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Molecular Biology Flashcards > Cell Membrane Structure > Flashcards

Cell Membrane Structure Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

Learning Outcomes

A
  • Outline the components of cell membrane
  • Understand the structures and functions of cell
    membrane
  • describe the roles of membrane proteins
    Reading:
  • Alberts et al. Molecular Biology of the Cell, Ch10
  • Alberts et al. Essential Cell Biology, Ch11
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2
Q

Membrane structure

A
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3
Q

Membrane structure

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4
Q

Freeze fracture

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4
Q

Plasma Membrane – Lipid bilayer

A

Very thin film of lipid and protein molecules held together mainly by noncovalent
interactions
dynamic, fluid structures, molecules move about in the plane of the membrane
Lipid bilayer – basic fluid structure, impermeable barrier (water-soluble molecules)

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5
Q

Building block #1 – Lipids

A

About 50% of the mass of most animal cell membranes (the remainder – protein)
~ 5 x 106 lipid molecules in a 1µmx 1µm area of lipid bilayer
109 lipid molecules in the small animal cell membrane
All lipid molecules are amphiphilic (amphipathic)
hydrophilic (“water-loving”) or polar end
hydrophobic (“water-fearing”) or nonpolar end

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6
Q

Phospholipid

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7
Q

4 major phospholipids

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8
Q

Cholesterol

A

Eukaryotic plasma membrane contain especially large amounts of cholesterol
- up to one molecule for every phospholipid molecule
Orientation of cholesterol – hydroxyl group close to the polar head groups of adjacent
phospholipid molecules when forming bilayer

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9
Q
A
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10
Q

Hydrophilic vs. hydrophobic in water

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11
Q

Phospholipids spontaneously form bilayers

A

Shape/amphiphilic nature of phospholipid cause spontaneous formation of lipid bilayer in
aqueous environments
Minimise the exposure of hydrophobic tails from water molecules – self-sealing property

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12
Q
A
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13
Q

Lipid bilayer is a 2D fluid

A
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14
Q

Membranes in cells get more help

A

Issues with liposome model
- liposomes do not fuse spontaneously (fusion proteins)
- Rare flip-flop (flippases or phospholipid translocators)
Newly synthesised phospholipid (ER) can form both cytosolic and
non-cytosolic monolayers of lipid bilayer

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15
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16
Q

Fluidity depends on temperature and composition

A

Double bonds (kink) – harder to pack
together - more difficult to freeze
Microorganisms with less temperature
controlling capacity may synthesise more
cis-fatty acid with temperature drop

Cholesterol modulates the properties
- tighten the packing (low permeability to water)
while maintaining fluidity

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17
Q
A

Fluidity depends on its composition

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18
Q

Phase separation

A
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19
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20
Q

Raft domain

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20
Q

Phase separation

A

Weak protein-protein, protein-lipid, and lipid-lipid interactions reinforce one another to
partition the interacting components into raft domains.
Functional group – e.g. converting extracellular signals into intracellular ones
Increased thickness

21
Q

Lipid droplets

A

Cells store an excess of lipids in lipid droplets
- can be used as building blocks for membrane synthesis or as a food source
- Adipocytes (fat cells) are specialised for lipid storage
- Most cells have many smaller lipid droplets
- Stored lipids are exclusively hydrophobic molecules (triacylglycerols and cholesterol esters)
- 3D droplet with monolayer of phospholipids

22
Q

Lipid droplets

A
23
Q

Asymmetry is FUCTIONALLY important

A

The asymmetrical distribution of
phospholipids and glycolipids in the
lipid bilayer of human red blood cells
(cholesterols are not shown)
Phosphatidylcholine
Sphingomyelin
Phosphatidylethanolamine
Phosphatidylserine
glycolipid

23
Q
A

Converting extracellular signal to intracellular ones
- Protein kinase C (PKC) enzyme requires (-) charged phospholipid – concentrated
phosphatidylserine in cytosolic face
- fragments of phospholipid act as short-lived intracellular mediators (phospholipase C)
- apoptosis: flip-flop of phosphatidylserine from cytosolic to extracellular monolayer

24
Q
A
25
Q

Glycolipids

A

Sugar-containing lipid: glycolipids
Exclusively found in the monolayer facing away
from cytosol
Based on sphingosine similar to sphingomyelin
Usually form lipid raft (separation)
Cell-recognition processes (cell-cell binding)
Entry points for certain bacterial toxins or viruses

SEC

26
Q

Glycolipids

A
27
Q

Building block #2 – membrane Proteins

A

About 50% of the mass of most animal cell membranes (the remainder – lipid)
~ 50 lipid molecules for each protein molecule (protein molecules are larger)
Lipid provides the basic structure of biological membranes, and proteins give its
characteristic functional properties.
Highly variable per membrane types
<25% mass in myelin membrane to serve electrical insulation for nerve cell axons
~75% mass in internal membrane of mitochondria for ATP production

28
Q

Various ways of membrane protein association

A
28
Q

Lipid anchors

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29
Q

a-helical conformation of transmembrane proteins

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30
Q

Many membrane proteins are Glycosylated

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30
Q

Transmembrane a helices interact with one another

A
31
Q

Many membrane proteins are Glycosylated

A

Most plasma membrane
proteins are glycosylated
Carbohydrates extensively
coat the surface of all
eukaryotic cells
Enormously diverse
Usually <15 sugars
Functions
Mechanical protection
Cell-cell recognition
and more

MC

31
Q

Some b barrels form large channels

A
31
Q

Some b barrels form large channels

A

Mostly found in the outer membranes of bacteria, mitochondria, and chloroplasts
Multipass membrane protein – pore forming proteins
Most multipass in eukaryotic cells are constructed from a helices

32
Q

Detergents

A

Detergent molecules are
amphiphilic and cone-shape
Forming micelles rather than
bilayers
Irregular shape due to packing
constraints

33
Q

Detergents

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33
Q

Na+-K+ pump in phospholipid vesicle

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34
Q

Membrane protein purification using detergents

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35
Q

Protein diffusion in plasma membrane

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36
Q

Membrane proteins with various functions

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37
Q

FRAP – fluorescence recovery after photobleaching

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38
Q

Confine proteins/lipids to specific domains

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39
Q

Cell Membrane

A
40
Q

Membrane bending proteins deform bilayers

A
41
Q
A

Molecular Biology Flashcards (28 decks)

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