DNA Replication

Question 1

where is DNA found

Answer 1

in the nucleus of eukaryotic cells

Question 2

describe DNA and it’s functions

Answer 2

• stores and transmits genetic information from one generation to the next
• double stranded nucleic acids made up of nucleotides arranged in a double-helix

Question 3

what are the nucleotide base pairs

Answer 3

Adenine - thymine
Guanine - cytosine

Question 4

what do cells need to do to have a complete copy of genetic information

Answer 4

cells need to make a copy of dna before dividing so that each daughter cell has a complete copy of genetic information

Question 5

what is the process of copying dna called

Answer 5

replication

Question 6

what happens during replication

Answer 6

each strand of original dna acts as a template for replication
- two identical dna molecules are produced

Question 7

1. where does a dna replication take place
2. when does it occur
3. describe interphase

Answer 7

1. takes place in the nucleus of eukaryotic cells
2. occurs before a cell divides during interphase (happens during the S phase of interphase)
3. cells prepare for cell division, grow, replicate DNA, and perform normal cell activities during interphase

Question 8

dna replication follows the semi-conservative model, describe it

Answer 8

(basically the new strand of dna contains 1 original + 1 new strand)
- two strands of dna unwind from one another
- base pairing allows each strand to serve as a template for a new complimentary strand
-produces two identical dna molecules (1 OG+ 1 new stand)

Question 9

describe dna replication in 3 steps

Answer 9

1. hydrogen bonds between bases break and the helix unwinds into two strands
2. each strand of dna acts as a template for base-pairing and synthesis of a new complementary strand
3. replication produces two identical dna double-helix strands (each w 1 OG + 1 new strand)

Question 10

name the 5 replication enzymes

Answer 10

1) helicase
2) topoisomerase
3) primase
4) DNA polymerase
5) ligase

Question 11

describe enzymes

Answer 11

• proteins that can build up or break down the substances that they act upon
• enzymes also have the ability to speed up chemical reactions
• enzymes assist in DNA replication

Question 12

1) helicase

Answer 12

unwinds or unzips the double helix by breaking the hydrogen bonds between complementary bases
- this forms a replication fork (the point at which two strands of DNA are separated and allow replication of each strand)

Question 13

2) topoisomerase

Answer 13

prevents the DNA double helix from becoming too tightly wounded
- topoisomerase moves ahead of the replication fork as DNA is unzipped by helicase
- it creates temporary nicks in the helix to release tension and prevent DNA from supercoiling
- it later seals up the nicks to avoid permanent damage

Question 14

DNA polymerase

Answer 14

replicates the DNA molecules to build a new strand of DNA
- reads the nucleotide sequence of the template strand and constructs a complementary strand of DNA
- proofreads for and repairs any nucleotide sequence mismatches during replication

Question 15

Primase

Answer 15

makes a primer that signal DNA Polymerase to where to add nucleotides
- makes an RNA primer complementary to the DNA template strand
- once the primer is in place, DNA polymerase adds nucleotides one by one to make a new DNA strand thats complementary to the template strand

Question 16

Ligase

Answer 16

joins DNA fragments together
- involve in any process that requires the sealing of broken bonds in the sugar-phosphate backbone of DNA
- fills in the spaces between DNA fragments to bridge together gaps in DNA during replication

Question 17

exonuclease

Answer 17

cuts out RNA bases from primer

Question 18

describe how + where replication starts

Answer 18

where: origins of replication
how: specialized proteins bind to the origin and separate the DNA (creating 2 Y-shaped replication forks)

Question 19

what do 2 replication forks create together + how do RFs move

Answer 19

they create a replication bubble
move: RFs move in opposite directions as replication proceeds

Question 20

why is dna an antiparallel molecule

Answer 20

because its composed of two strands that run alongside one another, but point in opposite direction
- two sugar-phosphate backbones are upside-down (antiparallel) relative to each other

Question 21

describe the orientation of nucleotides + describe leading and lagging strands

Answer 21

dna can only be replicated in the 5’ to 3’ direction
leading: (5’ to 3’) replicated continuously
lagging: (3’ to 5’) replicated discontinuously + forms Okazaki fragments
5’ = phosphate
3’ = sugar

Question 22

describe Okazaki fragments

Answer 22

on the lagging strand
- small section of dna nucleotides that are discontinuously replicated and are later linked together by ligase to create a complete strand of DNA

Question 23

summarize DNA replication in 4 steps

Answer 23

1. initiation: the point of origin of replication is identified, and then DNA strands are separated
2. primer synthesis: RNA primers are placed on the separated strands by primase
3. elongation: complementary strands are synthesized by DNA polymerase
4. termination: two replication forks converge, and remaining gaps are sealed

Question 24

initiation

Answer 24

replication begins with identifying the point of origin
- helicase unzips the DNA strands to form two replication forks
- topoisomerase works ahead of helicase to keep DNA from supercoiling
- single stranded binding proteins (SSB) coat the DNA around the replication fork to prevent it from rewinding during replication

Question 25

primer synthesis

Answer 25

- before DNA polymerase can add nucleotides, it must be primed - primase primes the strand for replication by adding complementary RNA nucleotides to the strand - the primers synthesized by primase signal DNA polymerase where to begin replication - later in replication, the RNA nucleotides will be replaced with DNA nucleotides by DNA polymerase

Question 26

elongation

Answer 26

- elongation is the process of adding nucleotides to the DNA strand, making it longer - DNA polymerase adds nucleotides to continuously build a complementary strand in a 5' to 3' direction on the leading strand - the lagging strand (3' to 5') is discontinuously replicated, creating Okazaki fragments

Question 27

describe how DNA polymerase proofreads each nucleotide base pair

Answer 27

- if it finds a nucleotide mismatch, it removes it and replaces it before continuing with synthesis - it is important that DNA polymerase fixes any errors - a mismatched DNA base can lead to an incorrectly coded for gene - could lead to synthesis of the wrong proteins or no protein

Question 28

termination

Answer 28

- the process of ending DNA replication - termination occurs when the two replication forks meet on the same stretch of DNA - replication forks converge until all intervening DNA is unwound - remaining gaps between the Okazaki fragments are sealed by ligase

Question 29

describe the outcome of DNA replication

Answer 29

two identical DNA double helices are created - each copy contains one old original and one newly synthesized strand