Biochemistry LS2101: Amino Acids and Proteins

Questions and Answers

What is the characteristic pH at which the net electric charge of an amino acid is zero called?

Isoelectric point (correct)

Equilibrium constant

PKa value

Titration point

Which property describes substances that can act as both acids and bases?

Dissociative

Amphoteric (correct)

Amphi-acidic

Electrolytic

For glycine, how is the isoelectric point (pI) determined?

It corresponds to the pKa of the carboxyl group.

It is the average of its side chain pKa values.

It is the arithmetic mean of the two pKa values. (correct)

It is equal to the molecular weight of glycine.

What role do amino acids play in relation to protons?

They can act as either proton donors or acceptors. Signup and view all the answers

What best describes the concept of enantiomers in biochemistry?

They are mirror-image forms of molecules that cannot be superimposed. Signup and view all the answers

What is the equation that represents the formation of a holoenzyme from an apoenzyme and a cofactor?

Apoenzyme + Cofactor = Holoenzyme Signup and view all the answers

What types of vitamins primarily function as coenzymes in biochemical reactions?

Water-soluble vitamins and fat-soluble vitamins A and K. Signup and view all the answers

Why are coenzymes important for metabolic reactions?

Coenzymes participate in reactions involving energy release and are essential for anabolic processes. Signup and view all the answers

What type of enzyme inhibitor binds tightly or covalently to an enzyme?

A prosthetic group. Signup and view all the answers

How do enzymes primarily affect chemical reactions?

Enzymes affect reaction rates but not the equilibria of the reactions. Signup and view all the answers

What is the primary function of tetrahydrofolic acid (THF) in the body?

THF primarily carries C-1 groups at all oxidation levels. Signup and view all the answers

How is vitamin D synthesized and what is its primary role?

Vitamin D is synthesized from 7-dehydrocholesterol and regulates calcium metabolism by stimulating gene expression. Signup and view all the answers

Describe the role of vitamin K in the body.

Vitamin K acts as a cofactor for the formation of gamma-carboxyglutamic acid in serine proteases related to blood clotting. Signup and view all the answers

What is the significance of lipoic acid in metabolism?

Lipoic acid relays electrons and acetyl groups between catalytic subunits of the pyruvate dehydrogenase complex. Signup and view all the answers

What are the antioxidants and their main role in the body?

Vitamin E, specifically a-tocopherol, serves as an antioxidant that prevents oxidative damage. Signup and view all the answers

What coenzyme is formed from Vitamin B1 and what role does it play in biochemical reactions?

Vitamin B1 is converted to thiamine pyrophosphate, which acts by nucleophilic attack on C=O to facilitate C-C bond cleavage. Signup and view all the answers

What are the primary functions of Vitamin B2 as it relates to coenzymes?

Vitamin B2 is incorporated into FMN and FAD, facilitating redox reactions by accepting and donating 2 electrons and 2 hydrogen ions. Signup and view all the answers

How does Vitamin B6 act as a coenzyme, and what type of bonds can it help cleave?

Vitamin B6 is converted to pyridoxal phosphate, which forms Schiff bases with amino groups, allowing cleavage of C-C, C-O, C-S, C-H, and C-N bonds. Signup and view all the answers

What is the role of Vitamin B12 in biochemical reactions?

Vitamin B12, in the form of 5'-deoxyadenosylcobalamin, exchanges hydrogen and other groups on adjacent carbon atoms, facilitating methyl group transfer. Signup and view all the answers

In what way does Nicotinamide function in redox reactions?

Nicotinamide is converted to NAD and NADP, functioning in redox reactions by accepting and donating 2 electrons and 1 hydrogen ion. Signup and view all the answers

What is the significance of pantothenic acid in metabolism?

Pantothenic acid is converted to a phospho-form coenzyme that activates acyl moieties for condensation and enolization reactions. Signup and view all the answers

Describe the function of biotin in biochemical reactions.

Biotin acts as a coenzyme that incorporates CO2 in carboxylation reactions, playing a key role in metabolism. Signup and view all the answers

What is the role of Vitamin C in collagen synthesis and overall health?

Vitamin C is essential for the hydroxylation of proline in collagen, which is critical for wound healing. Signup and view all the answers

Study Notes

Amino Acids Overview

Amino acids contain a central carbon atom (chiral center) bonded to an amino group (NH2), a carboxyl group (COOH), a hydrogen atom, and a variable R group (side chain).
Amino acids can exist as enantiomers, which are mirror images of each other due to the presence of a chiral center.

Classification of Amino Acids

Amino acids are classified based on their R groups, which determine their chemical properties, polarity, and roles in protein structure.

Amphoteric Nature

Amino acids can act as acids (proton donors) and bases (proton acceptors), showcasing their amphoteric nature.
Substances that exhibit this dual characteristic are referred to as ampholytes.

Titration Curves and Isoelectric Point

The titration curves of amino acids illustrate how their electric charge changes with pH.
The isoelectric point (pI) is the pH at which the net charge of an amino acid is zero, typically indicated by the average of the two pKa values.
For glycine, which lacks an ionizable side chain group, the isoelectric point can be calculated directly from its pKa values.

Peptides

Peptides are short chains of amino acids linked by peptide bonds.
They play critical roles in biological functions and can vary significantly in length and composition.

Enzymes

Enzymes are primarily proteins that catalyze biochemical reactions.
They bind weakly to substrates, facilitating various biochemical processes.

Function of Enzymes

Enzymes increase reaction rates without affecting the equilibrium position of reactions.

Catalysis Mechanisms

Acid-Base Catalysis: Protons transfer alters substrate chemistry.
Covalent Catalysis: Enzyme forms covalent bonds with the substrate, aiding reaction progress.
Metal Ion Catalysis: Metal ions assist in stabilizing charged intermediates or facilitating electron transfer.

Enzyme Inhibition

Enzyme inhibitors can block activity, affecting metabolic pathways.

Enzyme Composition

Many enzymes need cofactors for activity, indicated by the equation: Apoenzyme + Cofactor = Holoenzyme.
Cofactors are classified into two groups: metals and small organic molecules (coenzymes).
Prosthetic Group: A tightly bound cofactor essential for enzymatic function.

Vitamins as Coenzymes

Water-soluble and selected fat-soluble vitamins function as cofactors or coenzymes.
Coenzymes are crucial in energy release, catabolism, anabolic reactions, blood coagulation, and collagen integrity.

Water-Soluble Vitamins

Vitamin B1 (Thiamine): Converted to thiamine pyrophosphate; aids in C-C bond cleavage through nucleophilic attack.
Vitamin B2 (Riboflavin): Forms FMN and FAD; participates in redox reactions, accepting/donating electrons.
Vitamin B6 (Pyridoxal): Converted to pyridoxal phosphate; forms Schiff bases facilitating various bond cleavages.
Vitamin B12 (Cyanocobalamin): Acts in methyl group transfers; important in the synthesis of methionine.

Additional Water-Soluble Vitamins

Nicotinamide (Niacin): Forms NAD/NADP; functions in redox reactions.
Pantothenic Acid: Participates in activating acyl moieties for metabolic reactions.
Biotin: Involved in carboxylation reactions, strongly binds to avidin.
Vitamin C (Ascorbic Acid): Important for hydroxylation in collagen synthesis and potential immune support.
Folic Acid: Converted to THF; carries C-1 groups; more of a substrate than coenzyme.

Lipid-Soluble Vitamins

Vitamin A (Trans-retinol): Converted to cis-retinal; important for vision and growth.
Vitamin D: Converted to hormone regulating calcium metabolism and gene expression.
Vitamin E (a-Tocopherol): An antioxidant that aids in preventing sterility in animals.
Vitamin K: Essential for blood coagulation and formation of calcium-binding proteins.

Non-Vitamin Coenzymes

Lipoic Acid: Critical for electron/acetyl group transfer in the pyruvate dehydrogenase complex.

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Description

This quiz covers essential concepts related to amino acids, peptides, and proteins, focusing on their structures, properties, and functions. It also explores the classification of amino acids and their behavior as acids and bases. Perfect for students of Biochemistry.