Cell division notes

Interphase: Growth and Preparation

Period of cell cycle including G1, S, and G2 phases; cell grows, replicates DNA and centrosomes, and prepares for mitosis

G0 Phase

Resting or non-dividing phase; cell has exited the cycle

G1 Phase

Cell grows and carries out normal metabolic processes

S Phase

DNA and centrosome replication occur; in prokaryotes, binary fission substitutes for S phase

G2 Phase

Checks for DNA replication errors, prepares for mitosis, and replicates organelles; involves MPF (Mitosis Promoting Factor Protein)

M Phase

Cell division phase; includes karyokinesis (nuclear division) and cytokinesis (cytoplasmic division)

Microtubules

Cytoskeletal structures made of tubulin; move chromosomes during division

Centrosomes

Organize the spindle apparatus; contain two centrioles with a 9×3 microtubule arrangement

Polar Microtubules

Connect centrosomes to opposite poles

Astral Microtubules

Anchor centrosomes to the cell membrane

Kinetochore Microtubules

Attach to chromosomes at kinetochores and pull them apart

Cilia/Flagella Structure

Have a 9+2 arrangement of microtubules; function in cell movement

Surface-to-Volume Ratio

Low ratio = inefficient exchange of materials → possible cell death

Genome-to-Volume Ratio

Small nucleus cannot support large cell size → possible cell death

G1 Checkpoint

Checks cell size and DNA integrity

G2 Checkpoint

Checks accuracy of DNA replication

M Checkpoint

Ensures spindle fibers are properly attached to chromosomes

Cyclin + CDK

Proteins that promote cell cycle progression

Anchorage Dependence

Cells must be attached to a surface to divide

Density Dependence

Cells stop dividing when crowded or space is limited

Chromatin

Loose form of DNA

Chromosome

Condensed DNA made from chromatin

Genome

All genetic material (DNA) in a cell

Sister Chromatids

Identical copies of a chromosome

Dyad

A pair of sister chromatids joined together

Centromere

Region where sister chromatids are joined (like a staple)

Kinetochore

Protein site on centromere where spindle binds

Prophase

Chromatin condenses, spindle forms, nuclear envelope breaks down

Prometaphase

Spindle fibers attach to kinetochores

Metaphase

Chromosomes align at the metaphase plate

Anaphase

Sister chromatids pulled apart to opposite sides; cleavage furrow forms using actin and myosin (animal cells)

Telophase

Nuclear envelope reforms, chromosomes return to chromatin

Cytokinesis in Animals

Division via cleavage furrow

Cytokinesis in Plants

Division via cell plate and middle lamella

Ploidy Transitions in Meiosis

Diploid (2n) → Haploid (n) → Haploid (n)

Somatic Cells

Body cells (undergo mitosis only)

Gametocytes

Germ cells (can undergo meiosis or mitosis)

Gametes

Sex cells (sperm and egg)

Prophase I

Synapsis forms tetrads/bivalents via synaptonemal complex; crossing over at chiasmata

Metaphase I

Homologous pairs line up; independent assortment adds genetic diversity

Anaphase I

Homologous chromosomes (not sister chromatids) are pulled apart

Telophase I

Results in two haploid cells

Meiosis II

Sister chromatids separate, producing four genetically unique haploid gametes