Cell Bio lec 10

Motile systems

– Chromosome movement along mitotic spindle
– trafficking of RNAs, protein complexes, and vesicles using MT and MF

1. Subcellular level

Motile systems

– ciliated protozoa: cilia
– motile sperm: flagella

– actin-dependent cell migration & amoeboid
movement

2. cellular systems

Motile system

• muscle contraction

tissue level

Microtubule-based subcellular movement

Motility uses _____ conversion of chemical energy to
mechanical energy

energy,

Microtubule-based subcellular movement

ATP hydrolysis ——>

conformational change

Microtubule-based subcellular movement

Motor proteins or _________ – interact with cytoskeleton to produce motion at ______level

mechanoenzymes; molecular

Fast axonal transport

transport of ______/_________ (inside vesicles) produced in the cell body to nerve ending via fast axonal
transport

proteins/neurotransmitters

In nerve cells, kenisins mediate transport from the cell body
down the axon towards the____ ______

called. “ __________ axonal transport”

transport molecules toward ____ end of microtubules

nerve ending ; anterograde; plus

Dynein

particles are moved in _____ direction

called “_____ axonal transport

transport moleculed toward ____ end of microtubules

opposite;retrograde;minus

Walk” along MTs

– from cell body towards nerve ending
– RNAs, multiprotein complexes and membranous organelles

Kinesins

walk back towards cell body

Cytoplasmic dyneins

Cytoplasmic dyneins – associate with a protein complex called _______, which helps link dynein to cargo.

dynactin

Axonemal dyneins – activate microtubule sliding in _____?_______

cilia/flagella.

What are myosins and what is their function?

• ATP-dependent motor proteins

• Move along actin filaments

• Generate force for actin-based subcellular movement

• Large protein superfamily with 24 classes

What are the three main structural parts of myosin and their functions?

• Globular head: Binds actin and hydrolyzes ATP

• Neck (light chains): Regulates ATPase activity

• Tail (2 coiled heavy chains): Varies in length and binds to other myosins/cargo

Cilia and flagella – share a common structure called_______?

Axoneme – which is connected to a basal body

– Bundle of microtubules in a ‘9+2’ pattern
• 9 outer doublets of MTs
• 2 MTs in center ——→central pair of singlets

Axoneme

– nucleation site for MT assembly
– nine sets of triplet MTs

Basal body

• Microtubule-based motile structures

• 2–10 μm long

• Present in large numbers on ciliated cells

• Found in both unicellular and multicellular eukaryotes

Cillia

How do cilia move and what is their function?

• Beat in an oar-like pattern

• Generate force parallel to the cell surface

• Used to move fluid/material across the cell surface or propel cells (in some organisms)

Front: How do flagella move?

• Move with a propagated bending (wave-like) motion

• Generate force parallel to the flagellum

• Function is cell locomotion through fluid

Between the axoneme and basal body is a ________ zone in which the MTs take on the pattern characteristic of the axoneme

transition

Structure of a Cillia

1. Axoneme
• 9+2 MTs
2. Transition zone btw.
cilia and basal bodies
3. Basal bodies
– Triplet MTs

What is the 9 + 2 arrangement of an axoneme?

• 9 outer microtubule doublets surrounding 2 central microtubules

• Found in cilia and flagella

What are the A and B tubules in the axoneme?

• A tubule: Complete microtubule with 13 protofilaments

• B tubule: Incomplete microtubule with 10–11 protofilaments

• Central pair: Both are complete microtubules

What is axonemal dynein and where is it located?

• Axonemal dynein forms sidearms on each A tubule

• Uses ATP to slide adjacent microtubules

• Sliding is converted into bending, producing movement of cilia and flagella

The basal body looks like a centriole, with nine sets of _______ structure around the circumference.

triplets (three MTs)

______ cilloain sensory structures; have a “9 + 0” structure; that is, they lack the central pair.
______ cilia- also important in development; defects in them can result in disorders such as deafness

primary

Mammals have different kinds of muscles-skeletal, cardiac and smooth

muscle contraction

ATP-dependent motor proteins that exert force on actin MFs

Myosins

contain thin and thick muscles
– voluntary movement
– bundles of parallel muscle fibers (muscle cells)

Skeletal muscles

There are 24 known classes of myosins –
Functions:

1.Muscle contraction
2.Cell movement
3.Phagocytosis
4.Vesicle transport

_______ and “classic” kinesin are efficient motor proteins that share some similarities

Myosin II

What is the difference between myosins and kinesins?

• Myosins: Move on actin → short-distance movement (ex. muscle contraction)

• Kinesins: Move on microtubules → long-distance transport of vesicles/cargo

______ muscles are responsible for voluntary movement

skeletal

A muscle consists of parallel _____ fibres joined by tendon s to the bones that the muscles movie

muscle

Each fibre is long, thin, hghly specialized, ________ cell

multinucleate

Filaments in sketeltal muscles are aligned, giving myofobrils a pattern of _____ dark and light bands

alternating

These striations are characteristic of cardiac and skeletal muscle, called______ _______?

striated muscle

Dark bands are?

A bands

Light bands are

I bands

Muscle contraction is due to ____ _______ sliding past _____ _______, with no change in length of either

thin filament; thick filaments

The regulatory proteins ________ and ______regulate the availability of myosin binding sites on actin filaments in a calcium-dependent manner

tropomyosin and troponin

How is cardiac muscle similar to skeletal muscle?

Similarities:

• Striated appearance

• Contains actin and myosin filaments

How is cardiac muscle different from skeletal muscle?

Differences:

• Contracts spontaneously and continuously

• Not multinucleated

• Cells connect through intercalated discs with gap junctions → spread electrical signals (depolarization)

What are the key characteristics of smooth muscle?

• Involuntary contractions

• Maintains long-lasting tension

• Not striated (no Z lines)

• Uses dense bodies to anchor actin/myosin and generate contraction

What are the main types of other actin-based motility?

• Cell crawling (lamellipodia) → movement of cells using actin-based protrusions

• Amoeboid movement (pseudopodia) → “false feet” used by amoeba, slime moulds, and leukocytes

• Cytoplasmic streaming → actin-myosin movement that circulates cytosol inside cells