Nucleic acids

• DNA and RNA are polymers. What is the repeat unit called? 


  polynucleotides
• what is the structure of each nucleotide?

  -pentose sugar

  -nitrogenous base

  -phosphate group
• What is a nucleic acid strand

  A polymer made up of a repeat unit of nucleotides
• what is the structure of a RNA nucleotide?

  A ribose sugar with hydroxyl at carbon 2

  A phosphate group

  a Base
• What nitrogenous bases are found in RNA nucleotides ?

  Adenine, Uracil, Guanine, Cytosine
• What is the structure of a DNA nucleotide?

  -deoxyribose sugar with only hydrogen at carbon 2

  -phosphate group

  -Nitrogenous base
• what nitrogenous bases are on DNA nucleotides?

  Adenine, Cytosine, Guanine, Thymine
• What bases are purines?

  Adenine and guanine
• What bases are pyrimidines?

  Cytosine, Thymine and uracil
• what is the structure of pyrimidines?

  Single hexagonal ring structure
• what is the structure of purines?

  double ring structure (hexagonal and pentagon)
• How do purines and pyrimidines Bond?

  they bond by complementary base pairing
• How many hydrogen bonds form between Cytosine and Guanine

  Three

  
• How many hydrogen bonds form between adenine and thymine?

  Two

  
• what bond is between the pentose sugar and the nitrogenous base?

  Glycosidic bond
• What bond forms between carbon 5 on a pentose sugar and phosphate group?

  ester
• by what reaction are nucleotides joined?

  condensation reaction
• what does the phosphodiester bond consist of?

  2 ester bonds and a phosphate group

  Ester bond 1: between carbon 3 of one nucleotide and the phosphate group of the adjacent nucleotide

  Ester bond 2: between the phosphate group of the adjacent nucleotide and carbon 5 of the nucleotide
• what is the sugar-phosphate backbone?

  a chain of alternating phosphate groups and pentose sugars bonded by phosphodiester bonds
• How are condensation reactions to form the phosphate-sugar backbone catalyzed?

  DNA polymerase or RNA polymerase
• how can phosphodiester bonds be broken?

  hydrolysis (addition of water)
• What are DNA molecules made up of?

  Two polynucleotide strands bonded by hydrogen bonds between bases, running in opposite directions
• what is meant by antiparallel DNA strands?

  deoxyribose polynucleotide strands running parallel to each other but in opposite directions bonded by . One from the 5’ to 3’ direction, the other from the 3’ to 5’ direction

  
• what is meant by 5’ and 3’?


  refers to the carbon that is unbonded at either end of the DNA strand
• How are antiparallel strands held together in the DNA molecule?

  Held together by hydrogen bonds between complementary base pairs
• What is the shape of the DNA molecule

  Coiled into a double helix
• What is the difference between RNA and DNA molecules

  RNA is made up of RNA nucleotides with ribose sugars while DNA has deoxyribose sugars

  RNA is single stranded while DNA is double stranded and has a double helix shape

  RNA molecules are shorter than DNA molecules
• Describe how semi-conservative replication works?

  The DNA double helix separates into two polynucleotide strands

  Each strand acts as a template for the synthesis a=of a new complementary DNA strand

  so each new DNA molecule consists of one parent strand and one new strand
• what was the conservative DNA replication theory?

  a DNA double helix is formed containing two new strand and none of the original/ parent DNA strands
• Describe the Meselson-stahl experiment 


  bacteria was cultured in a growth medium containing only N15 (heavy nitrogen isotope)

  This meant that all nitrogenous bases were synthesized from N15

  N15 bacteria sample extracted and centrifuged, forming a band at the bottom due to heavy DNA

  N15 bacteria allowed to replicate in N14 growth medium (light)

  1 cycle of DNA replication allowed then re spun on centrifuge forming a band in the middle

  1 more DNA replication cycle showed a band in the middle and a band near the top
• how does a band formation in the middle show evidence for semi-conservative replication?


  it showed that each new DNA contained one N14 strand and one N15 strand, meaning a density of DNA between the heavy nitrogen and light nitrogen density

  This is only possible if if strands in the parent DNA molecule split and acted as templates for synthesis of new DNA
• What would have been seen in the centrifuge tube if DNA replication was conservative?

  after one round of replication, 50 % of DNA would be light (top of the tube) and 50% would be heavy (bottom of the tube)

  No band in the middle shows that there were no N14/N15 hybrid strands
• What would be shown as the conservative experiment progressed In the centrifuge tubes?

  N15 DNA percentage would slowly decrease while N14 DNA percentage would increase. This is because only N14 nitrogen can be used for DNA synthesis and synthesis of bases and there is no middle band
• which enzymes are involved in DNA replication?

  DNA helicase

  DNA polymerase
• what is the role of DNA helicase

  attaches to the end of the DNA molecule and moves along the molecule breaking hydrogen bonds between complementary base pairs of nucleotides
• Why are the hydrogen bonds between DNA strands broken during semi-conservative replication?

  So the parent strands are exposed and can act as templates for the synthesis of new DNA strands
• how are free nucleotides involved in DNA synthesis?

  they bind to complementary bases on the DNA parent template strand by complementary base pairing forming hydrogen bonds
• What is the role of DNA polymerase in DNA replication?

  binds to the 3’ end of the parent strand and moves along the parent strand and Lined up nucleotides catalyzing the condensation reaction, forming phosphodiester bonds, forming the sugar phosphate backbone of the new DNA strand
• In what direction Does DNA polymerase work in?

  3’ to 5’ direction
• Describe the process of semi-conservative DNA replication (6 marks)

  DNA helicase breaks hydrogen bonds between bases between DNA strands causing the molecule to unwind

  This exposes the parent strands, each acts as a template for new strand synthesis

  free nucleotides line up with exposed bases, forming hydrogen bonds by complementary base pairing

  DNA polymerase works from 3’ to 5’ catalyzing the condensation reaction, forming phosphodiester bonds between lined nucleotides

  DNA molecules containing 1 parent strand and 1 new strand recoil into double helix