DNA Structure & Replication Flashcards
1
Q
What does DNA stand for?
A
Deoxyribonucleic acid
2
Q
What did Erwin Chargaff in 1950 report about DNA?
A
Erwin Chargaff reported that DNA composition varies from one species to the next. (This evidence of diversity made DNA a more credible candidate for the genetic material)
3
Q
What are Nucleic Acids?
A
Nucleic Acids are polymers specialized for storage, transmission, and use of genetic material.
4
Q
What is the monomer of DNA?
A
Nucleotides
5
Q
What does a Nucleoside consist of?
A
Pentose sugar + N-containing base
6
Q
What does a Nucleotide consist of?
A
Pentose sugar + N-containing base + Phosphate group
7
Q
Are Pyrimidines single rings or double rings?
A
Single rings
8
Q
Are Purines single rings or double rings?
A
double rings
9
Q
Pyrimidines has Adenine and Guanine. True or False
A
False. Pyrimidines has Thymine and Cytosine
10
Q
Purines has Adenine and Guanine. True or False
A
True.
11
Q
What is the name of the DNA sugar?
A
Deoxyribose
12
Q
What is Chargaff’s rule?
A
Chargaff’s rule state that in any species there is an equal number of A and T bases, and an equal number of G and C bases. (However, it was not known how the entire molecule fit together)
13
Q
What did James Watson and Francis Crick introduce in 1953?
A
Watson and Crick introduced an elegant double-helical model for the structure of deoxyribonucleic acid/DNA. (They utilized Chargaff’s rule ad evidence from X-ray cystallography studies stolen from Rosalind Franklin)
14
Q
When did Rosalind Franklin figure of the DNA model?
A
1953
15
Q
At first, Watson and Crick thought the bases paired with A with A, and so on, but then changed their minds. Why?
A
Because such pairings did not fit the x-ray data, which suggested the double helix had a uniform diameter/width.
16
Q
What happened after Watson and Crick paired a purine with a pyrimidine?
A
It resulted in a uniform width consistent with the X-ray data from Rosalind Franklin
17
Q
purine + purine was too ________.
A
wide
18
Q
Pyrimidine + Pyrimidine was too __________.
A
narrow
19
Q
Purine + Pyrimidine was _________________________.
A
width consistent with X-ray data
20
Q
Adenine pairs only with Thymine. True or False
A
True
21
Q
Guanine only pairs with Cytosine. True or False
A
True
22
Q
How did Watson-Crick explain the Chargaff’s rule model?
A
In any organism the amount of A =T and the amount of G = C
23
Q
Why not Adenine and Cytosine or Thymine and Guanine?
A
Because of the way the hydrogen bond together (# of hydrogen bonds)
24
Q
Enzymes only fit in the molecule in a ______________
A
specific direction
25
The 2 sugar-phosphate backbones are __________ in a DNA structure.
anti-parallel
26
Since the two strands of DNA are complementary, each strands acts as what?
It acts as a template for building a new strand in replication.
27
What happens in a DNA replication to the parent molecule?
The parent molecule unwinds, and two new daughter strands are built based on base-pairing rules.
28
Each parental strand can now serve as a what?
template for a new complementary strand
29
How is the parent molecule held by?
Its held by hydrogen bonding, so its easy to break apart.
30
The daughter DNA molecules, each consist of one ________ strand and one ____ strand.
parental and new strand.
31
Strands of DNA are _____ but very long.
thin
32
A human has ____ strands of DNA
48
33
A human has ____ pairs in our DNA structure.
24
34
What does Watson and Crick's semiconservative model of replication predict?
when a double helix replicates, each daughter molecule will have one old strand (derived or "conserved" from the parent molecule) and one newly made strand.
35
What were the two competing models of the semiconservative model?
1. Conservative model (the 2 parent strands rejoin)
| 2. Dispersive model (each strand is a mix of old and new)
36
What are the 4 things a cell needs to do a DNA replication?
1. Energy
2. Template (we need to copy an existing DNA strand)
3. Enzymes (Many different enzymes)
4. Nucleotides (Adenine, Guanine, Thymine. Cysteine)
37
Define Helicase (protein)
Unwinds parental double helix at replication forks
38
Define Single-strand binding protein (protein)
Binds to and stabilizes single-stranded DNA until it can be a template. (like a double dutch)
39
Define Topoisomerase (protein)
Relieves "overwinding" strain ahead of replication forks by breaking, swiveling, and rejoining DNA strands. (helps reduce the stress as we unwind it, but it can break)
40
Define Primase (protein)
Synthesizes an RNA primer at 5' end of leading strand and of each Okazaki fragment ofl aging strand. (primer)
41
Define DNA pol III (protein)
Using parental DNA as a template, synthesizes new DNA strand by covalently adding nucleotides to the 3' end of pre-existing DNA strand or RNA primer. (forming phosphates groups)
42
Define DNA pol I (protein)
Removes RNA nucleotides of primer from 5' end and replaces them with DNA nucleotides. (removal of primers)
43
Define DNA ligase (protein)
Joins 3' end of DNA that replaces primer to rest of leading strand and joins Okazaki fragments of lagging strand.
44
Where does the DNA replication begin at?
origins of replication.
45
What is origins of replication?
where the two DNA strands are separated, opening up a replication "bubble" and separating the bases of hydrogen bonds.
46
How many origins of replication does a eukaryotic chromosome have?
It may have hundreds or even thousands.
47
How does DNA replication proceed?
In both directions from each origin, until the entire molecule is copied. (trying to make 2 strands, like a highway, one way goes one way as the other goes the opposite way)
48
The top strand of a DNA will be __________ to come out than the ______ because of the helicase.
easier
| end
49
You cannot start a DNA replication until you add a _______.
RNA primer (single stranded)
50
Why start with a RNA primer and not DNA?
because a DNA can copy its own very fast and RNA cannot.
51
DNA polymerases cannot initiate synthesis of a polynucleotide; they can only add nucleotides to the ___' end.
3'end.
52
The initial nucleotide strand is a short ______
RNA primer
53
What is primase?
Its an enzyme that can start an RNA chain from scratch and adds RNA nucleotides one at a time using the parental DNA as a template
54
How short is the primer? Why?
5-10 nucleotides long, and the 3' end serves as the staring point for the new DNA strand. It is short because it is just getting started.
55
At the end of each replication bubble is a _____________, a Y-shaped region where new DNA strands are elongating
replication fork
56
What is a replication fork?
is a point in a DNA molecule where the 2 strands separate during replication
57
What is a DNA polymerases?
Its an enzyme that catalyzes the elongation of new DNA at a replication fork
58
Most DNA polymerases require a ______ and a DNA _____________
primer*
| template strand*
59
The rate of elongation is how many per second in bacteria?
500 nucleotides
60
The rate of elongation is how many per second in human cells?
50 nucleotides
61
Ecoli can replicate every ___ minutes
20
62
We have thousands of DNA and bacteria only has 20 to 25 of DNA. Which is easy to replicate?
bacteria
63
The antiparallel structure of the double helix affects replication. Why?
It leads to the lagging and leading strand.
64
DNA polymerases add nucleotides only to the free ___ end of a growing strand
3'
65
DNA polymerases add nucleotides only to the free 3' end of growing strand, therefore A new DNA strand can elongate ONLY in the ___ to ___' direction
5' *
| 3' *
66
How is the leading strand started?
Along one template strand of DNA, the DNA polymerase synthesizes a leading strand continuously, moving toward the replication fork.
67
How does the lagging strand elongate toward the other new strand?
DNA polymerase must work in the direction away from the replication fork
68
How is the lagging strand synthesized?
as a series of segments called Okazaki fragments, which are joined together by DNA ligase.
69
DNA polymerases proofread newly made DNA, replacing any incorrect ____________
nucleotides
70
What happens in a mismatch repair of DNA?
it repairs enzymes correct errors in base pairing.
71
How can DNA be damaged?
By exposure to harmful chemical or physical agents such as cigarette smoke and x rays; it can also undergo spontaneous changes(very rare 10 to the 6)
72
What happens in a nucleotide excision repair?
an important process cells use to correct many different types of DNA damage. The nuclease cuts out and replaces damaged' stretches of DNA
73
Why would bacteria beat us in reproduction?
They can duplicate every 20 minutes
74
cells can only be damaged in _____________
cell division
75
Error rate after proofreading repair is low but not _____
zero
76
sequence changes may become permanent and can be passed on to the next ___________
generation (egg and sperm)
77
These changes (mutations) are the source of the genetic variation upon which ________________ operates
natural selection
78
During replication, the direction of synthesis of the new DNA on the leading strand and lagging strand is?
5' to 3' only.
79
How many hydrogen bonds does Adenine and thymine have?
2 hydrogen bonds (easy to break)
80
How many hydrogen bonds does guanine and cytosine have?
3 hydrogen bonds
81
Cytosine and thymine are pyrimidine which have 6 atoms. Name them.
4 carbon and 2 nitrogen
82
The 5' carbon has a ___________ group attached to it.
phosphate group
83
The 3' carbon a _________ group
hydroxyl group
84
Adenine and guanine are purines, How many atoms do they have?
5 carbon and 4 nitrogen
85
The hydroxyl groups on the _____and ____carbons link to the phosphate groups to form the DNA backbone
5'- and 3'-
86
why are the strands of DNA molecule said to be complementary?
because each strand can be used to make the other strand
87
Name the enzyme that joins individual nucleotides to produce a new strand of DNA
DNA polymerase
88
The principal enzyme involved in DNA replication is called?
DNA polymerase
89
The enzyme that proofreads each new DNA strand so that each molecule is a near-perfect copy of the original is ________
DNA polymerase
90
DNA polymerase CANNOT initiate synthese of a polynucleotide, they can only ____ nucleotides to the ___ end, The initial nucleotide strand is a short RNA primer.
* add
| * 3'
91
Nucleotide can only be added to the end of 3' prime. Why?
the shape of the enzyme
92
A primer is made of?
RNA
93
Enzymes called ________ catalyze the elongation of new DNA at a replication fork
DNA polymerases
94
Most DNA polymerases require a ______ and a DNA ______ strand.
* Primer
| * Template
95
DNA ligase joins 3' end of DNA that replaces primer to rest of leading strand and joins _______ of lagging strand
Okcazaki fragments
96
What does it mean when DNA polymerases proofread?
They proofread newly made DNA, replacing any incorrect nucleotides.
97
What happens in a mismatch repair of DNA?
Repair enzymes correct errors in base pairing.
98
What holds the double helix of DNA?
Covalent bonds
99
What holds the sides of a double helix of DNA?
hydrogen bonds
100
Limitations of DNA polymerase create problems for the linear DNA of ________ chromosomes
eukaryotic
101
The usual replication machinery provides no way to complete the 5' ends, which means?
repeated rounds of replication produce shorter DNA molecules with uneven ends.
102
The usual replication machinery provides no way to complete the 5' ends, so repeated rounds of replication produce shorter DNA molecules with uneven ends. Why is this not a problem with prokaryotes?
most have circular chromosomes
103
Every time your DNA replicates, your DNA gets longer. True or False
False. It gets shorter and shorter
104
Define chronological age
The age you are right now.
105
Define Biological age
how many times your cell is divided
106
Why does DNA replicate?
1. For growth and repair of the existing structure. (you)
| 2. To produce gametes (baby)
