48 Questions
During transcription, what is the function of RNA polymerase?
Synthesize an RNA version of the instructions stored in DNA
Which strand of DNA is used as the template during transcription?
One strand of DNA, known as the template strand
What type of nucleotides does RNA polymerase use during transcription?
Ribonucleoside triphosphates (NTPs)
What is the role of the non-template (coding) strand during transcription?
It matches the sequence of the mRNA (except U for T)
In bacteria, how many RNA polymerases are involved in transcription?
One
What is a characteristic feature of eukaryotic transcription start sites?
Presence of a TATA box
Which organism's RNA processing is more extensive?
Eukaryotes
How does translation initiation and termination complexity compare between bacteria and eukaryotes?
More complex in eukaryotes
What did Crick propose regarding the interaction between mRNA codons and amino acids?
An adapter molecule holding the amino acid in place while interacting with a codon
How are amino acids transferred from tRNAs to polypeptides?
Through the interaction of tRNAs with mRNA codons
In eukaryotes, how many general transcription factors are involved in transcription?
Many
What is a characteristic feature of bacterial promoter structure?
Proteins that associate with promoter
What is the role of the Shine–Dalgarno sequence in translation initiation in bacteria?
It is the binding site for the small ribosomal subunit
What does the initiator tRNA carry in bacteria during translation initiation?
Modified methionine (f-Met)
What occurs at the start of elongation in translation?
The initiator tRNA is in the P site and the E and A sites are empty
What is the composition of the ribosome's active site where peptide bond formation occurs?
Consists of ribosomal RNA
When does translocation occur in the ribosome?
When it slides one codon toward the 3′ end of the mRNA
What happens during translocation in the ribosome?
Movement of tRNAs and exposes a new codon for aminoacyl tRNA binding
What triggers the termination of translation?
When the A site encounters a stop codon
What is the next step after the arrival of aminoacyl tRNA during translocation?
Peptide bond formation
What occurs at the start of translation initiation in bacteria?
mRNA binding
What happens to most proteins before they become functional?
Undergo post-translational modification and extensive processing steps
What is crucial for determining a protein's function?
Protein folding
Where does the ribosome move during translocation in translation?
One codon toward the 3′ end of the mRNA
Which direction does RNA polymerase perform template-directed synthesis?
5' → 3'
What is the length of bacterial promoters?
40–50 base pairs
What is the function of sigma protein in bacterial transcription initiation?
Binds to the −35 and −10 boxes
How does termination occur in bacterial transcription?
RNA polymerase transcribes a termination signal
What distinguishes eukaryotic transcription from bacterial transcription?
Promoters
What is the role of spliceosomes in eukaryotic transcription?
Catalyze RNA splicing
How many distinct types of RNA polymerases do eukaryotes have?
Three
What is the function of the holoenzyme in bacterial transcription initiation?
Binds to the −35 and −10 boxes
What is the sequence of the −10 box in bacterial promoters?
TATAAT
What is the sequence of the −35 box in bacterial promoters?
TTGACA
What occurs during elongation in bacterial transcription?
RNA polymerase reads the DNA template and adds nucleotides to the 3’ end of the RNA
What was revealed by the discovery of split eukaryotic genes in 1977?
Presence of noncoding DNA (introns) and coding DNA (exons)
What is the function of adding a 5' cap and a poly(A) tail to pre-mRNAs?
To prevent degradation and enable translation
Where are untranslated regions (UTRs) found in mature mRNAs?
At both ends
What is the role of transfer RNA (tRNA) in translation?
To link amino acids to the growing polypeptide
How are amino acids attached to tRNA?
With the help of aminoacyl-tRNA synthetases
What allows tRNAs to read the 61 different codons?
Wobble pairing in the anticodon's third position
Where do tRNAs fit into during translation in the ribosome?
A site (acceptor or aminoacyl), P site (peptidyl), and E site (exit)
What is the site of protein synthesis according to the pulse-chase experiment by Britten and colleagues?
Ribosomes
In bacteria, when can ribosomes begin translating an mRNA?
Before transcription is complete
How are transcription and translation related in eukaryotes?
They are separated, with mature mRNAs being transported to the cytoplasm for translation
What is the role of the small subunit of ribosomes during translation?
It holds mRNA
How many tRNAs are there in most cells?
About 40
What is the length of transfer RNA (tRNA)?
75-95 nucleotides
Study Notes
Overview of Transcription and Translation Processes
- Pre-mRNAs undergo processing which includes adding a 5' cap and a poly(A) tail to protect against degradation and enable translation.
- Mature mRNAs contain untranslated regions (UTRs) at both ends.
- Translation is a complex process involving ribosomes, mRNA, and tRNAs.
- A pulse-chase experiment by Britten and colleagues showed that ribosomes are the site of protein synthesis, where proteins are synthesized and then released.
- In bacteria, ribosomes can begin translating an mRNA before transcription is complete, forming a polyribosome and producing many copies of a protein from one mRNA.
- In eukaryotes, transcription and translation are separated, with mature mRNAs being transported to the cytoplasm for translation by ribosomes and polyribosomes.
- Transfer RNA (tRNA) is used as the adapter molecule in translation, linking amino acids to the growing polypeptide.
- tRNAs are relatively short, 75-95 nucleotides long, and contain a CCA sequence at the 3' end as the amino acid binding site and an anticodon for mRNA codon binding.
- Amino acids are attached to tRNA with the help of aminoacyl-tRNA synthetases, with each amino acid having a specific synthetase.
- There are about 40 tRNAs in most cells, which can read the 61 different codons through wobble pairing in the anticodon's third position.
- Ribosomes, containing proteins and ribosomal RNA (rRNA), have a small subunit that holds mRNA and a large subunit where peptide bonds form during translation.
- During translation, tRNAs fit into three sites in the ribosome: A site (acceptor or aminoacyl), P site (peptidyl), and E site (exit) where tRNAs without amino acids exit the ribosome.
Test your knowledge of transcription and translation processes with this quiz. Explore key concepts such as mRNA processing, ribosome function, tRNA structure, and the intricacies of translation in both prokaryotes and eukaryotes.
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