Sec 4 Combined Science (Biology) Molecular Genetics topical questions

Complete the sentences: DNA is the ______; a gene is a ______ of DNA coding for one ______; chromosomes are ______ found in the nucleus.

Name the three parts of a DNA nucleotide.

State the complementary base pairing rule.

How many chromosomes are present in a human body cell, and how are they arranged?

A strand of DNA reads A–T–G–C–C–G–T. Write its complementary strand, showing the rule used.

Explain the statement: "One gene is one unit of inheritance coding for one polypeptide."

A DNA sample contains 22% guanine. Calculate the percentage of each of the other three bases.

Describe how DNA's structure suits its role as the information store of the cell.

A student writes: "Genes are made of chromosomes, which are made of cells." Identify and correct the errors, stating the true relationships among cells, chromosomes, genes and DNA.

Two DNA samples come from different plants. Sample X has 15% adenine; sample Y has 35% adenine. (a) Give all four base percentages for each. (b) Explain why the two samples can differ so much while the pairing rule stays the same.

Explain the full chain from a base sequence to a working protein, using haemoglobin as your example. Your answer should name DNA, gene, code, polypeptide and protein in order.

A strand reads C–A–T–G–G–C–T–A. (a) Write its complement. (b) State the percentage of thymine in this 8-base section's double-stranded form, showing your reasoning. (c) A base in the middle of the sequence is damaged and cannot pair. Explain, using base pairing, why the partner strand can be used to restore the original sequence.