Genome Organization & Regulation of Gene Activity
KEY TERMS
structural gene
regulator gene
operator
operon
promoter
inducer
repressor
activator
repressible enzymes
inducible enzymes
cAMP-CAP complex
intron
exon
chromatin
histone proteins
enhancers
transcriptional control
posttranscriptional control
QUESTIONS
1. Using a diagram, describe how the cAMP-CAP aids in the control of the lac operon
2. Explain why the models for the control of gene transcription in bacteria are not directly
applicable to eukaryotes.
3. Explain how a chromosome can contain large quantities of DNA.
4. What are histone proteins?
5. Explain "transcriptional control". Be sure to include transcription factors and activators.
6. What are transposons and what significance do they have?
7. Explain "post transcriptional control".
8. Why must gene activity be regulated?
9. What is a Genetic Mutation?
10. What is a Frameshift mutation? Give an example of how it affects the DNA.
11. What is a point mutation?
12. What is worse a point mutation or a frameshift mutation? Why?
13. Explain how nonfunctional proteins can have an effect on phenotype.
14. What are some causes of mutations?
1. The figure above depicts the DNA-protein complex that is assembled at the transcriptional
start site of gene X when the expression of gene X is activated in liver cells. Previous studies
have shown that gene X is never expressed in nerve cells. Based on the diagram, which of the
following most likely contributes to the specific expression pattern of gene X ?
(A) Expression of gene X produces large amounts of tRNA but undetectable amounts of mRNA.
(B) The general transcription factors inhibit the activation of gene X in liver cells by blocking the
activator from binding to RNA polymerase II.
(C) The activator is a sequence-specific DNA-binding protein that is present in some tissues but
not in other tissues.
(D) The enhancer is a unique DNA segment that is added to the nuclear DNA of some cells of an
organism during the process of mitotic cell division but not other cells.
Questions 2-5 refer to the following proteins and gene sequences and match each with the correct
description.
(A) Reverse transcriptase
(B) DNA polymerase
(C) DNA helicase
(D) Operator
(E) Promoter
2. Binds a repressor protein
3. Binds RNA Polymerase
4. Responsible for synthesizing DNA from a DNA template.
5. Breaks hydrogen bonds during replication
6. Which of the following is a true statement regarding gene regulation in prokaryotes?
(A) Nuclear DNA may be modified prior to transcription
(B) RNA is modified in the nucleus before translation
(C) Repressors may act to turn off operons in both inducible and repressible operons
(D) Genes are likely “on” when histone proteins are methylated.
(E) Genes are likely “on” when DNA is tightly condensed around histone proteins
7. Which of the following statements regarding eukaryotic splicing is correct?
I. Exons are excised before transcription.
II. Introns are excised before translation.
III. Introns are excised before leaving the nucleus.
(A) I only
(B) II only
(C) III only
(D) I and III only
(E) II and III only
8. The amount of expressed mRNA present in the eukaryotic cytoplasm may be influenced by all
of the following EXCEPT:
(A) the presence of a poly (A) tail
(B) the average length of introns
(C) the methylation of DNA
(D) the presence of activator proteins
(E) the acetylation of hisone proteins
9. Which of the following best explains why a human kidney cell is different from a human
pancreatic cell?
(A) Pancreatic cells contain DNA that is different from kidney cells.
(B) Pancreatic cells contain different RNA polymerases when compared to kidney cells.
(C) Pancreatic cells contain additional chromosomes when compared to kidney cells.
(D) Different ribosomes are active in pancreatic cells when compared to a kidney cell.
(E) Different sets of genes are “on” in a pancreatic cell when compared to a kidney cell.
Free Response
1. Gene regulation is important for proper cellular function.
A. Describe how the prokaryotic operon works. Relate operons to homeostasis by including
descriptions of events that may turn genes “on” and “off.”
B. Thoroughly describe 4 mechanisms of eukaryotic gene regulation.
2. Feedback loops and other control mechanisms are important to the homeostasis of a cell. The
hypothetical enzyme xyzase is able to break down the hypothetical sugar xyzose.
Thoroughly describe the way in which the xyz operon might exhibit negative feedback
regulation in order to maintain homeostasis in a bacterium. Be sure to comment on the
significance of all of the functional portions of the operon and the associated proteins.