MGD 9-10: transcription and translation Flashcards
where does transcription and translation take place within the cell?
transcription in the nucleus, translation in the cytoplasm
DNA –(transcription)–> mRNA –(translation)–> protein
what is a gene?
a stretch of DNA with a chromosomal locus
‘unit of inheritance’, ‘unit of transcription’
what is the structure of heterochromatin and euchromatin?
heterochromatin: solenoid fibre - genes not expressed
euchromatin: beads on a string - genes expressed
what are the different types of RNA?
mRNA tRNA rRNA miRNA noncodingRNA
mRNA and protein structure
mRNA: 5’–>3’
protein: N–>C terminus
what is needed in making a DNA (DNA replication)? what is the process?
enzyme: DNA polymerase (attach free bases)
activated substrate: dNTPs (free DNA bases)
template (DNA)
3 stage process: initiation, elongation, termination
what is needed in making mRNA?
enzyme: RNA polymerase (attach free bases)
activated substrate: NTPs (free RNA)
template: DNA
3 stage process: initiation, elongation, termination
what is required in translation (making a polypeptide)?
enzyme: ribosome (40s & 60s)
activated substrate: AA (to attach to codon)
template: mRNA
3 stage process: initiation, elongation, termination
briefly describe what happens in each step of DNA replication
- initiation: recognition origin of replication
initiation proteins
DNA polymerase - elongation: 5’ –> 3’ chain growth
- termination: when replication forks meet
briefly describe what happens in each step of transcription
1. initiation: promoter recognition transcription initiation factors RNA polymerase 2. elongation: 5'-->3' chain growth 3. termination: sequence dependent
where is the transcription initiation promotor sequence for eukaryotes?
TATA box at -30
variety of upstream sequences
complex regulation
where is the transcription initiator promotor sequence for prokaryotes
pribnow box at -10
upstream sequences at -35
‘simple’ regulation
what is RNA processing and when does it occur / what does it produce?
from pre-mRNA to mature mRNA:
- capping: at 5’end: protection against degradation (5’-5’ phosphate linkage)
- tailing or polyadenylation: at 3’ end, polyA tail protection against degradation (AAUAA)
- splicing: in the middle, removes introns (non-coding DNA) - sequence dependent
what are the nucleases used to degrade nucleic acids?
- endonucleases: breaks WITHIN polynucleotide, non-specific or specific
- exonuclease: degrades polynucleotide from END, 5’ or 3’ specific
how much of each type of RNA do we have?
rRNA - the most (80%) - few kinds but many of each
tRNA - mid (15%) - 100 kinds, many copies of each
mRNA - least (2%) - 100,000 kinds, few copies of each
what types of rRNA and ribosomes are present in prokaryotes?
3rRNAs + 56 proteins
30s + 50s subunits
70S ribosomes
what types of rRNA and ribosomes are present in eukaryotes?
4rRNAs + 82 proteins
40S + 60S subunits
80S ribosomes
what are features of the genetic code?
4 letter DNA TO 20 proteins read triplet non-overlapping and no gaps 5' to 3' template produces N to C polypeptide chain extension adaptor molecule required = tRNA
what is the initiation and termination codes of the genetic code?
initiation: AUG
termination: UAA, UAG, UGA
structure of tRNA, uncharged and charged?
tRNA - clover
uncharged - anticodon 3 bases
charged: amino acyl tRNA (has AA attached to tRNA)
5’ base of anticodon attaches to what of codon?
3’ base
where is the wobble position and what is it?
5’ base of anticodon & 3’ base of codon (complementary) (anticodon top, codon bottom)
allowing a single tRNA species to recognise more than 1 codon
briefly explain what happens in translaiton
- initiation: AUG codon recognised by methionyl tRNA ribosome
- elongation: N to C chain growth, aminoacyl tRNAs
- termination: stop codons
in detail, explain what happens in initiation of translation
- 5’ cap binds to the 5’ end (protect against degradation)
initiation factors, 40S subunit ribosome, Met-tRNA (start codon) all bind to the mRNA using GTP - the met-tRNA and 40s ribosome will move along the mRNA until AUG is found
- using ATP, Met-tRNA binds to AUG
- 60S subunit then bind to the whole complex through attaching to the 40S subunit
- GDP dissociates
In detail, explain what happens in elongation of translation
- the Met-tRNA sits in the p site (peptide)
- the next triplet is recognised by the tRNA holding the complimentary AA
- binding of the next aminoacyl-tRNA t the A site uses GTP
- both sites are now occupied and a peptide bond forms between the 2 amino acids (peptidyl transferase)
- the AA stay with the aminoacyl in the A site, the uncharged tRNA now moves out of the P site
- using a GTP, the ribosome complex moves along the mRNA sequence so that the A site now becomes the P site and so the process continues
what is used to form the peptide bond?
peptidyl transferase
In detail, explain what happens in termination of translation
keep moving along the mRNA until stop codon reached (UAA, UAG, UGA)
no tRNA are complementary to stop codon
the stop codon is recognised and the peptide and tRNA are hydrolysed (H2O) to release the protein into the cytoplasm
