BIO 1400 Lecture Notes - Lecture 2: Phosphodiester Bond, Pyrimidine, Purine
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There are four different nucleotides, four different building blocks. The phosphate group is always the same whether its dna or rna. Nitrogenous bases are either double ring structures (purines) or single ring (pyrimidines) The sugar phosphate backbone of the two two polynucleotides are on the outside of the helix. The variation in the backbone comes from the bases. Each phosphate group in the backbone has a negative charge. Dna or rna an entirely negative charge making it polar. Nucleotides are negatively charged because of the phosphate group. Every nucleotide bears a negative charge so the dna and rna are highly polar. Condensation/dehydration reactions: a molecule of water is stripped from the 2 monomers (together) and thus is formed. The 2 monomers are now connected by a covalent bond: in each polymer, the covalent linkage between the monomers gets its own name. In nucleic acids, the bond is called a phosphodiester bond.
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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. |