Download Lecture 7 DR MANAR - Dr-Manar-KSU

 Watson
and Crick were the first to make a
double-helical modle for the strucure of
deoxyribonucleic acid or DNA.
 DNA, or deoxyribonucleic acid, is the
hereditary material in humans and almost all
other organisms. Most DNA is located in the
cell nucleus (where it is called nuclear DNA),
but a small amount of DNA can also be found
in the mitochondria
 The
information in DNA is stored as a code
made up of four nitrogeneous bases: adenine
(A), guanine (G), cytosine (C), and thymine
(T).
 DNA bases pair up with each other, A with T
and C with G, to form units called base pairs.
Each base is also attached to a sugar
molecule and a phosphate molecule.
Together, a base, sugar, and phosphate are
called a nucleotide.
 An
important property of DNA is that it can
replicate, or make copies of itself. Each
strand of DNA in the double helix can serve
as a pattern for duplicating the sequence of
bases. This is critical when cells divide
because each new cell needs to have an
exact copy of the DNA present in the old cell.
They transmit heredity information and the amino acid sequence is
programmed by a gene to form a polypeptide. There are 2 types of nucleic
acids:
Ribose sugar ( no missed O)
Deoxyribose sugar ( one O is
missed on carbon 4)
Strands: single
Strands: Doubled
Bases: A, G, C & U
Bases: A, G, C & T
 It carries the heredity
information.
 It control protein synthesis by
directing mRNA synthesis.
 Antiparallel.
 Complementary
.
A nucleotide is consist
of
Attaches to sugar to result
in a backbone
Phosphate
group
Hydrogen bonds
Hydrogen bonds
Pentose
sugar
Nitrogen
base
Nitrogenous bases
Sugar-phosphate
backbones
The Nitrogenous
bases are:
They have
Hydrogen Bonds
between them
 They are synthesized by
Sugar
The first nucleotide
P group
Phosphodiester
link
The 2nd nucleotide
 The sequence of nitrogen bases in the polymers is unique for each
gene.
 The flow of this genetic material is DNA
mRNA
Protein.
 As mentioned before, RNA is a single ( strand ) and DNA is double
 The backbone of sugar and phosphate is on the outside, leaving
the nitrogen bases on the inside to form hydrogen bonds with
each other. ( Adenine is always with Thymine, and Guanine is
always with Cytosine.)

Copying the genetic
material
 When
a DNA molecule is copied each strand
is served as a template for ordering
nucleotides into a new complementary
strand
 Nucleotides line up along the template
according to the base-pairing rules and they
are linked to form new strands.
Separation of the two strands
Each strand works as a
template to produce new
strand
That’s why we say DNA is
complementary
According to the base-pairing
rules, new strands are
produced to link with the
original templates
 There
are there types of DNA replication the
most common replication and accepted by
Watson and Crick is SEMICONSERVATIVE
replication the other two types are
Conservative and dispersive.
Most
commo
n
Semiconservative
The daughter molecules will
have one old strand and one
new.
Conservative
The parental double helix
remains & a newly copy is
made
Dispersive
Each daughter molecule
contains a mixture of old &
new part.
Binding
protein to
keep them
apart
Elongated
by
polymeras
e
The
replication
starts with a
bubble called
the origin site
Replication
fork
The replication process happens in both directions. The new copied strand is
created from 5 -> 3 in the direction of 3 -> 5 according to the old strand.
That’s why we say DNA is antiparallel
 Several
enzymes and other proteins carry out
DNA replications such as :
1. Helicase
2. Primase
3. Polymerase
4. Ligase
The ends of the DNA molecules are replicated
by a special mechanism.
Creating the leading
strand
Primer:
Short RNA
segment
Primase:
DNA
polymerase
ligase:
Joins
Okazaki
fragments
A. One primer starts the new
chain.
B. Links nucleotides from RNA to
matching nucleotides of DNA.
C. The polymerase add more
nucleotides to the 3 end of the
primer’s chain.
D. Another polymerase replace
the primer’s with DNA
nucleotide to link with the
The leading strand’s direction is 5->3 going to 3->5 into the
template.
fork.
Creating the lagging strand
More than 1 primer is used. Form Okazaki fragments
which are joined by ligase to form the strand.
Okazaki’ fragmentsDNA polymerase III must work in the
direction away from the replication fork
 Before
DNA.
a cell can divide, it must duplicate its
 PLZ,OPEN
THE VIDEO
DNA Structure
http://www.youtube.com/watch?v=qy8dk5iS1f0
 PLZ,OPEN
THE VIDEO
DNA Replication Process
http://www.youtube.com/watch?v=teV62zrm2P0
 Q1:
Write whether each of the following
statements is True (T) or False (F):
 1-In the double helix the two strands of
DNA are complimentary.
2-The role of DNA polymerase in 
replication is to link the nucleotides one by
one in the 5’ 3’ direction.
3-DNA polymerase II is used for mRNA 
synthesis.
4- Elongation of new DNA is catalyzed by an 
enzyme called RNA polymerase.
 5-During the replication of DNA, _____.
both strands of a molecule act as
templates.

Q 2: Choose the correct answer (one answer only):

1-The pentose sugar in RNA is;-
a-Ribose.

b-Deoxyribose.
c-Fructose.


2-The short RNA segment that is complementary to DNA 
segment and is necessary to begin replication is known as;a-Primer.

b-Promotor.

c-Polymerase.

3-In DNA,adenine A always pairs with ;a-G.

b-C.

c-T.


4-To replicate the leading strand ---------- primer is required.
a-Many.
b-Two.



c-One.

5-The Okazaki fragments are joined by;a-DNA polymerase.
b-DNA ligase.
c-Primase.




6-Which is not a nucleotide base in DNA?
a-Uracil.


b-Adenine.

c-Cytosine.

7-A DNA strand having the sequence of C-G-A-T-T-G would be complementary to the sequence------------------------a-G-C-T-A-A-C

b-G-C-T-A-A-G

c-C-G-A-T-T-G

8-Each codon calls for a specific
a-Amino acid.
b-Protein.



c-Polypeptide.

9-Anticodons pair with -------------a- mRNA codons.
b-DNA codons.



c-tRNA anticodons.

10-An RNA molecule is-------------------a-A double helix.

b-Usually single- stranded.

c-Always double -stranded


