Gas Exchange Surfaces and Cell Membranes: Practice Questions

Genetic screening can be used to identify genetic disorders in a fetus. Which statement correctly compares amniocentesis and chorionic villus sampling (CVS)?

A student investigates the rate of an enzyme-catalyzed reaction. They observe that the initial rate of reaction increases as the substrate concentration is increased from \(0.1\text{ mol dm}^{-3}\) to \(0.5\text{ mol dm}^{-3}\). However, above \(0.8\text{ mol dm}^{-3}\), the rate remains constant despite further increases in substrate concentration.

What is the most likely molecular explanation for the constant rate observed at high substrate concentrations?

The antisense (template) strand of a gene contains the following sequence:

3'-TAC CGG ATC GGT-5'

A mutation occurs that changes the eighth base (A) to a G. Using the provided mRNA codon table excerpt (AUG = Met, GCC = Ala, UAG = Stop, UGG = Trp), what is the most likely consequence for the resulting polypeptide?

According to the triplet code, what is the minimum number of nitrogenous bases required in a coding sequence to provide instructions for a polypeptide chain consisting of 10 amino acids, assuming no start or stop codons are counted?

A protein is discovered to have a quaternary structure consisting of two different types of polypeptide chains. If a chemical agent specifically breaks only disulfide bridges within this protein, which of the following describes the most likely impact on the protein's levels of structure?

What is the functional difference between the DNA template strand (antisense strand) and the DNA coding strand (sense strand) during the process of transcription?

Explain why extreme increases in temperature above the optimum lead to a rapid decrease in the rate of an enzyme-catalysed reaction.

A point substitution mutation occurs in the coding sequence of a gene. Explain the molecular rationale for why a substitution in the third base of a codon often results in a neutral effect on the resultant polypeptide structure compared to a substitution in the first base position.

Enzymes are essential biological catalysts.

a) Define the term active site in relation to enzyme action.

b) Explain how the specific three-dimensional structure of an enzyme ensures that it only catalyses one specific reaction or a specific type of reaction.

Outline the process of transcription, explaining the specific role of the DNA template (antisense) strand and RNA polymerase in synthesising messenger RNA (mRNA).