W4 Cell Biology 2 - Julia Potter

Question 1

What is the cytoskeleton and what are its functions?

Answer 1

The cytoskeleton is an intracellular network of microfilaments and microtubules, which comprises at least 20-35% of all cellular protein.
It functions to maintain cellular shape, to provide intracellular motility such as movement of chromosomes for cell division, organelle translocation and cytoplasmic streaming, as well as cellular locomotion.

Question 2

What are the three types of microfilaments?

Answer 2

Thin, intermediate, and thick.

Question 3

What are thin filaments?

Answer 3

Filaments that are 6-8nm in diameter.
The backbone is made of actin. In many cells there is a layer of actin immediately below the plasmalemma, called the ectoplasm, which gives support to the membrain.
Actin is often associated with other proteins, such as tropomyosin, the Z-disc of striated muscle, or bundled such as in the core of microvilli.

Question 4

What are immediate filaments?

Answer 4

Filaments that are 10 nm in diameter.
Divided into two categories:
1. Members of the same family found in various cells, such as lamins which from internal lamina of cell nuclei.
2. tissue specific such as keratins which are abundant in epithelial cells.

Question 5

What are thick filaments?

Answer 5

Diameter >10 nm but variable on location.

Filaments contain myosin and are essential for movement and motility, which is accomplished by interacting with actin.

Question 6

What are microtubules?

Answer 6

Hollow cylinders of ~25 nm diameter and variable length.
Composed of protein called tubulin.
Tubulin exists in two forms which polymerise into 13 proto-filaments to create a microtubule.
Examples include centrioles and mitotic spindle of dividing cells, movement in cilia and flagella.

Question 7

What are the various types of cellular motion?

Answer 7

1. Cilia - function to continuously beat in synchronicity on surfaces of respiratory tract and fallopian tubes for movement of mucus.
2. Flagellum of spermatozoa - movement by oscillatory cycle to function in reproduction.
3. pseudopodia - an outward projection of cell probes desired direction and cytoplasm follows to move cell, such as WBCs.
4. Muscle cell movement.

Question 8

What are the various ways of movement into/out of a cell?

Answer 8

1. diffusion
2. carrier proteins.
3. channel proteins.
4. membrane invagination:
   a) pinocytosis = cell drinking; and is constitutive for incorporating water and solutes
   b) endocytosis = receptor-mediated, dependent on clathrin pits, involved for iron-transferrin, lipoproteins, growth factors, immunoglobulins.
   c) phagocytosis = cell eating; for ingestion of cell debris and bacteria
   d) exocytosis; particularly for cells that have secretory function

Question 9

How is the movement of vesicles governed in cells?

Answer 9

If from the Golgi, movement is governed by proteins called coatomeres.
If from endocytosis, movement is governed by a system of proteins called snare.