Biology - Cell Cycle

What is cell cycle?

The process of a cell growing, replicating DNA, and dividing into new cells.

Does:

• growth

• repair

• replacement

• reproduction

Cells are divided between somatic cells and gametes (sex cells).

What is Cell Division

Formation of daughter cells from a parent cell (a diploid). The daughter cells inherit the same DNA from its parent cells.

Chromosomes

What holds genetic information. Humans have 46, two sets of 23. Last chromosome is what determines the sex, XX = female, XY = male

Chromosome Formation

1. The nucleus contains chromatin (-) and a DNA histone protein complex (+). Chromatin coils around the histone proteins due to opposite charges attracting each other.

2. The DNA inside the chromatin replicates itself.

3. The chromatin with the DNA coils until a chromosome forms.

Parts of a Chromosome

Arms → Condensed chromatin fibers
Loci or segments → Contains the genes
Centromere → What attaches the sister chromatids through cohesion proteins
Kinetochore → Disk-like complex of proteins where the spindle fibers attach

Cell Cycle Interphase

The longest phase of the cell cycle.

1. G1 = Cellular growth

2. S = DNA replication

3. G2 = Integrity check, and spindle fiber formation

If the cell is senescent (deteriorating) or quiescent (dormant) then from G1 it goes to G0.

• senescent: cells are damaged, lacking organelles, or mutated. [Cells are stopped]

• quiescent: cells are dormant due to lacking nutrients. [Cells are paused to be fixed]

Cell Cycle M phase

Shortest phase of the cell cycle.

Mitosis/Meiosis (nuclear division) → Cytokinesis (cytoplasmic division)

Stages of Mitosis

1. Prophase (PREPARE)

   • Nucleus disappears. Chromosomes wrap into X shape and sister chromatids join together. Spindle forms.

1. Metaphase (MIDDLE)

   • Chromosomes line up in the middle. Cell checks if every chromosome is connected to the spindle fibers.

2. Anaphase (APART)

   • Sister chromatids separate, the spindle fibers pull each new chromosome to opposite poles of the cell.

3. Telophase (TWO)

   • With chromosomes at each opposite pole, a new nuclear envelope forms. The chromosomes uncoil.

RESULTS IN TWO OVALS (cytoplasm) THAT ARE CONNECTED WITH A NUCLEI PER OVAL.

Cytokinesis

Division of the cytoplasm in other words, COMPLETELY SEPARATING the ovals.
*for plant cells it’s rectangles or squares

After mitosis the cell has a cleavage furrow between the two cell membranes

Stages of Meiosis

Reduces a diploid cell (two sets of chromosomes) into four unique haploid gametes (sperm or egg cells with one set of chromosomes).

MEIOSIS 1 - Reduction division

1. Prophase

   • Chromosomes coil and pair up, here the genes cross over creating variety (called Chiasmata). The nuclear envelope breaks down.

2. Metaphase

   • The chromosomes line up in the middle.

3. Anaphase

   • The pairs are pulled apart to opposite poles. SISTER CHROMATIDS STAY ATTACHED.

4. Telophase

   • Nuclear membranes reform and the cell splits into two haploid daughter cells, each with a duped sister chromatid.

   • results in daughter cells

   • Then cytokinesis

MEIOSIS 2 (this time sister chromatids are separated) - Equational division

1. Prophase II

   • Chromosomes coil again in both cells. This time NO CROSSING OVER.

2. Metaphase II

   • Chromosomes line up in the middle.

3. Anaphase II

   • Sister chromatids are separated and pulled towards opposite poles

4. Telophase II

   • Nuclear envelope reforms and the cells divide.

   • results in granddaughter cells.

(STARTS WITH FOUR, or TWO pairs. because crossing over genetics shi → go middle → now some go left and some go right, and they’re lowkey like three now but sister chromatids are still together. cell separates into Daughter Uno and Daughter Dos

PART TWO. NO crossing over → go middle → sister chromatids separate, some go left some go right → cell separation, Daughter Uno has her own daughter, Daughter Dos has her own daughter, making FOUR IN TOTAL)