chapter 10

Question 1

what is a nucleotide vs nucleoside?

Answer 1

• nucleotide is composed of a nitrogenous base, a pentose sugar and a phosphate group
• nucleoside is just a nitrogenous base plus a phosphate suagr with no phosphate gorup

Question 2

deoxyribose vs ribose?

Answer 2

deoxyribose is found in DNA

ribose is found in RNA

Question 3

what are the 5 nitrogenous bases and their classifications?

Answer 3

• adenine
• guanine
• cytosine
• thymine
• uracil
  
  • adenine and guanine are purines
  • cytosine, thymine and uracil are pyrimidines

Question 4

uracil is a demethylated version of?

Answer 4

• thymine

Question 5

phosphate groups interact with the 3’ and 5’ C’s of the pentose sugar to form?

Answer 5

• phosphodiester bonds
  
  • the 3’ C is the one that has a downward pointing hydroxyl group on the left side of the nucleotide as usually portrayed, and the 5’ C is the one sticking up on the left

Question 6

what other role do nucleotides play in the body?

Answer 6

• cAMP and cGMP
• ATP and GTP
• FAD, FMN, NAD, NADP⁺ and CoA

Question 7

what is base pairing?

Answer 7

• caused by the formation of H bonds between complementary nucleotides
  
  • C and G- 3 H bonds
  • A and T or U- 2 H bonds
    
    • purines pair with pyrimidines

Question 8

what is Chargaffs rule?

Answer 8

• purines and pyrimidines will be present in a cell at a 1-1 ratio
  
  • C equals amount of G
  • T equals amount of A

Question 9

double-stranded DNA has what kind of orientation?

Answer 9

• antiparallel

Question 10

what are the 3 forms of DNA

Answer 10

• A DNA- “tighter helix” because most dehydrated, right handed. 11 b.p./turn, 23 A/10 b.p.
• B-DNA- most common 10.5 b.p./tuen, 34 A/10 b.p., right handed
• Z-DNA- “looser” DNA 12 b.p./turn. 38A/10 b.p., left-handed

Question 11

A DNA segment that is overwound or underwound is referred to as being?

Answer 11

• positively or negatively supercoiled
  
  • such supercoiling is a function of torsional strain in the molecule
  • under physiological conditions, DNA is usually negatively supercoiled

Question 12

what is hybridization?

Answer 12

• the process in which complementary base pairs combine
  
  • the driving force is the formation of the H bonds between the complementary bases
  • a single inconsistency between the nucleotides positioned along either of the 2 strands will decrease the energetic favourability of the strands annealing

Question 13

the temperatue at which half of the DNA strands of a sample are preesent in their single-stranded (ssDNA) state is defined as?

Answer 13

• the melting temperature (Tm) of the nucleic acid
  
  • the Tm depends on the length and the nucleotide sequence of a molecule
  • denaturation can also cause the dissociation of complementary strands by chemical means, using denaturants as urea

Question 14

melting curves of A and T and G and C

Answer 14