Chapter 3 - Nucleic Acids

Question 1

what are nucleotides composed of

Answer 1

• one phosphate group
• one pentose sugar
• one organic nitrogenous base

Question 2

how are the subunits joined to form a nucleotide molecule

Answer 2

covalent bonds

Question 3

DNA vs. RNA nucleotide number of strands

Answer 3

DNA: 2
RNA: 1

Question 4

DNA vs. RNA nucleotide pentose sugar

Answer 4

DNA: deoxyribose
RNA: ribose

Question 5

DNA vs. RNA nucleotide bases

Answer 5

DNA: A, T, C, G
RNA: A, U, C, G

Question 6

what is a purine, name the bases

Answer 6

• 2 nitrogen containing rings
  adenine and guanine

Question 7

what is a pyramidine, name the bases

Answer 7

• 1 nitrogen containing ring
  cystosine, thymine, uracil

Question 8

what is a nucleotide

Answer 8

the monomer from which nucleic acids are made

Question 9

what are the complementarty base pairs

Answer 9

cytosine and guanine
adenine and thyamine (DNA)
adenine and uracil (RNA)

Question 10

how are the complementary base pairs joined

Answer 10

weak hydrogen bonds

Question 11

how many hydrogen bonds between complementary base pairs

Answer 11

A-T (2)
C-G (3)

Question 12

how are polynucleotides formed

Answer 12

• condensation reaction
• phosphdiester bond forms between the 5’ phosphate group of one nucleotide and the 3’ hydroxyl group on the sugar of another

Question 13

describe the structure of DNA

Answer 13

• polymer of nucleotides
• 2 antiparallel helical chains of nucleotides linked by hydrogen bonds between complementary base pairs
• coiled to form a double helix
• stable structure

Question 14

what is the importance of complementary base pairing

Answer 14

• same distance between each pair of bases
• allows faithful DNA replication
• high fidelity of replication: bases can only pair with a specific other base

Question 15

define high fidelity of replication

Answer 15

making an accurate copy

Question 16

when is DNA replicated

Answer 16

interphase

Question 17

why is DNA replication semi-conservative

Answer 17

• one original strand that acts as a template
• one newly formed strand
• 50-50

Question 18

what method did meselson and stahl use to separate DNA by its density

Answer 18

centrifugation

Question 19

what enzymes are involved in DNA replication

Answer 19

• DNA helicase
• DNA polymerase

Question 20

role of helicase in DNA replication

Answer 20

• unwinds the double helix
• breaks hydrogen bonds between complementary base pairs
• separates the 2 strands

Question 21

what happens once the strands of DNA have been ‘unzipped’

Answer 21

• both strands are used as templates
• complementary base pairing occurs between template strands and free nucleotides

Question 22

role of DNA polymerase in DNA replication

Answer 22

joins adjacent nucleotides by phosphodiester bonds formed in condensation reactions

Question 23

what is mutation

Answer 23

• replication errors
• incorrect sequence of nucleotides when bases arent exactly matched

Question 24

what is the triplet code

Answer 24

3 bases code for an amino acid

Question 25

why is it the triplet code, not doublet?

Answer 25

enough combinations to code for the 20 needed amino acids

Question 26

why is the genetic code universal

Answer 26

same 4 DNA bases in all organisms

Question 27

how is the genetic code degenerate

Answer 27

more than one triplet codes for the same amino acid

Question 28

how is the genetic code non-overlapping

Answer 28

- start codon AUG - each triplet only read once, dont share bases

Question 29

significance of AUG

Answer 29

ensures the code is read from base 1, not 2 or 3

Question 30

function of base sequence in DNA

Answer 30

stores genetic information

Question 31

function of large size and helix of DNA

Answer 31

large size: can store alot of genetic info helix: compact

Question 32

what is ATP

Answer 32

- adenosine triphosphate - used for energy transfer in all cells of all living things

Question 33

structure of ATP

Answer 33

- nitrogenous base (always adenine) - pentose sugar (ribose) - three phosphate groups

Question 34

how does ATP release energy

Answer 34

- more energy is released than used when the weak bond holding the last phosphate group is broken as it free phosphate undergoes other reactions involving bond formation

Question 35

hydrolysis of ATP

Answer 35

ATP + H2O ---> ADP + Pi + energy

Question 36

why isnt ATP a good long-term energy store

Answer 36

unstable phosphate bonds mean cells dont store alot of ATP

Question 37

how is ATP reformed

Answer 37

phosphorylation of ADP

Question 38

properties of ATP

Answer 38

- small (in+out cells) - bonds between phosphate have immediate energy - easily regenerated - releases small quant energy, none wasted as heat - water soluble