The Intercellular Environment Flashcards
What is the ECM composed of, and how does it serve the tissues of an organism?
The ECM is composed of proteins and polysaccharides, and it provides structural support, tensile strength, and elasticity to tissues.
What is the ECM equivalent for plant cells?
The extracellular matrix of a plant cell is the cell wall.
What is the cell wall composed of, and how does it serve a plant cell?
The cell wall is composed of cellulose microfibrils and other polysaccharides and glycoproteins. The cell wall provides much of the support and structure for a plant cell. It also opposes the cell’s internal turgor pressure (up to 500 atm).
What is pressure potential, and how does a plant cell maintain its turgor pressure?
Pressure potential is the tendency of water to move in response to pressure. Water is free to flow into a plant cell (this is different from the controlled osmotic barrier of animal cells). The stiff cell wall pushes back with equal and opposite force on the water inside the cell, preventing it from blowing up like it would in an animal cell.
What price must a plant pay for having a cell wall and using it to oppose gravity?
There are constraints on movement (little cell migration), division (difficult cytokinesis), and signaling (small molecules only).
How does the sugar content of the ECM compare to the cell wall of a plant cell?
Both the ECMs of animal and plant cells have enormous amounts of sugar in them. The plant wall is different in that it is primarily composed of polysaccharides.
What is the basic unit that forms to make plant microfibrils, and how many of them do you need?
Cellulose is assembled together to form microfibrils. You need 20-50 cellulose chains to do so.
What are the four main classes of glycoproteins/proteoglycans in the animal ECM?
Collagens, fibronectins, laminins, and glycosaminoglycans (GAGs).
Compare N-linked glycans with glycosaminoglycans (GAGs).
N-linked glycans are the most common form of glycosylation. They generate more complex, branched forms of oligosaccharides attached to core proteins. GAGs have more sugar and fewer proteins.
Describe the composition of collagen.
Collagen is composed of 1,050 amino acid repeats in the pattern of glycine-X-Y (repeated 350 times). X is usually a proline and Y a lysine. These aa repeats assemble into a triple helix called a tropocollagen.
What are collagen fibrils formed from? Describe their structure.
They are formed from tropocollagen (the triple helix of amino acids). Staggered ends result in a banded appearance of collagen fibrils. Tropocollagen molecules in fibril are covalently X-linked. These collagen fibrils then assemble into collagen fibers.
Why does a lack of vitamin C result in scurvy?
Many prolines and lysines (two of three of the amino acids in tropocollagen) are hydroxylated; this modification requires vitamin C. VC is required for the hydroxylation and assembly of this protein into a triple helix (tropocollagen). With scurvy, tropocollagen cannot be assembled and collagen fibrils cannot be made. Hair and teeth fall out, wounds won’t heal, and the disease is quickly fatal.
Why doesn’t scurvy occur in most animals?
Most animals (with the exceptions of higher primates, bats, and fish) can synthesize their own vitamin C (L-gulonolactone oxidase).
Describe the characteristics of fibronectin (an ECM protein).
Fibronectin has critical roles in development/tissue integrity, forms a dimer linked by disulfide bonds, has a binding site for collagen and the cell, and is an important cross-linker within the ECM.
What role does fibronectin play in the formation of salivary glands?
Salivary glands normally form lobes. If you remove fibronectin from the gland, the proper development of the salivary gland fails to happen.
Describe the composition of glycosaminoglycans (GAGs) and proteoglycans (important ECM proteins).
Proteoglycan complexes are large complexes of proteins and polysaccharides (glycosaminoglycans), though they are mostly made of sugars.
How do proteoglycans maintain water balance?
They bind ions and water molecules and take up lots of space, acting like a sponge to soak up water.
List the three key components of proteoglycans and compare their monomer counts.
- Keratan sulfate (monosaccharide branches of <300)
- Hyaluronic acid (monosaccharide branches of about 25,000)
- Chondroitin sulfate (branches of <300)
How is a cell linked to the basal lamina?
Integrins and other membrane glycoproteins do this. These receptors are the mechanism by which the cell is linked to its surroundings. Integrins link F-actin to the ECM in focal contacts/adhesion plaques and also function as transmembrane receptors for collagen, laminin, fibronectins, and other ECM components.
Describe the structure and function of integrins.
Integrins are dimers that work as receptors. They are composed of a and B components that bind components from the ECM. Their purpose is to form a linkage between the cytoskeleton and the ECM, acting as a bridge.
What happens when integrins accumulate to work together?
Though integrins can work on their own, they can also work together to form points of strong adhesion. These points are called hemidesmosomes, and they are substrate-adhesion junctions. They act as a bridge between internal keratin intermediate filaments and external ECM filaments.
How do integrins play a role in the development and maintenance of multicellular organisms?
Integrins maintain muscle attachments. Pulling against the strong integrin junctions linked to the tendons allows for movement of the muscle. Integrins also guide nerve cell growth and control cell adhesion–a cell can migrate by integrin adhesions to its environment.
What are the five types of epithelia in the body, and what structure organizes all of them?
The types of epithelia are simple, stratified, columnar, cuboidal, and squamous. All of them are organized by the basal lamina.
What is the adhesion belt of adhering junctions?
The adhesion belt is a belt of actin filaments running through several cells and linked by the adhesion junction. It provides a band of strength to the cells.