Cytoskeleton-Intercellular-Junctions YouTube Lecture Handouts

Doorsteptutor material for competitive exams is prepared by world's top subject experts: get questions, notes, tests, video lectures and more- for all subjects of your exam.

Get video tutorial on: Examrace YouTube Channel

Illustration: Cytoskeleton-Intercellular-Junctions YouTube Lecture Handouts
Illustration: Cytoskeleton-Intercellular-Junctions YouTube Lecture Handouts

Cytoskeleton

For:

  • Structural Strength
  • Motility &
  • Cell Division

Includes

  • Microtubules
  • Intermediate filaments
  • Microfilaments
Illustration: Cytoskeleton

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
Illustration: Microfilaments
Illustration: Microfilaments

Actin Filament

Illustration: Actin Filament
Illustration: Actin Filament
Illustration: 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
Illustration: Intercellular Junctions

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

Illustration: Intercellular Communication
Illustration: Intercellular Communication

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
Illustration: Transport through Cell Membrane

Simple diffusion G. Donnan Equilibrium

Illustration: Transport through Cell Membrane

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)

Illustration: Conclusion

Osmosis

  • Is movement of solvent (water) from it՚s high concentration (dilute solution) to low concentration. (concentrated solution)
Illustration: Osmosis

Active transport

  • Primary active transport: energy is required eg. Na+ K+ Pump
  • Secondary active transport: eg. Transport of Glucose
Illustration: Osmosis
Illustration: Osmosis

Alpha Subunit- Various Binding

Sites

Illustration: Sites
Illustration: Sites
Illustration: Sites

Vesicular Transport

  • Endocytosis
  • Exocytosis
  • Transcytosis