Bio lecture 24 slide 6 to lecture 27
Which checkpoint checks whether there is a signal to divide, if the cell is big enough, and if there are enough nutrients?
G1/S checkpoint
Which checkpoint checks whether DNA replication is complete & if the new DNA is free of errors?
G2/M
What is checked during the mitotic checkpoint?
If all kinetochores are attached to the ends of microtubules
What problems may occur when attaching the chromosomes to microtubules?
1) Both kinetochores are not attached
2) Only one kinetochore is attached
If this happens, the cell will keep trying until all chromatids are attached to opposite poles
What happens when the proteins at the kinetochore sense if a microtubule is not attached?
A signal inactivates the APC, which prevents the destruction of proteins like securin and prevents anaphase
What is APC?
Anaphase protein complex is an enzyme which triggers the destruction (protein degradation) of securin
What causes cancer?
Accumulation of mutations because of uncontrolled cell division, which may happen if the signals controlling cell division are lost or ignored
What are the examples of conditions that may result in an uncontrolled cell division?
1) Genes required for a checkpoint process stop working (may result in division despite the chromosomes not being properly attached to the microtubules)
2) Genes required for proper response to growth factor signals stop working (which may result in division even without the proper signals)
How do inhibitory signals work in cell division?
Inhibitory signals are found in neighboring cells, which will stop a cell from dividing when in contact
Do single-stranded DNAs exist?
Yes, in some viruses, single-stranded DNA is found as the genetic material
What nitrogenous base is used in place of uracil in RNA?
Uracil
What is the role of Mg+++ ions in DNA replication?
Cofactor in enzyme function
What enzyme can catalyze DNA synthesis from deoxyribonucleotides and who identified it?
DNA polymerase, identified by Arthur Kornberg
Mention all existing deoxyribonucleotides/dNTPs (deoxynucleoside triphosphates)
dATP (deoxyadenosine triphosphate), dGTP (deoxyguanosine triphosphate), dCTP (deoxycytidine triphosphate), dTTP (deoxythymidine triphosphate)
What acts as a primer for DNA synthesis?
A free 3-OH' end (in the correct position)
How is a new DNA polymer formed?
By adding monomer nucleotides to the 3'-OH end via a dehydration reaction
What enzyme catalyzes the formation of phosphodiester bonds?
DNA polymerase III
Why was the R strain of pneumonia mixed with the S strain able to kill the mouse?
The R strain underwent transformation, which is a change in genotype and phenotype due to assimilation of foreign DNA
What is a phosphodiester bond in DNA?
Ester bonds that form between sugar and phosphate to form the backbone of nucleic acids
Is a loss of phosphates an exergonic or endergonic reaction?
Exergonic, powers the polymerization
Can DNA polymerase initiate synthesis of a polynucleotide?
No, it can only add nucleotides to an existing polymer free 3'-OH
What is used as reactants in DNA replication?
dNTPs (deoxynucleoside triphosphates)
Which enzyme unwinds the DNA helix at the origins of replication?
Helicase
What is the function of topoisomerase in DNA replication?
It relieves the strain due to twisting caused by helicase by cutting one strand, letting the DNA unwind by one turn, and then mending the cut
What does the single-strand binding proteins do in DNA replication?
Preventing the DNA single strands from reattaching and can easily be displaced by DNA polymerase
What is the function of the DNA clamp in the elongation process?
It keeps the DNA polymerase on the template
What does the RNA primase enzyme do in DNA replication?
It makes a primer (5-10 nucleotides long) out of RNA to indicate the starting point of DNA polymerase
Does RNA primase require a 3'-OH?
No
In which direction does DNA polymerase III synthesizes the new DNA?
5'-3'
What is the function of DNA polymerase I?
It removes the RNA one nucleotide at a time from the 5' end replaces it with DNA (adding to the 3' end of the adjacent DNA)
Can DNA polymerase join an existing 3' to 5' end?
No
What enzyme joins the gap between the 3' and 5' end in a lagging strand?
DNA ligase
How many leading and lagging strand will be available at each replication bubble?
2 leading and 2 lagging strands