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41 Cards in this Set
- Front
- Back
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What are the components of a nucleotide?
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1. Pentose Sugar- deoxyribose
2. Nitrogenous Base 3. Phosphate Group with 2 or 3 linkages attached to the 5 carbon of the sugar |
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Nitrogenous bases are divided into two sub-groups. What are they are which bases are in which group?
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Purines- Adenine, Guanine
(Gods Are Pure) Pyrimidines- Thymine, Cytosine, Uracil |
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Each nitrogenous base has a nucleoside- what are they?
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A nucleoside is that sugar and base, add a phosphate and it's a nucleotide. Adenosine, Guanosine, Cytidine, Thymidine are the nucleosides.
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Nucleotides are linked together by which type of bond?
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phosphodiester bonds
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Describe the two ends of a polynucleotide.
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5'-P end- free tri-phosphate group
3'-OH end- free hydroxyl these give polarity to DNA |
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In which direction are new nucleotides added during DNA synthesis?
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Occurs in the 5'-3' direction. The new nucleotide added to the 3'-OH. The beta and gama phosphates of the nucleotide are removed as a pyrophosphate molecule.
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How many hydrogen bonds are on nucleotide pairs?
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G-C has 3 hydrogen bonds
A-T (or A-U) has 2 hydrogen bonds |
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How many chromosomes does a somatic human cell have?
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23 pairs, 46 chromosomes. 22 autosomes, 1 sex chromosomes.A map of all 46 is called a karyotype
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What is cytogenetic mapping?
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The method of mapping a gene to a particular band of the chromosome
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Describe the arms of a chromosome.
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Each has two arms, a p (short) and q (longer) arm. Arms are separated by a pinched region called a centromere.
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What is chromatin?
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Complex of DNA and Proteins that make up a chromosome. Proteins consist of histone and non-histone proteins.
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What is the basic unit of chromosome structure?
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A nucleosome- a bead on a string of chromatin, includes 200 nucleotide pairs. Nuclease free a 'bead' from the string, salt dissociates it from the histone core.
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What makes up the octameric histone core of a nucleosome?
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2x H2A, 2x H2B, 2x H3, 2x H4
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Describe the bending of DNA around a histone.
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AT rich minor grooves positioned toward the protein, G-C rich minor groves on the outside.
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After DNA wraps around an octomeric histone, it is further packed in two ways. What are they?
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By histone H1 molecules and by histone N-terminal tails.
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How does the cell access the DNA in the chromatin structure for replication?
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ATP-driven chromatin remodeling complexes and enzymatic modification of the histone N-terminal tails.
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DNA serves as a template for it's own replication, what is this type of replication called?
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semi-conservative
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What enzyme catalyzes DNA synthesis?
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DNA polymerase
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In which direction does DNA strand elongation occur?
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5'-3', requires a primer and a free 3' end.
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Describe a leading strand.
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At the opening of a replication fork, one end is opening in the 3'-5 direction, so replication occurs quickly in the 5' to 3' direction in the same direction as the fork.
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Describe a lagging strand.
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At the opening of a replication fork, one end opens in a 5' to 3' direction, so replication must occur in pieces (Okazaki fragments) to occur in the 5' to 3' direction.
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Four proteins are involved in DNA replication, what are they?
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1. DNA primase- synthesizes RNA primers.
2. DNA polymerase- synthesizes new DNA fragments. 3. RNAse H- erases RNA primer. 4. DNA ligase- joins gaps in Okazaki fragments. |
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What does DNA helicase do?
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pry apart the double helix through hydrolysis of ATP.
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What do single strand DNA binding proteins do?
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binds to single strand DNA in front of DNA polymerase to prevent them from forming 'hairpins' using cooperative binding.
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What does a sliding-clamp protein complex do?
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holds the DNA polymerase on the DNA template.
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What does DNA topoisomerase do?
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prevents DNA tangling during replication
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The lecture describes 4 proof-reading mechanisms because there is one mutation for every billion nucleotides. What are they?
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1. Affinity of DNA polymerase for correct dNTP
2. 5'-3' polymerization 3. 3'-5' exonucleotide proof-reading 4. Mismatch repair |
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What are the two categories of point mutations?
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1. transitions- purine to purine or pyrimidine to pyrimidine
2. transversions- purine to pyrimidine or visa versa. |
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Some DNA mutations can occur post-replication. What can cause this?
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Chemical agents- deamination agents, alkylating agents, intercalculating agents. Physical mutagens- UV and Ionizing radiation.
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At what point does a DNA mutation becomes permanent and inherited?
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If mismatched DNA in maintained to the level of DNA replication.
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What is direct repair?
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Occurs after damage to DNA. A mismatch is switched for the right one.
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What is excision repair?
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Occurs after damage. A damaged nucleotide is excised and then resynthesized.
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What is mismatch repair?
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Same as excision repair except occurs after replication and is of a mismatch instead of a damaged nucleotide.
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What is recombination repair?
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Repairs a double strand break.
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What are common causes for 1) colon, 2) skin and 3) breast, ovarian, and prostate cancer respectively.
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Problems with 1) mismatch repair 2)nucleotide excision repair and 3)repair by homologous recombination.
Remember that they are due to mutations in DNA repair components. |
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Why does recombination occur?
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To provide variability without sacrificing fidelity. Important for meiosis.
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What is general (homologous) recombination?
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The breaking and joining of two homologous DNA double helices to exchange genetic material. Catalyzed by RecA proteins. Occurs in meiosis.
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What is a Holiday Junction?
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A cross-strand exchange complex involved in general recombination.
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What is site specific recombination?
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The movement of specialized nucleotide sequence between non-homologous sites. Uses transposons (mobile genetic elements, cut and paste) or retrotransposons (copy and paste).
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What are the three classes of transposable elements?
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1. DNA Transposons
2. Retroviral-like retrotransposons 3. Nonretroviral retrotransposons |
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What are the four nucleotides?
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Only nucleotides with triphosphates act as substrates for DNA.
Deoxyadenosine 5-triphosphate (dATP, A) Deoxycytidine 5-triphosphate (dCTP, C) Deoxyguanosine 5-triphosphate (dGTP, G) Deoxythymidine 5-triosphate (dTTP, T) |
