DNA
YUSRON SUGIARTO, STP, MP, MSc
3
DNA is wrapped tightly around histones
and coiled tightly to form chromosomes
DNA
• DNA is often called
the blueprint of life.
• In simple terms,
DNA contains the
instructions for
making proteins
within the cell.
DNA by the numbers
• Each cell has about 2 m
of DNA.
• The average human has
75 trillion cells.
• The average human has
enough DNA to go from
the earth to the sun more
than 400 times.
• DNA has a diameter of
only 0.000000002 m.
The earth is 150 billion m
or 93 million miles from
the sun.
Why do we study DNA?
We study DNA for
many reasons, e.g.,
• its central
importance to all
life on Earth,
• medical benefits
such as cures for
diseases,
• better food crops.
Chromosomes and DNA
• Our genes are on
our chromosomes.
• Chromosomes are
made up of a
chemical called
DNA.
DNA Structure
 DNA consists of two molecules that are arranged
into a ladder-like structure called a Double Helix.
 A molecule of DNA is made up of millions of tiny
subunits called Nucleotides.
 Each nucleotide consists of:
1. Phosphate group
2. Pentose sugar
3. Nitrogenous base
One Strand of DNA
• The backbone of
the molecule is
alternating
phosphate and
deoxyribose, a
sugar, parts.
• The teeth are
nitrogenous
bases.
phosphate
deoxyribose
bases
Nucleotides
Phosphate
Nitrogenous
Base
Pentose
Sugar
Nucleotides
 The phosphate and sugar form the backbone of
the DNA molecule, whereas the bases form the
“rungs”.
 There are four types of nitrogenous bases.
Nucleotides
A
Adenine
C
Cytosine
T
Thymine
G
Guanine
Nucleotides
 Each base will only bond with one other specific
base.
 Adenine (A)
 Thymine (T)
Form a base pair.
 Cytosine (C)
 Guanine (G)
Form a base pair.
Four nitrogenous bases
DNA has four different bases:
C
• Thymine T
• Adenine A
• Guanine G
• Cytosine
Two Kinds of Bases in DNA
• Pyrimidines are
single ring bases.
• Purines are double
ring bases.
N
N
O
C
C
C
N
N
C
N
C
C
C
N
C
N
N C
One Strand of DNA
• The backbone of
the molecule is
alternating
phosphate and
deoxyribose, a
sugar, parts.
• The teeth are
nitrogenous
bases.
phosphate
deoxyribose
bases
Thymine and Cytosine are
pyrimidines
• Thymine and cytosine each have one ring
of carbon and nitrogen atoms.
N
O
N
O
C
C
N
N
C
C
thymine
O
C
C
C
C
N
C
cytosine
Adenine and Guanine are purines
• Adenine and guanine each have two
rings of carbon and nitrogen atoms.
O
N
N
N
C
C
N
C
C
C
C
N
N
N
Adenine
N
C
N
C
Guanine
C
C
N
Two Stranded DNA
• Remember, DNA
has two strands
that fit together
something like a
zipper.
• The teeth are the
nitrogenous
bases but why do
they stick
together?
N
N
C
N
N
C
C
C
O
• The bases attract
each other because of
hydrogen bonds.
• Hydrogen bonds are
weak but there are
millions and millions
of them in a single
molecule of DNA.
• (The bonds between
cytosine and guanine
are shown here.)
C
N
Hydrogen Bonds
N
C
N
C
C
C
N
O
Hydrogen Bonds, cont.
• When making
hydrogen bonds,
cytosine always pairs
up with guanine,
• And adenine always
pairs up with
thymine.
• (Adenine and thymine
are shown here.)
O
N
O
C
C
C
N
C
C
Important:
• Adenine and Thymine always join
together
A T
• Cytosine and Guanine always join
together
C G
DNA Structure
 Because of this complementary base pairing,
the order of the bases in one strand determines
the order of the bases in the other strand.
A
T
C
G
T
A
C
G
A
T
G
C
T
A
DNA Structure
 To crack the genetic code found in DNA we need
to look at the sequence of bases.
 The bases are arranged in triplets called codons.
AGG-CTC-AAG-TCC-TAG
TCC-GAG-TTC-AGG-ATC
DNA Structure
 A gene is a section of DNA that codes for a protein.
 Each unique gene has a unique sequence of bases.
 This unique sequence of bases will code for the
production of a unique protein.
 It is these proteins and combination of proteins
that give us a unique phenotype.
DNA
DNA Replication Models
Replication fork
lagging strand
Leading strand
Replication fork
DNA Replication
DNA Replication
• DNA must be copied
• The DNA molecule produces 2
IDENTICAL new complementary
strands following the rules of base
pairing:
A-T, G-C
•Each strand of the
original DNA serves as a
template for the new
strand
DNA Replication
• Semiconservative
Model:
Watson and Crick showed:
the two strands of the
separate, and each
functions as a for synthesis
of a new complementary
strand.
.
DNA Template
Parental DNA
New DNA
DNA Replication
• Complementary base pairs form new strands.
DNA
Replication Quiz
1. Why is replication necessary?
2. When does replication occur?
3. Describe how replication works.
4. Use the complementary rule to
create the complementary strand:
A---?
G---?
C---?
T---?
A---?
G---?
A---?
G---?
C---?
A---?
G---?
T---?
Replication Quiz
1. Why is replication necessary?
So both new cells will have the correct DNA
2. When does replication occur?
During interphase (S phase).
3. Describe how replication works.
Enzymes unzip DNA and complementary
nucleotides join each original strand.
4. Use the complementary rule to
create the complementary strand:
A---T
G---C
C---G
T---A
A---T
G---C
A---T
G---C
C---G
A---T
G---C
T---A
Satu tim besar yang terdiri dari enzim dan protein lain menjadi pelaksana
replikasi DNA
Protein-protein yang berperan dalam replikasi DNA
1. Helikase: enzim yang berfungsi membuka heliks ganda di cabang replikasi, memisahkan
untai lama.
2. Protein pengikat untai tunggal: menjaga agar untai-untai tetap terpisah selama bertindak
sebagai cetakan dalam sintesis untai-untai komplementer yang baru.
3. Primase: membentuk primer
Satu tim besar yang terdiri dari enzim dan protein lain menjadi pelaksana
replikasi DNA
Protein-protein yang berperan dalam replikasi DNA
4.
DNA polimerase: pemanjangan untai DNA baru
5. Ligase: menggabungkan rantai DNA
Enzymology of DNA replication
DNA strand separation
Helicases: unwind double strand DNA
Single-strand DNA binding proteins (SSBs): participate in
DNA strand separation but do not catalyze the strand
separation process.
They bind to single strand DNA as soon as it forms and coat
it so that it cannot anneal to reform a double helix.
Topoisomerases: introduce transient single or double
stranded breaks into DNA and thereby allow it to change its
form, or topology.
DNA polymerases
Three DNA polymerases (I, II, III)
DNA polymerase I (102 KD): has three different enzymatic
activities
1) DNA polymerase
(proof reading to increase fidelity)
2) 3’-5’ exonuclease activity
(remove RNA primers or damage DNA on its path)
3) 5’-3’ exonulcease activity
3’-5’ exo
Pol III holoenzyme
10 subunits
Move at an extremely rapid rate (1000 nts/second)
Proof reading
Eukaryotes have multiple DNA polymerases
THANK YOU
YUSRON SUGIARTO, STP, MP, MSc