Dr. Reichlerís Bio 212    Name:__________KEY_______________
Exam #1  15 June 2001

Answer each question as succinctly as possible.  You may use the back if you need more space than is provided below the question.  Each question is worth 6 pts, unless otherwise noted, for a total of 100 points.  Read each question carefully, and donít hesitate to ask if a question seems unclear.  You may use drawings to answer some of these questions, but be sure to include a written description in addition to the drawing.

1. a.  What are 3 differences between DNA and RNA?
Any three of:
DNA- double stranded, has Thymine, lacks Oin sugar, only found in nucleus, unchanging through life of cell
RNA- single stranded, has Uracil, has O in sugar, found in both nucleus and cytoplasm, constantly produced and degraded

b. Describe 3 bonds that you might find within a DNA molecule.  Include what type of bond each one is, and where the bond is found.
Covalent band between nucleotides in a single strand, Hydrogen bonds between each strand, Hydrogen bonds between bases to make double helix

2. a.  Describe how DNA is packaged in a non-dividing cell.  Include what is involved and what it does.
DNA strands are looped around histone proteins, then the histone/DNA complex is further wrapped together to form nucleosomes.

b. What are the differences in DNA packaging when a cell is dividing compared to when it is not?
A dividing cell has further levels of packing, the histone/DNA complexes are looped along protein scaffold to form chromosomes.

 c. How does acetylation affect gene expression?  Where does the acetyl group get added to have this affect?
Acetylation increases gene expression, the acetyl group is added to the histone which loosens the connection between DNA and histone thereby allowing transcription factors etc to have access to the DNA.

3. a.  This is a drawing of a replication bubble.  The origin of replication is labeled.  Draw arrows to show all of the possible directions DNA polymerase would be moving on each of the parental strands of DNA.

b.  What parts of the DNA replication process would and would not take place if primase was not functioning correctly?
Would-  Helicase would unwind DNA
Would not-  DNA polymerase would not be able to bind, and the DNA would not be replicated

c. What errors in DNA replication would take place in a cell with no ligase?
The Okazaki fragments would not get ligated together, and so the lagging strand would not be covalently bound together.

4. a.  What is necessary for RNA polymerase to begin making RNA from DNA?
Transcription factors binding to the promoter region which recruits RNA polymerase

b. Describe 3 parts of the DNA sequence that do not directly code for amino acids.
Any three of:  introns, promoter regions, the non-coding strand, space between genes, stop codon

5. a.  What 3 things happen to the mRNA after it is produced by RNA polymerase and before it is transported to the cytoplasm?
5' cap added (modified guanine), poly-A tail added, introns spliced out

b.  If the mRNA for a certain protein is not properly processed, what effect might that have on the production of the protein and why?  (4 pts)
Any one of:  If 5' cap or poly-A tail is left off then the mRNA will be rapidly degraded, and no or very little protein made.  If poly-a tail left off, then the mRNA will not be transported to the cytoplasm and no protein will be made.  If introns are not spliced, there will be extra sequence that will code for extra amino acids and the protein will be made incorrectly.

6. a.  Below is a mRNA molecule.  Draw and describe what is happening as this mRNA is being translated.

b. How many nucleotides code for each amino acid, and what is significant about this number?
Three.  One or two does not give enough possible combinations to account for all 20 amino acids.

7. Both transcription and translation have start and stop sites, but DNA replication only has a start site.  Why?
The complete DNA sequence is replicated, therefore no stop site is needed.
8.  Using Strong Inference write a brief proposal to answer the following question:  What is the function of the poly-A tail?  Since there is not time to perform experiments before this test is over, your proposal only needs to include information from Rule 1 and 2 of Strong Inference.  (12 pts)
Rule 1, Devise multiple hypotheses
Rule 2, Design experiments to eliminate one or more hypotheses