DNA experiments Flashcards
before DNA scientist thought and why
protein was genetic material because many more combs (2o AA) and chromosoes have DNA and protiens
genes control
protein synthesis
why did scientist think that DNA is not unique and protein is
because DNA only has 4 neucletides
Frederick Griffith
smooth and rough bacteria in mice (DNA transformation)
griffith Bacteria
pneumococcus
S (smooth bacteria)
virulent (lethal)
Mice – pneumonia - death
(R) rough strain –
avirulent
Mice survive
Heat killed (S) strain
Mice survive
Heat killed (S) + live (R)
Mice died
Found living (S) in dead mice
transformation
type of permanent genetic change where the properties of 1 strain of dead cells are conferred on a different strain of living cells
griffith came up with what principle
“transforming principle” was transferred from dead to living cells
Avery, MacLeod, McCarty
Identified Griffith’s transforming principle as DNA
(just went farther with his reseracch)
Live (R) + purified DNA from (S) =
in avery experiemnt
🡪 R cells transformed
R + (S) DNA →
mouse dead
R + (S) protein→
live
DNA responsible for
transformation
scentist still didnt belive griffith and avery,macleod, maccarthy bcuz
they still belive that ther could of been cross contamination and som protine got inot the dna sample
Hershey and Chase
Bacteriophages and blender
Radioactive labels
for hershey and chase
Viral protein – sulfur
Viral DNA - phosphorus
quick procedure of hershey and chase experiment
infect bacteria, agitate in blender, centrifuge
what did hershey and chase find in sulfur sample
all radioactivity in supernatant (not in cells)
phosphorus sample
radioactivity in pellet (inside cells)
bacteriophages inject DNA into bacteria, leaving
proteinon outside
Rosalind Franklin (in lab of Wilkins)
X-ray diffraction on crystals of purified DNA
(found shape of DNA ) (HELIX SHAPE)
rosalind determined
Determine distance between atoms of molecules arranged in a regular, repeating crystalline structure
Helix structure
Nucleotide bases like rungs on ladder
James Watson and Francis Crick – 1953
made actual model of Dna
DNA now widely accepted as genetic material
Took all available info on DNA and put together
Showed
DNA can carry info for proteins
Serve as own template for replication
meselson and stahl
experiment to test the possible models of DNA replication. Grew bacteria in a heavy isotope of Nitrogen (15N), then transferred to light nitrogen.demonstrated that DNA replicated semi-conservatively,
be able to explain how mutagens can be passed on
write on paper memorize
DNA replication diagram (semiconservative model be able to explan it )
parent molecule strands separate the daughter DNA molecules will each contain one parental strand and one new strand
what are the 7 steps of DNA replication
1.DNA helicase
2.helix-destabilizing proteins (SSB)
3.topoisomerases
4.RNA primer
5.DNA polymerase
6.Origin of replication
7.DNA ligase
- DNA helicase
separates the 2 strands of DNA (“unzipping) (takes apart hydrogen bonds between base pair
- Helix-destabilizing proteins
bind to single DNA strands,prevents reforming of the double helix (they stabilize it open)
- topoisomerases
prevents knots/tangling/supercoiling -tightning
- RNA primer
made first at origin of replication
DNA polymerases can only add new nucleotides to a
existing DNA chain
DNA polymerase can add nucleotides base pairs to
original DNA template
RNA primer makes
primase (make DNA polymerase)
Primase will be displaced by DNA polymerase after the
1st few nucleotides or primer as added
Primers are later
degrade by enzymes and filled with DNA (so there is a cont. DNA nucleotide sequence)
- DNA polymerase
Polymers make DNA. it adds nucleotides to the 3’ end (where hydroxyl is )
DNA always grows in
5’ to 3’ direction
- Origin of replication
this is where you get a replication bubble it will get a y shaped fork
leading strand
nucleotides continuously added to 3’ end thoward fork
lagging strand
nucleotides add to 3’ prime end going away from fork_____> get short pieces of DNA
okazaki fragments
discontinuous,get short pieces of DNA
7.DNA ligase
joins fragments (links 3’ OH of one to 5’ phosphate of another =phosphodiester linkage) DNA ligase is going to seal up the sugar phosphate backbone and the ladder between the bases (ACTG) will form again
the bubbles in DNA
at the origin as replication happens proceeds in both directions you will end up with multiple bubbles along the same DNA strands then all of the bubbles will end up coming together then the 2 daughter DNA molecules separated in to two separate strands the bubble allows replication to go faster and make it more efficient since the DNA is larger makes separation of strand to go quicker
why are there little fragments while adding nucleotides to DNA strands
little fragments because DNA polymerase can only add nucleotides on to the 3’ and DNA is anti-parallel so they go opp sides
the proteins that participate in DNA replication form a large complex
DNA replication machine
the DNA replication machine may be stationary during the
replication process
what proofreads newly made DNA and replaces any incorrect nucleotides
DNA polymerases
In mismatch pairs of DNA
repair enzymes correct errors in base pairing
DNA can be damaged by
exposure to harmful chemical or physical agents (cigarettes and x-rays) it can also undergo spontaneous changes
In nucleotides excision repair
a nuclease cuts out and replaces damaged stretches of DNA
eveloitionary sig. of altered DNA nucleotides
these changes (mutations) are the source of the genetic variation upon which natural selection operates
telomeres
caps end of chromosome:short non-coding sequences repeated many times they are peotectants so no DNA info is lost when DNA is replicated so many times
lagging strands is discont., so DNA polymerase unable to complete replication leaving small parts unreplicated
small parts are lost with each cycle
germ cells
sex cells
telemorase
catalyzing the length of teleomere ( extends out lengthens and adds)
shortening Telomoer and cancer
telemoers can stop growing and parts of DNA can get lost and stop replicating so certian cells can stop replicatign which can help not spread cancer (Its good)
DNA+protiens=
chromosomes
BActeria chromosome
double stranded,circular, DNA +small amount of protien
DNA is supercoiled in nucleotide
eukaryotic chromosomes
liner DNA molecules and large amount of protiens
chromatin (DNA + Protien) in nucleus
Histones
DNA are wrapped tightly around them
