Nucleic Acids and Proteins - VCAA Past Exam Qs

The primary structure of a protein is important because it

• A - is the active, functional form of the protein

• B - has a very specific three-dimensional shape

• C - influences the way that the polypeptide folds

• D - directly controls the way that proteins are transported into a cell

Answer explanation

A - incorrect as the functional form of the protein is the 3D shape and therefore must be tertiary or quaternary

B - incorrect as 3D shape must be tertiary or quaternary

C - amino acids make up the primary structure - their R groups influence the folding of the protein

D - protein transport is not influenced by protein structure

Which one of the following organelles has the role of synthesising proteins from their monomers?

• A - Golgi apparatus

• B - ribosomes

• C - vesicles

• D - nucleus

Answer explanation

A - is incorrect. Golgi apparatus is involved in folding proteins and modifying by adding prosthetic groups. This organelle isn't involved in the creation of proteins.

C - is incorrect. Vesicles transport materials throughout a cell.

D - nucleus is incorrect as it doesn't synthesise proteins. However, the nucleus does provide instructions for protein synthesis.

Which one of the following statements about proteins is correct?

• A - The activity of a protein may be affected by the temperature and pH of its environment

• B - the primary structure of a protein refers to it's three-dimensional shape

• C - Proteins are not involved in the human immune response

• D - A protein with a quaternary structure will be an enzyme

Answer explanation

B - incorrect as primary structure refers to the order of amino acids

C - incorrect as proteins are involved in the human immune response, e.g. as antibodies

D - not all proteins with a quaternary structure will be an enzyme, therefore this statement is incorrect

Two different cells taken from the same human were viewed using a microscope.

The diagrams show the structure of the two cells, not drawn to the same scale.

Which one of the follow is a correct conclusion to reach when comparing the two cells?

• A - At any given time, the genes expressed in each cell may be different

• B - All proteins in each cell will have similar tertiary structures

• C - The two cells have the same proteome

• D - The two cells have different genomes

Answer explanation

A - correct as different genes may be expressed by the cells are likely to be different due to their different functions

B - Incorrect. The cells are likely to express different genes and therefore are likely to produce different proteins.

C - Incorrect. The cells are likely to express different genes and produce different proteins. Therefore, is is likely that they will not have the same proteome.

D - Incorrect. The two cells have the same genome as they come from the same human.

The proteome is

• A - the total DNA content that is present within one cell of an organism

• B - a complete set of chromosomes found inside the cell of an organism

• C - the entire set of proteins expressed by an organism at a given time

• D - the four hierarchical levels of protein structure

The diagram represents adjacent amino acids being joined together.

The joining of adjacent amino acids

• A - results in the formation of a nucleic acid

• B - is an energy-releasing reaction

• C - is catalysed by DNA ligase

• D - is a condensation reaction

Answer explanation

A - incorrect. This reaction results in the formation of a polypeptide

B - incorrect. This reaction requires energy

C - incorrect. DNA ligase is an enzyme that helps to join strands of DNA together (not amino acids)

D - correct. It is a condensation reaction as it produces water as a product

Consider the structure and functional importance of proteins.

Which one of the following statements about proteins is correct?

• A - A change in the tertiary structure of a protein may result in the protein becoming biologically inactive.

• B - Proteins with a quaternary structure will be more active than proteins without a quaternary structure.

• C - Two different proteins with the same amino acids will have identical functions.

• D - Denaturation will alter the primary structure of a protein.

Answer explanation

C - Incorrect as the number of amino acids doesn't determine the shape and function of the protein. Instead, it is the types of amino acids that determine their function.

D - Incorrect. Denaturation occurs when the temperature or pH isn't ideal for a protein. It results in a change in the 3D shape, rendering the protein inactive. However, it doesn't alter the sequence of amino acids.

The diagram represents part of a DNA molecule.

A single DNA nucleotide is shown by sub-unit(s)

• A - X alone.

• B - X and Y together.

• C - Y and Z together.

• D - X, Y and Z together.

Answer explanation

X represents a base (adenine, thymine, guanine or cytosine)

Y represents a 5- carbon sugar

X represents a phosphate group

It is all three components together that form a nucleotide which is a monomer of DNA (and RNA!)

A feature of DNA that can be seen in the diagram is

• A - the anti-parallel arrangement of the two strands of nucleotides.

• B - the process of semi-conservative replication.

• C - its ribose sugar-phosphate backbone

• D - its double-helix structure

The part of the molecule referred to as an anticodon can be found in

• A - DNA

• B - transfer RNA

• C - ribosomal RNA

• D - messenger RNA

Answer explanation

Transfer RNA (tRNA) transports amino acids to ribosomes where polypeptides are synthesised. Anticodons are sequences on the tRNA that help determine the amino acids to be used in protein synthesis.