biol 112 lec 6

what DNA tells the cell

which proteins to make

alkaptonuria

causes arthritis and pee to turn black

cause of alkaptonuria

genetic error resulting in missing enzyme that metabolizes tyrosine

auxotrophs

mutant organism that needs an extra nutrient to grow when the normal strain doesn’t

prototroph

normal strain (wild type) of an organism, doesn’t need additional nutrients

if organism lacks enzyme

can’t convert one compound to another, mutated gene that codes for enzyme

neurospora experiment findings

mutant alleles affecting enzymes found at each step in pathway, different strains had different mutations

one gene, one enzyme hypothesis

each gene codes for a single specific enzyme, each enzyme catalyzes a single step in a metabolic pathway

mRNA

messenger between DNA and ribosomes, transfers genetic info from nucleus to cytoplasm where proteins are made

central dogma

DNA → RNA → protein, can only move in one direction

RNA attributes

uracil instead of thymine, 2’ hydroxyl, forms double stranded helix when paired with DNA

DNA-RNA information transfer

RNA polymerase unwinds DNA and creates a complementary strand of RNA

RNA vs DNA polymerase

same except RNA polym makes RNA, doesn’t need 3’ hydroxyl to start, uses triphosphate ribonucleotides instead of deoxyribonucleotides

transcription

copying of DNA information to newly created mRNA strand

nucleotides per animo acid

3 nucleotides to each animal acid → 4³

phenylalanine code

UUU

lysine code

AAA

proline code

CCC

codon

3 DNA letters that code for 1 amino acid

stop codons

tell ribosome when protein is done, UAA, UGA, UAG

why more codons than animo acids

some are stop codons, several codons make same animo acid

degenerate code

DNA sequence determines animo acid sequence, but amino acid sequence doesn’t determine DNA sequence

translation

ribosomes in cytoplasm or rough ER decode mRNA to make animo acids

transfer RNA

adaptor between nucleic acid and protein, carries amino acids to RNA by binding anticodon to mRNA codon

anticodon

3 nucleotide loop sticking out of tRNA, bind using base-pair rules to codon in mRNA

ribosome mechanism

causes tRNA anticodons to bind to mRNA codons, catalyzes polymerization of amino acids on other end of tRNAs to create amino acid sequence based on mRNA sequence

aminoacyl tRNA synthases

enzymes, one for each amino acid, catalyzes attachment of certain amino acid to tRNA

changing aminoacyl tRNA synthase

will change the amino acid attached to the tRNA, even if the codon stays the same. eg, changing a phe tRNA with a phe anticodon to an ala tRNA will cause it to put an ala everywhere a phe is supposed to be