Transcription and translation Flashcards
(21 cards)
What is the typical gene structure of a eukaryotic cell?
1) Promoter
2) Coding sequence (exons)
3) Introns (Non-coding internal sequence)
4) UTR (Non-coding flanking sequence “untranslated regions”)
What is the meaning of Upstream and Downstream in gene sequences?
Upstream: genomic DNA that precedes the transcriptional start site in the 5′ direction
Downstream: DNA sequence located in the 3′ direction past the end of a gene
What is meant by the central dogma?
It is the flow of information in a biological system:
1) Transcription
2) Post-transcriptional processing
3) Translation
4) Post-translational modification
What are the components required for transcription?
1) DNA template
2) RNA polymerase II
3) Transcription Factor (If TFs are present on the promoter, RNA polymerase II binds to form an initiation complex)
What are the steps of transcription?
1) Initiation (Transcription factor at a higher- level binds and recruits RNA polymerase and initiation complex is formed)
2) Elongation (reading the DNA sequence from 3’ to 5’, mRNA synthesis occurs from 5’ to 3’
- The energy for elongation is derived from splitting the high-energy nucleoside triphosphate into monophosphate
3) Termination (When RNA polymerase reaches the terminator sequence, genes send signals therefore the TF detaches from the promoter region and triggers the release of mRNA from the transcription complex, RNA polymerase II recognizes the terminator signal —-🡪 triggers polyadenylation of 3’ end of mRNA and termination process)
What happens in the post-transcriptional modification (mRNA processing)?
1) Addition of a 5’ cap (7-methyl guanosine “protects the mRNA from denaturation”)
2) Addition of a 3’ tail (poly A tail)
3) Removal of introns (splicing, via spliceosomes “composed of snRNA removing the introns completing the maturation of the gene”)
where does translation occur?
cytoplasm
What are the required elements for translation?
1) mRNA: provides a template for polypeptide synthesis
2) Ribosomes: mRNA decoding cell organelle
3) tRNA: transfer each amino acid to the ribosome
Each amino acid is encoded by how many bases?
3 bases (each base is made up of AUGC)
How many amino acids are there in our body?
20
what is the initiation codon?
AUG (methionine)
What are the terminating codons?
1) UAA
2) UAG
3) UGA
What is the structure of tRNA?
- Cloverleaf-shaped adaptor RNA contains about 80 nucleotides
- 3′ end for the attachment with a specific amino acid, opposite end called anticodon: pairing with an appropriate complementary codon in the mRNA
- Each amino acid has one tRNA
What is the structure of the ribosome?
- Ribosome is a non-specific organelle (can combine with any mRNA and all tRNAs)
- Each large unit of ribosome contains 3 tRNA binding sites:
1) A-site = point of entry for the aminoacyl tRNA
2) P-site = site where Peptidyl-tRNA is formed (peptide bond formation, catalyzed by peptidyl transferase)
3) E-site = exit site - Moves along the mRNA from 5’ to 3’
- Identifies the start codon by the use of the Kozak box in eukaryotes
- One mRNA is screened by several ribosomes to produce large amounts of proteins quickly
What are the post-translational modifications?
1) Proteolysis; i.e., cleavage of the inactive precursors of enzymes
2) Glycosylation (addition of sugars “Glycosylation is required for the communication between protein”)
3) Phosphorylation (addition of a phosphate group on Ser or Thr residues)
4) Hydroxylation (Pro & Lys in collagen α chains)
- Then it is transported to the endoplasmic reticulum (EPR) for its folding
- Essential for the functioning of the protein
How many phosphate bonds are utilized in the process of AA activation for protein synthesis?
2
what catalyzes the hydrolytic step to release the polypeptide chain from the ribosome?
peptidyl transferase
GTP is required in which step in protein synthesis
the translocation of tRNA from A to P, this step is required by both eukaryotic and prokaryotic protein synthesis
what is the base sequence of the 3’ end?
CCA
What is shared in common between eukaryotic and prokaryotic cells regarding gene expression
Both prokaryotes and eukaryotes require RNA polymerase binding to an upstream promoter element
Where are the anti-codons located?
tRNA
