Genetics, Summer 2008                                              Name ______________

Exam 3

1. You have a sample of DNA.  You dilute your sample by a factor of 10 and then measured the A260 in a spectrophotometer.  You determine the value to be 0.5 nm.  What was the original concentration of your DNA sample?  Show your work. (3.5 points)

0.5 X 10 X 50 = 5 X 50 = 250 ug/ml

2. Pick one of the following techniques that use hybridization.

-PCR, Southern Blot, FISH. 

a. Which technique are you going to answer – PCR, Southern Blot or FISH?

b. What are the two molecules that hybridizing and are allowing to renature in this technique? (3 points)

c. How will you determine if the 2 molecules hybridized? (3 points)

PCR, 2 DNA molecules, electrophoresis

Southern Blot, 2 DNA molecules, autoradiogram or radioactive tag

FISH, chromosomal DNA + another DNA molecule, avidin biotin complex would fluoresce.

3.     Would the reassociation curve of E. coli which shows the C_ot values be to the LEFT or the RIGHT of the reassociation curve for viruses?  Circle one answer. (3 points)

It would be to the right since E. coli is more complex and larger than viruses.

4.     The following picture shows a gel after electrophoresis was performed? Is there anything wrong with the following gel?  If not, state what size band A is.  If you think there is a problem, then just state what the problem is. (3 points)

Large bands should be at the top and not at the bottom.

5.     What are 3 steps that are repeated in PCR?  Write them in the correct order in which they occur? (3 points)

Denature, anneal, extend

6.     The following diagram represents a transcription unit in a hypothetical DNA molecule:

7.      

5’TCG ATG ACA CAA ………….TTG ACA ATT CGC CGA CGT ACG GTT ATA ATA TAC GGC ATC GTC3’

3’AGC TAC TGT GTT ………….AAC TGT TAA GCG GCT GCA TGC CAA TAT TAT ATG CCG TAG CAG5’

1. Would you expect to find this sequence in a prokaryotic or eukaryote?  Explain why.  (3 points)

Prokaryote, TTGACA, TATAAT

2. Which strand is the template strand and which is the nontemplate strand? (3 points)

Bottom strand is template

3. What direction would transcription occur? (3 points)

To the right

8.     What are two ways that transcription is different between prokaryotes and eukaryotes? (8 points)

9.     What are two ways that DNA replication is different between prokaryotes and eukaryotes? (8 points)

Prokaryotes – bidirectional synthesis, Euk – multiple replication origins

Prokaryotes – no histones, Eukaryotes – histones must be removed first

Pro – PolyI and III

Euk – a, g poly.

Prok – circular DNA

Euk – linear DNA

10.  What are two ways that DNA replication is similar between prokaryotes and eukaryotes? 5’ to 3’ synthesis, use ligase on discontinuous strand, DNA unwinds, etc. (8 points)

11.  Describe two ways that DNA replication and transcription are different in prokaryotes? (8 points)

DNA replication requires a primer and transcription does not.

All of the DNA is replicated and both strands are used in replication while in transcription, only one strand of DNA is used and not all of it is copied.

14. If you had the following DNA molecule, what would be the amino acids produced from the N to C terminus of the protein? (3 points)

5’GCTTGCAAG3’

3’CGAACGUUC5’

1. Arg, Thr, Phe
2. Phe, Thr, Arg
3. Ala, Cys,Lys
4. Lys, Cys, Ala

Answer c

12.  Draw a hypothetical ribosome with a polypeptide attached and draw and label the following parts: (2 points each)

1. small ribosome subunit
2. large ribosome subunit
3. the 5’ and 3; ends of the mRNA
4. the tRNA
5. the A, P and E sites
6. Label where the release factor for translation will bind
7. Label the N and C terminal regions of the polypeptide 

In your diagram, make sure the A,P,E sites and the tRNA and mRNA are associated with the correct ribosomal subunit.

17. Translation is terminated because (3 points)

a.      a stop codon is reached on the mRNA

b.     a release factor is encountered at the A site on the tRNA

c.      a tRNA signaling stop is encountered

d.     answers a and b

e.      answers a, b and c

answer d

18.    In the following table, circle ALL of the words that are associated ONLY with prokaryotes.  If it is found in BOTH prokaryotes and eukaryotes, then you should not select it.  HINT:  There are 8 correct answers.  This question is worth 4 points but if you circle more than 8, I will deduct more than 8 points.

19.  In the following table, circle all of the words that are associated with ONLY translation.  These factors might be found in eukaryotes or prokaryotes.  As long as it is found in translation, then it is a correct answer.   If it is all involved with replication or transcription, then you should NOT select this as an answer. HINT:  There are 9 correct answers.  This question is worth 4.5 points.  If you circle more than 9 choices, I will deduct more than 4.5 points.

20. Describe two posters of noble Prize winners.

Poster 1 (6 points)

1. What was the person’s name?
2. Describe what they discovered?
3. Why was this important in their time and in our time?

Poster 2 (6 points)

A. What was the person’s name?

B. Describe what they discovered?

C.Why was this important in their time and in our time?

Extra credit:  5 points

How many different mRNA sequences can code for a polypeptide chain with the amino acid sequence Met-Ala-Ser?  Be sure to also include the stop codons. Explain how you arrived at this answer.

1 for Met

4 for Ala

6 for Ser

3 for stop

24X3 = 72