cell cycle and karyotypes

Why do cells divide?

For reproduction, growth, regeneration, wound healing, tissue repair, and embryogenesis.

Four major events of cell division

1. Cell division signals, 2. DNA replication, 3. DNA segregation, 4. Cytokinesis.

Prokaryotic cell division

Binary fission, assisted by the FtsZ protein.

Bacterial chromosome replication

Starts at the origin (Ori), proceeds bidirectionally, and ends at the termination sequence (Ter).

Prokaryotic cytokinesis

Septation where a furrow appears and FtsZ forms a Z-ring to pinch the membrane.

Interphase components

Consists of G1, S, and G2 phases; period of preparation for mitosis.

G1 phase

Period of cell growth, regular functioning, organelle production, and unreplicated chromosomes.

S phase

Phase where DNA replication occurs, forming sister chromatids attached at centromeres.

G2 phase

Preparation for mitosis, cell growth, organelle replication, and spindle apparatus synthesis.

G0 phase

A non-dividing state where cells do not actively divide.

M-phase promoting factor (MPF)

A cyclin-Cdk complex that controls the passage from G2 to M phase.

Activation of MPF

Phosphatase removes an inhibitory phosphate from the cyclin-Cdk complex in late G2.

Deactivation of MPF

Ubiquitin tags cyclin during late M-phase, leading to its degradation in the proteasome.

Restriction point (R)

The transition from G1 to S phase, regulated by G1/S cyclin-Cdk and the RB protein.

Role of RB protein

Serves as the STOP signal for the cell cycle until phosphorylated by cyclin-Cdk.

Four cell-cycle checkpoints

Surveillance points monitoring DNA integrity, replication, and spindle attachment.

Tumor suppressors

Regulatory proteins that halt the cell cycle or initiate apoptosis in response to damage.

p21-p53-RB signaling pathway

DNA damage activates p53, which induces p21 to inhibit cyclin-Cdk and arrest the cell cycle.

Human karyotype

Complete set of 46 chromosomes (22 autosomes, 2 sex chromosomes); humans are diploid (2n=46).

Ploidy

The number of chromosomal sets present in a cell.

Chromosomal aberration examples

Klinefelter syndrome (XXY) and Down's syndrome (Trisomy 21).

platelet derived growth factor

at the site of a cut and bleed; stimulation of cell division to heal the wound

Erythropoietin

a glycoprotein secreted by kidneys; stimulate red blood cell production in bone marrow

Interleukins

secreted by white blood cells; primary function in activation and differentiation of immune cells during inflammatory and immune responses

helices

separates 2 DNA strands so polymerase can replicate

topoisomerase

releases over-twisting, cuts, releases, seals

ssBP

preventing binding so replication can occur