Unit 3 - Transcription & Translation Flashcards
Overview
Transcription
Converts DNA to RNA
Overview
Which strand of DNA is transcribed?
template strand
Overview
Which direction does RNA transcribe itself?
5’ to 3’
Overview
Which direction does RNA move on the template strand?
3’ to 5’
Overview
RNA polymerase
Transcribes DNA on the template strand
Overview
mRNA
codes for protein
Prokaryotic Transcription
RNA Polymerase
A large enzyme with several channels
Prokaryotic Transcription
Core enzyme
synthesizes RNA
Prokaryotic Transcription
Sigma Factor
- recognizes promoter on DNA
- opens DNA helix
- relaesed after initiating transcription
Prokaryotic Transcription
Promoter
located on non-template strand found in
-10 or -35 box
Prokaryotic Transcription
How does transcription stop?
- RNA polymerase reaches a termination signal on DNA causing a “hairpin loop”
- polymerase and transcript fall off DNA
Overview
Promoter
- can only read 3’ to 5’ or 5’ to 3’
- found on either strand
- strand it is on becomes non-template strand
- recognized by sigma factor
Eukaryotic Transcription
DNA Packing
- creates chromatin (DNA + protein)
*
Eukaryotic Transcription
How many RNA Polymerase do eukaryotes have?
3
Eukaryotic Transcription
TATA Box
Recognized by TATA binding protein (TBP
Eukaryotic Transcription
TATA Binding Protein
Sub-unit of TF2D, opens DNA Helix for other promoters
Eukaryotic Transcription
Describe transcription initiation.
- TATA box is recognized by TBP (TF2D), which opens helix
- Other promoters pile on to create an initiation complex
- RNA Polymerase II binds to DNA and transcripts (only TF2D remains)
Eukaryotic Transcription
Where does transcription occur?
Nucleus
Eukaryotic Transcription
Describe RNA Polymerase II
- transcribes DNA to RNA
- has a phosphoryated tail
Eukaryotic Transcription
Describe the process of RNA processing.
- different factors bind to the polymerase tail
- the factors bind to the RNA as it is transcribed
Eukaryotic Transcription
Which end of the RNA does the cap bind to?
5’ (attatches at the start)
Eukaryotic Transcription
Exons
Region on mRNA that codes for protein
Eukaryotic Transcription
Intron
Region on mRNA that does not code for protein
Eukaryotic Transcription
What is splicing?
Introns are removed based on sequences near ends, can result in different functioned proteins from the same gene
Eukaryotic Transcription
Spliceosomes
Bind to two ends of intron and removes it from strand by forming the intron into a loop, consists of 5 snRNPs
Translation
What is translation?
mRNA is translated into amino acids/peptide chains (proteins)
Translation
Comapre eukaryotic and prokaryotic translation.
Eukaryotic translation can only occur after transcription, prokaryotic translation and transcription is synchronous
Translation
Genetic Code
Relationship between nucleotide sequence (codon) and amino acid, 64 codons, 20 amino acids
Translation
Which amino acids only have one codon?
MET and TRP
Translation
Is genetic code unveirsal?
Mostly, certain fungi and mitochondria have different codes
Translation
frame-shift mutations
When the a base is added/removed and shifts reading frame, leading to different proteins
Translation
tRNA
Transfer RNA: “adapters” that hold amino acids in place to interact with codons
Translation
How does mRNA specify amino acids?
tRNA
Translation
wobble hypothesis
Some tRNAs pair with a codon with the wrong third base
Translation
Describe redundancy in base-tRNA pairing.
Since multiple codons assosiate with the same amino acid, codons that begin with the same 2 bases can have more than 1 tRNA, ignoring the 3rd base
Translation
aminoacid tRNA synthase
activates amino acid with ATP and site where amino acid transfers to tRNA
Translation
Describe how amino acids attatch to their tRNAs
- tRNA synthase binds amino acid and ATP
- amino acid is activatied by ATP (AMP)
- tRNA binds to synthase
- amino acid is transferred to tRNA and detattches from synthase
Translation
Ribosomes
catalyze peptide bond formation and match tRNAs to codons
Translation
How does translation start?
- translation initiator factor finds 5’ cap
- initiator tRNA scans mRNA from 5’ to find start codon (AUG)
- small ribosomal subunits attatches and attracts the large
Translation
How does translation stop?
- ribosome hits a stop codon
- release factor binds to A-site
- adds water to end amino-acid chain
- everything falls off mRNA
Translation
Is a ribsome an enzyme or ribozyme?
ribozyme; most of its acitivty brought on my RNAs
Translation
When does the protein fold into its shape?
As chain is translated, it starts to fold
