Transcription And Translation Flashcards
What is the difference between the expression of genes in chromatin?
- EUCHROMATIN genes are expressed
- HETEROCHROMATIN genes are not expressed
What are the 3 stages of both transcription and translation?
- INITIATION
- ELONGATION
- TERMINATION
What is the promotor sequence commonly found in eukaryotes?
- TATA box
TATAAAA
ATATTTT
What is the role of the promotor region?
Signals where transcription factor binds, therefore the initiation of transcription
What is the role of transcription factors?
- Binding of transcription factor determines DIRECTION of transcription of gene (5’ to 3’)
- Determines where RNA polymerase will bind
What is the difference between upstream and downstream?
- UPSTREAM is in the 3’ to 5’ direction (right to left)
- DOWNSTREAM is in the 5’ to 3’ direction (left to right)
What does a mutation at -10 indicate?
Mutation is 10 bases upstream of the transcription initiation site
Where is the promotor sequence (TATA) located?
-30 upstream of the transcription initiation site
In which direction is mRNA synthesised?
5’ to 3’
Which strand is used as the template strand for mRNA?
3’ to 5’ bottom strand, so mRNA synthesised is a copy of the 5’ to 3’ coding strand
What is the enzyme responsible for the synthesis of mRNA?
RNA polymerase
What is the ORF?
Open reading frame of mRNA
What processing is required to transform pre mRNA to mature mRNA?
- 5’ Capping
- 3’ Polyadenylation
- Splicing of introns
Describe the process of 5’ capping
Addition of a methylated guanine to the 5’ end of the mRNA forming a 5’-5’ link
What is the role of 5’ capping?
- PROTECTS mRNA FROM DEGRADATION
- Recognised by translation initiation factors which allows subsequent binding of the 40s subunit to the mRNA strand
How is transcription terminated?
Transcription termination site sequence is recognised by SPECIFIC ENDONUCLEASE which cuts the chain a few bases downstream
What enzyme is used for the addition of a 3’ polyA tail?
PolyA polymerase
Describe how splicing occurs
- Removal of introns from pre mRNA using a SPLICOSOME
- HIGHLY SEQUENCE DEPENDANT
- Remaining exons are joined together using a ligase enzyme
What are the consequences of a mutation in an intron splice site?
- Results in the skipping and removal of the adjacent exon
- Shorter mRNA chain formed
- Shorter protein formed
What is UTR?
Untranslated regions of mRNA e,g, the 5’ cap and the 3’ polyA tail
What are the three types of RNA?
- rRNA (ribosomal)
- mRNA (messenger)
- tRNA (transfer)
How can 100000+ mRNA strands be synthesised from 25000 genes?
- SPLICING in eukaryotes can result in introns being left in (variable, sequence dependant)
- Transcription initiation can happen at different regions on the promotor
How many RNA polymerase molecules are present in eukaryotes?
- e
- RNA polymerase I (rRNA)
- RNA polymerase II (mRNA)
- RNA polymerase III (tRNA)
How is translation catalysed?
By RIBOSOMES
How do the structure of ribosomes differ in prokaryotes and eukaryotes?
- Prokaryotes have 70s ribosomes (30s+50s)
- Eukaryotes have 80s ribosomes (60s+40s)
What are ribosomes comprised of?
Many strands of rRNA and proteins
What is the role of translation?
Change the laughter of the mRNA code of nucleotides into polypeptide code of amino acids
What is a codon?
Triplet of bases that codes for one amino acid
Why is the genetic code described as ambiguous and degenerate?
- AMBIGUOUS as each codon only codes for one amino acid
- DEGENERATE as one amino acid Dan be coded for by multiple codons
What is the initiation codon that begins translation?
AUG which codes for methionine
What are the 3 termination (STOP) codons?
- UGA
- UAG
- UAA
Describe the structure of tRNA
- RNA stem loop that forms a clover model
- Contains an anticodon that is specific to a codon on mRNA that codes for an amino acid
Where does the amino acid bind on tRNA?
3’ end forming AMINO-ACYL tRNA
What is the significance of the wobble position?
- 5’ base of anticodon is IONISINE which can form a loose bond with the 3’ base of the codon, hence a wobble position as the tRNA is not tightly bound
- This allows the tRNA molecule to recognise more than one codon
What processes during translation require energy?
- MULTIPLE PROCESSES REQUIRE ENERGY IN THE FORM OF GTP
- Binding of 5’ cap binding initiation factors on 40s subunit
- Binding of tRNA to 60s subunit
- TRANSLOCATION of tRNA molecules from the P site to the A site
What is the role of peptidyl transferase?
- Catalyses the formation of a peptide bond between adjacent amino acids on the 3’ ends of tRNA molecules
- TRANSFER OF THE AMINO ACID FROM THE P SITE TO THE A SITE
What is a polysome?
- mRNA chain with multiple ribosomes attachted which are translating simultaneously
- Ribosomes attach at the 5’ and and fall off the 3’ end
How does bacterial transcription and translation differ from humans?
- Simple promotor region (Prinbow -10)
- Different transcription factors
- Single RNA polymerase
- NO POST TRANSCRIPTIONAL PROCESSING
- Smaller ribosomes (70s)
- Coupled transcription-translation (no nucleus)
What is a gene?
Section of DNA that codes for a polypeptide
