Unit 5 Cellular Energy Test

substrate-level phosphorylation

an enzyme transfers a phosphate group from a substrate molecule to ADP → ATP is formed

energy investment phase

- 2 ATP are invested to produce a more reactive molecule → in three reactions glucose is converted to an energized intermediate - a highly reactive six-carbon intermediate is split into two three-carbon intermediates

photosynthesis equation

- 6 CO2 + 6 H2O + light → C6H12O6 + 6 O2 - redox process → carbon dioxide is reduced to glucose + water is reduced to oxygen - endergonic → energy is used

ATP cycle

- ATP is a renewable resource - hydrolysis of ATP releases energy → used for cellular work - energy from cellular respiration → used for ATP synthesis

C4 plants

- CO2 is first fixed into a four-carbon compound - in hot and dry weather, the stomata are kept mostly closed to conserve water - the plant continues making sugars by photosynthesis → an enzyme in the mesophyll cells has a high affinity for CO2 and can fix carbon even when the CO2 concentration in the leaf is low - the resulting four-carbon compound acts as a CO2 shuttle → moves into bundle-sheath cells packed around the veins of the leaf, and releases CO2 - C02 concentration in these cells remains high enough for the Calvin cycle to make sugars and avoid photorespiration. - ex: corn and sugarcane

respiration (breathing)

- O2 is taken in by the lungs and passed to the bloodstream, then carried to the muscle cells → used in cellular respiration to produce ATP to power the muscles - chemical conversion of cellular respiration incorporate O2 into H2O of the cells → secreted as urine/sweat/etc or released in breath - CO2 originates from the glucose produced in cellular respiration, is carried from the blood to the lungs, and exhaled

enzyme regulation

- a cell's metabolic pathways cannot occur simultaneously → enzymes are coordinated through switching on/off encoded genes, or through regulators of activity (inhibitors: chemicals that interfere with an enzyme's activity)

NAD+

- a coenzyme that accepts electrons and is reduced to NADH - the enzyme dehydrogenase strips 2 hydrogen atoms from an organic fuel - 2 electrons and 1 proton are transferred to NAD+, while the other proton is released into surrounding solution - NADH then carries the electrons, passing them to the ETC

carotenoids

- contained in chloroplasts - various shades of yellow and orange - colors of fall foliage in certain → yellow-orange hues of longer-lasting carotenoids that show through once the green chlorophyll breaks down - broaden the spectrum of colors that can drive photosynthesis - photoprotection: they absorb and dissipate excessive light energy that would otherwise damage chlorophyll or interact with oxygen to form reactive oxidative molecules that can damage cell molecules - obtained from carrots and other vegetables and fruits → photoprotective role in our eyes

chlorophyll

- a light-absorbing pigment in chloroplasts that is central to the conversion of solar to chemical energy - built into the thylakoid membranes - a pigment is able to absorb certain wavelengths of light because it is able to absorb the specific amounts of energy in those photons - absorbed wavelengths are not visible → their energy has been absorbed by pigment molecules - leaves are green because green wavelengths are not absorbed but are transmitted and reflected - chlorophyll a absorbs mainly blue-violet and red light - chlorophyll b absorbs mainly blue and orange light → broadens the range of light that a plant can use by conveying absorbed energy to chlorophyll a → more energy captured from sunlight to be used in the light-dependent reactions - leaves with more chlorophyll are better able to absorb light required for photosynthesis - plants in lighting conditions unfavorable for photosynthesis synthesize more chlorophyll, to absorb the light required

chloroplast anatomy

- a typical mesophyll cell has about 30 to 40 chloroplasts - an envelope of two membranes encloses an inner compartment, which is filled with stroma: a thick fluid called - thylakoids: a system of interconnected membranous sacs suspended in the stroma is - thylakoid space: an internal compartment enclosed within thylakoids - grana: concentrated stacks of thylakoids

citric acid cycle

- acetyl CoA enters the citric acid cycle 1. enzymes strip CoA from acetyl and combine the two-carbon group with a four-carbon molecule present in the mitochondria to form the six-carbon molecule citrate 2. redox reactions harvest energy by stripping hydrogen atoms from citrate and then a five-carbon group, while NAD+ is reduced to NADH 3. twice, an intermediate compound loses a CO2 molecule 4. energy is harvested as ATP is produced in substrate-level phosphorylation 5. a four-carbon compound emerges 6. further redox reactions reduce 2 NAD+ to 2 NADH and FAD to FADH2 7. the cycle is completed when the original four-carbon molecule is regenerated and accepts a new acetyl group from acetyl CoA - products: 4 CO2, 6 NADH, 2 FADH2 - net output for every 1 molecule of glucose: 6 CO2, 10 NADH, 2 FADH2, and 4 ATP

CAM plants

- adapted to very dry climates → conserves water by opening its stomata and admitting CO2 only at night - CO2 is fixed into a four-carbon compound, which banks CO2 at night and releases it during the day - the Calvin cycle can operate, even with the leaf's stomata closed during the day ex: pineapples, cacti, and succulents (water-storing)

ATP

- adenosine triphosphate - negatively charged phosphates crowd together → mutual repulsion causes a high PE and the connecting bonds to be unstable + easily hydrolyzed - when the bond to the third group breaks → becomes ADP and energy is released → exergonic

lactic acid fermentation

- as pyruvate is reduced to lactate, NADH is oxidized back to NAD+ - muscle cells and certain bacteria regenerate NAD + by this process - muscle cells can switch to lactic acid fermentation when the need for ATP outpaces the delivery of O2 via the bloodstream - within an hour, lactate is carried by the blood to the liver, where it is converted back to pyruvate and oxidized - muscle soreness is not caused by lactate buildup, but by trauma to small muscle fibers, leading to inflammation and pain - used to make cheese, yogurt, soy sauce, and sauerkraut

exergonic reaction

- begins with reactants whose covalent bonds contain more PE than that of the products, this difference in PE = amount of energy released to the surroundings - ex: burning wood (composed of cellulose) → energy of glucose is released as heat and light (and O2+CO2 are produced) - burning is a one-step process, while cellular respiration has many steps, each a separate reaction

carbon dioxide concentration

- carbon dioxide, as with water, is one of the reactants in photosynthesis - if the concentration of carbon dioxide is increased, the rate of photosynthesis will therefore increase - at some point, the graph levels off as a factor may become limiting - CO2 is a substrate in the reaction with RuBP → more increase the rate of photosynthesis

electron transport chain (ETC)

- chain of carrier molecules (mostly proteins) built into the inner membrane of the mitochondria - NADH and FADH2 become oxidized to NAD+ and FAD as they deliver their electrons to the ETC - each carrier is reduced and oxidized as it accepts electrons and then passes them to the next carrier - electrons are at a lower energy level when associated with a highly electronegative atom, all matter wants to reach a lower energy state → why the electrons are pulled down the chain towards oxygen, the final electron acceptor - moving from a higher to lower energy state releases energy, which is used to pump protons into the intermembrane → active transport (low to high concentration of H+) - there are four protein complexes, three serve as proton pumps → NAD+ enters the ETC at protein complex I, while FAD enters at protein complex 2 (a lower energy level)

photosystems

- clusters of chlorophyll molecules in the thylakoid membrane - photosystem II functions before photosystem I - the electrons in photosystem II come from the chlorophyll a, and are replenished by water - the electrons in photosystem I come from photosystem II

intermediate

- compounds that form between initial reactant and the final product - in metabolic pathways, the product of one reaction serves as the reactant for the next reaction

light-harvesting complex

- consists of pigments bound to proteins → can absorb a larger surface area and spectrum of light than a single pigment - when a pigment absorbs a photon, the energy is transferred from molecule to molecule to the reaction-center complex

reaction-center complex

- contains a pair of special chlorophyll a molecules and a molecule called the primary acceptor - when a pigment molecule absorbs a photon, of the pigment's electrons is raised from a ground to excited state → the electron jumps to an energy level farther from the nucleus, where is has more PE (high energy + unstable) - when isolated pigments absorb light, they almost always jump back down to a ground state, releasing excess energy as heat → chlorophyll a emits lights + heat after absorbing photons - when an electron from chlorophyll a is excited, it is captured by the acceptor

applications of enzyme inhibitors

- drugs: antibiotics inhibit disease-causing bacteria, cancer drugs inhibit enzymes of cell division, antidepressants, blood pressure medicine, penicillin - pesticides/warfare gasses: inhibit transmission of nerve impulses → can induce paralysis and death

first law of thermodynamics

- energy is constant → can't be created/destroyed, only transferred/transformed - power plants convert energy stored in coal to electricity, plant cells convert light energy to chemical energy

catabolic

- energy is used to break down complex molecules - ex: cellular respiration, release of energy in sugars and fats

anabolic

- energy is used to build complex molecules - ex: photosynthesis, synthesis of proteins and DNA

potential energy (PE)

- energy matter possesses as a result of its structure or location - molecules have PE because of the arrangement of electrons in the bonds between their atoms - ex: a person at the top of a hill possesses PE - chemical energy: energy available for release in a chemical reaction, transformed to power the work of the cell

kinetic energy (KE)

- energy of motion - moving objects work by transferring motion to other matter - ex: the movement of legs can push bike pedals, which turns the wheels and moves the bike - thermal energy (random movement of atoms) and light

activation energy

- energy that must be absorbed to contort/weaken bonds in reactant molecules so they break + new ones form - there is an energy barrier that must be overcome for a reaction to begin → prevents high-energy and ordered molecules from spontaneously breaking down - energy is needed for reactant molecules to move to a high-energy state so the reaction can begin → the molecules will then naturally moves to a lower-energy state - metabolic reactions must occur quickly for a cell's survival - heat speeds up molecules so that bonds break and reactions can proceed (but this speeds up both beneficial/unnecessary reactions and can kill the cell) - enzymes

second law thermodynamics

- every energy conversion increase the entropy (disorder/randomness) of the universe - why organisms can't recycle energy → energy becomes unavailable to do work during energy conversions, as it is converted to thermal energy and released as heat - thermal energy = random molecular motion → more randomly arranged matter → greater entropy - explains diffusion → equal concentrations of a solute = more disorder → greater entropy

organic molecules that fuel cellular respiration

- free glucose molecules are not common in your diet → most calories are obtained from carbohydrates (sucrose and starch), fats, and proteins - carbohydrates can be funneled into glycolysis → enzymes in the digestive tract hydrolyze starch to glucose, or glycogen in the liver and muscle cells can be hydrolyzed to glucose - fats contain many hydrogen atoms and thus many energy-rich electrons → the cell hydrolyzes fats to glycerol and fatty acids → glycerol is converted G3P (an intermediate in glycolysis) and fatty acids are broken into two-carbon fragments that enter the citric acid cycle as acetyl CoA - a gram of fat yields more than twice as much ATP as a gram of carbohydrate, but many calories are stockpiled in each gram of fat → large amounts of energy must be expended to burn fat stored in your body - to be oxidized, proteins must first be digested to their constituent amino acids, most of which will be used to make its own proteins → enzymes can convert excess amino acids to intermediates of glycolysis or the citric acid cycle

energy payoff phase

- hydrogen atoms are transferred in a redox reaction that oxidizes the intermediate and reduces 2 NAD+ to 2 NADH, while a phosphate group is also attached to the substrate - 4 ATP are produced through substrate-level phosphorylation - water is produced as a by-product

photophosphorylation

- hydrogen ions from water buildup in the thylakoid space, creating a higher H+ concentration - energy released when electrons move down the ETC is used to pump hydrogen ions in the stroma up their concentration gradient, into the thylakoid space - the energy of this H+ gradient is used to diffuse H+ back through ATP synthase, driving a rotor which phosphorylates ADP to make ATP (goes to the Calvin Cycle)

compensation point

- if oxygen production or carbon dioxide uptake is used as a measure of photosynthetic rate, the graphs are slightly different - line does not go through the origin → oxygen production and carbon dioxide uptake are affected by respiration as well as photosynthesis - if a graph is plotted of carbon dioxide against light intensity, the compensation point is the light intensity at which the rate of photosynthesis is equal to the rate of respiration

enzyme concentration

- if substrates are not a limiting factor and cofactors are present, reaction rate increases linearly with enzyme concentration - doubling an amount of enzyme molecules would double the reaction rate

applications of the laws of thermodynamics

- in cars, the chemical energy of fuel is made available for work through combustion - gasoline and oxygen mix and produce the simple, energy-poor molecules of O2 and CO2 - most of the energy is lost as heat → only 25% becomes the KE of the car's movement - in cells, the chemical energy in organic molecules is used to produce ATP used for cellular work through cellular respiration - CO2 and O2 are released - only 34% becomes energy for cellular work → the rest generates heat → why exercise keeps the body warm - intricate structures of cells contribute to a decrease in entropy, but their production is accomplished at the expense of ordered forms of matter and energy taken in from the surroundings

glycolysis

- in the cytosol of the cell - does not require oxygen - 9 reactions of splitting sugar → glucose is oxidized - energy is released and stored in ATP and NAD+ → energy in ATP is used immediately, NAD+ is reduced to NADH, which is passed to the ETC for its energy to be used - pyruvate possesses 90% of the energy available to the cell from the initial molecule of glucose - net output for every 1 molecule of glucose: 2 pyruvate, 2 NADH, and 2 ATP are produced

oxidative phosphorylation

- in the inner membrane of the mitochondria - the cristae enlarge the surface area of the membrane → provides space for thousands of ETCS and ATP synthases - requires oxygen - net ATP output = 10 NADH * 3 ATP each + 2 FADH2 * 2 ATP each + 4 ATP = 38 ATP

competitive inhibitors

- inhibitor's that resemble an enzyme's substrate, which compete for entry into the active site - they block the actual substrate from binding → reduced productivity - overcome by increasing the concentration of substrate → higher chance that substrate will reach the active site instead

noncompetitive inhibitors

- inhibitors that bind to someplace on the enzyme other than the active site - the substrate can still bind to the active site, but the enzyme is prevented from doing its job - lowered concentration of functional enzyme molecules → reduced productivity

enzyme kinetics graphs

- initial rate of reaction = when the enzyme and substrate have just been combined and the enzyme is catalyzing as fast as it can before the substrate is used up - initial velocity (V0) = amount of product produced per unit time at the start of the reaction - for most enzymes, V0 increases at first, than hits a plateau → the enzyme is saturated - all the enzyme molecules are busy with substrates, and any additional substrate has to wait for available enzyme - the reaction is limited by the concentration of enzyme - V0 levels off at this maximum velocity (Vmax) - Km = the substrate concentration at half of Vmax, measures how quickly reaction rate increases with substrate concentration - also measures an enzyme's tendency to bind to its substrate (a lower Km = higher affinity for substrate) - always the same for a particular enzyme catalyzing a particular reaction

light intensity

- light intensity = energy hitting an area over some time period, higher light intensity → more packets of light called "photons" are hitting the leaves - rate of photosynthesis will increase because there is more light available to drive the reactions of photosynthesis - once the light intensity gets high enough → rate won't increase anymore because there will other factors that are limiting the rate of photosynthesis (amount of chlorophyll, H2O, CO2, etc) - at a very high intensity of light, the rate of photosynthesis would drop → light starts to damage the plant - light excites the electrons in photosystem II which starts the light-dependent reactions → more increase the rate of photosynthesis

leaf anatomy

- mesophyll: green tissue in the interior of a leaf where chloroplasts are concentrated - stomata: tiny pores on the underside of leaves where CO2 enters the leaf and O2 exits - veins: how water absorbed by the roots is delivered to the leaves, also used to export manufactured sugar to roots and other parts of the plant

enzymes

- molecules that function as biological catalysts → increase the rate of a reaction without being consumed - almost always proteins, but some RNA molecules function enzymatically - speeds the reaction by lowering the activation energy → contorts the bonds in reactants to a higher-energy state - the active site is made of different parts of polypeptide chain folded into a specific shape so they are closer together - for some enzymes, the binding site is very specific and allows only one kind of substrate - other enzymes are specific for the type of chemical bond, not an exact substrate, and will accept a wide range of substrates of a same general type

endergonic reaction

- net input of energy - reactants contain little PE compared to the energy-rich products, this difference in PE = amount of energy absorbed from the surroundings - ex: photosynthesis → starts with energy-poor O2 and CO2, energy is absorbed to produce energy rich sugar molecules

cofactors

- nonprotein helpers that bind to the active site and function in catalysis - can be inorganic, like ions of zinc and iron - can be organic, called coenzymes - vitamins help with nutrition because they function as coenzymes/materials for coenzymes

light dependent reactions

- occur on and inside the thylakoids - water is split → provides electrons and releases O2 - light energy is absorbed by chlorophyll molecules built into the thylakoid membranes → used to drive the transfer of electrons and protons from water to the electron acceptor NADP+, reducing it to NADPH - NADPH temporarily stores electrons and goes to the Calvin cycle - ATP is generated from ADP and a phosphate group

location of photosynthesis/cellular respiration

- photosynthesis takes place in prokaryotes, plants, and algae - cellular respiration takes place in plants, animals, fungi, protists, etc - plant cells have mitochondria + chloroplasts, animals cells have just mitochondria

pyruvate oxidation

- pyruvate is transferred to the mitochondrial matrix 1. pyruvate loses 2 oxygens and a carbon as CO2 2. a two-carbon compound is oxidized while NAD+ is reduced to NADH 3. coenzyme A joins the two-carbon compound to form the molecule acetyl CoA - products: 2 acetyl CoA, 2 CO2, and 2 NADH - net output for every 1 molecule of glucose: 2 acetyl CoA, 2 CO2, 4 NADH, and 2 ATP

ways to measure the rate of photosynthesis

- rate of oxygen output - rate of carbon dioxide intake - rate of carbohydrate production

glycolysis ancient metabolic pathway

- universal energy-harvesting process of life, virtually any living cell has the metabolic machinery of glycolysis - oldest-known fossils of bacteria resemble types of photosynthetic bacteria still found today - significant levels of O2, formed as a by-product of bacterial photosynthesis, did not accumulate in the atmosphere until about 2. 7 billion years ago → early prokaryotes most likely generated ATP exclusively from glycolysis - also does not occur in a membrane-bound organelle

rubisco

- remarkably inefficient → typical enzymes process thousands of molecules per second vs rubisco fixes only about three CO2 molecules per second - plant cells compensate for this slow rate by building lots of the enzyme → most plentiful single enzyme on the Earth - lack of specificity → oxygen and carbon dioxide molecules are similar in shape and chemical properties, so an oxygen molecule can bind comfortably in the site designed to bind to carbon dioxide - photorespiration: as O2 builds up in a leaf, rubisco adds O2 instead of CO2 to RuBP → rubisco attaches oxygen to the sugar chain and forms a faulty oxygenated product - different from cellular respiration → ATP is used instead of produced and no sugar is yielded - the plant cell must then perform a costly series of salvage reactions to correct the mistake → can drain away as much as 50% of the carbon fixed by the Calvin cycle - evolutionary relic from when the atmosphere had less O2 than it does today → the ability of rubisco's active site to bind O2 as well as CO2 would have made little difference → after O2 became so concentrated in the atmosphere this lack of specificity presented a problem

thermodynamics

- study of energy transformations in a collection of matter - system: matter under study - organism = open system → exchanges energy + matter with surroundings - surroundings: everything outside the system

fermentation lab

- sucrose = glucose + fructose - lactose = glucose + galactose - sucrose can be broken down by yeasts → undergoes fermentation - yeasts lack the enzymes to break down the sugars in lactose → does not ferment

electromagnetic spectrum

- sunlight is electromagnetic energy or radiation - visible light → 380-750 nm - photon: has a fixed quantity of energy - as the wavelength of light increases, the energy of its photons decreases

optimal temperature

- the KE of the substrate and enzyme molecules is ideal for the highest rate of collision between substrate and active site - at low temperatures, there are less collisions due to lower KE → lower enzyme activity - high temperatures can denature the enzyme - heat speeds up molecules, which will break hydrogen bonds and disrupt interactions between R group - tertiary structure is unfolded and structure is lost → the active site is altered and can't fit the substrate - most human enzymes function at 35-40°C (body temperature)

ATP vs heat energy

- the chemical energy in the bonds of glucose is released → 34% is stored in ATP, while the rest is released as heat - helps maintain constant body temperature - exercise requires energy, causing an increase in cell respiration, and thus release of heat → why sweating occurs the cool the body (evaporative cooling)

temperature

- the chemical reactions that combine carbon dioxide and water to produce glucose are controlled by enzymes - low temperatures → rate of photosynthesis is limited by the number of molecular collisions between enzymes and substrates - perfect temperature → highest rate of collisions between enzymes and substrates to have photosynthesis occur most effectively - high temperatures → enzymes are denatured

fermentation

- the harvest of energy in the absence of oxygen - ATP is generated through glycolysis, but NAD + must be present as an electron acceptor - under aerobic conditions the cell regenerates its pool of NAD+ when NADH passes its electrons into the ETC → fermentation provides an anaerobic path for recycling NADH back to NAD+ - 2 ATP is a lot less than the possible net output after oxidative phosphorylation, but it is enough to keep your muscles contracting for a short time when oxygen is scarce, and many microorganisms supply all their energy needs solely through glycolysis

optimal pH

- the pH at which enzyme activity is most efficient - close to neutrality, though most enzymes have a flexible working range of pH values - high acidity/alkalinity denatures enzymes - changes in H+ concentrations interfere with R group interactions → loss of shape → decreased activity

biosynthesis

- the production of organic molecules using energy-requiring metabolic pathways - not all food molecules are destined to be oxidized as fuel for making ATP → food also provides the raw materials the cells use for biosynthesis - cells must be able to make molecules to build its structures and perform its functions → proteins, fats, and carbohydrates can be made from intermediate molecules of glycolysis and the citric acid cycle - amino groups combine with amino acids from the citric acid cycle to form proteins - fatty acids from acetyl CoA and glycerol from G3P form fats - sugars from glucose become complex carbohydrates - basic principles of supply and demand regulate these pathways → feedback inhibition: if ATP accumulates in a cell, it inhibits an early enzyme in glycolysis, slowing down respiration and conserving resources → the same enzyme is activated by a buildup of ADP in the cell, signaling the need for more energy

chemiosmosis

- the pumping of H+ creates an electrochemical gradient, a form of stored energy - protons pass through phospholipid bilayer by facilitated diffusion through ATP synthase - ATP synthase is like a water wheel → it is turned by the flow of H+ moving down it's concentration gradient, which catalyzes the synthesis of ATP

metabolism

- the total of an organism's chemical reactions - metabolic pathway: a series of chemical reactions that build/break down complex molecules - cellular respiration → metabolic pathway in which a sequence of reactions slowly releases the PE stored in glucose

phosphorylation

- transfer of a phosphate group from ATP to another molecule - how the cell couples the hydrolysis of ATP to an endergonic reaction - chemical work: phosphorylation of reactants provides energy for the endergonic synthesis of products - transport work: phosphorylation of transport proteins drives the active transport of solutes across a membrane - mechanical work: phosphorylation of motor proteins in muscle cells causes the proteins to change shape and pull on their protein filaments → cell contraction

redox reaction

- transfer of electrons from one molecule to another - oxidation: loss of electrons vs reduction: gain of electrons - electron transfers always require a donor and acceptor → oxidation and redox always go together - exchanges of hydrogen atoms represent electron transfers → each atom consists of an electron and a hydrogen ion

C3 plants

- use carbon directly from the air and carbon fixation occurs when the enzyme rubisco adds CO2 to RuBP → first stable product of carbon fixation is a three-carbon intermediate compound - widely distributed → includes important agricultural crops like soybeans, wheat, and rice - hot, dry weather can decrease crop yield → plants close their stomata to reduce water loss and help prevent dehydration → prevents CO2 from entering the leaf and O2 from exiting → CO2 levels get very low in the leaf and photosynthesis slows + O2 released from the light reactions begins to accumulate (photorespiration)

alcohol fermentation

- used for brewing, winemaking, and baking - yeasts: single-celled fungi that normally use aerobic respiration to process their food, but can survive in anaerobic environments - yeasts and certain bacteria recycle their NADH back to NAD+ while converting pyruvate to C02 and ethanol - CO2 → provides the bubbles in beer and champagne, and also causes bread dough to rise - ethanol is toxic to the organisms that produce it, so yeasts release their alcohol wastes to their surroundings, where it usually diffuses away → why yeasts die when confined in a wine vat when the alcohol concentration reaches a certain percentage

feedback inhibition

- when too much of a product is made, it acts as an inhibitor to one of the enzymes in the pathway - used to regulate cellular metabolism - prevents waste of resources, as the excess product is used - only weak interactions bind inhibitor and enzyme → this inhibition is reversible - when the product is used up by the cell, the enzyme is no longer inhibited and the pathway functions again - inhibition is nonreversible when binded by covalent bonds

inhibition kinetics

- with competitive inhibitors, it takes more substrate to reach Vmax (higher Km) because more substate is needed to beat inhibitors to reach the active site - with noncompetitive inhibitors, Vmax is never reached but Km is the same → binding of substrate to enzyme isn't affected, there is just less useable enzyme

photosynthesis ETC

1. a proton provides the energy to boost an electron from photosystem II to a higher energy level 2. the electron is caught by the primary electron acceptor and loaded onto the electron transport chain 3. as the electron is passed between electron carriers, it releases energy, and reaches photosystem I at a lower energy level 4. the electron is excited by another photon and caught by the primary electron acceptor 5. the photoexcited electron is passed through a short ETC to NADP+, reducing it to NADPH (goes to the Calvin cycle) 6. the need to replenish electrons causes photolysis, the splitting of water into 2 electrons, 2 hydrogen ions, and 1 oxygen atom → the electrons go to photosystem II - oxygen diffuses out the leaf through stomata

catalytic cycle

1. enzyme begins with empty active site 2. the substrate enters the active site, attached by weak bonds → the active site changes shape to hold the substrate more snugly (induced fit) - may contort substrate bonds or place chemical groups of the amino acids of the active sit in place to catalyze the reaction - if two or more reactants → orients them properly for the reaction 3. the strained bonds of the substrate react → substrate becomes converted to product 4. enzyme releases products unchanged, ready for a new substrate

Calvin Cycle

1. ribulose biphosphate (RuBP) attaches to CO2 through the enzyme rubisco → carbon fixation - this forms an unstable six carbon molecule that splits into 2 three carbon molecules 2. energy from ATP and electrons from NADPH are used to produce the energy rich glyceraldehyde-3-phosphate (G3P) 3. one G3P molecule is a product, 5 remain in the cycle 4. energy from ATP is used to rearrange the atoms in the 5 G3P molecules to regenerate 3 RuBP - the cycle must turn three times to produce 1 complete G3P molecule → 9 ATP and 6 NADPH are consumed - plant cell uses G3P to make glucose, the disaccharide sucrose, and other organic molecules as needed

cellular respiration formula

6 O2 + C6H12O6 → 6 CO2 + 6 O2 + ATP + heat - reactants are supplied through breathing and eating

energy coupling

use of energy in exergonic reactions to drive endergonic reactions