Unit 3 AP Biology: Cellular Energetics

Free energy

the energy available in a system to do work

First Law of Thermodynamics

Energy cannot be created or destroyed, only converted from one form to another

Second Law of Thermodynamics

Living organisms must continually expend energy to maintain their ordered state

Entropy

A measure of the disorder or randomness in a system

Metabolism

the sum of all chemical reactions in an organism, divided into anabolism and catabolism 

Exergonic Reaction

A spontaneous chemical reaction that releases energy to its surroundings because the products have less free energy than the reactant

Endergonic Reaction

A type of chemical reaction in biology that requires an input of free energy to proceed

Activation energy

The minimum energy required to start a chemical reaction

Enzyme

biological catalysts that speed of chemical reactions by lowering the activation energy

Active Site

A specific region on an enzyme where the substrate binds to catalyze a chemical reaction

Substrate

A molecule upon which an enzyme acts

Lock and Key model

Enzyme specificity, the rigid active site of an enzyme fits a specific substrate perfectly, like a lock and its key

Induced Fit Model

The active site of an enzyme is flexible and changes shape to fit a specific substrate after the substrate binds to it.

Conformation Change

A structural alteration in a protein that changes its function, triggered by factors like ligand binding, phosphorylation or environmental change

Cofactor

A non-protein chemical compound or metallic ion required for an enzyme to function correctly

Coenzyme

An organic, non-protein molecule that binds to an enzyme and is essential for its activity

Denaturation

the process where a protein or nucleic acid loses its three-dimensional shape and function due to factors like extreme heat, pH changes or certain chemicals. 

Renaturation

the process where a denatured protein or nucleic acid returns to its original 3D structure and function

Enzyme Saturation

Occurs when all active site on an enzyme are all occupied by substrate molecules, and the reactant rate reaches its maximum

Inhibitor

A molecule that binds to an enzyme to decrease its activity

Reversible/Irreversible Inhibition

An inhibitor temporarily decreases enzyme activity without permanently changing the enzyme’s structure. A type of enzyme regulation where an inhibitor permanently binds to an enzyme and permornalty deactiving permanently deactivates and blocks substrate binding. 

Competitive Inhibition

Occurs when a molecule, the competitive inhibitor, resembles the normal substrate and competes with it to bind to the enzyme's active site

Non-competitive/allosteric inhibition

A form of enzyme regulation where an inhibitor binds to a site on the enzyme distinct from the active site, causing a conformational change that reduces the enzyme's catalytic efficiency

Allosteric Site

A regulatory site on an enzyme, distinct from the active site, where a regulatory molecule (an effector) binds

Photosynthesis

Involves the conversion of light energy into chemical energy in the form of glucose, using carbon dioxide and water

Cyanobacteria

Prokaryotic organisms that conduct photosynthesis, contributing to the Great Oxygenation Event, and are critical for nitrogen fixation

Light-Dependent Reactions

The first stage of photosynthesis, where light energy is converted into chemical energy in the form of ATP and NADPH

Light-Independent Reactions/Calvin Cycle

The second stage of photosynthesis occurs in the chloroplast's stroma. They use ATP and NADPH from the light-dependent reactions to convert carbon dioxide (𝐶𝑂2) into glucose

Chloroplast

The organelle responsible for photosynthesis in plant cells and algae, converting light energy into chemical energy in the form of glucose

Chlorophyll

The primary pigment that absorbs light energy for photosynthesis

Stroma

fluid-filled space inside the chloroplast that surrounds the grana

Thylakoid

A membrane-bound sac within a chloroplast where the light-dependent reactions of photosynthesis occur

Granum/Grana

Stacks of disc-like structures called thylakoids within chloroplasts that are the site of the light-dependent reactions of photosynthesis

Photosystem 1/2

Two protein-pigment complexes in the thylakoid membrane that work together in the light-dependent reactions of photosynthesis

Electron Transport Chain

The final stage of aerobic cellular respiration, located in the inner mitochondrial membrane, that uses energy from electron carriers like NADH to create a proton gradient across the membrane

Electrochemical Gradient

The combined effect of a chemical gradient (difference in solute concentration) and an electrical gradient (difference in charge) across a cell membrane, which dictates the net direction of ion movement

Photophosphorylation

The process in photosynthesis where light energy is converted into chemical energy in the form of ATP

Oxidation

The loss of electrons by a substance in a redox (reduction-oxidation) reaction

Reduction

The chemical process of gaining electrons, resulting in a decrease in oxidation state

Proton

A positively charged particle in an atom's nucleus that determines the element's atomic number

ATP/ADP

The primary energy-carrying molecule for cells, powering cellular processes like muscle contraction and nerve impulse propagation by releasing energy from its high-energy phosphate bonds

ATP Synthase

Uses a proton gradient to synthesize ATP from ADP and inorganic phosphate during oxidative phosphorylation

NADPH / NADP⁺’

A crucial electron carrier that accepts high-energy electrons during cellular respiration

G3P

A 3-carbon sugar that is a key intermediate in both the Calvin cycle and glycolysis

Aerobic cellular respiration

A three-stage process: Glycolysis (in the cytoplasm), the Krebs cycle (in the mitochondrial matrix), and the electron transport chain and chemiosmosis (in the inner mitochondrial membrane)

Anaerobic Cellular Respiration

The process of creating ATP without oxygen, which occurs entirely in the cytoplasm and relies on glycolysis followed by fermentation

Mitochondria

Cristae

Matrix

Intermembrane Space

Glycolysis

Glucose

NADH / NAD⁺

Pyruvate

Krebs Cycle

FADH₂

Oxidative Phosphorylation

Chemiosmosis

Fermentation

Lactic Acid Fermentation

Alcoholic Fermentation