Cytoskeleton-Intercellular-Junctions YouTube Lecture Handouts
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Cytoskeleton
For:
- Structural Strength
- Motility &
- Cell Division
Includes
- Microtubules
- Intermediate filaments
- Microfilaments
Microtubules
- Tubular, lumen dia 15 to 20 nm.
- Made of α tubulin & β tubulin. They form stacks of rings containing 13 subunits
Functions
- Form spindles which move the chromosomes
- Cell movement
- Transport secretary granules, vesicles & mitochondria
- Involved in the formation of Cilia & flagella
APPLIED
1. Anticancer drugs bind to microtubules & make them stable so that Mitosis stops & eventually cells die
2. Colchicine inhibits mitosis by interfering with structure of mitotic spindle (acts during metaphase) used in labs. For various studies
Intermediate Filament
- Filamentous ~10 nm
- Functions: Stable & give structural strength to cell
- Connect nuclear memb. To cell membrane.
- Form neurofilament in neurons & maintain axonal diameter
- Formation of cellular junction
Microfilaments
- Solid filaments dia. 6 to 8 nm
- Made of contractile proteins actin & myosin
- Extension of micro filaments with plasma memb. form microvilli & they increase surface area for absorption
- In muscle they make contractile protein
Actin Filament
Intercellular Junctions
Types of intercellular junctions
- Tight junctions
- Zona Adherens
- 3 Desmosomes/Hemi desmosomes
- 4 Gap junctions; permits transfer of sub. Between two cells
Tight Junction
- Also called zona occludens
- Adjacent cell membranes are fused & there is no space between two cells
Function- they prevent movement of ions from one side of membrane to another side
Memb. Proteins cannot float
Examples
- Apical region of epithelial cells of intestinal mucosa
- Apical region of renal tubular cells
- Capillary endothelium forming blood brain barrier
- In choroid plexus
Adherens Jun. /Zona Adherens
- Immediately below the tight junction
- Form a band
- Adjacent membranes are separated by 15 to 20 nm gap
- Permit water & ions
Desmosome
- Not band but patchy
- Cleft of 20 nm. between cells
- Dense accumulation of proteins at focal places
- Bundles of Intermediate Filaments project from intercellular junctional area
- They hold cells at their places
- Two types
A. Desmosomes
- Thickened area on both sides of memb. & cells are attached to each other
B. Hemidesmosomes
- Thickened area on one side only.
- Attach cell to basal lamina
Functions
- Attach cells to basal lamina
- Hold cells firmly together specially at the site of stretching
Gap Junctions
- Intercellular space 2 to 3 nm
- In between the cells channels are present, lined by proteins called Connexins
- Eg. Basal part of epithelial cells of intestinal mucosa, heart muscles
Functions- Permit movement of amino acids, glucose, ions up to mol. weight of 1000
Rapid propogation of electric potentials from cell to cell important in Smooth & Cardiac Muscles
CAMS
- Cells are attached to each other and to basal lamina by CAMs (cell adhesion molecules)
- CAMs are
- Integrins
- Cadherins
- Selectins
- Adhesion mol. of IgG family
Functions of CAMs
- Hold tissues together
- Imp. In inflammation & tissue healing
- Embryonic development
- Formation of nervous system
- Metastasis of tumors
- Rate of apoptosis is high if CAMs are abnormal
Intercellular Communication
Types
1. Neural: by neurotransmitters released at synapses
2. Endocrinal: by hormones; which reach cells via blood
3. Paracrine communication: chemical substance secreted by a cell reach to nearby cell by diffusion in ECF. eg. In pancreas
Apoptosis
- It is programmed cell death and is genetically controlled
- It is caused by enzymes Capases
Nucleus
- Present in all eukaryotic cells.
- Controls cellular activities.
- Essential for cell reproduction
Transport through Cell Membrane
Can be …
- Passive transport
- Active transport
- Vesicular transport
Passive Transport: sub. Move in the direction of gradient (electrochemical)
- Concentration gradient
- Electric gradient
Energy is not required
Can be …
- Diffusion
- Simple diffusion: sub. move in the direction of gradient through semi permeable membrane
- Facilitated diffusion: Gradient is required but a carrier is needed eg. Glucose transport
Simple diffusion G. Donnan Equilibrium
Conclusion
1. Product of diffusible ions is same in all compartments
2. All compartments are electrically neutral
3. Total number of ions is more in C (intracellular compartment)
Osmosis
- Is movement of solvent (water) from it՚s high concentration (dilute solution) to low concentration. (concentrated solution)
Active transport
- Primary active transport: energy is required eg. Na+ K+ Pump
- Secondary active transport: eg. Transport of Glucose
Alpha Subunit- Various Binding
Sites
Vesicular Transport
- Endocytosis
- Exocytosis
- Transcytosis