Part 1 Protein Synthesis

DNA replication vs. Protein Synthesis DNA ReplicationProtein Synthesis Produces...well.. DNA Occurs in order for mitosis or meiosis to occur Mainly for the production of new cells. Produces..well.. Proteins For functions within an already-created cell DNA codes for proteins

5.1: One gene-One Polypeptide Hypothesis Gregor Mendel discovered that certain ‘factors’ were responsible for the patterns of inheritance Worked with pea plants Did not know what these factors were.

Garrod’s Hypothesis Early 1900s First 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 pathway Enzymes 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 Tatum Demonstrated the one gene-one polypeptide hypothesis using a red bread mould. 2 strains used N. 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 mutant Unable 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 enzyme One 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 Ingram Studied AA sequence of hemoglobin from individuals with sickle cell anemia. Two α -chains Two β -chains Sickle cell blood cells: AA valine substitutes for only one glutamic acid residues in one of the β 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/Homework Page 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 18 th ).