Deoxyribonucleic Acid DNA Deoxyribonucleic Acid

Lesson Objectives At the end of this lesson you should be able to   Outline the simple structure of DNA Name the four bases and the base pairs in DNA Distinguish between coding and non coding structures Define triplet base code Outline the structure of RNA Name the bases in RNA Discuss the replication of DNA

What is DNA Hereditary material Carries and passes on genetic information It is a nucleic acid Made up of nucleotides

The DNA Double Helix Two parallel strands Each with a series of bases to the inside The bases are directly opposite each other The bases link each other in pairs These links form the steps of the ladder

The DNA Double Helix Hydrogen bond- link Parallel Strand Base Base

The Bases Adenine (A) Thymine (T) Cytosine (C) Guanine (G)

The Base Pair Rule The bases can occur in any sequence along a strand of DNA But the sequence must be complimentary to the sequence on the other strand

The Base Pair Rule Adenine can only join to Thymine A T Guanine can only join to Cytosine G C

Building DNA http://www.zerobio.com/drag_gr9/DNA/dna.htm

Building DNA http://learn.genetics.utah.edu/units/basics/builddna/

Learning Check What does DNA stand for? Name the four bases in DNA Which base complements Adenine? Which base compliments Guanine?

Non Coding DNA Only about 3% of DNA is composed of genes 97% of DNA is non coding DNA or junk DNA

Coding DNA The parts of DNA that contain information to make RNA or protein Coding DNA in genes are called exons

Non Coding DNA Do not contain critical information for the production of protein They are now thought to play a role in gene expression Non coding DNA within genes is called introns

Learning Check Label a gene and a piece of non coding DNA in the following picture

RNA Ribonucleic Acid Operates with DNA to make proteins Has Uracil instead of Thymine

Differences between DNA and RNA Double strand Sugar is deoxyribose Has Thymine Much longer Self replicating Only in the nucleus RNA Single strand Sugar is ribose Has Uracil Short molecule Not self replicating Found in nucleus and cytoplasm

Similarities between DNA and RNA Both are nucleic acids Both contain adenine, guanine and cytosine nucleotides Operate together to produce specific proteins

Learning Check What does RNA stand for? What three bases do DNA and RNA have in common? What base does RNA have instead of Thymine? Where do you find both DNA and RNA? Where else will you find RNA?

Nucleic Acid Structure Higher Level Nucleic Acid Structure

Nucleotides Nucleotides are carbon ring structures containing nitrogen linked to a 5-carbon sugar (a ribose) 5-carbon sugar is either a ribose or a deoxy-ribose In eukaryotic cells nucleic acids are either: Deoxyribose nucleic acids (DNA Ribose nucleic acids (RNA)

Base H+ Sugar A Nucleotide P O OH HO NH2 N - OH O CH2 H OH Phosphate 2’ 3’ 4’ 5’ 1’ OH

Coding and Non Coding Parts Non coding Structures Sugar – Phosphate Coding Structures Base Sequences

Purine Bases Adenine and Guanine Double ringed molecular structures Known as Purine Bases

Pyramidine Bases Thymine and Cytosine single ringed structures Known as Pyramidine bases

Purines Pyrimidines Uracil CH3 N O NH Thymine N Adenine NH2 NH2 O N NH (RNA) CH3 N O NH Thymine (DNA) N Adenine NH2 NH2 O N NH Guanine N O NH2 Cytosine

Base Numbers Number of Purine Bases = Number of Pyramidine Bases This led to the discovery of Base Pairing

Base Pairing Guanine And Cytosine H O N Guanine - N O H Cytosine + + - - + Three Hydrogen Bonds

Base Pairing Adenine And Thymine - + Adenine CH3 N O H + - Thymine Two Hydrogen Bonds

Base Pairing Guanine And Thymine CH3 N O H + - Thymine H O N Guanine + -

D N A B A S E S SUGAR-PHOSPHATE BACKBONE 3’Hydroxyl group 5’Phosphate group SUGAR-PHOSPHATE BACKBONE H P O HO CH2 OH NH2 N NH B A S E S O H P HO CH2 H2N N HN H OH P O HO CH2 CH3 HN N H2O D N A H P HO O CH2 N H2N H2O 3’Hydroxyl group 5’Phosphate group

The Watson - Crick Model Of DNA T A G C C G G C T A 3.4 nm 1 nm Minor groove The Watson - Crick Model Of DNA Major groove 0.34 nm

What have you learned Can you ………………   Outline the simple structure of DNA Name the four bases and the base pairs in DNA Distinguish between coding and non coding structures Define triplet base code Outline the structure of RNA Name the bases in RNA Discuss the replication of DNA

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