Barnes (Genetic material) Flashcards
1
Q
What did DeVries, Correns and Tschermak do?
A
- repetition of Mendel’s work (pea plants)
- distinguished between genotype and phenotype
- must be genetic material –> must be replicated, stored and expressed, variation by mutation
2
Q
What did Miescher do?
A
- WBCs
- studied chem composition of nuclei
- found nuclein (DNA)
- showed not protein, as not digested by pepsin protease and contains no S
- didn’t contain H, C, O, P
3
Q
What did Flemming do?
A
- salamanders
- dev novel microscopic techniques to observe fixed, stained cells
- discovered chromatin = fibrous structure in nucleus, easily stained
- postulated transforms into thread like chromosomes at mitotic division
4
Q
What did Sutton and Boveri do?
A
- grasshopper and worms
- used cytology and microscopy to find where genetic material carried
- grouping in pairs and separation consistent w/ Mendel’s laws of heredity
- diff combos of chromosomes would cause variation
- theory of inheritance = chromosomes req for embryonic dev, carry Mendel’s factors, linear structures w/ genes along
5
Q
What did Morgan do?
A
- investigated whether heritable mutations in Drosophila
- linked mutant white eye phenotype to unusual chromosome composition
- so genes must be on chromosome
6
Q
What did Garrod do?
A
- cause of alkaptonuria in humans
- what urine composition shows about metabolism
- noticed ran in families
- linked human disorders to metabolic defects
- build up of intermediates from breakdown of proteins cause disease
- proposed diseases inborn errors of metabolism and differences in metabolism between healthy people
7
Q
What did Beadle and Tatum do?
A
- established 1 gene-1 enzyme hypothesis
- niacin prod studied as model pathway
- niacin synthesised in series of biochem steps, by series of enzymes
- gen mutations in DNA of individual cells using X-rays
- X-rays cause DNA breaks in double helix, repaired imperfectly, causing stable mutations
8
Q
What is minimal growth media?
A
- contains only nutrients organism cannot synthesise itself, WT organism should be able to grow
9
Q
What is complete media?
A
- contains extra nutrients
- should make up for some defects in metabolic pathways and allow mutant cells to grow
- WT cells also able to grow
10
Q
What was the method for Beadle and Tatum’s experiment?
A
- used X-rays to gen many mutant cells
- grew each mutant in complete media 1st to get lots of identical cells
- grew identical cells (same mutation) in minimal media supplemented w/ intermediates
- observed growth
11
Q
What did Griffith go?
A
- S. pneumoniae
- S strain (smooth) w/ polysaccharide coat is pathogenic
- R strain (rough) w/o polysaccharide coat is not pathogenic
- polysaccharide coat forms capsule, protection from IS
- killed S by heating to high temp = mouse lives
- inject dead S into mice w/ live R = mouse dies
- as R cells transformed, changing genotype
12
Q
What did Avery, Macleod and McCarthy do?
A
- cont Griffith’s research to find molecule responsible for transformation
- systematically destroyed each component of S strain extract using enzymes that specifically digest each type of molecule
- combined w/ live R to test for transformation
- mouse only lived when DNA destroyed
- in order for bacteria to be virulent, req DNA encoding polysaccharide coat
13
Q
What did Hershey and Chase do?
A
- investigated which part bacteriophage T2 injected into bacteria
- labelled bacteriophage DNA w/ radioactive isotope
- infect unlabelled bacteria w/ radioactive phage
- separate phage ghosts from infected bacteria
- test bacteria and phage ghosts for radioactivity
- knew DNA contained phosphate and proteins contained S
- if DNA genetic material then P DNA would be bacteria labelled and S protein phage ghost labelled
14
Q
What did Kossul do?
A
- identified diff nucleobases in nucleic acids
- discovered thymine
15
Q
What did Levene do?
A
- nucleotides assembled into strings and components joined by covalent bonds
- thought 4 nucleotides in same seq in each DNA molecule, so too simple to make up genetic material of cell
16
Q
What did Chargaff do?
A
- used paper chromatography to separate and isolate nucleobase components of DNA from no. of species
- %A = %T and %G = %C (% AG purines = % CT pyrimidine)
- %AT compared to %GC varies between species
17
Q
What did Wilkins and Franklin do?
A
- used X-ray crystallography to study DNA structure
18
Q
What did Watson and Crick do?
A
- A-T and G-C H bonded
- antiparallel strands
- right handed double helix
- 1 helical turn every 10.5 bp
- major and minor grooves
19
Q
What were the 3 poss models for DNA rep?
A
- conservative
- semi conservative
- dispersive
20
Q
What did Meselson and Stahl do?
A
- grew bacteria in media containing 15N (“heavy” DNA)
- transfer to media containing w/ 14N (“light” DNA)
- separate heavy and light molecules by ultracentrifugation and DNA visualised w/ UV light
- after 1 gen, only single hybrid band, so not conservative
- after 2 gen, 2 bands equal density, 1 hybrid and 1 light, so must be semi conservative
- after 4 gen, 2 bands, light dominant and hybrid lighter
21
Q
What is the rep fork?
A
- where original DNA strand splits for rep
22
Q
What did Cairns do?
A
- rep incorporating radioactive molecules to visualise
- DNA rep bidirectional
- single origin rep in E. Coli
- 2 rep forks, moving in opp directions around circular chromosome
23
Q
How many origins of rep do euks have and what do they form?
A
- many
- rep bubble
24
Q
What did Kornberg do?
A
- used cell free system to study pol activity
- separated proteins in bacterial cell extract by electrical charge
- purified DNA pol I
- found template strand read 3’ to 5’
25
Q
What assay for DNA synthesis did Kornberg use?
A
- incubated in test tube –> conc DNA pol I from E. Coli, template DNA, nucleotide substrates inc radiolabelled dTTP, Mg2+
- omitting any of these stopped any long DNA strands being formed
- looked for long pieces of DNA containing radioactive nucleotides
- base composition of template and product same
- req free 3’ end to add nucleotides
26
Q
What are the general properties of DNA pols?
A
- add nucleotides 1 at a time, 5’ to 3’
- need to add new nucleotides onto existing nucleotide in chain
- needs primer
27
Q
What is a primer?
A
- short chain of nucleotides to build on
28
Q
What is the main pol for DNA rep in bacteria?
A
- DNA pol III
29
Q
Do pols have proofreading activity?
A
- most do
- 3’ to 5’ endonuclease activity to remove nucleotides if mistake made
30
Q
What is the role of primase?
A
- generates primer made of RNA
31
Q
What is the role of ligase?
A
- joins loose ends together into ss DNA
32
Q
What is the role of topoisomerase?
A
- relieves pressure from overwinding around rep bubble by making and resealing DNA breaks
33
Q
What is the role of helicase?
A
- breaks H bonds between 2 DNA strands, separating them
34
Q
What is the role of singel strand binding protein (SSB)?
A
- binds to separated strands, preventing reannealing
35
Q
What is the leading strand and how does DNA synthesis occur here?
A
- 5’ to 3’
- DNA synthesis points towards rep fork and proceeds continuously
36
Q
What is the lagging strand and how does DNA synthesis occur here?
A
- 5’ to 3’
- DNA synthesis points away from rep fork and is discontinuous
- primer synthesis and elongation
- primer removal w/ gap filling
- joining of Okazaki fragments
37
Q
What are Okazaki fragments?
A
- pieces of DNA stuck together to make up lagging strand
38
Q
What are telomeres and what problem do they solve?
A
- short DNA seqs repeated over and over at ends of chromosomes
- problem for lagging end, as primer removal at ends leaves gaps that can’t be filled, so little piece lost on every round of rep
- repetitive nature allows them to bind specific proteins, protecting vulnerable ends
39
Q
What is the role of telomerase?
A
- replenishes telomeres from DNA template
