What are the three fundamental needs for cell motility?
Energy, guidance, and mechanical interaction with an external substance.
What are the two major mechanisms of cell migration, and what cytoskeletal components do they use?
Swimming uses microtubules, while crawling uses actin microfilaments.
What is the primary function of microtubule-based motility?
To enable cells or fluid to move through a liquid, also known as ‘swimming’.
Name two types of cellular structures responsible for microtubule-based motility.
Cilia and flagella.
What is the function of flagella in individual cells like protozoa and sperm?
They are used to propel the entire cell through a liquid.
How do cilia facilitate movement in stationary cells, such as those in the respiratory tract?
They waft liquid along the cell surface, moving the liquid rather than the cell.
What protein are both cilia and flagella primarily made of?
They are both made of microtubules, which are composed of tubulin.
What is the major functional structure within both cilia and flagella?
The axoneme.
Describe the microtubule arrangement within an axoneme.
It has a ‘9+2’ assembly, consisting of nine outer doublets and two inner single microtubules.
The outer doublets of an axoneme are composed of a complete ‘A’ fibre and an incomplete ‘B’ fibre. How many protofilaments does each have?
The ‘A’ fibre has 13 protofilaments, and the incomplete ‘B’ fibre has 10.
What is the name of the motor proteins bound to the microtubule doublets in an axoneme?
Dynein.
How does dynein cause the bending motion in cilia and flagella?
Dynein arms on one doublet ‘walk’ along the adjacent doublet, causing them to slide, which results in a bend because the doublets are tethered at their base.
What energy source is required for the sliding motion of dynein in the axoneme?
ATP is required.
Describe the characteristic waveform of cilia.
Cilia exhibit a power stroke motion followed by a bending recovery stroke.
Which dynein arms are primarily responsible for generating the power of the ciliary beat?
The outer dynein arms.
Which dynein arms are primarily responsible for regulating the waveform of the ciliary beat?
The inner dynein arms.
What is the function of nexin crosslinkers within the axoneme?
They are linking proteins that connect microtubule doublets to each other to facilitate the bending motion.
What structure anchors the axoneme of a cilium or flagellum to the cell’s cytoskeleton?
The basal body.
A basal body has the same structure as a _____, which is a key component of the centrosome.
centriole
What is the microtubule arrangement within a basal body or centriole?
It is a ‘9x3’ array, meaning nine triplets of microtubules with no central pair.
What is the primary function of the centrosome in a cell?
It acts as the main microtubule organising centre (MTOC), from which microtubules sprout.
Actin-based motility is driven by motor proteins and a process known as _____.
turnover or ‘treadmilling’
What is the microfilament motor protein associated with actin-based motility?
Myosin.
In the myosin power stroke, what molecule binds to the troponin-tropomyosin complex to expose the myosin-binding sites on actin?
Calcium ($Ca^{2+}$).
