Module 1 Lecture 5: Cell Adhesion Molecules & Membrane Transport

Question 1

Other than creating a protective behaviour and housing internal structures of the cell, what does the plasma membrane do?

Answer 1

Involved in cell to cell adhesion

Question 2

By what means are cells held together?

Answer 2

Cell Adhesion Molecules (CAM), Extracellular Matrix (ECM), Specialized cell junctions

Question 3

What are cell adhesion molecules?

Answer 3

Help stick one cell to another cell; not as strong as other methods but mainly used for signalling

Question 4

What is the extracellular matrix?

Answer 4

Found in between two cells (in respect to tissue); it is filled with fibrous proteins embedded in interstitial fluid

Question 5

What is the interstitial fluid used for?

Answer 5

Provides a path to help diffuse nutrients, wastes and other soluble traffic between blood and tissue cells

Question 6

There are three proteins fibres apart of the extracellular matrix. Where are they woven through?

Answer 6

Through the interstitial fluid

Question 7

What are the protein fibres of the extracellular matrix called?

Answer 7

Collagen, Elastin, Fibronectin

Question 8

What is collagen fibre?

Answer 8

Most abundant protein in the body; forms cable-like fibres and used for mechanical strength

Question 9

What is elastin?

Answer 9

Elastic/rubbery protein fibre; for tissues that need to stretch and recoil (i.e. lungs)

Question 10

What is fibronectin?

Answer 10

Helps hold cells in position; promotes cell adhesion

Question 11

How is fibronectin linked to tumour metastasis?

Answer 11

Tumour cells metastasize when they get out of control and they destroy the fibronectin that holds them in place

Question 12

What is the ECM serve as?

Answer 12

Biological glue holding cells within tissues together but not letting them touch

Question 13

Which tissue is the ECM more abundant in? What secretes ECM?

Answer 13

Connective tissue; fibroblasts secrete ECM

Question 14

What do fibroblasts make in connective tissue?

Answer 14

The ECM’s structural proteins - collagen, elastin and fibronectin

Question 15

What are specialized cell junctions molecules

Answer 15

Help link cells together; either touching or not and each one of them are special to certain tissues

Question 16

What are the three specialized cell junctions named?

Answer 16

Desmosomes, Tight Junctions, Gap Junctions

Question 17

What are desmosomes? What are they most abundant in?

Answer 17

Adhering junctions; tissues subject to considerable stretching (skin, heart, uterus)

Question 18

What is the basic function of a desmosome?

Answer 18

Act like an anchor for two adjacent but non-touching cells

Question 19

Describe how desmosomes connect two cells without ripping it apart?

Answer 19

1) There are plaques on the cytoplasmic side of the plasma membrane; they help strengthen the fluid membrane on both sides of each cell
2) Intercellular filaments (a.k.a. cadherins) connect the cells to the plasma membrane and the plaque inside the cell increasing the rigidity of the membrane
3) Finally, the intracellular filaments (i.e. intermediate filaments) that are connected inside the cell relieve pressure on the membrane.

Question 20

What part(s) of the two adjacent cells connected is the desmosome formed from?

Answer 20

From the plaque end inside one cell, to the intercellular filaments to the beginning plaque inside the adjacent cell

Question 21

Would you be able to rip apart a desmosome junction?

Answer 21

No; strongest cell-to-cell connection

Question 22

What are tight junctions?

Answer 22

Adjacent cells where the plasma membranes are stitched together to seal off passageway between two cells

Question 23

An example of why tight junctions are important?

Answer 23

The intestinal lining for example; if it had any loose areas then it would be leaking + the possibility of other substances going into our gut would not be beneficial

Question 24

What’s the purpose for tight junctions?

Answer 24

Block off passage of molecules between cells; only passage way is through the cell membrane

Question 25

Where are tight junctions commonly found?

Answer 25

Primarily in sheets of epithelial tissue like the ones covering the body and line internal cavities

Question 26

What are tight junctions also known as?

Answer 26

Impermeable barrier

Question 27

How strong are tight junctions?

Answer 27

Not as strong as desmosomes; can rip off if it wants to

Question 28

What are gap junctions? What are they used for?

Answer 28

Junctions between two adjacent cells that transport small molecules and ions between them

Question 29

What forms gap junctions?

Answer 29

Connexons; small connecting tunnels

Question 30

Where are gap junctions abundant in?

Answer 30

Cardiac muscle and smooth muscle; where rhythmic contractions must be kept

Question 31

How do gap junctions help in synchronized contractions of a whole muscle mass?

Answer 31

Movement of ions helps transmit electrical activity

Question 32

Permeability, Impermeability, Selective Permeability

Answer 32

Plasma membrane classified into three types of permeableness

Question 33

What properties influence whether a substance can permeate the plasma membrane without help

Answer 33

1) Solubility of the particle in lipid
2) Size of the particle

Question 34

What molecule can easily permeate the membrane

Answer 34

small + Fat soluble molecule (O2)

Question 35

What are the two forces required to move a molecule across its gradient?

Answer 35

Passive force and active force

Question 36

What are passive forces?

Answer 36

Does not require the cell to use energy

Question 37

What are active forces?

Answer 37

Requires the cell to use energy