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Exam 1 bio tech
chap 16
| Question | Answer |
|---|---|
| Given a polynucleotide sequence such as GAATTC, explain what further information you would need in order to identify which is the 5' end. | You can't tell which end is the 5' end. You need to know which end has a phosphate group on the 5' carbon (the 5' end) or which end has an —OH group on the 3' carbon (the 3' end) |
| What role does complementary base pairing play in the replication of DNA? | Complementary base pairing ensures that the two daughter molecules are exact copies of the parental molecule. When the 2 strands of the parental molecule separate, each serves as a template on which nucleotides are arranged into new complementary strands. |
| Identify two major functions of DNA pol III in DNA replication. | DNA pol III covalently adds nucleotides to new DNA strands and proofreads each added nucleotide for correct base pairing |
| What is the relationship between DNA replication and the S phase of the cell cycle? | In the cell cycle, DNA synthesis occurs during the S phase, between the G1 and G2 phases of interphase |
| If the DNA pol I in a given cell were nonfunctional, how would that affect the synthesis of a leading strand? | Synthesis of the leading strand is initiated by an RNA primer, which must be removed and replaced with DNA, a task that could not be performed if the cell’s DNA pol I were nonfunctional. |
| . Describe the structure of a nucleosome, the basic unit of DNA packing in eukaryotic cells. | A nucleosome is made up of eight histone proteins, two each of four different types, around which DNA is wound. Linker DNA runs from one nucleosome to the next |
| . What two properties, one structural and one functional, distinguish heterochromatin from euchromatin? | Euchromatin is chromatin that becomes less compacted during interphase and is accessible to the cellular machinery responsible for gene activity. Heterochromatin remains condensed during interphase and contains genes inaccessible to this machinery |
| What provided the first evidence that genetic material is DNA | Experiments with bacteria and phages |
| What does it mean when we say that the two DNA strands in the double helix are antiparallel? What would an end of the double helix look like if the strands were parallel? | Each strand in the double helix has polarity; the end with a phosphate group on the 5' carbon ofthe sugar is called the 5' end the end with an — OH group on the 3' carbon ofthe sugar is called the 3' end. The two strands run in opposite directions. |
| What model of replication does DNA follow | DNA replication is semiconservative: The parental molecule unwinds, and each strand then serves as a template for the synthesis of a new strand according to base-pairing rules |
| How does DNA Poly repair | proofread new DNA, replacing incorrect nucleotides |
| How does mismatch repair repair | , enzymes correct errors that persist |
| How does “nucleotide excision repair work | a process by which nucleases cut out and other enzymes replace damaged stretches of DNA. the ends of eukaryotic chromosomal DNA get shorter with each found of replication |
| What do telemeres do? | The presence of telomeres, repetitive sequences at the ends of linear DNA molecules, postpones the erosion of genes. Telomerase catalyzes the lengthening of telomeres |
| Compare DNA replication on the leading and lagging strands, including similarities and differences. | On both lead and lag strands, DNA poly adds onto the 3' end of an primer. synthesizing DNA in the 5' - 3' direction. the lead strand synthesises continuously into the fork. The lag strand is synthesized bit by bit away from fork. Same Rate |
| what is chromatin in a eukaryotic cell made up of | DNA, histones, and other proteins. |
| nucleosomes | the most basic units of DNA packing. histones bind to each other and to the DNA to form nucleosomes |
| What is the basis for the difference in how the leading and lagging strands of DNA molecules are synthesized? | DNA polymerase can join new nucleotides only to the 3' end of a pre-existing strand, and the strands are antiparallel. |
| In analyzing the number of different bases in a DNA sample, which result would be consistent with the base-pairing rules? | A+G=c+T |
| The elongation of the leading strand during DNA synthesis | depends on the action of DNA polymerase |
| In a nucleosome, the DNA is wrapped around | Hiatones |
| E. coli cells grown on N15 medium are transferred to N14 medium and allowed to grow for two more generations (two rounds of DNA replication). DNA extracted from these cells is centrifuged. What density distribution of DNA would you expect in this experime | one low-density and one intermediate-density band |
| chemist combines in a tube molecules needed for replication. When she adds some DNA to the mixture, replication occurs, but each DNA molecule consists of a normal strand paired with numerous segments of DNA a few 100 nucleotides long. What she leave out? | DNA ligase |
| The spontaneous loss of amino groups from adenine in DNA results in hypoxanthine, an uncommon base, opposite thymine. What combination of proteins could repair such damage? | nuclease, DNA polymerase, DNA ligase |
| chargoffs rules | dna base composition varies between species A and T bases equal for each species |
| DNA composition | Phosphate sugar backbone, 4 nitrogenous bases; adenine guanine cytosine thymine linked by sugar phosphate bonds held together by hydrogen bonds |
| purines | adenine and guanine |
| pyramdines | thymines and cytosine |
| dATP | Adenine nucleotide used to make DNA |
| Replication steps | 1 primase makes primer to attach to origin and first okazaki 2 poly 3 works on lead while also finishing okazaki 3 poly 3 leaves and starts to work with primer on next okazaki |
| Replication steps 2 | 4 poly 1 removes RNA primer from completed okazaki and adds DNA 5ligase connects okazakis 6 poly 1 replaces RNA primer from origin leaving an open 3' |
| nucleotide excision repair combo | 1 Nuclease takes out fucked up dna 2 polymerase addds new dna 3 ligase connects dna segments |
| DNA Replication | process by which DNA is copied |
| Transformation | a change in genotype and phenotype due to the assimilation of external DNA |
| phage | bacteria eater |
| double helix | shape of dna 2 antiparrellel strands spiralling around an imaginary axis |
| antiparrell | arrangement of sugar phosphate backbones in a DNA double helix. Run in opposite 5-3' direction |
| origin of replication | where DNA replication begins. Prokaryotes have single origin eukaryotes have many |
| Helicase | enzyme that unwinds the double helix of DNA at fork, seperating 2 strands and using them as templates |
| single strand binding proteins | holds template strands apart as DNA synthesis takes place |
| toposmerase | protein that rejoins DNA strands. Keeps strands not involved in replication from tangling |
| Primer | Short RNA nucleotide chain with a 3' end that is needed to initiate replication |
| primase | enzyme that makes primer |
| Poly III | adds DNA to primer to complete DNA strands. Adds nucleotides to 3' end of existing chain. |
| Poly 1 | Remove primer RNA, and adds DNA |
| okazaki | 1000-2000 nukes in ecoli, 100-200 nukes in eukaryo |
| ligase | connects okazakis |
| mismatch pair | the cellular process that uses specific enzymes to remove and replace incorrectly paired nucleotides |
| chromotin | complex of dna and proteins that make up chromosomes |
Created by:
Virajasaur