2.6 Structure of DNA and RNA

Understanding

• U1 The nucleic acids DNA and RNA are polymers of nucleotides.

• U2 DNA differs from RNA in the number of strands present, the base composition and the type of pentose.

  	number of strands present	Base Composition	Type of Pentose
  DNA	2	A, C, G, T	deoxyribose
  RNA	1	A, C, G, U	ribose

• U3 Explain that DNA is double helix made of two antiparallel strands of nucleotides linked by hydrogen bonding between complimentary base pairs.

Application

A1 Crick and Watson’s elucidation (clarification) of the structure of DNA using model making*

• started off with cardboard cut-outs

  • how they learned that h-bonds occurred between nitrogenous bases

• realized that the strands had to run antiparellel

Skills

S1: Drawing simple diagrams of the structure of single nucleotides of DNA and RNA, using circles, pentagons, and rectangles to represent phosphates, pentoses and bases.

Nature of Science

NOS 1 Using models as representation of the real world- Crick and Watson used model making to discover the structure of DNA.

2.7 DNA Replications, Transcription and Translation

Understanding

• U1 State that the replication of DNA is semi-conservative and depends on complimentary base pairing.

• U2 Explain that DNA Helicase unwinds the double helix and separates the two strands by breaking hydrogen bonds.

• U3 Explain that DNA polymerase links nucleotides together to form a new strand, using a pre-existing strand as a template.

• U4 Transcription is the synthesis of mRNA copied from the DNA base sequences by RNA polymerase

• U5 Translation is the synthesis of polypeptides on ribosomes

• U6 The amino acid sequence of polypeptides is determined by mRNA according to the genetic code

• U7 Codons of three bases on mRNA correspond to one amino acid in a polypeptide.

• U8 Translation depends on complimentary base-pairing between codons on mRNA and anticodons on tRNA. balls

Application

Use of Taq DNA polymerase to produce multiple copies of DNA rapidly by the polymerase chain reaction (PCR)*

• PCR allows for strands of DNA to be replicated into the millions

• To speed up PCR, it is carried out at high temperatures

• special type of heat-stable DNA polymerase: Taq DNA polymerase

  • obtained from Thermus aquaticus, a bacterium that is adapted to living in hotsprings,

• Millions of copies of the DNA can be produced by PCR in a few hours because of the high temperatures used

Steps

1. DNA heated to 95°C to separate strands

2. DNA cooled to 53°C to allow primer to bind

3. DNA reheated to 73°C to separate strands

Production of human insulin in bacteria as an example of the universality of the genetic code allowing gene transfer between species.*

• The gene that codes for insulin has been transferred from humans to the bacterium E. coli and to other organisms, to produce insulin

• aa sequence for insulin in bacteria = aa sequence in humans

  • because of universality of genetic code

  • codons in bacteria = codons in human mRNA

• there are some exceptions

Skills*

S 1 Use a table of the genetic code to deduce which codons corresponds to which amino acids.*

1. Identify if the given nitrogenous base is the

   1. 5’ strand - match complementary letters, turn into codons, and chart

   2. 3’ strand - match same letter for codon, chart

   3. mRNA strand -order codon, chart

   4. Anti-codon - find opposite letter, chart

2. ALWAYS DOUBLE CHECK

S2 Analysis of Meselson and Stahl’s results to obtain support for the theory of semi-conservative replication of DNA

• E. coli cultures in N¹⁵ environments

• they were transferred to N¹⁴ environments

• After 1 generation, DNA was intermediate in density between N¹⁴ and N¹⁵

• After 2 generations, N¹⁴+N¹⁵ DNA was present along side solid N¹⁴ DNA

• simply: it kept a strand of the old DNA and created a new strand with the light nitrogen

S3 Use a table of mRNA codons and their corresponding amino acids to deduce the sequence of amino acids coded by a short mRNA strand of known base sequence.

S4 Deducing the DNA base sequence for the mRNA strand.

1. Template strand of DNA is usually 3’-XXX-5’

2. mRNA is always 5’-XXX-3’

2.8 Cell Respiration

Understanding

• U1 Cell respiration is the controlled release of energy from organic compounds to produce ATP

  U2 ATP from cell respiration is immediately available as a source of energy in the cell.

  U3 Anaerobic cell respiration gives a small yield of ATP from glucose.

  U4 Aerobic cell respiration requires oxygen and gives a large yield of ATP from glucose.

Application

A 1 Use of anaerobic cell respiration in yeasts to produce ethanol and carbon dioxide in baking.

A2 Lactate production in humans when anaerobic respiration is used to maximize the power of muscle contractions.

Skills*

S 1 Use a table of the genetic code to deduce which codons corresponds to which amino acids.*

1. Identify if the given nitrogenous base is the

   1. 5’ strand - match complementary letters, turn into codons, and chart

   2. 3’ strand - match same letter for codon, chart

   3. mRNA strand -order codon, chart

   4. Anti-codon - find opposite letter, chart

2. ALWAYS DOUBLE CHECK

S2 Analysis of Meselson and Stahl’s results to obtain support for the theory of semi-conservative replication of DNA

• E. coli cultures in N¹⁵ environments

• they were transferred to N¹⁴ environments

• After 1 generation, DNA was intermediate in density between N¹⁴ and N¹⁵

• After 2 generations, N¹⁴+N¹⁵ DNA was present along side solid N¹⁴ DNA

• simply: it kept a strand of the old DNA and created a new strand with the light nitrogen

S3 Use a table of mRNA codons and their corresponding amino acids to deduce the sequence of amino acids coded by a short mRNA strand of known base sequence.

S4 Deducing the DNA base sequence for the mRNA strand.

1. Template strand of DNA is usually 3’-XXX-5’

2. mRNA is always 5’-XXX-3’