Biochem Exam 2 - Mokrzan

Question 1

What is the extracellular matrix?

Answer 1

• a complex network of macromolecules in the extracellular space.
• it is secreted by the cells which inhabit it
• give structural and organizational support to tissues
• makes up a substantial part of the tissue volume

Question 2

What is collagen?

Answer 2

• makes up 30% of the total body protein
• 90% of it is Type 1
• it has a triple-helicle structure that is strengthened and stabilized by crosslinks
• there are fibrillar and non fibrillar collagens
• diff types and combinations of collagen molecules predominate in different tissues
• collagen is frequently remodeled and the synthesis of collagen is affected by physiological conditions such as diet or mechanical stress.
• osteogenesis or dentogenesis imperfect is the result of genetic mutation that causes the glycine in Type 1 collagen to be replaced by another amino acid

Question 3

What is elastin?

Answer 3

• it proved flexibility and resilience to the ECM
• is is the predominant ECM molecule in blood vessels
• it is found in tissues that require elasticity
• it is stabilized by two-way crosslinks
• elastin is not synthesized after adolescence

Question 4

What is fibronectin?

Answer 4

• it facilitates communication between intracellular and extracellular compartments
• it binds to other ECM molecules
• binds to integrin molecules on cells
• important for cell adhesion, growth, migration, and wound healing
• has insoluble and soluble forms: interaction with oral pathogen

Question 5

What is laminin?

Answer 5

• it is primarily found in basal lamina
• gives structural support to the ECM
• it is the major component of basement membranes in epithelial and muscle tissues
• binds to cells, often through the integrin family of proteins
• diseases of a abnormal laminin

Question 6

What are proteoglycans?

Answer 6

• these are the gel-formers of the ECM
• theses are structures of molecules, diversity
• they have many negative charges, which attract cations and water. The result is hydration of the ECM, which provides rigidity and durability.
• proteoglycans are <10% of ECM protein, but because their hydrophilicity, GAG chains fill more of the extracellular space
• makes up the core of aggrecan which is an enzyme
• can also bind growth factors, regulate enzyme activity and act as co-receptors
• lysosomal storage diseases

Question 7

What are cell junctions?

Answer 7

• specialized regions where cells are attached to each other and the ECM
• epithelial tissues are particularly rich in cellular junctions

Question 8

What are tight junctions?

Answer 8

• these are cell-to-cell junctions found in epithelia
• severely limit intercellular permeability and maintain cell membrane polarity (diff protein components of apical and basolateral membranes)
• formed by sealing strands anchored in the membrane
• required for active transport of solutes across the epithelial barrier
• all tight junctions are impermeable to macromolecules, but permeability to small molecules varies greatly, depending on the number of sealing strands and the different transmembrane proteins (occludin and claudin families) that comprise them.

Question 9

What are anchoring junctions?

Answer 9

bind cells to each other to the ECM. They are found in all tissues, especially those subject to mechanical stress.

Question 10

Types of anchoring junctions?

Answer 10

• adherens junctions
• desmosomes
• hemidesmosomes
• focal adhesions

Question 11

What are adheren junctions?

Answer 11

• are cell-to cell junctions found primarily in epithelia
• form a continuous adhesion belt just below the tight junction
• transmembrane proteins are cadherins (play important role in cell adhesion - form adheren junctions to bind cells within tissues together)
• connect bundles of actin filaments - contractile
• necessary for tight junction formation and epithelial tube formation in morphogenesis

Question 12

What are Desmosomes?

Answer 12

• cell to cell junctions that rivet cells together
• found primarily in epithelia and muscle cells
• contribue to tissue strength and durability
• transmembrane proteins are cadherins (play important role in cell adhesion - form adherens junctions to bind cells within tissues together)

Question 13

What are hemidesmosomes?

Answer 13

• resemble half-desmosomes, but bind cells to the ECM
• transmembrane adhesion proteins are the integrins
• attach the junctional epithelium to the tooth enamel

Question 14

What are focal adhesions?

Answer 14

• spot-type junctions that link the cell cytoskeleton to the ECM
• can contain as many as 100 diff proteins
• dynamic: they can form, change, or disappear in response to intracellular or extracellular signals
• they can transmit external mechanical signals via integrin receptors
• important in cell migration, motility, differentiation, proliferation, and orthodontic tooth movement.

Question 15

What are gap junctions?

Answer 15

• these are communicating junctions found in nearly all cells except skeletal, muscle, and blood cells
• allow small molecules and electrical charges to pass directly from cell to cell
• channels, called connexons (are structurally related transmembrane proteins that assemble to form vertebrate gap junctions), are hexameters of connexion proteins
• connexon permeability varies with the identity and combinations of connexins present
• gap junction permeability can be regulated by both intra- and extra- cellular signals
• allow the cells of a given tissue to function together quickly and in a coordinated fashion