Copy of DNA
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Transcript of Copy of DNA
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DNA
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DNA stands for deoxyribose nucleic acid
This chemical substance is present in the nucleusof all cells in all living organisms
DNA controls all the chemical changes which
take place in cellsThe kind of cell which is formed, (muscle, blood,
nerve etc) is controlled by DNAThe kind of organism which is produced
(buttercup,giraffe, herring, human etc) is controlled byDNA
DNA 2
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A HISTORY OF DNA Discovery of the DNA double helix
A. Frederick Griffith Discovers that a factor indiseased bacteria can transform harmless bacteriainto deadly bacteria (1928)
B. Rosalind Franklin - X-ray photo of DNA.(1952)
C. Watson and Crick - described the DNAmolecule from Franklins X -ray.
(1953)
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4
DNA by the Numbers
Each cell has about 2 m ofDNA.The average human has 75
trillion cells.The average human hasenough DNA to go from theearth to the sun more than
400 times.DNA has a diameter of only0.000000002 m .
The earth is 150 billion mor 93 million miles fromthe sun.
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DNA is a very large molecule made up of a long
chain of sub-units
The sub-units are called nucleotides
Each nucleotide is made up of
a sugar called deoxyribose
a phosphate group -PO 4 and
an organic base
DNA molecule3
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Ribose is a sugar, like glucose, but with only fivecarbon atoms in its molecule
Deoxyribose is almost the same but lacks oneoxygen atom
Both molecules may be represented by the symbol
Ribose & deoxyribose4
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DNA Nucleotide
OO=P-O
O
PhosphateGroup
NNitrogenous base
(A, G, C, or T)
CH2
O
C 1C 4
C 3 C 2
5
Sugar(deoxyribose)
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The most common organic bases are
Adenine (A)Thymine (T)
Cytosine(C)
Guanine (G)
The bases5
o Erwin Chargaff showed the amounts of the four bases onDNA ( A,T,C,G) In a body or somatic cell:
A = 30.3%G = 19.5%T = 30.3%C = 19.9%
Single ring PYRIMIDINES
Double ring PURINES
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The deoxyribose, the phosphate and one of the bases
adenine
deoxyribose
PO 4
Combine to form a nucleotide
Nucleotides6
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A molecule ofDNA is formed bymillions ofnucleotides joinedtogether in a longchain
PO 4
PO 4
PO 4
PO 4
sugar-phosphate
backbone+ bases
Joined nucleotides 7
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PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
2-stranded DNA 9
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The bases always pair up in the same way (Chargaffs Rule)
Adenine forms a bond with Thymine
and Cytosine bonds with Guanine
Bonding 110
Adenine Thymine
Cytosine Guanine
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PO 4
PO 4
PO 4
thymine
PO 4
PO 4
PO 4
PO 4
adenine
cytosine
PO 4
guanine
Bonding 211
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PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
Pairing up12
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Antiparallel Strands
One strand of DNAgoes from 5 to 3(sugars)
The other strand isopposite indirection going 3 to5 (sugars)
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The paired strands are coiled into a spiral called
A DOUBLE HELIX
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1
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A DIYMODEL OF PART OF A DNAMOLECULE
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16
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Before a cell divides, the DNA strands unwindand separate
Each strand makes a new partner by addingthe appropriate nucleotides
The result is that there are now two double-stranded DNA molecules in the nucleus
So that when the cell divides, each nucleuscontains identical DNA
This process is called replication
Replication16
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PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
THE STRANDS SEPARATE
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PO4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
PO 4
Each strand builds up its partner by adding the appropriatenucleotides
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The sequence of bases in DNA forms theGenetic Code
A group of three bases ( a triplet ) controlsthe production of a particular amino acid inthe cytoplasm of the cell
The different amino acids and the order inwhich they are joined up determines the sort ofprotein being produced
Genetic code 119
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Ser-Cyst-Val-Gly-Ser-Cyst Ala
ValVal-Cyst-Ser-Ala-Ser-Cyst-Gly
Val- Cyst-Ala-Ala-Ser-Gly
This is a small, imaginary protein molecule showing
how a sequence of 5 different amino acids coulddetermine the shape and identity of the molecule
Each amino acid (Serine, Cysteine, Valine, Glycine andAlanine) is coded for by a particular triplet of bases
Genetic code 2 20
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For example
Cytosine
Adenine Codes for Valine
Cytosine (C)
Guanine (G)
Adenine (A)
Codes for Alanine
Thymine
Coding21
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This is known as the triplet code
Each triplet codes for a specific amino acid
CGA - CAA - CCA - CCA - GCT - GGG - GAG - CCA -
Ala Val Gly Gly Arg Pro Leu Gly
Ala Val Gly Gly Arg Pro Leu Gly
The amino acids are joined together in the correctsequence to make part of a protein
Triplet code 22
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The proteins build the cell structures
They also make enzymes
The DNA controls which enzymes are made and
the enzymes determine what reactions take place
The structures and reactions in the cell determinewhat sort of a cell it is and what its function is
So DNA exerts its control through the enzymes
DNA and enzymes23
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A sequence of triplets in the DNA molecule maycode for a complete protein
Such a sequence forms a gene
There may be a thousand or more bases in
one gene
Genes24
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Question 1
Which of the following are components ofnucleotides?
(a) deoxyribose(b) amino acids
(c) phosphate
(d) enzymes
(e) organic bases
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Question 3
DNA molecules are formed from
(a) organic bases
(b) amino acids
(c) deoxyribose
(d) nucleotides
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Question 4
Which of the following are organic bases?
(a) Valine
(b) Guanine
(c) Thymine
(d) Serine
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Question 5
Replication of DNA occurs
(a) During cell division
(b) before cell division
(c) at any time
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QUESTION 6
A nucleotide triplet codes for
(a) a protein
(b) an amino acid
(c) an enzyme
(d) an organic base
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Answer
CORRECT
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Answer
INCORRECT