Sum7LS4Week4b(3slides)

Sum7LS4Week4b(3slides) - One Gene One Enzyme Errors of...

Info iconThis preview shows pages 1–6. Sign up to view the full content.

View Full Document Right Arrow Icon
1 One Gene One Enzyme • Errors of metabolism • Neurospora • Metabolic pathways The Central Dogma of Molecular Biology • Biological information flows from: DNA RNA Protein How do mutations help us understand how genes control phenotypes? • First clue came in 1902 from Archibald Garrod, an English physician who studied the rare disease alkaptonuria . • Those affected produce black urine…. The urine oxidizes upon exposure to air, causing it to turn black.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
2 Alkaptonuria • Garrod noticed that most of his patients were the offspring of first cousins. • He proposed that this disease, as with others such as albinism, are associated with heritable defects in specific enzymes which he called “inborn errors of metabolism.” Phe Metabolic Pathway • Many other conditions arise from defects in this pathway, which is for degradation of phenylalanine and conversion of tyrosine to other compounds. e.g., phenylketonuria (PKU) -- Symptoms include severe mental retardation, eczema and pigmentation defects • Today PKU patients are diagnosed at birth and treated through diet. Genes synthesize the enzymes • Garrod: One mutant gene one metabolic block
Background image of page 2
3 • Tried for 6 years (1935-1941) to link genes to chemical reactions in Drosophila. • Switched to a simpler organism: Neurospora crassa (bread mold) • Irradiated and isolated many arginine auxotrophs. Genetic Approach to Studying the Gene – Enzyme Connection Beadle ( Drosophila geneticist) and Tatum (biochemist), 1940’s Life-Cycle of Neurospora Crassa Heterokaryon-a transient diploid 1n 1n “A” cell (asexual spore) “a” cell (asexual spore) Ab aB octad mitosis progeny – recombinants and parentals Ab Ab AB AB ab ab aB aB meiosis four meiotic products Ab AB aB ab Sexual Phase transient diploid Ab/aB heterokaryon
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
4 Beadle and Tatum and Neurospora mutants • Mutagenized normal Neurospora cells; undergo meiosis… • Isolated individual cells (ascospores) into separate tubes with complete media (growth media that is rich with amino acids, nucleotides, etc… opposite of minimal media). • Tested each for the ability to grow on minimal media. Mutants • Certain cells did not grow on minimal medium. • The type of auxotrophy was tested on media with various supplements. Arginine Mutants Identified • After isolating mutants deficient in amino acid production, specific amino acid deficiencies were identified. • For the purpose of our discussion, we will focus on the arginine mutants. • Several independent arginine mutants were isolated.
Background image of page 4
5 Only if strains are mutant for different genes. X arg-2 arg-1 Complementation Testing of arg Mutants Are these mutations in the same gene or different genes? a b c d e f a - - + + + + b - + + + + c - - + - d - + - e - + f - Complementation Testing of Arg Auxotroph Mutants • Heterokaryons grown on minimal media… How many complementation groups are there?
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 6
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 11/23/2009 for the course LS 4 taught by Professor Ribaya during the Summer '08 term at UCLA.

Page1 / 33

Sum7LS4Week4b(3slides) - One Gene One Enzyme Errors of...

This preview shows document pages 1 - 6. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online