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Medical physiology I > Cell membrane > Flashcards

Cell membrane Flashcards

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USMLE® Step 1 flashcards
1
Q

What are the cell membranes made up of?

A

Cell membranes are made up of lipids and proteins.

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2
Q

What is the structure of cell membrane?

A

Cell membrane structure follows the fluid mosaic model.

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3
Q

How are the lipids in the membrane arranged?

A

They are arranged as a double layer (bilayer)

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4
Q

What compound is the most abundant in a membrane?

A

Phospholipids are the most abundant.

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5
Q

What do phospholipids contain?

A

They contain choline.

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6
Q

What is the important property of the lipids?

A

They are amphipathic, containing polar and nonpolar regions.

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7
Q

What is the other major lipid constituent?

A

It is cholesterol.

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8
Q

What is the proportion of cholesterol and lipids?

A

The ratio b/w cholesterol and lipids varies.

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9
Q

What is the function of cholesterol in the membrane?

A

Cholesterol stiffens membranes and decreases membrane permeability to small water soluble molecules.

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10
Q

What are the types of lipids are present in the membrane?

A
  • Phospholipids
  • Cholesterol
  • Glycolipids
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11
Q

What are glycolipids?

A

Glycolipids are lipids with sugars attached.

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12
Q

What type of glycolipids is present?

A

The main type of glycolipids present are negative charged containing sialic acid

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13
Q

What is the function of negative charged glycolipids?

A
  • They increase the concetration of cations, especially Ca2+, at the membrane surface.
  • Some act as receptors for bacterial toxins such as cholera toxins.
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14
Q

How are the lipids distributed in the bilayer?

A

They are distributed asymmetrically in the bilayer.

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15
Q

Where are glycolipids distributed?

A

They are distributed on the non-cytoplasmic surface of the plasma membrane.

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16
Q

Where are the choline containing phospholipids distributed?

A

They are distributed on the non-cytoplasmic surface.

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17
Q

Where are the phospholipids containing a terminal primary amino group distributed?

A

They are distributed on the cytoplasmic surface.

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18
Q

What the terminal primary amino groups on the phospholipids?

A
  • Phosphatidylserine

- Phosphatidylethanolamine.

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19
Q

Why is the asymmetrical distribution important?

A
  1. Many cytosolic proteins bind to specific head groups of the lipids found on the cytosolic surface.e.g.Protein kinase C binds to phosphatidylserine to function properly.
  2. Phosphatidylinositol on the the cytosolic face can be cleavedby phospholipases to produce the intracellular mediators diacylglycerol and IP3.
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20
Q

How many types of membrane proteins are there?

A
  • Integral proteins
  • Peripheral proteins
  • Glycoproteins
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21
Q

Where is the integral proteins located?

A

Integral proteins are firmly attached to or embedded in the phospholipid bilayer.

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22
Q

How are intergral proteins attached to the bilayer?

A

They are attached in 3 ways:

  • some span the lipid bilayer (transmembrane protein)
  • Some are imbeded but not cross the bilayer.
  • Some are anchored to a lipid in the bilayer by a covalent bond. e.g. glycophospholipid-linked protein
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23
Q

What are the main functions of integral proteins?

A
  • Receptors for hormones and neurotransmitters
  • Pores, channels or carriers
  • Enzymes
  • Adhesion molecules
  • Intracellular signaling e.g. GTP-binding proteins and kinases
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24
Q

What are the types of adhesion molecules?

A
  • Cell-matrix adhesion molecules (integrins)

- Cell-cell adhesion molecules (cadhedrin and neuronal cell-adhesion molecules)

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25
Q

How are peripheral proteins attached to the membrane?

A

They are loosely bound to proteins on either surface of the membrane.

26
Q

Can peripheral proteins be released from the membrane? How?

A

They can easily be released from membrane by high or low ionic strength solutions or high or low pH.

27
Q

What is the function of peripheral proteins?

A

They participate in the formation of a submembranous cytoskeleton.

28
Q

What are glycoproteins?

A

They are membrane proteins with carbohydrates attached to them.

29
Q

What are the main functions of glycoproteins?

A
  • They are involved in cell-cell interactions
  • They act as receptors for viruses and as antigenic determinates
  • They contribute to cell surface negativity.
30
Q

What is the mobility of lipid and proteins mobility in the membrane?

A

Both lipids and proteins move freely in the plane of the membrane.

31
Q

What is the mobility of cholesterol?

A

Cholesterol can’t flip membrane faces by themselves

32
Q

How can cholesterol flip membrane face?

A

The enzyme, flipase, can flip cholesterol from face to face.

33
Q

What are the functions of biological membranes?

A
  • Permeability barrier for water soluble substances
  • Form cell organelles.
  • Package and transport material within the cell.
34
Q

Why is the permeability barrier important?

A
  • It allows for the maintenance of large gradience across membrane.
  • It permits localization of cellular processes in the cell.
35
Q

What is endocytosis?

A

It is the uptake of of extracellular material in membrane bound vescicles.

36
Q

Does endocytosis require energy?

A

Endocytosis requires energy.

37
Q

What are the forms of endocytosis?

A
  • Phagocytosis
  • Pinocytosis
  • Receptor mediated endocytosis
  • Caveolae endocytosis.
38
Q

What is phagocytosis?

A
  • Triggered process

- Uptake of large particulate matter.

39
Q

How does phagocytosis occur?

A

Particles bind to receptors on the cell surface and trigger phagocytosis.

40
Q

List the different types of phagocytotic receptor.

A
  • Fc receptors bind to Fc tail of antibodies bound to pathogens.
  • Receptor for complement
  • Some receptors recognize oligosacharides of microorganism’s surface.
  • Phophatidylserine on apoptotic cells triggers phagocytosis.
41
Q

What is the size of phagocytotic vesicles? What determines it?

A

Phagocytotic vesicles are large in size. The diameter is determined by the size of the ingested material.

42
Q

Are all cells capable of phagocytosis?

A

Only some cells are capable of phagocytosis. e.g. macrophages and neutrophils.

43
Q

What is pinocytosis?

A
  • It is the fluid phase endocytosis by bringing in extracellular solution and dissolved solutes.
  • It is a non-triggered process.
44
Q

Where and how does pinocytosis occur?

A

It occur at membrane sites coated with the protein clathrin.

45
Q

In what cells does pinocytosis occur?

A

Pinocytosis occurs in all cells therefore it is a constitutive process.

46
Q

What is the size of the pinocytosis vesicles?

A

Pinocytosis vesicles are small and uniform in diameter.

47
Q

What is receptor-mediated endocytosis?

A

It is the uptake of specific substances bound to membrane receptors.

48
Q

How does the cell recognize what substance to endocytose?

A

The cell synthesizes receptors for specific substances and insert them into membrane.

49
Q

Do only receptors with ligands get endocytosed?

A

Receptors with and without ligands may be endocytosed.

50
Q

Describe the process of receptor-mediated endocytosis.

A

Receptors bind to adaptin which will in turn bind to clathrin to create a clathrin coated pit.

51
Q

Do all receptors bind to adaptin with or without ligand?

A

Some receptors only bind to adaptin if its ligand is bound.

52
Q

What happens after the coated pit is formed?

A

The region will be obligated to be endocytosed.

53
Q

What happens after the material is endocytosed?

A
  • The vesicle will shed its clathrin coat.
  • Fuse with endosomes
  • Ligand dissociate from receptors.
  • Receptors are recycled.
54
Q

What is caveolae endocytosis?

A

It is clathrin-independent endocytosis.

55
Q

How does caveolae endocytosis work?

A

Membrane sites with more cholesterol and sphigomyelin called the lipid raft which also have the protein caveolin will invaginate and bring in material.

56
Q

What kind of receptors does each caveolae contain?

A

It contain many types of receptors (ex: folate receptor) and intracellular signalling proteins (GTP-binding proteins)

57
Q

What other process is caveolae also involved in?

A

It is also involved in transcytosis in vascular endothelial cells transfering large molecules from blood to interstitial fluid.

58
Q

What is exocytosis?

A

It is a discharge of intracellular materials contained in membrane-bound vesicles.

59
Q

Does exocytosis require energy?

A

Endocytosis requires energy

60
Q

What is the main function of endocytosis?

A

It is the main method of secreting neurotransmitters and hormones.

Medical physiology I (3 decks)

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