Epidermis
The surface layer of skin, overlays the dermis
o Contains:
- Keratinocytes – epidermal cell that produces keratin
- Intermediate filaments linked to cell junctions in keratinocytes provide a great deal of structural support to the skin
- Defects in intermediate filaments in the skin (keratin) make the skin less resistant to physical stress= epidermolysis bullosa
- Melanocytes – melanin forming cell
- Pigment cell
Basal Lamina
Layer of extra cellular matrix secreted by epithelial cells
ECM- to cell~ epidermis cell connects to basal lamina by hemidesmosome junction
Dermis
Thick layer of tissue below the dermis
o Contains:
- Arteries
- Sweat glands
- Nerve vein
Cytoskeleton
complex network of interlinking filaments and tubules that extend throughout the cytoplasm.
Microtubules
A hollow tube formed from tubulin dimers
- Alpha tubulin and beta tubulin = dimer
o Cell movement by cilia and flagella
o Cell division (chromosome segregation)
o Vesicle transport
o Organelle arrangement
o Make up the spindles of the centrosome (mitosis, meiosis)
o Dynamic ~ ability to grow
- Plus, end assembles quickly
- Addition of subunits is quicker than the removal so its growing faster
- Minus end assembles slowly
- The rate of addition and subtraction of subunits is the same so it is growing slower than the plus end
Dynamic instability
- Switching between growing (polymerization) and shrinking (depolymerizing) states
- Polymerization- adding of subunits/monomers
- Depolymerization- removal of subunits/monomers
o Motor Protein
- Kinesin
- end
- Dynein
- end
- Involved in cilia and flagellar movement
o Cilia in paramecium, epithelium cells
o Flagella in unicellular algae and sperm
- Experiment: In the dark, melanin granules are dispersed outward by kinesin, causing the embryo to be darkly colored. In the light, melanin granules are aggregated toward the center by dynein, causing the embryo to be lightly colored.
Microfilament
A microfilament is a double helix of actin monomers
o Cell movement by crawling and vesicle transport
o Muscle contraction
o Cell division- Actin contractile ring (cytokinesis in animal cells)
o Bands of microfilaments span the circumference of the cell
o Make up microvilli (in intestinal cells, helps with absorption)
o Dynamic
- Plus, end assembles quickly
- Minus end assembles slowly
o Motor Protein
- Myosin
- Microfilament + Myosin = muscle contraction
Intermediate Filament
An intermediate filament is a strong fiber composed of intermediate filament proteins
o Cell shape and support
o Intermediate filament subunits
- Epithelial cells- keratins
- Fibroblasts- vimentins
- Neurons- neurofilaments
- Inside the nucleus- lamins
o Lamin vs laminin
- Lamin is intermediate filament and lamaninin is an extra cellular matrix protein.
- DO NOT CONFUSE THEM
o Intermediate filaments linked to cell junctions in keratinocytes provide a great deal of structural support to the skin
o Defects in intermediate filaments in the skin (keratin) make the skin less resistant to physical stress= epidermolysis bullosa
Sponge Experiment
Sponges of different species broken up into individual cells. Individual cells from both sponges were swirled together. The cells from each sponge sorted themselves out.
- Due to differing cell adhesion molecules on the surface of the sponge cells
Embryo Experiment
Tissues were broken up into individual cells. Individual cells from both tissues were mixed together. The cells from each tissue sorted themselves out and adhered to form new tissue.
- Also due to cell adhesion molecules
Cell Adhesion molecules: CAMS
Proteins located on the surface of cells involved in binding with other cells or with the extracellular matrix
o Cadherins
- Cell to cell
o Integrins
- Cell to extra cellular matrix
Adherens
CAM- cadherin
- Cytoskeleton attachment= microfilament
- Primary function= cell-cell adhesion (anchoring)
Desmosome
CAM-cadherin
- Cytoskeleton attachment- intermediate filaments
- Primary function- cell-cell adhesion (anchoring)
Hemidesmosome
CAM= integrin
- Cytoskeleton attachment- intermediate filaments
- Primary function- Cell-ECM adhesion (anchoring)
- Example: cell to basal lamina
Tight Junction
Claudin, occludins
- Primary function-epithelial boundary (barrier)
- Barrier to the passage of molecules between cells
Gap junction
Connexins
- Primary function-communication between animal cells
- Allows molecules to pass from one cell to another
- Animal cells
Plasmodesmata
Cell membrane
- Primary function: Communication between plant cells
- Only in plant cells
- Plant cell equivalent to gap junction
Extra Cellular Matrix
- Animal
Major component is collagen
o Secreted by cells in a mixture of proteins and polysaccharides
o Composed of large fibrous proteins
- Collagen
- Elastin
- Laminin
o Cells in connective tissues of animals reside in complex meshwork of extracellular matrix fibers
Extra Cellular Matrix
Plant
o Layers of cell wall – in plants the extracellular matrix is the cell wall
- Middle lamella:
- Made of carbohydrates
- Main mechanism by which plant cells adhere to one another
2. Primary cell wall - Made of cellulose fibers, pectin, and several other proteins
- Thin and flexible
3. Secondary cell wall - Made of cellulose and lignin
- Rigid
- Lignin is the substance that hardens the cell wall and makes it water resistant.
Binary Fission
Asexual reproduction common to bacteria
- Daughter cell is identical to parent
- Bi-directional synthesis
G1
Interphase:
the first growth period of the cell cycle, during interphase, in which the cell grows and cytoplasmic organelles are replicated. Many regulatory proteins are made and activated at this stage .
S phase
DNA synthesis (entire DNA in nucleus replicated)
- Period of cell cycle prior to mitosis, during which the chromosomes are replicated
G2 Phase
The second growth period of cell cycle, following DNA replication and preceding prophase of mitosis. During which the cell forms the materials that make up the spindle.
G0 Phase
Period where cell is neither dividing or preparing to divide
Ex. Neurons, liver cells, lens of eye
M Phase
Mitosis and cytokinesis
