RNA and the Genetic Code Flashcards
What does degenerate mean?
allows multiple codons to encode for the same amino acid
Start codon?
AUG
Stop codons?
UAA
UGA
UAG
Wobble base?
allows mutations to occur without affecting the protein
Silent mutations?
mutations with no affect on protein synthesis
Nonsense (truncation)?
mutations which produce a premature stop codon
Missense?
mutations which produce a codon that codes for a different amino acid
Frameshift mutations?
result from nucleotide addition or deletion and change the reading frame
What makes RNA different from DNA?
- substitution of a ribose sugar for deoxyribose
- uracil instead of thymine
- single stranded
- 2’ OH group, more reactive
mRNA?
carries the message from DNA in the nucleus via transcription of the gene, travels from nucleus into cytoplasm
tRNA?
brings in amino acids, recognizes the codon on the mRNA using its anticodon
rRNA?
makes up much of the ribosome, enzymatically active
Steps of transcription?
- Helicase unwinds, Topoisomerase relieves
- RNA Pol II binds to TATA box within promoter region of gene (25 base pairs upstream)
- hnRNA synthesized from DNA template (antisense) strand
Posttranscriptional modifications?
- 7 methylguanylate triphosphate cap added to 5’ end
- Poly A tail added to 3’ end
- splicing done by spliceosome, introns removed and exons ligated together
- alternative splicing combines different exons to acquire different gene products
Posttranslational modifications?
- folding by chaperones
- formation of quaternary structure
- cleavage of proteins or signal sequences
- covalent addition of other biomolecules (phosphorylation, carboxylation, glycosylation, prenylation)
Operons?
inducible or repressible clusters of genes transcribed as a single mRNA in prok
Transcription factors?
search for promoter and enhancer regions in DNA
Promoters?
within 25 base pairs of transcription start site
Enhancers?
more than 25 base pairs away from transcription start site
