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The Dynamic Cell > Proteins - Block 3 > Flashcards

Proteins - Block 3 Flashcards

1
Q

What is the structure of a collagen molecule like?

A

It is a triple-stranded helical filament, with three helical α chains wrapping around each other.

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2
Q

How does glycine influence the structure of collagen?

A

Gly residues exist in the core of the helical strand, facilitating the tight packing of the three strands.

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3
Q

How can collagen be cross-linked to form fibrils and then fibres?

A

Lysine residues form intramolecular and intermolecular cross-links (Lys-Lys crosslinking). The resulting fibrils aggregate in the same way to form a fibre.

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4
Q

What is the role of elastin?

A

Elastin endows tissues with elasticity.

Elastic fibres in the ECM provide resilience to recoil.

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5
Q

How does elastin’s structure result in its mechanism of elasticity?

A

> It contains α-helical segments with Lys residues, as well as long hydrophobic regions,

> The K residues can cross-link to form a 2D network, facilitated by lysyl oxidase,

> When a force, the unstructured hydrophobic segments can extend, and they can recoil back to the original position thanks to the cross-linked α-helical segments.

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6
Q

What is the role of fibronectin?

A

> It anchors cells and helps with cell migration <

a. It cross-links ECM molecule & links cells to the matrix, and b. it forms fibres

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7
Q

What is the basal lamina?

A

> > A specialised ECM «

> Underlying epithelia

> Surrounds muscle cells

> Acts as a filter in the kidney

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8
Q

What is the role of laminin?

A

> Important component of basal lamina

> Facilitates formation of 2D networks

> Interacts with other ECM proteins like type IV collagen “molecular sea” and perlecan

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9
Q

What are 4 functions of sophisticated local cell-cell //EGM partnerships? (L.O.)

A
  1. Imparting mechanical properties
  2. Enabling cells to recognise & co-operate each other
  3. Allow for the dynamic nature of tissues
  4. Allow selective diffusion of molecules
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10
Q

What two broad categories of subunit assemblies can a protein have?

A
  1. Identical//similar subunits
    > Defined small number (haemoglobin)
    > Defined large number (a few viruses)
    > Variable number (MTs, actin, clathrin coats)
  2. Several distinct subunits
    (nuclear pores, molecular machines)
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11
Q

Meaning & examples of a (1) full-time complex?

A

> Function as stable oligomer
Several subunits
Icosahedral or helical symmetry

e.g. haemoglobin, polio virus

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12
Q

Meaning & examples of a (2) part-time complex?

A

> Function as oligomer AND individual subunits

e.g. G-proteins, rhodopsin

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13
Q

Meaning & examples of a (3) transient complex?

A

> Occur briefly in signal cascade
Rapid transmission of information

e.g. Ras and Raf (GTP binding to one complex causes affinity for the other to decrease & the complex breaks down).

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14
Q

Meaning & examples of a (4) dynamic assembly?

A

> Rapid assembly//disassembly
AT//GTP-controlled

e.g. Actin (dynamic filaments) & tubulin (road network)

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15
Q

Which motor protein carries cargo to the + end of the microtubule?

A

Kinesin

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16
Q

Which motor protein carries cargo to the - end of the microtubule?

A

Dynesin

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17
Q

What functions does an Actin filament have?

A

> Mechanical support
Cytoplasm traffic routes
Cell migration
Muscle contraction

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18
Q

What functions does a MT have?

A

> Trafficking cargo

> Separating chromosomes

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19
Q

What are three examples of molecular machines?

A

> Proteosome
GroEL//GroES
Nuclear Pore

20
Q

What is (MM1) the Proteosome?

A

> “Garbage-disposal machine”
Recognises + unfolds old proteins (caps)
Proteolytic sites cut chain up (inner chamber)

21
Q

What is (MM2) GroEL//GroES?

A

> A folding machine.
Chamber lets in polypeptide; ATP binds, causing GroES cap to bind & its polar inner surface helps prevent competing reactions, allowing protein to fold.
When protein is made, ATP is hydrolysed and GroES cap opens up.

22
Q

What is (MM3) the Nuclear Pore?

A

> Pore in the nucleus
Very complex structure
Made of 456 protein molecules

23
Q

What are the 4 components of communication & their roles? (L.O.)

A
  1. Signal molecules = Messengers
  2. Receptors = Signal Transducers
  3. Intracellular Sig. Pathways = 2nd messengers
  4. Target effector = Transcription regulator
24
Q

What are the 4 types in intercellular communication? (L.O.)

A

A. Contact-dependent

B. Paracrine (cell > cell signal molecules)

C. Synaptic

D. Endocrine (bloodstream)

25
Q

What FORM is the information in cell signalling?

A

Signal molecules

26
Q

How is the signal READ in cell signalling?

A

Receptor proteins

27
Q

How is the read signal COMMUNICATED in cell signalling?

A

Intracellular signal pathway (2nd messenger)

28
Q

What EFFECT does the communicated signal have in cell signalling?

A

Influences the effector protein (which controls transcription)

29
Q

What are the 3 classes of cell SURFACE receptors?

A
  1. Ligand-gated channels
  2. G-protein coupled receptors (GPCRs)
  3. Enzyme-linked receptors
30
Q

What is the basic architecture of a GPCR?

GOOD TO KNOW

A

> 7 hydrophobic helical domains

> Extracellular loops N-terminal loops (ligands bind here!)

> Intracellular C-terminal loops (trimeric G-proteins associate here)

31
Q

What is the basic structure of a GPCR-associating G-Protein?

GOOD TO KNOW

A

> α, β and γ regions

> α is a GTPase.
α can dissociate from β and γ subunits, which then form a heterodimer.

32
Q

Where is the GTP//GDP binding site on a GPCR-associating G-Protein?

A

α has the GTP//GDP binding site at its interface with the β//γ subunits.

33
Q

How is a GPCR-associating G-Protein anchored to the inside of the membrane?

A

With a fatty acyl PT-modification that’s usually on the β//γ subunits.

34
Q

What regions of a GPCR-associating G-Protein are conformationally sensitive (cause a shape change)?

A

The “Switch Regions” on the α subunit that bind the outer PO4 of GTP.

35
Q

What is the effect of the α region of a G-protein dissociating?

A

> It binds to a GTP
The active conformation is activated
This interacts with effector proteins

36
Q

What does the β//γ heterodimer do when the α region of a G-protein dissociates?

A

It modulates other effector proteins.

37
Q

What causes the dissociated α region of a G-protein to re-associate?

A

> RGS proteins accelerate its hydrolysis of ATP

> It becomes inactive again

38
Q

What happens when dissociated α is inactivated (to complete the cycle)?

A

> It re-associates with β//γ
GDP is released
The G-protein re-associates with the GPCR

39
Q

What two factors influence the function of GPCRs?

GOOD TO KNOW

A
  1. Ligand binding to the GPCR

2. Influence of RGS proteins on the α active site

40
Q

What is the general action of a GPCR?

GOOD TO KNOW

A
  1. α subunit binds to membrane effector
  2. Effector activated; generates 2nd messengers
  3. GTP hydrolysed to GDP & dissociates
  4. α can now re-associate with β//γ
41
Q

What does the effects caused by different signals depend upon?

A

which signalling-pathway proteins are being expressed inside the cell.

42
Q

What are the characteristics of epithelial tissue?

GOOD TO KNOW

A

> Cells are tightly bound into sheets.
Not much ECM; thin layer (lamina).
cell-cell adhesions attach the cells & bear mechanical stress.

43
Q

What are the characteristics of connective tissue?

GOOD TO KNOW

A

> Cells are distributed sparsely.
Plentiful ECM.
Rich in fibrous polymers; matrix bears the mechanical stress.

44
Q

What are the three broad types of cell junction?

GOOD TO KNOW

A
  1. Tight Junctions - Zip cells together, regulate molecular transport between cells.
  2. Anchoring Junctions - Attach cells to each other and the ECM.
  3. GAP Junctions - Mediate chemical//electrical signals.
45
Q

What does the ECM provide for cells?

A

A habitat in which they can build & maintain solid structures.

46
Q

List some important components of the ECM.

IMPORTANT

A

> Glycosaminoglycans (GAGs): massive hydrated polysaccharides that form a gel OR attach to core proteins to make proteoglycans.

> Collagens: Principal ECM component, fibrous protein.

> Elastin: Forms a network that stretches when mechanical force is applied and relaxes again.

> Fibronectin: Links cells to ECM and each other (cross-linking). Has protein binding sites, some of which are cryptic and can only be revealed when the fibronectin fibrils are stretched. Interacts with actin; cells can migrate through the ECM along fibronectin fibrils.

> Laminin: Forms 2D network in basal lamina. Also a ligand for integrin and has binding sites.

47
Q

In what way is the ECM dynamic?

A

There is significant two-way information exchange between ECM and cytoskeleton via integrins.

The Dynamic Cell (8 decks)

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