Chapter 4: Cellular Metabolism

Cellular metabolism

Refers to the collective chemical processes that occur within living cells to accomplish these activities

Potential energy

It is stored energy

Kinetic energy

Energy of motion

First law of thermodynamics

States that energy cannot be created or destroyed

Second law of thermodynamics

States that a closed system moves toward increasing disorder, or entropy, as energy is dissipated from the system

Free energy

The energy in a system available for doing work

Exergonic

Reactions in cells release free energy

Endergonic

Reactions in cells that require the addition of free energy

Activation energy

This must be supplied before the bond is stressed enough to break

Catalysts

Chemical substances that accelerate reaction rates without affecting the products of the reaction and without being altered or destroyed by the reaction

Enzymes

They reduce the amount of activation energy required for a reaction

Cofactors

Small nonprotein groups which perform their enzymatic functions

Coenzymes

Contain groups derived from vitamins, most of which must be supplied in the diet

Ribosomal RNA

A major component of ribosomes, provides the activation energy that enables amino acids to assemble into polypeptide chains during the process of translation

Substrate

The molecule whose reaction it catalyzes

Enzyme-substrate complex (ES complex)

Formed during the binding of enzyme to substrate, in which the substrate is secured by covalent bonds to one or more points in the active site of the enzyme

Hydrolysis

Breaking with water

Hydrolysis reaction

A molecule is cleaved by the addition of water at the cleavage site

Condensation

Subunits of molecules are linked together by removal of water

Feedback inhibition

The final end product of a particular metabolic pathway inhibits the first enzyme in the pathway

Oxidation-reduction "redox" reaction

Involves a transfer of electrons from an electron donor (the reducing agent) to an electron acceptor (the oxidizing agent)

Heterotrophs

Organisms that cannot synthesize their own food but must obtain nutrients from the environment, including animals, fungi, and many single-celled organisms

Aerobes

Those that use molecular oxygen as the final electron acceptor

Anaerobes

Those that employ another molecule as the final electron acceptor

Cellular respiration

The oxidation of fuel molecules to produce energy with molecular oxygen as the final electron acceptor

Oxidation of fuel molecules

describes the removal of electrons from fuel molecules and not the direct combination of molecular oxygen with fuel molecules

Aerobic cellular respiration

Uses oxygen as the final electron acceptor and releases carbon dioxide and water from the complete oxidation of fuels

Hans Krebs

A British biochemist who described three stages in the complete oxidation of fuel molecules to carbon dioxide and water

Stage I

Food passing through the intestinal tract is digested into small molecules that can be absorbed into the circulation

Stage II

Also called glycolysis, most of the glucose is converted into two 3-carbon units (pyruvic acid) in the cell cytoplasm

Stage III

The final oxidation of fuel molecules occurs, with a large yield of ATP

Krebs cycle

Also known as citric acid cycle and tricarboxylic acid cycle

Triglycerides (neutral fats)

Are especially rich depots of metabolic energy because the fatty acids of which they are composed are highly reduced and free of water

Fatty acids

Are degraded by sequential removal of 2-carbon units, which enter the Krebs cycle through acetyl-CoA

Deamination

the amino group splits to form ammonia and a keto acid

Transamination

the amino group is transferred to a keto acid to yield a new amino acid