Quiz #8

Question 1

What is cell cycle control?

Answer 1

regulating cell division

eukaryotic cells have ways to coordinate and regulate division rates and timing

progression through cell cycle is uni-directional (forward only)

checkpoints prevent going forward unless it is safe to do so

in many cells, G1 checkpoint seems most important

Question 2

What is the G1/S checkpoint?

Answer 2

is there a signal to divide? (external signal)

is the cell large enough? (internal signal)

are there enough nutrients/energy reserves? (internal signal)

if yes to all, then cell proceeds to S phase

if cell receives go-ahead signal at G1, it usually completes S, G2, and M phases and divides

Question 3

What is the G2/M checkpoint?

Answer 3

is DNA replication complete?

is the new DNA free of errors?

if yes, then cell proceeds to M phase

Question 4

What is the mitotic (spindle assembly) checkpoint?

Answer 4

re all kinetochores attached to the ends of microtubules?

Question 5

What are some problems that can occur when attaching chromosomes to microtubules?

Answer 5

both kinetochores are attached, or only one kinetochore is attached

these conditions prevent entry into anaphase, the cell will keep trying to make proper microtubule-kinetochore connections until both sister chromatids are attached to opposite poles

specific proteins at the kinetochore sense if a microtubule is attached, if not a signal deactivates the APC (this prevents destruction of proteins like securin, and prevent anaphase)

Question 6

What is cancer?

Answer 6

uncontrolled cell division

the signals controlling cell division are lost or ignored

caused by accumulation of mutations (changes to specific nucleotides of the DNA)

genes required for a checkpoint process stop working, cell divides even though chromosomes are not properly attached

cell divides without proper signals, cell ignores signals that normally prevent cell division

Question 7

How did we discover that DNA was the main agent of heritable traits?

Answer 7

because DNA contained only 4 different deoxyribonucleotides, DNA was initially thought to be too simple to be responsible for the complexities of life on earth

instead proteins were initially considered a good candidate

Question 8

Who was Fredrick Griffith?

Answer 8

was studying Streptococcus pneumoniae, a bacteria that causes pneumonia

Strain S: causes disease and has a capsule
Strain R: does not cause disease and does not have a capsule

When injecting a mouse with dead S cells and live R cells, the mouse died, in the blood of this mouse living S cells that could reproduce were found

he called this phenomenon transformation

Question 9

What is a growth factor receptor?

Answer 9

if cell does not receive a growth signal it can enter a non-dividing state called G0 phase

Question 10

What is the phenomenon of transformation?

Answer 10

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

Question 11

Who was Oswald Avery?

Answer 11

came to the conclusion that DNA is causing the transformation that was seen through Griffith’s experiments

Question 12

How does transformation work?

Answer 12

isolate S strain DNA (fragmented)

incubate S strain DNA fragments with R cells

different DNA fragments taken up by different R cells (transformation)

a few R cells that took up S cell DNA became disease-causing S cells

the “transformed” cells also passed their “capsule” trait to next generation

thus it was found that DNA carries genetic info

Question 13

What was the Hershey and Chase phage-in-a-blender experiment?

Answer 13

studying the virus that infects E. coli

viruses that infect bacteria are called bacteriophages

phage infection transforms bacteria into phage factories where the bacterial cell is hijacked to create more and more phage

they showed that DNA is the transforming principle for a non-cellular life form, therefore, they showed the universality of DNA as the transforming principle

Question 14

Who was Erwin Chargaff?

Answer 14

the prevailing theory at the time was that DNA consisted of simple repeats of the bases GACT in all organisms

the work of Erwin Chargaff began to disprove this idea

he carefully measured the amount of each of the four bases of DNA (a, C, G, and T) in different organisms

Question 15

What were Chargaff’s Rules?

Answer 15

1. The amount of the different bases in DNA is consistent for any one species but different for different species
2. In any given species: the amount of base A equals the amount of base T, and the amount of base C equals the amount of base G

Question 16

Who was Rosalind Franklin?

Answer 16

Used X ray diffraction to show:
DNA was helical
probably double-stranded
bases were on the inside, sugar phosphate backbone on the outside
distance between two strands was uniform

Question 17

Who were Watson and Crick?

Answer 17

using published and unpublished data from many sources, Watson and Crick came up with a physical model that satisfied all of the information known about DNA

Question 18

How do the two strands of DNA fit together?

Answer 18

at first Watson and Crick thought the bases paired with like bases, but such pairings did not result in uniform width

purine + pyrimidine: width consistent with X ray data

bases pair by hydrogen bonding

Watson built a model with backbones running antiparallel (subunits run in opposite directions)

DNA is a right-handed helix

Question 19

How does DNA replicate according to Watson and Crick?

Answer 19

the parent molecule has two complementary strands

two strands separate

complementary nucleotides insert and pair with parent strand bases, forming 2 new double-stranded molecules

Question 20

What were the three models of DNA replication?

Answer 20

1. Conservative: two parental strands unchanged after serving as templates for new strands
2. Dispersive: parent strands are fragmented, making it easier to separate the strands, the new molecules consists of pieces of parental DNA and new DNA assembled as a mosaic
3. Semi-conservative (Watson and Crick): two parental strands separate and serve as templates for new strands