Protein Structure and Function - Chapter 5

Flashcards covering monomers, amino acids, peptide bonds, levels of protein structure, types and functions of proteins, denaturation, enzyme concepts, and side-chain properties.

What is the basic building block of proteins?

Amino acids.

What are the four main components of a general amino acid structure?

A central carbon (alpha carbon) bonded to an amino group (NH_2), a carboxyl group (COOH), a hydrogen atom, and a variable side chain (R group).

What are the three general categories of amino acid R groups based on their properties?

Nonpolar (hydrophobic), polar (hydrophilic), and electrically charged (acidic or basic, also hydrophilic).

What bond links amino acids to form a polypeptide and what reaction drives it?

A peptide bond forms between the carboxyl group of one amino acid and the amino group of the next; dehydration synthesis (loss of water) drives it.

How many different R groups (side chains) exist in amino acids?

Twenty different R groups.

What is a protein?

A biologically functional molecule made up of one or more polypeptides folded and coiled into a specific three-dimensional structure.

What determines the primary structure of a protein?

Inherited genetic information (DNA).

What is the primary structure of a protein?

A sequence of amino acids linked by peptide bonds.

In the example provided, how many amino acids long is the protein and how many possible sequences exist?

127 amino acids long; 20^{127} possible sequences.

What does secondary structure involve and what stabilizes it?

Regular folding of the backbone into patterns like alpha helices and beta pleated sheets; stabilized by hydrogen bonds between backbone atoms.

Name two common types of secondary structure.

Alpha helices and beta pleated sheets (beta sheets).

What stabilizes tertiary structure?

Interactions among R groups, including disulfide bridges (covalent), ionic bonds, hydrogen bonds, and hydrophobic interactions.

What is a disulfide bridge?

A covalent bond between sulfhydryl groups of cysteine residues that helps stabilize the protein’s 3D shape.

What is quaternary structure?

Two or more polypeptide chains come together to form a functional protein (e.g., hemoglobin).

Why is a protein's specific three-dimensional structure crucial?

The structure dictates its function; even a slight change in shape can impair or abolish its biological activity.

Give an example of a defensive protein.

Antibodies.

Give examples of storage proteins.

Ovalbumin (egg white), casein (milk), and seed storage proteins.

Which protein transport oxygen in the blood?

Hemoglobin.

What protein acts as a receptor in cell membranes?

Receptor proteins.

Which proteins are responsible for muscle movement?

Actin and myosin (contractile and motor proteins).

What class of proteins speeds up chemical reactions?

Enzymes (e.g., lysozyme).

What proteins provide structural support in tissues?

Keratin, collagen, and elastin.

Which hormone regulates blood glucose?

Insulin (a hormonal protein).

What happens to a protein during denaturation?

It loses its native 3D structure and usually its function due to disruption of non-covalent interactions.

What observable change occurs when egg whites are heated?

Proteins denature; the solution becomes opaque and the proteins become insoluble.

What happens if a protein is placed in an organic solvent?

Hydrophobic regions may refold so that they face the solvent; tertiary structure can be altered.

Besides heat and organic solvents, what other environmental factors can cause protein denaturation?

Extreme pH changes and high concentrations of salts.

What does the lock-and-key concept describe?

Enzymes have active sites with specific shape that binds substrates in a complementary manner to catalyze a reaction.