Membranes II Flashcards

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1
Q

How many residues are there per turn of an alpha helix?

How many A/residues is this?

A
  1. 6

1. 5

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2
Q

How are peptide bonds linked in alpha helices?

A

Peptide bond 1 is H bonded to peptide bond 4

Peptide bond 2 is H bonded to peptide bond 5
…etc

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3
Q

How are antiparallel beta-pleated sheets formed?

A

Adjacent beta-strands run in opposite direction

Every other side chain extends above or below the sheet

H bonds are perpendicular to chains

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4
Q

How thick is the entire lipid bilayer?

How thick is the hydrophobic region?

A

50 Angstroms

30A

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5
Q

How many amino acids are needed to span the lipid bilayer?

A

In an alpha helix:
1 residue = 1.5A

SO need approx 20 residues

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6
Q

What are porins?

A

Beta-barrel membrane proteins

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7
Q

How can you predict membrane protein structure from sequence?

A

Hydrophobicity analysis
- each individual amino acid has a hydrophobicity value

Look for regions of hydrophobic amino acids
-> indicative of alpha-helices
=integral membrane proteins

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8
Q

What doesn’t hydrophobicity analysis predict?

A

Beta-barrel membrane proteins

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9
Q

What contacts the hydrophobic lipid interior?

A

Hydrophobic amino acids

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10
Q

What are the most common membrane-spanning segments?

A

Alpha-helices

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11
Q

How are membrane proteins assembled?

A

Almost all proteins synthesis on ribosomes

Energetically unfavourable to move large hydrophilic portions through lipid bilayer

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12
Q

How do hydrophilic parts of membrane proteins get across the membrane?

A

Assemble in a protein conducting channel

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13
Q

What can transmembrane helices be surrounded by?

A

Lipid

Other helices - not as hydrophobic

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14
Q

What are the 4 main types of membrane proteins?

A

Transporters
Linkers
Receptors
Enzymes

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15
Q

What are the 2 types of membrane transport?

A

Carrier proteins:
transport small solutes
passive or active

Ion channels

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16
Q

Describe carrier proteins

A

Have specific solute binding sites

Switch conformation as to which side is open

17
Q

Describe channel proteins

A

Open = continuous channel
Selective - only some ions allowed through
Gated - opening + closing is regulated

18
Q

What are the 3 types of transport?

Which 2 are coupled transport?

A

Uniport
Symport
Antiport

Symport + antiport

19
Q

What is uniport?

A

Transports 1 type of molecule

20
Q

What is symport?

A

Transports 2 different molecules in the same direction

Against conc grad

21
Q

What is antiport?

A

Transports 2 different molecules in different directions

22
Q

Briefly explain how symporters are used in glucose transport

A

Na+ binds to symporter

= increases affinity for glucose

23
Q

Give an example of a passive transporter

A

Facilitative glucose transporters

ie GLUT1

24
Q

What is lactose permeate an example of?

A

A symporter

- transports lactose + protons in the same direction

25
Q

How are electrically charged molecules transported?

A

Electrochemical gradient
= conc grad + membrane potential

For a + charge:
Large EG when MP = -ve inside

Small EG when MP = +ve inside

Medium EG when MP = 0

26
Q

Give an example of an antiporter

A

Na-K ATPase

  • pumps3 Na+ out and 2K+ in using ATP