RNA and the Genetic Code Flashcards
Degenerate Code:
Allows for multiple codons to encode for the same
amino acid
Point Mutations: Silent
Mutations with no effect on protein synthesis.
Usually found in the 3rd base of a codon
Point mutations: Nonsense
Mutations that produce a
premature STOP codon
Point Mutation: missense
Missense: Mutations that produce a codon that codes
for a DIFFERENT amino acid.
Frameshift
Mutations:
Result from a nucleotide addition or deletion, and
change the reading frame of subsequent codons
Name the three types of RNA and state their functions
Messenger RNA (mRNA): Transcribed from DNA in the nucleus, it travels into the cytoplasm for translation. Transfer RNA (tRNA): Brings in amino acids and recognizes the codon on the mRNA using its anticodon. Ribosomal RNA (rRNA): Makes up the ribosome and is enzymatically active.
tRNA
Translates the codon into the correct amino acid.
Ribosomes:
Factories where translation (protein synthesis) occurs.
Eukaryotes: 80s ribosomes
Prokaryotes: 70s ribosomes
Initiation: Prokaryotes
Prokaryotes: When the 30S ribosome attaches to the
Shine-Delgarno Sequence and scans for a start codon; it
lays down N-formylmethionine in the P site of the
ribosome.
Initiation: Eukaryotes
Eukaryotes: When the 40S ribosome attaches to the 5’
cap and scans for a start codon; it lays down methionine
in the P site of the ribosome.
Elongation:
The addition of a new aminoacyl-tRNA into the A site of
the ribosome and transfer of the growing polypeptide
chain form the tRNA in the P site to the tRNA in the A
site. The now uncharged tRNA pauses in the E site before
exiting the ribosome. The A site tRNA moves to the P site
Termination:
Occurs when the codon in the A site is a stop codon;
release factor places a water molecule on the
polypeptide chain and thus releases the protein.
Posttranslational
Modifications
Folding by chaperones. Formation of quaternary
structure. Cleavage of proteins or signal sequences.
Covalent addition of other biomolecules
(phosphorylation, carboxylation, glycosylation,
prenylation).
DNA Ligase
Fuse the DNA strands together to create one strand.
Helicase:
Unwinds the DNA double helix
RNA Polymerase II:
Binds to the TATA box within the promoter region of the
gene (25 base pairs upstream from first transcribed
base).
hnRNA
Collective term for the unprocessed mRNA in nucleus
Posttranscriptional
Modification
The process in eukaryotic cells where primary transcript
RNA is converted into mature RNA. Introns cut out
Posttranscriptional Modifications: Exons
Exons: Exit the nucleus and form mRNA
Posttranscriptional Modification: Introns
introns: Spliced out so they stay in nucleus. Introns also
enable alternative splicing
Posttranscriptional Modification
Alternative splicing: Usually introns are cut away and
exons remain, but alternative splicing might change
that. A certain exon may be cut out, or an intron may
stay. This allows for the RNA segment to code for more
than one gene.
What is the purpose of the 5’ cap and poly A tail?
5’ Cap and Poly-A tail are added to the mRNA. The cap
and tail stabilize mRNA for translation.
Operons:
Inducible or repressible clusters of genes transcribed
as a single mRNA.
Inducible Systems:
Under normal conditions, they are bonded to a
repressor. They are turned on when an inducer pulls
the repressor off. Example: Lac operon.
Repressible Systems definition and example
Transcribed under normal conditions; they can be
turned off by a corepressor coupling with the
repressor and the binding of this complex to the
operator site. Example: Trp operon
Transcription
Factors
Search for promoter and enhancer regions in the DNA,
then bind to the DNA and recruit RNA polymerase
Promotors:
Are within 25 base pairs of the transcription start site.
Enhancers
Are more than 25 base pairs away from the
transcription start site.
