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Structure & Function of DNA

Understanding Growth & Development

The Structure of DNA • DNA stands for: deoxyribonucleic

acid• DNA is: the molecule of life and is

found in every organism• DNA stores: information for proper

cellular function

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The Structure of DNA, cont.• The complete DNA

molecule is arranged in a structure called a double helix

• Double helix – 2 coiled strands; twisted ladder

3

The Structure of DNA, cont. • DNA is: a large polymer that

contains the elements C,H,O,N & P• Polymer structure is made of single

units (monomers) called nucleotides

• 3 components of a nucleotide:5-carbon sugarPhosphate groupNitrogen-containing base

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The Structure of DNA, cont.• Sides of ladder:

Deoxyribose a 5-carbon (pentose) sugar

Phosphate group• Rungs of ladder:

2 nitrogen-containing bases joined with 2 or 3 hydrogen bonds

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The Structure of DNA, cont.• Nitrogen Bases:Cytosine - CGuanine - GAdenine - AThymine - T

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DNA Nucleotide

Phosphate

NitrogenousBase (A, G, C, or T)

Deoxyribose

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Nitrogen-containing Bases• Double ring PURINES

Adenine (A)Guanine (G)

• Single ring PYRIMIDINESThymine (T)Cytosine (C)

T or C

A or G

Base-Pairings• The DNA of all organisms follows

the rule of base-pairing:

Cytosine always bonds with Guanine andAdenine always bonds with Thymine

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1010

Base-Pairings• Three hydrogen bonds required

to bond Guanine & Cytosine

• Two hydrogen bonds are required to bond Adenine & Thymine

CG

1111

DNA

P

P

P

O

O

O

1

23

4

5

5

3

3

5

P

P

PO

O

O

1

2 3

4

5

5

3

5

3

G C

T A

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Historical Landmarks in the Discovery of DNA

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1868-Switzerland

• Johann Friedrich Miescher• Found it when working with

white blood cells that he took from pus drained out of a surgical wound.

1920-London• Frederick Griffith• Found that bacteria could acquire

something from each other to turn harmless bacteria into deadly bacteria, though he wasn't sure what.

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1944-New York

• Oswald Avery • Led a team that assessed Griffith’s

work• Discovered the molecule DNA was

what had caused the change.

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1950-New York• Edwin Chargaff • Found that the amount of adenine

was almost equal to the amount of thymine, and that the amount of guanine was almost equal to the amount of cytosine.

• Thus you could say: A=T, and G=C. • This discovery later became Chargaff’s

Rule.

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1952-London• Rosalind Franklin and Maurice Wilkins • Were able to obtain an x-ray image of

crystalized DNA• It showed a ladder with rungs twisted

in an “X” shape indicating DNA had a helix shape.

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1953-London• James Watson and Francis Crick• Published their findings about the

structure of DNA• Watson, Crick and Wilkins received a

Nobel Prize for their work in 1962

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All about you and your chromosomes

• Humans- 46 chromosomes-23 pairs• 22 autosomal pairs or 44 body

chromosomes• 1 pair of sex chromosomes-2 sex

chromosomes• XX-girl XY- boys• X in eggs only• Sperm will have either an X or a Y

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DNA ReplicationDNA structure in :• Prokaryotes - single, circular piece;

found in cytoplasm• Eukaryotes - arranged in multiple

threads called chromosomes; found in nucleus

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DNA Replication, cont.• Number of chromosomes varies

depending on organism: Fruit Fly - 8 Humans – 46 Chimpanzees - 48 Aquatic Rat - 92

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DNA Replication, cont.• Genes: sections of DNA on the

chromosomes• Genes: code for certain proteins that

provide instructions for cellular activity

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DNA Replication, cont.• Each cell of any type of organism

must be able to make copies of its DNA to pass on to daughter cells

• Replication – when DNA makes a copy of itself

• Both strands of DNA are complementary to each other

• Each serve as a template to make a new strand

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DNA Replication, cont.• DNA replication follows base-pairing

rules and is carried out by a group of enzymes:

a. Some unwind DNAb. Some break hydrogen bonds

between basesc. Some (DNA polymerase) add new

bases to make new DNA strands

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