Download Human genome sequence

Human genome sequence
DNA = DEOXYRIBONUCLEIC ACID
RNA = RIBONUCLEIC ACID
Strong acid hydrolyses DNA & RNA into 3 components:
•
•
•
nitrogenous base (4 different ones)
sugar
phosphoric acid
Mild acid hydrolyses DNA & RNA into 2 components:
•
•
Nucleoside = base—sugar
Nucleotide = base-sugar-phosphate
DNA & RNA are polymers of nucleotides
NUCLEOTIDE structure: nitrogenous
bases
6
7
PURINE
5
1N
N
8
2
N
3
amino NH2
4
N9
H
N
N
ADENINE — A
N
N
H
O
N
HN
GUANINE — G
amino
H2N
keto (carbonyl)
N
N
H
NUCLEOTIDE structure
4
PYRIMIDINE
3N
5
2
6
N
1
CYTOSINE — C THYMINE — T
NH 2
N
amino
O
HN
URACIL— U
keto (carbonyl)
CH3
O
HN
methyl
O
N
H
O
N
H
keto (carbonyl)
O
N
H
First difference between DNA and RNA:
DNA contains the bases A, G, C and T
RNA contains the bases A, G, C and U
NUCLEOTIDE structure
2. THE SUGARS — pentoses
5
HO CH2
D-ribose (RNA)
O
1
4
H
H
2
3
OH
D-2-deoxyribose
(DNA)
OH
5
HO CH2
OH
O
OH
1
4
H
H
2
3
OH
OH
H
Second difference between DNA and RNA:
DNA contains 2-deoxyribose
RNA contains ribose
NUCLEOTIDE structure
3. PHOSPHORIC ACID
O
O
pH 7
HO P
OH
OH
(H3PO4)
Phosphoric acid
O-
P
OH
O-
(HPO42-)
Phosphate ion
NUCLEOSIDE = base—sugar
NH2
N
N
N
N
adenine
DEOXYADENOSINE =
adenine—deoxyribose
HO CH2
O
H
H
OH
H
OH
deoxy ribose
NUCLEOTIDE structure
Base—sugar—phosphate
NH2
N
e.g. ADENOSINE
N
N
O
O-
adenine
5'
P HO
OCH2
O
O-
Adenosine 5'-monophosphate
(5'-AMP)
N
H
H
OH
OH
ribose
NUCLEOSIDE numbering
NH2
4
"Prime" mark: '
5
N3
6
The 3' and 5' positions
are very important for
understanding DNA and
RNA structure and
function
2
N
1
5'
HO CH2
O
1'
4'
H
H
3'
2'
OH
OH
O
Adenosine 5'-monophosphate (5'-AMP)
NH2
Adenosine 5'-diphosphate (5'-ADP)
N
Adenosine 5'-triphosphate (5'-ATP)
N
N
O
-
O
P
O-
O
O
-
OO
P
O-
-
OO
N
adenine
5'
P HO
OCH2
O
OH
H
OH
OH
ribose
How are mononucleotides linked together to
form the polymers DNA and RNA?
NH2
N
3',5'-phosphodiester
bond
O
O
N
O
5'
P HO
OCH2
O-
NH2
H
O
N
H
N
3' OH
OH
O
O
5'
P HO
O CH2
O
OH
3'OH
H
OH
O
POLARITY
NH2
A
N
N
N
O
O
N
C
NH2
5'
P HO
O CH2
O
N
OH
3'OH
H
O
N
OH
O
O
Single-stranded
polynucleotides have one free
5' end and one free 3' end —
they exhibit POLARITY
C
5'
P HO
OCH2
O-
NH2
H
O
N
H
N
3'OH
OH
O
O
5'
P HO
OCH2
O
OH
3'OH
H
OH
O
DNA is a double helix
What information did Watson and Crick use
in 1953 to arrive at their "double helix"
structure for DNA?
•
Studies of DNA
hydrolysis showed
that the repeating
unit was a
NUCLEOTIDE
• CHARGAFF's "rules"
%A = %T
%G = %C
%A = %T
%G = %C
%G = %(C + 5-MeC)
Plants have a particularly high
content of 5-MeC
Note that in addition to the bases A,G, C and T
there are some minor bases found in DNA
NH2
CH3
N
O
NHCH 3
N
H
5-methylCYTOSINE
prokaryotes and eukaryotes
N
N
N
N
H
6-methylADENINE
prokaryotes
X-ray diffraction patterns obtained by
Wilkins, Franklin & Gosling showed:
 helical structure with
repeats at 0.34 and 3.4 nm
 2 nm wide
 phosphates on outside of
structure
 Density of chain suggests
the helix contains 2
strands
Conclusion: DNA MUST be double-stranded
H
H
A
N
3 H-bonds
N
N
GC base pair
H
O
N
H3C
N
H
H
N
H
N
G
N
O
T
AT base pair
2 H-bonds
N
O
1.08 nm
H
H
N
N
N
H
H
N
N
H
H
N
C
O
H
1.08 nm
Double helical DNA
Minor
groove
Major
groove
3.4 nm:
One helical
turn
Base pairs
"stacked"
vertically
in interior
sugarphosphate
backbone
0.34 nm
10 bp
per turn
2 nm
2 nm
Strands are
Both strands coiled round a
ANTIPARALLEL
common axis
One runs
5' to 3'
5'
3'
3'
5'
Other runs
3' to 5'
Watson & Crick solved the structure of DNA in
1953
"...A structure this pretty just had to exist."
- James Watson in The Double Helix
The implications of the ‘Double Helix’
Based on the fact that DNA is the genetic material:
Stable
Faithful replication and propagation of life
– Two strands: one can form the template for DNA
replication
Faithful transmission of information to RNA
– One strand acts as template
RNA then transfers information to proteins
http://science.nhmccd.edu/biol/bio1int.htm
DNA replication
Protein Structure
Amino acid structure
H
H
N
H
C
R
O
C
OH
R is a chemical group that varies in different amino acids.
C is central “chiral” carbon.
Non-polar amino acids
Polar amino acids
Peptide
bonds result
from
dehydration
of A.A.s
Primary
structure is the
sequence of
A.A.s
Sickle-cell anemia cause
Secondary structure
Tertiary structure
Quaternary structure
If all cells come from other cells where
did the first ‘life’ come from?
The Miller-Urey experiment
Water is heated in a
closed apparatus
containing methane (CH4),
ammonia (NH3) and
hydrogen (H2) and an
electric discharge is
passed through the
mixture.
Many precursors can be produced in simple
pre-biotic conditions
• Some amino acids found (building blocks for
proteins)
• Some nucleic acids found e.g. adenine
• Some sugars found including ribose