Unit 2: Lecture 2

Question 1

In a set of 23 pairs of chromosomes, each chromosome has 2 chromatids. How many DNA double helices are there?

Answer 1

92

Question 2

How many chromatids does a chromosome have?

Answer 2

each chromosome has 2 chromatids before the cell divides

Question 3

How many pairs of homologous chromosomes do we have?

Answer 3

23

Question 4

Where does each chromosome in a pair of chromosomes come from?

Answer 4

one chromosome from mother, one from father

Question 5

What are the monomers of nucleic acids? What is its directionality?

Answer 5

nucleotides with 3’ and 5’ directionality based on numbering of ribose sugar

Question 6

Whta is a nucleotide?

Answer 6

nucleoside + phosphate groups

Question 7

What is a nucleoside?

Answer 7

ribose (in RNA) or deoxyribose (in DNA) sugar + base

Question 8

What is the nucleoside of adenine?

Answer 8

adenosine

Question 9

What is the nucleoside of guanine?

Answer 9

guanosine

Question 10

What is the nucleoside of uracil?

Answer 10

uridine

Question 11

What is the nucleoside of cytosine?

Answer 11

cytidine

Question 12

What is the nucleoside of thymine?

Answer 12

thymidine

Question 13

What is the nucleoside in ATP?

Answer 13

adenosine

Question 14

What are nucleotides important carriers of?

Answer 14

chemical energy (ie. ATP)

Question 15

What are nucleotides in DNA and RNA linked by?

Answer 15

phosphodiester bonds

Question 16

Which carbon would a nucleoside triphosphate be added to a growing nucleic acid?

Answer 16

3’

Question 17

What are the levels of structure of DNA?

Answer 17

primary (sequence)
secondary (double-helix)
tertiary (chromatin)

Question 18

What is the double-stranded DNA structure due to?

Answer 18

non-covalent interactions:

• H-bonds between bases
• stacking hydrophobic reactions

Question 19

What features of Watson and Crick’s double helix model of DNA are energetically favoured due to increased entropy of
water?

Answer 19

the base pair cluster inside the double helix

Question 20

What do stacking interactions in a double helix do?

Answer 20

help stabilize the strands and support the H-bonds between the bases

Question 21

Describe base stacking interactions.

Answer 21

purine and pyrimidine bases are essentially hydrophobic

Question 22

Why is DNA a double helix?

Answer 22

• sugar phosphate backbone (negatively charged) is hydrophilic, so
  they face the solution
• bases project towards the center, stacked one on top of the other, form a hydrophobic core, away from aqueous solution
• bases can H-bond with each other.

Question 23

What are Chargoff’s rules of DNA base pairing?

Answer 23

purines are based with pyrimidines

• AT base pairs form 2 H-bonds
• GC base pairs form 3 H-bonds

Question 24

Which DNA sequences would denature at the lowest temperature?

Answer 24

AT has fewer H-bonds therefore, the sequences with more As and Ts will denature at the lowest temperature

Question 25

What do mutations lead bases to?

Answer 25

mismatch, disturbed geometry

Question 26

Why are purines and purines not paired?

Answer 26

not enough space

Question 27

Why are pyrimidines and pyrimidines not paired?

Answer 27

too much space

Question 28

Describe the uniform structure of the general geometry of Chargaff’s base pairs.

Answer 28

purine-pyrimidine pair

• same distance between bases on the two strands
• same, regular hydrogen bonding pattern
• same stacking interactions between bases above and below

Question 29

What are the structural differences between RNA and DNA?

Answer 29

• RNA: 2’ hydroxyl (OH) group DNA: 2’ H, lacks an O –> “deoxy”ribose
• RNA: AUGC
  DNA: ATGC

Question 30

What does the hydroxyl group of RNA do?

Answer 30

the additional OH (reactive functional group) makes RNA less stable than deoxyribose

Question 31

What is DNA replication?

Answer 31

copying DNA for cell division

hereditary information is transmitted from generation to generation

Question 32

What is transcription and translation?

Answer 32

genes provide the information to synthesize RNA or proteins for the cell

transcription: gene expression, DNA template transcribed to RNA
translation: protein synthesis, mRNA codons translated into protein primary structure