Extracellular matrix (Smit)

29 important questions on Extracellular matrix (Smit)

Why do we need connective tissue?

Connective tissue offers protection to mechanical stress and is involved in transport of oxygen and nutrients.

What is the order of magnitude of collagen when starting small?

  • Single collagen polypeptide chain
  • Triple-stranded collagen molecule
  • Collagen fibril
  • Collagen fiber

What is the name of the cells that make extracellular matrix?

In skin, tendon, and many other connective tissues: fibroblasts
In bone: osteoblasts
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What is the function of collagen?

The function of collagen is to resist pulling forces.

What makes collagen strong?

To increase the strength, collagen is stacked.

What kind of collagen stacking does the cornea have?

Perpendicular stacking, this is so it can resist a lot of force and stay intact.

How is the extracellular matrix connected to the intracellular matrix?

In the intracellular matrix actin binds to an adapter protein, this binds to integrin. Integrin binds to fibronectin, which connects to collagen.

How can integrin activity be modulated?

It can be active via binding to fibronectin (outside-to-inside activation). Or it can be active through binding to cytoskeleton (inside-to-outside activation).

What is the function of proteoglycans?

The function of proteoglycans is to resist pressure forces.

What is the major component of the extracellular matrix in tendon and bone (dense connective tissue)?

Collagen.

What do proteoglycans consist of?

Proteoglycans are GAGs that are covalently linked to core proteins.

Are glycosaminoglycans (GAGs) positively or negatively charged?

GAGs are negatively charged.

How can glycosaminoglycans & proteoglycans protect against focal pressure? Give two examples that contain this.

GAGs have negative charges, this attracts Na+ ions. Na+ ions attract H2O, this forms a ‘gel’. Gel cannot be compressed so it is protected against focal pressure.
The eye is filled with it + the knee joint is made of this.

What is the function of the basal lamina?

The function of the basal lamina is the adhesion of collagen and lamina.

Which type of collagen is present in the basal lamina?

The basal lamina is composed of type IV collagen.

Where does the basal lamina bind to?

The basal lamina binds to epithelial cells at their basal side.

Looking at the gut, what way do the nutrients go and what way does the mucus go?

The nutrients go the the extracellular matrix, the mucus goes into the gut.

What is the function of a tight junction?

A tight junction seal neighboring cells together in an epithelial sheet to prevent leakage of molecules between them.

Which two proteins form a tight junction?

Claudins and occludins

What is the function of an adherence junction/adhesion belt?

The function of an adherence junction/adhesion belt is to join an actin bundle in one cell to a similar bundle in a neighboring cell.

What is a characteristic of an adhesion belt? And how is it possible?

An adhesion belt contains actin fibers, actin fibers can contract. So, contraction of the adhesion belt can change the shape of the epithelium.

What is the function of cadherin molecules?

Cadherin molecules connect intermediary filaments or actin in the cytoskeletons of neighboring cells.

What is the function of a desmosome?

A desmosome joins the intermediate filaments in one cell, to those in the neighboring cell.

How is a desmosome formed?

The intermediate filaments are anchored to a cytoplasmic plaque that is made of intracellular linker proteins. Cadherin proteins are attached to this plaque and they connect to each other in the intercellular space.

What is the function of a gap junction?

A gap junction forms channels that allow small water-soluble molecules, including ions, to pass from cell to cell.

How does a gap junction form?

A connexon is composed of six subunits. The two plasma membranes that interact with each other are aligned and parallel, in such a way that the connexons are exactly above each other, now a channel is formed.

What is the influence of dopamine on gap junctions?

The neurotransmitter dopamine reduces gap-junction communication within a class of neurons in the retina in response to an increase in light intensity.

What is the function of a hemidesmosome?

A hemidesmosome anchors intermediate filaments in a cell to the basal lamina.

How does a hemidesmosome form?

The intermediate filaments are connected to a plaque of linker proteins. This plaque is attached to integrin, which attaches to the basal lamina.

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