Exam 3 Review Questions

How many amino acids are in the eukaryotic protein, which has 3213 nucleotide long open reading frame, including the start and the stop codons?

1070 3213/3 = 1071 but do not count the stop codon so 1070 is right! The start codon counts because it translates to Met amino acid.

mRNA is translated in a _____ direction, and proteins are synthesized in a ____direction.

5' to 3'; amino to carboxy terminus

Methylation is an epigenetic change, which chemically modifies ____ in the chromosome.

DNA

During promoter recognition in prokaryotic transcription, this consensus sequence located (-10) is critical for holoenzyme binding.

Pribnow box

The selection of the starter methionine codon is helped by the ____ in prokaryotes and ____ in eukaryotes. Both sequences are at the 5' end of the mRNA.

Shine-Delgarno sequence; by the Kozak sequence

_______ activates the lac operon, when the _____ level is low.

The catabolite activator protein (CAP); glucose

Protein synthesis is terminated when _____.

The protein release factor binds to a stop codon at the A site of the ribosome

During rho-independent (intrinsic) termination of transcription in some bacteria, the formation _____ is critical.

a hairpin loop via inverted repeats

Which of the following conditions leads to maximal expression of the lac operon? a. lactose present, glucose absent b. lactose present, glucose present c. lactose absent, glucose absent d. lactose absent, glucose present

a. lactose present, glucose absent

In rho-dependent transcription termination, the rho factor initially binds to ______. a. mRNA b. DNA (near the end of the transcribed region) c. RNA polymerase d. the sigma subunit

a. mRNA *the rut site on mRNA

What binds to the -10 consensus sequence found in most bacterial promoters? a. the holoenzyme (core enzyme + sigma factor) b. the sigma factor alone c. the core enzyme alone d. mRNA

a. the holoenzyme (core enzyme + sigma factor)

When lactose is ______, the lac operon is _______, since a ________ binding to the operator within the operon.

absent; inactive; repressor is

Repressible operons are typical in _______, e.g., the ______. And inducible operons are typical in ______, e.g., the _______.

anabolic pathways; trp operon; catabolic pathways; lac operon

If glucose is absent, but so is lactose, the lac operon will be ______. a. activated b. repressed c. activated but only partially d. mutated

b. repressed

Which of the following RNA types is found only in eukaryotes? a. tRNA b. snoRNA c. mRNA d. rRNA

b. snoRNA

The anticodon for tryptophan (Trp) is 5'-CCA-3'. Which mRNA codon would the Trp-tRNA pair with? a. 3'-CCA-5' b. 5'-CCA-3' c. 3'-UGG-3' d. 5'-UGG-3'

d. 5'-UGG-3'

Which of the following are involved in posttranscriptional control? a. control of RNA splicing b. control of RNA shuttling c. control of RNA stability d. all of the above

d. all of the above

Which of the following is a type of regulation of gene expression unique to eukaryotes? a. attenuation b. use of alternate sigma factor c. chemical modification of histones d. alarmones

d. chemical modifications of histones

Which component of translation is frequently targeted by antibiotics? a. tRNA b. IF-2 c. the template mRNA d. the ribosome

d. the ribosome *the ribosome is frequently targeted by antibiotics because of the difference in size (70S prokaryotic and 80S eukaryotic) and does not affect the host cell

Control of gene expression in eukaryotic cells occurs at which level(s)?

epigentic, transcriptional, posttranscriptional, translation, and posttranslational levels

tRNA molecules with different anitcodons for the same amino acids are called ______.

iso-accepting tRNAs

A mutation prevents the catabolite activator protein (CAP) from binding to the promoter in the lac operon. What will the effect of this mutation be on the transcription of the operon?

it has lost the ability to be positively regulated, thus the Lac operon will never be fully activated even in the presence of lactose

Only part of the mRNA molecule is translated into protein. This translated region is called_____.

open reading frame (ORF)

What are epigenetic modifications?

the addition of reversible changes to histone proteins and DNA *some reversible changes are acetylation of histone tails and methylation of DNA *tip always associate histones to epigenetics!

In E.coli the gene lacI codes for the lac operon repressor. Which of the following statements is true about an E. coli strain, which is lacI-, that is the null mutant for lacI. a. there would be no lac operon repression, thus lacA, lacZ, and lacY genes would be constitutively expressed regardless of the presence of lactose. b. there would be no lac operon repression, thus lacA, lacZ, and lacY genes would be expressed only in the presence of lactose. c. there would be no lac operon repression, thus lacA, lacZ, and lacY genes would be expressed regardless of the presence of glucose. d. there would be no lac operon, thus, lacA, lacZ, and lacY genes would be expressed in the presence of allolactose.

a. there would be no lac operon repression, thus lacA, lacZ, and lacY genes would be constitutively expressed regardless of the presence of lactose

The lac operon consists of a promoter that initiates transcription for the lacI gene, which encodes a repressor protein. A separate promoter, LacP, within the operon initiates transcription of lacZ, which encodes B-galactosidase, and lacY, which encodes permease. The operator, lacO, is the DNA sequence where the repressor protein binds to inhibit transcription, and is positioned between the promoter and the permease and B-galactosidase genes. In this problem, the superscript (u) denotes an uninducible mutation, whereas the superscript (c) denotes a constitutively active mutant, and the superscript (-) indicates a null allele. What best describes B-galactosidase regulation for the bacteria with the following genotype LacI+ LacPu LacO+ LacZ+ LacY+ a. inducible b. absent c. constitutive d. no correct answers

b. absent because B-galactosidase can be repressed but it cannot be turned on

In bacteria, the elongation stage of transcription is carried out by _____. a. the RNA polymerase holoenzyme enzyme b. the RNA polymerase core enzyme c. sigma factor d. the omega subunit e. all of the above

b. the RNA polymerase core enzyme

Which of the following statement is true? a. aminoacyl-transfer RNA synthetase has no proofreading activity b. tRNA spontaneously reacts with an amino acid , since this reaction is thermodynamically favorable c. Aminoacyl-transfer RNA synthetase links the carboxyl group of an amino acid to a tRNA ribose hydroxyl group through an ester bond d. only on enzyme is needed to charge all tRNAs with the appropriate amino acid

c. Aminoacyl-transfer RNA synthetase links the carboxyl group of an amino acid to a tRNA ribose hydroxyl group through an ester group

In eukaryotes, what initially binds to the TATA box on the DNA template? a. sigma factor b. RNA polymerase c. TFIID d. mediator

c. TFIID

An operon encoding genes that are transcribed and translated continuously to provide the cell with constant intermediate levels of the protein products is said to be which of the following? a. repressible b. inducible c. constitutive d. activated

c. constitutive

The lac operon consists of a promoter that initiates transcription for the lacI gene, which encodes a repressor protein. A separate promoter, LacP, within the operon initiates transcription of lacZ, which encodes B-galactosidase, and lacY, which encodes permease. The operator, lacO, is the DNA sequence where the repressor protein binds to inhibit transcription, and is positioned between the promoter and the permease and B-galactosidase genes. In this problem, the superscript (u) denotes an uninducible mutation, whereas the superscript (c) denotes a constitutively active mutant, and the superscript (-) indicates a null allele. What best describes Permease (LacY) regulation for the bacteria with the following genotype LacIuLacP+LacOcLacZ-LacY+/LacI+LacP+LacO+LacZ+LacY- a. absent b. uninducible c. constitutive d. no correct answers

c. constitutive LacY is constitutive present because normal LacI+ is present on the right side and this is trans!

When tryptophan is present in sufficient quantities, the trp operon is ____, since the _____ binds to the operator within the operon.

turned off; tryptophan-activated repressor