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Biology Chapter 14
DNA Structure and Function part 2. (14.3-14.6)
| Question | Answer |
|---|---|
| What are the three suggested models for DNA replication? Which one was correct? | Conservative, semi-conservative, and dispersive. Semi-conservative is correct. |
| Describe the semi-conservative model for DNA replication. | It suggests that each of the two parental DNA strands act as a template for new DNA to be made. After replication, each double-stranded DNA includes one parental and one new strand. |
| What experiment supports the semi-conservative model? | The experiment conducted by Meselson and Stahl where they grew E. coli and weighted it with N15 and N14 and observed the DNA weight. |
| What is DNA polymerase? | This enzyme adds nucleotides one-by-one to the growing DNA chain. |
| What is an NTP? | Nucleoside triphosphates. These can serve as energy sources and the source of DNA nucleotides. |
| What are the 3 main types of polymerases for prokaryotes? | DNA pol 1, DNA pol 2, and DNA pol 3. DNA pol 3 is enzyme required for DNA synthesis; DNA pol 1 is accessory enzyme for DNA replication and along with DNA pol 2, is primarily used for repair. |
| How does replication machinery know where to begin? | There are specific nucleotide sequences called "origins of replication." |
| What is helicase and what does it do? | This enzyme unwinds the DNA by breaking the hydrogen bonds between the nitrogenous base pairs. This needs ATP hydrolysis |
| What is a replication fork? | Y-shaped structure formed during initiation of replication. The two rep forks are made at origin of replication and these are extended bi-directionally. |
| What is a single-stand binding proteins? | This protein coats the single strands of DNA near the replication fork to prevent the single-stranded DNA from winding back into a double helix. |
| What are the two restrictions of on DNA polymerase? | It is only able to add nucleotides only in the 5' to 3' direction and it requires a free 3'-OH group to add nucleotides by forming a phosphodiester bond between 3'-OH end and 5' phosphate of next nucleotide. |
| What is RNA primase? | This enzyme makes an RNA segment that is 5-10 nucleotides long and complementary to the template DNA. |
| What is a primer? | This is a short stretch of nucleotides that is required to initiate replication; in the case of replication, the primer has RNA nucleotides. |
| What is a primase? | This enzyme makes the RNA primer; the primer is needed for DNA pol to start synthesis of a new DNA strand. |
| What is the difference between the leading strand and the lagging strand? | On the leading strand, DNA is synthesized continuously, where as the lagging strand synthesizes DNA in short stretches called Okazaki fragments. |
| What does DNA polymerase 1 do? | It replaces the RNA primer with DNA. |
| What does DNA polymerase 3 do? | It uses an RNA primer made by primase to make the daughter DNA strand (DNA synthesis). |
| What is topoisomerase and what does it do? | This enzyme breaks and reforms DNA's phosphate backbone ahead of the replication fork, preventing the over-winding of the DNA double helix. It nicks the DNA strand and then reseals it. |
| What is DNA ligase and what does it do? | This enzyme seals the gaps between the Okazaki fragments, joining the fragments into a single DNA molecule. |
| What are Okazaki fragments? | DNA fragment that is synthesized in short stretches on the lagging strand. Each fragment needs a primer to start the synthesis of DNA. |
| What is the overall direction of the lagging strand? | It runs 3' to 5' |
| What is the overall direction of the leading strand? | It runs 5' to 3', the reverse of the lagging strand. |
| What is the sliding clamp and what does it do? | It is a right-shaped protein that holds the DNA polymerase in place as it continues to add nucleotides by binding to the DNA. |
| What is DNA ligase and what does it do? | This enzyme seals the nicks that remain between the newly synthesized DNA and the previously synthesized DNA. It also catalyzes the formation of a phosphodiester linkage between the 3'-OH and 5' phosphate |
| How many origins of replications do prokaryotes vs eukaryotes have? | Prokaryotes usually just have one, while eukaryotes have multiple. |
| What is the rate of replication of prokaryotes vs eukaryotes? | Prokaryotes replicate 1000 nucleotides per second while eukaryotes replicate 50-100 nucleotides per second. |
| What is the eukaryotic equivalent to the sliding clamp? | PCNA (proliferating cell nuclear antigen) |
| What is the difference between prokaryotic and eukaryotic chromosomes? | Prokaryotic chromosomes are circular and eukaryotic chromosomes are linear. |
| What is a telomere? | DNA at the end of linear chromosomes. |
| What is telomerase and what does it do? | This enzyme contains a catalytic part of an inbuilt RNA template; it functions to maintain telomeres at chromosome ends. |
| When is telomerase typically active or inactive? | It is active in germ cells and adult stem cells but it isn't active in adult somatic cells. |
| What is proofreading? | A function of DNA polymerase in which it reads the newly added base before adding another one to see if it is correct. |
| What is a mismatch pair? | This is a type of repair where errors are corrected after replication is completed. |
| How do mismatch pair enzymes recognize which of the two bases are incorrect? | The nitrogenous base adenine acquires a methyl group. The parental DNA strand will have methyl groups whereas the newly synthesized strand lacks them. |
| What is a nucleotide excision repair? | This type of repair removes damaged bases from the synthesized DNA strand and not mismatched ones. |
| Define a mutation. | This is a variation in the nucleotide sequence of a genome. |
| What is an induced mutation? | These result from an exposure to chemicals or environmental agents. |
| What is a spontaneous mutation? | This mutation happens in the cells as a result of chemical reactions taking place naturally without exposure to any external agents. |
| What are the two types of substitution mutations? | Transitions or transversions. |
| What is transition substitution? | This refers to a purine or pyrimidine being replaced by a base of the same kind; a purine (adenine) replaced by another purine (guanine). |
| What is transversion substitution? | This refers to a purine being replaced by a pyrimidine, or vice versa. |
| What is a silent mutation? | A mutation that is not expressed. |
| What is a missense point mutation? | This results in an amino acid substitution. |
| What is a nonsense point mutation? | This substitutes a stop codon for an amino acid and therefore halts the replication. |
| What is a frameshift mutation? | An insertion or deletion of nucleotides resulting in a shift in the reading of the frame or insertion of a stop codon. |
Created by:
tali_Alley
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