DNA carries the genetic instructions for living organisms. In 1953, Watson and Crick discovered that DNA has a double helix structure, with nucleotides on each strand connected through hydrogen bonds between complementary nucleotide base pairs (A-T, C-G). DNA replicates semi-conservatively prior to cell division, using each original strand as a template to produce two new double helices. Genes within DNA code for proteins through transcription and translation.

1. DNA
(Deoxyribonucleic acid)
Mr. Sagar Kishor Savale
[Department of Pharmacy (Pharmaceutics)]
2015-016
avengersagar16@gmail.com
Department of Pharmacy (Pharmaceutics) | Sagar savale
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2. History Of DNA
• Discovery of the DNA double helix
Frederick Griffith – Discovers that a factor in diseased bacteria can transform harmless
bacteria into deadly bacteria in (1928)
Rosalind Franklin - X-ray photo of DNA in (1952)
Watson and Crick - described the DNA molecule from Franklin’s X-ray in (1953)
• Watson & Crick proposed
• DNA had specific pairing between the nitrogen bases:
• ADENINE – THYMINE
• CYTOSINE - GUANINE
• DNA was made of 2 long stands of nucleotides arranged in a specific way called the “Complementary Rule”
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3. C
T
A
A
T
CG
GC
A
C G
AT
AT
A T
TA
C
TA
0.34 nm
3.4 nm
(a) Key features of DNA structure
G
1 nm
G
(c) Space-filling model
T
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4. DNA
• DNA = deoxyribonucleic acid.
• DNA carries the genetic information in the cell – i.e. it carries the instructions for making all the structures and
materials the body needs to function.
• DNA is capable of self-replication.
• Most of the cell’s DNA is carried in the nucleus – a small amount is contained in the mitochondria.
•
• Importance of DNA
• Molecule
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7. • 2’-deoxyribose sugar
• Four bases:
• Adenine, A
• Guanine, G
• Thymine, T
• Cytosine, C
• Purine bases
Adenine and guanine
Two carbon rings
• Pyrimidine bases
Thymine and cytosine
A single carbon ring
Base part
Sugar part
DNA = deoxyribonucleic acid.
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11. DNA Structure
• DNA is a nucleic acid, made of long chains of nucleotides
Nucleotide
Phosphate
group
Nitrogenous
base
Sugar
Polynucleotide Sugar-phosphate backbone
DNA nucleotide
Phosphate
group
Nitrogenous base
(A, G, C, or T)
Thymine (T)
Sugar
(deoxyribose)
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12. DNA has four kinds of bases, A, T, C, and G
Pyrimidines
Thymine (T) Cytosine (C)
Purines
Adenine (A) Guanine (G)
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14. DNA is a Double Helix
• Nucleotides
• A, G, T, C
• Sugar and phosphate form the
backbone
• Bases lie between the backbone
• Held together by
H-bonds between the bases
• A-T – 2 H bonds
• G-C – 3 H bonds
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15. DNA Double Helix
P
P
P
O
O
O
1
2
3
4
5
5
3
3
5
P
P
P
O
O
O
1
2 3
4
5
5
3
5
3
G C
T A
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16. H - Bonds
• 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 with dotted lines.
• When making hydrogen bonds, cytosine always pairs up with guanine
• Adenine always pairs up with thymine
• Adenine is bonded to thymine here
C
C
C
C
N
N
O
N
C
C
C
C
N
N
O
N
N
N
C
C
C
C
C
N
N
O
O
C
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17. • Hydrogen bonds between bases hold the strands together: A
and T, C and G
Ribbon model Partial chemical structure Computer model
Hydrogen bond
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19. Chargraff’s Rule
•Adenine and Thymine always join together
• A T
• Cytosine and Guanine always join together
• C G
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21. • Each strand is a template for a new strand
helicase
DNA polymerase
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22. The ladder model
• The structure of DNA can be understood more easily by untwisting the double helix and
displaying the molecule as if it were a ladder.
• The side rails of the ladder (the “backbone”) are alternating phosphate and sugar
molecules. The rungs are paired nitrogen base molecules held together by a hydrogen bond.
Nucleotide
Base pair
Backbone
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23. The base pairing rule
• Each “rung” of the DNA ladder is formed from two nitrogen bases.
• There are four bases – adenine (A), thymine (T), cytosine (C), and guanine (G).
• The base adenine always bonds with thymine (A-T), and cytosine always bonds with guanine (C-G).
• The binding of two nucleotides forms a base pair. In DNA, cytosine and guanine are bound together by 3 hydrogen bonds,
whereas adenine and thymine are bound by 2 hydrogen bonds.
Location of DNA
Most of the DNA occurs in the cell nucleus;
however, each mitochondrion contains
37 genes – this is referred to as
mitochondrial DNA.
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24. The function of DNA Genes
• A chromosome consists of segments of DNA known as genes.
• Genes contain the instructions for the construction of a particular protein, or RNA.
• It is estimated that there are about 20,000–25,000 genes in the human genome (i.e. about 3
billion base pairs).
• Genetic information is carried in the linear sequence of nucleotides in DNA
• Genetic information contains instructions to synthesize proteins
• DNA forms double helix with two complimentary strands holding together by hydrogen bonds
between A-T (2 bonds) and G-C (3 bonds)
• DNA duplication occurs using one strand of parental DNA as template to form complimentary
pairs with a new DNA strand.
• DNA is in nucleus in eucaryotes
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25. Introns and exons
• Genes consist of introns and exons
• Exons are sections of coding DNA – i.e. they contain instructions for making
proteins.
• Introns are sections of non-coding DNA (once called "junk DNA") – i.e. they
do not contain instructions for making proteins but are now believed to serve
other important functions.
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26. The Genetic Code
• Describes how nucleotide
sequence is converted to protein
sequence
• Unit of three nucleotides = a
codon
• A codon codes for a specific
amino acid (structural
component of protein)
• The four bases can form 64
different codons
• 20 amino acids are found from
the nature
• Regulatory codons
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27. Reading the code
• The sequence of bases is read in groups of three called codons.
• Thus the sequence:
AAGCCGTTTAGAGAGATTCCT
Is read as:
AAG CCG TTT AGA GAG ATT CCT
• Each codon represents one of the 20 different amino acids.
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28. DNA
chromatin
chromatin fibers
fibers connected to
chromosome scaffold
Condenced scaffold
Chromosome
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29. How DNA works
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30. Genes as Information Transfer
• A gene is the sequence of nucleotides within a portion of DNA that codes for a
peptide or a functional RNA
• Sum of all genes = genome
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31. Replication of DNA
• Semiconservative
• Daughter DNA is a double helix with 1 parent strand and 1 new strand
• Found that 1 strand serves as the template for new strand
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34. DNA Template
Each strand of the parent DNA is used as a template to make the new daughter strand DNA replication makes 2
new complete double helices each with 1 old and 1 new strand
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35. Replication Origin
• Site where replication begins
• 1 in E. coli
• 1,000s in human
• Strands are separated to allow replication
machinery contact with the DNA
• Many A-T base pairs because easier to break 2
H-bonds that 3 H-bonds
• Note anti-parallel chains
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36. Replication Fork
• Bidirectional movement of the DNA replication machinery
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37. DNA Polymerase
• An enzyme that catalyzes the addition of a
nucleotide to the growing DNA chain
• Nucleotide enters as a nucleotide tri-PO4
• 3’–OH of sugar attacks first phosphate of tri-
PO4 bond on the 5’ C of the new nucleotide
• releasing pyrophosphate (PPi) + energy
• Bidirectional synthesis of the DNA double
helix
• Corrects mistaken base pairings
• Requires an established polymer (small RNA
primer) before addition of more nucleotides
• Other proteins and enzymes necessary
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38. How is DNA Synthesized
• Original theory
• Begin adding nucleotides at origin
• Add subsequent bases following pairing rules
• Expect both strands to be synthesized simultaneously
• This is NOT how it is accomplished
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40. • Actually how DNA is synthesized
• Simple addition of nucleotides along one strand, as expected
• Called the leading strand
• DNA polymerase reads 3’  5’ along the leading strand from the RNA primer
• Synthesis proceeds 5’  3’ with respect to the new daughter strand
• Remember how the nucleotides are added 5’  3’
• Actually how DNA is synthesized
• Other daughter strand is also synthesized 5’3’ because that is only way that DNA can be
assembled
• However the template is also being read 5’3’
• Compensate for this by feeding the DNA strand through the polymerase, and primers and make many short
segments that are later joined (ligated) together
• Called the lagging strand
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41. DNA Replication Fork
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43. Starting Synthesis
• DNA polymerase can only ADD nucleotides
to a growing polymer
• Another enzyme, primase, synthesizes a short
RNA chain called a primer
• DNA/RNA hybrid for this short stretch
• Base pairing rules followed (BUT A-U)
• Later removed, replaced by DNA and the
backbone is sealed (ligated)
• Primers
• Simple addition of primer along
leading strand
• RNA primer synthesized 5’  3’,
then polymerization with DNA
• Many primers are needed along the
lagging strand
• 1 primer per small fragment of new
DNA made along the lagging strand
• Called Okazaki fragments
• Removal of Primers
Other enzymes needed to excise (remove) the primers
Nuclease – removes the RNA primer nucleotide by
nucleotide
Repair polymerase – replaces RNA with DNA
DNA ligase – seals the sugar-phosphate backbone by
creating phosphodiester bond
Requires Mg2+ and ATP
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47. Repair Mechanisms
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48. DNA Transcription
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49. DNA Translation
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50. A summary of transcription and translation in a eukaryotic cell
TRANSCRIPTION
RNA is transcribed
from a DNA template.
DNA
RNA
polymerase
RNA
transcript
RNA PROCESSING
In eukaryotes, the
RNA transcript (pre-
mRNA) is spliced and
modified to produce
mRNA, which moves
from the nucleus to the
cytoplasm.
Exon
RNA transcript
(pre-mRNA)
Intron
NUCLEUS
FORMATION OF
INITIATION COMPLEX
After leaving the
nucleus, mRNA attaches
to the ribosome.
CYTOPLASM
mRNA Growing
polypeptide
Ribosomal
subunits
Aminoacyl-tRNA
synthetase
Amino
acid
tRNA
AMINO ACID ACTIVATION
Each amino acid
attaches to its proper tRNA
with the help of a specific
enzyme and ATP.
Activated
amino acid
TRANSLATION
A succession of tRNAs
add their amino acids to
the polypeptide chain
as the mRNA is moved
through the ribosome
one codon at a time.
(When completed, the
polypeptide is released
from the ribosome.)
AnticodonA A A
U G G U U U A U G
E A
Ribosome
1
5
5
3
Codon
2
3 4
5
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51. Chromosomes
• 23 chromosome pairs  46 chromosomes
• 44 autosomes, 2 sex chromosomes
• X and Y –chromosomes
• XX  female
• XY  Male
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53. Sex Determination in Humans
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54. References
• www.wikipedia.org
• www.sciencedirect.com
• www.medscape.com
• www.biolife.com
• www.nature.com
• www.Googlescoler.com
• www.pubmed.com
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