Biology 1002B Lecture Notes - Lecture 14: Guanine, Deoxyribose, Dna Ligase
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20 Apr 2016
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[lecture 7 genome replication summary] September 30, 2013: purine and pyrimidine base- pairing in dna/rna. Two of the bases (adenine and guanine) are purines and the other two (thymine and cytosine) are pyrimidines. Purines bond with pyrimidines (a and t, c and g). These relationships are chargaff"s rules. In rna, thymine is replaced with uracil. The base pairing remains the same (a with u) This is complementary base pairing. The deoxyribose sugars are linked by the breaking of phosphate groups. This means dna polymerase can only add molecules at the 3i end (on the hydroxyl group) Because of the anti- parallel nature of dna, the template strand is read in the 3i to 5i end. The other must be replicated in short strands called okazaki fragments away from the replication fork. Leading strand: the new strand of dna synthesized in the direction of unwinding.
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QUESTION 1. Compared to eukaryotic genomes, only prokaryotic genomes:
A. contain DNA organized by histones. |
B. contain usually one, circular chromosome. |
C. contain plasmid DNA. |
D. have chromosomes contained in a nucleus. |
QUESTION 2. Azathioprine is a drug that may be prescribed to transplant recipients to reduce the chance of tissue rejection reactions. In its active state, it acts as a purine analogue, inhibiting DNA biosynthesis. This means that 6-mercaptopurine will be inserted in place of a purine containing nucleotides during DNA replication. Given this drug's mode of action, you would expect it to be incorporated into DNA in place of:
A. nucleotides containing guanine or cytosine. |
B. nucleotides containing adenine or thymine. |
C nucleotides containing adenine or guanine. |
D. nucleotides containing guanine nucleotide or uracil. |
QUESTION 3. RNA is distinguished from DNA because only RNA:
A. typically exists as a single-stranded molecule. |
B. has a 3' to 5' directionality. |
C. is composed of nucleotides that contain the sugar deoxyribose. |
D. is composed of nucleotides that contain the nitrogen bases T, C, G, and A. |
QUESTION 4. How are RNA nucleotides different from DNA nucleotides? To be marked correct, you'll need to select all true statements, as there may be more than one correct answer.
A. RNA nucleotides do not contain thymine. |
B. RNA nucleotides use the sugar ribose, while DNA nucleotides do not. |
C. RNA nucleotides lack phosphate. |
D. RNA nucleotides incorporate pyrimidine nitrogen bases, while DNA nucleotides only incorporate purine nitrogen bases. |