Nucleic Acids

• Explain the results.

  Results support the semi-conservative model.After one generation the DNA contained one parental Heavy N15 strand and one new N14 strand (mixed DNA) The second generation was produced as each strand from the mixed DNA acted as a template so some of the new DNA had two light strands and some still had a mix of light and heavy.

  
• How was the mass of the DNA determined?

  The DNA was treated to density gradient centrifugation and the heavier DNA sank lower in the tubes than the light DNA.

  
• Meselson and Stahl's experiment

  1. E.Coli bacteria grown in Heavy Nitrogen N15 so all organic bases in DNA became heavy.2. Bacteria then returned to normal environment with light Nitrogen N14.3. DNA from bacteria sampled at start, after one generation in N14 and after two generations in N144. At start all DNA was heavy.After one generation DNA was neither light or heavy it was in between. After 2 generations some was in between in mass and some was light.

  
• What did the results from Meselson's and Stahl's experiment suggest?

  That DNA replicated semi-conservatively.
• Why is DNA replication semi-conservative replication?

  The new DNA molecules have one original template strand and one new DNA strand.

  
• Stages of DNA Replication.

  1. DNA helicase unzips the two strands of DNA by breaking the Hydrogen Bonds.2. Each original DNA strand becomes a template3. Template strands attract free nucleotides in the correct sequence according to the base pairing rule.4. Nucleotides are joined together by DNA polymerase.5. New DNA strands contain one original template strands and one new DNA strand.

  
• rRNA


  Made in the nucleolus and forms over half the mass of a ribosome.

  
• tRNA shape

  A single polynucleotide chain folded into a clover shape.

  
• tRNA function

  Carries the amino acids to the mRNA/ribosomes where protein synthesis takes place.
• mRNA function

  Carries a copy of the DNA code from the nucleus to a ribosome in the cytoplasm where proteins are made.

  
• Function of DNA

  The Genetic Code of living organisms.Controls protein synthesis (e.g enzymes)DNA base sequence determines the primary structure of a polypeptideA gene is a sequence of DNA that codes for a polypeptide.Each sequence of 3 DNA bases on the template strand code for one amino acid.

  
• 3 Types of RNA

  Messenger RNA (mRNA)Transfer RNA (tRNA)Ribosomal RNA (rRNA)
• Components of single stranded RNA

  1. Ribose (pentose sugar)2. Phosphate3. Base Uracil instead of Thymine.
• DNA Shape

  Double Helix

  
• Base pairing in DNA

  Adenine pairs with ThymineGuanine pairs with Cytosine(Base pairing rule)

  
• Molecule of DNA structure

  2 Anti-parallel polynucleotide chains.Held together by Hydrogen bonds between the bases.

  
• Name the two types of nucleic acid

  1. Deoxyribonucleic acid (DNA)2. Ribonucleic acid (RNA)
• What is a nucleic acid?

  A chain of nucleotides.A polynucleotide.

  
• How are nucleotides joined together?

  Phosphodiester bonds form between the pentose sugar molecules and phosphate groups of the nucleotides (in condensation reactions)

  
• How are the sugar, phosphate group and base joined together?

  By condensation reactions.
• Draw a nucleotide

  1. Pentose sugar 2. A phosphate group 3. Nitrogenous base

  
• What is the sub-unit/ monomer of the nucleic acids (DNA and RNA)?

  Nucleotides