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biology > DNA Replication > Flashcards

DNA Replication Flashcards

1
Q

where is DNA found

A

in the nucleus of eukaryotic cells

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2
Q

describe DNA and it’s functions

A
  • stores and transmits genetic information from one generation to the next
  • double stranded nucleic acids made up of nucleotides arranged in a double-helix
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3
Q

what are the nucleotide base pairs

A

Adenine - thymine
Guanine - cytosine

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4
Q

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

A

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

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5
Q

what is the process of copying dna called

A

replication

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6
Q

what happens during replication

A

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

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7
Q
  1. where does a dna replication take place
  2. when does it occur
  3. describe interphase
A
  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
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8
Q

dna replication follows the semi-conservative model, describe it

A

(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)

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9
Q

describe dna replication in 3 steps

A
  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)
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10
Q

name the 5 replication enzymes

A

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

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11
Q

describe enzymes

A
  • 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
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12
Q

1) helicase

A

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)

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13
Q

2) topoisomerase

A

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

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14
Q

DNA polymerase

A

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

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15
Q

Primase

A

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

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16
Q

Ligase

A

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

17
Q

exonuclease

A

cuts out RNA bases from primer

18
Q

describe how + where replication starts

A

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

19
Q

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

A

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

20
Q

why is dna an antiparallel molecule

A

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

21
Q

describe the orientation of nucleotides + describe leading and lagging strands

A

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

22
Q

describe Okazaki fragments

A

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

23
Q

summarize DNA replication in 4 steps

A
  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
24
Q

initiation

A

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

25
Q

primer synthesis

A
  • 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
26
Q

elongation

A
  • 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
27
Q

describe how DNA polymerase proofreads each nucleotide base pair

A
  • 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
28
Q

termination

A
  • 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
29
Q

describe the outcome of DNA replication

A

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

biology (15 decks)

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