DNA as Genetic Material Flashcards
1) Give 2 pieces of evidence (experiments) that DNA is responsible for the transmission of genetic information
- Griffith pneumoccocus experiment
- Hershey-chase experiment
2) Describe the Griffith pneumoccocus experiment involving the mice
- Two strains of S.pneumoniae: S and R strains
- Mice injected with S strain die, R strain mice live
- When S strain was heat treated (to kill lethal component), the mice survived
- When heat treated S strain was mixed with non-lethal R strain, the mouse died
- so, there is a living lethal component of S strain, surviving the heat which the R strain has reactivated
3) After the mice experiments, which further experiments were conducted to make conclusions concerning DNA?
- Cytosol of heat killed S strain pneumoniae isolated
- Mixed with DNAase (inhibit DNA) -> mouse lives
- Mixed with trypsin (removes protein) -> mouse dies
- therefore, DNA must be the transforming principle (containing the lethal potential, even when heat treated)
4) Describe the Hershey-chase experiment and what was analysed to determine the conclusion?
- 2 bacteriophages (virsuses that infect bacteria) are used : 1 with a sulphur labelled protein capsule and 1 with a phosphorus labelled DNA core
- Each virus infects a bacteria, blend DNA and centrifuged to analyse cell contents, supernatant produced which was analysed
5) What was present in the supernatant of each bacteria?
- Sulphur labelled protein bacteria: no sulphur in cells, but present in supernatant
- Phosphorus labelled DNA bacteria: phosphorus in cells but not in supernatant
- As viruses transfer their genetic information to bacteria, this must be contained in the DNA (the carrier)
6) Which DNA bases have roughly the same amounts?
A and T
C and G
7) What does X-ray diffraction show about DNA?
DNA has a regular, repeating structure (equal spacing)
8) Describe the Watson and Crick model of DNA
- Right handed double helix
- 2 strands twisted together
- Antiparallel: 5’ end has a free 5’ phosphate on 5th carbon and 3’ end has a free hydroxyl group on 3rd carbon
- A-T bond has 2H bonds
- C-G bond has 3H bonds [H bonds can be disrupted by heat or chemicals, non-covalent]
9) How many nucleotides are there per turn of the DNA strand, what is the length of one turn and the diameter of the helix?
- 10 nucleotides per turn
- one turn is 3.4nm
- diameter of helix is 2nm
10) Define the major and minor grooves on a DNA double helix
- Major and minor grooves are on opposite sides of a turn
- Major groove is larger - greater distance between the same point on two adjacent turns
- Minor groove is smaller - less distance between the same point on two adjacent turns
11) Define replication, transcription and translation
- Replication : producing more DNA double helices, this is semi-conservative as each daughter helix has 1 parent strand and one synthesised strand
- Transcription: producing a molecule of mRNA (complementary to the template DNA strand)
- Translation : producing a polypeptide chain at a ribosome, which reads the mRNA strand and a tRNA molecule brings correct amino acids
12) Which two enzymes are involved in the breakdown and reformation of DNA?
- Nucleases: (e.g. restriction endonucleases) cleave sugar-phosphate backbone at defined points
- Ligases : (e.g. ligase) can form phosphodiester bonds between adjacent DNA nucleotides to form a strand
13) What type of strand does DNA form a double strand with?
- Reverse complement strand
- 5’ and 3’ ends switch (reverse) and complementary base pairs to the other DNA strand are made
14) Describe the structure of RNA
- Bases A,C,G,U
- Ribose sugar
- Single stranded
- G and C, A and U not equally matched
- More flexible structure
- G-C and A-U base pairing within molecules forms complex hairpin structures within RNA molecules
15) Describe the structures of mRNA, tRNA and rRNA
mRNA: collection of RNA chains of various lengths, relatively unstable
tRNA: collection of small RNA chains
rRNA: found in ribosomes, complexed with proteins (small/medium/large in size)
