ch 16

Question 1

How did the discovery of genetic role of DNA begin

Answer 1

Griffith worked with two strains of a strep bacterium
pathogenic S strain (smooth w capsule ) and harmless R strain (rough due to lack of capsule)
when he mixed heat-killed remains of the pathogenic strain with living cells of R strain, some living cells became pathogenic
called this transformation

Question 2

transformation

Answer 2

a change in genotype and phenotype due to assimilation of foreign DNA

Question 3

How did scientists confirm that the transforming substance was DNA

Answer 3

they purified various molecules from heat-killed pathogenic bacteria and tried to transform live nonpathogenic bacteria with each type
pnly DNA worked

Question 4

How was DNA’s function confirmed by Hershey and Chase
What was the experiment

Answer 4

they used bacteriophages which use bacterial cells for reproduction. they only consist of a protein coat and a nucleic acid core
they labeled viruses with either radioactive phosphorus (only found in dna) or radioactive sulfur (found only in proteins
they then allowed viruses to infect bacteria cells

Question 5

results of hershey and chase’s experiment

Answer 5

the labeled P virus into the bacteria cell made the bacteria radioactive, while its absence made the viral coats inactive
the labeled S virus into the bacteria cell made the bacteria inactive, while it kept the viral coats radioactive
meant that presence of DNA in p virus made bacteria active

Question 6

Erwin Chargaff

Answer 6

1.reported that DNA composition of bases (A,T,C,G) varies from one species to the next
^ this evidence of diversity made DNA a more credible candidate for genetic material
2. Chargaff also showed that %of A always = % of T and % of G always = %of C
3. purines always with pyrimidines

Question 7

DNA structure

Answer 7

polymer of nucleotides with nitrogenous base, a sugar, and a phosphate group
two antiparralel sugar-phosphate backbones, with the nitrogenous bases paired in the molecule’s interior

Question 8

how was a picture of the DNA molecule produced

Answer 8

wilkins and franklin used X-ray crystallography
a beam of x-rays strike a crystal and cause the beam of light to spread into many specific directions

Question 9

what did watson deduce from franklin’s images of dna

Answer 9

that dna was helical
and deduced the width of the helix and the spacing of nitrogenous bases
width suggested that DNA molecule was made up of two strands forming a double helix

Question 10

two purines

Answer 10

two rings
adenine and guanine

Question 11

two pyrimidines plus one

Answer 11

1 ring
thymine and cytosine
uracil

Question 12

dna characteristics

Answer 12

sequence of bases in a nucleotide strand is different from species to species
length of a strand of DNA (number of base pairs) is different from species to species
more complex organisms generally have greater #’s of base pairs

Question 13

how does DNA’s structure contribute to its function

Answer 13

antiparralel arrangement of two strands ensures that the bases are oriented properly, so they can interact/bond
each nucleotide has a phosphate group at the 5’ position of the sugar

Question 14

how are nucleotides joined

Answer 14

by linking 5’’ phsphate to 3’ position
DNA is always made in the 5’ to 3’ direction
you only add to 3’ end

Question 15

DNA replication how it can occur

Answer 15

since the two strands of DNA are complementary, each strand acts as a template for building a new strand in replication
in dna replication, the parent molecule unwinds, and two new daughter strands are built based on base-pairing rules

Question 16

DNA replication step by step

Answer 16

the parent moleculle has two comp. strands
first step is separation of two DNA strands (breaking hydrogen bonding between base pairs)
now, each parental strand serves as a template that determines the order of nucloetides along a new, complementary strand
the nucleotides are connected to form sugar-phosphate back-bones of the new strands
each daughter cell consissts of one parental strand and one new strand

Question 17

what does watson and crick’s semioconservative model of replication predict

Answer 17

when a double helix replicates, each daughter molecule will have one old strand and one newly made strand

Question 18

conservative model off replication

Answer 18

two parental strands reassociate after acting as templates for new strands, thus restoring the parental double helix

Question 19

dispersive model of replication

Answer 19

each strand of both daughter molecules contains a mixture of old and newly synthesized DNA

Question 20

replication bubble

Answer 20

replication begins at special sites called origins or replication, where the two DNA strands are separated, opening up a replication “bubble” –o–

Question 21

replication fork

Answer 21

at the end of each replication bubble is a replication fork
a y-shaped res=gion where new dna strands are elongating

Question 22

DNA polymerase

Answer 22

catalyzes the elongation of new DNA at a replication fork
adds nucleotides only to the free 3’ end of a graowing strand (5’ –> 3’)
only adds next ucleotid to the OH- group at the end of the growing strand and releases 2 phosphates

Question 23

leading strand

Answer 23

new strand
3’ template strand
DNA polymerase can synthesize a complementary strand continuously, moving towrd the replication fork

Question 24

lagging strand

Answer 24

nucleotide added in 5’ to 3’ in small sections
must be made in overall 3’to 5’ direction, dna polymerase works in direction away from replication fork
series of okazaki fragments joined together by DNA ligase and added in direction toward replication fork

Question 25

dna ligase

Answer 25

joins okazaki fragments by forming a bond between their free ends

Question 26

primer

Answer 26

DNA polymerase can’t synthesis segments without an initial nucleotide strand called a primer
primer = made of RNA with available 3’ end

Question 27

how many primers per strand

Answer 27

one primer for leading strand
a primer for each okazaki strand –> primed separately

Question 28

priming DNA and forming lagging strand steps

Answer 28

primase joins rna nucleotides into a primer
DNA polymerase III adds DNA nucleotides to the primer, forming Okazaki fragments
after reaching the next RNA primer, DNA pol III falls off
after second fragment is primed, DNA pol III adds DNA nucleotides until it reaches the first primer and falls off
DNA pol 1 replaces the RNA with DNA, adding to the 3’ end of fragment 2
DNA ligase forms a bond between the newest DNA and the adjacent DNA of fragment 1

Question 29

helicase

Answer 29

unwinds parental double helix at replication forks

Question 30

topoisomerase

Answer 30

corrects overwinding ahead of replication forks by breaking, swiveling, and rejoining DNA strands

Question 31

primase

Answer 31

synthesizes a single RNA primer at the 5’ end of the leading strand and/or each okazaki fragment

Question 32

DNA pol III

Answer 32

continuously synthesizes the leading strand, adding on the primer

elongates each okazaki fragment

Question 33

DNA pol I

Answer 33

removes primer from the 5’ end of leading strand and replaces it with DNA, adding on the adjacent 3’ end

removes the primer from 5’ end and replaces it with DNA

Question 34

DNA ligase

Answer 34

joins the 3’ end of the DNA that replaces the primer to the rest of the leading strand

joins okazaki fragments

Question 35

proofreading and repairing dna

Answer 35

dna polymerase proofreads newly made DNA, replacing any incorrect nucleotides
in mismatch repair of DNA, enzymes correct errors in base pairing
in nucleotide excision, repair enzymes cut out and replace damaged stretches of DNA

Question 36

limitations of dna polymerase and its complications

Answer 36

the usual replication machinery provides no way to complete the 5’ ends so repeated rounds of replication produce shorter DNA molecules

Question 37

telomeres

Answer 37

at the ends of nucleotide sequences
they postpone the erosion of genes near the end of DNA molecules
contain non-coding sequences

Question 38

telomerase

Answer 38

enzyme that catalyzes the lengthening of telomeres in germ cells, so that essential genes wouldn’t be cut off and missing in gametes due to non-coding regions