BIO 100: Topic 11 - Cell Division

Cell division

The process where one parent cell divides into two daughter cells

Purpose of cell division

Growth, repair, maintenance, and reproduction

Two types of cell division

Mitosis and meiosis

Mitosis

Type of cell division that makes identical body cells

Meiosis

Type of cell division that makes sex cells (gametes)

Daughter cells from mitosis

Genetically identical to the parent cell

Daughter cells from meiosis

Genetically different with half the chromosomes

Somatic cell

Any body cell that is not a gamete

Gamete

A sex cell (sperm or egg) with half the normal number of chromosomes

Chromosome

Condensed structure of DNA and proteins that carries genetic information

Chromatin

Uncondensed DNA in the nucleus during interphase

Sister chromatids

Identical copies of a chromosome attached at the centromere

Centromere

Region where sister chromatids are joined

Kinetochore

Protein structure where spindle fibers attach on the centromere

Homologous chromosomes

A pair of chromosomes, one from each parent, with similar genes

Diploid (2n)

Cell with two sets of chromosomes (one from each parent)

Haploid (n)

Cell with one set of chromosomes

Human diploid number

46 chromosomes

Human haploid number

23 chromosomes

Cell cycle

Series of events that cells go through as they grow and divide

Two main phases of cell cycle

Interphase and mitotic (M) phase

Interphase

Cell grows, replicates DNA, and prepares for division

G1 phase

First part of interphase; cell grows and performs normal functions

S phase

DNA is replicated, making two identical sets of chromosomes

G2 phase

Cell prepares for division; checks DNA and makes needed proteins

M phase

Mitotic phase; includes mitosis and cytokinesis

Cytokinesis

Division of the cytoplasm to form two separate cells

Mitosis division type

Nuclear division

Prophase

Chromatin condenses into chromosomes; spindle fibers form; nuclear envelope breaks down

Metaphase

Chromosomes line up along the middle (metaphase plate)

Anaphase

Sister chromatids are pulled apart to opposite sides of the cell

Telophase

Nuclear envelopes reform around each set of chromosomes; chromosomes uncoil

End result of mitosis

Two identical diploid daughter cells

Spindle fibers

Microtubules that help separate chromosomes during mitosis

Centrioles

Organelles that help organize spindle fibers in animal cells

Cleavage furrow

Indentation that forms during cytokinesis in animal cells

Cell plate

Structure that forms during cytokinesis in plant cells to divide the cell wall

Checkpoint

A control point in the cell cycle where signals regulate progression

G1 checkpoint

Checks for cell size, nutrients, growth signals, and DNA damage

G2 checkpoint

Checks for proper DNA replication and any damage

M checkpoint

Ensures all chromosomes are attached to spindle fibers

What happens if checkpoint fails

The cell may pause, repair damage, or undergo apoptosis

Apoptosis

Programmed cell death used to eliminate damaged or unnecessary cells

Uncontrolled cell division

Can lead to tumor formation and cancer

Cancer cell

Divides uncontrollably and ignores normal cell signals

Benign tumor

A mass of abnormal cells that remain at the original site

Malignant tumor

A cancerous tumor that invades surrounding tissue and spreads

Metastasis

The spread of cancer cells to other parts of the body

Growth factors

External signals that stimulate cell division

Proto-oncogenes

Normal genes that promote cell division when needed

Oncogenes

Mutated proto-oncogenes that cause excessive cell division

Tumor suppressor genes

Genes that slow down the cell cycle or promote apoptosis

Example of tumor suppressor gene

p53 gene, which halts the cycle if DNA is damaged

Meiosis overview

Type of cell division that creates haploid gametes for sexual reproduction

Key difference: mitosis vs meiosis

Mitosis makes identical cells; meiosis makes unique gametes

Importance of mitosis

Allows growth, cell replacement, and repair

Importance of checkpoints

Prevents damaged cells from dividing