DNA Structure

Question 1

Nucleosides

Answer 1

a 5 carbon sugar (pentose) bound to a nitrogenous base and are formed by covalently linking the base to C - 1’ of the sugar

Question 2

Nucleotide

Answer 2

when one of more phosphate groups are attached to C - 5’ of a nucleoside.

high energy compounds because of the energy associated with the repulsion between closely associated negative charges on the phosphate groups

building blocks of DNA

Question 3

if the pentose is ribose, the nucleic acid is

Answer 3

RNA

Question 4

if the pentose is deoxyribose, the nucleic acid is

Answer 4

DNA

Question 5

a molecule is aromatic if:

Answer 5

the compound is cyclic
the compound is planar
the compound is conjugated
the compound has 4n+2

Question 6

key features of the DNA double helix:

Answer 6

• the two strands of DNA are antiparallel; the strands are orientated in opposite directions.
• the sugar phosphate backbone is on the outside of the helix with the nitrogenous bases on the inside
• complementary base pairing
• the amount of A equals the amount of T and the amount of G equals the amount of C (the total of purines will always be equal to the total of pyrimidines overall) (Chargaff’s rules)

Question 7

A and T pairing is via _____;

C and G pairing is via

Answer 7

2 hydrogren bonds; 3 hydrogen bonds

the C & G pairing have a stronger interaction

Question 8

Chargaff’s rules:

Answer 8

%A = %T
%G = %C

Question 9

B DNA vs Z DNA

Answer 9

Z DNA is way too unstable therefore too difficult to be used in research; has a high G & C content and high Salt concentration; left handed DNA

B DNA has major and minor grooves; right handed DNA

Question 10

Denaturation can be caused by

Answer 10

heat
alkaline pH
formaldehyde
urea

Question 11

Histones

Answer 11

small pack of proteins that contain DNA

Example of a nucleoprotein (acid soluble that tend to stimulate processes such as transcription)

Question 12

Heterochromatin

Answer 12

dark, dense and silent

Question 13

Euchromatin

Answer 13

light, uncondensed and expressed

Question 14

telomere

Answer 14

ends of chromosomes
contain high GC content to precent unraveling of the DNA

During replication, telomeres are slightly shortened, although this can be (partially) reversed by the enzyme telomerase.

Question 15

In eukaryotes, DNA is would around ______ to form nucleosomes

Answer 15

histone proteins (H2A,H2B,H3 and H4)

Question 16

Centromeres

Answer 16

located in the middle of chromosomes and hold sister chromatids together until they are separated during anaphase in mitosis.

Contain high GC content to maintain a strong bond between chromatids

Question 17

Replisome aka replication complex

Answer 17

a set of specialized proteins that assist the DNA polymerases

Question 18

Single stranded DNA binding proteins

Answer 18

proteins that keep the unbound strands from reannealing or being degraded

Question 19

_______ causes torsional strain on the DNA molecule, which can be released by ______, which creates nicks in the DNA molecule

Answer 19

Supercoiling; DNA topoisomerase II (DNA gyrase)

Question 20

DNA polymerase III

Answer 20

can synthesize a new stand of DNA; they read the template DNA 3’ to 5’ and synthesize the new strand 5’ to 3’

Question 21

leading strand

Answer 21

requires only one primer and can then be synthesized continuously in its entirety

Question 22

lagging strand

Answer 22

requires many primer and is synthesized in discrete sections called Okazaki fragments

Question 23

RNA primers can be removed by ____ or ____, and filled in with DNA by DNA polymerase I

Answer 23

DNA polymerase I; RNase H (eukaryotes)

Question 24

DNA ligase

Answer 24

can fuse the DNA strands together to create one complete molecule

closes the gaps between okazaki fragments

lack the proofreading ability

Question 25

Sliding clamp

Answer 25

helps to strengthen the interaction between DNA polymerases and the template strand