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Western University
Biology 1002B
Tom Haffie

Independent Study and Lecture Outcomes Bio 1002B Midterm 1 Laura McCuaig Lecture 1: Introducing Bio 1002B and Chlamydomonas Independent Study Outcomes: identify criteria used to measure complexity. 1. Genome size- or the total number of genes in an organism 2. Gene (copy) number- or the number of copies of a gene in a given gene family resulting from gene duplication 3. Increase in the size- of organisms over course of evolution 4. The number of genes- that encode proteins; 5. The number of parts- or units in an organism (where parts might be segments, organs, tissues, and so forth) 6. The number of cell types- possessed by an organism 7. Increased compartmentalization- specialization, or subdivision of function over the course of evolution 8. The number of- gene, gene networks or cell-to-cell interactions required to form the parts of an organism; and/or 9. The number of interactions between parts of an organism, reflecting increasing functional complexity and/or integration over the course of evolution. • ** most common criteria are cell types and increase in organismal size • Increase in Numbers of Types of Cells o Number of cell types has increased over the course of animal evolution o E.g. sponges and cnidarians 6-12 cell types, 20-30 in flatworms, 50-55 in mollusks, 200-400 in humans • Increase in Organismal Size o Embryonic development accompanied by increasing size o Increase in size over evolution≠ increase in complexity o Evolution often leads to decrease in size for good reasons (eg. Parasites)  Parasitism became successful way of life for many invertebrates once relatively large hosts evolved 1 Bio1002B Midterm 1 identify the main structural components of Chlamydomonas cells. identify the relationship between Chlamydomonas and the evolutionary common ancestor of animals and plants.(check) • Chlamydomonas diverged from land plants 1 billion years ago • Chlorophytes (green algae, including Chlamydomonas and Ostreococcus) diverged from the Streptophytes (land plants and their close relatives) over a billion years ago 2 • These lineages are part of the green plant lineage (Viridiplantae), which previously diverged from opisthokonts (animals, fungi, and Choanozoa) • Chlamydomonas and angiosperm genes are de- rived from ancestral green plant genes, including those associated with photosynthesis and plastid function • Genes shared by Chlamydomonas and animals are derived from the last plant-animal common an- cestor and many of these have been lost in angio- sperms, notably those encoding proteins of the eukaryotic flagellum (or cilium) and the associated basal body (or centriole) • Chlamydomonas also displays extensive metabolic flexibility under the control of regulatory genes that allow it to inhabit distinct environmental niches and to survive fluctuations in nutrient availability Lecture Outcomes: roles of light as used by life • We use light for energy and information characteristics of Chlamydomonas that make it a useful model system • Single celled, two flagella, eukaryote • “a sexually active, light-harvesting, carbon-reducing, hydrogen-belching planimal” o genome sequence of chlamy; has attributes of plants and animals o distantly related to plants, more distantly related to animals function of basic components of Chlamydomonas cells 3 Bio1002B Midterm 1 • nucleus: houses genes, transcription, gene expression etc.. • basal body: found at base of cilium, where microtubules develop to produce flagellum • Endoplasmic reticulum: rough ER involved in synthesis of proteins and is also a membrane factory for the cell, smooth ER involved in synthesis of lipids. • ribosomes: site of protein synthesis • golgi: packaging and sorting of proteins • Mitochondria: center for cellular respiration • Chloroplast: has role in energy transduction • Pyrenoid: site of carbon fixation within chloroplast o Carbon fixation: the reduction of inorganic carbon 2CO ) to organic compounds by living organisms. • Eyespot: found within the chloroplast, harvests light for spatial information o Eyespot gives information allowing it to swim around o Swims towards light areas to maximize photosynthesis o Carotenoid pigment relative usefulness of various biological characteristics as measures of complexity • Complex system: more than one entity comes together, twisted together 1. Complexity in terms of physical size: • above is electron micrograph of eukaryotic chlamydomonas cell • clamydomonas cell is much bigger (1000x) than typical bacterium (ecoli) 2. Complexity in terms of genome size: • Genome size generally not a good indicator of complexity • PCG: Protein coding genes (better measure than genome size) E. coli Chlamy H. Sapiens 4 Genome 4 Mb 120 Mb 3,000 Mb PCG 4,000 15,000 20,000 Evolution of Multicellularity: • Differentiation into different types of cells (Volvox) • (Displays differentiation in reproductive and somatic cells) • to be part of a multicellular organism; you have to agree to die • evolution of multicellularity goes along with evolution of death advantages to Chlamydomonas in being phototactic. • the eyespot is responsible for phototaxis • chlamydomonas move towards light to harness energy of photons in photosynthesis reasons why Chlamydomonas might move AWAY from a light source. • too many photons of light could potentially lead to free radicals • production of ROS(reactive oxygen species) from intense white light can kill cell • chlamy cells will move towards dim light; move away very intense light because it can be damaging • the eyespot is nothing compared to human eye o it converts photons to electrical impulse that controls flagella movement o human eye is image forming • eyespot and eye are homologous (descended from common ancestor) • Darwin said the formation of the human eye is incredibly complex for natural selection to develop it • Eyespot and eye shared common ancestor; are these homologous? 5 Bio1002B Midterm 1 basic structure of rods and cones as photoreceptor cells. • Rods and cones are photoreceptor cells that sit on the retina • photoreceptor is molecule receiving the light • 6million cones, 120million rods in human eye • Photoreceptor: trap and harvest light (blue dot on disk). major components involved in phototransduction and their role. • photoreceptor hit by photon of light and its shape changes o cis-retinal to trans-retinal in photo transduction pathway 6 • G-protein transducin is activated, which in turn activates an enzyme (phosphdiesterase) • Sodium pump is regulated by cGMP, when bound sodium is transported into cell • Phosphodiesterase breaks bond in cyclicGMP • Phosphodiesterase cleaves 3’ bond, phosphate is only bound to ribose at 5’ position 5’ GMP, transporter shuts off • Sodium channel in outer membrane of photoreceptor cell • When shut off sodium transport it hyper-polarizes the membrane • This causes electrical current to run down the membrane of the photoreceptor cell • Optic nerve get 200 million bits of this kind of information every second Lecture 2: Light Lecture Outcomes: Relationship between excited states of a pigment and its absorption, fluorescence emission spectra. Region of the electromagnetic spectrum known as “visible light”. • 400-700nm is visible spectrum • The visible part of the spectrum is what photosynthesis uses Relationship between wavelength and energy content of a photon. • The energy of the light is inversely related to wavelength • Shorter wavelength=higher energy, longer wavelength=lower energy • Light can also be described as quanta of light (photons)  wave-particle duality properties of light • Photons have discrete amounts of energies • Blue light has more energy than red light 7 Bio1002B Midterm 1 Molecular characteristic of visible pigments that make them able to absorb light. • Pigments absorb light • Have conjugated ring system o Double bond followed by single bond o Results in an abundance of non-bonding Pi orbital electrons (available electrons to trap light) • Most electrons that attract light are not involved in bonding o Retinal is an exception*** it involves bonding electrons chloyphyll indigo Relationship between pigments and associated protein. • Pigment-protein complexes; pigments aren’t free, they bind to proteins non-covalently • If you isolate the proteins carefully, you can keep pigments attached • Pigments take energy of photons and trap them in a molecule via pigments • Gel electrophoresis of proteins you must stain the gel, but if you have pigment-protein complexes you can se attached pigments Four “fates” of the excited state of chlorophyll resulting from absorption of photons. • White light is mixture of all wavelengths • Chlorophyll has two excited states (lower and higher) • Single blue photon will excite an electron o The electron will rise to its higher excited state o Instant heat loss 10 -1s, and electron gets to lower excited state o This lower state is the same level that an electron would get to by a red photon o The amount of energy available comes from LOWER EXCITED STATE, decay of higher excited state is too fast 8 • Four fates of electron i. Heat: Lose all the energy to heat (get to ground state) ii. Fluorescence: Lose some energy to heat (get to sub-excited state and lose the rest as fluorescence) • Fluorescence has slightly longer wavelength than red, deep red colour iii. Photochemistry- use light to do work, use light to change structure of a pigment iv. Energy Transfer-to another molecule •This absorption/fluorescence spectra match excitation of chlorophyll Reason(s) why relative fluorescence is different in isolated chlorophyll vs. intact cells when exposed to light. •In-tact chlorophyll can’t see fluorescence 9 Bio1002B Midterm 1 o Energy transferred to reactions center to drive photochemistry as part of photosynthesis •Extracted chlorophyll can see fluorescence o No pathway for energy produced to be utilized, so it is released via heat and fluorescence, producing higher amounts of fluorescence What accounts for the fact that chlorophyll is green in colour •Chlorophyll is green because there is no green excited state; no state that can absorb a green photon •Green photon is either reflected or transmitted through Quantitative relationship between photons and excited electrons. • One photon can excite ONE electron (1:1 ratio) Relationship between energy of photon and energy required to excite electrons in order for photons to be absorbed. •The energy of the photon much match the amount of energy to get from ground state to excited state; if they match can absorb the photon General structure of photosystem. •Two parts: oAntenna (protein) surrounds Reaction Centre oChlorophyll bound to antenna Similarities and differences of the light capturing and photochemistry of phototransduction (retinal) vs. photosynthesis (chlorophyll). •Photochemistry occurs in the photoreceptor oIsomerization of retinal driven by photochemistry 10 oUnit is photoreceptor in retina oMeans we are changing the molecule •Photosynthesis 1. Energy Transfer oPhotons can be asbosrbed by pigments in antenna and transferred (no photochemistry) , this is not relevant in photoreceptor  Chl* + Chl Chl + Chl* (chlorophyll in excited state *)  Energy transferred to neighbouring chlorphyll oEnergy transfer in antenna, not an oxidation reduction; not a transfer of electrons 2. Photochemistry (reaction centre) oEnergy is funneled to reaction center where the photochemistry then takes place, you get oxidized chlorophyll that releases an electron  Oxidation of chlorophyll  Chl*Chl+ + e- (used in electron transport) How are excited states of antennae pigments organized to provide for energy transfer to reaction center. •Pigments must be very close together to allow energy to migrate Structure of rhodopsin. Rhodopsin=retinal +opsin 11 Bio1002B Midterm 1 • Rhodopsin is pigment-protein complex: retinal (pigment), opsin (protein) • Trans vs cis- formations, double bond prevents rotation of molecule 12 • 11 cis- means carbon 11 o absorbs a photon of light to give photoisomerization of molecule to produced all-trans retinal o photon captured excites electron in C=C double bondbond breaksbond reformed in trans configurations o takes place in the eye • photoisomerization: pi bond broken, so have single bond and bond reformation then occurs, occurs in photoreceptor • Need the light for energy to break the bond Effect of photon absorption by 11-cis retinal on retinal structure followed by association with opsin protein followed by interaction of transducin with opsin. • there is a little cleft in opsin where cis-retinal fits • when photoisomerization occurs, the opsin cannot accommodate the pigment anymore, and the protein changes shape • all trans retinal doesn’t fit in the “pocket”-lost from opsin • doesn’t occur in photosystem • Isomerization without light is very rare, occurs once every thousand years 13 Bio1002B Midterm 1 • Transducin can’t access the rhodopsin, only after the energy driven shift occurs • Binding to rhodopsin is what drives the rest of the transport process • In photosynthesis; o Whether it is antenna chlorophyll or reaction centre chlorophyll it doesn’t leave the protein o Retinal leaves the opsin • Once activation occurs (right hand image), the opsin becomes useless and gets ‘recharged’ to state on left • Pigment: chromofore Reasons why life has evolved to detect the narrow band of energy represented by “visible light”. • Everything that uses light in biology uses visible light • Visible light is the most dominant form of EM radiation that hits the earth o Evolution towards using a molecule that is more abundant • The energy in visible light is ‘perfect’ 14 o Want enough energy to excite a pigment or change the conformation of a molecule o X-rays and gamma rays would be too much radiation  results in ionization o Micro waves and radio waves don’t provide enough energy Lecture 3: Protein Structure and Function Independent Study Outcomes: Basic structure of an amino acid and what are the different classes of amino acids. • Proteins are polymers of amino acids 20 amino acids • General structure: central carbon atom attached to amino group (--NH )2 carboxyl group (--COOH), and Hydrogen atom • Remaining R group is 1 of 20 side chains • Referred to as residues • Proteins synthesized from 20 different amino acids • Grouped according to properties of side chains 1. Nonpolar 2. Uncharged polar 3. Negatively Charged (Acidic) polar 4. Positively charged (basic) polar Chemistry of the peptide bond and how it is formed. • Covalent bonds link amino acids into chains called polypeptides • Link is peptide bond formed by dehydration synthesis between –NH 2 group of one amino acid and the –COOH group of a second • N-terminal end has –NH 2 • C-terminal end –COOH • Amino acids added only to the –COOH end of the growing peptide strand • Polypeptide is string of amino acids; protein is specific 3D shape that is required for most functional proteins The four levels of protein structure. • Primary Structure: sequence of amino acids forming polypeptide • Secondary structure: regions of alpha helix, beta strand, or random coil in a polypeptide chain 15 Bio1002B Midterm 1 • Tertiary structure: folding of amino acid chain with its secondary structure, into overall 3D shape of a protein • Quaternary structure: polypeptide chains in a protein that is formed from more than one chain What bonding arrangements give rise to primary, secondary and tertiary structure./ How are alpha helices and beta sheets formed. • Primary Structure: complete amino acid sequence, determined by nucleotide sequence of coding region of protein’s corresponding gene. • Secondary Structure: folded structure based on hydrogen bonds between atoms of backbone. o Hydrogen bonds between H atom attached to nitrogen of the backbone and the O attached to one of the carbon atoms of the backbone o Alpha helix:  Formed when hydrogen bonds form between every N—H group of backbone and the C=O group of the amino acid four residues earlier.  Depicted as a cylinder or barrel (F-32) o Beta Sheet:  Formed by side-by-side alignment of beta  Sheet is formed by hydrogen bonds between atoms is each strands o Random coil/loop formation 16 • Tertiary structure: o Four major interactions between R groups that contribute to tertiary structure 1. Ionic bonds 2. Hydrogen bonds 3. Hydrophobic interactions 4. Disulfide bridges Lecture Outcomes: reasons why photosystems have antenna proteins while the eye doesn’t. • Why is there an antenna in photosystem and not photoreceptor? o We don’t want to harvest light in the eye because every photon hits a separate photoreceptor to form an image. In a photosystem must absorb as much energy as possible because that energy is used for growth. points of control for regulation of protein abundance. • Transcription: copying of DNA into messenger RNA o can regulate transcription of specific genes and alter abundance of mRNA o can measure transcript abundance- how much of the corresponding mRNA do we have? o Higher rates of transcription= more mRNA 17 Bio1002B Midterm 1 • Translation: mRNA to protein o can regulate translation to influence protein abundance • mRNA Decay o Dependent on how long mRNA stick around- they do not have an infinite life span (some decay within minutes or hours) factors affecting mRNA transcript abundance. • Balance between rates of transcription and rates of decay steps in making a Northern Blot for measuring mRNA transcript abundance. Northern Blot-Single Stranded DNA 1. Isolate total RNA and run on a gel o 97% RNA is ribosomal RNA- giant bands are rRNA o Humans have 20,000 expressed genes (transcripts), but we don’t see mRNA o Prokaryotic ribosomes are different than eukaryotic 2. Transfer gel to nylon membrane 3. Radioactive gene-specific “probe” o Label single stranded DNA radioactively and it will hybridize to mRNA corresponding to gene o Radioactive probe will stick to membrane exactly where complementary sequence is o Can expose radioactive probe to film to see abundance 4. Probe is 500 bases long, identical in sequence to RNA o Why doesn’t it pick up the Ecoli? o Ecoli doesn’t hybridize with the probe, since the bacterials mRNA of E.Coli doesn’t recognize the complementary sequence of human hexokinase, as E.Coli haa a different transcript sequence. 18 relative abundance of various types of RNAin typical cells. • 97% is ribosomal RNA • less than 3% is mRNA, we can’t see mRNA on gel steps in making a Western Blot for measuring protein abundance. • Transcript abundance-RNA blot • Western blot-Anti-body o Do western blot using an antibody o Incubate western blot with antibody o Antibodies bind specifically to the protein it is raised against; Heat Shock response: • Chlamydomonas cells shifted from growth temp of 24 degrees to 40 degrees: • Load equal amounts of isolated RNA and run on gel-Control grown • Cell is acclimating to the fact that it is at too high of a temperature 19 Bio1002B Midterm 1 • Can see abundances don’t match, why? o Making protein takes much longer than the transcript; can come up very fast, and then down very fast characteristics of constitutive vs. induced vs. repressed gene expression kinetics. • Constitutive: transcript abundance stays same o Heat shock doesn’t have an effect on every gene such as actin • Induced: transcript abundance goes up o hsp1 is example • Repressed: transcript abundance goes down varieties of defects that might account for lower levels of functional photoreceptors. Photoreceptor Abundance: • rgIII mutation in mouse impairs vision • Why does rgIII mutation yield lower functional photoreceptors/photoreceptor cell? 20 o Mutation changes a base, resulting in different tRNA, different mRNA, and therefore different protein will be made. o Problem with translation, not necessarily gene o The mRNA could have decayed quickly, translation never occurs o Anything that lowers amount of opsin could affect total number of photoreceptors o Protein decay o Functional photoreceptor also needs retinal (non-protein factor), so could have enough opsin, but not enough retinal –defect in retinal biosynthesis o Post-translation modification relationship among polypeptide, apoprotein, cofactor and functional protein. Retinal biosynthesis: • No gene needed to make retinal • Controlled by genes, because genes code for enzymes denoted by arrows in the diagram • Biosynthetic pathway occur because of enzyme catalyzed conversion • COFACTOR (retinal)+ APOPROTEIN (opsin) = FUNCTIONAL PROTEIN (rhodopsin) • Apoprotein is protein before it accepts the cofactor (not functional) • The synthesis of rhodopsin requires POST- TRANSLATIONAL MODIFICATION o Not every protein needs Post translational modification o Many enzymes require post-translational modification relationship between protein folding and function. • For a protein to be functional; o It must fold correctly into correct tertiary confirmation o Native conformation is correct tertiary structure • Polypeptide is string of amino acids that hasn’t folded properly, not yet a functional protein factors affecting proper protein folding (Anfensen's dogma) Anfesnsen’s Dogma • Knows protein is active, can denature using urea which disrupts tertiary bonding arrangements • If he removes urea, the protein refolds perfectly o Get back 90% of native conformation • Protein folding is spontaneous (take ms), and starts before end of translation 21 Bio1002B Midterm 1 • Protein folding is dependent solely on primary sequence of amino acids in polypeptide chain • Tertiary structure depends only on primary structure Lecture 4: Energy and Enzymes Independent Study Outcomes: Isolated, closed and open systems. • Isolated System: does not exchange matter or energy with its surroundings. (e.g. thermos) • Closed System: can exchange energy, but not matter, with its surroundings. (e.g. earth- releases heat energy, but no matter) • Open System: both energy and matter can move freely between the system and the surroundings. (e.g. the ocean) First law of thermodynamics • First Law of Thermodynamics: energy can be transformed from one form into another or transferred from one place to another, but it cannot be created or destroyed. (Principle of the conservation of energy) Second law of thermodynamics • Second Law of Thermodynamics: the total disorder of a system and its surrounding always increases. o Systems will move spontaneously toward arrangements with greater disorder—greater entropy • Cells only able to convert 40% of potential energy in glucose into a form useable for metabolism; heat is lost to environment • Unusable energy produced during energy transformations results in an increase in the disorder or randomness of the universe • Entropy: randomness or disorder. What is meant by the phrase "it takes energy to maintain low entropy" (section 4.1e) • It takes energy to maintain low entropy o i.e. need car mechanic to fix car when it starts breaking down • living cells have ability to create ordered structures or of less ordered starting materials • living cells are open systems • living things bring in energy and matter and use them to generate order out of disorder 22 o most of food we eat is to maintain our cells in their highly ordered state o cell components (proteins, organelles) become damaged and constantly need repair or replacements  by synthesis of proteins, carbohydrates, lipid molecules • living things give off heat and metabolic byproducts 2CO ) that are much les ordered, and increase the disorder/entropy of surroundings. Lecture Outcomes: meaning of potential, kinetic, chemical energy, closed, open vs. isolated systems, First Law of Thermodynamics, Second Law of Thermodynamics, entropy, spontaneous reaction, enthalpy (H), DH, exothermic, endothermic, Gibbs Free Energy, exergonic, endergonic, DG, catalyst, rate of reaction, energy of activation (EA), transition state, kinetic stability, active site, catalytic cycle Why life does not go against the second law. nd • 2 law of Thermodynamics- disorder of system+ surroundings increase • cells are highly ordered, but…. o cells are open systems; exchange energy and matter with surroundings o cells use energy to maintain order (low entropy) Why life needs to consume energy • cells emit lots of heat; this increases disorder of surroundings • huge amounts of energy in allows maintenance of low entropy Components of Gibbs Free Energy equation • ∆G = ∆H -T∆S • ∆ free energy= ∆ enthalpy- temperature( ∆ entropy) • enthalpy is potential energy o could be biosynthetic pathway, or breakdown of molecule in the cell o endothermic (+) o exothermic (-) • entropy is disorder o more disorder (+) o less disorder (-) • free energy o enerdergonic (+ G) o exergonic (- G) Whether or not a given reaction will be spontaneous, given DG • Reactions tend to be spontaneous (-∆G; exergonic) when… o Reaction is exothermic (e.g. glucose will spontaneously break down) o Products are more disorder (entropy goes up) 23 Bio1002B Midterm 1  Eg. 1: fermentation of glucose to ethanol  Melting of ice is spontaneous; driven by massive change in entropy  gas and liquid are more disordered than a solid (entropy) • some spontaneous reactions can take billions of years Role of enzymes in endergonic vs. exergonic reactions • Enzymes can increase rate of spontaneous reaction by 10 -10 20 • Why does life require enzymes? o Without enzymes, the temp needed would be much higher, and high temperature could denature proteins o Evolutionary advantage of enzymes was to get reactions to go fast without raising temperature What enzymes do and don’t do • ABC o AB; ΔG<0, enzyme could increase rate of reaction because its spontaneous o BC; ΔG>0, enzyme can’t make reaction proceed because its not spontaneous o Enzymes DO NOT provide energy for a reaction  Speed up exergonic reactions  Cannot make endergonic reactions go o ATP could supply energy Relationship between activation energy and rate of reaction. • EA(activation energy) represents a barrier o Reactants need to acquire certain amount of energy to get to transition state • Propane is thermodynamically unstable (exergonic), but kinetically very stable o Activation energy is barrier propane cannot overcome without energy from a match 24 How enzymes increase rate of chemical reactions. • Enzymes lower the activation energy • Molecules don’t need as much energy to get to transition state But how do enzymes lower energy of activation? • Green is active site of enzyme • Transition state Conformations o Catalytic site of enzyme mimics transitions state of energy profile o Transition state is kinetic barrier • enzymes aid precise orientation of two substrates • Enzyme forces A and B into correct conformation • The reaction would happen less frequently in absence of enzyme • Charge interactions • Enzyme provides charge environment • Conformational strain • molecule may need to be strained to undergo reaction 25 Bio1002B Midterm 1 Why biological systems need enzymes. • To increase rate of protein production at lower temperatures • Biological molecules can’t handle high amounts of heat Importance of tertiary structure to enzyme function Enzyme structure & catalysis • Enzyme massive compared to substrate • Active site is site of catalysis where action occurs • INDUCED FIT; o Substrate induces change in confirmation of the enzyme o Protein confirmation changes upon binding to substrate o Active sites only revealed upon correct tertiary conformation • Flexible Tert: o Tertiary shape of protein must be flexible to allow induced fit to occur Catalytic Cycle: • Rate of catalytic cycle dependent on enzyme; some can process 1000s of substrate molecules/sec Link between enzyme function and growth rate • Think of growth in terms of enzymes • Enzymes may work better at a higher temp because there is more collisions between the enzymes and the substrate 26 • At a certain temp the rate goes down because the enzyme denatures at high temperature How tertiary structure bonding arrangements are different depending upon the temperature habitat of the organism. Enzymes (proteins) denature • Some of the time the protein can re-nature after being denatured o (e.g. when frying an egg, you can’t convert cooked egg white into gelly egg white) • when denaturing, are breaking tertiary bonds • Heat, pH , chemicals (urea, detergents) can denature How is the tertiary structure of enzymes different among these four groups of organisms? (specifically the bonding arrangements) 27 Bio1002B Midterm 1 • The presence of more tert bonds should increase the strength of tertiary structure (more R group interactions/polypeptide sequence) and therefore make enzymes more resistant to higher temperatures • hyperthermophile that requires regularly higher temperatures get placed in a colder environment its structure takes more energy to bend (stronger R group bonding) and therefore can't flex to meet the shape of the incoming substrate (equally detrimental to growth rate and survival) Lecture 5: Membrane Structure & Transport Lecture Outcomes: meaning of hydrophilic, hydrophobic, fatty acid, saturated, membrane fluidity, hydrogenation, desaturase, membrane permeability, transmembrane protein, simple diffusion, facilitated diffusion, active transport, “ATP-Binding Cassette” (ABC) transporter, cystic fibrosis, Cystic Fibrosis Transconductance Regulator (CFTR), ∆F508, chaperone protein, “ER quality control”, proteosomes, proteases role of fatty acids in membrane structure. • Main membrane component is phospholipid • Phosphate containing head group-hydrophillic • Hydrophobic fatty acid tail o Lipid bilayers form spontaneously- no energy required o Lower energy state when fatty acids align together away from aqueous environment 28 relationship of fatty acid saturation levels on membrane fluidity. • Saturation determined fluidity of membrane o More unsaturation=more fluid membrane relationship of temperature on membrane fluidity. • If membranes are too fluid, to much ion transfer, membrane falls apart • If not fluid enough, electron transport stops • Maintaining membrane fluidity
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