Chapter 6A -Definitions

Cellular respiration

The process by which cells create usable energy in the form of ATP from a series of biochemical reactions, involving the breakdown of glucose.

Glucose

A simple 6-carbon sugar molecule with the formula C6H12O6.

ATP

Adenosine triphosphate, a high energy molecule that, when broken down, provides energy for cellular processes.

Aerobic Cellular Respiration

Cellular respiration that occurs in the presence of oxygen. Involves three stages, during which glucose and O2 are converted into ATP, CO2, and water.

Anaerobic Fermentation

A metabolic pathway that occurs in the absence of oxygen. Involves glycolysis, followed by further reactions that convert pyruvate into lactic acid in animals, or ethanol and CO2 in yeast.

Glycolysis

The first stage of aerobic cellular respiration in which glucose is converted to two pyruvate molecules.

Krebs Cycle

The second stage of aerobic cellular respiration, where multiple reactions occur to create ATP, NADH, FADH2, and the waste product CO2. Also known as the citric acid cycle or TCA cycle.

Electron Transport Chin

The third stage of aerobic cellular respiration, in which a series of protein complexes embedded in the inner membrane of a mitochondrion harness the stored energy in NADH and FADH2 to generate large amounts of ATP.

Mitochondrion (-ion)

A double-membrane-bound organelle that is the site of the second and third stages of aerobic cellular respiration.

Cytosol

The aqueous fluid that surrounds a cell’s organelles inside the plasma membrane.

Mitochondrial Matrix

The space inside the inner membrane of a mitochondrion. The site of the Krebs cycle.

Crista (-ae)

The folds of the inner membrane of a mitochondrion. The site of the electron transport chain.

Pyruvate

A three-carbon molecule that can be formed from the breakdown of glucose via glycolysis.

Nicotinamide Adenine

Dinucleotide (NAD)

A coenzyme that acts as a proton (H+) and electron carrier in cellular respiration. NAD can cycle between its NAD+ and NADH forms, depending on the reaction it takes part in.

Flavin Adenine Dinucleotide (FAD)

A coenzyme that acts as a proton (H+) and electron carrier in cellular respiration. FAD can cycle between its FAD and FADH2 forms, depending on the reaction it takes part in.

Coenzyme A

A large organic non-protein molecule that plays a key role in the modification of pyruvate to allow it to enter the Krebs cycle. Also known as CoA.

Acetyl-CoA

The product of the link reaction where pyruvate is conjugated to coenzyme A, creating the primary input into the Krebs cycle.

ATP Synthase

An enzyme in the inner mitochondrial membrane that uses the concentration gradient of H+ to synthesise ATP from ADP and Pi.

Catalyse

To increase the rate of a reaction.

Yeast

Unicellular eukaryotic organisms from the kingdom Fungi.

Lactic Acid Fermentation

The process of anaerobic fermentation in animals, where pyruvate produced via glycolysis is converted to lactic acid.

Lactic Acid

A 3-carbon molecule that is the product of anaerobic fermentation in animals. Also known as lactate.

Ethanol

A 2-carbon alcohol molecule that is produced along with carbon dioxide during anaerobic fermentation in yeast, bacteria, and plants.

Ethanol Fermentation

The process of anaerobic fermentation in yeasts, where pyruvate produced via glycolysis is converted to ethanol and carbon dioxide. Also known as alcohol fermentation.

Optimal

The point at which for a given condition (e.g. temperature), the maximum function of an enzyme occurs. Also known as optimum.

Denature

The point at which for a given condition (e.g. temperature), the maximum function of an enzyme occurs. Also known as optimum.

pH

A scale used to measure the acidity or basicity of an aqueous solution.

Saturation point

The point at which a substance (e.g. an enzyme) cannot receive more of another substance (e.g. a substrate).

Enzyme Inhibitor

A molecule that binds to and prevents an enzyme from functioning.

Competitive Inhibitor

A molecule that hinders an enzyme by blocking the active site and preventing the substrate from binding.

Non-competitive Inhibitor

A molecule that hinders an enzyme by binding to an allosteric site and changing the shape of the active site to prevent the substrate from binding.

Allosteric Site

A region on an enzyme that is not the active site.

Reversible Inhibition

Enzyme inhibition that involves weaker bonds that can be overcome.

Irreversible Inhibition

Enzyme inhibition that involves stronger bonds that cannot be broken.

End-product inhibition

A form of inhibition where the final product in a series of reactions inhibits an enzyme in an earlier reaction in the sequence .

Fossil Fuel

Fuel that formed over tens of millions of years from the remains of dead organic material. Fossil fuels are considered non-renewable.

Non-renewable

Refers to a resource that is replenished at a lower rate than it is being used, meaning that it will eventually run out.

Biofuel

Fuel created from organic material known as biomass.

Biomass

Organic material, including plants, animal by-products, and biological waste material. Biomass can be sourced from many industries, including farming, forestry, and food manufacturing.

Renewable

Refers to a resource that can typically be replenished at the same (or faster) rate than it is being used, meaning it is unlikely to run out.

Carbon Neutral

A state in which there is no net release of carbon dioxide into the atmosphere, meaning that there is a balance between the amount of CO2 that is emitted during combustion of a fuel and how much was originally absorbed during the formation process of that fuel.

Fermentation

The anaerobic chemical breakdown of high-energy organic molecules, typically via the action of enzymes. For many plants, fermentation involves the conversion of glucose to ethanol and carbon dioxide.

Bioethanol

A type of biofuel that is produced via the anaerobic fermentation of plants such as sugarcane or corn .

Hydrolysis

A chemical reaction in which water is used to break down the chemical bonds of a substance.

Food vs Fuel Debate

A central concern of large-scale biofuel manufacturing that questions the validity of using arable farmland to produce fuel, rather than food.

First-generation Biofuels

Biofuels produced from edible food crops such as corn or sugarcane. These compete directly with agricultural land.

Second-generation Biofuels

Biofuels produced from non-edible crops such as agricultural and forestry residues and municipal waste. These typically compete less with agricultural land.