OSU Bio 1113 Chapter 15

Chargaff's rules

1) base composition of DNA varies between species 2) in any given species, the number of A and T bases are equal and the number of G and C bases are equal

Hershey-Chase Experiment

1: proteins labeled with radioactive sulfur, phage insert genetic material and centrifuged, and examine and saw radioactive sulfur in liquid not pellet 2: DNA labeled with radioactive phosphorus, phage insert genetic material and centrifuged, and examine and saw radioactive phosphorus in pellet conclusion: DNA functions as phage genetic material

Suppose you are provided with an actively dividing culture of E. coli bacteria to which radioactive thymine has been added. What would happen if a cell replicates once in the presence of this radioactive base? A) DNA in both daughter cells would be radioactive. B)One of the daughter cells, but not the other, would have radioactive DNA. C) Radioactive thymine would pair with nonradioactive guanine. D) Neither of the two daughter cells would be radioactive. E) All four bases of the DNA would be radioactive.

A

DNA polymerase cannot replicate DNA unless an RNA primer is first attached to the template strand. This is because DNA polymerase can only... A- add onto existing 3′ hydroxyl groups B- replicate in a 5′ → 3′ direction C- replicate the leading strand D- add onto ribonucleotides

A- add onto existing 3′ hydroxyl groups

Suppose you are provided with an actively dividing culture of E. coli bacteria to which radioactive thymine has been added. What would happen if a cell replicates once in the presence of this radioactive base? A) one high-density and one low-density band B) one high-density and one intermediate-density band C) one low-density and one intermediate-density band D) one intermediate-density band E) one low-density band

C

The telomerase enzyme is able to lengthen the ends of linear chromosomes. Why is this important for cells? A- because more DNA is always better B- because telomere sequences mutate frequently during replication C- because telomeres shorten a little during replication D- because important genes located in the telomere need to be maintained

C- because telomeres shorten a little during replication

The basis of Meselson and Stahl's experiment demonstrating semiconservative replication of DNA was... A-the ability of bacteria to grow in the presence of different nitrogen isotopes for two generations B-the length of time it took 15N labeled bacteria to divide in the presence of 14N C-the conversion of 15N labeled DNA into half-labeled and unlabeled DNA when the bacteria were grown in the presence of 14N for two generations D-the ability of the bacteria to increase their tolerance to 14N after being acclimated to growth in 15N

C-the conversion of 15N labeled DNA into half-labeled and unlabeled DNA when the bacteria were grown in the presence of 14N for two generations

Which of the enzymes removes the RNA nucleotides of the primer and adds equivalent DNA nucleotides to the 3' end of Okazaki fragments? A- helicase B- DNA polymerase III C- ligase D- DNA polymerase I E- primase

D- DNA polymerase I

Which enzyme is incorrectly paired with its function? A- DNA polymerase III—synthesizes the leading strand B- DNA ligase—joins Okazaki fragments C- DNA helicase—unwinds DNA D- primase—corrects replication mistakes

D- primase—corrects replication mistakes

Frederick Griffith Experiment

S cells: pathogenic R cells: harmless dead s cells could still transform the harmless r cells to make living s cells

direction of DNA synthesis

always proceeds 5' to 3'

single-strand binding protein (SSB)

binds to and stabilizes single-stranded DNA

Pol III

can proofread/back up if mess up due to 3' to 5' exonuclease activity; specialized for bulk DNA replication at fork; rapid replication rate; complex with 10 different polypeptides and two polymerase cores that allows leading and lagging strand synthesis to occur at the same time

Meselson-Stahl Experiment

cultured bacteria in 15N (heavier) and 14N (lighter) isotopes and centrifuged so that they would separated based on density. after two generations this produced 1/2 of the DNA being at a low-density reading and 1/2 being at an intermediate reading, proving the semiconservative hypothesis

dispersive model

each strand is a nearly equal mix of old and new

telomerase

enzyme composed of protein and RNA; telomerase reverse transcriptase (TERT)- can make DNA complementary to an RNA template; lengthens the 3' end of a DNA strand; telomerase RNA component (TERC)

topoisomerase

enzyme that corrects (relaxes) "overwinding" ahead of replication forks by breaking, swiveling, and rejoining DNA strands

helicase

enzyme that disrupt hydrogen binds between complimentary bases and unwind the double helix at the replication forks

primase

enzyme that synthesizes an RNA primer

DNA polymerases

enzymes that add new nucleotides to a pre-existing chain (called a primer) according to a template

antiparallel elongation

leading strand: synthesized continuously and moves in the same direction as the replication fork lagging strand: synthesized discontinuously and moves in the direction opposite the replication fork because still has to be 5' to 3'

origins of replication

particular sites at which replication of DNA begins; starts by the two DNA strands being separated and opening up a replication "bubble"

primary structure of DNA

polymer; sugar phosphate backbone (polyanion); nitrogenous bases; phosphodiester bonds attach phosphates of one nucleotide to next

semiconservative model

predicts that when a double helix replicates, each daughter molecule will have one old strand (from the parent molecule) and one newly made strand

Pol I

specialized for okazaki fragment processing and DNA repair; relatively slow rate of synthesis; single polypeptide; 3 enzyme activities: 1) DNA polymerase activity 2) 5' to 3' exonuclease activity (allows to remove RNA primer and replace with DNA) 3) 3' to 5' exonuclease activity (allows to proofread)

"overwinding"

stress on winded parts of DNA strand caused by replication of lagging strand

lagging strand synthesis

synthesized in parts: okazaki fragments and then joined by DNA ligases

DNA v Protein as candidates for genetic material

system developed by Griffith, Avery, McCarty, and MacLeod determined DNA to be transforming agent. did this by extracting s cells and exposing to either enzymes that degrade DNA or proteins/RNA and when the one that degrades DNA produced the harmless, nonactive celss this was a sign that DNA was the carrier of genetic material

conservative model

two parent strands rejoin