Slides in this set
1. How DNA codes for proteins
A gene is a length of DNA that codes for one (or
In the human genome, there are about 25000 genes.
Each gene occupies a specific locus on a
Genes code for enzymes, they are involved in the
control of all metabolic pathways and thus in
synthesis of all non-protein molecules found in
the cells.…read more
The Genetic Code
- It is a triplet code ( a sequence of three
nucleotide bases) for an amino acid.
- It is a degenerate code (all amino acids have
more than one code.)
- Some codes don't correspond to an amino
acid, but indicate `stop',
- It is widespread, but not universal.…read more
How the nucleotide sequence code for the
amino acid sequence in a polypeptide.
Transcription- the first stage of protein synthesis.
· To be transcribed, a gene has to unwind and unzip
(hydrogen bonds between bases break as the gene dips
into the nucleolus).
· Activated RNA nucleotides bind to complementary bases
on the template strand (catalysed by the enzyme RNA
· The two extra phosphates are released, releasing energy
for bonding adjacent nucleotides.
· The mRNA produced is complementary to that on the
template strand and is therefore a copy of the base
sequence on the coding strand of the length of the DNA.
· The mRNA is released from the DNA and passes out of the
nucleus, through a nuclear pore, to a ribosome.…read more
`The assembly of polypeptides at ribosomes'
· The second stage of protein synthesis, when the
amino acids are assembled into a polypeptide.
· They are assembled into the sequence dictated by
the sequence of codons on the mRNA.
· The genetic code, copied from DNA to mRNA, is
now translated into a sequence of amino acids.
This is a polypeptide.
· It happens in ribosomes, which may be free in the
cytoplasm but many are bound to the rough
endoplasmic reticulum.…read more
- Assembled in the nucleolus of eukaryote cells, from
ribosomal RNA and protein.
- There is a groove in which the length of mRNA can fit.
The ribosome then moves along he mRNA, reading the
code and assembling the amino acids.
The sequence of amino acids;
- forms the primary structure of a protein
- primary structure determines the tertiary structure,
allowing it to fold up into the 3d shape.
- tertiary structure is what allows a protein to function.…read more