DNA Replication and Protein Synthesis

1. Why is DNA synthesis said to be “semiconservative”?
Tthe DNA that splits serves as a template for DNA synthesis, the template from the "old" DNA is combined with a new strand of DNA, resulting in two DNA strands composed of both a new and an old strand, therefore, semi-conservative.

2. What role do DNA polymerase, DNA primase (a type of RNA polymerase), helicase, topoisomerase, RNase H, and ligase play in DNA replication?
DNA polymerase: forms the complimentary strand in 5' to 3' (reads 3' to 5' )
DNA primase: create the formation of nucleotides (for RNA primer)
Helicase: breaks bonds between DNA strands
Topoisomerase: unwinds DNA strand
RNase H: removes the RNA primers
Ligase: "glues" the Okazaki fragments together

3. What is the difference between how the leading strand and lagging strand are copied during DNA replication? Why do they have to be synthesized differently in this fashion?
The synthesis of the leading strand is continuous while the lagging strand is done in Okazaki fragments since DNA polymerase can only read from the 5' to 3' direction; DNA synthese takes much more time in the lagging strand than the leading strand.

4. What would happen if insufficient RNase H were produced by a cell? What if insufficient ligase were produced by a cell?
Insufficient RNase H would leave the RNA primers still in tact and insufficient ligase would leave gaps between the fragments. As a result, the DNA would likely be defective.

5. What are four key differences between DNA polymerase and RNA polymerase? (“they are difference molecules” doesn’t count as one!)
-DNA requires a primer for synthesis, RNA does not
-RNA polymerase occurs only on one strand of DNA; each strand is a separate set of genes
-RNA polymerase acts as DNA polymerase, helicase, AND topoisomerase (performs three functions in one!) while DNA polymerase does only one function
-RNA nucleotide base pairing vs. DNA nucleotide base pairing during transcription (uracil vs. thymine)

6. Compare and contrast codons and anticodons.
Codons are 3-sequence nucleotide in mRNA, anticodons are tRNA that bind complimentary to the 3-sequence nucleotide in mRNA; anticodons are also dependent factors while codons are independent factors. Anticodons also carry a specific amino acid.

7. What is alternative splicing? Why is it necessary in eukaryotes?
Alternative splicing is the removal of introns, leaving exons to attack to themselves; when exons reform, they can be combined in different sequences which can create various proteins from the same gene which is necessary in eukaryotes.

8. During translation, what amino acid sequence would the following mRNA segment be converted into: AUGGACAUUGAACCG?
Met-Asp-Ile-Glu-Pro

9. How come there are only 20 amino acids when there are 64 different codons?
Many codons have the same amino acid code

10. How come prokaryotes can both transcribe and translate a gene at the same time, but eukaryotes cannot?
In eukaryotes, transcription occurs in the nucleus while translation occurs in the cytoplasm; prokayotes have no nucleus therefore they do both at the same time.

Insulin Review Article Questions

1. In what journal did this article appear? When?
Science, Vol. 208; 4 April 1980

2. What is the primary purpose of this paper?
Publications of findings in the nucleotide structure of preproinsulin mRNA

3. What is the structural difference between insulin and proinsulin?
ProInsulin is a precursor to insulin. Insulin has the variable C chain, while proinsulin does not.

4. What is complementary DNA (cDNA)?
A sequence of DNA nucleotides that chemically match the other strand of the double stranded structure.

5. What is meant by the "polyA tail" or "polyadenylation" of a gene?
It is the polypeptide attached to the end of chain A.

6. What is meant by the statement that "insulin A and B chains are highly conserved"?
The chains are protected from evolution (unchanging).

7. Which chain is most highly conserved?
A chain

8. What do the researchers believe is the purpose of the C chain?
To help form the 3-D shape of the proinsulin molecule

9. Why does it make sense that the C chain is more variable (less highly conserved) than the A chain and B chain?
The C chain just binds them together and doesn’t have such specific functions as chains A and B; also, the variability will not make the chain function differently.

10. What do the researchers believe is the purpose of the pre-peptide (D chain)?
To signal the transfer of the preproinsulin protein into the ER.

11. How does the human preproinsulin gene differ from rat preproinsulin (rat I and rat II)?
Different codons in the coding area.

12. What is the first codon in the coding region of the gene (at the start of the pre-peptide) and what is the first amino acid in the polypeptide?
AUG; methionine (Met)