Ch 14-3 Flashcards
What are the three stages of transcription?
Initiation, Elongation, Termination
What is the transcription initiation complex composed of?
RNA polymerase, aided by other smaller molecules, and transcription factors. Transcription factors can bind to or block RNA polymerase.
What unique sequences are part of the promoter and termination portions of the template DNA in eukaryotes?
The promoter region contains a TATA box, which is a sequence with lots of thymine and adenine.
The termination region includes a polyadenylation sequence of adenine with stop codons to signal the end of the transcript.
What end modifications are added to the mRNA transcript in eukaryotes?
A modified guanine is added to the 5’ end and adenine is added to the 3’ end.
What is the action of a spliceosome?
It removes introns, cutting out the internal aspects of the transcript.
What is an anticodon?
It is a region of tRNA that binds to and recognizes the codon on the mRNA.
It is complementary to the 5’ to 3’ mRNA sequence.
How are amino acids attached to tRNA?
Amino acids are attached to the 3’ end of the tRNA by aminoacyl-tRNA synthetases.
Each amino acid has a unique enzyme that produces an aminoacyl tRNA, also known as a charged tRNA.
What are the roles of the P site, A site, and E site in a ribosome?
P site - binds tRNA, which holds the growing polypeptide chain.
A site - binds the tRNA that brings in the next amino acid.
E site - discharges tRNA from the ribosome.
What happens during the initiation stage of translatio
The small subunit of a ribosome binds to mRNA and initiator tRNA. The initiator tRNA always carries methionine and aligns with the AUG start codon. The large subunit joins to form the translation initiation complex. This assembly requires proteins called initiation factors and GTP hydrolysis.
What is a signal peptide?
It is a sequence of about 20 amino acids that targets a ribosome to the endoplasmic reticulum. If a ribosome encounters a signal peptide, it will switch from a free state to a bound state.
Which of the following is NOT a stage of transcription?
○
A. Initiation
○
B. Translocation
○
C. Elongation
○
D. Termination
B
The TATA box is a sequence found in the:
○
A. Promoter region of DNA
○
B. Termination region of DNA
○
C. Anticodon region of tRNA
○
D. P site of a ribosome
A
Spliceosomes are responsible for:
○
A. Adding a 5’ cap to mRNA
○
B. Adding a poly-A tail to mRNA
○
C. Removing introns from pre-mRNA
○
D. Transporting tRNA to the ribosome
C
The anticodon of a tRNA molecule is complementary to:
○
A. The amino acid it carries
○
B. The rRNA in the ribosome
○
C. The codon on the mRNA
○
D. The signal peptide
C
Aminoacyl-tRNA synthetases are enzymes that:
○
A. Synthesize tRNA molecules
○
B. Break down tRNA molecules
○
C. Attach amino acids to tRNA molecules
○
D. Transport tRNA molecules to the ribosome
C
The growing polypeptide chain is held by the tRNA in the:
○
A. A site
○
B. P site
○
C. E site
○
D. Initiation complex
B
The first amino acid in a polypeptide chain is usually:
○
A. Alanine
○
B. Glycine
○
C. Lysine
○
D. Methionine
D
The movement of mRNA through the ribosome during translation occurs in the:
○
A. 5’ to 3’ direction
○
B. 3’ to 5’ direction
○
C. N-terminus to C-terminus direction
○
D. C-terminus to N-terminus direction
A
A release factor binds to the ribosome when:
A. The initiation complex forms
B. A peptide bond is formed
C. The tRNA translocates
D. A stop codon is reached
D
Polyribosomes allow for:
○
A. Multiple ribosomes to translate a single mRNA molecule simultaneously
B. Transcription and translation to occur simultaneously
C. The production of different proteins from a single mRNA molecule
D. The degradation of mRNA molecules after translation
A
The process of turning RNA into an amino acid sequence is called
Translation
tRNA molecules contain an __ that recognizes the codon on the mRNA.
Anticodon
The __ hypothesis explains why some tRNAs can recognize more than one codon.
Wobble
Ribosomes are composed of __ and proteins.
rRNA
The __ is where rRNA is synthesized and processed in eukaryotes.
Nucleolus
The ___ of the ribosome joins the initiation complex during the initiation stage of translation
Large subunit
__ factors are proteins involved in the elongation stage of translation.
Elongation
The formation of a peptide bond between amino acids is catalyzed by __.
rRNA
A __ targets a ribosome to the endoplasmic reticulum.
SIGNAL PEPTIDE
__ ribosomes can be found in both bacteria and eukaryotes.
Polyribosomes
T/f
The 5’ end of an mRNA molecule in eukaryotes is modified with adenine.
F
The 5’ end of an mRNA molecule in eukaryotes is modified with guanine.
T/f
tRNA molecules have a twisted and folded L-shape.
T
T/f
There are approximately 64 different tRNAs, one for each codon.
F
There are approximately 45 different tRNAs. Some tRNAs can recognize more than one codon.
T/f
Aminoacyl-tRNA synthetases ensure that the correct amino acid is attached to the appropriate tRNA.
T
T/f
Ribosomal proteins catalyze the formation of peptide bonds.
F
rRNA catalyzes the formation of peptide bonds.
T/f
The small subunit of the ribosome binds to the mRNA first during termination.
F
The small subunit of the ribosome binds to the mRNA first during initiation
T/f
GTP hydrolysis is required for both the initiation and elongation stages of translation.
T
T/f
The polypeptide chain grows from the N-terminus to the C-terminus.
T
T/f
Stop codons code for specific amino acids that signal the end of translation.
False
Stop codons do not code for amino acids. They signal the end of translation and are recognized by release factors.
T/f
Polypeptides can undergo post-translational modifications, such as folding and the addition of molecules like sugars or lipids.
T
