lecture 6- central dogma

What rare condition did Garrod study to link genes to enzymes?

Alkaptonuria, caused by a recessive mutation leading to homogentisic acid buildup.

What hypothesis emerged from studies on alkaptonuria and PKU?

the “one gene–one enzyme” hypothesis (later revised to one gene–one polypeptide)

phenylketonuria (PKU)

A genetic disease where phenylalanine isn’t converted to tyrosine due to a nonfunctional enzyme.

What are the two steps of gene expression in the Central Dogma?

transcription (DNA → RNA) and translation (RNA → protein)

What are the three main types of RNA and their functions?

• mRNA: Carries genetic code from DNA to ribosomes

• rRNA: Forms part of ribosome structure, catalyzes peptide bonds

• tRNA: Transfers amino acids to ribosome, matches codons

what enzymes synthesizes RNA from DNA

RNA polymerase

does RNA polymerase need a primer

No

What are introns and exons

Introns = noncoding sequences; exons = coding sequences

What removes introns from pre-mRNA?

The spliceosome.

codons

3-base sequences on mRNA that specify amino acids.

What are the start and stop codons?

start: AUG (methionine); Stop: UAA, UAG, UGA.

what does it mean that the genetic code is redundant but not ambiguous?

Multiple codons can specify the same amino acid, but each codon specifies only one amino acid.

What is the function of tRNA?

Matches codons to amino acids using its anticodon.

What enzyme charges tRNAs with the correct amino acid?

Aminoacyl-tRNA synthetase.

What is the wobble hypothesis?

Some tRNAs can pair with more than one codon due to flexibility at the 3′ base.

What are the ribosome tRNA binding sites?

A (aminoacyl), P (peptidyl), and E (exit) sites.

What happens during initiation?

Ribosome assembles, mRNA binds, and the start codon pairs with the initiator tRNA.

What occurs in elongation?

Amino acids are added one by one as the ribosome moves along the mRNA.

What triggers termination?

A stop codon enters the A site and a release factor frees the new protein.

What directs a protein to the rough ER?

a signal peptide

Name three posttranslational modifications.

• Proteolysis: Cleaving proteins

• Glycosylation: Adding sugars

• Phosphorylation: Adding phosphate groups

What are silent mutations?

Base changes that don’t alter the amino acid sequence.

What is a missense mutation?

A base change that causes one amino acid to be substituted for another.

What is a nonsense mutation?

A base change that results in a premature stop codon.

What is a frameshift mutation?

insertion or deletion of bases that shifts the reading frame.