DNA Structure 1

8/8/2019 DNA Structure 1

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Mr. ColemanBiology


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DNADNAis often calledthe blueprint of life..

In simple terms, DNAcontains theinstructions formaking proteins

within the cell.


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The DNA in a cell

is packed into anelaborate,multilevel system

of coiling andfolding


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We study DNA formany reasons, e.g.,

its central

importance to all lifeon Earth,

medical benefits

such as cures fordiseases,

better food crops.


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Chromatin: longstringy fibers ofDNA and Protein.

Is how DNA existswhen not dividing.

Chromosomes

made of

chromatin(Stringy DNA)


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DNA is a verylong polymer.

The basic shape

is like a twistedladder or zipper.

This is called a

double helix.


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The DNA doublehelix has two

strands twistedtogether.


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Sister chromatids:2 identical copiesof a chromosomemade before celldivision.

During CellDivision sisterchromatids

separate

Chromosome

duplication

SisterChromosomedistribution

todaughter

cells

Sister

chromatids


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DNA consists of two molecules that arearranged into a ladder-like structure calleda Double Helix.

A molecule of DNA is made up of millions oftiny subunits called Nucleotides.

Each nucleotide consists of:1. Phosphate group2. Pentose sugar3. Nitrogenous base


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Phosphate

Pentose

Sugar

NitrogenousBase


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The backboneof the moleculeis alternatingphosphateand

deoxyribose, asugar, parts.

The teeth arenitrogenousbases.

phosphate

deoxyribose

bases


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C C

C

OPhosphate

O

C

C

O -P O

O

O

O -P O

O

O

O -P O

O

O

Nitrogenousbase

Deoxyribose


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The phosphate and sugar form the backboneof the DNA molecule, whereas the bases formthe rungs.

There are four types of nitrogenous bases.


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Each base will only bond with one otherspecific base.

Adenine (A)

Thymine (T)

Cytosine (C)

Guanine (G)

Form a basepair.

Form a basepair.


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One strand of DNAis a polymer of

nucleotides.One strand of DNA

has many millions

of nucleotides.

nucleotide


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Cytosine C Thymine T Adenine A

Guanine G

DNA has four different bases:


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Pyrimidines arePyrimidines aresingle ring bases.single ring bases.

Purines are doublePurines are doublering bases.ring bases.

C

C

C

C

N

N

OO

N

C

C

C

C

N

N

N

N

N

C


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Adenine and Guanine are purines(composed of two rings of nitrogenatoms)


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Thymine and Cytosine are pyrimidines(composed of one ring of nitrogen

atoms)


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Thymine and cytosine each have oneThymine and cytosine each have onering of carbon and nitrogen atoms.ring of carbon and nitrogen atoms.

C

C

C

C

N

N

OO

N

cytosinecytosine

C

C

C

C

N

N

OO

OO

thyminethymine

C


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Adenine and guanine each have twoAdenine and guanine each have tworings of carbon and nitrogen atoms.rings of carbon and nitrogen atoms.

C

C

C

C

N

N

N

AdenineAdenineN

N

C

C

C

C

C

N

N

OO

N

GuanineGuanineN

N

C


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Remember, DNAhas two strandsthat fit togethersomething like azipper.

The teeth are thenitrogenous

bases but why dothey sticktogether?


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Because of this complementary basepairing, the order of the bases in onestrand determines the order of thebases in the other strand.


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G

G

A

T

T

A

A

C

T

G

C

A

T

C


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C

C

C

C

N

N

OO

N

C

C

C

C

NN

OO

N

N

NC

The bases attracteach other becauseof hydrogen bonds.

Hydrogen bonds areweak but there aremillions and millionsof them in a single

molecule of DNA. (The bonds between

cytosine and guanineare shown here.)


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When makinghydrogen bonds,cytosine alwayspairs up withguanine,

And adenine alwayspairs up withthymine.

(Adenine andthymine are shownhere.)

C

C

C

C

N

N

N

N

N

C

C

C

C

C

N

N

OO

OO

C


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Each cell has about 2 mof DNA.

The average human

has 75 trillion cells. The average human

has enough DNA to gofrom the earth to thesun more than 400times.

DNA has a diameter ofonly 0.000000002 m.

The earth is 150 billion m

or 93 million miles fromthe sun.


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To crack the genetic code found in DNA weneed to look at the sequence of bases.

The bases are arranged in triplets calledcodons.

A G G - C T C - A A G - T C C - T A G

T C C - G A G - T T C - A G G - A T C


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A gene is a section of DNA that codes for aprotein.

Each unique gene has a unique sequenceof bases.

This unique sequence of bases will code for

the production of a unique protein.

It is these proteins and combination ofproteins that give us a unique phenotype.


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Protein

DNA

Gene

Trait


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DNA Structure 1

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