CH.5 & 8.1 practice questions

1. Why is DNA synthesis said to be “semiconservative”? Because it make a copy of itself

2. What role do DNA polymerase, DNA primase (a type of RNA polymerase),helicase, topoisomerase, RNase H, and ligase play in DNA replication?

Polymerase- builds complementary strands

DNA primase- creates RNA primer to start replication

RNA primer- degraded by RNase H and replaced with DNA nucleotides by DNA polymerase

DNA ligase connects fragment at start of new strand to end strand

Topisomerase unwinds DNA and then helicase breaks H bonds

3. What is the difference between how the leading strand and lagging strand arecopied during DNA replication? Why do they have to be synthesized differently in this fashion? Leading strand- transcribed in continuously in 5’ to 3’ direction

Lagging strand- transcribed in segments in 5’ to 3’ direction. Some functions perform differently

4. What would happen if insufficient RNase H were produced by a cell? What if insufficient ligase were produced by a cell?

Not enough RNase H then RNA primers would not be removed.

Not enough ligase, fragments would not be sealed together, both would have defective DNA

5. What are four key differences between DNA polymerase and RNA polymerase? (“they are difference molecules” doesn’t count as one!)

RNA doesn’t need a primer

RNA catalyzes bond between 3’ nucleotide and phosphate of incoming nucleotide

DNA catalyzes connection of nucleotides to form complementary DNA strand 5’-3’ direction

Transcription & translation

6. Compare and contrast codons and anticodons? Every 3 mRNA nucleotides is a codon specifies and amino acid, +RNA have an anticodon region that specifically binds to its codon.

7. What is alternative splicing? Why is it necessary in eukaryotes?Exons are coding regions, introns are removed, humans have 30,000 genes but produce 100,000 proteins, translation occurs in cytoplasm

8. During translation, what amino acid sequence would the following mRNA segment be converted into: AUGGACAUUGAACCG? Methionine , Aspartic acid, Isoleucine , Glutamic acid, Proline(MET-ASP-LLE-GLU-PRO)

9. How come there are only 20 amino acids when there are 64 different codons? It takes 3 codons to make up 1 amino acid, there are different combinations to make up an amino acid. There are 3 codons that stop

10. How come prokaryotes can both transcribe and translate a gene at the sametime, but eukaryotes cannot? In prokaryotes- termination occurs in different sites and translation can begin even before transcription has been terminated. In eukaryotes transcription continues past its site and terminates randomly.