Protein Synthesis
Part 1Protein SynthesisDNA replication vs. Protein SynthesisDNA
ReplicationProtein SynthesisProduces...well.. DNAOccurs in order
for mitosis or meiosis to occurMainly for the production of new
cells.Produces..well.. ProteinsFor functions within an
already-created cellDNA codes for proteins5.1: One gene-One
Polypeptide HypothesisGregor Mendel discovered that certain factors
were responsible for the patterns of inheritanceWorked with pea
plantsDid not know what these factors were.
Garrods HypothesisEarly 1900sFirst to predict:ONE GENE ONE
ENZYME.Studied patients with alkaptonuria, genetic disorder in
which urine appears black because it contains alkapton.When exposed
to air, alkaptonuria darkens in colour. Individuals with
alkaptonuria have a defective alkapton-metabolizing enzyme: can not
be broken down.Hypothesized that a defective enzyme causes an
inborn error of metabolism along a reaction pathwayEnzymes are
under control of hereditary material. Error in ONE portion of the
hereditary material, and therefore, error in ONE enzyme.
Accumulation of substances and defective enzymes...
George Beadle and Edward TatumDemonstrated the one gene-one
polypeptide hypothesis using a red bread mould. 2 strains usedN.
Crassa: able to synthesize all AAs and vitamins required for
optimum growth b/c grown in minimally nutricious medium (salts,
sugars, B vitamin)N. Crassa (defective): exposed to X-rays and UV
light. If unable to grow on minimal medium, they were identified as
mutantUnable to manufacture one or more of the complex compounds
they required. Could grow on complete nutrient medium. Which AAs or
vitamin could the mutant strains not synthesize?How did they figure
it out?!Colonies of mutant strains placed in vials, each containing
minimal medium + one additional nutrient. One mutant strain grew on
minimal medium + arginine. Therefore, one or more of the enzymes
that synthesize arginine is defective.
NOTE: cells will only be productive if able to make arginine.
Also,the presence/absence of precursors is not important as long as
arginine can be produced. Some strains accumulated the precursor
and could not grow in the absence of ornithine, but could grown in
the presence of citrulline and minimal medium OR argininosuccinate
and minimal medium. Therefore, enzyme ____ defective. Some strains
could not grow in the absence of citrulline or ornithine and.
Therefore, enzyme(s) __________ defective.If precursor accumulated,
defect in enzyme ____.If ornithine accumulated, defect in enzyme
____.Beadle and Tatum determined the metabolic pathway of arginine
in this way. Later showed that each defective enzyme corresponded
to a mutation in a specific gene. gene one enzymeOne gene-one
enzyme hypothesis.
One gene-one enzyme?Genes also code for other proteins. Some
proteins consist of more than one polypeptide. Enzymes consist of
more than one polypeptide.Now known as the ONE GENE-ONE POLYPEPTIDE
hypothesis.Vernom IngramStudied AA sequence of hemoglobin from
individuals with sickle cell anemia. Two -chainsTwo -chainsSickle
cell blood cells:AA valine substitutes for only one glutamic acid
residues in one of the chains.
Change in AA (change in primary structure) change in secondary
structure of PP change in tertiary structure of PP will not fit
right with other PPs (change in quaternary structure).
Therefore, Ingram:Gene specifies the kind and location of each
AA in a given PP.
Seatwork/HomeworkPage 236, # 1, 2, 3, 4, 5, 6.
ALSO...
Good news: it is March Break.Even better news: you have
Homework!Check WIKI over the March Break. I will be putting up
small assignments throughout the break. You may have an assignment
or two that you will need to hand in when you come back. The last
day I will post any updates of this sort before the first day back
is Friday (March 18th).
