9.1 Cilia

Question 1

What is the similarities and differences between flagella and celia?

Answer 1

• both structures are motile organelles that move b/c of the activity of microtubule based motor proteins.
• movement differs between the two.

-Cilia are short and move in a asymmetric beating manner. It moves differently from right to leg than it does from left to right. The effect of this movement is to force fluid around the cell from right to left or left to right. As the cilia returns to its resting position, it bends to present a smaller profile to the fluid surrounding the cell and as a result, it exerts more force moving from right to left than it does moving left to right. Notice that the force is produced perpendicular to the axis of the cilia when it’s in its resting position. This makes cilia useful for
directional movement of fluid layers, such as is needed in airway epithelia and reproductive
tracts.

-flagella move in a symmetrical undulating manner. As a result this organelle would generate a propulsion force that would be parallel to the axis of the flagellum.

Question 2

What is the structure of mammalian cilia?

Answer 2

Mammalian cilia are plasma membrane-bound cell protrusions supported by a complex
microtubule structure called an axoneme.
 Cilia contain 9 outer doublets of microtubules and 1 inner doublet in an arrangement
known as the 9+2 configuration.
 One of each outer doublet is a complete microtubule (designated “A”) and bears dynein
arms. The other is incomplete (designated “B”).
 The inner doublet is surrounded by a protein dense sheath.
 Outer doublet microtubules are linked to the central sheath by spoke proteins and to each
other by a link made of the protein “nexin”.

Question 3

What is the 9+2 configuration in mammalian celium?

Answer 3

The most obvious feature in cilia are 9 outer doublet circles

The two microtubules are not equal. One is a complete circle (A microtubule) and the other is a half/incomplete circle (B microtubule).

The A microtubule has motor proteins (dynein) that looks like two dark regions of fuzzy electron dense material near the adjacent B microtubule.

In the center of the cilia are 2 central singlet microtubules.

This forms the 9+2 configuration.

Question 4

What motor protein produces movement in cilia and flagella?

Answer 4

Dynein - a minus end directed microtubule motor

Question 5

In cilia, what are spoke proteins?

Answer 5

a series of radial proteins that hold the outer doublets circles together in relation to inner pair of single microtubules

Question 6

In cilia, what is the nexiin protein?

Answer 6

it holds the microtubule doublets in register with each other

Question 7

What the sheat proteins in cilia?

Answer 7

ha layer of fibrous protein that wraps the inner two single microtubules in cilia.

Question 8

What is a basal body?

Answer 8

a specialized structure found at the base of the cilia where cilia attach to the cell surface.

The role of the basal body is to provide mechanical anchor for the cilium.

Question 9

How does the basal body anchor into the cell surface?

Answer 9

By a dense network of actin and other cytoskeletal filaments.

Also, within the basal body is a centriole, that plays a role in the nucleation of microtubules found in the cilia

Question 10

What is the centriole in the basal body made up of ?

Answer 10

centriole is made up of a circular array of microtubules. Some of the microtubules act as nucleation sites for the microtubules found in the attached cilium

Question 11

What are the similarities and differences between axonemes and centrioles?

Answer 11

SIMILARITIES: Both centrioles and axonemes are made up of a circular array of microtubules.

DIFFERENCES: In cilia, the outer nine arrays are doublets. in centrioles the outer nine arrays of microtubules are triplets. ( A, B, and C microtubules). C microtubules are found only in Centrioles. Centrioles also do not contain the the inner pair of single microtubules. Centrioles also lack dyneins (aka it is not motile)

Question 12

Why are the minus ends of ciliary microtubules close to the cell? Where is the plus end?

Answer 12

Microtubules in cilia are nucleated by basal bodies that are found at the site of attachment to the cell and this is why minus end are close to the cell. The plus ends of these microtubules are farthest away from the cell.

Question 13

How are dynein motor proteins attached to microtubules in cilia?

Answer 13

The tail domains are attached to the lattice of the A microtubule and the motor heads are free to interact w/the neighboring microtubule doublet.

Ciliary dynein is specialized to produce microtubule sliding by anchoring its tail to the “A”
microtubule

Question 14

Why does cilia need many dynein motors?

Answer 14

In order to move effectively. Microtubule motor proteins are not as strong as myosins, which is why cilia needs many dynein to help it move.

Question 15

How do microtubule motor proteins make a cilia bend?

Answer 15

Attaching microtubule doublets together w/in the nexin fibers means that microtubules can’t slide past each other very far. The action of motor proteins is then translated into a bending motion instead of a sliding motion.

Question 16

What would happen if the microtubule doublets in a cilia were free to move relative to each other?

Answer 16

The action of dyneins on an A microtubule would slide the adjacent B microtubule towards its plus end, as the motor proteins tried to reach the B microtubule’s end. (aka microtubule sliding during mitosis). Needs ATP to slide.

Question 17

What are chlamydomonaas? Why are they important in cilia?

Answer 17

Chlamydomonas is an alga, which means it is photosynthetic and it has two flagella. It also undergoes a life cycle that includes sexual reproduction and it is possible to study cilia in chlamydomonas using genetic approaches

it is so important b/c much of what is known about the development of cilia come from the study of chlamydomonas.

Question 18

what happens when two chlamydomonas with different

tubulin fusion proteins are mated?

Answer 18

1) The four cilia initially retain the tubulin subunits that were
present in the original, separated cells.

2)within a short time, new subunits are added to the cilia

3he new subunits are added at the end of the cilia
that is farthest from the cell.

this makes sense, because
the far end is where the plus ends of the microtubules are, and so that should make sense based
on our discussion of how microtubules grow in general.

Question 19

how do the
subunits for new growth get to the far end of the cilia, since they have to move from the cell,
down the very narrow cilium, which is already crowded with structural proteins?

Answer 19

By Kinesin!

these subunits are actively transported to the end of the cilia by another set of microtubule
motors. Since the motors are carrying material towards the plus ends of the ciliary microtubules,
you should recognize that these are going to be kinesin motors, and so dyneins generate force
and cilia that results in movement of the cilia and kinesins play an important role in the
maintenance and growth of cilia and flagella.

Question 20

What is required for maintenance of cilia?

Answer 20

Kinesin-dependent movement of ciliary subunits to the plus end is required for
maintenance of cilia.

Question 21

What are the functional significance of cilia and flagella?

Answer 21

Cilia and flagella are involved in airway maintenance and are required for function of
male gametes (sperm) and movement of gametes in both the male and female
reproductive tracts.

-male gametes are non-motile at some stages of their development and have to be passively
moved through the male reproductive tract. That movement is produced by cells lining the
reproductive tract that have cilia. Cilia clear debris from the upper respiratory tract. Toxins (such as those found in tobacco
smoke) can paralyze cilia in respiratory and reproductive systems

-The female reproductive system also has regions containing ciliated cells that are important for
fertility. Ovulation releases an egg cell into a space that is normally surrounded by a bell-shaped
extension of the fallopian tube, that’s called the infundibulum. The cells of the infundibulum and
fallopian tube are ciliated and the action of the cilia creates a current of fluid that helps to move
the egg.

Question 22

What does paralysis of cilia cause in reproduction system?

Answer 22

reproductive problems such as infertility and ectopic pregnancies.

Question 23

Why is it not surprising that smoking is associated with fertility problems?

Answer 23

Toxins found in tobacco smoke can paralyze cilia in respiratory and reproductive systems.

Question 24

How can human genetic disorders affect cilia?

Answer 24

it can affect components of cilia such as having cilium that lacks both inner and outer dynein arms. Or defect in the production of just the inner dynein arm.

AKA it can impair movement of cilia.

Individuals w/ these genetic defects suffer from chronic upper airway disorders and often have low fertility

Question 25

What is Kartagener’s syndrome?

Answer 25

a disorder affecting the movement of cilia. Patient with this have their heart on the right side of their body (instead of the left as normal)

-this syndrome is caused by small clumps of cells in the developing embryo that produces a circular cluster of cilia.The movement of these cilia transport signaling compounds that are
important for development and concentrates them on one side of the body axis. If these cilia are paralyzed, the structures develop randomly with regard to the body axis.

Question 26

What are single immotile cilia (primary cilia)

Answer 26

produced by cells of the body and play role in sensory, such as mechanical and chemical sensing.

Ex: kidney epithelial cells produce primary cilium and the cilium plays an important role in allowing the cell to detect and respond to the movement of surrounding fluid.

Question 27

What is polycystic kidney disease? how is it caused?

Answer 27

CAUSED: by defects in primary cilia (single immotile cilia)

• In patients with this disease, the cells lining the kidney tubules have a defect in a protein called polycistin, which is a calcium channel that opens when the cilium bends in response to fluid flow.
• in the absence of this signal, the cells lining kidney tubules remain in an immature state where they reproduce rapidly and develop cysts.