Protein Structure and Function – Review Flashcards (Sections 3.1-3.4)

Key concepts from Protein Structure and Function notes: amino acid structure, peptide bond formation, four levels of protein structure, protein types and functions, essential amino acids, protein synthesis and folding, diseases related to misfolding, and a sickle-cell example.

How does the structure of an amino acid affect its function?

The side chain (R group) determines chemical properties (size, charge, polarity) and drives interactions that influence folding and function.

How do amino acids polymerize to form polypeptides?

Through condensation (dehydration) reactions forming peptide bonds, releasing a molecule of water.

Name the four levels of protein structure.

Primary, Secondary, Tertiary, and Quaternary structures.

What defines the secondary structure of proteins?

Hydrogen bonds between backbone amide and carbonyl groups lead to alpha helices and beta sheets.

What characterizes tertiary structure?

3D folding driven by interactions among R groups (side chains) and the overall 3D shape of the protein.

What characterizes quaternary structure?

Arrangement and interaction of multiple polypeptide subunits in a protein, not present in all proteins.

What determines the primary structure of a protein?

The amino acid sequence encoded by the gene’s DNA.

In a polypeptide, which end is the N-terminus?

The amino (N) end of the polypeptide.

In a polypeptide, which end is the C-terminus?

The carboxyl (C) end of the polypeptide.

What is the function of enzymatic proteins?

To catalyze chemical reactions; digestive enzymes hydrolyze bonds in food molecules.

What is the function of defensive proteins?

Protection against disease; antibodies inactivate and help destroy pathogens.

What is the function of storage proteins?

Store amino acids; examples include casein (in milk) and ovalbumin (in egg white).

What is the function of transport proteins?

Transport substances; e.g., hemoglobin carries oxygen in blood; other transport proteins move molecules across membranes.

What is the function of hormonal proteins?

Coordinate an organism’s activities; e.g., insulin regulates blood glucose.

What is the function of receptor proteins?

Allow cells to respond to chemical stimuli by detecting signaling molecules.

What is the function of contractile and motor proteins?

Enable movement; actin and myosin drive muscle contraction and movement of cilia/flagella.

What is the function of structural proteins?

Provide support; examples include keratin, collagen, elastin.

How many essential amino acids are there?

Nine.

Why are some amino acids essential?

Humans cannot synthesize them all; they must be obtained from the diet.

Name three essential amino acids.

Examples: Lysine (K), Leucine (L), Isoleucine (I).

Which amino acids have positively charged side chains at physiological pH?

Lysine, Arginine, and Histidine.

Which amino acids have negatively charged side chains at physiological pH?

Aspartate (Asp, D) and Glutamate (Glu, E).

Name a nonpolar amino acid.

Examples: Glycine (G), Alanine (A), Valine (V), Leucine (L).

Which amino acid can form disulfide bonds important for folding?

Cysteine.

How many water molecules are needed to completely hydrolyze a polymer of 11 amino acids?

10 water molecules.

What is the polymer formed from amino acids called?

Polypeptide (which folds into a protein).

What reaction forms peptide bonds?

Dehydration synthesis (condensation) removes water to join amino acids.

What diseases are associated with protein misfolding?

Alzheimer’s disease, Parkinson’s disease, ALS, Type II diabetes, among others.

What is Titin and why is it notable?

Titin is the longest known protein, about 34,350 amino acids long.

Approximately how many protein molecules are there per liver cell?

About 7.9 x 10^9 protein molecules per liver cell.

What percentage of the dry weight of the body is protein?

More than 50%.

What is the role of molecular chaperones?

Help proteins fold correctly by assisting in the folding process.

What substitution causes sickle-cell anemia and how does it affect hemoglobin?

Glutamic acid is replaced by valine at position 6 in the beta-globin chain, promoting abnormal polymerization of deoxygenated hemoglobin and sickle-shaped red blood cells.