Apoptosis and Cell Cycle Quiz

The cell cycle control system is a network of proteins that regulates the progression of the cell cycle, ensuring that events occur in the correct order and that the cell only divides when necessary.

The G1/S checkpoint, also known as the restriction point, is a critical control point that determines whether a cell commits to DNA replication and enters the S phase.

The G2/M checkpoint ensures that the cell has successfully replicated its DNA and is ready for mitosis.

The metaphase to anaphase transition checkpoint ensures that all chromosomes are properly aligned on the mitotic spindle before sister chromatids separate and the cell divides.

Cyclin-dependent kinases (CDKs) are a family of protein kinases that are activated by cyclin proteins. CDKs play a crucial role in the regulation of the cell cycle.

Cyclins are a family of proteins that bind to and activate CDKs, leading to the phosphorylation of specific target proteins.

The anaphase-promoting complex/cyclosome (APC/C) is a ubiquitin ligase that targets specific proteins for degradation. It plays a critical role in the metaphase to anaphase transition.

Protein phosphatases are enzymes that remove phosphate groups from proteins, counteracting the effects of kinases and regulating the cell cycle.

A complex of a cyclin protein and a cyclin-dependent kinase (CDK), essential for the control of cell cycle progression. Different cyclin-CDK complexes are activated at specific stages of the cell cycle.

A key regulatory protein in the cell cycle, activated in late M phase. Its activation leads to the inactivation of other cyclin-CDK complexes, preparing the cell for a new cycle.

A checkpoint that ensures the alignment of chromosomes at the metaphase plate before moving to anaphase. It monitors spindle assembly and the integrity of the mitotic apparatus.

A family of proteins that function as molecular glue, holding sister chromatids together during DNA replication.

A protein kinase that plays a crucial role in the activation of the M-CDK complex. Its inactivation is necessary for the transition from G2 phase to M phase.

A cyclin-dependent kinase (CDK) that plays a key role in the initiation of DNA replication during the S phase. It helps activate the necessary proteins and enzymes for DNA replication.

A protein phosphatase that removes inhibitory phosphates from Wee1 and Cdc25. It plays a role in the activation of the M-CDK complex.

An inactive state of CDK activity, typically observed during the G1 phase. It represents a resting state where the cell is monitoring its environment before committing to a new cell cycle.

The length of kinetochore microtubules remains relatively constant during this process because new tubulin subunits are added at the plus end at the same rate as they are removed from the minus end. This dynamic equilibrium allows the microtubule to act as a pulling force, drawing the chromosome towards the spindle pole.

A protein complex known as the Anaphase-Promoting Complex or Cyclosome (APC/C) is responsible for initiating sister chromatid separation, marking the transition from metaphase to anaphase. It triggers a cascade of events that ultimately lead to the completion of mitosis.

The destruction of securin by APC/C activates separase, an enzyme that cleaves cohesin, the protein complex holding sister chromatids together. This allows the forces of the mitotic spindle to pull the sister chromatids apart.

As chromosomes are segregated, the contractile ring, composed of actin and myosin II, constricts, dividing the cytoplasm and eventually pinching off the two daughter cells. This is the critical step that completes cell division.

The plane of cell division in animal cells is determined by the orientation of the microtubules in the mitotic spindle. This ensures that organelles and other cellular components are distributed evenly between the two daughter cells.

In higher plants, the phragmoplast, a structure formed by microtubules, guides the formation of the cell wall, which ultimately divides the cell into two daughter cells.

In certain cell types, the spindle can be repositioned, leading to an unequal distribution of cellular components between the two daughter cells. This process is known as asymmetric division and is essential for development and tissue specialization.

A protein family that regulates apoptosis. Pro-apoptotic members promote cell death, while anti-apoptotic members inhibit cell death.

A mitochondrial protein that, when released into the cytosol, triggers the activation of caspases and apoptosis.

The process by which the outer mitochondrial membrane becomes permeable, allowing the release of cytochrome c and other apoptotic factors.

A pro-apoptotic Bcl-2 family protein that forms oligomers in the outer mitochondrial membrane, leading to MOMP.

An anti-apoptotic Bcl-2 family protein that binds to Bak and inhibits its oligomerization, preventing MOMP.

Pro-apoptotic proteins that can indirectly trigger MOMP by inhibiting anti-apoptotic Bcl-2 family proteins.

A protein complex formed by Apaf1, caspase-9, and cytochrome c, which initiates the caspase cascade during apoptosis.

A family of cysteine proteases that play a central role in apoptosis by cleaving and activating other proteins.

Apoptosis is a programmed cell death process that eliminates unwanted or damaged cells in a controlled and organized manner.

Caspases are a family of proteases (enzymes that break down proteins) that play a central role in apoptosis. These enzymes are cysteine proteases, meaning they have a cysteine residue in their active site. Caspases cleave their target proteins after an aspartate residue.

Initiator caspases are activated first in the apoptotic pathway. They then activate executioner caspases, which then cleave a variety of cellular proteins, leading to the cell's death.

Executioner caspases are activated by initiator caspases and are responsible for the breakdown of cellular components during apoptosis. They are responsible for the controlled dismantling of the cell.

The extrinsic pathway of apoptosis is triggered from outside the cell. It is initiated by the activation of cell surface death receptors, such as Fas, by their respective ligands.

The intrinsic pathway of apoptosis originates inside the cell. It is triggered by internal stress signals, often related to cellular damage or dysfunction. These signals can lead to the release of proteins from the mitochondria, such as cytochrome c, which initiates the apoptotic cascade.

Bcl-2 proteins are a family of proteins that regulate the intrinsic pathway of apoptosis. They act as gatekeepers of mitochondrial membrane permeability, controlling the release of apoptosis-inducing molecules. Some Bcl-2 proteins promote apoptosis (e.g., Bax, Bak), while others inhibit it (e.g., Bcl-2, Bcl-XL).

IAP (Inhibitor of Apoptosis Proteins) are a family of proteins that can inhibit the activity of caspase proteins. They act as negative regulators of apoptosis, preventing unwanted cell death. However, they can be inactivated or disrupted by other proteins like Smac.

IAPs (Inhibitors of Apoptosis Proteins) are a family of proteins that prevent apoptosis by inhibiting caspase activity. They act as a brake to ensure cells only die when it's needed.

Survival factors counteract the apoptotic signals by activating pathways that promote cell survival. They inhibit the pro-apoptotic proteins and can activate anti-apoptotic proteins to keep the cell alive.

One way survival factors inhibit apoptosis is by promoting the transcription of genes that encode anti-apoptotic proteins, like Bcl-2. These proteins inhibit the activation of caspases, preventing cell death.

Survival factors also activate the Akt kinase, which phosphorylates and inactivates Bad, a pro-apoptotic protein. This frees up Bcl-2 to prevent apoptosis.

During apoptosis, cells display 'eat me' signals on their surface, like phosphatidylserine. These signals indicate to neighboring phagocytes that the cell is meant to be engulfed and removed.

Phosphatidylserine is a phospholipid usually found on the inner leaflet of the plasma membrane. When apoptosis occurs, flippase is deactivated, and scramblase is activated, causing it to flip to the outer leaflet where it acts as a signal for phagocytosis.