Quiz on Proteins and Their Functions

Which macronutrient forms about 50% of the cellular dry weight?

• Lipids

• Carbohydrates

• Proteins

• Nucleic acids

Answer explanation

Proteins are the most abundant macronutrient in cells, constituting about 50% of the cellular dry weight. They play crucial roles in structure, function, and regulation of the body's tissues and organs.

Cholera toxin is an example of a protein acting as a:

• Hormone

• Receptor

• Toxin

• Structural component

Answer explanation

Cholera toxin is a protein that disrupts cellular processes, leading to severe diarrhea and dehydration. It is classified as a toxin because it causes harm to the host organism, unlike hormones or structural components.

The active component of most vaccines is typically:

• Lipids

• Carbohydrates

• Nucleic acids

• Proteins

Answer explanation

The active component of most vaccines is proteins, which can be whole proteins or protein fragments that stimulate an immune response. Other components like lipids and carbohydrates are not the primary active ingredients.

In terms of structure, protein function is determined by its:

• Size

• Shape

• Colour

• Temperature

Answer explanation

Protein function is primarily determined by its shape, which allows it to interact with other molecules in specific ways. Size, colour, and temperature do not directly dictate how a protein functions.

What percentage of body dry weight is composed of proteins?

• 10%

• 25%

• 50%

• 75%

Answer explanation

Proteins make up about 25% of the body's dry weight, playing crucial roles in structure, function, and regulation of tissues and organs. This makes 25% the correct choice among the options provided.

Which rule is used to determine the D- or L- isomer of an amino acid?

• Hand rule

• CORN rule

• Carbon rule

• Alpha rule

Answer explanation

The CORN rule helps determine the D- or L- configuration of amino acids by arranging the four groups around the chiral carbon. If the amino group (N) is on the left, it's L; if on the right, it's D.

Amino acids exist as zwitterions at a specific pH known as:

• pH 7

• Isoelectric point

• Dissociation constant

• Amino group pH

Answer explanation

Amino acids exist as zwitterions at their isoelectric point, which is the pH at which the net charge is zero. This is typically around pH 7 for many amino acids, making 'Isoelectric point' the correct choice.

Which amino acid is known for forming disulfide bonds?

• Lysine

• Glycine

• Cysteine

• Histidine

Answer explanation

Cysteine is the amino acid known for forming disulfide bonds due to its thiol (-SH) group. These bonds are crucial for stabilizing protein structures, unlike lysine, glycine, or histidine, which do not form such bonds.

The amino acid phenylalanine is metabolized into:

• Tryptophan

• Valine

• Tyrosine

• Methionine

Answer explanation

Phenylalanine is an essential amino acid that is converted into tyrosine through a hydroxylation reaction. Tyrosine is then used to synthesize neurotransmitters and hormones, making it the correct answer.

A disease caused by an inability to metabolize phenylalanine is:

• Sickle cell anemia

• Phenylketonuria

• Cystic fibrosis

• Diabetes

Answer explanation

Phenylketonuria (PKU) is a genetic disorder caused by the inability to metabolize phenylalanine due to a deficiency in the enzyme phenylalanine hydroxylase. This leads to harmful levels of phenylalanine in the body.