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Histology/Cell Biology > Plasma Membrane > Flashcards

Plasma Membrane Flashcards

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1
Q

What are the general features of the plasma membrane?

A
  • self-forming
  • contains proteins, lipids, and sugars moieties
  • contains molecules that anchor to ECM and cytoskeletal structures
  • asymmetrical with respect to lipid distribution and protein structure
  • includes the cell coat (glycocalyx)
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2
Q

Describe the basic organization of the plasma membrane

A

a phospholipid bilayer with hydrophobic tails facing the interior and the hydrophilic head groups facing out

not a rigid structure, both proteins and phospholipids diffuse

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3
Q

What molecules make the plasma membrane a selectively permeable structure?

A

Cholesterol and integral membrane proteins

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4
Q

What are the major classes of lipids found in the membrane?

A

phospholipids, glycolipids, and cholesterol

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5
Q

What is the diagnostic significance of the plasma membrane?

A

It contains specific proteins that may be targets for therapy or used for diagnosis

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6
Q

What are integrins and what is their mechanism of function?

A

Integrins are integral membrane proteins that integrate extracellular matrices with the cytoskeleton.

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7
Q

Describe the structure of the plasma membrane

A

Trilaminar structure:

electron dense inner region facing cytoplasm, electron dense outer region facing ECM, and translucent central portion

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8
Q

Describe the mechanism by which phospholipids diffuse through membrane versus flip-flop.

A

Lateral diffusion of lipids occurs passively in the plasma membrane (does not require enzymes).

Flip-flop occurs but needs to be facilitated by specialized proteins (scrambles and flippase).

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9
Q

Name the four main phosphate head groups and their typical orientations in the plasma membrane.

A

ethanolamine, choline, serine, inositol

PI and PS generally face cytosol
PC faces ECM

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10
Q

Where is sphingomyelin oriented in the plasma membrane? Why?

A

Sphingomyelin is primarily found on the ECM side of the plasma membrane.

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11
Q

Describe the differences between saturated and unsaturated fatty acids and their affect on the plasma membrane.

A

Saturated fatty acids are hydrocarbon chains formed completely with single bonds. As a result, these fatty acids pack together tightly which makes the plasma membrane

Unsaturated fatty acids are hydrocarbon chains formed with at least one double bond, causing a kink in the tail. Therefore these fatty acids create a more fluid plasma membrane but it can be more leaky, leading to the need for cholesterol.

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12
Q

What are two functions of cholesterol in the plasma membrane?

A
  1. Cholesterol helps with leakiness in the plasma membrane by intercalating between two phospholipids (between the kinks of an unsaturated tail adjacent to a saturated fatty acid).
  2. Cholesterol helps maintain membrane fluidity at physiological temperature, preventing the crystallization of adjacent fatty acid tails.
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13
Q

What is a main function of glycolipids with regarding to cell-cell signaling?

A

Glycolipids act as antigen determinants (A, B, O), depending on whether you have the enzymes to build the specific sugar groups.

It also functions as a toxin receptor.

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14
Q

What are the glycolipid sugar groups for each blood type?

A 
A = N-acetylgalactosamine
B = galactose
AB = both sugars
O = neither sugar
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15
Q

Describe some of the main functions of lipids in the plasma membrane.

A
  • cause charge differential across membranes
  • participate in signaling reactions
  • antigenic determinants
  • determine fluidity of membranes
  • influence clearance of cells from circulation
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16
Q

peripheral proteins

A
  • associate with other proteins that are embedded in the membrane via ionic interactions
  • easy to remove from membrane
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17
Q

integral proteins

A
  • contain hydrophobic inner domain that interfaces with fatty acid tails and hydrophilic ends on either side of plasma membrane
  • asymmetrically distributed
  • must use harsher treatments to remove them since they span the membrane
18
Q

What three types of proteins always face the extracellular environment? Why?

A
  • N-linked glycosylations
  • Intrachain disulfide bonds
  • GPI-linked proteins
19
Q

What type of protein faces the intracellular environment? Why?

A
  • Pre-sulfhydryl groups
20
Q

What role does isoprenylation play in the normal and abnormal functioning of cells?

A
  • cell-cell recognition
  • cell-matrix interactions
  • signal transduction processes
  • cell migration
  • transport
21
Q

glycocalyx

A

sugar moieties on the outer portion of the membrane (looks fuzzy in slides)

22
Q

What role does the glycocalyx play in the interaction of platelets and the lining of blood vessels (non-thrombogenic surfaces)? Biological significance?

A

causes repulsion between platelets and the blood vessel linings because sugar moieties on both cells is negative

23
Q

What size is the plasma membrane? Can it be viewed using a light microscope?

A

plasma membrane = 5-10nm

need special stains and should use electron microscope to see trilaminar structure (resolution of 2nm)

24
Q

What is the purpose of knowing whether the slide is looked at via LM or EM?

A
  • helps viewer determine whether they are looking outside or inside cell
  • use scale bars!!
25
Q

What are the net charges of the different phospholipids and why are these important?

A
  • phosphatidyl-ethanolamine = 0
  • phosphatidyl-serine = -1
  • phosphatidyl-choline = 0
  • phosphatidyl-inositol = -1

anionic phospholipids (PI and PS) generally facing cytosol –> important for signal transduction (activation of protein kinase C)

26
Q

What is the significance of flipped phospholipids?

A

When PS flips, it signals several biological processes:]

  • apoptosis–programmed cell death, important for development
  • hemostasis–important for blood clotting
  • RBC aging–recognition by macrophages
27
Q

annexin V

A
  • high affinity for PS

- can be used to identify different pathologies

28
Q

annexin V

A
  • high affinity for PS

- can be used to identify different pathologies

29
Q

N-linked glycosylations

A

formed in the ER

30
Q

CD (proteins)

A
  • cluster differentiation
  • used in diagnostics to identify surface proteins?
  • CD markers on integral membrane proteins
31
Q

fatty acyl group

A

synthesized in cytosol

anchored to membrane on cytosol side

32
Q

GPI-linkage

A

occurs in lumen of ER (like N-linked sugars)

33
Q

How does paroxysmal nocturnal hemoglobinuria (PNH) demonstrate the importance of GPI-linkages?

A

In PNH, hemolysis of RBC’s is the consequence of complement activity in normal serum (set of proteins put holes in membranes, killing cells). This complement system is generally inactive due to the presence of GPI-linkages. It is caused by a mutation of the PIG-A (phosphatidylinositol glycan class A) gene in marrow still cells. In other words, the GPI-linked moiety can’t be put on proteins. Normally, GPI-linkages act as an inhibitor to the complement activation pathway. Complement activation leads to the leakage of hemoglobin and red urine. Flow cytometry can be used to diagnosis PNH using CD 55 or CD 59 (antibodies).

34
Q

lectin

A

“sugar-loving”

important for cell-cell interactions (binds with surface carbohydrates)

35
Q

lipid rafts & caveolae

A
  • cholesterol- & sphingolipid-rich (microdomain)
  • lipids and proteins together
    exist in outer portion of PM
  • brings receptors and signaling molecules together
36
Q

different ways to bring material into cell?

A
  1. phagocytosis:
  2. pinocytosis:
  3. endocytosis:
37
Q

Na+ ion concentration inside and outside cell (mM)

A
  • intracellular: 5-15 mM (low inside)

- extracellular: 145 mM (high outside)

38
Q

K+ ion concentration inside and outside cell (mM)

A
  • intracellular: 140 mM (high inside)

- extracellular: 5 mM (low outside)

39
Q

Ca++ ion concentration inside and outside cell (mM)

A
  • intracellular: 10^-4 mM (extremely low inside)

- extracellular: 1-2 mM (very high outside)

40
Q

how are ion levels inside/outside cell controlled?

A
  • channel-mediated–bulk flow of ions (passive)

- transport protein–requires ATP, one ion at a time (active)

41
Q

What role do microvilli play in Na+ absorption?

A
  • presence of microvilli increases absorption of nutrients such as Na+
  • passive transport of Na+ into epithelial cell (paired with glucose)
  • Na+/K+ pump on basal domain pumps Na+ out of cell into basement membrane vasculature (needs ATP, moving against gradient)
42
Q

functions of PM

A
  • pivotal in: endocytosis/exocytosis, adhesion, movement (chemotaxis), signal transduction
  • selectively permeable barrier controlling movement of nutrients and waste

Histology/Cell Biology (12 decks)

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