Biology 1002B Lecture Notes - Lecture 15: Dna Ligase, S Phase, Polynucleotide
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20 Apr 2016
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September 29, 2013: 2a watson and crick brought together information from several sources to work out dna structure. Dna contains four difference nucleotides. Each nucleotide consists of the 5- c sugar deoxyribose, a phosphate group, and one of the four nitrogenous bases (atcg) Adenine and guanine are purines(nitrogenous bases built from a pair of fused rings of carbon and nitrogen atoms. Thymine and cytosine are pyramidines (built from a single carbon ring) A=t, c=g this is known as chargaff"s rules. Dna contains nucleotides joined to form a polynucleotide chain. In the chain, the deoxyribose sugars are linked by phosphate groups in an alternating sugar- phosphate- sugar- phosphate pattern, thereby forming a sugar- phosphate- backbone. Entire linkage including the bridging phosphate group is called a phosphodiester bond. Polynucleotide chain of dna has polarity (directionality) At one end of the chain, a phosphate group is bound to the 5" carbon of the sugar 5" end.
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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. |