Nucleotides and nucleic acids Flashcards
1
Q
What does DNA
stand for?
A
Deoxyribonucleic acid
2
Q
What does RNA
stand for?
A
Ribonucleic acid
3
Q
What is the
monomeric unit for
nucleic acids?
A
Nucleotides
4
Q
What are the 3
components of a
nucleotide?
A
-phosphate group
-pentose (5 carbon
sugar) either
deoxyribose or ribose
-nitrogenous base
5
Q
Name the 5
nitrogenous bases
A
- thymine
- quanine
- adenine
- cytosine
- uracil
6
Q
Name the 4 bases
present in DNA
A
- thymine
- adenine
- guanine
- cytosine
7
Q
Name the 4 bases in RNA
A
- uracil
- adenine
- guanine
- cytosine
8
Q
Which base is never
found in DNA?
A
Uracil
9
Q
Which base is never
found in RNA?
A
Thymine
10
Q
How are
polynucleotides
formed?
A
-condensation reactions occur -between the phosphate on carbon 5 of one nucleotide and the hydroxyl group on carbon 3 of another nucleotide -water is released -phosphodiester bond formed
11
Q
What sort of bond is
formed between
nucleotides?
A
Phosphodiester
12
Q
How are sequences of
RNA/DNA given?
A
From the 5’ end to
3’ end
13
Q
What are the two
types of bases?
A
Purines and pyrimidines
14
Q
What is the structure
of purines?
A
Double ringed
15
Q
What is the structure
of pyrimidines?
A
Single ringed
16
Q
Which bases
are purines?
A
Adenine and guanine
17
Q
Which bases are
pyrimidines?
A
Cytosine, thymine,
and uracil
18
Q
What does
complementary base
pairing allow?
A
-DNA to be copied
and transcribed
19
Q
What type of bonds
hold bases together?
A
Hydrogen bonds
20
Q
How many hydrogen
bonds form between
Adenine and Uracill
Thymine?
A
2
21
Q
How many hydrogen
bonds form between
Guanine and
Cytosine?
A
3
22
Q
In order to allow for the bases to form hydrogen bonds what must happen to one of the polynucleotide chains?
A
It must be rotated
through 180 degrees
23
Q
How does the sugar
phosphate backbone
run on one of the polynucleotide chains? How does the other polynucleotide chain run? What is
this called?
A
From 5’ to 3’ and the other from 3’ to 5’
The antiparallel nature of DNA
24
Q
Describe the steps
involved in extracting
DNA
A
-sample ground up using pestle and mortar -sample mixed with detergent -salt is added -protease is added -ice cold ethanol is added down the side of the test tube
25
Why is the sample
ground in the
extraction of DNA?
it breaks down the
| cell walls
26
Why is detergent
added to the sample
in the extraction of
DNA?
breaks down the cell
membrane, releasing
the cell contents into
solution
27
Why is salt added to
the sample in the
extraction of DNA?
```
neutralises charges
on phosphates in
sugar phosphate
backbone
breaks the hydrogen
bonds between DNA
and water
makes DNA
less soluble
```
28
Why is protease
added to the sample
in the extraction of
DNA?
breaks down the
proteins associated
with DNA
29
Why is ethanol added
to the sample in the
extraction of DNA?
```
Causes the DNA to
form a white
precipitate between
the layer of the
sample and the
ethanol
```
30
```
Why is a low
temperature
maintained
throughout the
process of DNA
extraction?
```
Reduces rate of
enzyme controlled
reactions that break
down DNA
31
Why should the
| ethanol be ice cold?
Helps to make DNA
| more insoluble
32
At what point in the
cell cycle does DNA
replication occur?
S phase
33
```
Why is it important
that DNA replication
results in 2 genetically
identical molecules of
DNA?
```
```
-ensures the
continuation of
species
-ensures cells and
structures in a
species are
maintained
```
34
Why is DNA
replication described
as being semi-
conservative?
```
-Each one of the two
daughter molecules
contains one original
strand of DNA and
one newly
synthesised strand
-the original strand
acts as a template for
a new strand
```
35
What is the
relationship between
the two daughter
molecules?
They are genetically
| identical
36
```
What is the
relationship between
the daughter
molecules and the
original DNA
molecule?
```
they are identical
37
Which two enzymes
are used in DNA
replication?
DNA helicase
| DNA polymerase
38
What is the role of
| DNA helicase?
```
-unwinds DNA
from histones
-unzips DNA by
breaking Hydrogen
bonds betwem
complementary base
pairs
```
39
What is the role of
| DNA polymerase?
```
-catalyses the
reaction to form
phosphodiester
bonds between the
free nucleotides to
form a sugar
phosphate backbones
```
40
Outline how DNA
| is replicated
```
-DNA helicase
unwinds DNA from
histones and unzips
DNA by breaking
Hydrogen bonds
between
complementary base
pairs
-free nucleotides are
attracted to the
exposed nucleotides
on the strand of DNA
by base
complementarity
-DNA polymerase
forms phosphodiester
bonds between
nucleotides
-two genetically
identical molecules of
DNA are formed
```
41
What does the
unzipping mean for
DNA nucleotides?
They are exposed
42
Due to the
nucleotides being
exposed, what
happens?
```
Free nucleotides are
attracted to the
exposed nucleotides
by base
complementarity and
form hydrogen bonds
```
43
Where do the free
nucleotides come
from?
Our diet
44
How do free
nucleotides enter the
nucleus?
From the cytoplasm
through the nuclear
pores
45
What is a primer?
```
A short piece of RNA
or DNA with a
complementary
sequence to part of
the DNA template
```
46
What direction does
| DNA synthesis occur?
5' to 3'
47
What is the difference
between the leading
strand and lagging
strand?
```
The leading strand is
built continuously
whereas the lagging
strand is built
discontinuously
```
48
Why is there a leading
strand and a lagging
strand?
The antiparallel nature
| of DNA
49
Why are primers
| needed in DNA
DNA polymerase
requires them in order
to bond to the 3' OH
group
50
```
What does the
discontinuous
building of the lagging
strand lead to the
production of?
```
Okazaki fragments
51
Which experiment
was used to prove
that DNA replication is
semi-conservative?
The Meselsohn and
| Stahl experiment
52
Which two techniques
did the Meselsohn
and Stahl experiment
use?
Mass labelling and
| density centrifugation
53
```
Which isotope was
used for mass
labelling in the
Meselsohn and Stahl
experiment?
```
N- 15
54
Why was N-15 used in
the Meselsohn and
Stahl experiment?
```
It could be
incorporated into the
nitrogenous bases
and therefore track
the movement of
them
```
55
Which part of the
nucleotide was
labelled in mass
labelling?
The nitrogenous
| bases
56
What was observed in
the key Meselsohn
and Stahl experiment?
band of DNA was
formed inbetween the
N-15 and N-14 bands
57
```
How did the key
Meselsohn and Stahl
experiment prove
DNA replication is
semi-conservative?
```
```
-the initial molecule of
DNA contained only
N-15 nucleotides
-as DNA replication is
semi-conservative the
DNA which was newly
synthesised in the
N-14 growth media
would contain one
strand with N-15
nucleotides and one
strand with N-14
nucleotides
-so the band would
be in the middle
```
58
```
If DNA replication was
conservative what
would have been
observed in the key
Meselsohn and Stahl
experiment?
```
band of DNA at the
N-14 and N-15
positions
59
```
If the E.coli were
allowed to divide
twice in the key
Meselsohn and Stahl
experiment in N-14
what would be seen?
```
A band at N-14 and in
the middle in the ratio
1:1
60
```
If the E.coli were
allowed to divide
three times in the key
Meselsohn and Stahl
experiment in N-14
what would be seen?
```
band at N-14 and in
the middle in the ratio
3:1
61
Explain why
complementary base
pairing is important in
DNA replication
```
-reduces occurrences
of mutation
-allows for formation
of hydrogen bonds
-DNA is replicated
without error
```
62
What is a mutation?
A change in the
sequence of DNA
bases within a gene
63
How do mutations
| Occur?
A base changing
64
What are 2 possible
consequences of
mutations?
evolution
| genetic disorders
65
Give 3 differences
between DNA and
RNA?
```
-DNA has a double
stranded structure
whilst RNA has a
single stranded
structure
-In DNA A bonds to T
and G bonds to C, in
RNA A bonds to U and
G bonds to C
-DNA is too big to
leave the nucleus,
RNA is small enough
to leave the nucleus
```
