Copy of DNA

8/11/2019 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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A DIYMODEL OF PART OF A DNAMOLECULE

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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

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Copy of DNA