Lecture 9 Flashcards
Chromosone are composed of ________
DNA
Describe the experiment conducted by Fred Griffith in the 1920’s.
- Injected two strains of S. pneumonaie into mice (one lethal (S-strain) and one harmless (R-strain))
- heat killed the S-strain and injected it into mice –> mice survived
- when cells of the heat killed the S-strain mixed with the R-strain and injected it into the mice –> mice died
- this represented the phenomenon “transformation” which is the ability of the unknown factor to transform a harmless strain into a harmful one
What ideas did Avery, MacLeod and McCarthy add to Griffiths experiments in 1944?
- they isolated individual components from S-strain cells and tested their ability to transform the R-strain
- conclusion: the molecule that contains the heritable information is DNA
What did Hershey and Chase conclude about DNA from their experiments in 1952?
- they concluded that DNA enters bacteria and carries genetic information
What are the primary, secondary, and tertiary structures of DNA?
- Primary structure: the nucleotide sequence
- Secondary structure: An regular, stable structure taken up by some or all of the nucleotides
- Tertiary structure: Complex 3D folding of nucleic acid (e.g bacterial nucleoids)
What is the difference between a nucleoside and a nucleotide?
- nucleoside: base + sugar (adenosine)
- nucleotide: base + sugar + phosphate (adenosine monophosphate AMP)
How do ribose and deoxyribose sugars differ from one another?
- In RNA the 2’ carbon has a hydroxyl group where as in DNA it only as a hydrogen attached. The hydrogen is less reactive than the hydroxyl which is important in RNA splicing reactions
phosphodiester linkages
- forms a repeating backbone
- the 5’ phosphate of one nucleotide unit is joined to the 3’ hydroxyl group of the next nucleotide creating the phophodiester linkage
What is the difference in structure between a purine and a pyrimidine?
- Purines have 2 rings (Guanine, Adenine)
- Pyrimidines have 1 ring (Cytosine, Uracil (RNA), Thymine (DNA))
What is a B-Glysosidic linkage
- The pentose forms a covalent bond with the base called a B-Glycosidic linkage (a bond joining a sugar to another group)
What is the secondary structure of DNA?
The double helix
- two strands that interact via base pairing (hydrogen bonding), and wound around the same axis
- strands run in opposite direction
- parallel: 5’ to 3’
- antiparallel: 3’ to 5’
What are the complementary base pairs in DNA?
- base pairing occurs through hydrogen bonding between complementary bases
- Adenine forms 2 H-bonds with thymine or uracil (A=T, A=U)
- Guanine forms 3 H-bonds with cytosine
What is base stacking
- base stacking between hydrophobic bases minimizes contact with water and is very important for stabilizing the double helix
- base stacking gives arise to van Der wall interactions and dipole-dipole interactions
- bases are not directly on top of one another
How many base pairs are there per turn in a DNA double helix?
10.5 base pairs/turn
Who determined the double helix structure of DNA and defined base pairing specificity
- James Watson and Francis Crick
