Biol Exam 3

Describe the molecular biology/chemistry involved in yogurt production.

Milk is mostly water Also contains various inorganic ions as well as many organic molecules including: - Lipids, carbohydrates (lactose), dozens of proteins - Major proteins found in milk Yogurt is made by incubating Lactobaccillus acidophillus bacteria with milk at ~110 F - Carries out lactate fermentation Fermentation produces lactic acid (lactate), the acid changes pH oof milk, changing the protein structure: proteins denature and coagulate, changing consistency - Fermentation will deprotonate and acidifying the milk resulting in denaturing of the protein and changing consistency

Role of H2O in PS

Water is oxidized in PS (electrons stripped away) Light excites PSII electron (endergonic) PSII electron spontaneously transferred to acceptor molecule (exergonic) where it leaves a void in PSII - Void is filled by splitting water - Liberates O2 to let us breathe - PSII (680) is more EN

Oxygenic Photosynthesis

Water is the electron donor where oxygen is going to be oxidized Type of PS seen in plants, algae, and cyanobacteria CO2 + 2H2O-> [CH2O] + O2 CO2 is reduced

Explain why fermentation is important economically

We have many different products that we eat today that use fermentation like cheese, wine, yogurt, nail polish remover, rubbing alcohol, vineagar, soy sauce

Explain why the evolution of photosynthesis was so important in organismal evolution.

Evolution of oxygenic PS was very important evolutionary step because prior to evolution there was no ability to process glucose like in aerobic respiration now There was no aerobic respiration so when O2 accumulated in the Earth's atmosphere it caused the evolution of aerobic respiration that eld to many of our advanced forms. (couldn't process glucose like with aerobically aspiring organisms now can) - Glucose was not utilized efficiently because only utilized fermentation or anaerobic respiration Using glucose more efficiently now (extract more usable energy)

Analyze the regulatory effects of different molecules on the Krebs Cycle

Accumulation of NADH will negatively regulate the citric acid cycle because it is one of the products Acetyl CoA and ATP (pyruvate dehydrogenase complex is a point of reregulation where they are negative regulars) - CoA, NAD+, and AMP and ADP are all positively regulated

Compare the cellular processes of fermentation and aerobic respiration. Speculate on the types of cells/organisms that carry out these processes.

Aerobic Cellular Respiration: - Who contain a mitochondria and have oxygen - Long turn, large production of ATP (36-38) - Reactants: glucose, ATP, pyruvate, NADH, FADH2, O2 (NAD+) - Products: CO2, H2O, and ATP - Final electron acceptor: oxygen - Long term in humans Anaerobic Respiration-> bacteria, prokaryotes - Lack mitochondria and don't have oxygen - Fermentation: produces ATP without oxygen, final electron acceptor is pyruvic acid or another organic molecule (sulfate or nitrate as electron acceptor) - Reactants: glucose, ATP, pyruvate, NADH - Products: NAD+ -- Ethanol Fermentation: ethanol and CO2 -- Lactic Acid: Lactic acid - Only 2 ATP total produced by glycolysis - Carried out in short term in humans and yeast

Compare and contrast electron transport during aerobic respiration and photosynthesis.

Aerobic Respiration: - Electrons move from component to component based on EN differences - If NADH and once approach first complex, the electrons will spontaneously be stripped away so they flow spontaneously down EN gradient where get to O2 which is most EN - Flow down hill (exergonic) - O2 is the final electron acceptor Photosynthesis: Two points where electrons are blocked Have spontaneous flow of electrons until get to P680 - H2O transports molecules to all through complex's (protons released into the thylakoid lumen) - EN values at P680 n ground state before photoexcited goes then to P680+. For it to go to phenophyen, needs to be photoexcited to P680+ because P680 more EN than Ph so need to excited it -- Need light absorption event to elevate the energy level to P680 for it to less likely to hold onto electron in the photo excited state. P680+ has less EN and then goes back down again in the cascade fashion until get to P700 - At P700 at ground state has a higher EN and it can't transport electrons without getting photoexcited. Needs to get photoexcited to change the electron potential and then electrons will flow spontaneously until get to final electron acceptor NADP+ to get NADPH (endergonic system) Also called the Z-scheme Referred to flow of electrons through the ETS - Light excites PSII electron (endergonic) - PSII electron spontaneity transferred to acceptor molecule (Ph) exergonic - Electron flow continues until reaches PSI (exergonic) -- Spontaneous flow of electrons accompanied by release of Free E. The free E moves through Cytb6/f from stroma to thylakoid lumen against H+ gradient where H+ gradient is used to drive ATP synthesis - Light excites -- PS1 electron (endergonic) PSI electron spontaneously transferred to acceptor molecule (A) exergonic -- Electron flow continues until reach NAD+->NADPH (exergonic)

Describe the form and fate of the carbons in the Krebs cycle. Students should specifically be able to: recall the role of oxaloacetate; identify the first intermediate of the Kreb's cycle; summarize the inputs and the overall outcome of the Krebs cycle

Also called tricarboxylic acid cycle (several intermediates contain three carboxylate groups) Takes the 2 remaining C's with form of acetyl and combine the 2C's First intermediate of Krebs cycle is the citrate - Formed through where Acetyl-CoA that has 2 C's and then combined with Oxaloacetate that has 4 C's where will form citrate which is the first intermediate which has 6 C's - Oxaloacetate is regenerated in one full turn of the citric acid cycle where 2 CO2 molecules are therefore released during each turn of the cycle (need to get back to 4C's from the 6C's we started with so needs to release 2 CO2) Pyruvate first decarboxylated where 2C's are linked to CoA to form citrate - Protons are slowly stripped away to be used in the ETC later Cycle must occur twice per glucose molecule (since have two pyruvate molecules) Once form citrate will have 6C's and when get right before starting off with oxaloacetate, will have 4C's One turn will produce 3NADH, one ATP, one FADH2, and releases 2 CO2molecules Input: 2 Acetyl molecules (per glucose) Product: NADH, FADH2, ATP (reduced electron carriers with some usable energy), and CO2 (takes inorganic C to make organic C) Energy Transfer: ATPs can be used directly, but most of energy from glucose is now carried by electron carriers (NADH and FADH2) where these will participate in oxidative phosphorylation) 4 total CO2 molecules released because after each turn release 2 CO2 molecules so go through two turns of cycle which will release 4 CO2 molecules

Describe the structure of the chlorophyll molecule.

Also known as pigment molecules (main pigment molecule) Selectively absorbed certain wavelengths of light and will reflect the other wavelengths Green pigment molecule (color reflecting) Contains a porphyrin ring - Has alternating single/double bonds (resonance) -- Resonance means that it is capable of transferring and capturing the photoexcited electrons (move light energy) - Capable of 'capturing' and transferring light E - Out and available to absorb light Phytol side chain - Hydrophobic with anchors molecule to thylakoid membrane- - All hydrocarbons

Gluconeogenesis

Biosynthesis of glucose from noncarbohydrate organic source - From non-carbohydrate sources where include lactate, pyruvate, AA, and glycerol Occurs when glucose levels are low - Strenuous activity, starvation, depletion of carbohydrates (adkins) Occurs in livers and kidneys-> not all cells express these enzymes Under low Oxygen levels, muscles cells carry out glycolysis and lactate fermentation

Glycogenesis

Buildup of G6P would indicate energy needs of cell are being met and the glycogen synthesis pathway (glycogenesis) will be initiated - Needs are met= glucose will be stored away so - Needs are met if buildup because demand is slowed down because intermediate's start accumulating - If have a buildup, then energy needs are met so start synthesizing glycogen because will store it because don't need to convert it to usable energy Glycogen synthesis pathway If G6P begins to build up, it will be catalyzed by phosphoglucomutase - If G6P starts to build up will push the reaction towards G1P (isomerized to glucose 1) which is funneled to glycogenesis pathway If energy needs of a cell are met - G6P is converted to G1P (catalyzed by phosphoglycomutase) - Triggers Glycogenesis when G1P is produced (pathway that synthesizes glycogen where takes excess glucose and store it as glycogen) (dont need to keep catabolizing it where will use it for short term energy reserve) G1P has nucleotide attached to it which activates it and makes it more usable as a substrate to be added to existing glycogen chain (activation step used to catalyze next step) formation of glycogen from glucose

Provide an overview of the process of aerobic respiration. Describe specifically where all of the events are taking place (i.e. which subcellular location).

C6H12O6 + 6O2-> 6CO2 + 6H2O + Energy (ATP) - Use oxygen and transfer organic C that is reduced to fully oxidized fully inorganic C - Transfer unusable energy in form of glucose to useable energy in form of ATP Glycolysis-> occurs in cytoplasm - Transfer of glucose to pyruvate with oxidative phosphorylation with some ATP release - Electrons carried via NADH Citric Acid Cycle - In the mitochondria with substrate level phosphorylation where electrons are carried via NADH and FADH2 into oxidative phosphorylation to produce some ATP Oxidative Phosphorylation: Electron Transport and Chemiosmosis - Uses oxidative phosphorylation - Get majority of ATP and in mitochondria Glucose converted to pyruvate with ATP and reduced electron carrier (NAD+ becomes NADH)-> pyruvate enters in Mitochondria matrix where there is a pyruvate transporter in the IMM

Describe and explain the different mechanisms that influence and/or regulate the Calvin cycle. Explain the importance of such regulatory mechanisms.

CC can be regulated by Light energy - As light reactions occur, protons are driven into the thylakoid lumen - Protons are driven from the stroma to thylakoid lumen when the light energy photoexcites an electron indicating a high proton concentration - CC is in the stroma - Light energy drives the ETC in he chloroplast -- Indirectly influences pH changes -- Stroma: Loses h+, pH increases -- Thylakoid lumen: gains the H+, pH decreases -- Generates ATP and NADPH which are products for CC and phosphorylate and reduce CC intermediates CC can be regulated by the pH as well - As light reactions occur, P+s are actively driven into thylakoid lumen causing pH of the stroma to increase because there is less presence of the H+ - pH of the lumen will decrease because of the presence of the H+'s - While light energy is driving ETC in chloroplast, the H+ in the stroma is going to decrease; only active att pH of 8 for rubsico - With the changes in pH, in the CC, Rubisco is an enzyme. So with a change in pH (environmental factors), it is going to trigger the activation of the enzymes in the CC (trigger conformational changes). Light is driving system which is driving the movement of electrons to thylakoid lumen so increase in pH will activates some of the CC enzymes by higher pH Certain CC enzymes are sensitive to redox status (whether oxidized or reduced will determine if inactive or activated) - So if there is no light, then there is no electron transport without the light - This means no movement of electrons or H+s which will mean nothing ets reduced and everything stays the same oxidized form -- CC enzymes remain inactive in the dark -- In the oxidized form the enzyme is inactive so can't activate the enzyme or functioning. -- However when reduced and takes electrons from carriers, it will be in its active form (conformation change based on REDOX mechanism, not pH) --- Can only be reduced when in the daytime when electrons are being actively moved. Only active when reduced Genetic Regulation of CC enzymes - Genes for CC enzymes are expressed only in photosynthetic tissues - These enzymes are not synthesized in tissues that are not exposed to light - Parts not exposed to light like roots will not expresses genes of like Rubisco (only light exposing parts will express Rubisco)

Write a summary equation for photosynthesis.

CO2 + 2 H2A -> [CH2O] +2A - 2H2A-> electron donor - Utilizes light energy - CH2O is a carbohydrate Photosynthesis requires some type of electron donor when beginning so it gets oxidized during PS - Identity of electron donor will determine the type of PS

From where is the CO2 derived that is fixed in the Calvin Cycle?

CO2 comes from the atmosphere where it is fixed in the CC Carbon that enters is inorganic and then it will be reduced to form carbohydrates

Describe the catabolism of triglycerides.

Carbohydrates enter from various points where glycerol does enter through our fats Fats for fatty acids go through betta oxidation prior to getting tot acetyl CoA - Fats are highly reduced compounds - They liberate more E per gram out of cats compared to carbs and proteins - Compact storage form of E - Triglycerides are important for long-term E storage where especially in hibernating/migrating species (reserves in seeds during germination) Catabolism of Fats - Hydrolysis is to liberate glycerol and FAs - Glycerol goes through glycolytic pathway - FAs get linked to CoA and metabolized via beta-oxidation Proteins are catabolized to individual AA and then depending on AA will enter on some point in the pathway

Explain why metabolic pathways are comprised of many, small steps from reactants to products rather than just one large step.

Catabolic pathways drive regeneration of ATP from ADP and phosphate - ATP synthesis requires ADP and inorganic phosphate which requires energy (anabolism) (uses energy from exergonic reaction) - Anabolism: requires energy to come in where ATP hydrolysis is breaking bonds and releasing energy in ADP + inorganic phosphate to yield energy (catabolism here where energy is used to fuel the catabolic reactions) In cells, process doesn't occur in one step - Many steps are slow and controlled - C6H12O6 + 6O2 -> 6CO2 + 6H2O + energy Protons/electrons (H+/e-) are stripped from organic molecules (C6H12O6) (taking organic fuel molecule and slowly strip away the reduction energy so take away protons and electrons and transfer them somewhere else and see gradients do work) - Carried by mobile electron carriers to ETC - Eventually transferred to oxygen Free energy released during transfer of H+/e- used to drive ATP synthesis (overall goal) We can't go directly from glucose to energy because if there is a certain amount of free energy associated with it where it is all either released at once which is not good for cells or we can release it in small, controlled steeps - Overall still get the same free energy released - If release all at once will result in an explosion and that is not favorable - In small, controlled steps through glycolysis and ETC and Krebs cycle and oxidative phosphorylation, still get the same ATP, but it is controlled and harnessed Autotrophs and heterotrophs use macromolecules produced by autotrophs as energy sources - Fuel molecules are oxidized to produce usable chemical energy (glucose is a fuel molecule) (energy funneled to ATP production) - Aerobic respiration: total process by which food molecules are ultimately oxidized by cells, using oxygen

Describe the biochemical changes that give rise to fall leaf color.

Chlorophyll is predominant pigment in green tissues (masks the other pigments) during the summertime However, as it turns into fall, there are changes in daylength and light intensity that cause the breakdown of chlorophyll and decreased biosynthesis of new chlorophyll - So other pigments become unmasked and they are more apparats whereas chlorophyll is going to be less and less (biosynthesis of it will slow down)

Explain the role of Coenzyme A in aerobic respiration.

CoA is supposed to attach to pyruvate to form Acetyl CoA that is then used to generate citrate from oxaloacetate CoA combined with remaining acetate from oxidative decarboxylation of pyruvate in order for form acetyl CoA which enters into TCA cycle

Describe the Cori cycle. Describe the abnormal conditions that occur when the Cori cycle takes place.

Cori Cycle is when conditions are strenuous activity with low O2 levels High metabolic activity with low O2 Muscle cells catabolize glycogen, due to low O2 will do lactate fermentation where pyruvate will enter lactate fermentation - Does glycolysis to form pyruvate and then pyruvate forms the lactate Lactate leaves muscle cells and carried through blood stream and ends up in liver cells whether Gluconeogenesis occurs - Gluconeogenesis is starting from noncarbohydrate source to convert the molecules into usable glucose to go back into blood stream Keeps glucose at homeostatic range and allows supply of glucose (because under high metabolic activity, muscle cells depleted and lost their glucose as well as glycogen storers. So any source of energy is new coming glucose from glycogenotic pathway) This can not be carried out long term because eventually, using more ATP then able to generate by glycolysis (consuming more ATP then generating) Glucose stored in our bodies as glycogen for short-term energy reserves

Describe the Warburg effect. How can the Warburg effect be used in the study of cancer?

Discovered by Otto Warburg in 1920 Observed that cancer cells consume more glucose compared to normal cells - Accompanied by elevated lactate levels in cancer cells acidic EC space What was weird was that the rates and levels were high even in aerobic environment (presence of O2) - If oxygen is present, carry out aerobic respiration - If oxygen is not present will do fermentation - However cancer cells will do fermentation pathway (even in presence of oxygen-> what the Warburg effect is) Cancer cells therefore use much more glucose in order to obtain ATP because not utilizing glucose efficiently (only get 2 ATPs instead of 40) - Use more glucose because of higher growth rate and because they are using it much more inefficiently By increasing the amount oof metabolites moving through glycolysis (because of higher metabolism, running things more through glycolsis) - More metabolites are available for the synthesis of other molecules (nucleotides, lipids, and AA)

Explain why is fermentation necessary

During fermentation, pyruvate is reduced by NADH (reason why is because NADH is going to be oxidized to NAD+) Need to have NAD+ for glycolysis to occur because if run out of NAD+, then don't have anywhere for NADH to release electrons. So this mechanism allows regeneration of NAD+ so that it can be used in glycolysis

Explain the driving force behind electron movement through the electron transport chain. What drives the concomitant movement of protons across the IMM?

Electrons move from glycolysis and Krebs cycle produced to the ETC that are used in oxidative phosphorylation - All reduced electrons comes and holds onto the PE that has ben stripped away from organic fuel molecules ETC localized in IMM - NADH comes from glycolysis, oxidative decarboxylation of pyruvate, or KC - Will approach first complex and delivers the electrons to it with the reduced form of NADH until get to complex 3 where there is the final electron acceptor in ETC that has O2 and will yield H2O ATP synthase is not part of ETC, just uses the proton gradient that is generated from ETC Driving force: electrons will spontaneity move from complexes with lower EN tot complex with greater EN (go from something less spontaneous to more spontaneous) - When electrons are transferred to a more EN molecule, the more EN molecule is reduced and energy is released More negative something is, less likely to hold onto something that is negative so the electrons will flow spontaneity downhill towards more EN -- Start NADH which is more negative in reduced potential goes throws complex 1 and 2 and then goes to O2 which is the most EN on this scale The position of each component is determined by its standard reduction potentials (How EN is it? - Less EN are at the top and more are components are the bottom - Electron transfer from components at the top to bottom is spontaneous and exergonic (-delG) Electrons flow spontaneously from complex to complex due to EN differences Oxygen is required because it is the final electron acceptor which gets reduced to form H2O Low pH= high [H+] Free energy released by movement of electrons through ETC is coupled tot transport of protons not the intermembrane space. Means the pH of matrix is higher than the pH of intermembrane space because coupling movement of electrons which is spontaneous with movement of protons which is not spontaneous (going against the gradient) - Active transport would this because protons are going against gradient from matrix to IMM and uses the delG released Spontaneous flow of electrons releases free Energy where it is coupled to active transport of protons across the IMM. - Generates the proton gradient across IMM Overall Idea: -Have reduced electron carriers that were produced by oxidizing organic molecules - Electron carriers deliver electron to ETC where the electrons flow spontaneity from one compartment to next which is going to drive the protons movement into the IMM - Will have a high proton concentration in space where diffuse through ATP synthase (delG is released so free energy is coupled worth generating of ATP from ADP and phosphate) If take electrons away, nothing will occur because no place for electrons to be oxidized and no place to dump the electrons so NADH will remained reduced unless with fermentation

Describe how energy and matter move through the biosphere.

Energy moves in a single pathway where matter cycles between heterotrophs and phototrophs

Describe the process of beta-oxidation of fatty acids. How many rounds are required for a given fatty acid?

FAs are even number of C's where beta-oxidation is the catabolic process for FAs - FAs are degraded in series of repetitive cycles - Each cycle will remove 2 C's at a time in form of acetyl and will be attached to then Co-A - Continues until the FA is completely degraded Cycle generates - Acetyl CoA-> (oxidize the fats and produce the reduced co-enzymes where reduced Coenzymes: NADH and FADH2 (go to ETC) Beta-oxidation can occur in Mitochondria and peroxisomes Ex: If start out with 8 C's carbonyl at end will attach to CoA molecule - Then the beta C (2nd C), will convert the beta C CH2 into a double bond where remove an H (oxidize it). Will also get reduced electron carrier that will be taken to ETC (FAD+->FADH) - Then will hydrate the reaction where add a OH to C with double bond and an H group to other C. Then oxidize again where will lose the H in OH and form a double bond with C -- Reduce NAD+ to NADH - Then spilt the bond off from where he double bond is and add a CoA (will attach carbonyl that will spilt off the 2Cs) - So at every step there is a loss of 2 (right now there are 6) - Will go until get to acetyl CoA There is still usable energy to run remaining FA through beta-oxidation to get remaining energy out - Once get down to 4 Cs's will spilt the 4 and end up with 2 acetyl CoA's in the last step

Oxidative Phosphorylation

Formation of ATP via oxygen-dependent electron transport (strip electrons from organic molecules) Process is driven by an electrochemical gradient formed using free energy released during electron transport

Describe in detail the structure of the mitochondria. Explain how this structure is related to its functions.

Found in all eukaryotic cells Site of aerobic respiration Comparable in size to bacteria (evidence suggests evolved from proteobacteria ancestor) Structure of Mitochondria: - Surrounded by a double membrane (outer mitochondrial membrane OMM and inner mitochondria membrane IMM) -- Highly folded-> increases the surface areas -- Folds= cristae -- Localized to the IMM Electron transport systems and ATP synthase complexes -- Spaces within membranes --- Intermembrane space: between the OMM and IMM Matrix: within IMM Krebs cycles enzymes Mitochondrial DNA Mitochondrial ribosomes (70S and sensitive to antibiotics) Function of Mitochondria - Maternally inherited in animals - Number of mitochondria vary per cell (1000-2000 in a highly active liver cell while in muscles less than 50) - Localized to regions of high metabolic activity (concentrated in species areas) Ex: sperm cells where mitochondria are coiled around the tail Function of Outer Membrane of Mitochondria - Phospholipid synthesis, fatty acid desaturation, and fatty acid elongation Function of Inner Membrane Mitochondria - Electron transport, proton translocation for ATP synthesis, oxidative phosphorylation, pyruvate import, fatty acyl CoA import, and Metabolite transport Function of Matrix - Pyruvate oxidation, citric acid cycle, ATP synthesis, Beta oxidation of fats, DNA replication, RNA synthesis (transcription), and protein synthesis (translation)

Outline the general fate of food molecules (protein, lipids, carbohydrates).

Glucose is the man energy source of cells Cells also use alternative fuel molecules like proteins and fats Alternative fuel molecules make up ½ of the average diet

Regarding glucose usage by the cell, describe the scenarios that would result in glycolyis compared to glycogenesis, and vice versa. Why does the cell "decide" to use one over the other?

Glycolysis is when cell requires energy and so it utilizes glucose to form 2 pyruvate molecules with 2NADH and 2ATP Glycogenesis converts glucose into glycogen which is going to be used when there is enough G6P in the cell and energy demand is low so the cell will convert G6P to G1P to where energy demand has been met and energy is put into storage that can be used later If ATP concentration increases in a cell, one consequence is that phosphoglucomutase will catalyze the conversion to G1P (the energy needs are met and so that means there is accumulation of G6P so will be stored away in form of glycogen)

Summarize the net ATP yield from the oxidation of glucose in aerobic respiration. Compare that to the net ATP yield from glycolysis alone.

Glycolysis: 2ATPs by substrate phosphorylation Aerobic respiration-> 36-38 ATPs (more efficient at energy extraction) Glycolysis: 2 ATP Krebs Cycle: 2 ATP also by substrate phosphorylation Oxidative Phosphorylation and Chemiosmosis: 32 or 34 ATP

Analyze the regulatory effects of different molecules on glycolysis

If AMP accumulates inside of the cell and have a high concentration, the molecule that will be positively regulated Help to convert unusable energy to useable energy (energy needs of cell) (only used when need energy) If Acetyl CoA is accumulating, it means the cell has enough energy. Says that there is no demand and so the energy needs are met-> so feedback negatively Citrate is intermediate Krebs cycle where if start accumulating, that. Should mean that energy needs of cell are met and same with ATP AMP is break down product of ATP. So if it starts to build up, that tells us that ATP is actively consumed because there is more of a demand on that pathway (only one to positively regulate glycolysis)

Lactate Fermentation

If can't oxidize NADH, won't generate NAD+ which is needed to do glycolysis (2nd part of the energy payoff phase) Once pyruvate is generated, it will convert to lactate while NADH is going to be oxidized to NAD+ which can be used in glycolysis again Lactate converted from pyruvate Occurs in human red blood cells

Glycogenolysis

If energy needs of cell are not met and cell doesn't have an incoming source of glucose causes glycogenolysis to be triggered which catabolizes glycogen Activation of glycogen phosphorylase (adding an inorganic phosphate group instead of H2O) where liberates a G1P and G1P is going to be converted to G6P where G6P is catabolized via glycolysis - Caused by reversible reaction - Will tap into glycogenesis and ST energy storage where glycogen phosphorylase enzyme will breakdown glycogen one residue at a time by adding a phosphate group where will transform to G1P that then can be reversed to G6P and will get consumed in glycolysis

Describe the catabolism of proteins. Differentiate between endoproteases and exoproteases.

If needed, protein catabolism can be used to produce ATP (but they are the last choice compared to carbs and proeins for energy source) Used for starvation like after depletion of carbohydrates and lipids as well as seed germination Proteins are catabolized by hydrolysis of peptide bonds Protein catabolism begins with hydrolysis of peptide bonds to liberate small peptide and AA - Proteolysis; catalyzed by various types of enzymes: Exopeptidases; Cleave the N-terminal or C-terminal amino acids only Endopeptidases: Cleaves internal peptide bonds Depending on identity fo AA, it is funneled through various catabolic pathways like pyruvate, acetyl CoA, TCA intermediate (AA enter aerobic respiration pathway at various points which are the three above) - Entry points depends on identity of AA

Describe the fate of pyruvate in both aerobic and anaerobic environments.

In aerobic pathway, pyruvate will go through cellular respiration if have mitochondria In anaerobic pathway, O2 not present so cell will do ethanol or lactate fermentation or if cell doesn't have mitochondria

Describe the two photosystems used in photosynthesis. Explain how the structure of the photosystems is designed to funnel light energy to the reaction centers. Describe the "special pair" of chlorophyll molecules found in each reaction center.

Inside chloroplasts there are large complex called Photosystems - Have chlorophylls accessory pigments, and associated proteins which are involved in light transduction events - Light is funneled to reaction center where there is special pair of chlorophyll molecules which will transfer energy to the next component in the transfer chain Found in thylakoid membrane Two types of PS in oxygenic species - PSII (680): has absorption max of 680nm (comes before PSI) - PSI (P700): has absorption maximum of 700 nm The first stage of photosynthesis is to capture light (solar) energy - Light behaves as a stream oof particles called photons - When photon is absorbed by a pigment like chlorophyll, the energy of the photon is transferred to an electron in the pigment (when chlorophyll molecule absorbs a photon and when it occurs, the photon excites the electrons where have a higher energy level called a photoexcited state - Chlorophyll is most stable in ground state. Once light is absorbed, it raises the free energy of electron. Electron is photoexcited

As related to fatty acid production and catabolism, explain why it makes sense that most naturally-produced fatty acids typically have an even number of carbons.

It makes sense because after each round of catabolism, you take away 2 C's for acetyl CoA FAs are produced and catabolized using 2C units in form of acetyl CoA which are building blocks that are in units of 2

Describe electron flow during the "light reactions". Specifically explain: the driving force behind the flow of electrons; what happens as a result of the electrons moving through the electron transport system of photosynthesis; and what are the products of the light reaction?

Light energy is absorbed by various pigment molecules Light energy is funneled to reaction centers (special pair of chlorophyll that transport electrons to next part of electron transport chain) by resonance energy transfer Each reaction center has a special pair of chlorophyll molecules (transfer of the photoexcited electrons PSII is beginning where electrons move over to cytochrome B6 complex, then go to PSI - Light absorption begins at PSII electrons will get transferred and move down until cytochrome b6F - PSII is where have H2O repopulate the electrons that are transferred away - Photoexcitation will cause electrons to leave leaving electron void in PSII so it will be refilled by splitting H2O (h2o replaces the electrons transferred Once get to cytochrome b6F is where protons move across the system where go from the stroma to the thylakoid lumen (protons move across inner mitochondria membrane) Electrons continue movng until get to PS1 where have another light absorbing event that drives movement of electrons where get NADP+ to get to NADPH - Electrons in mitochondria ended up in O2 (o2 was terminal acceptor) - NADP+ is the terminal acceptor where NADPH will be used in Calvin cycle Protons move across the thylakoid membrane just like in mitochondria and ATP synthase will take advantage of proton gradient - Protons diffuse across membrane where release free energy that is coupled with ATP production - It was called oxidative phosphorylation in mitochondria, it is called photo phosphorylation where driven by light movements of electrons Electrons move spontanteoly from less EN molecules to molecules with higher EN (both in photosynthesis and mitochondria) Similar to mitochondria, proton transport in the chloroplast is coupled to flow of electrons. The coupled transport of protons results in proton transport from stroma to thylakoid lumen via Cyt b6/f. ATP synthesis will take place in the stroma - Coupled means that electron flow is spontaneously where will go into the lumen of the thylakoid. Electrons flow spontaneously where any spontaneous process releases free energy so that free energy is coupled with movement of protons - Protons will move against their gradient because actively transporting them into thylakoid lumen, that would mean ATP synthesis is in the stroma (build up of protons in one space and then go into lumen) Requires input of light energy to cause electrons to flow and spontaneous will be coupled with movement of protons across the thylakoid membrane (protons from stroma to thylakoid lumen) - During the light reactions will have higher proton concentration in the thylakoid lumen (go from low to high). Electrons are not transported to ATP synthase at end of the ETC

Explain why referring to the Calvin Cycle as the "dark" reactions is really not accurate.

Light reaction's and dark reactions occur simultaneously in the presence of light where dark reactions do not operate in the dark CC doesn't actually operate in the dark - Mechanisms in place to allow CC to operate when only light present Light and dark reactions only occur when light energy is available Dark reaction name because don't directly use light energy What regulates CC to only happen in the daytime is presence of light energy and changes in pH

Regulatory Effects and Metabolic Pathways that affect Aerobic Respiration

Metabolic pathways are controlled by feedback regulation where each step is catalyzed by an enzyme (what is feeding back to regulate the enzymes) - Intermediates and/or products 'feedback' to provide information (what sort of info is feed back to say abut needs of a cell) -- Pathway is producing too much product -- Pathway is not making enough product to meet the cells needs If there is a demand (need for a product) - Products of pathway are consumed - Pathway continues to supply products (will not build up because will be used up) - So continue supplying until there is a demand When there is a decrease in demand - Products start to build up - Accumulation of products serve as feedback signal to stop/slow down supply - Once there is a decrease, not actively consumed so concentration will build up so will want to stop making so much of it (different for each molecule)

Compare and contrast chemiosmosis during oxidative phosphorylation in mitochondria and photophosphorylation in chloroplasts.

Most direct source of ATP synthesis during photophosphorylation is electrochemical h+ gradient across the thylakoid membrane because it is driving the ATP Synthesis Chemiosmosis: movement of ions across a selectively permeable membrane, down their electrochemical gradient - Phosphorylation: food converted into ATP - Photophosphorylation: light energy used to release ATP

Explain the role(s) of electron carriers in the cell and describe their general structure.

NAD+/NADH (nicotinamide adenine dinucleotide) - Can be reduced or oxidized (donate or accept protons of molecules) - NAD+ is oxidized form of NADH FAD/FADH2 has proton that is oxidized or reduced and is reversible In glycolysis, electrons/protons are removed from G3P by NAD+ thereby oxidizing G3P - NAD+ can't be oxidized because already oxidized (needs to be reduced so electrons/protons removed from G3P to make NADH)

Describe the role of ATP and NADPH in the Calvin cycle.

Need the ATP and NADPH from the light reactions to drive the dark reactions Photosynthesis is an endergonic and anabolic process O2 liberated during photosynthesis comes from the H2O that is oxidized (H2O is electron donor) where CO2 is used to create the carbohydrate Carbon assimilation rxns in photosynthesis take place in the stroma

Differentiate between organisms/cells based on their usage of oxygen (i.e. aerobic or anaerobic?; obligate or facultative?).

Obligate aerobes (requires oxygen) Obligate anaerobes (can't use oxygen and is toxic to them) Facultative anaerobes (facultative aerobes) -> can survive with or without oxygen; Muscle cells is example

Ethanol Fermentation

Once pyruvate is generated, will need to decarboxylyze to acetaldehyde A Once acetaldehyde is generated, this is step where NAD+ is regenerated and acetaldehyde is converted to ethanol

Autotrophs

Organism that makes its own food

Heterotrophs

Organism that produces organic compounds from other organic compounds

Describe the accessory pigments used by phototropic organisms.

Other pigments besides chlorophyll that plants absorb Carotenoids: types of pigments that give reds, oranges, yellows (Beta-carotene) Phycobilin's: blue range and then there are red ones

Describe PDH and the oxidative decarboxylation of pyruvate by PDH.

PDH (Pyruvate Dehydrogenase): Enzyme complex involved in conversion of pyruvate to acetyl CoA where pyruvate is going to be reduced - Highest level of proteins structure is quaternary Large multimeric protein complex Contains several enzymes, coenzymes, and regulatory proteins PDH complex catalyzes the oxidative decarboxylation of pyruvate - Reaction that links glycolysis with the Krebs cycle Pyruvate will enter mitochondria for aerobic respiration (this is part that links glycolysis to the Krebs cycle) - Pyruvate will enter matrix with PDH - Decarboxylation will occur where PDH catalyzes oxidative decarbolyzation where remove a CO2 group from pyruvate (pyruvate comes in through IMM transport carrier) - Second step is the reduction of NAD+ to NADH - Third step is take CoA and link the two remaining Carbons from the chan with it to form Acetyl CoA (S-CoA) (sulfydryl group is where acetyl group will link to carrier molecule) CoA is acetyl carrier (takes acetyl group from somewhere and delivers it somewhere else where transfer acetyl to a component and NADH and FADH2 are the electron carriers Pyruvate with 2 remaining C's will bind to SH to form thioester bond with higher energy Oxidative Decarboxylation of Pyruvate to form Acetyl CoA - Pyruvate is: -- Decarboxylated-> remove CO2 where removing 1 C from pyruvate -- Oxidized-> Transfer e- to NAD+ to form NADH -- Remaining acetate (2C) is linked to CoA (linked through thioester group) to form Acetyl CoA

What is PDG-PET?

PET Scan: imagining technique hat exploits Warburg Effect Consume glucose that is radioactive which is FDG, uptake provides a way to asses glucose uptake rates in the cells - Take away oxygen and put radioactive fluorine Can be used to diagnose, stage, and monitor different types of cancer Positron Emission is detecting radio label

Describe the process of photophosphorylation. Again, you should be able to explain what is driving the process.

Phosphorylation of ADP to ATP using energy from the sun by activation of the PSII During light reactions, electrons flow spontaneously from molecule with low EN to high EN Proton transport in chloroplast is coupled to flow of electrons resulting in proton transport from stroma to thylakoid lumen via Cyt b6/f ATP synthesis/photophosphorylation takes place in stroma

Explain the possible fates of photoexcited electrons.

Photoexcitation is when energy transferred from a photon energizes the electron - Form the ground state in a low energy orbital to excited state in a high energy orbital First step of photosynthesis is photoexcitation Fates of photo-excited electrons: - Excited state is going to be unstable and energy must be dissipated - Can either return to ground state -- As go back down it releases heat and photon fluorescence -- When photoexcited pigment fluoresces, wavelength of fluorescent light is longer than wavelength of absorbed light because as go back down, you are releasing both beat and photon fluorescence's. Both values will have to equal the energy absorbed (can't have photon be more energy than absorbed because losing some energy in form of heat so will have a longer wavelength) ---- Will have less energy than light absorbed because as photon is emitting out, it is losing heat as energy so will have less energy meaning that longer wavelength - Transfer to another (more stable) molecule -- Photochemical energy dissipation -- Chlorophyll is at the ground state where once absorbs photon of light, it will get photoexcited where have higher free energy level -- Instead of going to ground state, will get transferred to a different molecule ---- Beginning of photosynthesis ---- Photoexcitation where photoexcited electron is transferred to next molecule in ETC

Link together the processes of photoreduction, photophosphorylation and carbon fixation generate a complete picture of phototrophic energy conversion (i.e. photosynthesis). Your description should include the subcellular locations of the events involved.

Photophosphorylation: using H+ gradient to synthesize ATP, where H+ gradient is created by coupling H+ movement with exergonic movement of electrons that are helped by photons;ATP synthesis driven by energy derived from the sun/proton gradient Carbon fixation: carbon atoms from atmospheric carbon dioxide are fixed - covalently joined to solid organic compounds ultimately forming carbohydrates; initial fixation and reduction of CO2 to form simple 3-C carbohydrates; stroma Photoreduction: using a series of electron carriers to transport excited electrons from chlorophyll to NADP+, forming NADPH

Describe in detail the structure and function of the chloroplast.

Photosynthetic organelle that is 5-10 micrometers Has three membrane systems - Outer membrane - Inner membrane: encloses the stroma where it is a gel-like matrix where Calvin Cycle and other process take place (inside the intermembrane is where the stroma is located) - Thylakoids: flat, saclike structures in the stroma Interior of thylakoid is the thylakoid lumen - Lumen contains H+ ions Mitochondria only have 2 membranes (outer and inner membrane with matrix)

Explain how light energy is absorbed by the different plant pigments to generate the colors we see.

Photosynthetic organisms can capture all the visible light wavelengths - Absorbance spectra of different types of pigments where spam entire visible light wavelength - We see green primarily because there is a lot of chlorophyll because it is the primary pigment where it masks the others present Pigments absorb certain wavelengths and will reflect others Selectively absorbed certain wavelengths of light and will reflect the other wavelengths

Explain how the movement of electrons back to their ground state is beneficial to plants.

Plants take advantage of this because plants can't move Excess light absorption must be dissipated - Dissipation occurs via chlorophyll florescence Helps dissipate heat and help regulate temperature - Plants can't move where if on hot sunny day, there is a lot of excess energy that they are forced to withstand. So with dissipation, through chlorophyll fluoresce helps them get rid foo excess energy

ATP Synthase

Proton gradient across membrane which is used to generate ATP; on the IMM Has a F1 and F0 complex where F1 is used to generate ATP ATP synthase: functions as an enzyme-complex and a proton transporter ETC—generated proton gradient is used to drive ATP synthesis (use higher proton gradient due to ATP synthesis) Protons flow through IMM into matrix by facilitated diffusion because go from high proton concentration to low proton concentration and requires a use of a proton channel too get through (spontaneous process

Describe a redox reaction. Identify the species undergoing oxidation and those undergoing reduction in such a reaction.

Redox reaction is oxidation-reduction reaction Involves a change in oxidation numberer Oxidation: loss of electrons; gain of O; LOSS OF H (E-/ H+) Reduction: Involves Gain of electrons GAIN OF H (e-/H+) LEO GER (Lose Electron Oxidation; Gains Electron Reduction) Glucose is oxidized resulting in CO2 (loses Hydrogens) and Oxygen is reduced (gain hydrogen) in aerobic respiration

Explain how glucose is labeled for use as a tracer molecule.

Radioactively labeled compounds, radiotracers or radiolabels, are used to follow the fate of individual types of molecules in the body Use of radiolabels relies on existence of naturally occurring isotopes of common elements (atoms of same element with different atomic weight) Radiolabeling or isotopic labeling is used to follow fate of biochemical intermediates in metabolic studies Glucose will be tagged with radioactivity or utilizing naturally occurring radioactive isotopes - Will have radio label attached and wherever the radio label proiton of molecule, will be able to see it - If go through glycolysis will spilt 2 3C intermediate, but still utilized by cell in metabolism so will see cells when take up in glucose

Explain phenylketonuria (PKU). Why do individuals with PKU have to avoid aspartame?

Recessive genetic disorder involved defect in metabolism of phenyalanine - Lack of phenylalanine hydrolase (PAH) enzyme to convert phenylalanine to tyrosine - Results in build up of phenylalanine which can lead to CNS damage and brain damage Tested for at birth where babies treated with low protein/low phenylalanine diet, particularly during growing years PKU patients must avoid high protein foods like aspartame which is an artificial sweetener - Aspartame catabolism produces phenylalanine which must be avoided because then there is going to be a buildup of it even more

Differentiate between the energy levels within the visible light spectrum, e.g. does red light or violet light contain more energy?

Red light has larger wavelength which means lower energy Violet has a smaller wavelength which means higher energy Higher wavelength= smaller energy (lower wavelength=higher energy)

Describe the general structure and function of NADP+/NADPH. Compare its structure and function to that of NAD+/NADH.

Same as NADH except that it is phosphorylated Does same function as NAD+ and NADH where it is a reversible oxidized or reduced NADP+/NADPH is used during photosynthesis while NAD+/NADH used during cellular respiration NADPH used mostly for anabolic reactions while NADH used for catabolic reactions Difference of single phosphate has no effect on ET properties Difference is in the structure where allowing different substrates to bind to each other

Anoxygenic Photosynthesis

Something other than water is the electron donor like H2S (hydrogen sulfide) to produce elemental S Type of PS seen in purple-sulfur bacteria, heliobacteria, and others

Describe the structure/function of a leaf. What are the stomata and guard cells? Describe their structure/function.

Stomata: - Pores in plant surfaces - Found in upper and lower epidermis of leaves and stems - Surrounded by Guard cells; regulated by guard cells Guard Cells: Open and close stomata to regulate gas exchange with the environment. - Change the osmotic pressure to regulate if stomata is open or closed in the leaf - CO2 from atmosphere diffuses into plant body -- CO2 then gets 'fixed' in Carbon Assimilation Reactions. The plant is battling the CO2 is coming in because water will diffuse out - O2 and H2O vapor diffuse out together If lose too much H2O, stomata will close (most restrictive thing)

Explain how alternative carbohydrates (i.e. other than glucose) and other organic molecules (e.g. glycerol) are metabolized and from where they are derived.

Sucrose, maltose, lactose, mannose, glycogen(starch), glycerol (comes from FA lipids) All funnel through glycolytic pathway at one point Carbohydrates are broken down into respective monosaccharide subunits which are funneled into glycolytic pathway at some point - Glycerol is from FA and lipids which will enter down as one of the 3C intermediate

Describe the glycolytic pathway, highlighting the driving forces behind the steps of the pathway. Describe the pathway inputs and the pathway outputs. What is involved in the 'energy investment phase'? What is involved in the 'energy payoff' phase? (Note: students should recall the pathway intermediates, but do not need to memorize the enzymes of the glycolytic pathway, except where noted during lecture).

Take glucose and get two pyruvate molecules (catabolic event) (break down glucose to form pyruvate-> 2 3C pyruvate molecule) - Glucose is overall oxidized and will be exergonic reaction - Take away the hydrogens and will be exergonic reaction Energy investment Phase: - Use ATP to get intermediates to certain energy level - Input ATP and add phosphate groups to intermediates to get to higher free energy level (priming intermediates) - Glucose is phosphorylated where enzyme catalyzed is kinase (transfer phosphate from ATP) to get Glucose-6-phosphate (C6 gets phosphorylated) - Pathway converted from glucose 6 to fructose-6-phosphate (isomerases it) (aldose sugar to ketose sugar) (creates another C to stick out of the plane of ring) - So now another available hydroxyl to be phosphorylated and get then fructose-1,6-bisphosphate (2 phosphate groups) -- Fructose more unstable and have higher energy intermediate because of two phosphate groups - Pathway is spilt with cleavage into two DHAP (dihydroxyacetone phosphate) and Glyceraldehyde-3-phopshate -- Metabolic intermediates where phosphorylated intermediates of both glycolysis pathway and photosynthesis -- Enzyme that catalyzes their isomerization (reversible reaction). What causes it to go from one direction to the other is concentration difference. The concentration will change where if it shifts in either direction, it will drive the reaction in that certain direction. -- G3P is substrate for next reaction where DHAP is going to get converted to G3P which will be consumed in the next step because it is the substrate for energy payoff phase - Preparation/priming oof intermediates (like consuming ATP) - Cleavage-> fructose 1,6 cleaved into the 2 3C intermediates (Energy investment phase) Energy Payoff Phase: - Produce more ATP then input and get reduced electron carriers - Consuming G3P that was produced and this is where electron carriers utilized G3P is the substrate in this reaction where electron carriers are utilized with NAD+ - NAD+ leaves as NADH where NAD+ is reduced - Initially they come in oxidized where their goal is to remove protons/electrons from fuel molecules (slowly strip away protons and electrons from organic molecules where they are funneled over to ETC-> electron carriers are) -- Oxidation step in glycolysis - Have double phosphorylated intermediate where it is used to drive ATP production through substrate level phosphorylation -- Get to a very high energy intermediate called phosphoenolpyruvate -- When get converted to pyruvate get ATP out - Oxidation of G3P to get reduced electron carrier (NADH) - ATP produced, NADH Produced, and pyruvate is finally product of glycolysis Overall Net Products: Glucose -> 2 pyruvate + 2H2O 4 ATP formed- 2ATP used-> 2ATP 2NAD+ + 4e- +4H+ ->2NADH + 2H+ We have 2 listed throughout because glucose is cleaved into 2 3C Pathway occurs twice per glucose

Explain specifically the role of phosphoglucomutase in glucose metabolism.

The enzyme used to convert G6P to G1P, initiating glycogenesis - the pathway which synthesizes glycogen to store glucose. Phosphoglucomutase is an enzyme used when you have generated a lot of G6P to convert to G1P and perform glycogenesis

Substrate Level Phosphorylation

The formation of ATP by directly transferring a phosphate group to ADP from an intermediate substrate in catabolism. Formation of ATP via direct transfer of a Phosphate group from propylated substrate to ADP What occurs during glycolysis and Krebs cycle (where ATP formed in this product) Mechanism is very different from Oxidative Phosphorylation

Explain how membrane structure is related to membrane function in chemiosmosis.

The phospholipid bilayer where if electron carriers weren't there, then oxidative phosphorylation wouldn't occur

Summarize the reactions of the Calvin cycle, specifically the three phases, and describe changes that occur in the carbon skeletons of intermediates.

Three Phases of CC: Carbon fixation: CO2 + Rubuloise-1,5-bisphopshate (RuBP) - Calvin cycle is known as dark reactions because it doesn't directly require light - Rubisco catalyzes the carbon fixation - Will first require 3 Ribulose-1-5-bisphosphate= RuBP, where it will - Incoming 3CO2 will join with an acceptor molecule 3 Ribulose-1-5-bisphosphate= RuBP where will have 5 C's -- Acceptor molecule will get regenerated at every turn of cycle - Fixation step is catalyzed by Rubisco -- Expect to get 6 C intermediate however it becomes hydrolyzed so fast that we get 3 C intermediate -- So will have 6 total molecules because have 3CO2 and 3 RuBP which will make a total of 18 C's and intermediate has a 3C's so 18/3 is 6 Reduction: using products of light reactions, the 3c intermediates are phosphorylated (ATP) and reduced (NADPH); generate triose phosphate products - ATP then comes in from light rxns to create the doubly phosphorylated intermediates and get 1,2-bisphosphglycerate - Then use NADPH is oxidized to NADP+ to remove a phosphate group and to give us something called triosephosphate (products of Calvin cycle) (intermediate is reduced by NADPH) - Get reduced 3C triose phosphate (6 total Glyceraldyde-3-phospahte) - 1 trioseP leaves the cycle-> synthesis of organic molecules Regeneration: 5 trioseP stay in cycle to regenerate RuBP - For every 6 glyceraldyude-3-phospahet produced, one will leave the pathway and be utilized for other biosynthesis mechanisms -- 5 will stay in because we are trying to regenerate he RuBP molecules where go through a series of reactions to generate 3 Ribulose-5- Phosphate -- It is singly phosphorylated and to get to RuBP need to phosphorylate again so will use ATP from the light rxns to help convert to RuBP

Explain why fats contain more extractable energy per gram compared to carbohydrates or proteins.

Two main types of energy storage are polysaccharides (starch and glycogen) and triglycerides (fats) Comparatively fats have more extractable energy per gram where fats are 9 kcal/g and carbs/proteins are 4 kcal/g Fats contain more extractable energy due to their state of reduction - Contain long strings of CH2 groups in hydrocarbon tails -- More H atoms a molecule contains, the more ATP that can be formed when molecule is oxidized -- Fats contain a greater store of energy because they are considered more reduced (more extractable H+/e-) Each acetyl CoA will deliver acetyls to Krebs cycle. Fats are producing more usable energy because of their reduced state. The more H+/e's, then generate a higher gradient of protons for ATP (more usable energy because have more extractable hydrogens compared to proteins and carbohydrates) Ideal long-term storage because nonpolar: therefore are stored in anhydrous form - Proteins and carbs are more highly hydrated, so they weigh more - Get more extractable energy per gram - Nonpolar; stored in a form that weighs less to other molecules

Describe in general the two main stages of photosynthesis.

Two major events occur: Energy transduction reactions - Known as light reactions - Light-driven movement of electrons (electrons derived from H2O) (need input of light to flow the electrons) - In mitochondria, reduced electron carriers brought the electrons from glucose (strip away electrons and protons from fuel molecules to make ATP gradient) - Produce ATP and NADPH with release of O2 because strip electrons away from h2o Carbon Assimilation Reactions - Dark reactions - CO2 is fixed into carbohydrates using products from the light reactions -- Means CO2 is reduced to form carbohydrates -- Takes CO2 from atmosphere Connected to each other because use products from light reaction to drive carbon fixation in light reactions

Photoheterotrophs

organisms that acquire energy from sunlight but depend on organic sources of carbon (like glucose) (like bacteria) (start from organic compound)

Photoautotrophs

organisms that use solar energy to synthesize energy-rich organic molecules using inorganic starting materials (CO2) (plants; humans depend on them for oxygen and glucose)