Chapter 9: DNA and Its Role in Heredity Flashcards
What criteria needed to be demonstrated before people could accept that DNA was the genetic material? (Circumstantial evidence)
present in the cell nucleus and in condensed chromosomes
doubled during S phase of cell cycle
was twice as abundant in diploid as haploid cell
showed the same patterns of transmission as the genetic info it was supposed to carry
Miescher
took bandages isolated nucleus, a solution came out that he called nuclein
said eh I bet this is genetic material
bacteriophage
viruses that infect bacteria
transformation experiments
bacteria strain A + strain B DNA —–> bacteria strain B
transgenic
artificially modified organism
Chargaff’s rule
A nd T
C and G
Nucleotide
deoxyribose in DNA, sugar in general
phosphate group
Purines
A and G
double ring
Pyrimidine
C and T
single ring
helical
spiral shape
like spring
DNA
Franklin’s Crystallography results
antiparallel
strands run in opposite directions
What defines DNA structure?
double stranded helix of unifrom diameter
right handed
antiparallel
outer edges of nitrogenous bases exposed in major and minor grooves, which exist because the helices fromed by backbones are not evenly spaced
the surfaces of A-T and G-C base pairs are chemically distinct
the binding of proteins to specific base pair sequences is the key to DNA-protein interactions
True or false: all regions of all DNA are right handed
false
Z-DNA= left handed regions
What functions is the double stranded helix essential to?
storage of genetic info (tons of nucelotides allow for lots of storage)
Precise replication during the cell division cycle (complementary base pairing)
susceptibility to mutations
expression of the coded information as phenotypes [not obvious in the structure]
Semiconservative replication
each strand of the parental DNA acts a template for a new strand, which is added by base pairing
What are the two general steps for DNA replication?
double helix unwound to separate the two template strands and get them ready for base pairing
new nucleotides form complementary base pairs with the templates and then linked by phosdiester bongs
template read in 3’ to 5’
Deoxyribonucleoside triphosphosphates (dNTPs) deoxyribocucleotides
each carry three phosphate groups
during synthesis they release the outer two in an exothermic reaction, giving the nergy for phosphodiester bond formation
between the third phosphate and the 3’ sugar position
DNA polymerase
catalyzes the addition of nucleotides as the new DNA chain grows
origin of replication
ori
pre-replication complex, with DNA polymerase, binds to it
replication forks
once the pre-replication complex is binded to the DNA, where replication happens
opens up in one direction
What does DNA replication begin with?
primer
primer
starter strand that DNA polymerase can hook on to
generally short strand of RNA
degraded at the end
Primase
enzyme that adds primer
one nucleotide at a time
Leading strand
one of the newly synthesized strands
can dontinuously grow at 3’ end
Lagging strand
one of the newly synthesized strands
can’t grow continuously because it orients away from the fork
short backward stretches
Okazaki fragment
short stretches of new DNA on the lagging strand
True or false: each Okazaki fragment needs a new primer
true
Processive
DNA polymerase is this
it catalyzes many sequential polymerization reaacitons each time it binds to a DNA molecule
DNA ligase
connects the okazaki fragments
True or false: chromosomes become a little shorter with each cell division
true
Telomeres
repetitive sequences at the end of each strand
prevents chromosomes form joining together
TTAGGG
repeats bind proteins to them
#aglets
Telomerase
enzyme
catalyses the addition of lost telomeric seuences in continually dividing cells
What happens when the chromsome ends become too short and their protective role is lost?
apoptosis and cell death
contains an RNA sequence that acts as a tenokate for the DNA sequence
What are the two major repair mechanisms?
Proofreading- right after DNA polymerase inserts a new nucleotide when it recognizes the mistake, it removes the wrong base and tries again
Mismatch repair- after DNA has been replicated another set of proteins checks it out if there is an error, a section of the DNA will be removed and replaced
Polymerase chain reaction
allows researchers to mak emultiple copies of short DNA sequences
amplification
uses a sample of double stranded DNA template
some short primers
dNTPs
DNA polymerase
salts ans buffers
True or false: mutations are changes in the nucleotide sequence of DNA that are passed form one cell or organism to another
True
Somatic Mutations
occur in somatic (body) cells
passed on to daughter cells
ex. patch of skin with sane mutation
NOT PASSED ON TO OFFSPRING (unless you are a plant and you follow 0 rules)
Germline mutations
occur in cells of the germ line
give rise to new gametes
a gamete with mutation passes it on to new organism
Silent mutations
do not affect gene function
either not expressed or have no effect
most mutations in large genomes are silent
Loss-of-function mutations
rither loss of expression of a gene or in the production of a nonfunctional protein or RNA
some prevent transctiption or cause it to happen too soon
sometimes, the protein doesn’t work
generally recessive inheritance
Gain-of-function mutation
protein with altered function
usually dominant
common in cancer
Conditional Mutations
cause phenotypes only under certain restrictive conditions
wild-type expressed under permissive conditions
many temp sensitive
Point mutation
gain, loss, or substituion of a single nucleotide
if in a gene, results in a new allele, which may result in a new phenotype
Chromosomal Mutations
extensive changes in chromsome structure
change position or orientation of DNA segment without removing genetic info or cause a segment to be duplicated or lost
Mutagens
environmental substances that cause mutations such as radiation or chemicals
cause point mutations
Deletions
a type of chromosomal mutation
removal of part of the genetic material
ex. DNA molecules breaks at two points, the two ends rejoin and the middle is gone
Duplications
a type of chromosomal mutation
ex. homologues break at different positions and then reconnect at wronf partners
one would lack a section (deletion)
another would have two (duplication)
Inversions
can also result from breaking and rejoining
a segment may be removed but then flipped so it runs in the opposite direction
Translocations
segments of the chromosome break off and become joined to different chromosome
may involve reciprocal exchanges
often lead to duplications and deletions
Spontaneous Mutations
permanent changes in the genetic material that occur without outside influence
what can cause spontaneous mutations to occur?
DNA polymerase makes a mistake (some are not caught)
Four nucleotide bases of DNA have alternate structure that affect base paring- each nucleotide can exist in two different forms(tautomers), one common one rare can pair wrongly
Bases in DNA may change because of spontaneous chemical reactions- deamination converte amino to a keto to change C to U usually repaired
Meiosis isn’t perfect- nondisjunction and aneuploidy
Gene sequences can be disrupted- random chromsome breakage/rejoining
Induced Mutations
some agent from outside the cell (mutagen) causes a permanent change in the DNA sequence
What causes induced mutations?
chemicals alter nucleotide bases some chemicals add groups radiation damages the genetic material can produce highly reactive chemicals can break down the sugar-phosphate backbone
True or false: mutations tend to occur in certain places
true
True or falsee: mutagens can only be artificial
false, they can also be natural
Benefits of mutations
raw material of evolution
Costs of Mutations
can be harmful if result in loss of function of genes or other things that are needed for survival
