DEOXYRIBONUCLEIC ACID DNA

O.L Lesson Objectives At the end of this lesson you should be able to 1. Outline the simple structure of DNA – 2 strands and A,T,C, G complement 2. Distinguish between coding and non coding structures 3. Describe the triplet base code 4. Outline the structure of RNA – refer to Uracil and complement to DNA 5. Know the function of mRNA 6. 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 Parallel Strand Base Hydrogen bond- link

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

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 DNA Double strand Sugar is deoxyribose Has Thymine Very long Self replicating Found mainly in the nucleus (Where it stays) (small amounts found also in mitochondria & chloroplasts) RNA Single strand Sugar is ribose Has Uracil Short molecule Not self replicating Found in nucleus and cytoplasm – can move out of nucleus to 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 1. What does RNA stand for? 2. What three bases do DNA and RNA have in common? 3. What base does RNA have instead of Thymine? 4. Where do you find both DNA and RNA? 5. Where else will you find RNA?

H.L Objectives At the end of this section you should know ….. DNA structure – deoxyribose sugar, sugar, phosphate and 4 named nitrogenous bases Nucleotide structure Specific Purine and Pyramidine couples – complementarybase pairs Hydrogen bonding Double helix

NUCLEIC ACID STRUCTURE Higher Level

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 deoxyribose In eukaryotic cells nucleic acids are either: Deoxyribose nucleic acids (DNA) Ribose nucleic acids (RNA)

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

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 Toblerone Chocolate is a Pyramid

Pyrimidines NH 2 O N N NH N Guanine N N Adenine N N NH 2 N O N O N Cytosine Purines Uracil (RNA) CH 3 N O N O NH N O N O Thymine (DNA) No need to remember these - just the names and headings

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

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

CH 3 N O N O N H + - Thymine N N N N H N H - + Adenine Base Pairing Adenine And Thymine Two Hydrogen Bonds

Base Pairing Guanine And Thymine CH 3 N O N O N H + - Thymine H O N N N N N H H Guanine + + -

SUGAR-PHOSPHATE BACKBONE H P O HO O O CH 2 HOH P O O HO O O CH 2 H P O OH HO O O CH 2 NH 2 N N N N O O N NH N N N O NH 2 N B A S E S DNADNA O H P O HO O O CH 2 HO O H2NH2N N HN N N H H P HO O O CH 2 O O N O H2NH2N N H H2OH2O HOH P O HO O O CH 2 CH 3 O O HN N H2OH2O 5’Phosphate group 3’Hydroxyl group 5’Phosphate group 3’Hydroxyl group

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

What have you learned Can you ……………… 1. Outline the simple structure of DNA 2. Name the four bases and the base pairs in DNA 3. Distinguish between coding and non coding structures 4. Define triplet base code 5. Outline the structure of RNA 6. Name the bases in RNA and know the function of mRNA 7. Discuss the replication of DNA

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