ap bio cellular energetics

Metabolism

totality of an organism's chemical reactions, emergent property of life that arises from orderly interactions between molecules, manage material + energy resources of cell

Metabolic pathway

specific molecule is altered in a series of defined steps resulting in a certain product, steps catalyzed by enzymes, mechanisms that regulate balance metabolic supply + demand, can have 1+ starting molecule/product, energy from downhill catabolic pathways stored + drive uphill reactions of anabolic pathways

Catabolic pathways

release energy by breaking down complex molecules to simpler compounds (breakdown pathways), ex. cellular respiration - breakdown glucose + org fuels in presence of oxygen to CO2 + H2O

Anabolic pathways

consume energy to build complicated molecules from simpler ones (biosynthetic pathways), ex. synthesis of protein from amino acids

Bioenergetics

study how energy flows thru living orgs

Energy + types

capacity to cause change, rearrange a collection of matter, kinetic energy - energy associated w/ relative motion of objects, moving objects work by impart motion to other matter, thermal energy - kinetic energy associated w/ random mvt of atoms/molecules, heat - thermal energy in transfer from one object to another, potential energy - energy that matter possesses because of its location or structure, ex. molecules have energy bc arrangement of electrons in bonds between atoms, chemical energy - potential energy available for release in a chemical reaction, complex molecules (glucose) high in chem energy, can be broken down into energy to power processes

Thermodynamics

study of the energy transformations that occur in a collection of matter

Open system

energy and matter can be transferred between the system and its surroundings, organisms absorb light/chem energy + release heat/metabolic waste

First law of thermodynamics

energy of the universe is constant (principle of conservation of energy)

Second law of thermodynamics

Every energy transfer or transformation increases the entropy of the universe, entropy - measure of molecular disorder/randomness, more randomly arranged a collection of matter is, the greater its entropy, system put energy to work only when temperature difference that results in thermal energy flowing as heat from a warmer location to a cooler one, entropy of system can decrease as long as the total entropy of the universe—the system plus its surroundings—increases

Spontaneous process

given process leads to an increase in entropy + can proceed without requiring an input of energy (energetically favorable)

Nonspontaneous process

process that leads to a decrease in entropy + will happen only if energy is supplied, increase in order is balanced by an organism's taking in organized forms of matter and energy from the surroundings and replacing them with less ordered forms

Free energy

portion of a system's energy that can perform work when temperature and pressure are uniform throughout the system (Gibbs free energy), ΔG \= ΔH + -TΔS [ΔG \= G final - G initial, ΔH \= change in total energy (enthalpy), ΔS \= change in entropy, T \= absolute temp in Kelvins], ΔG dep on pH, temp, concentration of reactants/products, only -ΔG reactions are spontaneous, measure of system's tendency to change to a more stable state

Equilibrium

forward and reverse reactions occur at the same rate + no further net change in the relative concentration of products and reactants, process is spontaneous and can perform work only when it is moving toward equilibrium

Exergonic reaction

proceeds w/ net release of free energy, ΔG \= -
energetically favorable, magnitude of ΔG rep maximum amount of work the reaction can perform, greater the decrease in free energy, the greater the amount of work that can be done, breaking of bonds req energy, energy stored in bonds \= potential energy that can be released when new bonds are formed after the original bonds break, as long as the products are of lower free energy than the reactants

Endergonic reaction

absorbs free energy from its surroundings, ΔG \= +, nonspontaneous, ΔG \= quantity of energy required to drive the reaction, reactions in an isolated system eventually reach equilibrium and can then do no work, *metabolism as a whole is never at equilibrium is one of the defining features of life

ATP powers:

1) Chemical work - the pushing of endergonic reactions that would not occur spontaneously
synthesis of polymers from monomers, 2) Transport work - the pumping of substances across membranes against the direction of spontaneous movement, 3) Mechanical work, beating of cilia, the contraction of muscle cells, and the movement of chromosomes during cellular reproduction

Energy coupling

use of an exergonic process to drive an endergonic one, ATP responsible for mediating most energy coupling in cells + acts as the immediate source of energy that powers cellular work

ATP

contains the sugar ribose, with the nitrogenous base adenine and a chain of three phosphate groups (the triphosphate group) bonded to it, bonds between phosphate groups broken w/ hydrolysis, when terminal phosphate bond is broken by addition of a water molecule, a molecule of inorganic phosphate leaves the ATP which becomes ADP
reaction is exergonic, phosphate bonds high energy bc reactants high energy relative to products, releases great energy, three groups - charged + when crowded together \= instability + compressed spring, if ΔG of an endergonic reaction is less than the amount of energy released by ATP hydrolysis, then the two reactions can be coupled so overall coupled reactions are exergonic

Phosphorylation

transfer of a phosphate group from ATP to some other molecule, such as the reactant

Phosphorylated intermediate

recipient molecule with the phosphate group covalently bonded to it, more reactive than non phosphorylated molecule, transport + mechanical work nearly always powered by ATP hydrolysis, leads to change in protein shape + ability to bind to other molecules

ATP cycle

shuttling inorg phosphate + energy, proceed rapidly
free energy required to phosphorylate ADP (add phosphate group to ADP) comes from exergonic breakdown reactions in the cell, ATP regeneration endergonic, ATP \= revolving door for energy to transfer from catabolic to anabolic pathways

Enzyme

macromolecule (protein) that acts as a catalyst, chemical agent that speeds up a reaction without being consumed by the reaction, most names end in -ase, every chem reaction involves bond breaking + forming, changing molecule by contorting starting molecule into unstable shape w/ absorbed energy, when new bonds form energy released as heat + molecules return to stable state, 4k diff enzymes identified, proteins have mutations (changed amino acids) change active site shape + create diff enzymes

Activation energy

initial investment of energy for starting a reaction, energy req contort reactant molecules so bonds can break, energy needed to go uphill, supplied by heat absorbed from surroundings which causes atoms to accelerate, barrier deter reaction rate

Transition state

reactants in unstable condition when molecules absorb enough energy for bonds to break, proteins, DNA, complex molecules rich in free energy + potential decomp spontaneously (laws of thermo favor breakdown), orgs no use heat bc would denature proteins/kill cells + would speed up all reactions (not just necessary ones)

Catalysis

process by which catalyst selectively speeds up reaction w/o itself being consumed, enzyme lower activation energy barrier, cannot change ΔG/make endergonic to exergonic, only hasten reactions that would occur anyway, enable cell have dynamic metabolism that routes chems thru metabolic pathways, enzymes specific to reactions + deter which processes occur in cell

Substrate

A specific reactant acted upon by an enzyme

Enzyme-substrate complex

temporary complex formed when enzyme binds to substrate, enzyme + substrate -\> enzyme-substrate complex -\> enzyme + products, enzyme can recog substrate, specificity from shape + primary sequence, Rate of conversion function of initial substrate concentration

Active site

pocket on enzyme where catalysis occurs, formed by few amino acids, rest provide structure

Induced fit

tightening of enzyme binding to substrate after initial contact, usually held by weak interactions: H bonds, ionic bonds, R group of active group amino acids catalyze substrate into product, reversible - enzyme catalyze forward/backward reaction for net effect toward equilib

Enzyme Functions

Proper orientation of substrates to react, put substrates into transition form by bending chem bonds, microenviron more conducive to reaction, eirectly particip - brief bonding

Saturated

all enzymes engaged when substrate concentration high enough

Optimal conditions

conditions (temp, pH) where enzyme works best, pH generally around 6-8

Cofactors

nonprotein helper req for catalytic activity, can be perm bound/loosely bound to active site, some inorg (Zn, Fe, Cu), coenzyme - cofactor in org form

Competitive inhibitors

reduce enzyme activity by entering active site in place of substrate, bind w/ weak interactions, prevented by increasing substrate concentration, some inhibitors irreversible + attached w/ covalent bonds

Noncompetitive inhibitors

impede reactions by binding to another part of enzyme not active site, change enzyme shape

Allosteric regulation

protein's function @ one site affected by binding of regulatory molecule to sep site, con rates of important reactions, inhibit/stim activity, usually constructed of 2+ subunits w/ active sites, one catalytically active shape + one inactive shape, reg molecule bind to reg site (allosteric site) where subunits join, stabilize active/inactive site, shape change of one subunit caused by reg molecule transferred to all others

Cooperativity

substrate binds to one active site + trigger shape change in all active sites, amplify enzyme response to substrates

Feedback inhibition

metabolic pathway halted by inhibitory binding of its end product to enzyme that acts early in pathway, some enzymes have fixed locations + others in solution

Energy

Living cells require transfusions of energy from outside sources (food + sun) to perform their many tasks, enters ecosystem as sunlight + exists as heat, org compounds possess potential energy as a result of the arrangement of electrons in the bonds between their atoms, compounds participate in exergonic reactions act as fuels, enzymes degrade complex org molecules w/ high PE -\> simpler waste products w/ less energy, some energy for work + other dissipated as heat

Fermentation

partial degradation of sugars/org fuels that occur w/o use of oxygen, glycolysis + reactions regen NAD+ by transferring electrons from NADH to pyruvate, NAD+ can then be reused to oxidize sugar by glycolysis, which nets two molecules of ATP by substrate-level phosphorylation

Aerobic respiration

oxygen consumed as reactant w/ org fuel, eukaryotic + prokaryotic cells carry out, organic compounds + oxygen -\> carbon dioxide + water + energy, fuel \= carbs, fats, proteins, C6H12O6 + 6O2 -\> 6CO2 + 6H2O + energy (ATP + heat), exergonic (ΔG \= -686 kcal/mol), products store more energy than reactants, can occur spontaneously w/o energy input

Anaerobic respiration

process harvest chem energy w/o oxygen, some prokaryotes carry out

Cellular respiration

include both aerobic and anaerobic, originate as synonym for aerobic bc related to organismal respiration in which breathe in oxygen, stages: 1) glycolysis, 2) pyruvate oxidation, citric acid cycle, 3) oxidative phosphorylation

Redox reactions

partial/complete transfer 1+ electron from one reactant to another, aka oxygen reduction reaction, Oxidation - loss of electrons from one substance, Reduction - addition of electrons to another substance, Reducing agent - electron donor, reduces other substance in reaction, Oxidizing agent - electron acceptor, removes electron from other substance, O2 one of most powerful, very electronegative, not all completely transfer electron, some change degree of sharing in covalent bonds, energy must be added to pull electron away from atom, more electroneg atom \= more energy req take electron away, electron lose PE when shift from less electroneg atom to more electroneg atom

Redox Reactions in Cell Respiration

In cell resp, glucose oxidized and O2 reduced, org molecules w/ H good fuel bc bonds are energy released when electrons fall down energy gradient during transfer to O, energy state changed, fuels w/ C-H bonds -\> fuels w/ C-O bonds, main energy yielding foods (carbs, fats) reservoirs of electrons associated w/ H, activation energy \= barrier hold back flood of electrons to lower energy state, glucose broken down in steps catalyzed by enzymes, electrons stripped from glucose + travel w/ proton as H+

NAD+

oxidized form, coenzyme accept electrons + -\> NADH, most versatile electron acceptor, in sev redox steps

NADH

reduced form, temp store electrons during cell resp, electron donor to electron transport chain, dehydrogenase remove H+ from glucose (oxidizing it), enzyme delivers two electrons w/ one proton to NAD+ to form NADH, other proton released as H+ into solution, electrons lose little PE when transferred to NAD+, NADH \= stored energy to be tapped for ATP when electrons fall down energy gradient to O2

Electron transport chain process

\# of molecules (proteins) built into inner membrane of eukaryotic cell's mitochondria/plasma membrane of prokaryotes, electrons from glucose shuttled by NADH -\> higher end of chain, @ bottom end O2 captures electrons + H+ to form water, exergonic reaction, electrons cascade in series of redox reactions + lose small amt energy @ each step, electron fall down to more stable location in electronegative O atom, like gravity pull objects downhill *Glucose -\> NADH -\> electron transport chain -\> oxygen*

Glycolysis

in cytosol begin degradation process by break glucose into 2 molecules of pyruvate, in eukaryotes pyruvate -\> mitochondria + oxidized into acetyl CoA, in prokaryotes process occur in cytosol

Citric acid cycle

breakdown of glucose to CO2 complete, functions as a metabolic furnace that further oxidizes organic fuel derived from pyruvate, aka Krebs cycle

Oxidative phosphorylation

ATP produced w/ energy from redox reactions of electron transport chain, gen 90% ATP from respiration

Substrate level phosphorylation

enzyme catalyzed formation ATP by direct transfer phosphate group -\> ATP from intermed substrate in catabolism

Glycolysis Process

Split glucose into two 3 C sugars, smaller sugars oxidized + remaining atoms rearranged form two pyruvate molecules, energy investment phase - cell spend ATP, energy payoff phase - ATP produced by substrate-level phosphorylation + reduced to NADH by electrons released from the oxidation of glucose, net energy yield: 1 glucose \= 2 ATP + 2 NADH, no C released as CO2, occur even if O not present, if present chem energy in pyruvate + NADH can be extracted by next stages

Pyruvate Oxidation Process

Pyruvate enter mitochondria via active transport + converted to acetyl CoA, step links glycolysis + citric acid cycle, carried out by multienzyme complex that catalyzes three reactions, pyruvate's carboxyl group fully oxidized + given off as CO2, first step of CO2 being released, remaining two-carbon fragment is oxidized and the electrons transferred to NAD+, storing energy in the form of NADH, coenzyme A is attached via its sulfur atom to the two-carbon intermediate, forming acetyl CoA, acetyl CoA has high PE, used to transfer the acetyl group to a molecule in the citric acid cycle, a reaction that is therefore highly exergonic

Citric Acid Cycle Process

Pyruvate broken down to three molec inclu molecule of released during the conversion of pyruvate to acetyl CoA, cycle gen 1 ATP/turn by substrate-level phosphorylation but most of the chem energy is transf to and FAD during redox reactions, reduced coenzymes NADH and FADH2 shuttle their cargo of high-energy electrons into the electron transport chain, cycle has eight steps, each catalyzed by a specific enzyme, or each turn of the citric acid cycle, two C enter in the relatively reduced form of an acetyl group + two diff C leave in the completely oxidized form of molecules, acetyl group of acetyl CoA joins the cycle by combining with the compound oxaloacetate, forming citrate, citrate - ionized form citric acid, next seven steps decompose the citrate back to oxaloacetate, for each acetyl group entering the cycle, 3 NAD+ are reduced to NADH, electrons are transferred not to FAD, which accepts 2 electrons and 2 protons to become FADH2, in many animal tissue cells, GTP molecule produced by substrate-level phosphorylation, GTP is a molecule similar to ATP in its structure and cellular function, may be used to make an ATP molecule/directly power work in the cell, in the cells of plants, bacteria, animal tissues, ATP molecule formed directly by substrate-level phosphorylation, the output represents the only ATP generated during the citric acid cycle, 1 glucose \= 6 NADH, 2, FADH2, equivalent 2 ATP

Electron transport chain

Prokaryotes, these molecules reside in the plasma membrane, folding of the inner membrane to form cristae increases its surface area, providing space for thousands of copies of each component of the electron transport chain in a mitochondria, infolded membrane with its concentration of electron carrier molecules is well-suited for sequential redox reactions that take place along electron transport chain, most comps of chain are proteins that exist as multiprotein complexes

Prosthetic groups

nonprotein components such as cofactors and coenzymes essential for the catalytic functions of certain enzymes

Electron transport chain steps

Each comp of chain reduced when accept electrons from "uphill" neighbor w/ lower affinity for electrons, returns to its oxidized form when passes electrons to "downhill" neighbor w/ higher affinity for electrons, electrons acquired from glucose by NAD+ during glycolysis + citric acid cycle transferred from NADH to first molec of electron transport chain, in next redox reaction flavoprotein (prosthetic group) returns to oxidized form as passes electrons to iron-sulfur protein, iron-sulfur protein then passes the electrons to ubiquinone (electron carrier is small hydrophobic molecule, only member of the electron transport chain not a protein, indiv mobile w/in the membrane rather than residing in a particular complex), cytochromes - most of the remaining electron carriers between ubiquinone and oxygen are proteins, prosthetic group (heme group) has an iron atom that accepts and donates electrons, sev types in electron transport chain, last cytochrome of the chain (cyta3) passes its electrons to oxygen in O2, each O also picks up pair H+ from aqueous solution, neutralize charge of added electrons + forming water, another source electrons FADH2, donate an equivalent number of electrons (2) as NADH for oxygen reduction but 1/3 less energy for ATP synthesis, make no ATP directly

ATP synthase

enzyme that makes ATP from ADP and inorganic phosphate
multisubunit complex with four main parts, each made up of multiple polypeptides, protons move one by one into binding sites on rotor + cause it spin in way that catalyzes ATP production from ADP and Pi, chain \= energy converter uses exergonic flow of electrons from NADH and FADH2 to pump across the membrane from the mitochondrial matrix to intermembrane space, H+ move back across the membrane + diffuse down its gradient, ATP synthases are the only sites that provide a route through the membrane for H+, est gradient is major function of the electron transport chain

Chemiosmosis

energy stored in the form of a hydrogen ion gradient across a membrane is used to drive cellular work such as the synthesis of ATP, energy-coupling mechanism uses energy stored as an H+ gradient across a membrane to drive cell work, in mitochondria energy for proton gradient formation from exergonic redox reactions + ATP synthesis is work performed., chemiosmosis in chloroplasts also gen ATP, but light drives both the electron flow down an electron transport chain and the resulting H+ gradient formation, prokaryotes gen H+ gradients across their plasma membrane

Proton-motive force

force drives H+ back across the membrane thru the specific H+ channels provided by ATP synthase, prokaryotes use the proton-motive force to gen ATP + pump nutrients/waste products across membrane, to rotate their flagella

Oxidative phosphorylation process

glucose → NADH → electron transport chain → proton-motive force → ATP, 4 ATP produced directly by substrate-level phosphorylation during glycolysis + citric acid cycle to many more molecules of ATP gen by oxidative phosphorylation, each NADH transfer pair electrons from glucose to electron transport chain contrib enough proton-motive force to gen maximum 3 ATP, inexact bc:, 1) phosphorylation + redox reactions not directly coupled to each other so ratio NADH : ATP not a whole number
1 NADH gen enough proton-motive force for 2.5 ATP, 2)ATP yield dep on type of shuttle used transp electrons from cytosol into mitochondria, NADH produced in glycolysis must -\> mitochondrion by electron shuttle systems, dep shuttle in a particu cell type the electrons are passed to NAD+/FAD in the mitochondrial matrix, if to FAD, 2 ATP result from each NADH orig genin the cytosol, if to mitochondrial NAD+ then 3 ATP per NADH, 3) Pm force generated by the redox reactions of respiration drive other kinds of work, ex mitochondrial uptake of pyruvate from the cytosol, all the proton-motive force used then one glucose molecule gen max 28 ATP produced by oxidative phosphorylation + 4 ATP from substrate-level phosphorylation \= 32 ATP, cell resp efficient in energy conversion, rest of the energy stored in glucose is lost as heat, humans use maintain high body temperature + dissipate the rest thru sweating/cooling mechanisms, may be beneficial under certain conditions to reduce the efficiency of cellular respiration

Alcohol Fermentation

pyruvate -\> alcohol, releases from the pyruvate, which is converted to the two-carbon compound acetaldehyde, acetaldehyde is reduced by NADH to ethanol which regen supply NAD+ needed for continuation of glycolysis, bacteria carry out

Lactic acid fermentation

pyruvate is reduced directly by NADH form lactate as end product, regen NAD+ with no release of CO2

Different types of ATP production

ferm, anaerobic, aerobic use glycolysis oxidize glucose/other org fuels to pyruvate w/ net produc 2 ATP by substrate-level phosphorylation, NAD+ oxidizing agent, 1) diff is the mechanisms for oxidizing NADH to NAD+ which is req sustain glycolysis, in fermentation final electron acceptor is org molecule, in cell respiration electrons carried by NADH are transferred to electron transport chain + move stepwise down a series of redox reactions to final electron acceptor, 2) diff amt ATP produced, in aerobic respiration, final electron acceptor is O, in anaerobic respiration, final acceptor is molecule less electronegative than O, more ATP produced by the oxidation of pyruvate in mitochondria which is unique to resp, w/o electron transport chain energy still stored in pyruvate unavail to most cells, cell respiration harvests much more energy from each sugar molecule than fermentation can, aerobic respiration yields 16 times as much ATP per glucose molecule like fermentation, 32 molecules of ATP for respiration comp w/ 2 molecules ATP produc by substrate-level phosphorylation in fermentation

Obligate anaerobes

carry out only fermentation or anaerobic respiration and cannot survive in the presence of oxygen, a few cell types can carry out only aerobic oxidation of pyruvate, not fermentation

Facultative anaerobes

survive use either fermentation or respiration, under aerobic conditions, pyruvate converted to acetyl CoA and oxidation cont in citric acid cycle via aerobic respiration, under anaerobic conditions, lactic acid fermentation occurs + pyruvate serves as electron acceptor to recycle NAD+, make the same amount of ATP when facultative anaerobe must consume sugar at a much faster rate when fermenting than when respiring, ancient prokaryotes use glycolysis make ATP before O present in Earth's atmosphere

Glycolysis reactants + products

Glycolysis can accept wide range carbs for catabolism, polysaccharides can be hydrolyzed to glucose monomers that enter glycolysis/citric acid cycle, the digestion of disaccharides provides glucose and other monosaccharides as fuel for respiration, other 2 maj fuels (proteins and fats) can also enter the respiratory pathways used by carbohydrates, proteins must first be digested to individual amino acids, amino acids that will be catabolized must have their amino groups removed via deamination, nitrogenous waste is excreted as ammonia, urea/waste product, carbon skeletons are modified by enzymes to intermediates of glycolysis + citric acid cycle

Glycolysis + metabolic pathways

Catabolism can harvest energy stored in fats obtained from food/from storage cells in the body, after fats digested to glycerol + fatty acids, glycerol can convert to glyceraldehyde-3- phosphate (intermediate of glycolysis), energy of fatty acids accessed as fatty acids split into 2C fragments via beta oxidation, molecules enter the citric acid cycle as acetyl CoA
NADH and FADH2 also gen during beta oxidation + can enter electron transport chain leading to further ATP production, gram of fat oxidized by respiration generates twice as much ATP as a gram of carb, food must provide the C skeletons cells req to make their own molecs, some organic monomers obtained from digestion can be used directly, intermediaries in glycolysis and the citric acid cycle diverted to anabolic pathways as precursors so cell synthesize the molecules it req, glucose can be synthesized from pyruvate, fatty acids can be synthesized from acetyl CoA, anabolic (biosynthetic) pathways - do not generate ATP but instead consume it, glycolysis + citric acid cycle function as metabolic interchanges enable cells to convert one kind of molecule to another as needed

Metabolism

Metabolism is versatile + adaptable, supply + demand reg metabolic economy, if a cell excess certain amino acid uses feedback inhib prevent diversion interm molec from the citric acid cycle to the synthesis pathway of that amino acid, end product of anabolic pathway inhibits enzyme catalyzing early step pathway + prevent diversion of key metabolic intermediates from more urgent uses, rate of catabolism reg: if ATP levels drop, catabolism produce more ATP, when ATP meet demand resp slows down, sparing valuable organic molecules for other functions, con catabolism based reg activity of enzymes at strategic points in the catabolic pathway, one point in third step of glycolysis, phosphofructokinase catalyzes the earliest step irrev commits substrate to glycolysis, by con the rate of step, cell can speed up/slow down entire catabolic process, pacemaker of resp, allosteric enzyme with receptor sites for specific inhibitors + activators, inhib by ATP + stim by AMP (derived from ADP), when ATP levels are high, inhibition of this enzyme slows glycolysis + vice versa, citrate, the first product of the citric acid cycle, is inhib, synchronizes rate of glycolysis + citric acid cycle, if intermediaries from citric acid cycle are diverted to other uses glycolysis speeds up to replace these molecules, metabolic balance aug by the con other enzymes at other key locations in glycolysis + citric acid cycle, cells are thrifty, expedient, and responsive in their metabolism

Photosynthesis

conversion process transforms sunlight energy into chemical energy stored in sugars + other org molecs, nourish entire living world in/directly, 6CO2 + 12H2O + light energy -\> C6H12O6 + 6O2 + 6H2O, product not glucose, 3C sugar used to make glucose, 6CO2 + 6H2O + light energy -\> C6H12O6 + 6O2, overall chem change \= reverse of cell resp, chloroplast split H2O -\> hydrogen + oxygen, both photosynthesis + cell resp involve redox reactions, photosynth is endergonic, light reactions + calvin cycle

Autotrophs

self feeders, sustain self w/o eating anything derived from other living beings, produce org molecs from CO2 + inorg raw materials from environ, ultimate source org compounds, producers of ecosystem, plants - only req water/minerals from soil + CO2 from air, algae, some protists/prokaryotes

Photoautotrophs

org use light as energy to synthesize org substances, all heterotrophs dependent on photoautotrophs for food + oxygen

Heterotrophs

unable make own food, live on compounds produced by other orgs, consumers, eat other plant/orgs, decomposers - heterotrophs eat animal remains/org litter (feces, fallen leaves), fungi, prokaryotes, fossil fuels \= store of Sun's energy from past

Endosymbiotic theory

orig chloroplast was photosynthetic prokaryote that lived inside an ancestor of eukaryotic cells

Chloroplast

eukaryotic organelle absorbs energy from sunlight + drives synthesis of org compounds from CO2 + water, fwo membranes, integrate both stages photosynthesis, stroma - dense fluid, thylakoid - sacs, segregate stroma from thylakoid space, third membrane system, chlorophyll - green pigment gives leaves their color, reside in thylakoid membranes, granum - stack of thylakoids, mesophyll - tissue in leaf interior, main location of chloroplasts (30-40/cell)

Stomata

microscopic pores, where CO2 enter + O2 exits, water absorbed by leaf -\> roots thru veins

Light reactions

convert solar energy to chem energy (in form NADPH + ATP), in thylakoids - outside NADP+ and ADP pick up e- and phosphate, NADPH + ATP released to stroma, water is split provide source electrons + protons, give off O2, e- + protons -\> acceptor NADP+ (NAD + phosphate group), use solar energy reduce NADP+ -\> NADPH, add 2 e- and 1 H+, phosphorylation - chemiosmosis power addition phosphate group to ADP

Calvin cycle

produce sugar, in stroma, C fixation - incorp CO2 from air into org molecs, reduce fixed C to carb by addition of e-, reducing power from NADPH + ATP, light indep (but occur during day bc need NADPH + ATP)

Electromagnetic energy

disturbance of electric + magnetic fields, ie. light

Electromagnetic spectrum

entire range of radiation, visible spectrum - detected as various colors by humans, 380-740 nm, drives photosynthesis

Photons

discrete particles w/ fixed quantity of energy, amt energy inversely related to wavelength

Pigments

substances absorb visible light, diff pigments absorb diff wavelengths, absorbed wavelengths disappear, energy elevate e- to orbital w/ more PE, ground state -\> excited state, only photons w/ energy \= (excited state - ground state) absorbed, @ excited state unstable, drop down + release energy as heat

Fluorescence

excited electrons fall back to the ground state + photons are given off

Spectrophotometer

measure pigment ability absorb various wavelengths of light, direct beams of light thru pigment + measure fraction transmitted

Absorption spectrum

graph plot pigment's light absorption vs wavelength

Chlorophyll a

key light capturing pigment particips directly in light reactions, appear blue-green, active spectrum photosynthesis greater bc chlorophyll b + carotenoids, violet blue + red light work best for photosynthesis bc absorbed

Chlorophyll b

accessory pigment, appear olive green

Carotenoids

sep group accessory pigments, hydrocarbons shades of yellow + orange bc absorb violet + blue-green light, ohotoprotection - absorb + dissipate excessive light energy that damage chlorophyll/form dang oxidative molecs

Action spectrum

profile relative effectiveness of diff wavelengths of radiation in driving process, illuminate chloroplasts w/ light of diff colors then plot wavelength vs measure photosynthetic rate (CO2 consumption or O2 release)

Chlorophyll d/Chlorophyll f

absorb higher wavelengths of light

Photosystem

reaction-center complex surrounded by light-harvesting complexes, convert light to chem energy, used for sugar synthesis

Reaction-center complex

org assoc proteins holding special pair chlorophyll a molecs + primary electron acceptor, primary electron acceptor - molec capable accept e- + becoming reduced, solar-powered transfer of e- from reaction-center chlorophyll a pair to primary e- acceptor \= first step of the light reactions, as soon as chlorophyll electron excited to higher energy level, primary e- acceptor captures it in redox reaction

Light-harvesting complex

various pigment molecs bound to proteins, enable harvest light over larger surface area + portion of spectrum, antennae for reaction-center complex, when pigment molec absorb photon energy transferred from pigment molec to pigment molec until passed to pair chlorophyll a in reaction center

Photosystem II

function first in light reactions, reaction-center chlorophyll a \= P680

Photosystem I

reaction-center chlorophyll b \= P700

Linear electron flow

route e- flow during light reactions, involve PS I/ PS II, produce ATP, NADPH, O2

Light reactions steps

Net e- flow from H2O to NADP+, 1) Photon of light strikes pigment molec in light-harvesting complex of PS II + boost one of its e- to higher energy level, as e- falls back to its ground state e- in nearby pigment molecule simult raised to excited state, process cont w/ energy relayed to other pigment molecs until it reaches P680 pair of chlorophyll a molecules in PS II reaction-center complex, excites e- in this pair of chlorophylls to a higher energy state, 2) e- transferred from excited P680 to primary e- acceptor, resulting form of P680 w/o negative charge of e- \= P680+, 3) enzyme catalyzes splitting of water molec into 2 e-, 2 H+, and O, e- supplied one by one to the P680+ pair w/ each e- replacing one transferred to primary electron acceptor, H+ released into thylakoid space + O combine w/ O gen by split of another water molec, forming O2, 4) each photoexcited e- passes PS II to PS I thru e- transp chain (e- carrier plastoquinone (Pq), cytochrome complex, protein called plastocyanin (Pc)), each comp carries out redox reactions as e- flow down e- transp chain + release free energy used pump protons into thylakoid space, contrib to proton gradient across thylakoid membrane, 5) PE stored in proton gradient used to make ATP in chemiosmosis, 6) light energy thru light-harvesting complex pigments to PS I reaction-center complex + excite e- of the P700 pair of chlorophyll a molecules located there, photoexcited e- transferred to PS I's primary electron acceptor + create e- "hole" in the P700 (P700+), 7) photoexcited electrons passed in series redox reactions from primary e- acceptor of PS I down 2nd e- transport chain thru protein ferredoxin (Fd) (chain does no create proton gradient + no produce ATP), 8) enzyme reductase catalyze transfer e- from Fd toNADP+, 2 e- req for reduction to NADPH, NADPH e- at higher energy level than in water (start), so more readily avail for reactions of Calvin cycle, removes H+ from stroma

Cyclic electron flow

alternative path use photosystem I but not photosystem II
e- cycle back from ferredoxin to cytochrome complex then via plastocyanin molec to P700 chlorophyll in PS I reaction-center complex, no produc NADPH + no release O, generate ATP, sev of currently existing groups photosynthetic bacteria have single photosystem related to either PS II or PS I, not both, part of evolutionary leftover, photoprotective