lecture 5

Question 1

cell junctions in epithelial cells

Answer 1

• epithelial cells interact with eachother and the extracellular matrix through junctions to form tissues
• sheets of epithelial cells cover external surfaces and organs
• all junctions present in epithelial cells
• top 3 junctions hold sheet of cells together

Question 2

polarized epithelial cells

Answer 2

junctions are arranged in a specific order

tight junction
adherens junction
desosome
gap junction
hemidesmosome

Question 3

tight junction

Answer 3

creates a seal between cells
- prevents mixing of the extracellular environements

• act as fences in the membrane
• composed of 2 transmembrane proteins
• claudin and occludin
• required in both cells
• the extracellular domain in one cell interacts with the extracellualr doman i the neighboring cell

Question 4

anchoring junctions

Answer 4

-provides mechanical strength to epithelium
- cell-cell anchoring junctions, adheres junctions
- cell-ECM anchoring junction

Question 5

adherens junctions

Answer 5

• form an adhesion belt, encircles the inside of the plasma membrane
• transmembrane adhesion proteins = cadherins (cadherin protein from neighbouring cells interact with eachother
• intercellular linked proteins, link cadhering proteins to actin filaments

Question 6

desmosomes

Answer 6

• linked to keratin filements and connect to a enightbouring cell
• transmembrane adhension proteins, specific cadherin family members
• intracellular linker proteins

Question 7

hemidesmosomes

Answer 7

• anchor keratin filaments to the basal lamina

-integrins, bind to laaminin in the basal lamina

Question 8

gap junction couple cells

Answer 8

• couple cells electrically and metabolically
• allows passage of ions and metabolites, not very selective
• passes through cAMP, nucleotides, glucose, amino acids
• does not pass macromolecules, proteins, nucleic acids

Question 9

gap junctions are gated

Answer 9

• can be in an open or closed state

Question 10

plant plasmodesmata: intercellular junctions

Answer 10

-plant cells
- intercellular junctions
- allows for communication between cells
- different structure than gap junctions
- moves small molecules

Question 11

extracellular matrix

Answer 11

3 major classes of macromolecules
1. glycosaminoglycans (GAGS) and proteoglycans
2. fiborus proteins
3. glycoproteins

ecm is the primary component in connective tissue

Question 12

GAGS

Answer 12

• long, linear, chains of a repeating disacharide
• highly negatively charged

hyaluronan
- a simple GAG
- long chain of repeating disacharide subunits

Question 13

connective tissue ECM: proteoglycans

Answer 13

• subclass of glycoproteins
• protein with a least one sugar side chain which must be a glycosaminoglycan

Question 14

connective tissue ECM: collagen

Answer 14

• fibrous protein
• privides tensile strength
• resist stretching

structure
- three chains wound arounf eadhother in a triple helix
- assemble into ordered polymers to form collagen fibrils, can pack together inti collagen fibers

• secreted as a procollagen

Question 15

Connective tissie ECM: elastin

Answer 15

• fibrous protein

networks of elastin
- gives tissues elasticity

Question 16

basal lamina

Answer 16

• seperates epithelia from underlying tissue
• attatchment site for epithelia
• anchored by hendesmosomes
• organzied by laminin