Gene Expression and Regulation

Genetic Code

specifies which nucleotide sequence corresponds to which amino acid

How many AA and codons are there?

20 AA and 64 codons

How is the genetic code redundant?

more than 1 codon can specify the same AA

Transcription steps

initiation (RNA pol binds promoter elements), elongation (mRNA synthesis from DNA template), and termination (end of transcription)

Prokaryotic RNA Pol

pol recognizes promoter sequence

Eukaryotic RNA pol

pol uses TFs and activator proteins to bind specifically to the promoter (TATA box)

Prokaryote Ribosome

3 rRNAs with 54 proteins

Eukaryotic Ribosome

2 rRNAs with 82 proteins

rRNA

ribozyme that joins AA

tRNA

carries anticodons that binds mRNA and AA binds the other end

Translation Initiation

small ribosomal subunit binds mRNA, finds AUG, first tRNA binds AUG codon

Missense mutation

AA codon potentially disrupts function

Nonsense mutation

AA codon to stop codon

Silent mutation

codes for same AA or not in the coding region

Frameshift mutations:

indels that alter codons and change reading of all codons

Suppressor (reversion) mutations

second mutation reverses effect of first mutation

Translation Elongation

requires large ribosomal subunit with peptide and amino sites

Translation Termination

stop codon on mRNA has no tRNA so it binds release factor where the peptide cuts from the last tRNA and released into the cytoplasm. the ribosomal subunits will separate and the protein will fold