transcription and translation Flashcards
how is RNA different to DNA ?
single stranded
stem loop structure (one continuous strand)
contains uracil instead of thymine
what are the three main classes of RNA ?
rRNA - combines with proteins to form ribosomes
tRNA - carries amino acids to be incorporated into the protein
mRNA - carries the genetic information
which RNA is stable ?
rRNA
tRNA
which RNA is unstable ?
mRNA
describe the structure of tRNA
cloverleaf structure
what are RNA polymerases ?
multi-subunit complexes
create rRNA
how many RNA polymerases do prokaryotic cells and eukaryotic cells have ?
prokaryotic - 1 type
eukaryotic - 2 type ( Pol l, ll, lll )
what synthesises all mRNA ?
Pol ll
what are the steps of transcription ?
RNA polymerase binding
DNA chain separation
transcription initiation
elongation
termination
Explain the steps of transcription
RNA polymerase binding
- detects initiation sites on DNA (promoters )
- requires transcription factors
DNA chain separation
-Unwinding of DNA
Transcription initiation
- Selection of first nucleotide of growing RNA
- Required additional general transcription factors
Elongation
- Addition of further nucleotides to RNA chain
- RNA synthesised in 5’ – 3’ direction
Termination
- Release of finished RNA
what is TFIID ?
general transcription factor required for all Pol ll transcribed genes
what is required for specific regulation of transcription ?
specific transcription factors
what are coding and non-coding regions ?
exons - coding
introns - non-coding
are exons and introns transcribed together ?
yes
when and how are introns removed ?
before translation into the protein
removed by splicing
describe the ends of mRNA ?
a “cap” of modified GTP is added
AAUAAA - sequence is recognised
what do tRNA do during translation ?
anticodons of tRNA form base pairs with codons of mRNA
how many combinations can be made from base pairs ?
64 possible combinations, 20 amino acids
what is required for translation ?
amino acids
tRNAs
aminoacyl-tRNA synthetases
protein factors
ATP/GTP
ribesomes
mRNA
what is the start codon for translation ?
AUG
what are the steps of translation ?
Initiation
elongation
termination
explain the steps of translation
Initiation
- GTP provides energy
- Ribosomal subunit binds to 5’ end of mRNA, moves
along until start codon found
- Initiator tRNA pairs to start codon
- Large subunit joins assembly and initiator tRNA is
located in P site
Elongation
- Elongation factor brings aminoacyl-tRNA to A site
- GTP is hydrolysed
- Second elongation factor regenerates the first to pick
up next aminoacyl-tRNA
- Peptidyl transferase catalyses peptide bond formation
between amino acids in P and A sites
Termination
- Occurs when A site of ribosome encounters a stop
codon (UAA, UAG or UGA)
- Finished proteins cleaves off tRNA
Initiation
- GTP provides energy
- Ribosomal subunit binds to 5’ end of mRNA, moves
along until start codon found - Initiator tRNA pairs to start codon
- Large subunit joins assembly and initiator tRNA is
located in P site
elongation
- Elongation factor brings aminoacyl-tRNA to A site
- GTP is hydrolysed
- Second elongation factor regenerates the first to pick
up next aminoacyl-tRNA
Termination
- Occurs when A site of ribosome encounters a stop
codon (UAA, UAG, UGA - Finished proteins cleaves off tRNA
