Immortality Fact: There Are Some Creatures Whose DNA Renders Them Virtually Immortal. Can you link the pictures? Viking's in America Fact: DNA Proves Vikings Likely Brought Back Native American Wives Centuries Before Columbus Radioactive DNA Fact: People Born After 1955 Have Radioactive Carbon in Their DNA

A level Biology Year – Structure of DNA

The Big questions THE BIG QUESTION: Can you describe the structure of DNA? How the structure of DNA adapted to its function?

Learning objectives Describe the structure of a nucleotide Describe the structure of DNA Describe the structure of RNA Challenge: Relate DNAs structure to its function Maths skill: Calculate the DNA base frequencies

DNA WHAT DO WE KNOW?

Research prep notes recap Using your text book name, draw and label this structure Explain how DNA is formed form this structure What term can we use to describe this structure? Why?

DNA is a polymer made up of individual units called nucleotides

Nucleotide Structure 3 components: – Pentose sugar (ribose in DNA) – Phosphoric acid – Organic base (always contains nitrogen) Phosphate sugar base Stay the same Changes Contains nitrogen & carbon Pentose sugar (5 Carbon atoms)

4 Bases Purines – – Double ringed structure Pyrimidines – – Single ringed structure

Bondings The base and sugar join with a: glycosidic bond The phosphate and sugar join with an: ester bond Both require a condensation reaction to occur 

H H OH Phosphate Sugar Base 2 condensation reactions occur in the formation of a nucleotide: Ester bond Glycosidic bond

Type of BasePurinePyrimidine Structure Bonding relationships Adenine Guanine Thymine Cytosine = hydrogen bond

Strands run anti parallel

Phosphodiester Bonds: the sugar-phosphate-backbone

Tell me… 4 names of bases in DNA 3 components of a nucleotide 2 ends of a strand are called 1 place where a condensation reaction occurs 2 types of bonds in a nucleotide 1 difference between purine and pyrimidine bases

Complementary Base Pairing *Purines always pair with pyrimidines* A joins to T (2 hydrogen bonds) C joins to G (3 hydrogen bonds) Therefore, when discussing the proportions of a particular base, you will always find A=T and C=G or! A+C = G+T see

C A G T 2 hydrogen bonds 3 hydrogen bonds 5’5’ 3’3’ 3’3’ 5’5’ 0.34nm 2nm

C A G T 5’5’ 3’3’ 3’3’ 5’5’ 0.34nm 2nm A T C G 5C 3C 5C 3C 5C 3C

C A G T 2 hydrogen bonds 3 hydrogen bonds 5’5’ 3’3’ 3’3’ 5’5’ 0.34nm 2nm A T C G

Mathematical skills: proportion of base pairs in DNA Worked Example 1: If there is 20% guanine in a gene, how much Adenine, cytosine and thymine are there? G and C pair so there must be 20% C That leaves 60% A and T. Since they are complementary 60 ÷ 2 = 30% of A and T Worked example 2: A gene has 3246 bases, 956 are adenine, what % of cytosine, thymine and guanine is there? 956 ÷ 3246 x 100 = 29.45% = A and T. 100 – (29.45 x 2) = 41.1% ÷ 2 – 20.55% = C and G (667 bases each)

Mathematical questions 1. In a sample of DNA, there was 17% thymine. a) Calculate the percentage of cytosine in the molecule.(1 mark) b) What is the percentage of purine bases in the sample?(1 mark) 2. A sample of DNA from the lambda bacteriophage virus was sequenced and was found to be made up from base pairs base pairs were adenine and thymine. a) How many of the bases in the molecule will be cytosine?(1 mark) b) Calculate the percentage of the DNA molecule which is made up from guanine. (1 mark) 3. Pyrimidines make up 29.50% of a DNA sample. a)Find the percentage of adenine.(1 mark) b)Predict the percentage of guanine that will be found in a molecule of mRNA that is made by transcribing this DNA sample. Assume that all the bases are equally distributed on each of the two strands in the DNA molecule. (1 mark)

Points to remember: DNA stands for deoxyribonucleic acid It is a polymer of mono- Each nucleotide has three components: pentose sugar (deoxyribose) phosphate group organic base (4 types - purines/pyrimidines) 2 condensation reactions occur when the base and sugar form a glycosidic bond phosphate and sugar form an ester bond Phosphodiester bonds build a sugar phosphaphate backbone on each strand of DNA, with the bases all facing inwards The 2 strands of the DNA molecule form anti-parallel to one another; one strand runs 5’ to 3’ and the other strand runs 3’ to 5’ The strands wind around one another into a double helix (like a twisted ladder)

EXPLANATION Task Feature of DNAWhy it has this feature Complementary based pairing of double helix Hydrogen bonding between complementary bases 4 different bases Double stranded DNA molecule An extremely large molecule It is extremely stable A helical structure

The Big questions THE BIG QUESTION: Can you describe the structure of DNA? How is DNAs structure adapted to its function?

Learning objectives Describe the structure of a nucleotide Describe the structure of DNA Describe the structure of RNA Challenge: Relate DNAs structure to its function Maths skill: Calculate the DNA base frequencies

Challenge question DNA Molecules with any desired base sequence can be synthesised in the lab, It is also possible to determine the base sequence of a DNA molecule. For these reasons it has been suggested that oil shipments could be tagged with DNA of a known sequence. If an oil slick were found, the DNA could be sequenced, identifying the offending ship. Suggest some other potential applications for “DNA labelling” Challenge question DNA Molecules with any desired base sequence can be synthesised in the lab, It is also possible to determine the base sequence of a DNA molecule. For these reasons it has been suggested that oil shipments could be tagged with DNA of a known sequence. If an oil slick were found, the DNA could be sequenced, identifying the offending ship. Suggest some other potential applications for “DNA labelling”

DNA is a non-overlapping code …….what evidence supports this theory? What is meant by a degenerate code? -Suggest why this is beneficial to living organisms

The Big questions THE BIG QUESTION: Can you compare and contrast the structure of the nucleic acids DNA and RNA? How is RNAs structure adapted to its function?

Recap and Research task DNARNA BOTH

Application task You need to make a model of DNA using pipe cleaners and paper (label using stickers). Think about the key components of DNA and try to make it explicit in the model. Now make a complimentary model of RNA Evaluate each others… What key facts does it show? What misconceptions does it present?

The Big questions THE BIG QUESTION: Can you compare and contrast the structure of the nucleic acids DNA and RNA? How is DNAs structure adapted to its function?