Flashcards in exam 3b Lecture 30 Cilia Deck (54):
What are the two kinds of cilia?
Motile cilia and nonmotile cilia
What type of cilia do most cells have?
Which type of cilia is highly conserved?
Motile cilia and flagella
What do nonmotile cilia do?
What cells are ciliated with nonmotile cilia? What cells are not ciliated?
Almost all kinds of cells are ciliated. Blood cells and fat cells are not ciliated.
What are flagella for eukaryotes? Prokaryotes?
For eukaryotes, flagella are cilia. Same thing. For prokaryotes, flagella are not cilia.
How are eukaryotic flagella and prokaryotic flagella different?
Eukaryotic flagella contain hundreds of proteins. Prokaryotic flagella contain a single major protein.
What does motility of prokaryotic flagella result from? Eukaryotic flagella?
Prokaryotic flagella motility results from rotation of a rotor complex driven by flow of protons. Eukaryotic motility relies on motor proteins.
What drives ciliary motility?
How is dynein associated with cilium?
Dynein arms are permanently attached to A tubule.
What is the A tubule of a cilium?
The cargo of the dynein arm.
How do dyneins walk? What do they depend on?
They walk along B tubule of adjacent doublet in an ATP-dependent manner.
What is an axoneme?
The structural core of the cilium.
Structure of the axoneme.
Let’s look at the cross section. In the middle, there are two central singlet microtubules connected to each other. They are surrounded by an inner sheath. Radial spokes jut out from inner sheath and connect with outer doublet microtubule.
What makes up the outer doublet microtubule?
An A microtubule and a B microtubule. The A tubule is cargo of the dynein arm.
How are outer doublet microtubules connected to radial spokes and to each other?
Radial spokes are connected to the A microtubule. Nexin proteins connect the doublet microtubules to each other.
How are dynein arms attached to A tubule?
There is an inner dynein arm alongside the nexin and an outer dynein arm faced towards the plasma membrane.
How many microtubules are in a cilium?
Nine doublets and two central singlet microtubules.
How do we prove role of axonemal dynein in motility in vitro?
We can take isolated axonemes (demembranated cilia) in vitro. Without ATP, they remain immotile. With ATP there is a beat with frequency and wave from seen in intact cells.
What happens when cilia lose outer dynein arms via high-salt extraction or mutation?
This results in reduced beat frequency but no change in wave form because wave form is conferred by inner dynein arms.
On sliding, what causes two microtubule doublets to slide apart?
Ciliary dynein drive the sliding.
If you have isolated axonemes and you treat them with ATP plus light protease, what happens? Why use light protease?
This results in doublet sliding driven by dynein arms. Light protease was used to break links between tubules but not affect arms.
If you have isolated axonemes and you treat them with ATP alone, what happens?
This leads to axonemal beating as doublet sliding is converted to bending.
Mechanism of motility of cilia.
The dynein arms connect to minus end of adjacent doublet. The sliding converts to bending because of cross-links keeping doublets together.
How do the radial spokes and the central apparatus of the cilium work?
The central apparatus rotates during beat cycle. It may act as a distributor, signaling through radial spokes to activate sequentially specific sets of dynein arms.
How does central apparatus make ciliary beat pattern?
The central apparatus may use radial spokes to activate specific sets of dynein arms around circumference of axoneme and along the length of the axoneme.
How is primary ciliary dyskenisia related to motile cilia?
This human disease has symptoms of impaired mucus clearance from the lungs, and can cause male and female infertility. Due to cilia immotility.
What is Kartagener syndrome, or situs inversus?
Random left-right asymmetry. Individuals with this condition have the heart on the right side. Normal arrangement of organs – apex of heart on left side.
How is Kartagener syndrome (situs inversus) related to motile cilia?
This arrangement depends on motile cilia that develop early in the node region (200 cells). The cells have a single cilium. The cilia beat to propel signals molecule in the TGF-beta family to the left side. This asymmetry leads to normal organ asymmetry.
What role do nonmotile cilia usually have?
How do nonmotile cilia work in olfactory sensory neurons?
These modified cilia display olfactory receptor proteins on plasma membrane. The receptors are G protein coubled. Their ligands are smell molecules and signals are sent to brain.
How do nonmotile cilia work in retinal rod cells?
The outer segment of these cells is a specialized primary cilium. The cilia are near the pigmented epithelial cells. A cilium connects the outer and inner segment of the cell. In the inner segment there is protein synthesis. In the outer segment, discs of photoreceptive membranes. These cells phagocytose and shed outer segment often.
What do defects in connecting cilium of retinal rod cell cause?
What are ciliopathies.
Disease related to loss of cilia or loss of signaling proteins on cilia.
How do primary cilia act on cells?
As flag poles or antennae. They have receptor molecules on membranes.
What do signals gathered by primary cilia accomplish?
They use a number of signaling pathways to transmit info to cell body that results in changes to cytoskeleton, cell division, etc…
What is polycystic kidney disease (PKD)?
The primary cilium on kidney epithelial cells senses fluid flow over the cell surface. A signaling pathway controls cell division in the organ. PKD results from defects in cilium assembly (IFT defects) or in receptor proteins on the ciliary membrane.
How do kidneys respond to PKD?
With hypoproliferation. Large cysts of cells are formed that block organ function.
What is Intraflagellar transport (IFT)? Does motility matter?
Movement of materials from centriole to tip of cilium (anterograde) and from tip to centriole (retrograde). Motility does not matter.
What motors carry out anterograde transport? Retrograde transport.
Kinesin motors carry out anterograde transport. Cytoplasmic dynein motors carry cargo from tip to base.
As organelles grow out, how are materials acquired to make assembly and growth possible?
Some materials diffuse. Others are transported, which is basis of IFT.
What are rafts in IFT?
Rafts are formed by oligomerization of IFT particles. They include assembly components and are transported by kinesin II along doublets of microtubules.
What motor transports rafts in IFT?
How do materials come back to centriole from tip of cilium in IFT?
The rafts dissociate into smaller oligomers of IFT particles and are returned to the base of the flagellum by cytoplasmic dynein, which moves to the minus end.
To which polarity does cytoplasmic dynein travel?
The minus end.
Where is growth of cilia nucleated?
From a centriole located in the cell body.
What is a centriole?
A basal body. Part of the centrosome in animal cells.
What covers the core of the cilium?
An extension of the plasma membrane.
What is the structure of a cross sectioned centriole?
It has nine sets of triplet microtubules. The triplet is made of an A, B and C microtubule.
How do cilium doublets grow?
They extend from A and B tubules in centriole.
What is the center of ciliary growth in animal cells?
Where is pericentriolar material found in animal cells?
In the centrosome.
Where is centrosome located?
Centrosomes are located near nucleus.