Study Unit 5: The genetic code and translation
1) Genes encoding proteins:
1. Traditionally we thought that 1 gene encodes 1 polypeptide which makes
1 protein
2. Now we know that the same gene might encode different polypeptides
via post-translational modifications
3. One gene, One enzyme Hypothesis test:
Bread mold (Neurospora) was used for this experiment
Neurospora is haploid
Experiment:
Using this experiment, they could determine the biochemical
pathway for metabolic processes (how different amino acids
are produced)
Example question: draw and explain the biochemical pathway
using this table (+ indicates that growth occurred and –
indicates that no growth occurred)
Mutant Ornithine Citrulline Arginine
strain
Group I + + +
Group II - + +
Group III - - +
, Interpreting the table:
Group I has a mutation that makes it incapable of
producing ornithine, if ornithine is added growth occurs
(we can assume that ornithine will be converted to
citrulline and then arginine in this biochemical pathway)
Group II has a mutation that makes it incapable of
producing citrulline (that is why no growth occurs when
ornithine is added but growth does occur if citrulline is
added)
Group III has a mutation that makes it incapable of
producing arginine (that is why no growth occurs if
ornithine/citrulline is added and growth does occur if
arginine is added)
The full biochemical pathway explained:
4. The structure and function of proteins:
Proteins are made of a sequence of amino acids linked together
with polypeptide chain
Sequence of amino acids is the primary structure, this folds to form
secondary and tertiary structure
Non-polar amino acids:
1) Genes encoding proteins:
1. Traditionally we thought that 1 gene encodes 1 polypeptide which makes
1 protein
2. Now we know that the same gene might encode different polypeptides
via post-translational modifications
3. One gene, One enzyme Hypothesis test:
Bread mold (Neurospora) was used for this experiment
Neurospora is haploid
Experiment:
Using this experiment, they could determine the biochemical
pathway for metabolic processes (how different amino acids
are produced)
Example question: draw and explain the biochemical pathway
using this table (+ indicates that growth occurred and –
indicates that no growth occurred)
Mutant Ornithine Citrulline Arginine
strain
Group I + + +
Group II - + +
Group III - - +
, Interpreting the table:
Group I has a mutation that makes it incapable of
producing ornithine, if ornithine is added growth occurs
(we can assume that ornithine will be converted to
citrulline and then arginine in this biochemical pathway)
Group II has a mutation that makes it incapable of
producing citrulline (that is why no growth occurs when
ornithine is added but growth does occur if citrulline is
added)
Group III has a mutation that makes it incapable of
producing arginine (that is why no growth occurs if
ornithine/citrulline is added and growth does occur if
arginine is added)
The full biochemical pathway explained:
4. The structure and function of proteins:
Proteins are made of a sequence of amino acids linked together
with polypeptide chain
Sequence of amino acids is the primary structure, this folds to form
secondary and tertiary structure
Non-polar amino acids:
