Biology 111B Study Questions 16: Gene Regulation
1. A brain cell differs from a liver cell because: (circle ALL correct answers)
a. they contain different genesb. they express different genes
c. they use a different genetic code
d. they have different ribosomes
2. In eukaryotes, most of the genes in each cell are active. ____True____ False
3. Regulation of _____________ is the most common form of control of gene expression.
a. genetic contentb. transcription
c. translation
d. enzyme activity
4. Define the following terms:
operon
operator
effector
activator
positive control
negative control
repressible operon
inducible operon
5. How can you recognize whether a system is under positive or negative control?
6. What is typically the function of genes that are in repressible operons? In inducible operons?
7. What molecule typically serves as the effector in repressible operons? In inducible operons?
8. Describe how each of the following control systems would work.
a. an inducible operon under positive control
b. a repressible operon under positive control
c. an inducible operon under negative control
d. a repressible operon under negative control
9. Can an operon have more than one control system? Describe how both positive and negative control works in the lac operon (see Campbell et al. pp. 337-341)
10. For both inducible and repressible sequences, think about the effects of mutations in the following sites. Assume the mutations prevent binding of what would normally bind. Would each mutation cause the genes to be constantly turned on or constantly turned off?
Mutation Constantly ON or OFF? DNA-binding domain of a repressor protein
control element
promoter
effector in an inducible system
effector in a repressible system
operator
DNA-binding domain of an activator protein
11. What is the effect in inducible and repressible sequences of a molecule that binds to the effector binding site but does not change the shape of the DNA binding site the way the effector does?
12. In a particular system, a mutation in the regulator-binding site on the DNA (such that the regulator protein cannot bind to the DNA) causes transcription to be always on. Is this system under positive or negative control? How do you know?
What would be the answer if the same kind of mutation caused transcription to be always off?
13. In an inducible operon under positive control, what effect on transcription would the following scenarios have?
a. A compound that binds to the effector site on the regulatory protein in place of the effector and causes the regulatory protein to be unable to bind to the DNA.
b. A compound that binds to the effector site on the regulatory protein in place of the effector and causes the regulatory protein to be permanently atttached to the DNA.
14. What are two chemical modifications that more or less permanently "turn off" transcription in regions of DNA?
15. The amount of protein made from a given mRNA molecule depends mostly on
a. the degree of DNA methylationb. the rate at which the mRNA is degraded
c. the presence of certain transcription factors
d. the number of introns present in the mRNA
e. the types of ribosomes present in the cytoplasm
16. What is an enhancer and how does it work?
17. What is meant by the "DNA-binding domain" of a protein?
18. In what ways can the amount of protein product be regulated after transcription has occurred?
19. Prokaryotes have operons that coordinate the control of related genes. How do eukaryotes accomplish coordinated control of related genes that might be scattered over many chromosomes?