Barnes - History of DNA

Question 1

name mendels 2 laws and which experimental methods were used to reach these conclusions?

Answer 1

segregation - alleles separate to form separate gametes
independent assortment - genes act separately in meiosis
used: genetics chem and microscopy

Question 2

what did friedrich meischer discover and how did he do this?

Answer 2

studied wbc composition from pus

• found ‘nuclein’ knew it wasnt protein because not digested by protease/no sulphur in it
• contained h c o p
• didnt know anything about its function

Question 3

what did walther flemming discover and how did he do this?

Answer 3

studied cell division in salamander cells (big chromosomes)
found chromatin - thought it formed chromosomes at mitotic division
correctly deduced chromosome movement in mitosis => allows precise division

Question 4

what did devries, correns and tshermar discover and how did they do this?

Answer 4

repeated mendels work

• distinction between genotype and phentoype
• ‘factors’ transmitted from gen to gen influence traits
• ‘heredity determinants’ stay the same gen to gen
• MUST be some kind of genetic material

Question 5

what did walter sutton and theodor boveri discover and how did they do this?

Answer 5

sutton: used grasshoppers & boveri used ascaris worm
- chromosomes group in pairs then separate
- reduction of chromosomes in gametes
- observations consitant with mendels laws
- suggested different combos of chromosomes = variation
developed chromosome theory of inheritance
- chromosomes are required for embryonic development
- chromosomes carry mendels factors
- chromosomes are linear with genes along them

Question 6

what did thomas hunt morgan discover and how did he do this?

Answer 6

found a fly with white eyes instead of WT red

• linked phenotype with unusual chromosome composition
• genes are carried on chromosomes

Question 7

what did archibald garrod discover and how did he do this?

Answer 7

studied urine composition and what is says about metabolism

• noticed disease runs in families
• human disease linked to mendelian inheritance
• linked human disorders to metabolic defects
• buildup of intermediates from protein breakdown => disease
• proposed metabolic disorders caused by missing steps in chemical pathways

Question 8

what did beadle and tatum discover and how did they do this?

Answer 8

used neurospora to establish one gene, one enzyme hypothesis
they studied synthesis of niacin (B3) from tryptophan
they generated mutations using X-rays
generated auxotrophic mutants

Question 9

what did frederick griffith discover and how did he do this?

Answer 9

used mice with strep. pneumoniae
described the ‘transforming principle’
transformed smooth coat bacteria into rough –> recovered bacteria with smooth structure but rough ‘transformation principle’ (genes)
he didnt know what is ‘transforming principle’ was

Question 10

what did avery, macleod and mccarthy discover and how did they do this?

Answer 10

used smooth and rough bacteria from griffiths experiment
systematically destroyed each component of smooth strain using specific enzymes before recombining with rough
when everything but DNA was destroyed the mouse infected lived

Question 11

what did hershey and chase discover and how did they do this?

Answer 11

they tested what T2 bacteriophage injected into the host cell and what it was made up of
used radioactively labelled P and S isotopes in the phage and infected unlabelled bacteria
collected phage ghosts from supernatant
tested for radioactivity with geiger counter
(most of S radioactivity in supernatant/P in pellet which confirms that DNA (containing P) is the source of genetic material)

Question 12

what did kossel discover?

Answer 12

identified the different nucleobases in nucleic acids

discovered thymine

Question 13

what did levene discover?

Answer 13

showed nucleotides make up DNA (phosphodiester linkage)
nucleotides assembled into backbone
components joined by covalent bond
levene thought the 4 bases repeated and therefore was too simple to be the genetic info
-created tetranucleotide hypothesis - 4 bases in equal quantities

Question 14

what did chargaff discover and how did he do this?

Answer 14

inspired by avery et al.
used paper chromatography to separate nucleobase components of diff species
his rules: %A=%T %G=%C %purine=%pyrimadine
%AT=%GC - this means tetranucleotide theory is wrong

Question 15

what did wilkins and franklin discover and how did they do this?

Answer 15

used x-ray crystallography to study DNA shape
observed x-pattern = helical shape
regular pattern –> repeating even structure
distance of 1 turn = 3.5nm

Question 16

what did watson and crick discover?

Answer 16

AT & GC are H bonded pairs
antiparallel strands
r-handed helix
1 turn ebery 10.5 bp
major and minor grooves

Question 17

how many h bonds are there between A & T and G & C? which bases are purines and pyrimidines

Answer 17

AT: 2
GC: 3
AG purines
TC pyrimidines

Question 18

what did meselson and stahl discover and how did they do this?

Answer 18

grew bacteria in 15N media, transferred to media with 14N (1st gen heavy, 2nd is light) and separated by ultracentrifugation used CsCl gradients to work out density and viewed DNA using UV light
saw that
1st gen bacteria 1 band was observed
2nd gen there were 2 bands therefore semi-conservative replication

Question 19

what did cairns discover and how did he do this?

Answer 19

incorporated radioactive molecules into the DNA visualised using autoradiography
observed 1 unlabelled band in 1st gen and 2 unlabelled bands in 2nd gen
concluded: semiconservative replication is correct / single replication origin in E. coli / 2 replication forks moving in opposite directions around circular chromosome

Question 20

what did kornberg discover and how did he do this?

Answer 20

used cell extract to study polymerase

• separated using e- charge (in hope of getting pol)
• in one fraction pol activity increased 2000x
• incubated DNA pol from E.coli; template DNA from diff sources; nucleotide substrates (incl. dTTP); Mg2+
• looked for long radioactive molecules (showing pol had synthesised them)
  concluded:
• All four nucleotides and Mg2+ are required
• A free 3’ end to add new nucleotides onto: replication proceeds 5’ to 3’

Question 21

name 3 properties of DNA polymerases

Answer 21

add nucleotides 5’ to 3’
need to add nucleotides onto existing nucleotide from the chain
needs to be a primer to build from

Question 22

name the main polymerase used in DNA replication in bacteria; and 2 other polymerase functions

Answer 22

main pol = pol III
4 other pol’s (incl. 1) involved in DNA repair & other functions
most pol’s have a proofreading capability

Question 23

what does the enzyme primase do?

Answer 23

generates a primer and ligase joins the new DNA stretches together
(primers are actually RNA)

Question 24

what does helicase do?

Answer 24

breaks H-bonds between strands

Question 25

what does topoisomerase do?

Answer 25

relieves pressure from overwinding around the replication bubble by making and resealing breaks in DNA

Question 26

what does single-strand binding protein do?

Answer 26

SBB binds to separated strands preventing them from renannealing

Question 27

what are telomeres and why are they an important part of a chromosome?

Answer 27

telomeres are short seqs of DNA repeated multiple times at chromosome ends
they are important because they are lost in each round of replication due to primer removal
telomerase enzyme replenishes telomeres from an RNA template