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Topic 1: DNA and Proteins

8 dot points, in syllabus order. Each dot point has a focused answer, with exam-style questions and worked answers where available.

How do enzymes speed up reactions and what changes their activity?

Explain how enzymes catalyse reactions via the active site and how temperature, pH, concentration and inhibitors affect their activity

Enzymes are protein catalysts that lower activation energy via a specific active site; activity depends on temperature, pH, substrate and enzyme concentration, and inhibitors.

8 min read →

How do cells control which genes are expressed and when?

Explain how gene expression is regulated, including the lac operon in prokaryotes and differential expression in eukaryotes

Cells regulate which genes are expressed; the lac operon is the prokaryotic model and differential gene expression explains how identical eukaryotic cells specialise.

9 min read →

How do scientists copy, separate and modify DNA?

Describe the principles of PCR, gel electrophoresis and the production of genetically modified organisms

PCR amplifies DNA through temperature cycles, gel electrophoresis separates fragments by size, and GMOs are made by inserting genes using restriction enzymes, ligase and vectors.

9 min read →

How do changes to DNA arise and what effects do they have?

Describe gene and chromosomal mutations, their causes (mutagens), and how they affect proteins and phenotype

Mutations are changes to DNA; point and frameshift mutations alter proteins to differing degrees, chromosomal mutations affect whole segments, and mutagens raise mutation rates.

8 min read →

How does the information in a gene become a functional protein?

Explain how transcription produces mRNA from a gene and how translation uses that mRNA to build a polypeptide

Gene expression has two stages: transcription copies a gene into mRNA in the nucleus, and translation at the ribosome reads mRNA codons via tRNA to assemble a polypeptide.

9 min read →

How is genetic information stored in DNA and copied before cell division?

DNA is a double helix of nucleotides whose complementary base pairing allows semi-conservative replication.

How the double-helix structure of DNA stores genetic information and how complementary base pairing enables accurate semi-conservative replication.

8 min read →

How does the structure of a protein determine what it does?

Proteins fold from amino acid chains into specific 3D shapes that determine their function.

The four levels of protein structure, how amino acid sequence determines shape, and how a protein's specific 3D shape determines its biological function.

8 min read →

How does a sequence of bases specify a sequence of amino acids?

The genetic code is a triplet, degenerate, near-universal code that maps codons to amino acids.

The properties of the genetic code: triplet codons, degeneracy, the start and stop codons, and how a codon table is used to translate mRNA into amino acids.

8 min read →