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INTRODUCTION TO GENETICS
Genetics is the study of heredity, the process in which a parent passes certain gene onto their children. A person's appearance – height, hair color, skin color, and eye color -- are determined by genes.
Gene: a gene is a nucleotide sequence in DNA that specifies a polynucleotide or RNA.
History
• 1946 – DNA is the main constituent of genes (Avery)• 1950 – First X-ray pictures of DNA (Franklin)• 1953 – DNA structure revealed (Watson and Crick)• 1970 onwards - Multiple conformations and structures, initially from
fibers• 1973 - X-ray structure confirms double helix (Rich)• 1974 - t-RNA structure (Kim)• 1980 – Structure of first complete turn of B DNA (Dickerson)
Location of DNA
In Prokaryotes:- DNA is not separated from the rest of cellular components.
In eukaryotes :- DNA is located in the nucleus , and separated from the rest of the
cell by nuclear envelope.
DNA is bound to proteins forming a complex called chromatin.
Less than 0.1% of the total DNA in a cell is present in mitochondria.
Euchromatin= diffuse chromatinHeterochromatin= dense chromatin
P= petit (small)
Chromosome
23 pairs of chromosomes
In eukaryotic cells, a linear structure composed of a single DNA molecule complexes with protein.
Chromosome Number in Various Organisms
Organism Total Chromosome Number
Human
Chimpanzee
Dog
Cat
Mouse
Mosquito
Potato
Tomato
46
48
78
72
40
6
48
24
Histones
Electron micrograph of nucleosomes Attached by strands of nucleic acid.
Solenoid
H2A dimer
H2B dimer
H3-H4 tetramer
DNA Strands
Watson and Crick’s double-helical model of DNA
1. The DNA molecule consists of two polynucleotide chains wound around each other in a right-handed double helix
2. The two chains are antiparallel.
3. The sugar-phosphare backbones are on the outsides of the double helix, with base orientated toward the central axis.
4. The bases in each of the two polynucleotide chains are bonded together by hydrogen bonds. The specific pairings observed are A bonded with T (2 hydrogen bonds) and G bonded with C ( 3 hydrogen bonds) and its according to Chargaff’s rule. They are called complementary base pairs. 5.The base pairs are 0.34 nm apart in the DNA helix. A complete turn (360˚) turn of the helix takes 3.4 nm, therefore there are 10 base pairs per turn. 6.
Determination of structure of DNA DNA is composed of nucleotides.
Nucleotides is composed of a base, a sugar and phosphate.
PO
O
O-
O O
CC
C C
H
H
H
OH
H
CH2
1
23
4
5Base
BASE
Uracil (U) instead of Thymine in RNA.
Purine Pyrimidine
• Adenine (A)
• Guanine (G)
Cytosine (C)
Thymine (T)
SUGAR
Deoxyribose (DNA)
Ribose (RNA)
O
CC
C C
H
O H
H
OH
H
CH2
1
23
4
5
OO
CC
C C
H
H
H
OH
H
CH2
1
23
4
5
O
C
CHO
OHH
OHCH
CH2OH
OHCH
D-Ribose
C
CHO
OHH
OHCH
CH2OH
OHCH
D-Ribose
Reduction
C
CHO
HH
OHCH
CH2OH
OHCH
2-deoxy-D-Ribose
Alpha and Beta Anomers
C
CHO
OHH
OH C H
CH2OH
OHCH
OHCH
D-Glucose
C OHH
OH C H
CH2OH
CH
OHCH
Alpha-D-Glucose
C OHH
O
C OHH
OH C H
CH2OH
CH
OHCH
Beta- D-Glucose
COH H
O
Hemiacetal linkage formation Hemiacetal linkage formation
Differ in configuration of –OH group on anomeric carbon atom.
The Glycosidic Bond• Connects ribose sugar to the base
O-glycosides: when hydroxyl group on anomeric carbon of a sugar reacts
with an alcohol (sugar) O-glycoside is formed.
O-glycosidic linkage is present in disaccharides and polysaccharides.
So, disaccharides, oligosaccharides and polysaccharides are O-glycosides.
N-glycosides
N-glycosides: when hydroxyl group on anomeric carbon of a sugar reacts
with an amine N-glycoside is formed.
N-glycosidic linkage is present in nucleotides, RNA and DNA.
So, nucleotides, RNA and DNA are examples of N-glycosides.
Nucleotides
Monomeric units of nucleic acids.
Each nucleotide consists of a heterocyclic nitrogenous base,
a pentose sugar and phosphate.
Base
C
O
C
C C
H
OH
H
OH
H
CH2
1
23
4
5
Sugar
PO
O
O-
O
Phosphate
PO
O
-O-
PO
O
O-
PO
O
O-
O
CC
C C
H
OH
H
OH
H
CH2
1
23
4
5
O Base
Nucleoside
Nucleoside monosphosphate (NMP)
Nucleoside diphosphosphate (NDP)
Nucleoside triphosphosphate (NTP)
Nucleotides
BASE NUCLEOTIDE
Adenine (A)
Guanine (G)
Cytosine (C)
Thymine (T)
Uracil (U)
Adenosine
Guanosine
Cytidine
Thymidine
Uridine
C
NH2
Adenine
C
CC CH
H
H
N
N
N
N
1
2
34
5
67
9
C
O
Guanine
C
CC CH
H
H
N
N
N
N
1
2
34
5
6
8
7
98
C
NH2
Cytosine (C)
CH
CHC
N
NH
1
2
34
5
6
O
C
O
Thymine (T)
C-CH3
CHC
HN
NH
1
2
34
5
6
O
• • •A
GC
T
T
CG
A
• • •• • •• • •
• • •A T
• • • C
• • • AT
G
• • •AG
C
T
T
C
G
A
• • •• • •• • •
• • •A
GC
U
U
CG
A
• • •• • •• • •
• • •A U
• • • C
• • • AU
G
• • •AG
C
U
U
C
G
A
• • •• • •• • •
Base pairing
Hydrogen bonds
H
H
CC
CN
NC
N
C
N
N
H
H
H
Adenine
1
23
4
6 5
7
8
9
CC
C
CN
N
O
H
CH
HH
Thymine
12
3
45
6
N
Cytosine
H
H
H
CC
C
CN
N
H
H
H
ON
CC
CN
NC
N
C
N
O
H
Guanine
H
3‘ end
5‘ end3‘ end
5‘ end
5’ end
Phosphate backbone
PO
O
O
CH2O
-
PO
O
O
CH2O
-
PO
O
O
CH2O
-
Phosphodiester bonds
Phosphodiester bonds
3’ end
PO
O
O
CH2O
-
O
DNA Strands Are Antiparallel
5’ end
PO
O
O
CH2O
-
PO
O
O
CH2O
-
P O
O
O
CH2 O
-
3’ end
PO
O
O
CH2O
-
P O
O
O
CH2 O
-
5’ end
5
3
PO
O
O
CH2O
-
5
3P O
O
O
CH2 O
-
5
3
P O
O
O
CH2 O
-
3’ end
5
3
5’-carbon of the sugar is above 3’-carbon: The strand is said to run in 5’to 3’ direction.
3’-carbon of the sugar is above 5’-carbon: The strand is said to run in 3’to 5’ direction.
The two strands run in opposite direction.
Angstrom Unit= 0.1 nanometer
The A form, which predominates in DNA-RNA hybrids, is similar to the B form , but is more compact.
In the Z form, the bases of the two DNA strands are positioned toward the periphery of a left-handed helix.It is designated “Z” because, in each strand , a line connection the phosphates “zigs” and “zags”.
Predominates in vivo Predominates in DNA-RNA hydrinds
Types of DNA
有難う御座います
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