Genetic Expression Flashcards
Define/Explain the steps of Central Dogma
Flow of information in the cell
DNA->transcription->mRNA->translation->protein
What is the promotor
DNA sequence that directs/regulates transciption
site of RNA polymerase
-35 to -10
What direction do you read the template strand
3’ -> 5’
How many nucleotides form a protein
three
DNA is read (transcription occurs) in the _’ to _’ end
3’ to 5’ (making RNA 5’ to 3’)
What direction does the template run away from the promotor
3’ to 5’
Transcription changes _____ into ______
DNA into RNA
What is RNA polymerase
Enzyme of transcription
- binds double stranded DNA at promotor
- unwinds double helix, create transcription bubble
- initiate transcription at +1
- aligns first two ribonucleotides (5’ end of new mRNA)
How is the template strand chosen
Based on direction of promotor
What happens at termination of transcription
RNA sequence that signal the end (terminators), RNA polymerase dissociates (falls off)
Where does transcription happen, where does translation happen (in eukaryotes)
transcription: in nucleus
translation: in cytoplasm
Post-transcriptional processing only happens in _________ because ________________________.
- eukaryotes
- transcription occurs in the nucleus, translation occurs in cytoplasm (time btw end of transcription and start of translation)
What modifications occur in post-transcriptional processing? Why?
- Addition of methyl guanosine cap at 5’ end: “hides” the 5’ end from exonuclease digestion
- Addition of 100-200 adenosines to 3’ end (poly-A tail): prevent and delay exonuclease digestion, aids in translation initiation
What is RNA splicing
removal of introns
What are introns and exons
Introns (remove): non amino acid coding regions (intervening sequences) found on genes DNA but not mature RNA
Exons (leave): amino acid coding regions
What is the spliceosome
Enzyme, complex of snRNPs, recognize sequence at intron/exon boundaries
Steps of RNA splicing
1) SnRNPs bind intron/exon boundaries and loop out the intron
2) intron cut out by cutting at 5’ end of intron
3) excised intron in lariat shape (created by 5’-2’ linkage of RNA)
4) exons ligated together
Why splice?
remove interrupting sequences, alternative splicing (mix and match of exons makes similar but not identical proteins from same gene. Ex. neuron vs muscular protein)
Translation changes _____ into ______.
RNA into protein
What signals start and stop of translation
start and stop codons
mRNA vs tRNA
mRNA: codon
tRNA: anticodon (antiparallel and complementary to mRNA)
Function of tRNA
carry appropriate amino acid to ribosome
Function of Aminoacyl tRNA synthetases
“the translator”
pairs correct amino acid based on anticodon sequence, covalently links amino acid to tRNA in sequence dependent manner
proteins are synthesized in what direction
N->C by reading mRNA 5’->3’
Large vs small ribosomal subunits in prokaryote vs eukaryotes
Prokaryotes: 70s=30s(small)+50s(large)
Eukaryotes: 80s=40s(small)+60s(large)
The large ribosomal subunit contains _____ and its function is ______. The small ribosomal subunit contains _______ and is involved in _________________.
rRNA, catalytic, rRNA, recognition of mRNA
The three sites of the large subunit
A:approach
P:polymerization
E:exit
What is the ribosomal binding site
small ribosomal subunit in prokaryotes, sequence in mRNA that is recognized by base pairing with rRNA
What are the three steps in translation (in prokaryotes)
Initiation, elongation, termination
Briefly explain initiation phase in translation
ribosomal binding site positions the small subunit such that AUG sits in P-site, the large subunit then associates such that F-met tRNA sits in P-site
“harmburger”
Briefly explain elongation phase
BIND-BOND-SHIFT
1) Bind: tRNA a.a. approaches the A site and binds to mRNA (codon-anticodon)
2) Bond: peptide bond forms btw first and second tRNA and the growing a.a. chain moves to tRNA in A-site
3) Shift: 5’ ribosome shifts down mRNA (towards 3’) in a one codon step. tRNA in E-site dissociates
Briefly explain Termination phase
Stop codons (UAA, UAG, UGA) stalls ribosome unless a release factor enters. Ribosome components dismantle and are recycled. Amino acid chain dissociates from tRNA in P-site.
When do transcription and translation occur together
In prokaryotes! Ribosomes read mRNA as its being transcribed
What direction do ribosomes move in
towards 3’ end
How many RNA polymerase can be active on one gene
Multiple! You can make many copies of mRNA from one copy of DNA
What is a silent mutation?
Base pair substitution, but it works out and leads to the same amino acid (different codons can code the same protein)
What is a missense mutation?
Base pair substitution that leads to the coding of a different amino acid
What is a nonsense mutation?
Base pair substitution leads to coding pre mature stop codon.
What is a frameshift mutation?
- Base addition (or insertion) leads to premature stop
2. Base deletion results in every amino acid after being affected
When does a mutation not affect the reading frame
Deletion of multiples of three
What causes sickle cell anemia
Single base pair substitution (MISSENSE), misshapes red blood cells so they do not carry oxygen well
Explain how mutations can be spontaneous or induced
Spontaneous: errors in DNA replication (1x10^10 copied during replication result in mutation)
Induced: x-rays, gamma-rays, oxidizing agents, base analogs
Mutagens also cause cancer (carcinogens)
