4 RNA polymerases RNA processing Splicing of pre-mrna Introns Vs exons tRNA Protein synthesis Post-transitional modifications Chaperone protein Flashcards
RNA polymerases have no proofreading function in ____ (prokaryotes/eukaryotes).
Eukaryotes
A gardener finds a cap mushroom and decides to eat it. Later, liver failure develops. How did this happen?
The mushrooms likely contain α-amanitin, which inhibits RNA polymerase II and causes severe hepatotoxicity
In eukaryotes, ____ makes tRNA, ____ makes mRNA, and ____ makes rRNA
RNA polymerase
III; II; I
Of the RNA types, ____ is the largest RNA, ____ is the most abundant RNA, and ____ is the smallest RNA.
mRNA; rRNA; tRNA (massive, rampant, and tiny, respectively)
In prokaryotes, which enzyme makes rRNA, mRNA, and tRNA?
RNA polymerase (one single multisubunit complex)
Where does RNA polymerase II open DNA?
At the promoter site
What is rifampin’s mechanism of action?
Inhibition of RNA polymerase in prokaryotes
What is actinomycin D’s mechanism of action?
Inhibition of RNA polymerase in both prokaryotes and eukaryotes
Where does eukaryotic RNA processing occur?
In the nucleus
Which three modifications take place during eukaryotic RNA processing?
Capping on the 5′ end, polyadenylation on the 3′ end, and splicing out of introns
Approximately how many adenosine monophosphates are added to the 3′ end of mRNA during polyadenylation?
200
What is the term for the initial (unprocessed) RNA transcript in eukaryotes?
Heterogeneous nuclear RNA (hnRNA)
What function does the sequence AAUAAA serve in eukaryotes?
Polyadenylation signal
Poly-A polymerase ____ (does/does not) require a template.
Does not
A science experiment is done to add the 7-methylguanosine cap. Where does this occur in the cell?
In the nucleus—it is added to the 5′ end of the hnRNA
What is the role of cytoplasmic P-bodies in RNA processing?
Location of mRNA quality control—accomplished using exonucleases, decapping enzymes, and micro-RNAs
What binds to a primary mRNA transcript and forms a spliceosome?
Small nuclear ribonucleoprotein particles (snRNPs) and other proteins
snRNPs form a lariat-shaped loop in order to do what?
Isolate an intron for removal
A patient presents with a malar “butterfly” rash and renal disease. What antibodies does her disease make?
She has lupus, associated with spliceosomal snRNP antibodies (anti-Smith); mixed connective tissue disease (MCTD) has anti-U1 RNP antibodies
____ (Exons/Introns) contain the genetic information to code for protein.
Exons (exons exit and are expressed)
What is the name for the intervening noncoding segments of DNA within a gene?
Introns (introns are intervening sequences and stay in the nucleus)
β-thalassemia mutations can result from ____, a process that combines exons to make unique proteins in different tissues.
Alternative splicing, which, in this case, yields a pathologic protein
What mechanism allows the same gene to encode for multiple proteins?
Alternative splicing
A patient’s cancer cells undergo genetic analysis. What splicing-related phenomenon may be implicated in the tumor’s initial oncogenesis?
Abnormal splicing variants
What part of a tRNA lies opposite from its 3′ aminoacyl end?
The anticodon end
Which three-nucleotide sequence do all eukaryotic and prokaryotic tRNAs have at their 3′-ends?
CCA (Can Carry Amino acids)
• Where on a tRNA does the amino acid that will be incorporated into the protein bind?
The 3′ end
Does charging a tRNA molecule with an amino acid require energy?
Yes, as ATP is hydrolyzed in the process
If a tRNA had a methionine bound to it, what would the sequence of the codon it binds read, in 5′-to-3′ order? And the anticodon?
Codon = AUG; anticodon = CAU
• What are the substrates of the reaction that is catalyzed by aminoacyl-tRNA synthetase (the “matchmaker”)?
The uncharged tRNA and the appropriate amino acid, ATP
What does aminoacyl-tRNA synthetase do?
It scrutinizes the amino acid before and after it binds to tRNA, hydrolyzing the bond if an incorrect amino acid is present
Which sequence is necessary for tRNA-ribosome binding?
Thymine, pseudouridine, cytosine (TΨC), found on the T-arm
What is the purpose of the D-arm?
Ensures identification by the correct aminoacyl-tRNA synthetase
What hypothesis states that only the first two positions of a triplet codon on mRNA have a precise pairing with the tRNA anticodon?
Wobble hypothesis
The wobble hypothesis primarily explains the ____ (unambiguous/degeneracy/universal/commaless) nature of the genetic code.
Degeneracy
What are the two subunits of the eukaryotic ribosome called?
The 60S subunit and the 40S subunit—40S + 60S leads to 80S (Eukaryotic = Even)
____ (Eukaryotes/Prokaryotes) have ribosomes with 50S and 30S subunits.
Prokaryotes; 30S + 50S leads to 70S (prOkaryotes are Odd)
A scientist studying protein synthesis wants to block initiator methionine tRNA. He makes an inhibitor blocking the A site. Will this work?
No, as the initiator methionine tRNA does not bind at the A site (it is the sole exception; all other aminoacyl-tRNA combinations bind here)
At the start of protein synthesis, what process occurs at the same time as the hydrolysis of methionine’s bond with its tRNA?
The formation of a peptide bond between methionine and the second amino acid in the polypeptide
When referring the “P site” of a ribosome, what does the “P” stand for?
Peptide—the P site accommodates the growing polypeptide chain
Which molecules are responsible for assembling the 40S subunit with the initiator tRNA?
Eukaryotic initiation factors (IFs)
In what direction relative to the mRNA does the ribosome shift after the formation of a peptidyl bond?
Toward the 3′ end
When the ribosome shifts after the formation of a peptidyl bond, to what position does the tRNA with the growing peptide chain go?
The P site (translocation)
What molecule provides the energy for the binding of tRNA to the ribosome/mRNA complex?
Guanosine triphosphate (GTP tRNA = Gripping)
What molecule provides the energy for the translocation of the ribosome along the mRNA?
Guanosine triphosphate (GTP tRNA = Going places)
When the ribosome shifts after the formation of a peptidyl bond, where is the uncharged tRNA found?
• In the E position (holds Empty tRNA as it Exits
In protein synthesis, what are the three steps of protein elongation?
Aminoacyl-tRNA binding to A site, transfer of growing peptide chain to amino acid at the A site by the ribsome, and, finally, translocation
A patient takes an antibiotic that blocks the prokaryotic 30S subunit from assembling. How does it interfere with protein synthesis?
It inhibits formation of the initiation complex, causing misreading of mRNA
• A patient with a MRSA infection takes an antibiotic that inhibits translocation by binding the 50S subunit. Does this affect human cells?
No—the 50S subunit is prokaryotic, so human cells are minimally targeted by this drug
In termination, what recognizes the stop codon and frees the completed protein from the ribosome?
Release factor
What is an example of protein trimming after translation?
Removing N- or C-terminal propeptides from a zymogen to yield a mature protein (example: conversion of trypsinogen into trypsin)
A scientist wants to write about covalent alterations. Name six kinds of posttranslational protein modifications that are involved.
Phosphorylation, glycosylation, hydroxylation, methylation, acetylation, and ubiquitination
• What is a chaperone protein?
An intracellular protein that is involved in facilitating and/or maintaining protein folding
A scientist studies Hsp60, a protein expressed in yeast to prevent misfolding at high temperatures. How are these proteins classified?
Heat shock proteins̬class of chaperone proteins that facilitate and maintain proper protein folding)
