Biology › Understanding Cell Cycle Regulation
During the G1 phase of the cell cycle, in which form will Eukaryotic DNA be found?
Chromatin
Chromosomes
Plasmid
Unfolded continuous strand
Chromatid
Chromosomes and Chromatid are both incorrect because eukaryotic DNA is condensed into these tightly packed chromosomal structures during M phase of mitosis. Plasmids are not found in eukaryotes and an unfolded continuous strand of DNA would be too long to fit within a nucleus. Thus, Chromatin is the correct answer choice; chromatin is a protein-DNA complex in a loosely packed form which allows for gene transcription which is necessary during the G1 phase of the cell cycle.
During the cell cycle, there are several checkpoints to ensure proper cell growth and division. Which checkpoint ensures that each duplicated chromatid is appropriately attached to cellular machinery in order to segregate properly?
Metaphase checkpoint
G1 checkpoint
G2 checkpoint
G0 checkpoint
During mitosis, the metaphase checkpoint ensures that each duplicated chromatid is attached to the spindle apparatus. If the metaphase checkpoint is not satisfied, the cell will not enter anaphase. This checkpoint is essential for preventing aneuploidy, a condition in which there are an abnormal number of chromosomes in a cell.
The G1 checkpoint determines if the cell will enter the S phase to replicate DNA and prepare for cell division. Quiescent cells, cells that do not frequently divide, are often stopped at the G1 checkpoint for long periods. The G2 checkpoint is used to prevent the cell from entering mitosis if there were errors in the replication of DNA during the S phase. Failure to pass the G2 checkpoint can result in apoptosis. There is no G0 checkpoint.
Most cells spend the vast majority of their time in __________.
interphase
meiosis
mitosis
anaphase I
prophase
Most cells spend about 90% of their time in interphase. Note that mitosis and meiosis comprise only about 10% of the cell cycle.
There are several checkpoints during the cell cycle to ensure proper growth and division. Which checkpoint of the cell cycle is considered the "point of no return?"
G1 checkpoint
G2 checkpoint
Metaphase checkpoint
Telophase checkpoint
There is no point of no return. The cell can always go back and resume normal cell function.
Once the cell passes the G1 checkpoint, the cell becomes committed to the cell cycle and enters the S phase where DNA is replicated. The checkpoint is to ensure the cell has grown enough and has enough resources to begin DNA replication. The next checkpoint is the G2 checkpoint, where the cell checks and makes sure the DNA replicated correctly before beginning mitosis. If the cell does not pass this checkpoint, it commences apoptosis and dies.
What is the initial checkpoint in a mammalian cell cycle whose major function is to allow or disallow a cell to mitotically divide?
G1 checkpoint
G2 checkpoint
M checkpoint
G3 checkpoint
S checkpoint
The G1 Checkpoint is the correct answer, because if a cell gets a signal at this checkpoint then the cell goes on to complete the S, G2, and M phases and will end up dividing. If this signal is not received at the G1 checkpoint then the cell enters the non-dividing G0 phase.
Out of all phases in the cell cycle, most cells spend the majority of their life in __________.
Interphase
Metaphase
Anaphase
Telophase
Prophase
Cell division, or mitosis, is a rather small portion of a cell's life and includes prophase, metaphase, anaphase and telophase. The majority of a cell's life is spent in interphase.
Which of the following best describes the two primary purposes of Active S cyclin-CDK phosphorylation in the cell cycle?
The activation of each assembled pre-replication complex AND the prevention of new complexes from forming.
The activation of each assembled pre-replication complex AND targeting mitotic cyclins for degradation.
The prevention of new complexes from forming AND targeting mitotic cyclins for degradation.
The targeting of mitotic cyclins for degradation AND promoting the expression of enzymes needed for DNA replication.
The activation of each assembled pre-replication complex AND promoting the expression of enzymes needed for DNA replication.
Active S cyclin-CDK phosphorylation in the cell cycle is primarily intended to ensure that each portion of the cell's genome is copied once and only once. Daughter cells that do not copy a complete genome will likely die; however, carrying extra copies of certain genes will also negatively affect daughter cells, and phosphorylation of proteins that make up pre-replication complexes safeguards against this.