Chapter summary
Molecular genetics, at a glance
Scan the key ideas, or hide the answers and try to recall them.
01
DNA, genes and chromosomes
How are these three terms connected?
Key idea and reminders
A chromosome contains a long DNA molecule carrying many genes. A gene is a sequence of nucleotides with instructions for a polypeptide and is a unit of inheritance.
- Genes are sections of DNA, not separate objects stored alongside DNA.
- A chromosome carries many genes along its DNA.
- At this syllabus level, a gene codes for one polypeptide and can be passed from parent to offspring.
Keep in mind: A gene is a DNA nucleotide sequence. Its information is used to make a polypeptide; the gene and its protein product are different kinds of molecule.
02
DNA structure and base pairing
How can one strand tell you the bases on the other?
Key idea and reminders
DNA has two nucleotide strands twisted into a double helix. Each nucleotide contains sugar, phosphate and a base; A pairs with T, and C pairs with G.
- A nucleotide contains a sugar, a phosphate group and one base.
- Sugar and phosphate form each strand's backbone; bases face inwards.
- Complementary pairing is A with T and C with G. Complementary does not mean identical.
Keep in mind: They are complementary: each A is opposite T, and each C is opposite G. The paired letters are not identical.
03
From a gene to a polypeptide
How does DNA information affect what a cell can do?
Key idea and reminders
The sequence in a gene carries information used to assemble a particular amino acid sequence. The polypeptide can fold into a protein with a specific role.
- The genetic code is carried by the sequence of DNA bases.
- A gene specifies a polypeptide; its amino acid sequence contributes to its shape and function.
- DNA is used as information. It is not converted into the protein as a raw material.
Keep in mind: The DNA sequence supplies information for synthesis. The protein is built from amino acids; it is not made by converting DNA material into protein.