Quiz #8 Flashcards
What is cell cycle control?
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
What is the G1/S checkpoint?
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
What is the G2/M checkpoint?
is DNA replication complete?
is the new DNA free of errors?
if yes, then cell proceeds to M phase
What is the mitotic (spindle assembly) checkpoint?
re all kinetochores attached to the ends of microtubules?
What are some problems that can occur when attaching chromosomes to microtubules?
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)
What is cancer?
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
How did we discover that DNA was the main agent of heritable traits?
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
Who was Fredrick Griffith?
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
What is a growth factor receptor?
if cell does not receive a growth signal it can enter a non-dividing state called G0 phase
What is the phenomenon of transformation?
a change in genotype and phenotype due to assimilation of foreign DNA
Who was Oswald Avery?
came to the conclusion that DNA is causing the transformation that was seen through Griffith’s experiments
How does transformation work?
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
What was the Hershey and Chase phage-in-a-blender experiment?
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
Who was Erwin Chargaff?
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
What were Chargaff’s Rules?
- The amount of the different bases in DNA is consistent for any one species but different for different species
- 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
Who was Rosalind Franklin?
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
Who were Watson and Crick?
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
How do the two strands of DNA fit together?
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
How does DNA replicate according to Watson and Crick?
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
What were the three models of DNA replication?
- Conservative: two parental strands unchanged after serving as templates for new strands
- 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
- Semi-conservative (Watson and Crick): two parental strands separate and serve as templates for new strands
