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)
16) How does an unpaired loop form in mRNA molecules?
- When mRNA folds and forms base pairs with another section of the same strand (possible but less common in DNA)
17) Describe how the DNA genome is packaged in eukaryotic cells
- DNA is supercoiled (extra coiling for packing into nucleus)
- Chromosomes are made of chromatin and nucleosomes are made of chromosomes
- Chromosomal DNA stores genetic info for life and all cells need a full set (except non-dividing, RBCs)
- Genetic info used for replication, mitosis
18) Describe the organisation of DNA in the human genome
- 23 chromosomes
- ~ 21,000 genes
- 2% of genome encodes protein, rest is code for utilisation of gene products/ producing different products and outcomes (instructions)
