body from foreign pathogens Contractile  Examples: actin, myosin  Function: effect muscle contraction Storage  Examples: legume storage proteins, egg white (albumin)   Function: provides nourishment in early development of the embryo and the seedling Amino Acids Are the monomers that make up proteins Fundamental structure: Central carbon atom (α-carbon) Amino group (-NH2) Carboxyl group (-COOH) Hydrogen Side chain (R-group) Amino acids have Diverse Chemical Properties 20 common amino acids commonly found in proteins Each amino acid has a different R group (variant group) R-groups determine the chemical nature of each amino acid o Non-polar aliphatic o Polar o Positively charged o Negatively charged o Non-polar aromatic More on Amino Acids Amino acids are represented by a single upper-case letter or three letters o Valine = V or Val o Aspartic Acid = D or Asp Essential amino acids the following must be supplied in diet for humans o Isoleucine  o Leucine o Cysteine The sequence and number of amino acids determine the proteins shape, size and function Peptide Bond Formation Amino acid monomers are linked via a peptide bond formation (dehydration synthesis reaction) Carboxyl group of one amino acid is linked to the amino group of the incoming amino acid A molecule of after is released as a part of the reaction What’s the Difference between Polypeptides and Proteins? Polypeptide - a chain of amino acids joined together in peptide linkages Protein - a polypeptide or multiple polypeptides o Often combined with non-peptide prosthetic groups o Has a unique structure and function o Many proteins are modified following translation (process of creating a new protein) The Shape of Proteins is Crucial to their Function Protein shape is based upon four levels of structure 1. Primary structure 2. Secondary structure 3. Tertiary structure 4. Quatenary structure Primary Protein Structure The unique sequence of amino acids in a polypeptide Protein function could be compromised if alterations in the order of amino acids was to be made Amino acid sequence is based upon gene encoding that protein A change in the nucleotide sequence of DNA could lead to a change in amino acid This could lead to a change in protein structure and function Sickle cell anemia - How a Change in One Amino Acid can Impact Human Health Normal hemoglobin - amino acids at position seven is glutamic acid Sickle cell hemoglobin - glutamic acid is replaced by a valine The result of a single amino acid changes out of 600 amino acids that code for human hemoglobin Sickle cells are crescent shaped, while normal cells are disc-shaped Secondary Protein Structure Local folding of the polypeptide 1. α- helix – formed by hydrogen bonding between oxygen in carbonyl group and an amino acid 4 positions down the chain 2. β-pleated sheet - hydrogen bonding between atoms on the backbone of the polypeptide chain Certain amino acids tend to form an α- helix Others favor formation of β-pleated sheet Tertiary Structure The unique three-dimensional structure of a polypeptide Due to chemical interactions between R-groups on amino acids Ex. 1 – R-groups with like charges are repelled from one another Ex. 2 – R-groups that are hydrophobic will cluster in interior of protein Ex. 3 – cysteine side chains form disulfide bridges Examples of Tertiary Structures Hydrophobic interactions Ionic bonding Hydrogen bonding Disulfide linkages Quaternary Protein Structure Interactions between several polypeptides that make up a protein Weak interactions between subunits help stabilize the structure Denaturation and Protein Folding Protein structure and shape can be chnaged if chemical interactions are broken Protein structure/shape can change with altering primary structure due to: o Changes in pH o Changes in temperature Denaturation – changes in protein structure that leads to changes in the function Example: heating an egg to extreme temperatures can lead to irreversible denaturation of egg protein (albumin in egg goes from liquid to solid) Nucleic Acids Constitute the genetic material of livig organisms Two types of nucleic acid: 1. Deoxyribonucleic acid (DNA) 2. Ribonucleic acid (RNA) Location of nucleic acids Nucleus of eukaryotic cells Mitochondria Chloroplasts  Prokaryotic cells (not membrane enclosed) Role of DNA in the Cell DNA codes for the genome of cell – entire genetic content Chromatin – complex of DNA and histone proteins Chromosomes – threadlike structures containing tightly wound and packed chromatin DNA codes for thousands of genes Genes contain instructions for prodcuing proteins or various forms of RNA DNA controls all cellular activities by turning genes on or off Role of RNA in the Cell RNA is primarily involved in protein synthesis Types of RNA 1. Messenger RNA (mRNA) - intermediary nucleic acid that leaves the nuclues and contains blueprint for protein synthesis 2. Transfer RNA (tRNA) - serves as a bridge between nucleotides and amino acids (translation) 3. Ribosomal RNA (rRNA) - assists in protein synthesis Monomers of Nucleic Acids DNA and RNA consist of monomers know as nucleotides Nucleotides consist of three parts: 1. Nitrogenous base 2. Pentose sugar 3. One or more phosphate groups Types of Nitrogenous Bases Pyrimidine – cytosine, thymine, uracil Purines – adenine, guanine Types of Pentose Sugars  Deoxyribose (found in DNA) Ribose (found in RNA) DNA exhibits a Double Helix Structure The sugar and phosphate lie on the outside of the helix Nitrogenous bases are stacked in the interior The strands of the helix run in opposite directions (antiparallel orientation) Each base from one strand interacts via hydrogen bonding with a base from the opposing strand Base-pairing in DNA The two strands run antiparallel to one another One strand runs 5’ to 3’ The other 3’ to 5’ Adenine forms hydrogen bonds with thymine (A-T) Guanine base pair with cytosine (G-C) The DNA Code can be Written (Transcribed) into RNA DNA can express a particular gene by synthesizing RNA via the process of transcription RNA base sequence is complementary to DNA sequence but in RNA the base uracil is used in place of thymine Example of transcription: if DNA sequence is AATTGCGC then mRNA complement is UUAACGCG RNA and the Production of Proteins Various forms of RNA play important roles in protein translation Ribosomes are made up of proteins and rRNA – the mRNA transcript binds with ribosomes and the rRNA has catalytic activity  The bases of the mRNA are read in sets of three bases (codons) The tRNA base pairs with the codon and delivers the correct amino acid Peptide linkages are made at the ribosome—polypeptide continues to grow Protein Translation Overview Ribosome has two parts: a large subunit and a small subunit 1. The mRNA sits in between the two subunits 2. A tRNA molecule recognizes a codon on the mRNA 3. binds to it by complementary base pairing 4. adds the correct amino acid to the growing peptide chain Lecture 10: Cells Cells Are the building blocks of all organisms In a single-celled organism, the cell is everything Size varies, most are too small to be seen by the naked eye Microscopes make small cells easier to see Multicellular Organisms are Organized in a Hierarchy Cells are the basic unit Tissues are composed of interconnected cells with a common function Several tissues combine to form an organ Organs working together make up an organ system Multiple systems that function together form the entire organism The Two Parameters Most Important in Microscopy Magnification and Resolving Power Magnification The process of enlarging an object in appearance Resolution The ability of a microscope is to distinguish two adjacent structures as separate: The higher the resolution, the better the clarity and detail of the image Microscopes with Different Optical Systems Produce Images for Different Studies Compound light microscopes bend visible light to provide magnification Transparent objects (like cells) must be treated with chemical stains to distinguish different parts Electron Microscopes Achieve higher magnification and resolution using beams of electrons Transmission electron microscopes can show fine detail within cells Scanning electron microscopes provide 3-D exterior views Cell Theory An underlying principle of biology Cells are basic units of life All living organisms are made of cells All cells come from preexisting cells Cells have 4 Common Components 1. An enclosing plasma membrane which separates the cell’s interior from the environment 2. Cytoplasm made of cytoskeleton in which other components of the cell are found  3. DNA - the genetic material of the cell 4. Ribosomes which synthesize proteins Characteristics of Prokaryotes Lack membrane-enclosed internal compartments (e.g. nucleus) Most have a cell wall containing peptidoglycan Are believed to be much like the first cells Organisms in the domains Archaea and Bacteria are Prokaryotes Generalized Structure of a Prokaryotic Cell Chromosomal DNA is localized in a nucleoid Ribosomes are in the cytoplasm The cell membrane is surrounded by a cell wall Prokaryotic Cells are Smaller than Eukaryotic Cells Reasons for small side of prokaryotic cells: Surface area to volume ratio is more favorable for moving material in and out of the cell They lack modifications found in eukaryotes that aid internal transport Factors Limiting Cell Size Surface area -to- volume ratio As cells get bigger, volume increases faster than surface area 10/10/24 Lecture 11: The Eukaryotic Cell Eukaryotic Plasma Membrane Phospholipid bilayer with embedded proteins Cytoplasm Region between the plasma membrane and the nuclear envelope This consist of organelles suspended in gel-like cytoskeleton plus the cytoskeleton 70-80%of the cytoplasm is water but it has semi-solid consistency due to proteins within it Nucleus Usually only one per cell Usually the largest organelle Bigger itself than most prokaryotic cells Nuclear Envelope This is a double membrane Separates DNA from cytoplasm Separates transcription from translation Nuclear pores perforate this membrane Connect nucleoplasm to cytoplasm Regulate flow of molecules back and forth Large molecules require nuclear localization signal (NLS) to pass Nucleolus This is a region inside the nucleus where ribosomes are assembled from RNA and proteins Ribosomes Made of two different-sized subunits Slightly larger in eukaryotes Made of special RNA (rRNA) and proteins During protein synthesis, ribosomes assemble amino acids into proteins Mitochondrion Site for conversion of stored energy (macromolecule molecular bonds) to more useful form (ATP) Inner membrane is folded Folds are called cristae Area enclosed is the mitochondrial matrix Peroxisomes Reactions that break down fatty acids and amino acids occur here May detoxify poisons Contrasting Animal and Plant Cells Both have microtubule organizing centers (MTOCs), but animal cells also have centrioles associated with the MTOC This complex is called the centrosome Animal cells each have a centrosome and lysosomes, but plant cells do not Plant cells have a cell wall, chloroplasts and other specialized plastids and a large central vacuole - animal cells do not Animal Cells Include: Intermediate filament, ribosomes, rough endoplasmic reticulum, nucleus, nucleolus, chromatin, Golgi apparatus, Golgi vesicle, cytoplasm, vacuole, peroxisome, secretory vesicle, smooth endoplasmic reticulum, lysosomes, microfilament, centrosomes, microtubule, plasma membrane, mitochondria Plant Cell Include: Plasmodesmata, cell wall, plasma membrane, cytoplasm, central vacuole, cytoskeleton, chloroplast, plastid, peroxisome, Golgi apparatus, mitochondria, ribosomes, nucleus, rough and smooth endoplasmic reticulum Centrosome Consist of two centrioles that lie at right angles to each other Each centriole is a cylinder made up of nine triplets of microtubules Nontubulin proteins hold the microtubule triplets together Plant Cell Walls Is a rigid protective structure external to the plasma membrane Plant cell walls differ from prokaryotes because they are made up of cellulose rather than peptidoglycan Chloroplasts Are double-membrane organelles; have their own ribosomes and DNA like mitochondria The inner membrane encloses an aqueous fluid (stroma) that contains a set of interconnected and stacked fluid-filled membrane sacs called thylakoids Each stack of thylakoids is a granular (plural = grana) The Central Vacuole Plant cells have a large vacuole that occupies most of the area of the cell This central vacuole helps regulate water concentration under changing environmental conditions, and contributes to cell expansion The Endomembrane System Consists of internal membranes and organelles in eukaryotic cells that work together to modify, package, and transport lipids and proteins Includes: nuclear envelope, lysosomes, vesicles, endoplasmic reticulum, Golgi apparatus and the plasma membrane. Lysosomes In animal cells Contain digestive enzymes These breakdown large biomolecules and even out organelles Endoplasmic Reticulum (ER) Interconnected membranous sacs and tubules Modifies proteins (Rough ER) and synthesizes lipids (Smooth ER) Rough Endoplasmic Reticulum Ribosomes attached to the cytoplasmic surface manufacture proteins New proteins are modified (by folding or obtaining side chains) in the lumen of the RER Makes phospholipids for cellular membranes Phospholipids or modified proteins are not destined to stay in the RER, they reach their destinations via transport vesicles Smooth Endoplasmic Reticulum Is continuous Has few or no ribosomes on its surface Functions of SER Synthesis of carbohydrates, lipids, and steroid hormones Detoxification of medications and poisons Storage of Ca++ Golgi Apparatus Lipids and proteins get sorted, packaged and tagged, while within transport vesicles, to get to the right place The receiving side of the apparatus is called the CIS face; the opposite side is the TRANS face Transport vesicles from the ER fuse with the CIS face and empty their contents into the lumen of the golgi apparatus As the proteins and lipids travel through the Golgi, they are further modified so they can be sorted (this involved adding short chaining of sugar molecules) Cytoskeleton A network of protein fibers Has serval functions: Helps maintain the shape of the cell Hold some organelles in specific positions Allows movement of cytoplasm and vesicles within the cell Three Components of Cytoskeleton Microfilaments Intermediate filaments Microtubules Each are different sizes and have different functions Microfilament Narrowest of the three types (movement and structure) Involved in movement (has no role in cell movement, just structure) Determine and stabilizes shape (movement and structure) Made from actin monomers Microtubules Widest component of the three Provide framework for moto proteins to move structures within a cell Made of tubulin dimers Cilia and Flagella Cilia is shorter and more numerous than Flagella Extracellular Structures Plant cell wall: Support Barrier to infection Plasmodesmata connected cells Extracellular matrix in animals (3 components): Collagens and fibrous proteins Glycoproteins Linking proteins Intercellular Junctions Provide direct channels of communication between cells Plants and animals do this differently Plasmodesmata Channels that pass between cell walls in plants to connect cytoplasm and allow materials to move from cell to cell Gap Junctions Connect Animal Cells Form channels that allow ions, nutrients, and other materials to move between cells Develop when 6 proteins form an elongated doughnut-like structure in the plasma membrane Lecture 12: Membranes and Transport Plasma Membrane Functions Defining the outer border of all cells and organelles Managing what enters and exits the cell Receiving eternal signals and initiating cellular responses Fluid Mosaic Model A mosaic of components (phospholipids, cholesterol, proteins, and carbohydrates) that give the membrane a fluid character Phospholipids 2 fatty acid chains (non-polar)– hydrophobic tails A glycerol molecule, a phosphate group (polar) - hydrophilic head Each fatty acid can either be saturated or unsaturated: Carbons are saturated (maximum amount of hydrogen) with H- all single C-C bonds Unsaturated is when at least one double C=C bond occurs Phospholipid Bilayer Arrange themselves in a bilayer Polar head face outward Hydrophobic tails face inward Proteins The second major component of membrane Functions as transporters, receptors, enzymes, or in binding and adhesion Integral proteins – integrated completely into the bilayer Peripheral proteins – occur only on the surfaces Integral Proteins Has one or more regions that are hydrophobic and others that are hydrophilic The location and number of regions determine how they arrange within the bilayer Carbohydrates Located on the exterior surface of the plasma membrane, bound to either proteins (forming glycoproteins (sugar + protein)) or to lipids (forming glycolipids (sugar + lipid)) Receptor Proteins Our immune systems T cells have CD4 receptor glycoproteins that recognize HIV as “self” Membrane Fluidity The membrane needs to be flexible but not so fluid that it cannot maintain its structure Fluidity is affected by: Phospholipid type - phospholipids with saturated fatty acids can pack together more closely than theses with unsaturated fatty acids (therefore, more SFA, more rigid, less fluidity) Temperature - cold temperatures compress molecules making membranes more rigid Cholesterol - acts as a fluidity buffer, keeping membranes fluid when cold and from not getting too fluid when hot. Plasma Membranes Are asymmetric The inner surface differs from the outer surface For example: Interior proteins anchor fibers of the cytoskeleton to the membrane Exterior proteins bind to the extracellular matrix (outside of the cell) glycoproteins bind to substances the cell needs to import Transport The plasma membrane is selectively permeable (allows some molecules to pass through, but not others) This allows cytosol solutions (inside the cell) to differ from extracellular fluids Transport acrross a membrane can be either: Passive - requiring no energy Active - requiring energy (ATP) Passive Transport The simplest type of passive transport is diffusion Diffusion: occurs when a substance from an area of high concentration moves down its concentration gradient Only small non-polar molecules (O2, CO2, lipid hormones) can diffuse through biological membranes Factors That Affect Diffusion Rates Concentration gradients - greater difference, faster diffusion Mass of the molecules - smaller molecules diffuse more quickly Temperature - molecules move faster (more fluid) when temperatures are higher Solvent density - dehydration increases density of cytoplasm which reduces diffusion rates Solubility - more non-polar (lipid-soluble) materials, diffuse faster Surface area - increase surface area speeds up diffusion rates Distance traveled - the greater the distance, the slower the rates; important factor of affecting upper limit of cell size Pressure - in some cells (i.e. kidney cells) blood pressure forces solutions through membranes speeding up diffusion rates Facilitated Passive Transport Facilitated transport, a.k.a. facilitated diffusion, moves substances down their concentration gradient through transmembrane, integral membrane proteins Two types of facilitated transport proteins: Channel proteins Carrier proteins Channel Proteins The top, bottom, and inner core are composed of hydrophilic amino acids - attract ions &/or polar molecules Some are open all the time Others are gated, only opening when a signal is received Important examples: Aquaporins - specific to H2O Muscle cells have gated ion channels allowing muscle contraction when opened Carrier Proteins Are specific to a single substance They bind to that substance, change shape, and “carry it” to the other side Many allow movement in either direction, as concentration gradients change Osmosis The diffusion of water across the membrane Water always moves from an are of higher water concentration to lower water concentration Differences in water concentration occur when a solute cannot pass through the selectively permeable membrane Osmolarity Describes the total solute concentration (salt, sugar, etc) Low osmolarity - less solute, more water Hypotonic: extracellular fluid has lower osmolarity (less solute, more water outside the cell) then the cytosol - water enters the cell Isotonic: extracellular fluid has the same osmolarity (equal solute and water in and outside of the cell) than the cytosol - water does not move Hypertonic: extracellular fluid has higher osmolarity (high solute, less water outside the cell) than the cytosol - water leaves the cell Active transport Used anytime an ion or molecule (like glucose) is transported through a membrane protein Against its concentration gradient (from low to high concentration) or against its electrochemical gradient Energy is always required for active transport Two types of active transport Primary - where ATP provides the energy Secondary - where an electrochemical gradient provides the energy Occurs through transmembrane, integral carrier proteins called pumps There are 3 types of pumps: Uniporter: carries one molecule or ion Symporter: carries two different molecules or ions, in the same direction Antiporter: carries two different molecules or ions, in different directions Electrochemical Gradient Arise from the combined effects concentration gradients and electrical gradients Primary Active Transport Moves an ion or molecule up its concentration gradient, using energy from ATP hydrolysis Secondary Active Transport Uses an electro chemical gradient, created by primary active transport to move a different substance against its concentration gradient Bulk Transport Sometimes cells need to import or export molecules/particles that are too large to pass through a transport protein Is a type of active transport Energy is required Importing by bulk transport is called endocytosis (into the cell) Exporting is called exocytosis (outside of the cell) There are two types of endocytosis: Phagocytosis - (cellular eating), the cell membrane surrounds a particle and engulfs it Pinocytosis - (cellular drinking), the cell membrane invaginates, surrounds a small volume of fluid, and pinches off Exocytosis Vesicles containing substances fuse with the plasma membrane The contents are then released to the exterior of the cell