C1 HL: glycolysis, krebs cycle, ETC, chemiosmosis, CRP

HL only

Glycolysis

The process in the cell’s cytoplasm by which glucose is broken down into 2 pyruvate molecules to produce ATP. It’s the first step of cell respiration.

Process of glycolysis

1. Energy investment: Glucose (6-carbon) is phosphorylated using 2 ATP molecules to form fructose-1,6-bisphosphate and 2 ADP molecules.

2. Fructose-1,6-bisphosphate is split into two 3-carbon molecules G3P (lysis).

3. Energy payoff: Each G3P molecule is oxidized, converting 2 NAD into 2 NADH. Then, G3P is converted into pyruvate through substrate-level phosphorylation, generating 4 ATP in total. The net gain is 2 ATP, 2 NADH, and 2 pyruvate.

Pyruvate

A molecule that is produced from the breakdown of glucose in glycolysis and is the starting molecule for cellular respiration.

Matrix of a mitochondria

Enclosed region of the inner membrane of mitochondria containing enzymes and products for Krebs cycle.

Link reaction

The process by which pyruvate, inside the mitochondrial matrix, is converted to acetyl CoA through oxidation and decarboxylation before entering the Krebs cycle. The net products are: 2 ATP, 4 NADH, 2 acetyl CoA.

Oxidative decarboxylation

The process of removing a carboxyl group from a molecule while also transferring electrons to NAD.

Krebs Cycle

The series of chemical reactions, which are a part of aerobic cell respiration, that occur in the mitochondrion matrix and produce ATP, NADH and FADH.

Oxaloacetate

A 4-carbon molecule used in the first step of the Krebs cycle which is combined with acetate (from acetyl CoA) to form citrate.

Citrate/citric acid

A 6-carbon intermediate molecule that is formed from the combination of acetate and oxaloacetate in the Krebs cycle.

FAD

A coenzyme that carries electrons from one reaction to another in the electron transport chain. It can be reduced to FADH.

ETC

A series of protein complexes in the inner membrane of the mitochondria that transfer electrons and pump protons to create a proton gradient.

Proton gradient/Electrochemical gradient

The difference in proton (H⁺) concentration across the inner mitochondrial membrane that occurs during the pumping of protons in ETC in aerobic cell respiration. It drives protons (H⁺) back into the matrix from the intermembrane space through the enzyme ATP synthase.

Intermembrane space

Small space between the inner membrane and outer membrane of mitochondria. Here, the electrons carried from NADH power the pumping of hydrogen ions (H⁺) or protons across the membrane from the matrix

Proton motive force

The electrochemical gradient created by the transfer of protons across a membrane, which can be used to power ATP synthase.

Chemiosmosis

The process by which energy stored in the proton gradient is used to produce ATP. ATP is generated as protons move down the electrochemical gradient from the intermembrane space back into the mitochondrial matrix through the enzyme ATP synthase.

ATP synthase

Enzyme which is embedded in the inner mitochondrial membrane and is used to generate ATP during chemiosmosis. As protons move down the electrochemical gradient, they go through this enzyme and generate energy stored in the form of ATP.

inorganic phosphate (Pi)

A molecule containing a phosphate group that can be used to phosphorylate other molecules and transfer energy. For example, it is powered by proton motive force to turn ADP into ATP.

Anaerobic cell respiration

A type of cell respiration that occurs in the absence of oxygen. In order to regenerate ATP, lactic acid fermentation or alcohol fermentation occurs in animals and fungi/bacteria/some plants, respectively. This type of cell respiration is much less effective and produces less ATP, but it’s faster. It occurs during periods of short but intensive exercise (in animals).

Lactic acid fermentation

A type of anaerobic respiration in animals in which pyruvate is converted to lactate by the reduction of pyruvate with NADH using an enzyme, producing and NAD which can then continue glycolysis and generate more ATP.

Ethanal

A molecule produced in the first step of alcohol fermentation through decarboxylation of pyruvate with a release of CO2.

Ethanol

A molecule produced in alcohol fermentation as a result of the reduction of ethanal by NADH.

Alcohol fermentation

A type of anaerobic respiration (in yeast, bacteria and some plants) in which pyruvate is converted to ethanol and carbon dioxide, producing ATP and NAD that can then continue glycolysis.