MGD 9-10: transcription and translation Flashcards Preview

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Flashcards in MGD 9-10: transcription and translation Deck (27):

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 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

1. initiation: recognition origin of replication
initiation proteins
DNA polymerase
2. elongation: 5' --> 3' chain growth
3. 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:
1. capping: at 5'end: protection against degradation (5'-5' phosphate linkage)
2. tailing or polyadenylation: at 3' end, polyA tail protection against degradation (AAUAA)
3. splicing: in the middle, removes introns (non-coding DNA) - sequence dependent


what are the nucleases used to degrade nucleic acids?

1. endonucleases: breaks WITHIN polynucleotide, non-specific or specific
2. 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

1. initiation: AUG codon recognised by methionyl tRNA ribosome
2. elongation: N to C chain growth, aminoacyl tRNAs
3. termination: stop codons


in detail, explain what happens in initiation of translation

1. 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
2. the met-tRNA and 40s ribosome will move along the mRNA until AUG is found
3. using ATP, Met-tRNA binds to AUG
4. 60S subunit then bind to the whole complex through attaching to the 40S subunit
5. GDP dissociates


In detail, explain what happens in elongation of translation

1. the Met-tRNA sits in the p site (peptide)
2. the next triplet is recognised by the tRNA holding the complimentary AA
3. binding of the next aminoacyl-tRNA t the A site uses GTP
4. both sites are now occupied and a peptide bond forms between the 2 amino acids (peptidyl transferase)
5. the AA stay with the aminoacyl in the A site, the uncharged tRNA now moves out of the P site
6. 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