AQA A Level Biology
Topic 4 Genetic
information, variation
and relationships
between organisms
Model answer notes by @biologywitholivia
__
Topic Understand Memorise Practise
4.1 DNA, genes and chromosomes
4.2 DNA and protein synthesis
4.3 Genetic diversity can arise as a
result of mutation or during meiosis
4.4 Genetic diversity and adaptation
Required practical 6
4.5 Species and taxonomy
4.6 Biodiversity within a community
4.7 Investigating diversity
, AQA A Level Biology Topic 4 Genetic information, variation & relationships between organisms biologywitholivia.co.uk
4.1 DNA, genes and chromosomes
Compare and contrast DNA in eukaryotic cells with DNA in prokaryotic cells
Similarities:
● Nucleotide structure is identical - deoxyribose attached to phosphate and a base
● Adjacent nucleotides joined by phosphodiester bonds, complementary bases joined by hydrogen bonds
● DNA in mitochondria / chloroplasts have similar structure to DNA in prokaryotes
○ Short, circular, not associated with proteins
Differences:
● Eukaryotic DNA is longer
● Eukaryotic DNA is linear, prokaryotic DNA is circular
● Eukaryotic DNA is associated with histone proteins, prokaryotic DNA is not
● Eukaryotic DNA contain introns, prokaryotic DNA does not
What is a chromosome?
● Long, linear DNA + its associated histone proteins
● In the nucleus of eukaryotic cells
What is a gene?
A sequence of DNA (nucleotide) bases that codes for:
● The amino acid sequence of a polypeptide
● Or a functional RNA (eg. ribosomal RNA or tRNA)
What is a locus?
Fixed position a gene occupies on a particular DNA molecule.
Describe the nature of the genetic code
Triplet code A sequence of 3 DNA bases, called a triplet, codes for a specific amino acid
Universal The same base triplets code for the same amino acids in all organisms
Non-overlapping Each base is part of only one triplet so each triplet is read as a discrete unit
Degenerate An amino acid can be coded for by more than one base triplet
2
Topic 4 Genetic
information, variation
and relationships
between organisms
Model answer notes by @biologywitholivia
__
Topic Understand Memorise Practise
4.1 DNA, genes and chromosomes
4.2 DNA and protein synthesis
4.3 Genetic diversity can arise as a
result of mutation or during meiosis
4.4 Genetic diversity and adaptation
Required practical 6
4.5 Species and taxonomy
4.6 Biodiversity within a community
4.7 Investigating diversity
, AQA A Level Biology Topic 4 Genetic information, variation & relationships between organisms biologywitholivia.co.uk
4.1 DNA, genes and chromosomes
Compare and contrast DNA in eukaryotic cells with DNA in prokaryotic cells
Similarities:
● Nucleotide structure is identical - deoxyribose attached to phosphate and a base
● Adjacent nucleotides joined by phosphodiester bonds, complementary bases joined by hydrogen bonds
● DNA in mitochondria / chloroplasts have similar structure to DNA in prokaryotes
○ Short, circular, not associated with proteins
Differences:
● Eukaryotic DNA is longer
● Eukaryotic DNA is linear, prokaryotic DNA is circular
● Eukaryotic DNA is associated with histone proteins, prokaryotic DNA is not
● Eukaryotic DNA contain introns, prokaryotic DNA does not
What is a chromosome?
● Long, linear DNA + its associated histone proteins
● In the nucleus of eukaryotic cells
What is a gene?
A sequence of DNA (nucleotide) bases that codes for:
● The amino acid sequence of a polypeptide
● Or a functional RNA (eg. ribosomal RNA or tRNA)
What is a locus?
Fixed position a gene occupies on a particular DNA molecule.
Describe the nature of the genetic code
Triplet code A sequence of 3 DNA bases, called a triplet, codes for a specific amino acid
Universal The same base triplets code for the same amino acids in all organisms
Non-overlapping Each base is part of only one triplet so each triplet is read as a discrete unit
Degenerate An amino acid can be coded for by more than one base triplet
2
