Structure and Function of Proteins (LEC)

What are the general functions of proteins?

Proteins serve various functions including: catalysis, regulation, defense, transport in blood, oxygen delivery (globular proteins); and form structural components like extracellular matrix, contractile proteins, and participate in signal transduction (structural proteins).

Describe the synthesis of proteins.

Protein synthesis involves transcription of DNA to messenger RNA (mRNA) followed by translation of mRNA into a polypeptide chain. Peptide hormones are formed by cleavage from larger precursor proteins.

What are the hierarchical levels of protein structure?

1. Primary structure: Sequence of amino acids in a protein.
2. Secondary structure: Repeated elements in 3D structures like alpha-helices and beta-pleated sheets, stabilized by hydrogen bonds.
3. Tertiary structure: Location of all atoms in a protein due to interactions of amino acid side chains, including functional domains.
4. Quaternary structure: Composition of proteins with two or more polypeptide chains.

What bond forces maintain protein structure?

1. Covalent bonds: Strong (larger than 50 kcal/mol), e.g., peptide bonds, disulfide bonds.
2. Noncovalent bonds: Weaker (1-20 kcal/mol) that include hydrogen bonds, ionic bonds, and hydrophobic interactions, which specify protein folding.
3. Hydrophobic forces: Nonpolar amino acids group together in the protein interior, excluding water.
4. Van der Waals forces: Weak bonds (less than 1 kcal/mol) stabilize structures like the alpha-helix.

What defines the secondary structure of proteins?

Secondary structures include α-helix and β-pleated sheet.

• Alpha-helix: Right-handed spiral, with 3.6 residues per turn, stabilized by hydrogen bonds parallel to the imaginary axis, with side chains projecting outward.
• Beta-pleated sheet: Stabilized by hydrogen bonds between peptide chains, with alternating amino acid side chains above and below the plane of the sheet.

How does prion disease affect protein secondary structure?

In prion disease, normal prion proteins lose alpha-helices and increase beta-pleated sheets, altering their structure.

What role do chaperone proteins play in protein folding?

Chaperone proteins assist in the proper folding of proteins, bind aggregated proteins, help misfolded proteins refold, and direct proteins for degradation.

What is protein denaturation in vivo?

In vivo, proteins denature when their 3D structure is disrupted, affecting noncovalent and disulfide bonds but not hydrolyzing peptide bonds. Denaturation can be reversible or irreversible due to conditions like enzymatic degradation or low pH.

What is protein denaturation in the laboratory?

In laboratory settings, proteins can be intentionally denatured for disinfection through high temperatures, strong acids/bases, or detergents like sodium dodecyl sulfate (SDS), which disrupt ionic and hydrogen bonds.