Transfers genetic information from DNA to ribosomes
Components of a DNA nucleotide
Deoxyribose
Phosphate group
Adenine
Cytosine
Guanine
Thymine
Components of an RNA nucleotide
Ribose
Phosphate group
Adenine
Cytosine
Guanine
Uracil
Purine bases
Adenine and guanine
Pyrimidines
Thymine, uracil and cytosine
Phosphodiester bonds
Formed in condensation reactions to join nucleotides
DNA molecule
Double helix composed of two polynucleotides joined by hydrogen bonds between complementary bases
RNA
Relatively short polynucleotide chain
Genetic code
Order of bases on DNA, consisting of triplets of bases coding for particular amino acids (codons)
Gene
Sequence of bases on a DNA molecule coding for a sequence of amino acids in a polypeptide chain
Locus
Location of a gene
Introns
Non-coding sections of DNA
Exons
Coding regions of DNA
Genetic code
Non-overlapping
Degenerate
Contains start and stop codons
Each amino acid is coded for by one or more combination of triplets, resulting in 64 possible triplets
Genes are separated by non-coding repeats of bases
A change in the base sequence of DNA alters the amino acid sequence and the protein, which can have various effects
Harmful mutations
Cystic fibrosis
Sickle cell anaemia
Eukaryotic cells
DNA molecules are long and linear, found in the nucleus and associated with histones to form chromosomes
Prokaryotic cells
DNA is short and circular, not associated with proteins
Homologous pairs
Two chromosomes that carry the same genes, but can carry different alleles
Allele
Alternative form of the same gene
Protein synthesis
1. Transcription (in nucleus)
2. Translation (in cytoplasm)
mRNA
Long single strand created during transcription, with base sequence complementary to DNA
tRNA
Small molecule made up of around 80 nucleotides, folded into a clover leaf shape with an amino acid attachment site and an anti-codon
Transcription
DNA uncoils, one strand used as template to make mRNA, mRNA moves out of nucleus
Translation
mRNA attaches to ribosome, tRNA collects amino acids and carries them to ribosome, amino acids join by peptide bonds to form polypeptide chain
Ribosomes can join up to 15 amino acids per second, and up to 50 ribosomes can move along the same mRNA strand
Substitution mutation
One nucleotide in the DNA sequence is replaced by another
Deletion mutation
A nucleotide in the DNA sequence is lost, leading to a frameshift
Polyploidy
Changes in the whole set of chromosomes, resulting in more than two sets
Non-disjunction
Chromosomes fail to separate correctly in meiosis, resulting in gametes and zygotes with one more or one less chromosome
Polyploidy
Many modern wheats
Non-disjunction
Down's syndrome
Meiosis
Produces genetically different haploid gametes through independent assortment of chromosomes and crossing over of chromatids
Genetic diversity
Total number of different alleles in a population
Niche
Role of a species within its environment
Stages of Meiosis
1. Meiosis 1: Homologous chromosomes pair up, crossing over may occur, cell divides with each daughter cell containing one chromosome from each homologous pair
2. Meiosis 2: Chromatids of each chromosome are separated producing 4 haploid daughter cells
Genetic diversity
The total number of different alleles in the population