If you're studying a life science (e.g. - biomed, bioscience, physiology, sports science, sports physiology etc), then this detailed set of lecture notes on DNA structure will help you smash your first set of exams on cell/molecular biology!
DNA is a major part of the Cell and Molecular biology...
DNA Structure and Function: 21/10/19
Genetics = science about heredity and variation of living organisms
- Heredity = (inheritance) – ability of organism to pass on biological properties to offspring
(progenies)
- Variation = divergence of species (or individuals) in their biological properties
Heredity = same/similar, Variation = different
DNA = core substance of genes
DNA = coding (most chromosomal, plasmid DNA etc.) and non-coding (centromeric, telomeric and
regulatory DNA)
There was little knowledge of DNA early on:
- Griffith (old scientist) did experiment on mice with strains of bacteria
- One caused pneumonia one didn’t
- He killed pathogenic one with heat and mixed with the living non-lethal bacteria
- Some living cells (non-lethal) became pathogenic
- Said trait was passed onto further descendants
- Phenomenon was called transformation
- ‘transforming substance’ later identified as DNA
(Capsules protect S cells from antibodies – so are pathogenic)
- Viral DNA can program cells
- Studies that viruses infect bacteria suggested evidence that DNA = Genetic material
- Bacteriophage = virus – infects bacterial cells by injecting genetic material
- Bacteriophage = used in genetic research
Virus = DNA/RNA enclosed in protective protein coat
T2= bacteriophage (phage) that is used in research
- Unknown if viral protein or DNA was used to reprogram host cells
- Hershey and Chase used E. coli bacteria as host cells:
In a strand of DNA:
2 Findings of Chargaff’s rules:
- AT and CG
1) Base composition of
DNA varies between
- Phosphate of 1 nucleotide = attached
species
to sugar of another nucleotide forming
sugar phosphate backbone
2) A% = T% and C% = G%
- 5’ to 3’
, DNA = Polymer of nucleotides
- Each nucleotide = Pentose sugar, N2
containing base, Phosphate group
- ATCG
- Chargaff stated base composition of DNA
varies from one species to another
- Evidence of diversity = more proof DNA =
genetic material
- Cytosine and Thymine = Pyrimidine bases – (6 membered rings)
- Uracil = part of RNA – replaces thymine
- Adenine and Guanine = Purine bases – (6 membered ring bound to 5 membered ring)
Franklin and Wilkins used X-ray crystallography to study molecular structure of DNA and picture of
DNA was produced
Watson used X-ray pictures, deduced DNA = helical
Pictures aided in deducing width of helix and spacing of bases
Pictures showed 2 strands present – so double helix
Watson and Crick showed DNA = antiparallel strands
Several different bonds in DNA:
- Sugar-Phosphate bonds = covalent
- H2 bonds between base pairs (holds strand together)
- Van der Waals between stacked base pairs (holds molecule together)
It was concluded 2 outer sugar-phosphate backbones present – N2 bases in interior
Purine (AG) paired with Pyrimidine (CT) = uniform width consistent with X-ray data
Specificity of base pairing = due to chemical side groups on bases – forming H2 bonds with
complementary pair
A-T = 2 Hydrogen bonds, C-G = 3 Hydrogen bonds
DNA Replication:
- Core process – making heredity possible – properties from mother cell to daughter cell
- Replication = semiconservative – every strand of DNA = template for comp. strand
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