AP Bio Unit 3 (Cellular Energetics)

Enzymes, Photosynthesis, Cellular Respiration

enzyme

protein that lowers the activation energy for a reaction

how to optimize enzymatic activity?

multiple substrates binding in an optimal position to the enzyme, breaks stress bonds, ideal environment (temperature, pH, and substrate concentration)

catalyst

something that helps a chemical reaction occur

induced fit model

substrate bind to active site, then enzyme changes shape slightly to better fit substrate

substrate

compound that binds and reacts to enzyme

active site

place at which the substrate binds

how does temperature affect enzymatic activity?

higher temperature → higher enzymatic activity due to increased kinetic energy (to a certain point; after that point, enzymatic activity decreases?

how does pH affect enzymatic activity?

every enzyme has a specific pH at which is acts at peak/optimal efficiency, anything below or above that will decrease enzymatic efficiency

how does substrate concentration affect enzymatic activity?

higher substrate concentration → higher enzymatic activity until saturation point is reached (no increase in enzymatic activity after saturation point is hit/crossed)

denaturation (reversible vs irreversible)

change in an enzymes shape that impacts its ability to bind to substrate

often caused by environmental changes

reversible denaturation - when enzyme can return to its original shape if the environment returns to optimal condition for the enzyme

irreversible denaturation - when enzyme cannot return to its original shape even if the environment returns to optimal condition

allosteric activity

when a foreign substance binds in the allosteric site (a site away from the active site) and changes the shape of the enzyme to either increase affinity for the substrate (allosteric activation) or decrease affinity for the substrate (allosteric inhibition aka noncompetitive inhibition)

competitive inhibition

when a foreign substance binds to the active site, preventing a substrate from binding to the enzyme

feedback inhibition

when the product of a series of reactions can inhibit the pathway in order to maintain homeostasis

enzyme compartmentalization

when certain enzymes are only stored in certain organelles of a cell for improved efficiency

non-protein helpers

bind to enzyme in order to promote enzyme function (cofactors and coenzymes)

what are the two major steps of photosynthesis?

1. light dependent reactions

2. Calvin cycle

what are the steps of light reactions?

occurs in the thylakoid membrane

1. light excites electrons in chlorophyll

2. water is split into protons (H+), electrons, and O2 (waste product)

3. electrons flow from PSII → ETC → PSI releasing energy, which is used to pump H+ into thylakoid (creating proton gradient)

4. chemiosmosis: H+ rushes out of thylakoid, spinning ATP synthase → ATP produced

5. electrons arrive at PSI, and light excites them → NADP+ reduced to NADPH

what are the steps of the Calvin cycle?

occurs in the stroma (fluid around thylakoid)

1. CO2 attaches to RuBP (5-carbon molecule) by Rubisco creating an extremely unstable 6-C molecule that immediately breaks down into 2 PGA (3-C) molecules

2. ATP and NADPH (from light reactions) power chemical changes, allowing G3P to be created (2 G3P create 1 glucose)

what are the inputs and outputs of each major step of photosynthesis?

Light reactions: light → ATP + NADPH + O2

Calvin cycle: ATP + NADPH + CO2 → G3P

stomata

openings in underside of leaf that allows for gas exchange (take in CO2 and release O2)

can NADPH be produced without light?

no

what is the final electron acceptor in the light dependent reactions

NADP+

was photosynthesis present in the first organisms on Earth?

no

photorespiration

when RuBisCo fixes O2 instead of CO2 in the first step of the Calvin cycle, inefficient photosynthesis

how many CO2 molecules does a plant need to make one glucose?

6 CO2

what are the four major steps of cellular respiration?

1. glycolysis

2. transition between glycolysis and Krebs/TCA/citric acid cycle

3. citric acid/Krebs/TCA cycle

4. electron transport chain

describe glycolysis (cellular respiration)

cytoplasm

anaerobic

glucose → 2 pyruvate, 2 net ATP, 2 NADH\

describe the transition phase between glycolysis and the Krebs cycle (cellular respiration)

mitochondrial matrix

aerobic

pyruvate → 2 acetyl CoA, 2 CO2, 2 NADH

describe the Krebs cycle (cellular respiration)

mitochondrial matrix

aerobic

acetyl Co-A → 6 NADH, 2 FADH2, 2 ATP, 4 CO2 (released)

describe the electron transport chain (cellular respiration)

inner mitochondrial membrane

aerobic

NADH + FADH2 drop off electrons → electrons move through ETC providing energy for H+ to be pumped into the intermembrane space → H+ diffuses, which spins ATP synthase

NADH + FADH2 → 28 ATP, H2O

what is the final electron acceptor in glycolysis?

oxygen

what is the goal of fermentation?

to regenerate NAD+ for glycolysis when O2 is not present

only glycolysis produces ATP in fermentation