DOC PREVIEW
MIT 7 03 - Study Guide

This preview shows page 1-2-3 out of 9 pages.

Save
View full document
View full document
Premium Document
Do you want full access? Go Premium and unlock all 9 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 9 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 9 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 9 pages.
Access to all documents
Download any document
Ad free experience

Unformatted text preview:

Name: ___________________________ 7.03 - Genetics - Fall 2004 Massachusetts Institute of Technology Professor Chris Kaiser Professor Gerry Fink Professor Leona Samson 1Name: ___________________________ 2Name: ___________________________ 1. Drawn below is part of a wild-type gene. The DNA sequence shown encodes the last amino acids of a protein that is normally 380 amino acids long. The bracketed codon indicates the correct reading frame of this gene. The lower strand of the gene is used as the template during the transcription of mRNA from this gene. …GCTAAGTATTGCTCAAGATTAGGATGATAAATAACTGG–3’ …CGATTCATAACGAGTTCTAATCCTACTATTTATTGACC–5’ (a, 6 pts) In the copy of the sequence drawn below, circle one base pair that you could change to make a mutant form of the gene that produces a protein that is now 381 amino acids long. Indicate the identity of one new base pair that could take its place. …GCTAAGTATTGCTCAAGATTAGGATGATAAATAACTGG–3’ …CGATTCATAACGAGTTCTAATCCTACTATTTATTGACC–5’ (b, 6 pts) In the copy of the sequence drawn below, draw a slash between two base pairs where you could add one extra base pair in order to make a single mutant form of the gene that produces a protein that is 373 amino acids long. …GCTAAGTATTGCTCAAGATTAGGATGATAAATAACTGG–3’ …CGATTCATAACGAGTTCTAATCCTACTATTTATTGACC–5’ (c, 9 pts) Multiple mutant suppressor tRNAs could suppress the early termination defect in part (b) by allowing a longer protein to be produced from that mutant form of the gene. Make a list of all of the tRNA genes that could produce such mutant suppressor tRNAs if each tRNA gene contained a single base substitution. (Use the notation: “ala-tRNA.”) 3Name: ___________________________ 2. You are studying the regulation of a bacterial gene called nytT, which is expressed only when the bacterial strain is grown in the dark. You isolate two mutations, nytA1– and nytB1–, which affect the regulation of nytT. Genotype Is nytT expressed in the dark? Is nytT expressed in the light? Strain 1 nytA+ nytB+ nytT+ (wild type) yes no Strain 2 nytA1– nytB+ nytT+no no Strain 3 nytA+ nytB1– nytT+no no Strain 4 nytA+ nytB+ nytT+ / F’ nytA1–yes no Strain 5 nytA+ nytB+ nytT+/ F’ nytB1–yes no You grow P1 phage on an otherwise wild-type strain that contains a transposon insertion carrying a gene that confers tetracycline resistance. The transposon insertion in this strain is linked to the nytT locus with a cotransduction frequency of 85%, and this insertion does not alter normal nytT regulation. You use the resulting lysate to infect a nytA1– strain, and select for tetracycline resistance. None of the 30 Tetr cotransductants you examine express the nytT gene under any conditions. You obtain the same results when you use the same P1 lysate to infect a nytB1– recipient strain. (a, 5 pts) Can you conclude if nytA1– is constitutive or uninducible? If so, state whether nytA1– is constitutive or uninducible, and state what was the most important piece of information (for example, which strain in the table) you used to reach your conclusion. (b, 5 pts) Can you conclude if nytA1– is dominant or recessive? If so, state whether nytA1– is dominant or recessive, and state what was the most important piece of information (for example, which strain in the table) you used to reach your conclusion. 4Name: ___________________________ (c, 8 pts) Can you conclude if nytA1– acts in cis or in trans with respect to nytT? If so, state whether nytA1– acts in cis or in trans, and state what was the most important piece of information (for example, which strain in the table) you used to reach your conclusion. (d, 10 pts) Diagram all possible models for regulatory pathways for nytT that can explain the behavior of the nytA1– and nytB1– mutations. (Please diagram only linear pathways in which each gene is controlled by no more than one regulator. Please do not include any steps that invoke unknown players.) For each model, include only the following: wild-type nytA, nytB, and nytT, and “bright light.” 5Name: ___________________________ 3. After you perform the experiments from Question #2, you decide to continue studying the regulation of the bacterial gene nytT, which is expressed only when the bacterial strain is grown in the dark. You decide to map the two mutations, nytA1– and nytB1–, which you isolated in Question #2. Please refer to the table in the introduction to Question #2 for information about how these mutations affect the regulation of nytT. You find that the nytA and nytB loci are linked using P1 cotransduction experiments. You isolate a transposon insertion that carries a gene encoding kanamycin resistance. This transposon insertion is near to, but not between, the nytA and nytB loci. (a, 6 pts) You grow P1 phage on an otherwise wild-type strain that contains the transposon insertion carrying kanamycin resistance. You use the resulting lysate to infect a nytB1– strain, and select for kanamycin resistance. Drawn below are the E. coli chromosome and the DNA transduced by P1 during this cotransduction experiment. (Please note that these drawings are not to scale.) Redraw the DNA transduced by P1 so that it lines up with the homologous region of the E. coli chromosome. Then draw in the recombination events necessary to achieve the cotransduction of Tn-Kanr and the nytB locus. Tn-KanralaA+trpA+ thrA+sucA+araA+malA+galA+alaA+ileA+nytB1–leuA+valA+lacA+trpA+ 6Name: ___________________________ (b, 5 pts) In the transduction experiment described in part (a), out of a total of 50 Kanr cotransductants, 15 can express the nytT gene in the dark and 35 cannot. Express the distance between the transposon and the nytB locus as a cotransduction frequency. To map the nytA and nytB loci, you set up two reciprocal crosses: In the first cross, you grow P1 phage on a Kanr strain that contains the transposon insertion and the nytA1– mutation, and use the resulting phage lysate to infect a nytB1– strain. You select for kanamycin resistance (Kanr), and among 100 Kanr transductants, you find that only 13 are able to express nytT. (All 13 show normal nytT regulation.) In the second cross, you grow P1 phage on a Kanr strain that contains the transposon insertion and the nytB1– mutation, and use the resulting phage lysate to infect a


View Full Document

MIT 7 03 - Study Guide

Documents in this Course
Exams

Exams

22 pages

Exams

Exams

64 pages

Exam 1

Exam 1

66 pages

Exam I

Exam I

93 pages

Exam Two

Exam Two

12 pages

Exams

Exams

27 pages

Exam 1

Exam 1

41 pages

Load more
Download Study Guide
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Study Guide and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Study Guide 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?