Protein Structure, Enzymes, and Cellular Respiration Key Concepts

Amino Acid

The individual molecular building blocks (monomers) that make up a protein.

Polypeptide

A chain of many amino acids linked together before it folds into a functional protein.

R Variant Group

The part of an amino acid that differs between the 20 types; its polarity and charge determine how the protein folds and functions.

Primary Structure

The specific linear order of amino acids in a polypeptide chain.

Secondary Structure

An intermediary folding step (such as alpha helices or beta sheets) held together by hydrogen bonds between the carboxyl and amino groups.

Tertiary Structure

The complex three-dimensional folding of a single polypeptide, stabilized by ionic bonds, disulfide bridges, and hydrophobic interactions.

Quaternary Structure

The most complex level of folding, where multiple tertiary subunits bond together to form a functional protein.

Denaturation

The process where a protein loses its shape and function due to changes in heat, pH, or chemicals.

Enzyme

A specialized protein that acts as a biological catalyst to speed up chemical reactions.

Catalyst

A substance that increases the rate of a reaction by decreasing the required activation energy.

Activation Energy

The initial input of energy needed to start any chemical reaction.

Substrate

The specific molecule(s) that an enzyme acts upon.

Active Site

The specific region on an enzyme where the substrate binds and the chemical reaction is catalyzed.

Induced Fit Model

The theory that an enzyme's active site is fluid and slightly changes its shape to wrap around the substrate.

Competitive Inhibition

When a molecule similar in structure to the substrate binds to the active site, blocking the substrate and slowing the reaction.

Non-competitive Inhibition

When an inhibitor binds to an allosteric site (not the active site), changing the enzyme's shape so the substrate can no longer fit.

Allosteric Site

A secondary binding site on an enzyme used for regulation.

Cofactor

A non-protein substance that assists an enzyme in performing its function.

ATP (Adenosine Triphosphate)

The primary energy molecule used by cells; aerobic respiration produces about 30-32 ATP per glucose molecule.

Glycolysis

The first step of respiration (occurring in the cytoplasm) where glucose is broken down into two pyruvate molecules, producing a net of 2 ATP and 2 NADH.

Aerobic Respiration

A high-efficiency energy-producing process that requires oxygen and occurs within the mitochondria.

Anaerobic Respiration (Fermentation)

A less efficient process that produces energy (2 ATP) without the use of oxygen or mitochondria.

Redox Reactions

Chemical reactions involving the transfer of electrons: Oxidation is the loss of electrons (LEO), and Reduction is the gain of electrons (GER).

NADH / FADH2

Electron and proton carriers that transport high-energy electrons to the Electron Transport Chain.

Acetyl CoA

The 2-carbon molecule formed from pyruvate that enters the Krebs Cycle.

Krebs Cycle (Citric Acid Cycle)

A series of reactions in the mitochondrial matrix that regenerates oxaloacetate and produces CO2, ATP, NADH, and FADH2.

Electron Transport Chain (ETC)

A series of proteins in the inner mitochondrial membrane that use energy from electrons to pump H+ ions, creating a concentration gradient.

ATP Synthase

A protein that acts like a turbine, using the flow of H+ ions down their gradient to synthesize ATP from ADP.

Oxaloacetate

The four-carbon molecule that interacts with Acetyl CoA to start the Krebs Cycle and is regenerated at the end of the cycle.