Untitled Quiz

Proteins are organic compounds with high molecular weight composed of carbon, oxygen, hydrogen, and nitrogen, and may also contain sulfur, phosphorus, and metal ions.
They are polymers formed from subunits called amino acids linked together by peptide bonds.
Molecules greater than 50 amino acids are classified as proteins, while those with less than 50 are known as polypeptides.

Nutritional Role: Provide essential amino acids, sulfur, and nitrogen to the body.
Catalytic Role: All enzymes are proteins.
Defensive Role: Antibodies (immunoglobulins) are protein-based.
Plasma Proteins: Contribute to the osmotic pressure of the blood.
Hormonal Role: Many hormones are proteins in nature.
Transport Role: Proteins assist in lipid transport in the blood, forming lipoprotein complexes. They also carry hormones (e.g., thyroid hormones) and minerals (e.g., calcium, iron, copper). Hemoglobin, a protein, is responsible for oxygen transport from the lungs to tissues.
Structural Role: Proteins are the primary structural components of bones, muscles, and cell membranes.
Blood Clotting: Coagulation factors are proteins.
Control of Gene Expression: Most factors involved in DNA replication, transcription, and mRNA translation are proteins.

Amino acids are organic acids containing an NH2 group.
They are the building blocks of proteins and are obtained from proteins by hydrolysis.
The general formula of an amino acid includes a carboxyl group (COOH) and an amino group (NH2), except for Proline and Hydroxyproline.
In α-amino acids, both the COOH and NH2 groups are attached to the same α-carbon atom, making them amphoteric (can act as both an acid and a base).
At physiological pH (approximately 7.4), the carboxyl group is dissociated, forming a negatively charged carboxylate ion (COO-), and the amino group is protonated, forming a positively charged ion (-NH3).
All amino acids, except glycine, are optically active (can rotate plane-polarized light). This is due to the four different groups attached to the α-carbon. Glycine, with two hydrogen atoms attached to the α-carbon, is optically inactive.

Neutral Amino Acids: Contain one amino group and one carboxyl group.
- Aliphatic Amino Acids: e.g., Glycine, Alanine, Valine, Leucine, Isoleucine (also known as Branched-chain amino acids)
- Hydroxy Amino Acids: Contain an (-OH) group in their side chain. e.g., Serine, Threonine, Tyrosine, Hydroxyproline, Hydroxylysine
- Sulfur-containing Amino Acids: e.g., Cysteine, Methionine
- Aromatic Amino Acids: e.g., Tyrosine, Phenylalanine, Tryptophan
- Heterocyclic Amino Acids: Contain a ring other than a benzene ring. e.g., Histidine (Imidazole ring), Tryptophan (Indole ring), Proline, and Hydroxyproline (Pyrrolidone ring)
- Imino Acids: Contain an imino group (-NH). e.g., Proline, Hydroxyproline.
Acidic Amino Acids: Contain two carboxyl groups and one amino group. e.g., Aspartic acid, Glutamic acid. They can also exist in the tissue in the form of amides. e.g., Asparagine, Glutamine.
Basic Amino Acids: Contain two amino groups and one carboxyl group. e.g., Arginine, Citrulline, Ornithine, Lysine, Hydroxylysine.

Glucogenic Amino Acids: Can be converted to glucose.
Ketogenic Amino Acids: Can be converted to ketone bodies.
Ketogenic & Glucogenic Amino Acids: Can be converted to both glucose and ketone bodies.

Essential Amino Acids (Indispensable Amino Acids): Not synthesized in the body, must be obtained from the diet for optimal growth and health. Deficiency can lead to nutritional deficiency diseases. Included are:
- Valine
- Leucine
- Isoleucine
- Phenylalanine
- Tryptophan
- Methionine
- Threonine
- Lysine
- Histidine
Semi-Essential Amino Acids:
- Arginine and Histidine are synthesized in amounts sufficient for healthy adults but not for growing children, lactating and pregnant women, and convalescent patients. Therefore, they are essential for these groups.
Non-Essential Amino Acids (Dispensable Amino Acids): Can be synthesized in the body. Their deficiency does not affect growth and health. They include all the amino acids not listed as essential.

Hydrophobic Amino Acids: Repel the aqueous environment, do not ionize or participate in hydrogen bond formation, and often reside in the core of proteins.
Hydrophilic Amino Acids: Interact with the aqueous environment, participate in hydrogen bond formation, and are often found on the external surfaces of proteins or in the reactive centers of enzymes.