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Nucleic acids
Do you know that DNA is like the boss of RNA.
While DNA stays in it's office (Nucleus), it
sends RNA to the workstations (Cytoplasm)
with its messages.
Guess who?
WATSON
discovered
the structure
of the DNA
molecule
CRICK
awarded
the Nobel
Prize
D
Deoxyribo :the pentose
does not have any oxygen
in position 2.
N
Nucleic: these molecules were first
found in the nucleus of the cell , before
being found in mitochondria,
chloroplasts (of plant cells), and in the
cytoplasm of prokaryotes
Acid: only two of the three acid groups
of the phosphoric acid are used to form
the DNA chain. The third one gives the
phosphoribo-backbone an acidic
property.
A
This is the IIry structure of DNA
DNA double helix
Synthesis of mRNA
rRNA
rRNA
QUESTIONS
Regarding components of DNA
a
b
nX = Y
c
X
1. Identify X and Y ;
2. name the components that make up X
Y
3. Which two components make a nucleoside? a&b / a&c / b&c
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4. Identify the two types of bases and give examples
X
Y
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5. What is “base pairing” in DNA ?
6. What are the bases involved in DNA base pairing shown
in figure 1 & 2?
Figure: 2
Figure: 1
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7.The structure shown on to your
right is the (Iry / IIry / IIIry)
structure of DNA
b
a
8.Fill in the blanks in relation to areas
labeled ‘a’ and ‘b’
8.1 ‘sugar phosphate backbone’ is
indicated by area ……..
8.2 Area……... shows hydrophobic
properties where as area……
shows hydrophilic properties.
9.Which one of the following is
indicated by ‘c’
a. covalent hydrogen bond
b. non covalent hydrogen bond
c. di-sulfide bond
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c
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E
10. Identify the components A - D
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D
C
A
B
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11. Identify the components
labeled x,y& z that make
up RNA nucleotide
x
Give examples for Z
12. What are the 3 major
types of RNA? List their
functions
x
z
y
13. What are the other
types of RNA that are
present in cells?
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14. What are the
differences between DNA
and RNA structures?
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15. What is the process shown below
16. List the factors that will enable process A.
A
B
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17. What information is coded into DNA?
18. What is a "codon"?
19. What are the four pairs of DNA bases that
form in the double helix?
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20. How can A distinguish T from C?
21. Which DNA double helix do you think would be harder
to separate into two strands: DNA composed
predominantly of AT base pairs, or of GC base pairs?
Why?
22. The DNA double helix looks like a twisted ladder. What
makes up each rung of the ladder? What holds the rungs
together at the sides?
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23. Is there mostly empty space between the atoms
in a DNA double helix?
24. In a DNA double helix, why doesn't an A or T
form two hydrogen bonds (out of the three
possible) with C or G?
25. How many kinds of 5-membered rings are in
DNA?
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•DNA : some facts...
• The Watson and Crick model of a double helix structure provides an
answer to the regularity of the composition in bases and its physiological
properties (replication in the cell). It is confirmed by diffraction data.
Models using beads are useful to handle the concept.
• E. coli has a single circular DNA molecule of 4,600,000 base pairs. The
total length is 1.4 mm.
• In addition to functioning as building blocks of nucleic acids, nucleotides
are important because they are used to store and transfer chemical
energy (e.g. ATP).
• In man, the DNA molecule in a diploid cell, if fully extended, would have
a total length of 1.7 metres. If you unwrap all the DNA you have in all
your cells, you could reach the moon ...6000 times!
• a branched DNA assay is a test for specific nucleic acid chains typically
used to detect Reverse transcriptase viruses such as HIV. In the assay,
Branched DNA is mixed with a sample to be tested. If the branched DNA
binds to viral RNA, then the luminescent compound will react, and the
result can be measured via luminometer
RNA: Some facts
• Approximately, 5-10% of total weight of a cell is RNA (compare
with only about 1% DNA!).
• The extra hydroxyl group in RNA makes it more susceptible to
damage by hydrolysis; that's why DNA is the ultimate repository of
genetic information.
• RNA is the genetic material (like DNA for other organisms) in some
viruses (which don't have DNA).
• RNA is found in the nucleus and in the cytoplasm but DNA is found
only in nucleus.
• DNA is capable of self-replication, but only when assisted or
catalysed by proteins (enzymes) but RNA is capable of both self
replication and catalysis.
•
"RNA World hypothesis" states that before the emergence of
the first cell, RNA was the dominant and probably the only
form of life.
ANSWERS
1.
X – Nucleotide
Y – Polynucleotide
2.
a – phosphate;
b – base;
c –deoxyribose sugar
3. b and c
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4. X – Purine
(Adenine, Guanine)
Y – Pyrimidine
(Cytosine, Guanine, Uracil)
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5. Binding of a Purine with its respective
Pyrimidine
6. Figure 1 – Adenine and Thyamine
Figure 2 – Cytosine and Guanine
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7. Iry
8. 8.1 a
8.2 b
9. b non covalent hydrogen bond
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10. a – chromosome
b. protein scaffold
c - super coil
d –Nucleosome
e – DNA double helix
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11 – X phosphate
y – ribose sugar
z – base (Adenine, Guanine, Uracil, Cytosine )
12.
messengerRNA (mRNA):
Carries the genetic information
out of the nucleus into cytoplasm
for protein synthesis.
transferRNA (tRNA):
Decodes the information in mRNA.
ribosomalRNA (rRNA):
Makes up ribosome, constitutes
50% of a ribosome, which is a
molecular assembly involved in
protein synthesis.
13. a.catalyticRNAs (cRNA) ; b.Small Nuclear RNA (snRNA)
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14.
1
Characters
DNA
RNA
2
Molecule
Double stranded,
helical
Single stranded,
straight or variously
folded and twisted.
3
Pentose sugar
Deoxyribose
Ribose
4
Pyrimidine base
Thymine
Uracil
5
Complementary
base pairing
Always present and Normally absent, but
exists between A = T may be present in
and G = C
twisted segments of a
molecule.
If present, pairing is
between A = U and G =
C
6
Ratio of Purines:
Pyrimidines
Always 1:1
Back to the Question
Not necessarily 1:1
15.
A - Denaturation
B – Renaturaton
16. extreme pH, low ionic strength heat
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17.
The DNA in each organism (for example tree, insect, person, dog,
or bacterium) contains plans for making all of its proteins. There are
many thousands of kinds of proteins in each organism. Proteins are
chains of building blocks called amino acids. The DNA specifies the
order or sequence in which the amino acids must be hooked
together for each protein. The complete DNA sequence for each
protein is called a "gene".
18.
A codon is three consecutive bases in a gene. Each codon codes
for one amino acid in a protein.
19.
AT, CG, GC, and TA.
Back to the Question
20.
On the basis of the number and direction of hydrogen bonds T or C
can form with A. Each base can form either two or three hydrogen
bonds in a matched pair. The AT pair forms two, and the GC pair,
three. However, when C is lined up against A, no hydrogen bonds
can be formed (because donors do not line up with acceptors
21.
GC, because it has one more hydrogen bond per base pair
22.
Each rung is made of a base pair. and their attached sugar
(deoxyribose) rings. The rungs are held together by the phosphates
and sugars that make up the DNA "backbone".
Back to the Question
23.
No.
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The "thin" and "thick" renderings show covalent bonds. These
renderings hide the atoms so you can see the bonds clearly, and get a
sense of the skeletal layout of DNA. In contrast, the "space fill"
rendering shows the way the atoms of DNA occupy space.
24.
The middle hydrogen bonds run in opposite directions. In the middle
bond, T donates a hydrogen to an acceptor on A. C does not have a
hydrogen to donate in the middle position; rather, it accepts a hydrogen
from G's middle position. The same is true of the "third hydrogen bond"
(the one that is absent in an A-T pair). T has no hydrogen to donate to
the acceptor on G in the third position.
25. Three: the pentose ring, and the two 5-membered rings in the
purines.