BIOCHEM TEST 1 (Nucleotides, Vitamins, Cosubstrates, and Coenzymes)

Q: What is a purine?

A: A nitrogenous base with a double-ring structure; examples are adenine and guanine.

Q: What is a pyrimidine?

A: A nitrogenous base with a single-ring structure; examples are cytosine, thymine, and uracil.

Q: What is a base in nucleic acids?

A: A heterocyclic amine (purine or pyrimidine) with basic properties.

Q: What is a nucleoside?

A: A base covalently linked to a 5-carbon sugar (ribose or deoxyribose).

Q: What is a nucleotide?

A: A nucleoside with one or more phosphate groups attached to the 5′-carbon of the sugar.

Q: What is a cofactor?

A: A non-protein helper (metal ion or organic molecule) required for enzyme activity.

Q: What is an activator ion?

A: A loosely bound metal ion that aids enzyme function.

Q: What is a metalloenzyme?

A: An enzyme with a tightly bound essential metal ion.

Q: What is a coenzyme?

A: A tightly bound organic molecule required for enzyme activity.

Q: What is a cosubstrate?

A: A loosely bound coenzyme that binds and releases during each reaction cycle.

Q: What is a prosthetic group?

A: A tightly or covalently bound non-protein group required for enzyme activity.

Q: What is a vitamin?

A: A small organic molecule required from the diet, often a coenzyme precursor.

Q: What is an apoenzyme?

A: The inactive protein part of an enzyme without its necessary cofactor/coenzyme.

Q: What is a holoenzyme?

A: The active enzyme consisting of the apoenzyme and its cofactor/coenzyme.

ATP

Structure: Adenine base + ribose sugar + three phosphate groups (α, β, γ)

Precursor Function: RNA synthesis

Substrate Function: Main energy molecule; donates phosphate groups in metabolic reactions; forms cAMP for signaling; often requires Mg²⁺ as a cofactor

dATP

Structure: Adenine + deoxyribose + three phosphate groups

Precursor Function: DNA synthesis

Substrate Function: Substrate for DNA polymerase; provides energy for DNA replication

GTP

Structure: Guanine + ribose + three phosphate groups

Precursor Function: RNA synthesis

Substrate Function: Energy for protein synthesis; forms cGMP for cell signaling

dGTP

Structure: Guanine + deoxyribose + three phosphate groups

Precursor Function: DNA synthesis

Substrate Function: Used by DNA polymerase during DNA replication

CTP

Structure: Cytosine + ribose + three phosphate groups

Precursor Function: RNA synthesis

Substrate Function: Helps make phospholipids and sphingolipids

dCTP

Structure: Cytosine + deoxyribose + three phosphate groups

Precursor Function: DNA synthesis

Substrate Function: DNA polymerase substrate

dTTP

Structure: Thymine + deoxyribose + three phosphate groups

Precursor Function: DNA synthesis

Substrate Function: Used during DNA replication

UTP

Structure: Uracil + ribose + three phosphate groups

Precursor Function: RNA synthesis

Substrate Function: Used in sugar metabolism and glycogen synthesis

Inhibitors of adenosine

Caffeine, tea (theophylline), and chocolate (Theobromine) Act as competitive inhibitors of adenosine

Q: What is NAD⁺, its vitamin precursor, function, and deficiency state?

• Precursor: Niacin (Vitamin B3)

• Function: Redox reactions in energy metabolism

• Deficiency: Pellagra—dermatitis, diarrhea, dementia

Q: What is NADP⁺, its vitamin precursor, function, and deficiency state?

• Precursor: Niacin (Vitamin B3)

• Function: Reductive biosynthesis (e.g., fatty acids)

• Deficiency: Pellagra

Q: What is FMN, its vitamin precursor, function, and deficiency state?

• Precursor: Riboflavin (Vitamin B2)

• Function: Oxidation reduction reactions as part of flavoproteins. FMN can accept 2 hydrogen atoms to form FMNH2. FMNH2 Usually covalently linked to enzyme.

• Deficiency: Magenta tongue, dermatitis

Q: What is FAD, its vitamin precursor, function, and deficiency state?

• Precursor: Riboflavin (Vitamin B2)

• Function: Oxidation reduction reactions, transfers 2 electrons

• Deficiency: Magenta tongue, dermatitis

Q: What is Coenzyme A (CoA), its vitamin precursor, function, and deficiency state?

• Precursor: Pantothenic acid (Vitamin B5)

• Function: Carries activated carboxylic acids via thioester linkage

• Deficiency: No well-defined deficiency

Q: What is Pyridoxal phosphate, its vitamin precursor, function, and deficiency state?

• Precursor: Pyridoxine (Vitamin B6)

• Function: Amino acid metabolism (e.g., transamination)

• Deficiency: Anemia, dermatitis, convulsions

Q: What is Thiamine pyrophosphate (TPP), its vitamin precursor, function, and deficiency state?

• Precursor: Thiamine (Vitamin B1)

• Function: Decarboxylation of α-keto acids

• Deficiency: Beriberi—weight loss, confusion

Q: What is Tetrahydrofolate (THF), its vitamin precursor, function, and deficiency state?

• Precursor: Folic acid (Vitamin B9)

• Function: One-carbon transfer reactions

• Deficiency: Anemia, growth failure

Q: What is Biotin, its vitamin precursor, function, and deficiency state?

• Precursor: Biotin (Vitamin B7)

• Function: Carboxyl group transfer, CO₂ addition

• Deficiency: Hair loss, dermatitis

Q: What is Lipoic acid, its vitamin precursor, function, and deficiency state?

• Precursor: Synthesized in body

• Function: Redox reactions, acyl group transfer. Lipoic acid is not considered a vitamin because we can generate it. It is a necessary coenzyme.

• Deficiency: None under normal conditions

Q: What is Ascorbic acid, its vitamin precursor, function, and deficiency state?

• Precursor: Vitamin C

• Function: Collagen synthesis, antioxidant

• Deficiency: Scurvy—gum bleeding, poor healing

Q: What is Vitamin B₁₂, its function, and deficiency state?

• Precursor: Cobalamin

• Function: Two reactions within the cell. 1-2 hydride shift. Important for the metabolism of amino acids to form heme and fatty acids. Requires transport protein IF

• Deficiency: Megaloblastic anemia, neurological symptoms