Cell Junction

Question 1

What are cell junctions/intercellular bridges?

Answer 1

Cell junctions (or intercellular bridges) are a class of cellular structures consisting of multiprotein complexes that provide contact or adhesion between neighboring cells or between a cell and the extracellular matrix in animals.

Question 2

Types of cell junctions?

Answer 2

1. occluding/tight junctions
2. communication/gap junctions
3. anchoring junction

Question 3

1. what are occluding/tight junctions?
2. what are gap junctions?
3. what are anchoring junctions?

Answer 3

1. occluding junctions: are junction that regulate the movement of solutes and water between epithelial layers.
2. gap junctions: allow for direct chemical communication between adjacent cellular cytoplasm through diffusion without contact with the extracellular fluid.
3. anchoring junctions: junctions that anchor cell to cell or cells to ECM.

Question 4

• There have been approximately 40 proteins identified to be involved in tight junctions.
they are classified into 4 classes/ types. what are the classes and their corresponding functions?

Answer 4

1. scaffolding proteins- organize transmembrane proteins
2. signaling proteins- involves in barrier regulation, and gene transcription
3. regulatory proteins- regulate membrane vesicle targeting
4. transmembrane proteins- such as occludin, and claudin. claudin is the protein molecule responsible for the selective permeability between epithelial layers.

Question 5

types of occluding/tight junction?

Answer 5

1. bicellular tight junction

2. tricellular tight junction

Question 6

types of anchoring junctions?

Answer 6

1. desmosomes: anchor cell to another cell.
2. hemidesmosomes: Anchorcells to ECM.
3. adheren: anchor cells to both other cells and ECM.

Question 7

mention the role of each of the types of anchoring junction

Answer 7

1.	Desmosomes: anchor cell to cell
Also known as macula adherens 
2.	Hemidesmosomes: anchor cell to ECM
Also known as integrin adhesomes
3.	Adheren: Anchor to both ECM and cells to cell.

Question 8

a

Answer 8

a

Question 9

a

Answer 9

a

Question 10

Adherens junctions are specialized cell junctions that form by linking the __________ to transmembrane proteins known as __________.

Answer 10

D. actin cytoskeleton . . . cadherins

Question 11

Adherens junctions are specialized cell junctions that form by linking the __________ to transmembrane proteins known as __________.

Answer 11

D. actin cytoskeleton . . . cadherins

Adherens junctions are formed by linking the actin cytoskeleton to transmembrane proteins known as cadherins. Cadherins are capable of interacting with other cadherins from neighboring cells on the exoplasmic face of the cell membrane. This interaction forms a physical link essentially connecting the actin cytoskeletons of the two adjacent cells, thus promoting force transduction.
Desmosomes are another type of cell junction that link the intermediate filaments of the cytoskeleton to cadherins.

Question 12

Which of the following cell junctions is involved with anchoring the extracellular matrix to the cell?

I. Adherens junctions
II. Desmosomes
III. Hemidesmosomes
IV. Gap junctions

Answer 12

Adherens junctions and Hemidesmosomes

Of the choices, only adherens junctions and hemidesmosomes are responsible for anchoring the extracellular matrix. This is accomplished by associating the actin cytoskeleton (for adherens junctions) or the intermediate filament cytoskeleton (for hemidesmosomes) with transmembrane proteins known as integrins. Integrins interact with the extracellular matrix.
Desmosomes are responsible for anchoring adjacent cells to one another by connecting their intermediate filament cytoskeletons with cadherins. Gap junctions connect the cytoplasm of adjacent cells and allow the free flow of small molecules between them.

Question 13

Which of the following statements is NOT TRUE about gap junctions?
Possible Answers:
A. Gap junctions have some functionality of permitting cells to adhere to one another.
B. Gap junctions permit the travel of small molecules back and forth between adjacent cells.
C. Gap junctions form channels that are comprised of connexin proteins.
D. Gap junctions contribute to electrical coupling of adjacent cells.
E. Gap junctions prevent molecules and ions from traveling between cells in the extracellular space.

Answer 13

F. Gap junctions prevent molecules and ions from traveling between cells in the extracellular space.

“Gap junctions prevent molecules and ions from traveling between cells in the extracellular space” is incorrect because this describes the function of tight junctions. Gap junctions electrically couple two cells by permitting the formation of small channels that connect two cells.

Question 14

Which of the following proteins forms channels that permit electrical communication between cells across gap junctions?

Answer 14

C. Connexin

Explanation:
Most of the other proteins listed are structural, but do not form any kind of pore or channel through which an electrical message can cross. Connexins are required for this function of gap junctions.

Question 15

What are the two major proteins that comprise tight junctions, cellular junctions that prevent fluids from traveling between cells and generally contribute to morphology by holding cells together?

Answer 15

E.Claudins and occludins

Explanation:
While each of the proteins listed contributes to cell structure and function, the tight junction requires claudins and occludins to anchor the cytoskeleton of two adjacent cells to one another. These are the primary structural components of tight junctions.

Question 16

What is the main purpose of gap junctions?

Answer 16

A. Allows molecules and ions to travel between cells

Explanation:
Gap junctions can be thought of as small tunnels between cells. They allow for the immediate transport of ions and molecules between the cells. Gap junctions are prominent in cardiac myocytes, and help spread action potentials via electrical synapses to coordinate the contraction of the heart.

Question 17

Which cellular junction will be most useful in preventing the movement of material between cell membranes?

Answer 17

C. Tight junctions

Explanation:
The movement of substances between cells is most commonly controlled by tight junctions. These junctions can be regulated, which can alter how strongly they resist the movement of material between cells, like those in the digestive tract during absorption.

Question 18

In communicating junctions, we have two categories. State them, any location in body, and their dissimilarities.

Answer 18

We have two types of communicating junctions which include Gap junctions and Chemical synapse.
Gap junctions are found throughout the body. This includes epithelia, which are the coverings of body surfaces, as well as nerves, cardiac (heart) muscle, and smooth muscle (such as that of intestines).
Chemical synapse is only located between axonal and dendritic processes of neurons.
Their dissimilarities are as follows:
Gap junction

➢ There is no synaptic cleft except channels between two adjacent cells.
➢ When it is in nervous system, It involves use of ions for nerve impulse transmission.
➢ Apart from neurons, it is also found in between other adjacent cells such as cardiac muscle fibre, smooth muscle fibre and epithelia.

Chemical synapse
➢ There is synaptic cleft between adjacent cells.
➢ It involves use of chemical messenger for transmission of action potential.
➢ It only occurs between adjacent neurons.

Question 19

In communicating junctions, we have two categories. State them, any location in the body, and their dissimilarities.

Answer 19

We have two types of communicating junctions which include Gap junctions and Chemical synapses.
Gap junctions are found throughout the body. This includes epithelia, which are the coverings of body surfaces, as well as nerves, cardiac (heart) muscle, and smooth muscle (such as the intestines).
Chemical synapse is only located between axonal and dendritic processes of neurons.

Gap junction
 There is no synaptic cleft except channels between two adjacent cells.
 When it is in the nervous system, It involves the use of ions for nerve impulse transmission.
 Apart from neurons, it is also found in between other adjacent cells such as cardiac muscle fiber, smooth muscle fiber, and epithelia.

Chemical synapse
 There is a synaptic cleft between adjacent cells.
 It involves the use of a chemical messenger for transmission of the action potential.
 It only occurs between adjacent neurons.