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Biochemistry and Cell Biology Year 1 > The cytoskeleton > Flashcards

The cytoskeleton Flashcards

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1
Q

What is the cytoskeleton?

A

A large dynamic network of protein filaments which supports the cell

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2
Q

What is the function of the cytoskeleton?

A

Shape - cell shape, position of organelles and cytoplasm organisation
Strength- Prevents the cell from being damaged
Movement - within the cell and the cell itself

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3
Q

What are the 3 filaments?

A

Actin/ microfilament - shape, whole cell locomotion, pinches 1 cell into 2
Microtubules - Position of organelles, intracellular transport, mitotic spindles
Intermediate filaments - mechanical strength

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4
Q

What are microfilaments?

A

G actin
Held non covalent bonds
The monomers form a protofilament
2 protofilaments twist to form a helix
Thin but flexible
Can come together to form linear bundle 2D networks 3D gels
Large cleft which binds ATP
Point in the same direction (polarity)

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5
Q

What is nucleation?

A

The first steps in the formation of a new structure via self assembly - when you have 3 monomers the probability of forming of a polymer is increased

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6
Q

Outline the dynamic behaviour of microfilaments

A

Plus end has a greater rate of polymerisation, when the G actin is in the polymer it has ATPase activity so ATP is hydrolysed into ADP which allows the G actin to dissociate at the minus end as they are less tight (depolymerisation)

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7
Q

What is treadmilling?

A

Subunits are added much faster at plus end and dissociate much faster at the minus end.
The overall length stays the same
This is essential for cell motility and alterations in cell shape

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8
Q

What are the actin cytoskeletal networks?

A

Branched
Random
Stress fibres
Bundled

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9
Q

What is the importance of cell motility?

A

Embryogenesis
Inflammatory response
Wound healing
Metastasis

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10
Q

What is morphological polarisation?

A

Leading edge of the cell is larger than the back
Lamellipodia - branched network of actin
Filopodia - finger like projections - bundled networks
These spread the front of the surface then contractile force from myosin from the back propels the cell forwards

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11
Q

What are microtubules?

A

Polymerisation of tubulin to form a heterodimer consisting of an alpha and beta tubulin which forms protofilaments
non covalent
13 protofilaments form long hollow cylinders
Stiff
Vertical interactions between alpha and beta
Lateral interactions between alpha/alpha and beta/beta
Polar
Beta can hydrolyse GTP to GDP

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12
Q

Outline dynamic instability within microtubules

A

Driven by rate of tubulin addition and rate of GTP hydrolysis
If rate of GDP formation is higher than addition of polymers then depolymerisation occurs
Polymerise and depolymerise at the plus end

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13
Q

What is the centrosome?

A

Also the Microtubule organising centre
Has a pair of centrioles and pericentriolar matrix (proteins)
90 degrees to each other
Pericentriolar matrix contains gamma tubulin this is where the microtubules are anchored

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14
Q

What motor proteins are associated with microtubules?

A

Kinesin- moves towards the +end of the microtubule= anterograde (away from centre) - has a neck hinge region and globular heads associated with ATP or ADP
Dynein - moves towards the - end - retrograde = towards the centre

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15
Q

Outline the process of intracellular trafficking

A
  1. Start with microtubule surface and kinesin molecule
  2. Kinesin is anterograde
  3. Lagging head is ATP bound which is strongly associated with the MT. The leading head is ADP bound is weakly associated with MT
  4. Hydrolysis of ATP causes lagging head to dissociate from the MT
  5. Leading head binds to ATP causing a conformational change
  6. Lagging head moves forward and the cargo gets transported
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16
Q

What are intermediate filaments?

A

Provide mechanical strength
Composed of different protein subunits
Non polar
No motors
Fibrous 10nm
2 monomers together form a dimer coiled 2 dimers join to form a tetradimer then 8 of these form a filament

17
Q

What is the extracellular matrix?

A

An intricate network of proteins, carbohydrates and water
Supports for cell and tissue
Regulator of cellular signalling
Secreted by cells normally fibroblasts

18
Q

How is the ECM present in epithelial tissues?

A

Basal lamina

19
Q

What does the ECM consist of ?

A

Glycosaminoglycans (GAGs) - oligosaccharides covalently bonded to a protein = proteoglycans - 36
Fibrous proteins - 40 types of collagens. elastin also important
Glycoproteins - 200 types

20
Q

How are the 3 filaments present in the small intestine?

A

Actin - enable microvilli formation and connects cell junctions to maintain a physical barrier
Microtubules - From basal to apical surfaces providing intracellular network
IF- Anchor across the cell providing structure and strength via desmosomes

21
Q

What are the 3 types of cell junction?

A

Anchoring junctions - anchor cytoskeleton between cells or between cells and the ECM
Occluding junctions - prevents the passage of ions and small molecules between cells - tight junctions
Communicating junctions- direct connections between the cytoplasm of 2 cells - gap junctions

22
Q

What are the types of anchoring junction?

A

Adherens junctions
Desmosomes
Actin- linked- cell- matrix junctions (Focal Adhesions)
Hemidesmosomes

23
Q

What are adherens junctions?

A

Between 2 cells
Cell to cell adhesion, regulation of actin cytoskeleton and signalling
Cadherins
Single pass
Catenin (binds the cadherin to F actin) and vinculin (adaptor proteins)

24
Q

What are tight junctions?

A

Between 2 cells
Seal gaps between cells prevent diffusion within the membrane
Proteins - claudins and occludins
Multi pass

25
Q

What are gap junctions?

A

Between 2 cells
Provides channels which connect the cytoplasm of two cells
Connexins
Multi pass
Permeable to small molecules
Gated and sensitive to voltage, pH, Ca2+ and neurotransmitters

26
Q

What are desmosomes?

A

Between 2 cells
Strong adhesion, resistance to mechanical stress, signalling
Cadherins
Single pass
Intermediate filaments
Adaptor proteins - Plaque (dense matrix of proteins)
Found in tissues subject to mechanical stress - heart/ skin

27
Q

What are hemidesmosomes?

A

Between the cell and the ECM
Stable adhesion of basal epithelial cells to the underlying basement membrane
Integrins
Each subunit is single pass
Intermediate filaments
Adaptor proteins - plaque (dense matrix of proteins)

28
Q

What are focal adhesions?

A

Between the cell and the ECM
Cell ECM adhesion, signal transduction and cell migration
Integrins
Each subunit is single pass
Actin
Adaptor proteins - Talin and vinculin

29
Q

What are cadherins?

A

Have homophilic binding which is dependent on extracellular Ca2+
They bind weakly but adherens junctions have multiple in parallel

Biochemistry and Cell Biology Year 1 (11 decks)

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