AP Biology 12 - Cellular Energetics

enzyme

biological catalyst, catalytic protein

enzyme substrate

the reactant that an enzyme acts on, enzyme binds on it forming an enzyme-substrate complex

active site

region on the enzyme where the substrate binds

induced fit of substrate

brings chemical groups of the active site into positions that enhance their ability to catalyze the reaction

catalysis in the enzymes active site

in an enzymatic reaction, the substrate binds to the active site, the active site can lower an Ea barrier by orientating substrates correctly, straining substrate bonds, providing a favourable microenvironment, covalently bonding to the substrate

effects of local conditions on enzyme activity

each enzyme has an optimal temperature which it can function, each enzyme has an optimal pH in which it can function

cofactors

nonprotein enzymes helpers, like metal ions such as zinc, iron, and copper, that function in a way that allow catalysis to occur, coenzymes are organic cofactors like vitamins

competitive inhibitors

bind to the active site of an enzyme, competing with the substrate, they are often chemically similar to the substrate

noncompetitive inhibitors

bind to another part of an enzyme, causing the enzyme to change shape and making the active site less effective

regulation of enzyme activity helps control metabolism

chemical chaos would result if a cell's metabolic pathways were not tightly regulated, to regulate metabolic pathways, the cell switches on or off the genes that encode specific enzymes

allosteric regulation

term used to describe cases where a protein's function at one site if affected by binding of a regulatory molecule at another site, may either inhibit or stimulate an enzymes activity, each enzyme has active and inactive forms, the binding of an activator stabilizes the active form of the enzymes, the binding of an inhibitor stabilizes the inactive form of the enzyme

feedback inhibition

the end product of a metabolic pathway shuts down the pathway, prevents a cell from wasting chemical resources by synthesizing more product than is needed

regulating

uses internal control mechanisms to moderate internal change in the face of external, environmental fluctuation

conforming

allows its internal condition to vary with certain external changes

ecotherms

gain their heat through mostly external sources, lower metabolic rates

endotherms

higher metabolic rates, enables animal to maintain a high level of aerobic metabolism

modes of heat exchange

conduction, convection, radiation, and evaporation

insulation

major thermoregulatory adaptation in mammals and bird, reduces heat flow between animal and its environment, integumentary system is the insulating material

circulatory adaptations

many endotherms and some ectotherms can alter the amount of blood flowing between the body core and the skin, countercurrent (blood vessels) heat exchangers are important for reducing heat loss

vasodilation

blood flow in the skin increases, facilitating heat loss

vasoconstriction

blood flow in the skin decreases, lowering heat loss

cooling by evaporative heat loss

many types of animals lose heat through evaporation of water in sweat, panting augments the cooling effects in birds and many mammals, bathing moistens the skin, helping to cool an animal down

behavioral responses

both endotherms and ectotherms use behavioral responses to control body temperature, some terrestial invertebrates have postures that minimizes absorption of solar heat

feedback mechanisms in thermoregulation

mammals regulate body temperature by negative feedback involving several organ systems, the hypothalamus contains nerve cells that function as a thermostat

oxidation

loss of electrons

reduction

gain of electrons

oxidizing agent

electron receptor (reduced) NAD+ (accepts electrons)

reducing agent

electron donor (oxidized)

glycolysis

breaks down glucose into two molecules of pyruvate, occurs in the cytoplasm and has two major phases, energy investment phase and energy payoff phase

krebs cycle

completes the energy-yielding oxidation of organic molecules, before it can begin pyruvate must be converted to acetyl-CoA which links the cycle to glycolysis, takes place in the mitochondrial matrix, oxidizes organic fuel derived from pyruvate, generating one ATP, 3 NADH, and 1 FADH2 per turn

oxidative phosphorylation

chemiosmosis couples electron transport to ATP synthesis, following glycolysis and the krebs cycle, NADH and FADH2 account for most of the energy extracted from food, these two electron carriers donate electrons to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation

chemiosmosis

energy-coupling mechanism, electron transfer in the electron transport chain causes proteins to pump H+ from the mitochondrial matrix to the intermembrane space, H+ then moves back across the membran, passing through channels in ATP synthase, ATP synthase uses the exergonic flow of H+ to drive phosphorylation of ATP, energy stored in a H+ gradient across a membrane couples the redox reactions of the electron transport chain to ATP synthesis, the H+ gradient is referred to as a proton-motive force, emphasizing its capacity to do work

fermentation

enables some cells to produce ATP without the use of oxygen, cellular respiration requires O2 to produce ATP, glycolysis can produce ATP with or without O2, in the absence of O2 glycolysis couples with fermentation to produce ATP

types of fermentation

alcohol fermentation and lactic acid fermentation, consists of glycolysis plus reactions that regenerate NAD+, which can be reused by glycolysis

fermentation and cellular respiration compared

both use glycolysis to oxidize glucose and other organic fuels to pyruvate, the processes have different final electron acceptors: an organic molecule in fermentation and O2 in cellular respiration, cellular respiration produces much more ATP

photosynthesis

process that converts solar energy into chemical energy

chloroplasts

leaves are the major locations of photosynthesis, their green color is from chlorophyll the green pigment within chloroplasts, light energy aborbed by chlorophyll drives the synthesis of organic molecules in the chloroplast, through microscopic pores called stomata CO2 enters the leaf and O2 exits, found in mesophyll the interior tissue of the leaf

H2O in photosynthesis

oxidized, split into H and O incorporating the electrons of H into sugar molecules

CO2 in photosynthesis

reduced

photosynthetic pigments

light receptors, pigments are substances that absorb visible light, different pigments absorb different wavelengths, wavelengths that are not absorbed are reflected or transmitted, leaves appear green because chlorophyll reflects and transmits green light

photosystem

reaction center associated with light harvesting complexes, consists of reaction center surrounded by light-harvesting complexes, the light-harvesting complexes (pigment molecules bound to proteins) funnel the energy of photons to the reaction center, a primary electron acceptor in the reaction center accepts an excited electron from chlorophyll A, solar-powered transfer of an electron from a chlorophyll A molecule to the primary electron acceptor is the first step of the light reactions, there are two types of photosystems in the thylakoid membrane, the two photosystems work together to use light energy to generate ATP and NADPH

photosytem 2

functions first and is best at absorbing a wavelength of 680nm

photosystem 1

best at absorbing a wavelength of 700nm

noncyclic electron flow

the primary pathway, involves both photosystems and produces ATP and NADPH

cyclic electron flow

uses only photosystem 1 and produces only ATP, generates surplus ATP satisfying the higher demand in the calvin cycle

calvin cycle

uses ATP and NADPH to convert CO2 to sugar, regenerates its starting material after molecules enter and leave the cycle, the cycle builds sugar from smaller molecules by using ATP and the reducing power of electrons carried by NADPH, carbon enters the cycle as CO2 and leaves as a sugar named G3P, for net synthesis of one G3P the cycle must take place three times fixing three molecules of CO2, three phases (carbon fixation (catalyzed by rubisco), reduction, regeneration of the CO2 acceptor (RuBP))