Lecture #8 - Cytoskeleton and ish Flashcards
Cytoskeleton - what does it do and what three things does it contain?
- Helps maintain cell SHAPE and POSITION of organelles (organelles don’t function optimally unless right position)
- Unlike the body’s skeletal system the cytoskeleton rapidly disassembles and reassembles - allows CHANGES in cell structure
- Highly dynamic but still provides stability
- microtubules
- intermediate filaments
- microfilaments
Microtubules
- Composed of?
- May radiate out from?
- Resist?
- Provide?
- Look like?
- Composed of TUBULIN subunits
- May radiate out from an organizing centre (CENTROSOME)
- Resist COMPRESSION
- Provide cell MOTILITY:
• whole cell
• organelle movement - Pipe in a helix form - can build up larger or become smaller
Whole cell motility - how does it work?
Move by CILIA: “rowing-like” motion perpendicular to the direction of movement
• when cells are fixed in place the beating of cilia can move fluid past the cells
• Power stroke and recovery stroke (comes back up bendingly)
*Can also move by Flagella - undulates
Organelle motility
- How does it work?
- Does what?
- ATP-powered motor proteins can “walk” organelles along microtubules
- Can thus TRANSPORT vesicles to targets or damaged organelles from distant sites e.g nerve terminals
The vesicles have a receptor motor
Microfilaments
- What is it?
- Forms what?
- Resists what?
- What does it do?
- Provides what?
- Look like?
- Function
- Double chain of ACTIN subunits
- Forms LINEAR STRANDS and they run in three directions (with the aid of branching proteins)
- Resists TENSION
- Cortical network under plasma membrane helps maintain cell SHAPE
- Provide a GEL-LIKE consistency to outer cytoplasm (meshwork makes it somewhat solid)
- Ropes that are twisted together into one long rope
- Cell shape, changes in cell shape, muscle contraction, cytoplasmic streaming in plant cells, cell motility (amoeboid movement), division of animal cells
Linear actin microfilaments support movement in…..
Linear actin microfilaments support movement
• in muscle - they are arranged in parallel with the motor protein myosin
• can achieve cellular or organism movement
(even in non-muscle cells, there are actin filaments and they interact with myosin but they’re more ‘spectacular’ in muscles)
Intermediate Filaments:
- Composed of?
- More or less dynamic MT/MF
- Function?
- Look like?
- Various PROTEINS including
keratins, vimentins and
lamins - LESS DYNAMIC than MT or MF (because not made of subunits - can’t build, breakdown quickly etc)
- Maintain cell SHAPE (TENSION bearing elements)
• ANCHOR organelles
• formation of nuclear lamina
• neuronal processes – neurofilaments - Supercoiled into “CABLES”
How are cells joined together?
Cell junctions (tight, desmosomes and dap) and the ECM (?)
Tight junctions
- Do what?
- May form what?
- Prevent what?
- Keeps neighbouring cells TIGHTLY PRESSED together
- May form a continuous
SEAL - PREVENT movement of FLUID
across cell layers
Desmosomes
- Are what?
- Attachments between what?
- Act like what?
- Anchoring junctions
- Attachments between sheets of cells (e.g. muscle - when contracts, all the cells come w/ it bc held together by des)
- Act like rivets (a “torn muscle” is a torn desmosome)
Gap junctions
- What are they?
- Allow what?
- A point of CYTOPLASMIC
CONTACT between cells - Ions and molecules may
pass from cell to cell
• allow rapid intercellular
COMMUNICATION
Extracellular matrix
- What is it?
- Composed of what?
- In many tissues, cells do not make direct contact with other cells - cells lie within an extracellular matrix (no junctions bw fibroblasts)
- Material secreted by cells (fibroblasts)
• mainly glycoproteins (protein with carbohydrate) - proteoglycans in Hubs
• most abundant glycoprotein is collagen
Collagen fibres - give 3 details (they’re the purple thick things around the cell in the ECM)
- Great tensile strength
- Approx 50% of total body protein
- Like other proteins collagen is “turned over” and must be replaced
It’s similar in structure to intermediate filaments
How does scurvy come about?
A lack of vitamin C results in a failure of collagen synthesis
• hydroxyproline amino acids not formed
• collagen fibres cannot cross-link correctly
• results in scurvy
Collagen embedded in a proteoglycan matrix (green thin strings around cell in ECM)
Proteins with extensive sugar additions
• traps water in ECM
• resists compression and retains shape
