DNA DEOXYRIBONUCLEIC ACID Lesson Objectives At the end of this lesson you should be able to 1. 2. 3. 4. 5. 6. 7. 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 Parallel Strand 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 DNA RNA Double strand Single strand Sugar is deoxyribose Sugar is ribose Has Thymine Has Uracil Much longer Short molecule Self replicating Not self replicating Only in the nucleus 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 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? 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 deoxyribose In eukaryotic cells nucleic acids are either: Deoxyribose nucleic acids (DNA) Ribose nucleic acids (RNA) A Nucleotide OH HO H+ Phosphate P NH2 Base O N H O 5’CH2 H N O N N 1’ 4’ 3’ OH 2’ H OH Sugar 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 NH2 Adenine N N N CH3 (DNA) N Guanine NH N O O Thymine Uracil (RNA) NH N O N N Pyrimidines NH2 NH O N O NH2 Cytosine N N O Base Numbers Number of Purine Bases = Number of Pyramidine Bases This led to the discovery of Base Pairing Base Pairing Guanine And Cytosine - + + + - Three Hydrogen Bonds Base Pairing Adenine And Thymine + - Adenine - Thymine + Two Hydrogen Bonds Base Pairing Guanine And Thymine + + 3’Hydroxyl group OH P HO NH2 O N O CH2 O O O N O CH2 HO P O H P CH2 O O HO N O OH H H2O NH N NH2 N O O CH2 O H O H N O O O P HO H O OH 5’Phosphate group CH2 HO CH2 3’Hydroxyl group H2O N O O P NH2 HO P O H O HO O D N A OH N N 5’Phosphate group H - - - -G C - T CA - - - G T A G A T - - Major groove A T C G C - 3.4 nm 1 nm - - - - - - - The Watson - Crick Model Of DNA - - Minor groove G T A A T C G C - - - - 0.34 nm What have you learned Can you ……………… 1. 2. 3. 4. 5. 6. 7. 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 End