Chapter 14
Chapter 15
Chapter 16
Catch All
100
What's the difference between anabolism and catabolism? Of the learned operon systems, which fits in each category?
anabolism: building up a product, repressed by molecules it creates, i.e. trp operon catabolism: breaking down a molecule, induced by molecule that's broken down, i.e. lac operon
100
What are three types of covalent modifications of histones? Will each increase or decrease tx?
methylation: decrease Acetylation: increase phosphorylation: increase
100
What are the two types of double-stranded RNAs STP mentioned in class? Describe each and their role with translation.
miRNA: micro, represses translation, interacts with a host of mRNAs siRNA: small-interfering, added in experimentally, usually only interacts with 1 mRNA
100
Which of the following is NOT a way in which transcription factors become activated? A. alternative splicing B. dimerization C. covalent modification D. ARE elements E. sequestration
A, D
200
Describe how is cAMP related to cellular glucose levels.
low Glc -> high cAMP; if Glc is low, there's less glycolysis so less ATP production thus a higher level of AMP which gets converted to cAMP
200
True or False: removing entire histones from DNA leads to loose, heterochromatin-like structure and decreased transcription.
False: removing histones results in looser, unwound DNA but it is MORE accessible to tx machinery
200
Name and describe the two methods of mRNA stabilization.
PolyA tail length: longer = more stable, so can be translated more often Destabilizing sequence (ARE): generally in 3' UTR of mRNA, between stop codon and PA tail, bound by protein that that targets mRNA for degradation
200
Low iron levels are to high ________ levels as low cAMP levels are to high ________ levels.
transferrin, glucose
300
What would happen in the lac operon system if lactose and glucose are ample in the cellular environment?
lactose/Glc high means cAMP is low, no inducer binding to CAP activator, lactose binds the repressor so tx levels are low
300
An individual genome mutation leads to the increased transcription of transacetylase enzymes, molecules that acetylate DNA. In a strand of DNA acted upon by transacetylase, would you expect transcription to increase or decrease and why?
increase by acetylation leads to histones not being bound within DNA as easily b/c of added charges so DNA is more free without these proteins
300
What are the two important structures related to Fe regulation in a cell? When Fe is high in the cell, which structure's genes are translated less and how does this happen?
transferrin and ferritin; when Fe is high it binds to IRP and keeps it from binding to IRE, when IRE is not bound transferrin translation goes down
300
What are the three major ways in which histones are modified? What is the result of each modification? How is this the result?
acetylation: increased tx, loss of +/- interaction between backbone and histones so unravels methylation: decreases tx, inhibits activator proteins phosphorylation: increases tx, adds very (-) charge so repulsion b/n histone and backbone increases
400
Would a mutation that inactivated the lac repressor and prevented it from binding to the lac operator site result in constitutive expression of the lac operon under all conditions? Explain. What's a disadvantage of constitutive expression of it?
not necessarily, only if it was in a glucose absent environment b/c high glucose would inhibit transcription; wastes energy to transcribe genes not needed
400
Tx factors usually contain one or more motifs that play key roles in their function. What is the function of the following motifs? A. helix-turn-helix B. zinc finger C. leucine zipper
A. DNA binding, sits in major and minor grooves B. DNA binding, binds zn atoms allowing it to sit in major groove C. protein dimerization of 2 tx factor proteins
400
Suppose a vertebrate organism carries a mutation that causes some cells that normally differentiate into nerve cells to become muscle cells instead. Analyzing the mutation reveals that it was in a gene that encodes a methyltransferase. Explain how an alteration in a methyltransferase could produce this phenotype.
the MT could be responsible for methylating and thereby inhibiting a gene that causes a cell to become a muscle cell. the MT could be inactivated by the mutation so it is unable to methylate the gene and inhibit its expression
400
An individual consumes a diet deficient in thiamin, one of the major constituents of TPP, an important coenzyme for correct functioning of the citric acid cycle. How would this affect the riboswitch operation of the thi operon for both tx and tl?
low thiamin means TPP is likely not being produced in great amounts thus b/c TPP is low tx and tl can be completed b/c TPP is not binding to the RNA and conformationally changing it
500
In the lac operon, how would gene expression be affected if one of the following segments was missing? a. lac operon promoter b. operator site c. lacA gene
A. no tx would take place and lac operon wouldn't be expressed B. no regulation would take place, constitutive expression C. none of transacetylase would be made but rest of operon would work
500
Briefly describe three ways that ATP-dependent chromatin-remodeling complexes may change chromatin structure.
1. change position of nucleosomes, 2. evict histones, 3. replace histones with histone variants i.e. with covalent modifications
500
Imagine that the an organism becomes infected with a virus that destroys ferritin's ability to form its tertiary structure and its capacity of iron storage. Would this individual experience increased or decreased transferrin translation and how? Should they be careful of iron consumption?
decreased transferrin production b/c excess Fe is binding IRP and taking it off the IRE so transferrin mRNA is degraded. b/c of excess Fe the individual should not consume as much
500
The 3-4 stem loop and U-rich attenuator found in the trp operon is an example of rho-independent termination. Think back to the function of rho-independent terminators described in ch. 12. Would you expect attenuation to occur if the tryptophan levels were high and mutations at the end of the trpL gene changed the UUUUUUUU sequence to UGGUUGUC? Explain why or why not.
U-rich region is disrupted with the G's and C's so it would prevent attenuation; the U rich region is responsible for mRNA dissociation and with fewer U's and more G's and C's that have more hydrogen bonds it's less likely to happen
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