Genetics
DNA & Protein synthesis
A gene is a sequence of Nucleotide bases that code for a specific protein or polypeptide. Genes are
mainly located on the Chromosomes however some can be found in mitochondria. Each gene
occupies a specific LOCUS on the chromosome. Genes are involved in the control of all metabolic
pathways and the synthesis of all non-protein molecules in cells.
The genetic code
Triplet code – every three amino acids or CODON code for an amino acid
There are multiple codons for each amino acid except methionine
Some codons code for ‘STOP’
The codons are widespread but not universal; genes can be used in genetic engineering to
place genes in different organisms.
Transcription
mRNA is produced
The template strand of DNA is used as a template for RNA nucleotides
The hydrogen bonds between DNA bases are broken by DNA HELICASE
Activated RNA nucleotides, ATP, GTP, CTP and UTP bind to their complementary nucleotides
of the template strand of the gene.
The extra phosphoryl groups on the activated RNA nucleotides are released, this releases
energy for the nucleotides to be bonded by phosphodiester bonds
The RNA is released from the DNA gene and passes out of the nucleus through a pore in the
nucleur envelope to a ribsome.
Translation
Ribosomes
Built up of two subunits
There is a groove down the centre that mRNA slides down to be translated
Transfer RNA
Have 3 exposed bases at the end of their structure where an amino acid can bind
At the other end there is an anti-codon which is complementary to the codon which codes
for the next amino acid in the polypeptide sequence
How translation occurs
1. The first codon of the gene is always AUG, the tRNA’s anticodon then forms hydrogen bonds
with the mRNA’s codon
2. The amino acid which it has transferred is then bonded (via peptide bond) with the next
codon using ATP and an enzyme.
3. The ribosome then moves down the mRNA...