Biol 130 First Midterm Notes

Unit 1 Introduction to the st al unitedlyular ph maven Robert Hooke make the low microscope (30x magnification) viewed slices of shilling c al unneuroticed st totallyular telephoneula (little rooms). Antoni Van Leeuwenhoek worked with glass huge improvement in quality of lenses intimately 300x magnification became possible inaugural to observe * iodine- prison cellphoneed organisms wolfcules * protists from pond pissing * b biteria from his mouth alterher of microbiota * blood cells * banded pattern in muscle cells * sperm from 1830s Compound microscope improved magnification and resolution and allowed visualisation of objects less than 1 ? . 1000-1500x magnification Beginning of Cell hypothesis Robert brownish (botanist) noniced that e real get cell contained a round edifice called it kernel- core Matthias Schleiden (an early(a) botanist) all plant tissues argon composed of cells embryonic plant always arose from a single cell Theodor Schwann (zoolog ist) similar observations in brute(prenominal) cells recognition of morphologic similarities btw plants and animals * Cell Theory formulated by Schwann Cell Theory 1. all organisms consist of one or more cells 2. he cell is the basic unit of an soupconical structure for all organisms 3. added 20 old age by and by all cells arise moreover from pre-existing cells fact (scientific) an assay to state our best current understanding, mingy on observations and experiments(valid only until revise or replaced) Steps in Scientific Method 1. make observations 2. custom inductive reasoning to develop tentative explanation (hypothesis) 3. make predictions groundingd on your hypothesis 4. make further observations or design and obtain out moldled experiments to test your hypothesis 5. nterpret your results to see if they support your hypothesis Theory a hypothesis that has been well-tried critically under many anformer(a)(prenominal) opposite conditions andby many contrary in vestigators . using a variety of diametrical approaches. By the time an explanation is regarded as a opening it is widely recognized by nigh scientists in the cell * the solid ground of wisdom evolution, germ theory, cell theory *If a theory is thoroughly tested and confirmed over many years by such ample numbers of investigators that there is no doubt of its validity it may last be regarded as a law.Gravity, laws of thermodynamics, laws that govern behaviour of gases Strands of Cell biota 13 cytology 1600s Hooke looks at cork Leeuwenhoek looks at lots of things 1800s Brown notes nuclei bio-chemistry deductive reasoning of urea in lab fermentation done by cells glycolysis Krebs regular recurrence all(prenominal) cell comes from a cell Schleiden & Schwann formulate cell theory electron microscopy stains & dyes genetics Mendel, pea plants desoxyribonucleic sour chromosomes chromosome theory 1930s deoxyribonucleic acid prongy gyre desoxyribonucleic acid sequencing Dolly the sheep nano-technology genetic code unhorse MicroscopyBright field light passes through exemplar, business is slow and specimen is hard to see Phase contrast contrast is counterchanged by changing light in microscope DIC uses optical modifications to change contrast between cell and background due to density differential Staining stain apply to visualize cell and subdivisions, only some stains pile be apply on living cells 14 bright field phase contrast DIC unstained (sperm cells) stained blood cells tissue small intestine light Microscopy fluorescent dyes bind to protein or deoxyribonucleic acid to see where they be in cells tracks work Electron Microscopy(S fecesning & Transmission)SEM scan sur panorama of specimen to form con postr by detecting electrons from outer surface. Good surface images TEM forms image from electrons leaving through specimen therefore fine details of internal organelles 16 SEM TEM Basic Properties of Cells * ar passing complex and organized * sections tinges macromolecules (organelles ) enclosed in plasma tissue layer * use the alike(p) genetic program exchange Dogma * deoxyribonucleic acid RNA protein * ar capable of reproducing themselves * must first replicate genetic material acquire and use power (bioenergetics) and impart out a variety of chemic reactions (cellular metabolism) * guide many processes that be highly conserved at the molecular level * tissue layer structure, genetic code, adenosine triphosphate synthesizing enzymes, actin filaments, eukaryotic flagella, * engage in many mechanical activities * transport of materials in/out, inside * assembly and disassembly of structures * drive / drawment * suffice to environmental star signs * move away or toward stimuli * respond to hormones, growth factors, etc * are capable of self- regularisationhomeostasis more or less evident when control sy root words wound down defects in DNA replication, DNA repair, cell cycle control Two Classes of Cells karyon = nucleus Prokaryotic Cells lack of nucleus, NO CYTOSKELETON( really small), tissue layer squinch organelles. Mostly unicellular. Bacteria and Archaea. Single, circular strand of DNA( someer proteins). Cell border in addition to PM 1-10 uM in diameter. 2 types 1. Eubacteria all impart cells walls shut out for mycoplasma(resistant to antibiotics that target cell wall deductive reasoning). Mycoplasma(smallest) Cyanobacteria (largest and approximately complex). 2.Archaeabacteria all have cell walls and are known as extermophiles, relate broad range of habitats, halophiles=salty, acidophiles=acid, thermophiles= tropic. Eukaryotic Cells 10x larger than prokaryotic cells, membrane bound nucleus/organelles. More complex DNA due to histones/proteins. 4 conventions 1. Protists- truly diverse group mostly single cells algae, urine molds, slime molds, phylum Protozoa 2. Fungi single cell(yeast) or multi-cellular(mushrooms) and have cell walls. Heterotr ophs depend on external source of radical compounds 3. Plant cells- multi-cellular and have cell walls. . Animals- multi-cellular, no cell walls and are heterotrophs Cytoplasm everything between plasma membrane and nuclear membrane, includes all membrane-bound organelles (except nucleus) Cytosol only fluid atom Endomembrane system internal membranes that are every in direct contact or connected via deportation of vesicles (sacs of membrane). including nuclear envelope / membrane, endoplasmic reticulum (ER), Golgi apparatus, lysosomes, vacuoles Nucleus stores genetic information Endomembrane remains creates intracellular compartments with different functions.Endoplasmic reticulum (ER rough, smooth), Golgi apparatus, lysosomes. Mitochondria generate energy to power the cell Chloroplasts capture energy from sunlight, convert to carbohydrate Cytoskeleton regulates cell shape, movements of materials deep down the cell, movement of the cell itself Flow of Traffic in EMS Roug h ER entailment of proteins for export (secretion) insertion into membranes lysosomes Golgi apparatus collection, advancement & distri exclusivelyion Lysosomes * cell stomachs have enzymes that can digest * all 4 classes of biological macromolecules worn-out organelles (mitochondria replaced every 10 days) * material brought into cell by phagocytosis Phagocytosis plasma membrane engulfs smaller molecule and then called phagosome. Lysosome takes it in and digests, small particles are releases into the cytoplasm. Autophagy lysosome digests a change organelle, small particles are released into cytosol. mitochondria (all eukaryotic cells) and chloroplasts (plant cells) * contain DNA that encodes some (but not all) of their own proteins * have unusual double layers of membranesOrigin of Eukaryotic Cells Endosymbiont Theory * at a time believed that eukaryotes evolved gradually, organelles becoming more and more complex * now accepted that azoic eukaryotes originated as predat ors * certain organelles (mitochondria, chloroplasts) evolved from smaller prokaryotes engulfed by larger cell * later chloroplasts and the ability to perform photosynthesis Symbiosis Mutual Advantage advantage to force cell * aerobic respiration (aerobic bacteria mitochondria) * photosynthesis (cyanobacteria chloroplasts) advantage to bacteria * protected environment supply of carbon compounds from host cells some separate prey Evidence Supporting Endosymbiont Theory mitochondria and chloroplasts * are similar size to bacteria, reproduced by fission interchangeable bacteria * have double membranes, uniform with engulfing mechanism * have their own ribosomes, which resemble those of prokaryotes rather than eukaryotes in cost of size, composition and sensitivity to antibiotics * have their own genomes, which are organized a comparable those of bacteria last but not to the lowest degree * are genetically similar to proposed parent bacteria rather than ukaryotic cells Cytos keleton important in * cell shape * cell motility * movement / position of organelles * movement of materials at bottom cell * movement of chromosomes during mitosis Cytoplasm in a living cell is never static * cytoskeleton is ceaselessly being taken apart and rebuilt * organelles and vesicles are racing back and forth * can cross the cell in 1 second * unattached proteins moving randomly, but rapidly * can visit every corner of the cell within a few seconds * contents of cytosol are in constant thermal motionCommon to all cells * selectively permeable plasma membrane * genetic code mechanism of organization and translation * ATP for the transfer of energy and metabolic pathways Model Organisms 45 Unit 2a Intro to Cellular Chemistry Most Common Elements in Living Organisms * C H O N make up 96% also P and S are common in addition * Exist as complex macromolecules and simpler forms like pee system and carbon dioxide nucleus dense core in centre, consists of protons and neut rons electrons continually orbit the nucleus of protons delineate feature of an element = miteic number protons + neutrons = wad of an atom = crowd number by default, an atom is neutral, with protons = electrons electrons influence reactivity of an atom Atomic mass = atomic number + of neutrons (electrons are neglected because mass is so small) Isotopes akin number of protons but different number of neutrons in the same element Anion gain electron and are negatively supercharged Cation lose electron and are positively chargedOutermost valence shell influences an atoms reactivity * electrons in outermost shell valence electrons * one and only(a) valance electrons determine the number of trammel nets an atom can make * atoms with change valance shell = most stable, atoms that are closest to filling are most reactive * elements abundant in organisms have at least one unpaired valence electron Some Definitions covalent mystifys 2 or more atoms share pairs of va lence electrons * strong bewilders of biological systems non-covalent bonds, including * ionic bonds * total heat bonds (H-bonds) * aquaphobic interactions olecule group of atoms held together by energy in a stable association compound molecule composed of cardinal or more different types of atoms Types of Covalent Bonds * electrons shared equally * non- opposite covalent bond * can be single (like H2), double (O2) or heretofore triple, depending on number of electrons shared * electrons not shared equally * polar covalent bond * one of the atoms has a stronger pull on the electrons than the some early(a) * pull on electrons = electronegativity * water is the most abundant molecule in biological organisms * human body is 70% water water as a solvent can dissolve more types of molecules than other molecule known * the polarity of water is key to its role in biology hydrogen bonding electrical attraction between negatively charged atom and partial positive of hydrogen hydr ophobic no affinity for water water fearing hydrophilic affinity for water water engaging dot-base Reaction substance that gives up (donates) protons acid (increases H+ in solution) substance that accepts protons base (decreases H+ in solution) chemical reaction that involves transfer of protons acid-base reaction * most olecules act as either an acid or a base * water can be two (both gives up and accepts protons) weak acid very few molecules dissociated (acetic acid, water) strong acid readily gives up protons (hydrochloric acid) when pH = pKa species is 50% ionized Carbon is the most important element in biology carbon atoms give biomolecules their shape but other atoms attached to carbons determine their reactivity * critical H, N, O containing attachments called functional groups *learn orgo functional groups for this courseMacromolecules * large, organized molecules that are typically created by polymerization * biological macromolecules (biomolecules) provide the stru cture and carry out the activities of a cell 4 groups * carbohydrates(polysaccharides) * lipides(fats) * proteins * nucleic acids * monomers of groups are different chemical reactions used to make the custody are similar Overview of Macromolecules 3 Proteins more functions than any other group of macromolecule * enzymes catalysis hurry chemical reactions transport through cell membranes, in circulation * support cytoskeleton, fibres of cartilage, hair, nails * signalling / regulative hormones, membrane proteins, intracellular messengers * movement- of the cell itself contractile proteins, flagella within the cell labor proteins * defense antibodies, complement proteins Proteins are Polymers * aminic acids are connected in linear polymers of a specific sequence * 20 genetically encoded amino acid monomers to pick from * string of amino acids (AAs) = peptide or polypeptide polypeptide folded and coiled into a specific conformation = protein * sometimes 2 or more peptide trains (subunits) combine to form mature, functional protein amino deadly twist AAs are ionized under physiological conditions ionization increases solubililty, facilitates interactions with each other and other solutes, increases reactivity (zwitterions) 7 non-ionized ionized R group unique to each AA oxygens tend to pull electrons away, making it easy to lose proton gains a proton Amino Acid Side Chains R Groups * nonpolar hydrophobic R groups no charged or electronegative atoms to form H bonds * water-insoluble in water * R groups bury themselves with the peptide chain to hide from water * polar side chains soluble in water * electroneutral but partial charges can form H-bonds * charged groups containing acids or bases highly soluble in water AA are think together by covalent peptide bonds carbon from carboxyl group is linked to N fulfilment of amino group. R groups and central Cs do not participate in the bond. Condensation Reaction making the chain Hydrolysis breakout the chain Polypeptide chain side chains extend from peptide-bonded backbone * chain is flexible can rotate at single bonds on either side of peptide bonds * so side chains are not all projecting to one side * chains can be from 2-3 to thousands of AAs in continuance * backbone is directional, convention is to number AA residues starting at N terminus this is the primary sequence Sickle Cell Anemia disorder in which red blood cells are abnormally shaped. Caused by single point transformation which results in substitution of single amino acid in one chain of hemoglobin protein Protein StructurePrimary Structure unique sequence of amino acids Secondary Structure Folding into elements of structure, hydrogen bonding between amino acids(R groups not involved). 2 shapes alpha helix and beta pleated sheet(parallel and antiparallel). * learn more Tertiary Structure- interactions of elements of secondary structure forming a global fold, folded into these unique shapes by ionic bonds (electrostatic),hydrogen bonds, disulphide bridges, hydrophobic interaction, van der waals dipole-dipole(all non-covalent except for S-S). Order of amino acids determines final shape.Maintain globular shape even if very weak. Quaternary Structure more than one polypeptide chain put together to form the final functional protein, linked by covalent and non-covalent interactions. Protein state segment of polypeptide that forms a compact, stable and independently folding structure. Often the building blocks for larger, more complex proteins. Disulfide bonds * covalent stabilization of protein structure found in secreted proteins (destined for a more hostile extracellular environment) * formed in ER (oxidizing environment)Once folded, do proteins ever unfold? changes in physical or chemical conditions (pH, salt concentration, temperature) disruption of H-bonds, ionic bonds, disulfide bridges, etc that maintain the proteins shape protein denatures or unfolds Possible to renatur e Do proteins ever fold incorrectly? any mutation that leads to a missing or incorrect amino acid can lead to incorrectly folded protein WHY 32 Possible outcomes mutation leads to incorrectly folded protein * protein never functions properly loss of function protein folds properly at first but unfolds under certain conditions eventually loss of function * protein misfolds AND is deposited in insoluble aggregates within cell * loss of function and disruption of other aspects of cell activity * many human diseases now known to be associated with misfolded proteins . Alzheimers, cystic fibrosis, type II diabetes, retinitis pigmentosa, Parkinsons, Creutzfeldt-Jakob, some cancers *read about catalysts and enzymes in Janelles notes, page 8-9 Nucleic Acids Information Polymers * deoxy ribo nucleic acid (DNA) sequence of subunits in DNA polymer directs RNA synthesis * ribo nucleic acid (RNA) * RNA directs ordering of AAs in a peptide chain * information stored as DNA sequences enables liv ing organisms to pass on hereditary information * also allows each cell to pass on hereditary information to the next generation of cells Monomers of Nucleic Acids Deoxyribo nucleotides phosphate + deoxyribose + nitrogenous base(A,C, G, or T) Ribo nucleotides phosphate + ribose + base (A,C,G, or U) Nucleic acids are linear (un branching) polymers of nucleotides * each nucleotide consists of three parts * a nitrogenous base a (5-carbon) pentose saccharify * a phosphate group Purines = A&GPyramidines= C,T and U * Ribose + base = nucleoside * Ribose + base + phosphate = nucleotide Functions of Nucleotides * monomeric units of RNA and DNA * important signal molecules within cells * cyclic adenosine monophosphate (cAMP) * important agents in energy transfer reactions * cleave come to phosphate group to release stored energy * act as coenzymes organic fertiliser non-protein molecules required for enzyme function * usually ampere-containing nucleotides combined with B vitamins 8 c ompressing reaction 5 end beginning of chain. Chains always built 5 3.Look at above example phosphate group is 5 3 end where new bases can be added polymerisation rxns are endergonic * making phosphodiester bonds requires energy * energy comes from addition of 2 phosphate groups. * Activated nucleotides = nucleotide triphophates The most famous phosphorylated nucleotide adenosine triphosphate = ATP 11 adenine 4 5 5 6 1 2 3 9 4 8 7 1 3 2 O P CH2 O O O P O O O P O O O OH OH O NH2 N N N N ribose adenine + ribose (= adenosine) Secondary Structure of DNA two strands of DNA align in antiparallel written text with bases facing inwards. H-bonds form between bases. P P P P P P P P C C G G AA T T P O O O O O O O O O O O C G OH P remark 3 H-bonds between C and G, 2 between A and T. scarcely space in the sugar phosphate backbone is for Pyramidine and Purine to bond together. Features of DNA Double Helix * stabilized by H-bonds between complementary bases and hydrophobic interactions betw een bases * entire molecule water-soluble because charged phosphates backbone face outward * major and minor grooves are significant in regulation of gene transcription Higher Order DNA Structure DNA molecules can adopt higher order structure Allows for compact packaging and strict regulation of gene expression RNA vs DNA like DNA sugar-phosphate backbone covalently linked by phosphodiester bonds * 4 different bases contradictory DNA * uracil (U) kind of of thymine (T) * pairing is A-U, C-G * sugar is ribose instead of deoxyribose * hydroxyl group makes ribose lots more reactive * RNA is much less stable than DNA Secondary Structure of RNA like DNA * H-bonds form between complementary base pairs unlike DNA * most of the time, this base-pairing is between bases on the same strand * leads to formation of stem and loop structures with single-stranded regions and double-stranded antiparallel regions * H-bonding is spontaneous, stabilizes the molecule final molecule is single-stranded * Complex folds can result in some RNA having catalytic activity Carbohydrates * Group of molecules that contain carbon, hydrogen and oxygen in a 121 ratio (CH2O)n Only monomers are in this ratio, oligomers you lose water * Monomer= monosaccharide * Dimer=disaccharide * Trimer=trisaccharide/oligosaccharide Types 1. Monosaccharides simple sugars 2. Oligosaccharides small chains (oligo=few) * committed to proteins glycoproteins * Attached to lipids glycolipids 3. Polysaccharides very long sugar chains Typical geomorphological Features of Sugar Monomers carbonyl group (either ketone or aldehyde) * lots of -OH groups * vary in length of carbon skeleton (C3, C5, C6, ) triose, pentose, hexose * isomeric forms (glucose, fructose, galactose) * superposable chemical groups place differently * monosaccharides often form rings in solution Isomers same atoms, different arrangements structural isomer identical groups but bonded to different carbons stereo (optical) isomer identical groups bonded to same carbons but in different orientations sixteen different hexose structures possible, all with formula C6H12O6 C OH C OH OH H C OH H HO C H C O H C OH H H C OH H C OH H C OH H HO C H H C OH H structural isomer stereo- isomer H C C O HO C H H C OH H C OH H HO C H H C OH H fructose glucose galactose *arrangement of hydroxyl groups make a big difference in biological function Disaccharide 2 sugar monomer * glucose + fructose = sucrose(table sugar) * glucose + lactose = lactose * glucose + glucose = malt sugar Formation of disaccharides by condensation reactions. monomers are linked when C1 of one monosaccharide binds to a C on another often C4 geometry of bond different depending on hether OH group of C1 is in ? or ? position which C of other sugar is involved in linkage 7 C1, ? C4 ?-glucose ?-glucose maltose, ? -1,4 glycosidic bond ?-galactose ?-glucose lactose, ? -1,4 glycosidic bond (glucose has flipped over) C1, ? C4 Polymerization to build Polysaccharides a mylum both are storage forms for energy starch plants glycogen animals both consist of ? -glucose monomers linked by ? -1,4 bonds both coil into a helix (due to geometry of linkages) starch is mixture of unbranched amylose and branched amylopectin glycogen is highly branched lycogen morphologic Polysaccharide in Plants Cellulose 9 polymer of ? -glucose, joined by ? -1,4 linkages each glucose is flipped relative to close ones allows for H-bonding between adjacent strands extremely stable most abundant organic molecule on earth parallel strands joined by H-bonds Structural Polysaccharide in Animals Chitin a component of cell walls of fungi, exoskeletons of arthropods (insects, crustaceans), radulas of molluscs, beaks of cephalopods second most abundant organic molecule on earth like cellulose, joined by ? 1,4 linkages but rather than glucose, monomer is N-acetylglucosamine like cellulose, also strengthened by H-bonding btw strands 10 Structural Polysaccharide in Bacteria Peptidogl ycan component of bacterial cell walls the most complex CHO so far two different alternating monomers linked by ? -1,4 bonds chain of amino acids attached to one of the sugars peptide bonds instead of H-bonds (stronger) implication of how monosaccharides are linked * ? -1-4 linkages of starch and glycogen readily hydrolyzed * ? 1-4 linkages in structural polysaccharides very resistant to enzymatic degradation For example enzymes that digest cellulose (cellulase) produced only by certain classes of bacteria, fungi and protozoa Difference between glycosidic bonds from peptide and phosphodiester bonds in common * condensation reactions different * peptide and phosphodiester bonds always occur at the same position within their monomers * each sugar monomer has several hydroxyl groups, and geometry of glycosidic bonds is highly variable Functions of Carbohydrates Structural * cellulose, chitin and peptidoglycanCell-cell recognition * membrane proteins covalently bonded to oligosacchari des Energy Storage * ? -1,4 linkages of starch and glycogen are readily hydrolyzed to release stored energy Lipids * group of carbon-containing compounds that are largely non-polar / hydrophobic * significant proportion of a given lipid molecule is hydrocarbon * the only macromolecule that is not a polymer major groups of lipids in cells * fats / oils energy storage * sterols * cholesterin membrane component * steroids hormones * * Phospholipids * major component of biological membranesFats (Triacylglycerols, Triglycerides) * form that fat is stores in apidose tissie * glycerol with 3 oleaginous acids attached * the link between glycerol and fatty acid = ester bond condenstation rxn (liberates water) * hydrophobic * fatty acid(carboxylic acid with long hydrocarbon tail) Saturated Fatty Acid have maximum number of hydrogen atoms on each atom straight and flexible because of only single bonds Unsaturated Fatty Acid contain at least 1 double bond. The double bond is rigid and cr eates a kink in the chain. The rest of the chain and is free to rotate about C-C bonds.Cis H on the same side of double bond dont solidify easily Trans H on the opposite side of the double bond. Hydrogenation making a fat saturated/more solid at room temperature to improve shelf life therefore less healthy. Sterols group of steroids based on cholesterin(important component of cell membrane) Phospholipids * 1 glycerol, 2 fatty acids, 1 phosphate group(polar calculate group) * Amphipathic = hydrophilic and hydrophilic regions their most important feature with respect to biology Micelles sphere with hydrophobic tails hiding in centre . bottom of the inning only occur with relatively short tails Lipid Bilayer common Structure for all Biological Membranes composition varies with type of organism (prokaryote vs animal vs plant vs ) type of cell within organism (muscle, liver, sperm, egg, ) type of membrane within cell (plasma membrane, Golgi, ER) inner versus outer layer differ ent patches or domains within a particular membrane Fig 11-4 two almost apposed sheets of lipids, studded with proteins lipids serve as permeability barrier proteins perform most of the functions carbohydrates (sugars) attached to protein and lipids in a non-random manner *all membrane lipids are amphipathic Lipid bilayers form spontaneously hydrophobic molecules would exclude water, clustering together to minimize energy cost of organizing water molecules * form large droplets or surface film * amphipathic molecules are subject to conflicting forces * solved by formation of bilayer * energetically most favourable stable, spontaneous * lipid bilayers are * closed no free edges * self-sealing * important feature for cell fusion, budding, locomotion Fluid Mosaic Model * The plasma membrane is expound to be fluid because of its hydrophobic integral components such as lipids and membrane proteins that move laterally or sideways throughout the membrane.That means the membrane is not solid, but more like a fluid. * phospholipids are constantly moving spinning in place travelling laterally within leaflet * phospholipids are occasionally flipped to the opposite leaflet during membrane synthesis but they rarely flop back * even proteins cruise easily through the membrane Membrane fluidity how easily lipid molecules move within a membrane leaflet Alignment of phospholipid tails * tightly packed tails membrane more viscous, less fluid * freely moving tails higher fluidity What aspects of phospholipid composition influence this? length of fatty acids * from 14-24 carbons, 18-20 carbons most common * degree of saturation of fatty acids double bonds * typically one saturated fatty acid and one with one or more double bonds Cholesterol * under physiological conditions, cholesterol makes membrane stiffer less fluid * cholesterol can make up to 50% of plasma membrane lipid in some animal cells Regulation of Membrane Fluidity fluid state must be maintained for normal c ell function strategies for maintaining membrane fluidity * change composition of membranes * alter phospholipids desaturate fatty acids (to deal with cold) eg cold water vs adoring water fish * change length of FA chains (yeast, bacteria) * adjust amounts of cholesterol (animals) these mechanisms have been demonstrated in * pond fish dealing with striking day / night temp differences * cold-resistant plants * extremophile bacteria living in hot springs * winter wheat preparing for autumn polyunsaturated FAs * sperm reduce their cholesterol just before fertilization Functions of Lipids * storage of chemical energy * signal molecules * vitamins * wax coating on leaves * biological membranes