junctional complexes, cell cycle

zonula occludens

• tight junctions

• most apical

• barrier preventing leakage (ex: stomach)

membrane proteins in zonula occludens

• occludin

• claudin

cytoplasmic proteins in zonula occludens

• ZO-1

• actin

zonula adherens

• usually just below tight junctions (zonula occludens)

• intermembrane space of 15 nm

membrane proteins in zonula adherens

cadherins (form homotypic dimers)

cytoplasmic proteins in zonula adherens

• α-actinin (actin-binding proteins)

• vinculin

• actin (and myosin) (terminal web)

desmosome

• macula adherens

• strongest junctional complex

• largest intercellular space of 25 nm

• contains plaque for strength

membrane proteins in desmosome

• desmocollin

• desmoglein (grab plaque on inside)

cytoplasmic proteins and filaments of desmosome

• desmoplakins I and II

• plakoglobin (reinforcement)

• desmocalmin

• tonofilaments (bind to plaque and confer strength)

hemidesmosome

• plaque contains BP 200

• TM contains α6 integrin, β4 integrin, and BP 180

bullous phemphigoid

body produces antibodies against proteins in TM causing space between basement membrane and basal cells

gap junctions

• intracellular space of 2 nm

• channel 1.5 nm in diameter

• connexons couple across intercellular space to make pores/channels between cells

connexon

channel composed of 6 connexins

stem cell

self-renewing cell

steady state

number of newly originated cells by the stem cells are equal to the number of dead cells on the surface of the epithelium

turnover time

time required to change the whole population of epithelial cells (30 days)

radioautography

provides a means to study the turnover of epithelial (and other) cells

purpose of cell division during embryogenesis and postnatal development

produce growth

behaviour of cells in adulthood

• static

• expanding

• renewing

cell cycle (interphase and mitosis)

1. G1 (presynthesis of DNA, 25 hours, 2n)

2. S (synthesis of DNA, 8 hours)

3. G2 (post DNA duplication, 3 hours, 4n)

4. mitosis (2.5 hours, 2n)

mitosis

1. preprophase (intranuclear condensation of chromosomes)

2. prophase (visualization of chromosomes and mitotic spindle, 1 hour)

3. metaphase (chromosomes in equatorial plane, loss of nuclear envelope and nucleolus, < 1 hour)

4. early anaphase (longitudinal splitting of chromosomes)

5. late anaphase (migration of chromosomes to the poles)

6. telophase (nuclear restitution, nuclear envelope and nucleolar formation, end of cell division, minutes)