Deoxyribonucleic Deoxyribonucleic Acid (Acid (DNADNA))

Stanley Mikles, 2009

DNA is a polymerDNA is a polymer

a a polymer is a long is a long chain molecule chain molecule

made up of many made up of many smaller moleculessmaller molecules

a DNA polymer is a long chain of nucleotides

Parts of a nucleotide

Deoxyribose sugar

Nitrogen base

Phosphate

P O

O

HO

Phosphate

HO

C C

O

CC

H H

H

HH

OH

Deoxyribose Sugar

C C

N

C

O

OH

NH2

N

Nitrogen Base

1.1. Deoxyribose sugarDeoxyribose sugar

Composition of a Nucleotide

2.2. phosphate groupphosphate group

3.3. 1 - nitrogenous 1 - nitrogenous basebase a.a. thyminethymine

b.b. adenineadeninec.c. cytosinecytosined.d. guanineguanine

O

O

CH3

H

H

NN

NN

Thymine

N

H

N

NN

NN

Adenine

H

N

H

N

O

H

H

NN

NN

Cytosine H

O

H

N

NN

NN

Guanine

HN

H

NN

H

N

N

N

N

O

CH2

OH H

P O

O

HO

O

N H

H

H

O

Deoxyribose Guanine

Phosphate

1 of 4 possible Nucleotides

(one of 4 possible nitrogen bases)

Steps of Replication of DNA

B.B. enzymes break hydrogen enzymes break hydrogen bonds bonds

between nitrogen basesbetween nitrogen bases

A.A. molecule untwistsmolecule untwists

C.C. other enzymes bond new other enzymes bond new nucleotides to the split nucleotides to the split

strand of strand of the DNAthe DNA

(enzyme: DNA polymerase)(enzyme: DNA polymerase)

D.D. Result is 2 separate identical Result is 2 separate identical molecules of DNAmolecules of DNA

E.E. new molecules of DNA retwistnew molecules of DNA retwist

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

T C A A TG C T G T A C G C C T A A T T G G C G C T G A T T T A G

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

T C A A TG C T G T A C G C C T A A T T G G C G C T G A T T T A G

T C A A TG C T G T A C G C C T A A T T G G C G C T G A T T T A G

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

Making Proteins from DNAMaking Proteins from DNA

Proteins are polymers of amino acids.

Proteins are long molecules made up of amino acids molecules.

Remember: a polymer is a long chain Remember: a polymer is a long chain molecule made up of many smaller molecule made up of many smaller

moleculesmolecules

““Protein Synthesis”Protein Synthesis”

The whole The whole point of DNA is point of DNA is

to be a to be a template for template for

making making proteins.proteins.

There are 20There are 20amino acids.amino acids.

1st Base in the Codon

2nd Base in the Codon 3rd Base in the codon

U C A G

U Phenylalanine Serine Tyrosine Cysteine U

Phenylalanine Serine Tyrosine Cysteine C

Leucine Serine Stop Stop A

Leucine Serine Stop Tryptophan G

C Leucine Proline Histadine Arginine U

Leucine Proline Histadine Arginine C

Leucine Proline Glutamine Arginine A

Leucine Proline Glutamine Arginine G

A Isoleucine Threonine Asparagine Serine U

Isoleucine Threonine Asparagine Serine C

Isoleucine Threonine Lysine Arginine A

Methionine (start) Threonine Lysine Arginine G

G Valine Alanine Aspartate Glycine U

Valine Alanine Aspartate Glycine C

Valine Alanine Glutamate Glycine A

Valine Alanine Glutamate Glycine G

Transcription of DNA to RNATranscription of DNA to RNA

(Think of transcription likere-writing a language into another

form. It is the same language.)

Ribonucleic Acid

Single stranded

Has uracil in place of thymine

Three types of RNA

Three types of RNAMessenger RNA

mRNA

Transfer RNAtRNA

Ribosomal RNArRNA

1.1. Enzyme unzips DNA molecule Enzyme unzips DNA molecule at the start codon and stopping at at the start codon and stopping at

the first stop codon.the first stop codon.

Steps of Transcription

A G T T A C G A C A T G C G G A T T A A C C G C G A C T A A A T T A C G C C T A A T T G G C G C T G A T T T C A A TG C T G T A

DNA polymerasecuts bonds betweennitrogen bases

A G T T A C G A C A T G C G G A T T A A C C G C G A C T A A A T T A C G C C T A A T T G G C G C T G A T T T C A A TG C T G T A

2. Free RNA nucleotides in Nucleoplasm form

complementary base pairs on DNA strand forming an mRNA (messenger RNA) strand

A U G C G G AU U A U C C G C G U C U A A

RNA nucleotidesbonding to DNA

A G T T A C G A C A T G C G G A T T A A C C G C G A C T A A A T T A C G C C T A A T T G G C G C T G A T T T C A A TG C T G T A

A U G C G G AU U A U C C G C G U C U A A

3. mRNA strand breaks away from DNA by enzyme action

T A

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

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

T C A A TG C T G

4. DNA re-zips asmRNA breaks off.

mRNA strandmRNA strandbreaks awaybreaks away

DNA Rezips

B.B. RNA ProcessingRNA Processing

1.1. Not all nucleotides in DNA code for Not all nucleotides in DNA code for making making proteins.proteins.

2.2. Some regions of a DNA molecule Some regions of a DNA molecule do not code for anything.do not code for anything.

3.3. These regions are called These regions are called intronsintrons(intervening regions).(intervening regions).

4.4. Regions that do contain information for Regions that do contain information for coding for proteins are called coding for proteins are called exonsexons..

5. When mRNA in transcribed from DNA, both

introns and exons are copied.a. The introns must be removed

from the mRNA before it can function as a

proteinb. Enzymes in nucleoplasm cut out

the introns and paste mRNA back

together.6. mRNA then leaves the nucleus

From RNA to proteinFrom RNA to protein

translation:

changing mRNA code into a protein:

a sequence of amino acids

Think of translation as re-writing a message into another language.

The message is the same, but the language is different.

1.1. Transfer ribonucleic acid Transfer ribonucleic acid (tRNA)(tRNA)a.a. about 75 nucleotides longabout 75 nucleotides long

b.b. twisted so that only three twisted so that only three nucleotides are nucleotides are

available for available for bondingbondingc.c. one tRNA for one amino one tRNA for one amino

acidacid

A U G C G G A U U A U C C G C G U C U A A

Met

Transfer Ribonucleic AcidTransfer Ribonucleic Acid

tRNAtRNA

Amino AcidAmino Acid

AnticodonAnticodon

PhenylalaninePhenylalanine SerineSerine TyrosineTyrosine CysteineCysteine

LeucineLeucine ProlineProline HistadineHistadine TryptophanTryptophan

IsoleucineIsoleucine ThreonineThreonine GlutamineGlutamine ArginineArginine

MethionineMethionine AlanineAlanine AsparagineAsparagine GlycineGlycine

ValineValine LysineLysine

AspartateAspartate

GlutamateGlutamate

20 Amino Acids20 Amino Acids

Scientists have found a few more amino acids, like pyrrolysine and selenocysteine, that help to build

proteins.

1st Base in the Codon

2nd Base in the Codon 3rd Base in the codon

U C A G

U Phe Ser Try Cys U

Phe Ser Try Cys C

Leu Ser Stop Stop A

Leu Ser Stop Trp G

C Leu Pro His Arg U

Leu Pro His Arg C

Leu Pro Gln Arg A

Leu Pro Gln Arg G

A Ile Thr Asn Ser U

Ile Thr Asn Ser C

Ile Thr Lys Arg A

Met (start) Thr Lys Arg G

G Val Ala Asp Gly U

Val Ala Asp Gly C

Val Ala Glu Gly A

Val Ala Glu Gly G

2.2. start codon on mRNA start codon on mRNA strand attaches to ribosomestrand attaches to ribosome

3.3. tRNA molecules, each tRNA molecules, each carrying carrying

an amino acid, approach an amino acid, approach ribosomeribosome

4.4. tRNA molecules with tRNA molecules with complementary anticodon complementary anticodon pairs with mRNA codon.pairs with mRNA codon.

5.5. tRNA remains until next tRNA remains until next tRNA tRNA arrivesarrives

6.6. mRNA shifts along mRNA shifts along ribosome ribosome

to next codonto next codon

7.7. Next tRNA molecule Next tRNA molecule carrying carrying

the amino acid that the amino acid that possesses possesses

the complimentary the complimentary anticodon anticodon

bonds bonds

8.8. An enzyme joins the two An enzyme joins the two amino amino acids forming a acids forming a

peptide bond between them between them

9.9. tRNA from 1st amino acid tRNA from 1st amino acid falls falls

away away

10.10. process continues until process continues until ribosome ribosome

reaches stop codon bringing reaches stop codon bringing about termination about termination

11.11. enzyme breaks off last enzyme breaks off last tRNAtRNA12.12.result is a chain of amino result is a chain of amino

acids: acids: polypeptidepolypeptide: : proteinprotein

The End!The End!

The End?The End?

Not Quite!Not Quite!

Control of Gene ExpressionControl of Gene Expression

GeneA segment of a chromosome that A segment of a chromosome that

controls (codes for) the controls (codes for) the production of a certain protein.production of a certain protein.

Protein:

Gene Expression:

large, complex polymer of amino acids which provides structure for

tissues and helps carry out cell metabolism.

the production of the protein that the gene is coded for, which then allows for the operation of that

protein.

Genetic Changes

Mutation:Mutation:

any mistake in DNA or RNA any mistake in DNA or RNA sequence of nucleotidessequence of nucleotides

Results of Mutation:Mutation:

Failure to produce proteinFailure to produce protein

Production of wrong proteinProduction of wrong protein

Over production of proteinOver production of proteinwhether right or wrongwhether right or wrong

point mutation:change in a single base pairchange in a single base pair

frame shift mutation

a.a. additionsadditions

b.b. deletions deletions

Chromosomal mutations1. parts broken off or lost

during mitosis or meiosis

2. re-joining wrong3. join backward4. effects: incorrect

distribution of genes to gametes during meiosisa. deletionsb.b. insertionsinsertionsc.c. inversionsinversions

Causes of Mutationsmutagen: any agent that can cause a mutagen: any agent that can cause a

change in the DNAchange in the DNAA. radiation

1.1. X-raysX-rays2.2. gamma raysgamma rays3.3. ultraviolet raysultraviolet rays

B. chemicals1.1. dioxindioxin2.2. asbestosasbestos3.3. benzenebenzene4.4. formaldehydeformaldehyde5.5. alcoholalcohol

C. high temperatures

Rep

air

ing

DN

AR

ep

air

ing

DN

A

The End!

The End?

Not Quite!

The search for knowledge continues!

Controversies about Controversies about DNADNA