Cilia / flagella Flashcards
Are cilia and flagella the same structure?
Yes - used interchangeably. 1/2 tends to be flagella, many tends to be cilia.
Where are centrioles?
In the centre of the centrosome.
What is chlamydomonas?
Green algal model organism very similar to yeast. Helped us understand how cilia form.
What are motile cilia used for?
Body patterning.
What are non-motile cilia used for?
Sensing.
What are ciliopathies?
Diseases involving defective cilia.
What did Theodor Boveri (cell biology pioneer) say?
Centrosome (and centrioles within) is the true division organ of the cell.
What is the structure of centrioles?
Highly organised microtubule cylinders (9 triplets of MTs) (radially symmetric). There are 2 per centrosome, organised at right angles to each other.
How often do centrioles replicate?
Once per cell cycle. Cells must inherit 1 centriole (2 orthogonal MT cylinders).
What is the function of a centriole?
Forms the base of cilia / flagella.
How do we know the centrioles are not involved in cell division?
- MT nucleation (making spindles / segregating chromosomes) is in the PCM.
- Centriole destruction does not inhibit cell division.
- Higher plants and some animals don’t have centrioles.
- Drosophila don’t need centrioles to develop into a mature fly (KO experiment).
What problems did develop in the centrioleless Drosophila?
Severe issues where cilia function was required (sperm cells or sensory neurons).
Why do we think centrioles are present in centrosomes?
They are hitchiking on existing segregation machinery so that the centrioles are always present in both daughter cells.
What is the difference between cilia and flagella?
- Number on a cell
- Beat pattern
- Frequency of beats
What are cilia / flagella?
MT extensions of the centriole.
What is the structure of cilia / flagella?
Highly organised microtubule cylinders (9 doublets of MTs) (radially symmetric). Also 2 central independent MTs. ‘9 + 2 MT organisation’. Continuations of 2/3 of the centriole MTs.
What beat pattern do flagella have?
Beating side to side like a fish swimming (faster).
What beat pattern do cilia have?
A stroking pattern (slower), in coordination with other cilia.
Where are motile 9 + 2 ciliated cells found?
- Respiratory tract
- Cerebrospinal fluid (cortex)
- Female reproductive tract (fallopian tubes)
- Sperm cells
What do cilia do?
- Move fluid (or eggs)
- Move cells within fluid
- Sense
How do the cilia beat?
Dynein proteins connect the adjacent doublet MTs. They move the doublet along the neighbouring doublet, causing the cilia to bend. It bends until it can’t go further, then snaps back.
Where are motile 9 + 0 ciliated cells found?
- Embryo (nodal cilia)
Where are non-motile 9 + 2 ciliated cells found?
- Inner ear (kinocilium)
Where are non-motile 9 + 0 ciliated cells found? (SENSORY)
- Kidney
- Bile duct
- Pancreas
- Bone / cartilage
- Eye (rod cells)
- Nose (olfactory neurons)
What properties of chlamydomonas make it useful for study?
- Simple genetics
- Can KO genes
- Has chloroplasts so photosynthesises
- Has 2 cilia giving it motility
- Has eyespot causing negative phototaxis
What have centrioles previously been known as?
Basal bodies (base of flagella).
What did study of chlamydomonas reveal about centrioles?
- How they are built
- How they are dynamic
Are cilia proteins synthesised in the cilia?
No (no ribosomes) - they are transported to it from a different site in the cell.
What is the size of cilia?
Very small.
How was it discovered that cilia are dynamic?
One chlamydomonas cilium was cut off - it grew back and the other one shrank to meet it. Then they both grew back together.
What is happening when the cilia are at a steady state?
Turnover - tubulin subunits being added and removed.
Where does growth of cilia occur?
Tips, not base.