RNA and the Genetic Code

central dogma

DNA to RNA to Proteins

genetic code

degenerate, multiple codons encode same amino acid

initiation sequence

AUG, methionine

termination sequences

UAA, UGA, UAG

wobble

third base in codon allows mutations to occur without affecting the protein

silent mutations

no affect on protein synthesis

nonsense mutations

premature stop codon

missense mutation

produces codon that codes for a different amino acid

frameshift mutation

nucleotide addition or deletion and changes reading frame

RNA vs DNA

ribose vs deoxyribose sugar, uracil vs thymine, single stranded vs double stranded

mRNA

carries message from DNA in nucleus via transcription of gene, travels to cytoplasm for translation

tRNA

brings in amino acids, recognizes codon on the mRNA using its anticodon

rRNA

makes up most of the ribosome, enzymatically active

transcription step 1

helicase and topoisomerase unwind DNA

transcription step 2

RNA polymerase II binds to TATA box in promoter region

promoter region

within 25 base pairs upstream from first transcribed base

transcription step 3

hnRNA synthesized from DNA template strand

posttranscriptional modifications

7-methylguanylate triphosphate cap added to 5’ end , poly-A tail added to 3’ end, splicing of introns by splicesome

alternative splicing

combines different exons to acquire different gene products

translation

occurs at ribosome, initiation, elongation, and termination

posttranslational modifications

folding by chaperones, formation of quaternary structure, cleavage of proteins/signal sequences, and covalent addition of other biomolecules

gene expression prokaryotes

operons, Jacob-Monod model

operons

inducible as repressible clusters of genes transcribed as a single mRNA

inducible operon

starts off, inducer binds repressor, complex cannot bind to operator, structural genes are transcribed

repressible operon

on to start, repressor binds corepressor, binds to operator and represses enzyme synthesis

transcription factors

search for promoter and enhancer regions of DNA

enhancers location

more than 25 base pairs away from transcription start site

methylation

silences gene expression, heterochromatin high

acetylation

opens chromatin