Nucleotides

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Nucleotides

• Specification
• State that deoxyribonucleic acid (DNA) is a
  polynucleotide, usually double stranded, made up
  of nucleotides containing the bases adenine (A),
  thymine (T), cytosine (C) and guanine (G)
• State that ribonucleic acid (RNA) is a
  polynucleotide, usually single stranded, made up
  of nucleotides containing the bases adenine (A),
  uracil (U), cytosine (C) and guanine (G)

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Polynucleotides

• Nucelic acids come in two forms DNA and RNA
• They hold all the information to make proteins
  which is what all living things are made up of
• Almost all of the DNA in a eukaryotic cell is
  found in the nucleus
• RNA is found in 3 different forms

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Monomers

• The monomer of all nucleic acids (DNA and RNA) is
  called a nucleotide
• Each single nucleotide is made up of one
  phosphate group, one sugar molecule, one organic
  nitrogenous base
• All three sub-units are joined by covalent bonds

P
Base
S
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Nucleotides

• There are five different nucleotides called A, T,
  C, G and U
• The phosphate group in all nucleotides is the
  same
• The sugar molecule is a 5 carbon sugar either
  deoxyribose in DNA or Ribose in RNA
• The 5 possible bases are adenine A, Thymine T,
  Guanine G, Cytosine C, and Uracil U

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Joining nucleotides together

• A condensation reaction occurs between the
  phosphate group of one nucleotide and the sugar
  of another nucleotide
• Repeating the bonding gives a long chain of
  nucleotides
• This forms the backbone of the molecule

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Nucleotides to Nucleic Acids

• Chains of nucleic acids bond together to make
  nucleic acids
• Only nucleic acids carrying the same sugar
  (ribose or deoxyribose) can be binded together
• This makes nucleic acids either RNA or DNA

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Too Much Nucleic Acid

• Uric acid is produced when excess purines
  (Adenine and Guanine) are broken down in the
  liver
• It is excreted in urine
• Some people have too much uric acid in the blood
  which is turned into crystals that are deposited
  at the joints making them swollen (this is called
  gout)

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Task

• Using Cambridge Biology p124- 126, outline the
  structure of DNA- you must include the key words
  in bold in the paragraphs
• When finished, complete the DNA modelling task
  titled Have Your DNA and Eat It
• Then complete the questions on the printed slide-
  they will be peer assessed next lesson!

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Questions

1. Outline how DNA replicates
2. Define the term anti-parallel
3. Write down the complimentary strand sequence for
   DNA and RNA- ATTAGGCTAT
4. If a DNA is 20 Thymine, what percentage of each
   of the other types would it contain?
5. What type of disease can result from DNA copying
   going wrong?

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Questions

1. Outline how DNA replicates semiconservatively-
   the double helix is untwisted, the hydrogen bonds
   between the bases are broken apart and unzip to
   expose the bases, free DNA nucleotides are
   hydrogen bonded onto the exposed bases according
   to the base pairing rule A-T G-C, covalent bonds
   are formed between the phosphate of one
   nucleotide and the sugar of the next to seal the
   backbone
2. Define the term anti-parallel prallel, but with
   chains running in opposite directions
3. Write down the complimentary strand sequence for
   DNA and RNA- ATTAGGCTAT DNA TAATCCGATA RNA
   UAAUCCGAUA
4. If a DNA is 20 Thymine, what percentage of each
   of the other types would it contain? 20 Adenine,
   30 Cytosine, 30 Guanine
5. What type of disease can result from DNA copying
   going wrong? Cancer may occur if DNA is not
   copied properly

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DNA- Information Storage

• DNA is a long chain polymer of nucleotide
  monomers
• The polymer is called a polynucleotide
• A DNA molecule forms when two polynucleotide
  molecules come together forming a ladder like
  structure

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Hydrogen Bonding and Base Pairing

• The two DNA strands run parallel to each other
• The term anti-parallel is used because the
  strands run in opposite directions to one another
• The chains are always the same distance apart
  because bases pair up in a specific way.
• When a purine appears on one side, a pyrimidine
  appears on the other
• Adenine always pairs with thymine, and guanine
  always pairs with cytosine
• As the strands come together, hydrogen bonds form
  between the bases
• The base pairing is described as complimentary

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Double Helix

• In a complete DNA molecule, the anti-parallel
  chains twist, like twisting a rope ladder, to
  form the final structure known as a double helix

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Making Copies

• DNA replication takes place during interphase of
  the cell cycle
• It is the process that creates identical sister
  chromatids

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Making Copies

• In order to make a new copy of a DNA molecule
• The double helix is untwisted
• Hydrogen bonds between the bases are broken apart
  to unzip the DNA and expose the bases
• Free DNA nucleotides are hydrogen bonded onto the
  exposed bases according to the base pairing rules
  (A-T and C-G)
• Covalent bonds are formed between the phosphate
  of one nucleotide and the sugar of the next to
  seal the backbone.

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Making Copies

• This continues all the way along the molecule
  until two new DNA molecules (double helices) are
  formed, each is an exact replica of the original
  DNA molecule because of the base pairing rules.
• This process is known as semi-conservative
  replication.
• Each new DNA molecule consists of one conserved
  strand plus one newly built strand

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How is the Structure of DNA related to its
function?

• The sequence of bases acts as information storage
  in the form of codes to build proteins
• The molecules are long to store more information
• The base pairing means that complementary strands
  of information can be replicated
• The double helix gives the molecule stability
• Hydrogen bonds allow for easy unzipping for
  copying and reading information

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Reading the Instructions

• RNA
• Contains the sugar ribose
• Has uracil instead of thymine
• Usually single stranded
• Exists in 3 forms

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Base Pairing of RNA

• Contains the purines adenine and guanin and the
  pyrimidines cytosine and uracil
• Base pairing of A-U and G-C occur

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Three forms of RNA

• mRNA messenger RNA is made as a strand that is
  complimentary to one strand of the DNA molecule
  (the template strand) it is therefore a copy of
  the other DNA strand as it contains the opposite
  bases plus Uracil
• rRNA is ribosomal RNA and is found in ribosomes-
  it decodes mRNA into amino acids
• tRNA transfer RNA carries amino acids to the
  ribosomes where they are bonded together to form
  polypeptides

Task Now complete the Protein Synthesis sentence
sort
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Sentence Sort What are the instructions for?

• The sequence of bases on DNA make up codes for
  particular proteins- they code for the sequence
  of amino acids
• The sequence coding for a particular protein (a
  gene) can be exposed by splitting the hydrogen
  bonds in the particular area of the DNA molecule
• RNA nucleotides from a complementary strand
  (mRNA) which is a copy of the DNA coding strand
  (or gene)
• The mRNA peels away from the DNA and leaves the
  nucleus through a nuclear pore
• The mRNA attaches to a ribosome
• The tRNA molecules bring amino acids to the
  ribosome in the correct order, according to the
  base sequence of the mRNA
• The amino acids are joined by peptide bonds to
  give a protein with a specific primary structure
  which can then give rise to the secondary and
  tertiary shape of the protein

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Task

• Complete a windows movie explaining the steps
  involved in protein synthesis
• Success Criteria
• No more than one minute
• Include scientific information and diagrams
• Explain simply the terms transcription and
  translation

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Questions

1. Explain why the MRNA strand produced in the
   nucleus is complementary to the template strand,
   and a copy of the coding strand
2. If a DNA template strand code reads ATTCGCGTTAAT,
   what would the complementary MRNA strand read?
3. Suggest why MRNA is less stable than DNA, and
   explain why this is a necessary feature of MRNA
4. Make a table to compare and contrast the
   structure of DNA with that of RNA

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Questions

1. Explain why the MRNA strand produced in the
   nucleus is complementary to the template strand,
   and a copy of the coding strand complementary RNA
   nucleotides are lined up against each base on the
   template strand, producing a complementary
   strand. As base pairing rules apply, this lining
   up will be the same as it appears on the coding
   strand- apart from U in RNA replacing T in DNA
2. If a DNA template strand code reads ATTCGCGTTAAT,
   what would the complementary MRNA strand read?
   UAAGCGCAAUUA
3. Suggest why MRNA is less stable than DNA, and
   explain why this is a necessary feature of MRNA
   RNA is single stranded and so less stable, as
   nucleotide bases are exposed and not paired. It
   also contains uracil instead of thymine, which
   may contribute to the lower stability of the
   molecule. mRNA results in the production of
   proteins. If the cell is to control protein
   production, the disintegration of mRNA stops too
   much of a certain protein being made, and so
   allows for regulation of the protein levels in a
   cell
4. Make a table to compare and contrast the
   structure of DNA with that of RNA