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BC3003: Introduction to Cell Biology & Biomembranes > Membrane Proteins > Flashcards

Membrane Proteins Flashcards

1
Q

What are the THREE classes of membrane proteins?

A
  1. Integral
  2. Lipid-Anchored
  3. Peripheral
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2
Q

How do Integral Proteins attach to the membrane?

A

Spans the bilayer

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3
Q

How do Lipid-Anchored Proteins attach to the membrane?

A

Covalently bound to lipids

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4
Q

How do Peripheral Proteins attach to the membrane?

A

Indirectly associate with membrane via non-covalent interactions with lipid head or other membrane proteins

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5
Q

How many hydrophobic amino acids are associated with the Integral membrane protein membrane spanning region?

A

20-25

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6
Q

What do Hydropathy plots predict?

A

Transmembrane helices of Integral Proteins

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7
Q

How long is the α-helix in the membrane spanning region of Integral proteins?

A

3-4nm

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8
Q

Which class of Integral membrane protein has its amino terminus in the cytosol?

A

Type II

(all other types have carboxyl terminus in cytosol)

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9
Q

What is the difference between Type I and Type III Integral membrane protein?

A

Type I has a signal sequence that is cleaved during insertion into the membrane

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10
Q

What is the structural difference of Porins compared to other transmembrane proteins?

A

Barrel shape comprised of 16 β-stands that span membrane

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11
Q

What is CMC?

A

Critical Micelle Concentration

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12
Q

What happens to detergents above and below CMC?

A
  • BELOW CMC - detergents dissolve as single molecules in water
  • ABOVE CMC - detergent molecules cluster to form micelles
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13
Q

What are Detergents used in purifying membrane proteins?

A
  • Amphipathic molecules
  • Solubilise lipids and membrane proteins
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14
Q

What are the characteristics of Ionic detergents?

A
  • Charged
  • Disrupts hydrogen and ionic bonds
  • Denature proteins at high concentrations
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15
Q

What are the characteristics of Non-Ionic detergents?

A
  • Don’t denature proteins
  • Useful in purification of membrane proteins
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16
Q

Which side of the cellular membrane do GPI-linkages occur?

A

Extracellular side

17
Q

Which side of the cellular membrane does Acylation and Prenylation occur?

A

Cytosolic side

18
Q

What is Acylation?

A

FA attached to protein

19
Q

What is the carbon skeleton of Myristic acid?

A

14:0

20
Q

What is the carbon skeleton of Palmitic acid?

A

16:0

21
Q

Which amino acid does Palmitoylation occur on?

A

Internal Cys (or Ser)

22
Q

Which amino acid does Myristolation occur on?

A

N-terminal Gly

23
Q

What is an example of a gene that undergoes Acylation by Myristoylation?

A

v-Src oncogene

24
Q

What is the structure of Farnesyl?

A

C15, 3x Isoprenes

25
Q

What is the structure of Geranylgeranyl?

A

C20, 4x Isoprenes

26
Q

Which amino acid does Farnesyl OR Geranylgeranyl attach to?

A

Cys at/near C-terminus

27
Q

What is the attachment sequence of Farnesyl OR Geranylgeranyl?

A

Cys-Φ-Φ-X

(Φ = hydrophobic aa)

28
Q

What is an example of enzymes that undergoes Prenylation?

A
  • Small GTPases
  • Ras, Rab etc
29
Q

How is GPI linked to a membrane protein?

A

Linked to C-terminus of protein via Phosphoethanolamine

30
Q

What is an example of an enzyme that undergoes GPI linkage?

A

Placental Alkaline Phosphatase (PLAP)

31
Q

TRUE OR FALSE:
Carbohydrates can only be attached to membrane proteins

A

False.
Can be attached to both membrane proteins AND lipids

32
Q

What are carbohydrates attached to lipids called?

A

Glycolipids
* attached to glycerol or sphingosine backbone

33
Q

What are large polysaccharide sugars attached to membrane proteins called?

A

Proteoglycans

34
Q

What are small oligosaccharides attached to membrane proteins called?

A

Glycoproteins

35
Q

On which THREE amino acids does Glycosylation occur on Glycoproteins / Proteoglycans?

A
  • Serine
  • Threonine
  • Asparagine
36
Q

Which side of the membrane does Glycosylation occur?

A

Only occurs on the exoplasmic side of the membrane

BC3003: Introduction to Cell Biology & Biomembranes (15 decks)

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