chapter 16: molecular basis of inheritance

Question 1

what are Watson and Crick know for discovering?

Answer 1

known for discovering the structure of DNA (stoled from Franklin), a double helix with repeating sugar-phosphate units connected in a strand

Question 2

what did Franklin discover doing her experiments?

Answer 2

Franklin’s experiments revealed the helical shape of DNA

Question 3

what are the base pairs in DNA?

Answer 3

• adenine (A) and thymine (T) pair together
• cytosine (C) and guanine (G) pair together

Question 4

what is the central dogma?

Answer 4

a theory stating that genetic information flows in one direction (DNA-RNA-protein)

Question 5

how many chromosomes does a bacterium have?

Answer 5

one

Question 6

what is a replication fork? how many are formed once the origin of replication is opened?

Answer 6

• it is an area of single stranded DNA that is a template for synthesis of new DNA
• two forks are formed once opened

Question 7

what is the function of DNA polymerase I?

Answer 7

it removes RNA primer from 5’ end and replaces them with DNA nucleotides

Question 8

whats the function of DNA polymerase III?

Answer 8

once it recognizes an RNA primer, it begins to synthesize a new DNA strand in the 3’ to 5’ direction

Question 9

what is the semiconservative model of DNA?

Answer 9

semiconservative replication produces two copies that each contained one of the original strands and one new strand

Question 10

summary of Meselson and Stahl experiment

Answer 10

their experiments demonstrated that DNA replicates semi-conservatively

Question 11

what are okazaki fragments?

Answer 11

short lengths of DNA produced by the lagging strand (later they are joined by DNA ligase)

Question 12

what is the leading strand?

Answer 12

synthesized in the same direction as the movement of the replication fork, it’s synthesized continuously (runs in 3’ to 5’)

Question 13

what is the lagging strand?

Answer 13

synthesized in the opposite direction of leading strand, is synthesized in short fragments that are ultimately stitched together, forming Okazaki fragments (runs in 5’ to 3’)

Question 14

what’s topoisomerase?

Answer 14

it helps to relieve the strain in the double helix ahead of the replication fork, by breaking/swiveling/and rejoining DNA strands

Question 15

what does DNA polymerase do? what direction does it go in?

Answer 15

• synthesizes new DNA only in the 5’ to 3’ direction

Question 16

what does DNA polymerase start with? what does it put into the growing DNA strand?

Answer 16

• starts with a RNA primer
• they add nucleotides to the growing DNA chain

Question 17

what is a nuclease?

Answer 17

an enzyme that cuts DNA or RNA (that is damaged)

Question 18

what is the function of DNA ligase?

Answer 18

• joins Okazaki fragments of the lagging strand

Question 19

what is Chargaff’s rule?

Answer 19

if you know the one base, you can calculate the other (ex. A=50%, then T=50%)

Question 20

what is the difference between purines and pyrimidines?

Answer 20

purines have 2 rings and pyrimidines have 1 ring

Question 21

what end is a phosphate attached to? what end is OH attached to?

Answer 21

phosphate is attached to the 5’ carbon and OH is attached to the 3’ carbon

Question 22

what way does DNA ligase work?

Answer 22

3’ end to 5’ direction

Question 23

what’s the function of helicase?

Answer 23

it unwinds (separates) DNA strands by breaking hydrogen bonds (at the beginning of the replication fork)

Question 24

what’s the function of a single-strand binding protein?

Answer 24

protect the 2 strands from cleavage and stabilize the strands, preventing them from joining back together (binds after replication fork)

Question 25

what’s the function of primase?

Answer 25

it synthesizes an RNA primer at 5’ end of leading strand and at 5’ end of each Okazaki fragment of lagging strand

Question 26

what does DNA polymerase need to attach too?

Answer 26

it must attach to something double-stranded or a primer

Question 27

what is the base pairing in RNA?

Answer 27

• cytosine (C) pairs with guanine (G)
• adenine (A) pairs with uracil (U)
• thymine (T) pairs with adenine (A)

Question 28

what direction does DNA synthesis occur?

Answer 28

5’ to 3’

Question 29

is DNA replication usually accurate or not?

Answer 29

yes, DNA replication has a high fidelity (accuracy)

Question 30

summary of a “mismatched pair”

Answer 30

• a thymine dimer distorts a DNA molecule
• a nuclease enzyme cuts out the damaged DNA strand
• repair synthesis by DNA polymerase I, fills in the missing nucleotides
• DNA ligase seals the free end to the new DNA to the old DNA, making the strand complete