Biology 101 - Biochemical Basics Part 4

One full cycle produces 3 NADH molecules and 1 FADH2.

Other products include carbon dioxide, which is released as waste, and one molecule of GTP.

• ethanol

• lactate

Alcohol fermentation, which takes place in yeast and certain bacteria, involves the reduction of pyruvate to ethanol. Lactic acid fermentation, which takes place in human muscle cells as part of anaerobic respiration, involves the reduction of pyruvate to lactate.

Pyruvate decarboxylation

Under aerobic conditions, pyruvate (a three-carbon molecule) is converted to a two-carbon acetyl group. This group then attaches to coenzyme A.

Acetyl-CoA, a two-carbon compound, is the substrate entering the cycle. It immediately reacts with oxaloacetate to form a six-carbon compound (citrate).

Coenzyme A is released in this process and can be used again.

Protons are pumped from the mitochondrial matrix to the intermembrane space.

A molecule that increases the rate of a reaction without being consumed itself.

Catalysts change the kinetics of a reaction, not the thermodynamics. In other words, they lower the activation energy without altering the equilibrium or free energy change of a reaction.

A biological catalyst that structurally facilitates a chemical reaction. Like all catalysts, enzymes increase the rate of a chemical reaction without being consumed.

Most enzymes are proteins, but RNA molecules called ribozymes also have enzymatic activity.

Enzymes must be at a certain optimal temperature to maintain their structure.

The structure of an enzyme, especially in relation to its active site, is essential to its function as a catalyst. Like other proteins, enzymes denature, or lose their original conformations, above a certain temperature. However, reactions generally progress more slowly at low temperatures, further narrowing the range of optimal activity.

A lowered activation energy increases the reaction rate.

Each reaction must overcome an activation energy barrier to progress from reactants to products. When this barrier is lower, reactants are more likely to collide with sufficient energy, speeding up the reaction.

Enzymes can only maintain their functional structure at a certain optimal pH.

The structure of an enzyme, especially in relation to its active site, is essential to its function as a catalyst. The active site often contains positively or negatively charged groups, which contribute to the specificity of the site. Changes in pH can affect these sites, reducing enzyme activity.

At higher-than-optimal temperatures, most human enzymes lose function and cannot support necessary biological processes.

Most human enzymes function most efficiently at an optimal temperature of 37 ºC. While these enzymes can remain active at slightly higher temperatures, their function is impaired.

Specificity

The substrate(s) that can be accommodated by an enzyme are determined by the shape of its active site. For example, proteases are specific to protein substrates, while lipases act on lipid-based substrates.

It wrongly portrays all enzymes as being rigid and inflexible.

In reality, the active site of an enzyme can change its conformation to facilitate binding to the substrate.

• Cofactors are a broad group of compounds that are required for the proper functioning of enzymes.

• Coenzymes are a class of small, organic cofactors.

Cofactors can also be inorganic substances, such as ions.

Vitamins

Vitamins are often used to synthesize coenzymes, which are non-protein organic compounds that are essential for proper enzyme function.

This is an example of negative feedback. In such processes, increased concentration of a product decreases the rate of the reaction that forms that product.

Glycolysis involves the breakdown of glucose to form ATP, among other products. If increased amounts of ATP are already present, glycolysis will slow.

This is the study of energy transformations within organisms. Specifically, it concerns the energy released and used during the formation and breaking of chemical bonds.

Bioenergetics is closely related to thermodynamics, especially Gibbs free energy.

The change in Gibbs free energy, or ΔG, determines reaction spontaneity.

A negative ΔG means the reaction will be spontaneous, while a positive ΔG denotes a nonspontaneous reaction.

exergonic

In such reactions, ΔG is always negative, meaning that free energy is released.

The opposite type of reactions are endergonic. In these processes, ΔG is positive and the reaction will not proceed spontaneously.

The catalyzed reaction will have a lower activation energy.

Note that the overall change in free energy will be the same for the catalyzed and uncatalyzed reactions.