Cell adhesion, cell junctions, and transport

What is the basic principles of cell transport

it is how substances move through, in and out of cell membrane through passive transport, osmosis and active transport

What is selectively permeable characteristics

allowing some substances to pass through lipid bilayer while blocking other substances

What is passive transport

does not require metabolic energy (ATP)

diffusion of random movement toward equilibrium

What factors affect speed of diffusion

Diameter of molecules (smaller size=faster diffusion)

Temperature of solution (higher temperature= faster diffusion)

Concentration gradient in the system (greater concentration gradient in system= faster substance will diffuse)

What is simple diffusion

process in which molecules/atoms/ions diffuse through semipermeable membrane down their concentration gradient with NO assistance of transporter proteins

What type of molecule can pass through the membrane in simple diffusion

molecule that is hydrophobic

soluble in lipids

When will simple diffusion stop

when equilibrium is met

What is facilitated diffusion

passive transport of molecules across a cell membrane where channel/carrier proteins assist movement of molecules from region of high concentration to low concentration

no ATP

What is a uniport

type of facilitated diffusion transporter that allows movement of one type of molecule powered by its concentration gradient

what is osmosis

diffusion of water across membranes depending on the concentration of solute molecules on either side of the membrane

What is hypertonic solution

higher solute concentration

What is isotonic solution

equal solute concentration

What is hypotonic solution

lower solute concentration

What are Aquaporins (AQPs)

facilitated transport that allows water and small neutral solutes across biological membranes that constituted by 13 water channel proteins

What are the three classes of Aquaporins

1. aquaporins transporting exclusively water

2. aquaglyceroporins transporting water and small solutes

3. Unorthodox aquaporins, unknown function, poor water permeability, but permeable to other small uncharged solutes

What is active transport and the two types

transport that requires energy input to move substances against their concentration

Two types:

Primary active transport involves hydrolysis of ATP

Secondary active transport uses the energy from an ion concentration gradient or an electrical gradient

What is electrogenic pumps

pumps involved in establishment and maintenance of membrane voltages

Sodium-Potassium pump is a electrogenic pump

How does the sodium potassium pump work

1 ATP molecule allows 3 Na+ ions pump out of a cell for every 2 K+ pumping into the cell

What is secondary active transport and an example of it

uses electrochemical gradient set up by primary active transport to move other substances against their gradients

Example: movement of sodium ions down their gradient is coupled to uphill transport of other substances by a shared carrier protein. Like when carrier protein lets sodium ions move down their gradient, and simultaneously brings a glucose molecule up its gradient into the cell

What is the difference between transporters, symport and antiport

Symport: co-transport where two molecules are moved across membranes, usually propelled by the concentration gradient of one of them (move in same direction either in or out of cell)

Antiport: two types of molecules that move in opposite directions

What type of active transport is the sodium-glucose cotransporter (SGLT)

secondary active transport

What are the two types of Macromolecule transport

Endocytosis: cells take in substances by engulfing them in a vesicle, it is active process

Exocytosis: cells expels materials in vesicles that fuse with cell membrane, also requires energy

What is Phagocytosis

aka “cellular eating”, part of membrane engulfs a large particle or cell, phagosomes form and usually fuse with lysosomes

What is Pinocytosis

aka “cellular drinking”

smaller vesicles form and bring in fluids and dissolves substances, as in the endothelium near blood vessels 

What is Receptor mediated endocytosis

depends on receptors to bind to specific molecules (their ligands), receptors are integral membrane proteins

What is the basic principles of cell adhesion

process in which cells bind to each other to form tissues and organs

Critical for development of tissue architecture

What is/are cell adhesion molecules

mediates the adhesion between cells

prominent parts of intercellular connections, attach cells to basal lamina and other cells, many bind to laminins

What are the four different families of cell adhesion molecules

1. Cadherins

2. Integrins

3. Immunoglobulin superfamily (igsf)

4. Selectins

What are Cadherins and how are they identified

Ca²⁺ dependent cell-cell adhesion molecules that mediate adhesion between cells and tissues

Identified based on tissue types in which they were first identified

what are the four different classes of cadherins

Epithelial cadherin (E-Cadherin)

Neural cadherin (N-cadherin)

Placental cadherin (P-cadherin)

Vascular endothelial cadherin (VE- cadherin)

What are Integrins and their function

Heterodimers

Cellular interaction with ECM and neighboring cells, and regulation of intracellular signaling

• stable adhesion cells to basement membrane

• formation of ECM

• interaction with neighboring cells (platelet plug formation immune response)

What is Immunoglobulin superfamily (IgSF) adhesion molecules and function

Calcium dependent transmembrane glycoproteins

homophilic or heterophilic binding

What does the IgSF-CAM extracellular domain contain

Ig-like intra-chain disulfide-bonded loops with conserved cysteine residues

What are the different types of CAM (IgSF) adhesion molecules (7 of them)

1. Intercellular CAM (ICAM)

2. Vascular CAM (VCAM)

3. Platelet-endothelial CAM (PECAM-1)

4. Neural CAM (NCAM)

5. Endothelial cell selective adhesion molecules (ESAM)

6. Junctional adhesion molecules (JAM)

7. Nectin and other CAMs

What are selectins 

Single chain transmembrane protein, calcium dependent and heterophilic binding with carbohydrates

What are the three different types of selectins

1. L-selectin (leucocyte)

2. E-selecting (Endothelial cells)

3. P-selectin (Platelets and endothelial cells)

What are Selectin’s function

role in acute and chronic inflammation

allow margination and chemotaxis of WBCs

Role in cancer metastasis

What are the four main cell junction classes from apex to base

1. adherens junctions

2. desmosomes

3. tight junctions

4. gap junctions

What are cell junctions

structures that connect cells to each other or to ECM, and made up of protein complexes that perform variety of functions

What are the general functions of cell junctions (there are4) and their function

Adhesion: maintain epithelial tissue integrity of epithelial tissue via establishing intercellular cytoskeleton network → anchors cells

Signaling regulate passage of chemical/electrical signals between cells

Polarity: regulate cell polarity

Molecular transport: regulate molecular transport

What are adherens junctions 

transmembrane proteins which bind to cadherins on neighboring cells, creating homophilic interaction, link cadherins to actin cytoskeleton inside:

• Catenins (α- catenin, β-catenin)
  

What are desmosome junctions

linked to intermediate filaments, providing tensile strength and stability

what are tight junctions

connection between cells of epithelial and endothelial tissues, forming barrier regulating passage of molecules/ions

what are gap junctions

intercellular connections allowing direct communication between adjacent cells, and formed by connexins (protein)

What proteins are in the network of tight junctions

claudins, occludins, junctional adhesion molecules (JAMs)

What are gap junctions crucial for

maintaining tissue homeostasis and allowing cells to synchronize their functions