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BIO 1090 > Membranes > Flashcards

Membranes Flashcards

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1
Q

3 simple states

A

micelle, liposome, bilayer sheet

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2
Q

Functions of biological membranes

A
  • cell boundary
  • define / enclose compartments
  • control movement of material in and out of cell
  • allow response to external stimuli
  • enable interactions between cells
  • provide scaffold for biochemical activities
  • first 5 are unique to plasma membrane
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3
Q

which type of membranes don’t have a bilayer?

A

micelle

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4
Q

What is a lipid bilayer

A

polar / hydrated biological membrane made up of phospholipids

  • proteins are embedded in the lipid bilayer
  • about equal in protein and lipid contents
  • also includes cholesterol and associated sugar
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5
Q

The plasma membrane

A
  • separates the interior of the cell from the outside environment
  • consists of a semipermeable lipid bilayer
  • regulates the transport of materials entering and exiting the cell
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6
Q

Fluid mosaic model

A

describes the structure of the plasma membrane

  • fluid refers to individual lipid molecules move
  • mosaic refers to diverse particles penetrate the lipid layer
  • components are mobile and can interact
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7
Q

amphipathic

A

having both hydrophobic and hydrophilic regions

- lipid bilayer is hydrated due to hydrophilic region

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8
Q

Types of proteins found in the membrane

A

integral (transmembrane), peripheral, lipid anchored

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9
Q

What makes biological membranes dynamic?

A
  • lipids move easily, laterally, within leaflet
  • lipid movement to other leaflet is slow
  • membrane proteins diffuse within the bilayer
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10
Q

integral membrane proteins

A

span the lipid bilayer via alphahelixes that form with hydrophobic amino acids

  • permanently imbedded in the membrane
  • functions include channel / transport molecules across the membrane, cell-cell communication, attachment
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11
Q

Peripheral membrane protiens

A

associate with surfaces of the bilayer and with other integral protein anchors

  • usually exist on the inside of the cell
  • can attach via polar head group interactions or via protein-protein interactions with integral membrane proteins
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12
Q

Myelin sheath

A
  • the myelin sheath of a neuron consists of very low amounts of protein
  • consists of layers of plasma membrane forming insulation around the nerve axon
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13
Q

symmetry of biological membranes

A

Asymmetrical

  • two leaflets have distinct composition
  • outer leaflet usually contains glycolipids and glycoprotiens
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14
Q

Membrane fluidity

A

determined by the nature of lipids in the membrane

  • unsaturated lipids: increase fluidity
  • saturated lipids: decrease fluidity
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15
Q

How does temperature affect fluidity?

A
  • warming increases fluidity: liquid crystal
    (fluid like consistency)
  • cooling decreases fluidity: crystalline gel
    (gel like consistency)
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16
Q

How does membrane fluidity affect cell function?

A

membrane fluidity must be maintained

- changes in temperature and lipid composition can result in the desaturation of the lipids or exchange of lipid chains

17
Q

unsaturated vs saturated fatty acid chains

A

Unsaturated: have one or more double bonds that introduce kinks in the phospholipid, reducing tightness of packing
Saturated: lacks double bonds, resulting in phospholipids with straight structure that favours tight packing

18
Q

How does cholesterol effect the membrane?

A

Cholesterol modulates membrane fluidity

  • amphipathic structure of cholesterol allows it to pack tightly with phospholipids, alters flexibility
  • add to liquid crystal membrane: fluidity decreases
  • add to crystalline gel membrane: fluidity increases
  • important for maintaining homeostasis of membranes
19
Q

True or false: cells with different functions have membranes with different protein compositions?

A

True

20
Q

Transmembrane domain

A

a hydrophobic (uncharged) peptide sequence that spans the PM

  • permanently insert proteins into the PM
  • alpha-helical
  • foster protein-protein interactions
21
Q

movement of different substances across the membrane

A

small, uncharged molecules - move across the membrane easily. Ex: O2, CO2, NO2, H2O
large, charged, polar molecules - cannot easily cross lipid bilayers

22
Q

4 basic mechanisms for moving molecules across membranes

A
  1. simple diffusion
  2. diffusion through a channel
  3. carrier-mediated diffusion
  4. active transport
23
Q

Which basic mechanism requires an input of energy?

A

Active transport - often uses chemical energy in the form of ATP

24
Q

Passive transport

A

Does not require an input of energy

  • consists of simple diffusion, diffusion through a channel and carrier mediated diffusion
  • moves molecules from high concentration to low concentration
25
Q

simple diffusion

A
  • very small uncharged molecules
  • flow down the concentration gradient
  • molecules like CO2 and O2
  • H2O travels via osmosis
26
Q

diffusion through a channel

A
  • ion channels are integral membrane proteins that form an aqueous pore
  • selective and only allow certain ions to pass
  • move down the concentration gradient
    Voltage gated channels: responds to changes across the membrane
    ligand gated channels: responds to binding of a specific molecule which causes conformational change in structure
27
Q

What is the target of toxins?

A

Ion channels

  • Tetrodotoxin is an Na+ channel blocker (potent neurotoxin)
  • Curare is an acetylcholine competitive antagonist of the acetylcholine receptor
28
Q

Aquaporins

A

specific water channels

- water moves through aquaporins channels in a single file line

29
Q

Facilitated diffusion

A
  • compound binds specifically to integral membrane protein (facilitated transporter)
  • change in transporter conformation allows the compound to be released on the other side of the membrane
30
Q

Transportation of glucose across the membrane

A

Glucose fits like a lock and key in the transporter that induces a conformational change in the transporter. The glucose is released on the other side of the membrane and the protein is ready to receive the next glucose

31
Q

Na+ - glucose symporter

A
  • sodium concentration outside is high because of Na K ATPase
  • 2 sodium and 1 glucose start on outside of the cell
  • follows facilitated diffusion
  • Energy is provided by a chemical gradient of high Na+ concentration outside of the cell
32
Q

Active transport

A

compound to be transported binds specifically to integral membrane protein (active transporter)

  • moves AGAINST concentration gradient
  • Requires an input of energy
33
Q

Sodium Potassium pump

A
  • most common example of active transport
  • The S-P pump moves sodium from inside the cell to outside the cell
  • involves 4 proteins
  • For the hydrolysis of 1 ATP molecule we are transporting The 3 sodiums out and 2 potassiums in
34
Q

What property of integral membrane proteins allows them to remain imbedded in the lipid bilayer?

A

They have a transmembrane domain made of hydrophobic amino acids

35
Q

Roles of integral membrane proteins

A
  • transporter
  • receptor
  • enzyme
  • anchor

BIO 1090 (7 decks)

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