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8/3/2019 1 DNA Structure
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Dr:AbouSree Ellethy
Dentistry- 1432-1433
DNA & RNA structure &
function Objectives
Types of purine & pyrimidine bases and sugars present in nucleic acids.
Define nucleoside, nucleotide, DNA & RNA and name their structural components
Define nuclear DNA, name its different forms and show structure of its B form.
Define (Codon & types) - gene- (coding & non-coding) .
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The building units for Carbohydrates are««««««.
Amino AcidAmino Acid
Fatty acidFatty acid
MonosaccharidesMonosaccharides
The building of fats units are «««««
SugarsSugars
Fatty acidsFatty acids
Amino AcidsAmino Acids
The building units for Proteins are««««««.
SugarsSugars
Fatty acidsFatty acids
Amino AcidsAmino Acids
The building units for Genetic materials are ««««???????????
««««««««««««
««««««««««««
««««««.««««««.
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The building units for Carbohydrates are««««««.Amino AcidsAmino Acids
Fatty acidsFatty acids
SugarsSugars
The building of fats units are «««««
SugarsSugarsFatty acidsFatty acids
Amino AcidsAmino Acids
The building units for Proteins are««««««.
SugarsSugars
Fatty acidsFatty acidsAmino AcidsAmino Acids
The building units for Genetic materials are ««««???????????
««««««««««««
««««««««««««
««««««.««««««.
Revision
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- Pyramidines: Thymine and cytosine have single-ring structures.
- Purines: Adenine and guanine have double-ring structures.
Nitrogenous Bases
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AdenineAdenine (A) would(A) wouldformform 2 hydrogen2 hydrogen bondsbonds
only withonly with thyminethymine (T(T))
GuanineGuanine (G) would form(G) would form
3 hydrogen bonds3 hydrogen bonds onlyonly
withwith cytosinecytosine (C(C).).
Base pairing hasBase pairing hasbalanced ratio of (A = T)balanced ratio of (A = T)
& (G = C) bases& (G = C) bases basedbased
Chargaff·s RuleChargaff·s Rule
Sugars & Bases Pairing
Deoxy ribose Ribose
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If there is 30% AdenineAdenine, how much CytosineCytosine ispresent?
Answer:Answer:
There would be 20% CytosineCytosine
Adenine (30%) = Thymine (30%)Adenine (30%) = Thymine (30%)
Guanine (20%) = Cytosine (20%)Guanine (20%) = Cytosine (20%)
Therefore, 60% ATherefore, 60% A--T + 40% CT + 40% C--GG
Question:Question:
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Nucleobase+ deoxy sugar Nucleobase + Sugar
Deoxy-adenosine Adenosine
Deoxy-thymidineThymidine
Deoxy-cytidineCytidine
Deoxy-guanosineGuanosine
Deoxy-uridineUridine
A base is linked via a glycosidic bond to sugar unit like Ribose or
Deoxyribose sugars.
Nomenclature by adding -idine to the root name of pyrimidines or -osine
to the root name of purines.
Nucleosides
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Nucleotides represent mono phosphonucleotides, di-phosphonucleotides & tri-phosphonucleotides.
The phosphoryl group is added on C-5 of the pentose.
P
S B
Covalent Bonds
Nucleotide consists of 3Nucleotide consists of 3 components:components:
1. A phosphate group
2. A sugar :Deoxyribose.
3. A Nitrogenous Base
Held Together by Covalent Bonds.
Nucleotides
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Purines nucleotides: Adenine or Guanine + sugar+ phosphate group
Cytosine
Pyramidines nucleotides: Cytosine and Thymine + sugar+ phosphate group
Thymine
GuanineAdenine
Nucleotides
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O
H
H
H
HH
CH2
DeoxyriboseDeoxyribose sugar sugar ((O on C2 is missedO on C2 is missed))
O
OH
H
H
HH
CH2
Ribose sugar Ribose sugar
((no missed Ono missed O))
Ribo-Nucleic-AcidDeoxiribo-Nucleic-Acid
Single stranded nucleic acidSingle stranded nucleic acidDouble stranded nucleic acidDouble stranded nucleic acid
Bases: A, G, C, T Bases: A, G, C, U
DNA & RNA Structure
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B-DNA is the most common right-handed (20
angstrom diameterA
The length for one complete turn of the double
helix (34 Å).
The width of the double helix (20 Å).
A single turn of B-DNA about the axis of the
molecule contains ten base pairs (3.4 Å /bps.)
The distance spanned by one turn of B-DNA is 3.4
nm. The width (helical diameter) of the double helix
in B-DNA is 2 nm.
complementary base-pairing (watson-crick)
A-T
G-C
B form of DNA
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Definition: It is three successive nucleotides of an mRNA that encode a
specific amino acid in polypeptide chain.
There are 64 codons code for the 20 amino acids.
There are more than one codone for the same amino acid
Start codon is (methionine, AUG)
Stop codons are (UAA, UAG & UGA)
Codon
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Defination: Altering the nucleotide sequence
Example Original DNA Template C A A T G C T A C
1. Substitution: one base pair for another.
C A A C G C T A C
2. Deletion: missing a base.
C A A T --- C T A C
3. Addition: adding an extra baseC A A T- A- G C T A C
4. Inversion: bases are rearranged.
C A G A T C T A C
Types of Mutations:
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Types of Mutations:
A- Point mutation
1. Silent= codons contain the changed base will code for the same amino acid.
Example: UCA UCU codes for Serine
2. Mis sense= codons contain the changed base may code for a different
amino acid UCA= serine CCA=proline
3. Non sense= codons contain the changed base may become a Termination
codon UCA= serine UAA=stop codon
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B-Frame- shift mutation
Deletion or addition of one or two base to DNA sequence, leading to
change in reading frame (reading sequence)
Types of Mutations:
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Gene:A segment of DNA on the chromosome that codes for a specific protein.
(1) (2) (3) (4)
(5)Gene composed of
Enhancers: control elements or sequences that activate promotors.
Promotors: DNA sequences activate synthesis of new DNA strand.
Exons: coding DNA sequences (share protein synthesis)
Introns: they are non coding DNA sequences (does not share protein synthesis)
Structure of gene