Cell Biology Chapter 7: Interactions Between Cells and Their Environment

What are interactions of cells with their environment important for?

- cell migration

- axon outgrowth to targets

- cell division and survival

- differentiation

- organization into tissues

What are junctions for?

To communicate and adhere cells to one another

Are cells tightly or loosely packed in the epithelium?

Tightly packed

What happens when you scrape your skin and begin to bleed?

You remove the top layer which is the epidermis and got into the dermis which is below is that contains blood vessels which became and exposed and destroyed

What happens when a blister forms?

Your basal membrane detaches causes a space to form allowing the top layer of skin to die off while liquid enters into the space

What is glycocalyx?

An extracellular coating/ layer of carbohydrates that provides protection to the cell

What does glycocalyx surround?

It is around proteins, lipids, and molecules that bind to the cell surface

Why do cells have a net negative charge?

Partly because of the glycocalyx

What does glycocalyx mediate?

- cell-cell and cell-substratum interactions

What does glycocalyx provide for cells?

Mechanical and chemical protection

What does glycocalyx serve as for cells?

Serves as a barrier to particles moving toward the plasma membrane

What does the glycocalyx bind?

Important regulatory factors that act on the cell surface

What is the extracellular matrix?

An organized network of secreted extracellular material present beyond the immediate vicinity of the plasma membrane

What type of cells have a lot of extracellular matrix around them?

Chondrocytes

How thick is the basement membrane?

50-200nm

What does the basement membrane surround?

muscles, nerve, and fat cells

What does the basement membrane underlie?

epithelial cells of the skin, digestive & respiratory tracts, and the lining of blood vessels

What does the basement membrane provide?

Mechanical support

What does the basement membrane serve as?

Migratory substratum

What serves as a selective barrier for macromolecules (e.g. in the kidney)?

Basement membrane

What collagen type is in the basement membrane?

Collagen IV

What type of collagen is in the dermis?

Collagen I

What contains a very thick basement membrane?

The glomerulus of the kidney

What does the basement membrane of the kidney do?

It keeps proteins in the blood when it is filtered

What is kidney failure in diabetics caused by?

Thickening of the glomerular basement membrane

What are proteoglycans?

Huge protein-polysaccharide complexes (they are space filling)

What are fibronectins?

Dimers that have ECM and cell-binding domains (they are normally attached to the integrin that is on plasma membrane)

What is the shape of a laminin?

Cross shaped

Where are integrins located?

On the cell surface and are receptors for the ECM

What are collagens?

Family of fibrous glycoproteins that are only located in the extracellular space

What glycoprotein has high tensile strength that resists pulling forces?

Collagen

What is the most abundant protein in the body for humans/ animals (>25%)?

Collagen

What is collagen produced by?

Fibroblasts, smooth muscle cells, epithelial cells, bone

How many different types of collagen are there?

19 types

What are collagens restricted to?

Specific locations

Can collagens be mixed, even in the same fiber?

Yes

What is the structure of collagen?

Trimers of 3 alpha chains as a triple helix

What do collagen molecules for?

Fibrils

How are collagen fibrils formed?

By staggering parallel molecules to increase strength

What is the banding pattern caused by in collagen?

Staggering molecules with fibrils that are bundled together to form fibers

What are collagen fibrils strengthened by?

Cross-linking of lysine and hydroxylysine amino acids

What does the cross linking of collagen (lysine and hydroxylysine aa's) throughout result in?

Decreased elasticity of skin and brittleness

What does collagen provide for the extracellular matrix?

Insoluble framework

What does collagen type and arrangement determine for ECM?

Its physical properties

Why are collagen fibers in tendons parallel?

For high tensile strength

Who is collagen structured in the cornea?

In sheets where parallel fibers are perpendicular to adjacent sheets

Why is collagen structured the way it is in the cornea?

To give strength and minimize scattering of light

What is scar tissue made up from burns and injuries?

Accumulation of fibrillar collagens

What is osteogenesis imperfecta?

Mutations in type I collagen gene

What does osteogenesis imperfect cause?

Fragile bones, thin skin, and weak tendons

What are type II collagen mutations? What do they cause?

They alter cartilage and cause dwarfism and skeletal deformities

What is Ehler- Danlos syndrome?

Different collagen mutations

What does Ehler- Danlos syndrome cause?

Hyperflexible joints and highly extensible skin

What type of collagen is restricted to the basal membrane (basal lamina for humans)?

Type IV

How were collagenous proteins extracted from the basal membrane?

Using salt solutions because they are held together by non-covalent bonds such as ionic bonds

How is type IV collagen molecules arranged in basal membranes?

Lattice pattern with non-helical trimers with globular ends

What is Alport syndrome?

Inherited mutation of type IV collagen when the kidney basal lamina is disrupted

Where are there large amounts of proteoglycans?

In the extracellular matrix

What type of side chains do proteoglycans have?

Covalent GAG side chains

What are GAGs?

glycosaminoglycans - linear polysaccharies of repeating disaccharide units

Why are GAGS acidic?

Due to sulfate and carboxyl groups attached to sugar rings

How do proteoglycans form huge complexes?

By core proteins linking to hyaluronic acid (non-sulfated GAG) backbone

How do proteoglycans form hydrated gels?

By binding cations and water molecules

What are key characteristics of proteoglycans?

They fill space and resist compression

How do collagens and proteoglycan complement each other?

To give the extracellular matrix strength and resistance to deformation (similar to cartilage)

What is a modular protein?

dimer of 2 arrays of many cell and extracellular binding domains (ex: Fibronectin)

How many Fibronectin domains does each polypeptide have?

30 similar Fn domains

How many functional units are fibronectin domains arranged into?

5 or 6

What do the cell surface receptors (integrins) bind to?

RGD and other sequences in fibronectin

What is RGD?

Arg., gly., asp.,

What does RGD form?

Loop that sticks out for cell to bind via integrin receptor

How are the C-terminal ends of polpeptides linked? (fibronectin)

By disulfide bonds

Where is fibronectin localized to?

Basement membranes and connective tissue

What do fibronectin in connective tissues serve as?

Pathways for neural crest cell migration

What are the pathways that are important for embryonic development?

Fibronectin and extracellular matrix pathways

Is testing neural crest cells on a cover slip in vivo or in vitro?

In vitro

What is important to morphogenesis?

Fibronectin

What is morphogenesis?

the physical processes that give an organism its shape (what it morphes into)

What do Fn anti-bodies do to cleft formation?

Inhibits cleft formation

Where is neural crest cell migration the most extensive?

Out of neural tube

What do neural crest cells form?

All peripheral nervous system, melanocytes, and some facial bones

What are embryonic cell migrations guided by?

Extracellular molecules

What are laminins?

Family of proteins with 3 polypeptide chains that resemble a cross

How many different trimers are there for laminins?

20 different trimers

What are laminins linked by?

Disulfide bonds

What family of proteins influence cell migration, growth, and differentiation?

Laminins

What can laminins binds to?

Other laminins, cell surface receptors, proteoglycans, and other basal membrane proteins

What are the 2 cross-linked networks of basal membranes?

Collagen IV and laminin

How are collagen IV and laminins connected in basal membranes?

Entactin molecules

Are extracellular molecules static?

No

Can extracellular molecules be remodeled? When does this occur?

- Yes (degraded and reconstructed)

- Occurs during development or after tissue injury

What are matrix metalloproteinases responsible for?

Degration of extracellular molecules

1) Secreted

2) Membrane-bound forms

What diseases can occur due to excessive matrix metalloproteinases?

- arthritis

- multiple sclerosis

- atherosclerosis

- tooth decay

- cancer

What are the major extracellular membrane receptors on all cells?

Integrins

What subunits do integrins have?

Alpha and beta

How many different alpha integrin subunits are there?

18

How many different beta integrin subunits are there?

8

How many different combinations of integrin alpha and beta subunits are there?

25 different combinations

What type of cell surface receptors do most cells express? What does this allow?

Multiple integrins which allows binding to multiple ECM components

Do integrins bind to 1 or more ECM components?

More than 1