MBG 2040 Lecture Notes - Lecture 6: Tobacco Mosaic Virus, Ribonuclease, Deoxyribonuclease
Structure of DNA and Chromosomes
Outline:
• Functions of genetic material
• Structures of DNA and RNA
• Chromosome structure in prokaryotes and viruses
• Chromosome structure in eukaryotes
Outcomes:
• Explain how genetic information is stored in deoxyribonucleic acid (DNA)
• Define the composition and structure of DNA
• Explain how DNA is organized and packaged in prokaryotes and eukaryotes
The genetic material must replicate, control the growth/development of the organism, and allow the
organism to adapt to changes in the environment.
Evidence that DNA is the genetic material:
• Recall bacterial transformation
• *see slide
• 1944: Avery, MacLeod, and McCarty determined what type of molecule is the "transforming
principle" in S. pneumoniae
o Type IIR cells --> IIR colonies
o Type IIR Cells + protein from heat-killed type IIS cells --> IIR colonies
o Type IIR Cells + DNA from heat-killed type IIS cells --> IIS colonies
o Type IIS cell DNA + protease --> IIS colonies
o Type IIS cell RNA + RNAase --> IIS colonies
o Type IIS cell DNA + DNAase --> no colonies
*Conclusion: the hereditary "transforming principle" is DNA
Evidence that RNA is genetic material:
• Tobacco mosaic virus (TMV) has RNA and protein, but no DNA
• Different strains have different coat proteins
• RNA specifies the coat protein
Key Points:
• Genetic information of most organisms is stored in deoxyribonucleic acid (DNA)
• In some viruses, the genetic information is present in ribonucleic acid (RNA)
Structure of DNA and RNA:
• Nucleic acids are composed of nucleotides
o Nitrogen containing bases:
• Pyrimidines:
▪ Thymine (in DNA)
▪ Cytosine
▪ Uracil (in RNA)
• Purines:
▪ Adenine
▪ Guanine
• Sugar (Pentose)
o Deoxyribose (-H *no hydroxyl group)
o Ribose (-OH)
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Document Summary
Outline: functions of genetic material, structures of dna and rna, chromosome structure in prokaryotes and viruses, chromosome structure in eukaryotes. Outcomes: explain how genetic information is stored in deoxyribonucleic acid (dna, define the composition and structure of dna, explain how dna is organized and packaged in prokaryotes and eukaryotes. The genetic material must replicate, control the growth/development of the organism, and allow the organism to adapt to changes in the environment. Evidence that rna is genetic material: tobacco mosaic virus (tmv) has rna and protein, but no dna, different strains have different coat proteins, rna specifies the coat protein. Key points: genetic information of most organisms is stored in deoxyribonucleic acid (dna) In some viruses, the genetic information is present in ribonucleic acid (rna) In vivo dna is negatively supercoiled: *see slide, relaxed, nicked, circular dna undergoes one 360 degree left-handed rotation --> negatively supercoiled, covalently closed dna.