Biochemistry Practice Questions

Glycation is a non-enzymatic, spontaneous covalent attachment of reducing sugars to free amino groups on proteins. The extent of glycation increases with time and glucose concentration, and advanced glycation end products (AGEs) can form.

Ribose is a pentose, a simple sugar (monosaccharide) that has five carbon atoms per molecule. It is synthesized in the body and obtained in small amounts from consumption of ripe fruits and vegetables.

The optimum pH for enzymes varies for different enzymes and even enzymes with similar actions may have different optimal pH based on where they act. For example, trypsin, a digestive enzyme that acts in the small intestine has an optimal pH of 8 while pepsin, which acts in the more acidic milieu of the stomach, has an optimal pH of 2.

A catabolic enzyme engages in destructive metabolism, which involves degrading or breaking down complex molecules into simpler ones with the resulting release of energy.

In the body, the breakdown of food in the gastrointestinal tract by a variety of digestive enzymes is an example of a catabolic process. The opposite of catabolism is anabolism.

Anabolism is the opposite of catabolism and is a set of metabolic pathways that serve to create, construct, or synthesize larger molecules from smaller ones, such as the synthesis of carbohydrates, proteins and fatty acids.

Anabolic processes consume or require energy rather than releasing energy. Examples of anabolic processes include gluconeogenesis, glyoxylate cycle, and glycosylation.

Allosteric enzymes change conformation when allosteric effectors bind at non–active-site (allosteric) sites. These effectors can be activators (increase activity) or inhibitors (decrease activity).

Proteolytic enzymes, also known as proteases, catalyze the splitting or breakdown of proteins into smaller peptide fractions and amino acids. The process of accomplishing this breakdown is called proteolysis.

Peptidases are a subgroup of proteases that catalyze the hydrolysis of peptide linkages; they are present in plants and yeast and in the body. In the body, they are involved in digestion.

Amylase is the class of enzymes involved in the breakdown and digestion of starches into simple sugars to supply energy.

Amylases are glycoside hydrolases and act on α-1,4-glycosidic bonds. Plants and some bacteria make amylases. In the body, they are present in saliva and are produced by salivary glands and the pancreas.

The stable three-dimensional shape and orientation of a protein determine its function and chemical reactivity.

Proteins are composed of series of as many as twenty different L-α-amino acids. Proteins are distinguished by their configurations into three broad classes: globular proteins, fibrous proteins, and membrane proteins.

The biosynthesis of a protein molecule uses information encoded in genes.

The amino acid sequence of the protein is delineated by the nucleotide sequence of the gene that encodes the protein. Codons, sequences of three adjacent nucleotides along a DNA or messenger RNA molecule, designate the specific amino acid to be incorporated into a polypeptide.

Peptide bonds are the primary linkages of all proteins. They are the chemical connections that form between the carboxyl group (COOH) of one amino acid and the amino group (NH₂) of adjacent amino acids. A dipeptide contains two amino acids, a tripeptide three, a tetrapeptide four, and so on.

Protein catabolism is the digestion, or breakdown of macromolecules into amino acids able to transit through cells’ plasma membranes.

The products of protein catabolism are used to synthesize new amino acids or are converted to other compounds via the citric acid cycle. Protein catabolism is most often carried out by proteases.

The citric acid cycle oxidizes acetyl-CoA to CO₂, producing NADH and FADH₂ and a GTP/ATP. These reduced cofactors feed the electron transport chain to drive ATP synthesis in aerobic respiration.

The substrate of the citric acid cycle is acetyl coenzyme A. It is derived from glycolysis by a decarboxylating dehydrogenase activity of pyruvate dehydrogenase.

The cycle yields the following intermediates: citrate, cis-aconitate, iso-citrate, alpha-ketoglutarate, succinyl-CoA, succinate, fumarate, malate, and oxaloacetate.

At the conclusion of each cycle, the four-carbon oxaloacetate has been regenerated, and the cycle begins again.

Adenosine triphosphate (ATP) is an energy-carrying nucleotide (adenine + ribose + three phosphates) that powers cellular processes.

In aerobic respiration, cells typically generate about 30–32 ATP per glucose.

Oxidative phosphorylation occurs on the inner mitochondrial membrane in eukaryotes (plasma membrane in prokaryotes) after glycolysis and the citric acid cycle.

It produces the majority (~26–28) of the ~30–32 ATP made per glucose in aerobic respiration.

NADH and FADH₂ generated by the TCA cycle donate electrons to the electron transport chain, which powers phosphorylation of ADP to ATP.

Free or unesterified fatty acids are released by the hydrolysis of triglycerides within adipose tissue. Free fatty acids can be used as an immediate source of energy by multiple organs and tissue and can be converted by the liver into ketone bodies.

Because free fatty acids can interact with a variety of enzyme systems, they must be rapidly sequestered in tissues to ensure that their activities are closely regulated.

An ester is formed when an alcohol combines with an acid in a reaction to form an organic compound.

While fatty acids occur in nature in their free (unesterified) state, they are most often found as esters linked to glycerol, cholesterol, or long-chain aliphatic alcohols and as amides in sphingolipids.

Omega-3 fatty acids have their first carbon–carbon double bond three carbons from the methyl (ω) end of the chain.

Dietary sources include oily fish (e.g., salmon, sardines, mackerel) and the plant omega-3 α-linolenic acid (e.g., flaxseed oil).