HW 05 - Cell Cycle

It is bound to the origin of replication only during replication In eukaryotes, the initiator is a protein complex called the origin recognition complex (ORC) which has 6 essential subunits. ORC's appear to remain attached to origins even when replication is not initiated. Additional regulatory signal are needed to initiate replication

All of the following are TRUE regarding the origin recognition complex (ORC) EXCEPT: A) It binds to origin recognition sequences B) It is bound to the origin of replication only during replication C) It is found only in eukaryotes D) It is a complex of six proteins

Stimulates protease activity in SOS response An SOS response in E. coli describes the coordinate induction of many enzymes. including repair activities, in response to irradiation or other damage to DNA. It results from activation of protease activity by RecA to cleave LexA repressor

Which of the following is an activity of the RecA protein? A) Recognition of Holliday structure results in cleavage at chi site B) Mediates unwinding of duplex at chi site C) Stimulates protease activity in SOS response D) Promotes excision repair

It is continuously active throughout the cell cycle The APC becomes activated in mid to late M phase

Which of the following statements about the anaphase-promoting complex (APC) is FALSE? A) It is continuously active throughout the cell cycle B) It promotes the degradation of proteins that regulate M phase C) It inhibits M-Cdk activity D) M-Cdk stimulates its activity

Once a cell decides to enter the cell cycle, the time from start to finish is the same in all eukaryotic cells Variations occur in the cell cycle between different cell types. Not only can the length of the cell cycle phases differ, but in certain cell types some cell cycle phases may be absent

Which of the following statements about the cell cycle is FALSE? A) Once a cell decides to enter the cell cycle, the time from start to finish is the same in all eukaryotic cells B) An unfavorable environment can cause cells to arrest in G1 C) A cell has more DNA during G2 than it did in G1 D) The cleavage divisions that occur in an early embryo have short G1 and G2 phases

The highly conserved alpha helices of the cyclin box bind to the PSTAIRE motif of CdK and the kinase adopts the active conformation The structurally conserved 100 amino acid cyclin box consists of five alpha helices which bind to a highly conserved PSTAIRE motif in the Cdk. Upon binding of cyclin, structural changes in the kinase result in active conformation

How is the active conformation of the Cyclin-dependent Kinase (CdK) formed? A) The CdK is always in the active conformation and cyclin binds the substrate and delivers it to the kinase B) The highly conserved alpha helices of the cyclin box bind to the PSTAIRE motif of CdK and the kinase adopts the active conformation C) The highly conserved alpha helices of the cyclin box bind to the PSTAIRE motif of CdK and the cyclin adopts the active conformation D) The highly conserved beta sheets of the cyclin box bind to the PSTAIRE motif of CdK and the kinase adopts the active conformation

S phase In eukaryotes, replication of the DNA is confined to the S phase of the cell cycle. Only some of the replicons are engaged in replication at any point in S phase. Each origin initiates once and only once

In eukaryotic cells, DNA replication occurs during: A) S phase B) G1 phase C) Metaphase D) Anaphase

Occurs when DnaA-ATP binds hemimethylted oriC DnaA-ATP binds fully methylated oriC. DnaA-ADP is inactive. SeqA bound to hemimethylated DNA inhibits reinitiation from recently replicated daughter origins

Initiation at oriC A) Is regulated by DnaA-ATP levels and SeqA B) Occurs when DnaA-ATP binds hemimethylated oriC C) Is temporarily regulated and occurs once per cell cycle, similar to eukaryotes D) Occurs when SeqA binds hemimethylated oriC

Cdk degradation precedes entry into the next phase of the cell cycle The cyclins are degraded in a cell-cycle-dependent fashion, and they are required for Cdk activity

Levels of Cdk activity change during the cell cycle, in part, because__________. A) The Cdks activate the cyclins B) Cyclin levels change during the cell cycle C) Cdk degradation precedes entry into the next phase of the cell cycle D) The Cdks phosphorylate each other

Falls toward the end of M phase as a result of ubiquitylation and degradation The concentration of mitotic cyclin rises gradually during G2 an dis ubiquitylated and degraded during late M phase

The concentration of mitotic cyclin (M cyclin) __________. A) Rises markedly during M phase B) Is highest in G1 phase C) Is activated by phosphorylation D) Falls toward the end of M phase as a result of ubiquitylaiton and degradation

The nuclear envelope breaks down Interphase refers to the stages (G1, S, G2) of teh cell cycle between cell divisions (M phase). During interphase chromatin, is in a less condensed state

Which of the following events does not usually occur during interphase? A) The centrosomes are duplicates B) The nuclear envelope breaks down C) DNA is replicated D) Cells grow in size

Cyclin dependent kinases cdc28, cdc2, and CDC2Hs were the first cyclin dependent kinases identified in cerevisiae, Spombe and humans, respectively. Each protein can also be called CdK1

The products of the Sp cdc2, CDC2Hs, and Sc cdc28 genes are A) p53 proteins B) Cyclins C) Cyclin dependent kinases D) Cyclin kinase inhibitors (CKIs)

Yeast cells have only one Cdk, whereas humans have many Cdks Although it is true that yeast cells have one Cdk and human cells have many, this statement does not provide any evidence for the conservation of function across evolutionary time

Which of the following is NOT good direct evidence that the cell-cycle control system is conserved through billions of years of divergent evolution? A) Yeast cells have only one Cdk, whereas humans have many Cdks B) The amino acid sequences of cyclins in plants are similar to the amino acid sequences of cylcins in humans C) A yeast cell lacking Cdk function can use the human Cdk to substitute for its missing Cdk during the cell cycle D) The Cdk proteins in humans share conserved phosphorylation sites with the Cdk proteins in yeast

It describes the use of site-specific recombination in RecA response to damage to DNA in E. coli RecA can be activated by many treatments that damage DNA or inhibit replication in E. coli. This causes it to trigger a complex series of phenotypic changes called the SOS response, which involves the expression of many genes whose products include repair functions

What is the SOS response, and where is it found? A) It describes the cleaving of DNA repair enzymes in eukaryotes B) It describes the use of site-specific recombination in RecA response to damage to DNA in E. coli C) It describes the coordination of many enzymes in response to damage to DNA in E. coli D) It describes the major repair system in eukayrotic cells

The cells produced would get smaller and smaller G1 is the phase during which cell growth occurs. S is the phase when DNA synthesis occurs. G2 is a period of growth and preparatin for mitosis. M includes both mitosis and cytokinesis

What would be the most obvious outcome of repeated cell cycles consisting of S phase and M phase only? A) The cells produced would get smaller and smaller B) Cells would get larger and larger C) The mitotic spindle could not assemble D) Cells would not be able to replicate their DNA

The cell would enter M phase under conditions when normal cells would not Normal cells arrest at the G2 checkpoint if DNA replication is incomplete or DNA is damaged. Cells without this mechanism may enter M phase with unreplicated or damaged DNA, whereas normal cells would not.

Which of the following descriptions is consistent with the behavior of a cell that lacks a protein required for a checkpoint mechanism that operates in G2? A) The cell would be unable to enter G2 B) The cell would pass through M phase more slowly than normal cells C) The cell would enter M phase under conditions when normal cells would not D) The cell would be unable to enter M phase

Growth of the cell Cell size increases throughout interphase and not during M phase. All of the other phenomena are observed in M phase

Which of the following does not occur during M phase in animal cells? A) Breakdown of nuclear envelope B) Condensation of chromosomes C) Growth of the cell D) Attachment of chromosomes to microtubules

Inactivation of an enzyme that ubiquitylates M cyclin A cell with a mutation that prevents ubiquitylation of M cyclin could enter mitosis but could not exit mitosis properly

You have isolated a strain of mutant yeast cells that divides normally at 30 C but cannot enter M phase at 37 C. You have isolated its mitotic cyclin and mitotic Cdk and find that both proteins are produced and can form a normal M-Cdk complex at both temperatures. Which of the following temperature-sensitive mutations could NOT be responsible for the behavior of this strain of yeast? A) A decrease in the levels of a transcriptional regulator required for producing sufficient amounts of M cyclin B) Inactivation of a phosphatase that acts on the mitotic Cdk kinase C) Inactivation of a protein kinase that acts on the mitotic Cdk kinase D) Inactivation of an enzyme that ubiquitylates M cyclin