genetics unit one

griffiths experiment

pneumonia and mice

bacteria type was thought to be unchangeable (fixed); now knew this wasnt correct bc it somehow transformed

hershey and chase

studied bacteriophage

• infect bacteria and guide production of new phage

  • must have genetic info

what can you use to follow changes in experiments

radioactive isotopes

nucleotides have

phosphorous not sulfur

amino acids have

sulfur not phosphorous

purine

have two rings

pyrimadine

have one ring

what does bacteria need to do to replicate

go into a cell

dna replication

semi conservative

strands are complimentary

helicase

breaks h bonds between strands

h bonds

hold strands together

autoradiography

isolate dna and putit on side

cover w photography film

origin of replication

where replication begins

in large chromosomes, replication starts at multiple parts

is dna all replicated at the same time

no

helicase

separates dna strands, eventually the dna gets coiled too muchn and the dna cant unwind anymore

topoisomerase

cuts a strand so that it doesnt coil as much

single stranded binding proteins

binds to single strands to hold them apart so they dont bind together again before replication

how are new dna strands produced

dna dependend, dna polymerase

adds new nucleotides on the 3’ end—> not on the template strands

dna poly synthesizes new dna in the

5’—>3’ direction

reads template strand

3’—>5’

nucleotide triphosphate (NTPs)

provide energy to lengthen polymer

all nucleotides carry

3 phosphate groups

rna primase

dna dependent

dna poly limitations

directionality

needs a starting point (RNA primase)

RNA primase

makes mistakes

makes RNA

sometimes falls off

dna dependent

rna polymerase (makes rna polymer)

doesnt need a starting point

dna poly 3 adds nucleotides to the

3’ end of the rna primer

leading strand

long continuous segments

lagging strands

short, discontinuous segments

how to get rid of rna primer

dna poly 1

has 5’—>3’ exonuclease that removes primer

polymerase replaces dna

exonuclease

removes nucleotides at the end

specifically the 5’ end

dna ligase

seals nicks in dna strands

forms covalent bonds between nucleotides

how does topoisomerase fix the cuts it makes

it fixes itself

does the leading or lagging strand move towards the helicase

the leading strand

end replication problem

the chromosome end loses dna over time because the RNA primer is removed and there isnt a 3’ end to ad onto

chromosomes get shortened

telomeres

specialized region at the end of chromosomes

composed of repeated dna sequences

#repeats can vary

replicated using telomerase

telomerase

rna dependent dna polymerase

uses rna template

dna poly adds to 3’ end using rna template

what does telomerase control prevent

cancer bc having telomerased allows cells to divide

telomerase turns off naturally in some cells

telomeres get shorter as cells divide

dna sequencing

can read dna

sanger dideoxy sequencing

requires a single stranded template

all four dNTPs in each rxn

DNA polymerase

ssDNA primer

why use DNA primers instead of primase

DNA primers are specific to one sequence of DNA while primase can be specific to anywhere along the sequence

we want longer primers because they’re more specific

how is dideoxy different from deoxy

dideoxy doesnt have an OH group; it stops a reaction

what does the incorporation of dCTP allow

the chain to keep growing, but incorporation of ddCTP terminates chain elongation

why does DNA have a negative charge

phosphorous

how do you read sequences of dna from gel electrophoresis

going from shortest to longest

what are flourescent labels used for

nucleotides to make it easier to determine sequences

capillary gel electrophoresis

tube that uses a laser to detect the flourescent light as it passes through

when do you get DNA info, before or after the primer?

after

the primer isnt included in the info that is drawn

is it bad to have extra nucleotides after the primer

no as long as you have the nucleotides you need

what does the primer need to be relevant to the strand

complimentary

PCR

DNA replicaiton; efficeitn and fast

mimicks the process of dna replication

you only copy one specific region youre interested with

extremely sensitive- 1 molecule of dna is enough template

key differences w PCR and dna replication

just one enzymes is needed for PCR

two ssDAN synthetic (man-made) primers (18-30 bases)

• enables specificity

• requires knowledge of the region’s sequence

replication repeated multiple times

where do primers attach

the 3’ end

dna fingerprinting

uses regions of dna that can vary from person to person (alleles)

single nucleotide polymorphisms (SNPs)

single nucleotide differences

short tandem repeats (STRs, aka microsatelites)

short repeated sequences on a chromosome

alleles have different repeat amounts, produce different sized fragments when copied by STR

how many copies does each person have of each chromosome/genesj

2 copies

what does the chance of an accidental primer match depend on

how many STRs are used

there are about 40 different STRs taht can be used

different people have different combinations of alleles

how is info organized in the DNA

23 chromosomes (Human)

range from 48-249×10^6 million base pairs (bp) long

carry info for about 20,000 different genes

code for 80-400,000 different genes

symour benzer

bacteriophage experiments

phage kill (lyse) host cell and create plaques (holes)) in a “lawn” of bacteria grwon on a betri dish

plaque size depends on how quickly the phage lyse the bacteria (slower = smaller plaques)

identified two types of phage

what types of phage did seymour benzer determine

wildtype and mutants

wildtype (rt)

made small plaques

dominant

mutant (r#)

made large plaques (recessive)

benzer’s experiment

infect bacteria w/two different phage

create bacteria that are partial (pseudo) diploids

see waht types of phage are obtained

diploids

contain two versions of phage DNA

complimentation test

test to determine if two recessive mutations affect the same or different genes

what did benzer’s experiment suggest

DNA present the same bacteria could potentially recombine

the mutations were at different locations in the same genetic unit (gene)

cis

two mutations (genes/sequences) are on the same copy of the chromosome

trans

two mutations (genes/sequences) are on different copies of the chromosome

how do bacteria make new phage

teh phage particles must inject genetic info for how to make phage particles into the bacteria

purines

A and G

pyramidines

T and C

why does DNA have a relatively consistent thickness

because purines always bond with pyramidines

what does the ratio of bonding nucleotides equal

one

(G/C) = 1

(A + C)/(T + G) = 1

(A + G)/(T + C) = 1

how many bonds does A - T have

2 hydrogen bonds

how many bonds do G - C have

3 hydrogen bonds

telomerase is what dependent what polymerase

rna dependent dna polymerase

when reading gel electrophoresis how do you know what strand you are reading and what directionality youre reading

youre reading the complimentary strand in gel electrophoresis

the shortest bands are at the 5’ end and the longest bands are at the 3’ end of the complimentary strand (it reads 5’-3’ because the template strand is read 3’-5’)

where is the OH group

at the 3’ end

where is the phosphate group

at the 5’ end

why does a polynucleotide strand have polarity

because the sugar phosphate backbone is held together by a phosphodiester bond between the 3’ hydroxyl of the sugar of one nucleotide and the 5’ phosphate of the adjacent sugar. thus one end of the polynucleotide has a free 5’ phosphate group and the other has a free 3’ OH group. the ends are not chemically the same

polynucleotide

a single strand of DNA

why do the two ends of a dna strand differ chemically

because there is a new hydroxyl group at the new 3’ ends and a new phosphate group at hte new 5’ ends

when inverting dna, do you change the original directionality

no

if you replicate dna two times, what percentage would be new dna

75% new and 25% old

when looking at a table for how long it takes for transformants to replicate, how do you know which has markers closest to the origin of replication

the markers closer to the origin of replication is replicated earlier than DNA that is farther away

which end of the chromosome causes the end of replication problem

the 3’ end because the template strand wont be replicataed where the primer was removed

does telomerase make new primers

no it elongates the template strand

An individual has a mutation that alters Telomerase function. Compared to other people, this

individual’s nucleotide repeats at the end of their chromosomes are the same length but have a

different sequence compared to other people. Briefly describe what the mutation has done.

the mutation alters the sequence of the RNA used asa template by telomerase enzyme

diploid

two copies of each chromosomef

are humans diploid

yes

we have one copy of a chromosome from each parent to make two copies of each chromosome

how many alleles can an individual have at any locus

two alleles

what creates alleles of different lengths among individuals

different individuals can have different numbers of repeats, which creates alleles of different lengths

what does PCR amplify with STR regions

it amplifies the STR region from both chromosomes

what happens if two alleles are different lengths in PCR

PCR produces two differently sized DNA fragments

what happens if the two alleles are the same length

PCR produces one fragment size

when would gel electrophoresis produce one band out of two different alleles

it separates dna by size

if the dna is the same size fragment they will travel together and one band will form

allele

variant form of a gene/DNA sequence

one from your mom and one from your dad

complementation

each chromosome compliments (Fills in for) what the other is missing

two mutations re on different genes

what are the three parts of a dna molecule

phosphate

deoxyribose sugar

nitrogenous base

fredrick griffith

dr w/british ministry

isolated different strands of bacteria from pneumonia

smooth and rough

the strains differently able to cause illness in mices strain

proved that bacteria was changeable

there was a transformable principle

later, avery, macleod, and mccarty demonstrated that the transforming principle was DNA