Ch 3.5 Cell Growth & Divisi`on

Cell Cycle

• The cell cycle is the ordered sequence of events that a cell undergoes to grow and divide. It is composed of two major phases: interphase and the mitotic phase.

What is Interphase?

• the period of growth and DNA replication, accounting for approximately 90% of the cell cycle). Interphase is subdivided into three stages:

  • G1 phase, S phase, and G2 phase.

What is G1 Phase?

• the first stage of interphase where the cell grows, carries out normal metabolic processes, and prepares for DNA replication.

What is S Phase (Synthesis)

• DNA replication occurs. Each chromosome is duplicated, resulting in two identical sister chromatids attached at the centromere. Histone synthesis also occurs.

What is G2 Phase?

• the final stage of interphase where the cell continues to grow, produces proteins, and organelles required for cell division, and checks for DNA errors before mitosis.

What is M Phase ?

• the phase of the cell cycle where mitosis and cytokinesis occur, resulting in the division of the parent cell into two daughter cells.

4 main stages of M phase?

• Prophase, Metaphase, Anaphase, Telophase

What is Prophase of the M Phase?

• the first stage of mitosis where chromatin condenses into chromosomes, the nuclear envelope breaks down, and the mitotic spindle begins to form from the centromes.

What is Metaphase of the M phase?

• the second stage of mitosis in which chromosomes align at the cell's equatorial plate, ensuring proper separation during anaphase.

  • Each sister chromatid is physically attached to spindle microtubules from opposite poles.

What is Anaphase of the M Phase?

• the third stage of mitosis where sister chromatids are pulled apart towards opposite poles of the cell, ensuring that each new daughter cell will receive an identical set of chromosomes.

  • Each chromatid is considered a full chromosome now

What is Telophase of the M phase?

• the final stage of mitosis where chromosomes begin to de-condense back into chromatin, the nuclear envelope re-forms around each set of chromosomes, and the mitotic spindle disassembles.

What is Cytokinesis?

• The division of the cytoplasm, which usually overlaps with telophase. It results in the formation of two separate daughter cells.

  • In animal cells, a cleavage furrow (formed by a contractile ring of actin and myosin filaments) deepens to pinch the cell in two.

What is the G1 checkpoint?

• The first checkpoint in the cell cycle, occurring at the end of G1 phase, which assesses the cell's size, DNA integrity, and nutrient availability to ensure the conditions are favorable for DNA synthesis.

What is the G2 Checkpoint?

• The second checkpoint in the cell cycle, occurring at the end of G2 phase, that checks for DNA damage, ensures all DNA is replicated, and assesses the cell's size and resources before proceeding to mitosis.

What is the M checkpoint?

• The checkpoint in the cell cycle that occurs during metaphase, ensuring that all chromosomes are properly aligned at the metaphase plate before the cell proceeds to anaphase.

What are the key regulators of the cell cycle?

Proteins such as cyclins and cyclin-dependent kinases (CDKs) that control the progression of the cell cycle by activating or deactivating specific target proteins.

What are CDKs?

Cyclin-dependent kinases (CDKs) are a family of protein kinases that, when activated by binding to cyclins, regulate various stages of the cell cycle by phosphorylating target proteins.

What are Cyclins?

• Proteins whose concentrations fluctuate rhythmically throughout the cell cycle. They bind to and activate CDKs, allowing them to phosphorylate target proteins, which then drive the cell cycle forward.

What is loss of control?

Loss of control refers to a situation in which regulatory mechanisms of the cell cycle fail, leading to unregulated cell division and potential tumor formation.

What are Proto-oncogenes?

• Normal genes that promote cell growth and division. Mutations can convert them into oncogenes, which are cancer-causing genes that lead to excessive cell proliferation.