Lecture 10 Flashcards
1
Q
What is the function of the cytoskeleton?
A
- Maintaining cell shape
- Forming cell adhesion
- Assisting in cellular movement
2
Q
What is the 3 dimensional system of tubular and filamentous structures that makes up the cytoskeleton?
A
- Microtubules
- Microfilaments
- Intermediate filaments
3
Q
Structure of microtubules?
A
- Composed of two different tubulin monomers (alpha and beta tubulin)
- Microtubules will self assemble in vitro when these two monomers bond together to form a dimer
- Then the next step is called nucleation. It is when several of these dimers bind together, forming a hollow ring called the microtubule seed
- The dimers align so all of the alpha tubule tails are on one side called the minus end, and all of the beta tubule heads are on the other side called the plus end
- They are rigid and are the thickest filament
4
Q
Function of microtubules?
A
- They form the axoneme of the cilium and flagellum
- They form the components of the centrioles
- They also form the spindle fibres of cell division
- Associated with intracellular movement in the axons of nerve cells
5
Q
Structure of microfilaments?
A
- Also known as Actin filaments
- Found in the cytoplasm
- Largely composed of the protein actin
- Many actin molecules will join together to form actin polymers
- Actin polymers will twist around each other to form an actin filament
- They are found in most animal cells and in some plant cells
- They are concentrated in networks or bundles just below the plasma membrane
- They are dynamic (can lengthen-actin polymerisation and shorten-actin depolymerisation very frequently)
6
Q
Function of microfilaments?
A
- Mainly involved in the gross movement of the cell
- Intestinal microvilli are produced by the microfilaments
7
Q
Structure of intermediate filaments?
A
- Heterogeneous in composition (Any given cell will have more than one type
One type of filament usually predominates) - Size is in between actin filaments and microtubules
- This is a separate system of rope-like filaments found in most cells
- Non-alpha-helical (globular) domain at the N and C-termini which surrounds the alpha-helical rod domain.
- Basic building block is parallel dimer.
- Dimer is formed through interaction of the rod domain to form a coiled coil
8
Q
Five main types of intermediate filaments?
A
- Type I & II- keratins divided into acidic and basic types
- Type III - vimentin-like proteins, found in cells of mesodermal origin
- Type IV - neurofilaments, found in nerve axons
- Type V - nuclear lamins - forming the nuclear lamina
9
Q
Explain the role of centrioles in cell division and centrosome formation.
A
- Prior to cell division the centrioles replicate and move to the opposite poles of the cell
- Most cells’ centrioles duplicate by the growth of new daughter centriole at right angles to the ‘old’ centriole
- One new centriole and one old centriole form areas known as centrosomes
10
Q
Describe the microtubular structure of centrioles in the animal cell.
A
- Usually found as two cylindrical structures at right angles to one another,
- Typically one pair per cell during interphase
- Composed of 9 sets of triplets arranged as a cylinder - The protein that forms this is called Tubulin)
- Called a 9x3 structure (9+0 structure) of microtubules. There are 9 tubule fibres around the outside of the centriole, and each of them has 3 proteins in it.
11
Q
Centrioles?
A
- Characteristically found in all animal cells and ciliated plant cells
- Usually found in the cytoplasm in an area near the nucleus
- Often associated with the Golgi apparatus
- This area is called the Microtubule Organizing Centre
12
Q
Show the origin of the microtubular spindle fibres from y-tubulin rings in the centrosome.
A
- Microtubules originate from y-tubulin rings in the centrosomal matrix (Distal appendages) not from the centrioles
- Each y-tubulin ring serves as the nucleation site (starting point) for one microtubule
- An aster of microtubules (fibres) extends to form the visible spindle fibres of cell division
- Some spindle fibres bind to the chromosomes at the centromere
13
Q
Explain the significance of the intercellular junctions noting the three main types.
A
- Most cells in tissues are attached to other cells
- The cells in tissues are separated by an intercellular space of between 20-30nm wide, but in some areas of specialised intercellular junction more direct contact is maintained between adjacent parts of the two membranes
Three main types:
- Adhering (Anchoring) Junctions
- Tight Junctions
- Gap Junctions
14
Q
Describe the structure and function of the adhering junctions.
A
Structure:
- The intercellular space is normal, but filled with transmembrane proteins called cadherins
- Adhering: The cadherin attachment is via linker proteins to actin microfilaments in the cytoplasm.
- Desmosomes: disc-like plaques in cytoplasm
Function:
- Principal mechanical interlinks between cells
- Strong junctions that tightly bind adjacent epithelial cells, such as those found in outer layer of mammalian skin
- Serve as a bridge connecting the actin cytoskeleton of neighbouring cells through direct interaction
15
Q
Recall the clinical condition of pemphigus vulgaris which involves the desmosomes.
A
- Pemphigus vulgaris is an autoimmune, intraepithelial, blistering disease affecting the skin and mucous membranes.
- Autoantibodies target proteins of the desmosome leading to disruption of cell adhesion.
- Adjacent layers of the skin can pull apart and allow abnormal movements of fluid within the skin, resulting in blisters and other tissue damage.
