Biochemistry: Amino Acids and Their Function

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Questions and Answers

What is the pH at which the net charge of a zwitterion is zero called?

Isoelectric point (correct)

Buffer point

Charge balance point

Neutralization point

Which type of amino acid possesses one amino group and two carboxyl groups?

Zwitterionic amino acid

Basic amino acid

Acidic amino acid (correct)

Neutral amino acid

What characterizes a weak acid in terms of dissociation?

It fully dissociates in solution.

It only exists in its conjugate base form.

It only dissociates partially. (correct)

It does not release any hydrogen ions.

How do basic amino acids behave during electrophoresis?

They are attracted to the cathode. Signup and view all the answers

Which classification of amino acids must be obtained from dietary sources?

Essential amino acids Signup and view all the answers

Where do nonpolar amino acids generally reside in an aqueous environment?

In the interior of the protein Signup and view all the answers

What role do nonpolar side chains play in protein stabilization when in a hydrophobic environment?

They orient towards the lipid membrane Signup and view all the answers

Which amino acid is known for having a rigid structure that contributes to collagen formation?

Proline Signup and view all the answers

Which of the following amino acids contains a polar hydroxyl group for hydrogen bonding?

Threonine Signup and view all the answers

What is the effect of disulfide bonds in proteins?

They stabilize protein structure Signup and view all the answers

Which amino acids are classified as proton donors?

Aspartic and Glutamic acid Signup and view all the answers

Histidine differs from lysine and arginine in which way?

It is weakly basic and depends on the ionic environment Signup and view all the answers

How does cysteine contribute to protein structure?

Through the formation of disulfide bonds Signup and view all the answers

What are the components that amino acids contain?

Amine group, carboxylic acid, and side chain Signup and view all the answers

Which function is NOT associated with amino acids?

Synthesis of fatty acids Signup and view all the answers

At physiological pH, how do amino acids exist?

As both negatively and positively charged ions Signup and view all the answers

Which classification is NOT used for amino acids?

Structural classification Signup and view all the answers

Which of the following statements about amino acid side chains is true?

The nature of the side chains dictates the amino acid's role in proteins Signup and view all the answers

Which type of amino acids are classified as having acidic side chains?

Aspartic acid and glutamic acid Signup and view all the answers

Which characteristic is associated with amino acids in metabolic fate classification?

Amino acids can be either glucogenic, ketogenic, or mixed Signup and view all the answers

Which of the following is NOT a function of amino acids?

Direct synthesis of carbohydrates Signup and view all the answers

Which of the following amino acids cannot be fully synthesized and is considered semiessential?

Cysteine Signup and view all the answers

Which amino acids are classified as ketogenic amino acids?

Leucine and Lysine Signup and view all the answers

What configuration do human amino acids predominantly adopt?

L-configuration Signup and view all the answers

Which of the following amino acids is optically inactive?

Glycine Signup and view all the answers

What chemical structure is present in all amino acids?

An α-carboxyl group Signup and view all the answers

Which classification of amino acids exclusively produces glucose?

Glucogenic amino acids Signup and view all the answers

What distinguishes the amino acid Proline from others?

It has a secondary amino group Signup and view all the answers

At physiological pH, what state do α-carboxyl groups of amino acids exist in?

Deprotonated and negatively charged Signup and view all the answers

Study Notes

Biochemistry

Biochemistry studies chemical processes in living organisms.

Amino Acids

Biologically important organic compounds containing amine (-NH2) and carboxylic acid (-COOH) groups.
Each amino acid has a specific side chain (R functional group).
Amino acids serve various functions:
- Building blocks for peptides and proteins.
- Nitrogen transfer for synthesis of DNA, RNA, and urea.
- Regulate protein turnover and signal transduction.
- Synthesis of neurotransmitters like epinephrine.
- Detoxifying non-soluble toxins.
- Buffering action.
- Energy production.

Amino Acid Structure

Approximately 300 amino acids exist in nature, but only 20 are found in proteins.
All amino acids contain a carboxyl group, a primary amino group (except proline), and a unique side chain (R-group) attached to the α-carbon atom.
At physiological pH (≈ pH 7.4), the carboxyl group becomes negatively charged (–COO–) and the amino group is protonated (–NH3+).
In proteins, most carboxyl and amino groups participate in peptide bond formation, leaving only side chains for chemical reactions.

Amino Acid Classification

Side Chain Chemistry Classification:
- Nonpolar side chains: Hydrophobic interactions, tend to cluster in the interior of proteins in aqueous environments, or on the outside surface when in hydrophobic environments.
- Uncharged Polar side chains: Contain polar atoms (S, N, O), capable of hydrogen bonding (e.g., serine, threonine, tyrosine).
  - Disulfide bond: The –SH group in cysteine can oxidatively form a disulfide bond with another cysteine residue, stabilizing protein structure.
- Acidic side chains: Proton donors with negatively charged carboxylate groups (–COO–) (e.g., aspartic acid and glutamic acid).
- Basic side chains: Proton acceptors, fully ionized and positively charged at neutral pH (e.g., lysine and arginine). Histidine is weakly basic.
Other Classifications:
- Neutral amino acids: Contain one amine group and one carboxyl group. Can be further classified as nonpolar or polar based on the side chain.
- Acidic amino acids: Contain one amine group and two carboxyl groups.
- Basic amino acids: Contain two amine groups and one carboxyl group.
Nutritional classification:
- Nonessential amino acids: Can be synthesized by the body.
- Essential amino acids: Must be obtained from the diet.
- Semiessential amino acids: Can be partially synthesized but require intake for optimal health.
Metabolic fate classification:
- Ketogenic amino acids: Primarily converted into ketone bodies (e.g., Leucine and Lysine).
- Glucogenic amino acids: Primarily converted into glucose.
- Mixed fate amino acids: Converted into both glucose and ketone bodies (e.g., Isoleucine, threonine, phenylalanine, tryptophan, and tyrosine).
Optical classification:
- Enantiomers: Mirror image isomers of each other, with a chiral (asymmetric) carbon center.
- L-configuration: The configuration of amino acids found in human proteins.

Protein

Proteins are linear polymers of L-α amino acids linked by peptide bonds.

Acidic, Basic, and Buffering Properties of Amino Acids

Both free amino acids and some amino acids in peptide chains can act as buffers, regulating body pH.
Buffer: A solution that resists changes in pH, consisting of a weak acid and its salt or a weak base and its salt.
Zwitterion: A neutral molecule with equal positive and negative charges.
Isoelectric point (pI): The pH at which the net charge of an amino acid is zero.

Electrophoresis

A technique that separates charged molecules based on their movement towards an electrode with an opposite charge.
Negatively charged proteins move towards the positive electrode (anode).
Variations in the mobility pattern of plasma proteins can indicate certain diseases.
Basic amino acids are closer to the cathode (Arg, Lys, and His).
Acidic amino acids are closer to the anode (Asp and Glu).

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Description

Explore the fascinating world of amino acids in biochemistry. This quiz covers their structures, functions, and roles in living organisms, including protein synthesis and neurotransmitter regulation. Test your knowledge and deepen your understanding of these crucial biological compounds.