Biochemistry - Cell Connections

Question 1

Structure and function of plasmodesmata in plant cells

Answer 1

• Places where a hole is punched in cell wall to allow direct cytoplasmic exchange between 2 cells
• Linked with plasma membranes that are continuous with the membranes of the two cells
• Has a thread of cytoplasm extending through it, containing an even thinner thread of E.R.

Question 2

Role of connexons in gap junctions in animal cells

Answer 2

• Gap junctions: channels between neighbouring animal cells that allow for transport of ions, water, + other substances
• Connexon: elongated donut-like structure made up of a set of six membrane proteins called connexins
• When the pores align, a channel forms between cells

Question 3

Role of claudins in tight junctions in animal cells

Answer 3

• Tight junctions: watertight seal between 2 adjacent animal cells
• Claudins hold cells tightly against each other
• Claudins: individual groups of tight junction proteins that interact with a partner group on opposite cell membranes
• Groups of claudins are arranged into strands, forming branching networks with larger numbers of strands for a tighter seal

Question 4

Importance of tight junctions

Answer 4

• Keeping liquid from escaping between cells
• Allow a layer of cells (e.g. those lining an organ) to act as an impenetrable barrier

Question 5

Role of cadherins and cytoplasmic plaque in desmosome formation

Answer 5

• Cadherins: specialized adhesion proteins found on membranes of both cells that interact in the space between them, holding membranes together
• Inside cell, cadherins attach to cytoplasmic plaque which connects to the intermediate filaments (part of cytoskeleton) + helps anchor the junction

Question 6

Example of tissue containing desmosomes (+ importance)

Answer 6

• Skin, cardiac muscle
• Desmosomes pin adjacent cells together, ensuring cells remain connected in an unbroken sheet in tissues that stretch