2.6 structure of dna and rna
essential idea: The structure of DNA allows efficient storage of genetic information.
nature of science: Using models as representation of the real world—Crick and Watson used model making to discover the structure of DNA. (1.10)
Understandings:
• The nucleic acids DNA and RNA are polymers of nucleotides.
• DNA differs from RNA in the number of strands present, the base composition and the type of pentose.
• DNA is a double helix made of two antiparallel strands of nucleotides linked by hydrogen bonding between complementary base pairs.
Applications and skills:
• Application: Crick and Watson’s elucidation of the structure of DNA using model making.
• Skill: Drawing simple diagrams of the structure of single nucleotides of DNA and RNA, using circles, pentagons and rectangles to represent phosphates, pentoses and bases.
Theory of knowledge:
The story of the elucidation of the structure of DNA illustrates that cooperation and collaboration among scientists exists alongside competition between research groups. To what extent is research in secret ‘anti-scientific’? What is the relationship between shared and personal knowledge in the natural sciences?
Guidance:
• In diagrams of DNA structure, the helical shape does not need to be shown, but the two strands should be shown antiparallel. Adenine should be shown paired with thymine and guanine with cytosine, but the relative lengths of the purine and pyrimidine bases do not need to be recalled, nor the numbers of hydrogen bonds between the base pairs.
• The nucleic acids DNA and RNA are polymers of nucleotides.
• DNA differs from RNA in the number of strands present, the base composition and the type of pentose.
• DNA is a double helix made of two antiparallel strands of nucleotides linked by hydrogen bonding between complementary base pairs.
Applications and skills:
• Application: Crick and Watson’s elucidation of the structure of DNA using model making.
• Skill: Drawing simple diagrams of the structure of single nucleotides of DNA and RNA, using circles, pentagons and rectangles to represent phosphates, pentoses and bases.
Theory of knowledge:
The story of the elucidation of the structure of DNA illustrates that cooperation and collaboration among scientists exists alongside competition between research groups. To what extent is research in secret ‘anti-scientific’? What is the relationship between shared and personal knowledge in the natural sciences?
Guidance:
• In diagrams of DNA structure, the helical shape does not need to be shown, but the two strands should be shown antiparallel. Adenine should be shown paired with thymine and guanine with cytosine, but the relative lengths of the purine and pyrimidine bases do not need to be recalled, nor the numbers of hydrogen bonds between the base pairs.
2.7 DNA replication, transcription, and translation
Essential Idea: Genetic information in DNA can be accurately copied and can be translated to make the proteins needed by the cell.
Nature of science: Obtaining evidence for scientific theories—Meselson and Stahl obtained evidence for the semi-conservative replication of DNA. (1.8)
Understandings:
• The replication of DNA is semi-conservative and depends on complementary base pairing.
• Helicase unwinds the double helix and separates the two strands by breaking hydrogen bonds.
• DNA polymerase links nucleotides together to form a new strand, using the pre-existing strand as a template.
• Transcription is the synthesis of mRNA copied from the DNA base sequences by RNA polymerase.
• Translation is the synthesis of polypeptides on ribosomes.
• The amino acid sequence of polypeptides is determined by mRNA according to the genetic code.
• Codons of three bases on mRNA correspond to one amino acid in a polypeptide.
• Translation depends on complementary base pairing between codons on mRNA and anticodons on tRNA.
Applications and skills:
• Application: Use of Taq DNA polymerase to produce multiple copies of DNA rapidly by the polymerase chain reaction (PCR). • Application: Production of human insulin in bacteria as an example of the universality of the genetic code allowing gene transfer between species.
• Skill: Use a table of the genetic code to deduce which codon(s) corresponds to which amino acid.
• Skill: Analysis of Meselson and Stahl’s results to obtain support for the theory of semi-conservative replication of DNA.
• Skill: 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.
• Skill: Deducing the DNA base sequence for the mRNA strand.
Guidance:
• The different types of DNA polymerase do not need to be distinguished.
Aims:
• Aim 8: There are ethical implications in altering the genome of an organism in order to produce proteins for medical use in humans.
• The replication of DNA is semi-conservative and depends on complementary base pairing.
• Helicase unwinds the double helix and separates the two strands by breaking hydrogen bonds.
• DNA polymerase links nucleotides together to form a new strand, using the pre-existing strand as a template.
• Transcription is the synthesis of mRNA copied from the DNA base sequences by RNA polymerase.
• Translation is the synthesis of polypeptides on ribosomes.
• The amino acid sequence of polypeptides is determined by mRNA according to the genetic code.
• Codons of three bases on mRNA correspond to one amino acid in a polypeptide.
• Translation depends on complementary base pairing between codons on mRNA and anticodons on tRNA.
Applications and skills:
• Application: Use of Taq DNA polymerase to produce multiple copies of DNA rapidly by the polymerase chain reaction (PCR). • Application: Production of human insulin in bacteria as an example of the universality of the genetic code allowing gene transfer between species.
• Skill: Use a table of the genetic code to deduce which codon(s) corresponds to which amino acid.
• Skill: Analysis of Meselson and Stahl’s results to obtain support for the theory of semi-conservative replication of DNA.
• Skill: 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.
• Skill: Deducing the DNA base sequence for the mRNA strand.
Guidance:
• The different types of DNA polymerase do not need to be distinguished.
Aims:
• Aim 8: There are ethical implications in altering the genome of an organism in order to produce proteins for medical use in humans.