4.1 DNA, genes, and chromosomes
Eukaryotic Prokaryotic, mitochondria, chloroplast
Same nucleotide structure joined by phosphodiester bonds
Long Short
Linear Circular
Associated with histone proteins Not associated with proteins
Have introns No introns
● Chromosome: long, coiled DNA molecule and its associated proteins
● Gene: base sequence of DNA that codes for: the amino acid sequence of a
polypeptide, a functional RNA
● Locus: fixed position of a gene on a DNA molecule
● Triplet: sequence of 3 DNA bases that codes for a specific amino acid
● Genetic code is universal, non-overlapping, degenerate
○ Universal: each triplet codes for the same amino acid in all organisms
○ Non-overlapping: each base is part of only one triplet
○ Degenerate: an amino acid can be coded for by more than one triplet
● Exon: sequence of DNA that codes for an amino acid sequence
● Intron: non-coding sequence of DNA
4.2 DNA and protein synthesis
● Genome: the complete set of genes in a cell
● Proteome: the full range of proteins a cell is able to produce
● tRNA has a cloverleaf structure made of nucleotides
● 3 bases form an anticodon at one end, allowing it to bind to a complementary
mRNA codon
● Amino acid binding site at the other end carries a specific amino acid that is
complementary to the mRNA codon
, Transcription:
● DNA helicase breaks H bonds between complementary base pairs, separating the
DNA molecule
● Only one strand acts as a template and the bases are now exposed
● Free RNA nucleotides align by complementary base pairing
● RNA polymerase then joins the adjacent nucleotides by forming phosphodiester
bonds
● pre-mRNA is then spliced to remove sections of non-coding introns
● Mature mRNA strand leaves the nucleus
● In prokaryotic cells, mRNA is directly formed and splicing does not occur as there
are no introns
Translation:
● mRNA attaches to a ribosome which moves to the start codon
● tRNA brings an amino acid to the ribosome, its anticodon binds to the
complementary mRNA codon
● The ribosome then moves along the mRNA to read the next codon, allowing the
next tRNA to bind, bringing another amino acid
● The 2 amino acids that have been brought by the tRNA molecules join by a peptide
bond with the use of ATP
● Once the amino acid brought by the tRNA molecule has been added to the growing
polypeptide chain, the tRNA is released
● The process of adding amino acids to the polypeptide chain repeats until the
ribosome reaches a stop codon, releasing the polypeptide chain
4.3 Genetic diversity can arise as a result of mutation or
during meiosis
● Mutation: change in the base sequence of chromosomes
● Occurs spontaneously during DNA replication and includes base deletion and
substitution
○ Base deletion: when one or more bases are removed from a DNA sequence
causing frame shift, resulting in a different amino acid that is coded for
○ Base substitution: when one base is replaced by another. As the genetic
code is degenerate, not all base substitutions will result in a different amino
acid being coded for so may have no effect
○ Mutations cause change in base sequence of DNA, changing primary
structure, changing tertiary structure
● Mutations in number of chromosomes can occur due to non-disjunction during
meiosis
○ Non-disjunction: homologous chromosome pair failed to separate leading to
a gamete with one more or one less chromosomes
● Mutagenic agent: increases rate of mutations
Meiosis:
Eukaryotic Prokaryotic, mitochondria, chloroplast
Same nucleotide structure joined by phosphodiester bonds
Long Short
Linear Circular
Associated with histone proteins Not associated with proteins
Have introns No introns
● Chromosome: long, coiled DNA molecule and its associated proteins
● Gene: base sequence of DNA that codes for: the amino acid sequence of a
polypeptide, a functional RNA
● Locus: fixed position of a gene on a DNA molecule
● Triplet: sequence of 3 DNA bases that codes for a specific amino acid
● Genetic code is universal, non-overlapping, degenerate
○ Universal: each triplet codes for the same amino acid in all organisms
○ Non-overlapping: each base is part of only one triplet
○ Degenerate: an amino acid can be coded for by more than one triplet
● Exon: sequence of DNA that codes for an amino acid sequence
● Intron: non-coding sequence of DNA
4.2 DNA and protein synthesis
● Genome: the complete set of genes in a cell
● Proteome: the full range of proteins a cell is able to produce
● tRNA has a cloverleaf structure made of nucleotides
● 3 bases form an anticodon at one end, allowing it to bind to a complementary
mRNA codon
● Amino acid binding site at the other end carries a specific amino acid that is
complementary to the mRNA codon
, Transcription:
● DNA helicase breaks H bonds between complementary base pairs, separating the
DNA molecule
● Only one strand acts as a template and the bases are now exposed
● Free RNA nucleotides align by complementary base pairing
● RNA polymerase then joins the adjacent nucleotides by forming phosphodiester
bonds
● pre-mRNA is then spliced to remove sections of non-coding introns
● Mature mRNA strand leaves the nucleus
● In prokaryotic cells, mRNA is directly formed and splicing does not occur as there
are no introns
Translation:
● mRNA attaches to a ribosome which moves to the start codon
● tRNA brings an amino acid to the ribosome, its anticodon binds to the
complementary mRNA codon
● The ribosome then moves along the mRNA to read the next codon, allowing the
next tRNA to bind, bringing another amino acid
● The 2 amino acids that have been brought by the tRNA molecules join by a peptide
bond with the use of ATP
● Once the amino acid brought by the tRNA molecule has been added to the growing
polypeptide chain, the tRNA is released
● The process of adding amino acids to the polypeptide chain repeats until the
ribosome reaches a stop codon, releasing the polypeptide chain
4.3 Genetic diversity can arise as a result of mutation or
during meiosis
● Mutation: change in the base sequence of chromosomes
● Occurs spontaneously during DNA replication and includes base deletion and
substitution
○ Base deletion: when one or more bases are removed from a DNA sequence
causing frame shift, resulting in a different amino acid that is coded for
○ Base substitution: when one base is replaced by another. As the genetic
code is degenerate, not all base substitutions will result in a different amino
acid being coded for so may have no effect
○ Mutations cause change in base sequence of DNA, changing primary
structure, changing tertiary structure
● Mutations in number of chromosomes can occur due to non-disjunction during
meiosis
○ Non-disjunction: homologous chromosome pair failed to separate leading to
a gamete with one more or one less chromosomes
● Mutagenic agent: increases rate of mutations
Meiosis:
