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BIO 202 > Membrane Structure and Function > Flashcards

Membrane Structure and Function Flashcards

1
Q

Most abundant lipids in membranes =

A

phospholipids

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2
Q

Phospholipid Composition

A

Polar Head =
1) Glycerol backbone
2) Phosphate Group
3) Side Chain (off of phosphate)

Hydrophobic Tails =
1) Fatty acid chains (2)

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3
Q

Phosphate

A

PO4 -

–> Charged group

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4
Q

Ampiphatic

A

Meaning to have BOTH hydrophilic and hydrophobic regions

(like phospholipids do)

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5
Q

Saturated

A

ONLY single bonds (has greater rotation)

1) Physically more rigid
2) More compact
3) Can fit more into one unit of volume

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6
Q

Unsaturated

A

Contains double bond/s (has less rotation at sites of double bond)

1) Physically less rigid –> More fluid
2) Has “kinks”
3) Can’t stack well

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7
Q

Saturation of phospholipids exist in a…

A

RANGE –> More of a “dimmer switch” analogy rather than a traditional light switch

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8
Q

The plasma membrane is a…

A

Phospholipid bilayer

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9
Q

Phospholipid Bilayer

A

A double layer of phospholipids in which the polar heads face out and the tails face in (to each other)

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10
Q

The bilayer structure of membranes creates…

A

A membrane that is an effective cellular barrier

–> The membrane is largely impermeable to charged/polar molecules

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11
Q

The membrane is impermeable to charged/polar molecules because…

A

Of the ampiphatic nature of the phospholipids and their created bilayer

–> Charged/polar molecules cannot pass (diffuse ) through the hydrophobic interior of the membrane

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12
Q

Fluid-Mosaic Model

A

Fluid = Refers to phospholipids

Mosaic = Refers to proteins

“A mosaic of protein molecules bobbing in a “fluid” bilayer of phospholipids”

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13
Q

Distribution of proteins in a membrane is…

A

NOT random

–> Groups of proteins are often associated in long-lasting, specialized patches where they carry out common functions

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14
Q

Fluidity of Membranes

A

Membranes are not static sheets of molecules locked rigidly in place

–> It is dynamic, it moves

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15
Q

Lateral Movement

A

Side to side movement of lipids in a membrane

–> Very frequent, rapid

–> “Like partygoers elbowing their way through a crowd”

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16
Q

2 types of membrane movement:

A

1) Lateral movement
2) Flip-flop movement

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17
Q

Flip-Flop Movement

A

When a lipid switches sides across the membrane (to the opposite layer)

–> Very rare, but can happen

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18
Q

Issue of the flip-flop movement is…

A

Very difficult to do as the polar head must enter the non-polar region of the bilayer to come out the other side

–> Requires A LOT of energy to do so

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19
Q

Do proteins move in membranes?

A

YES, they can but many do not

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20
Q

Moving Proteins

A

–> Proteins move at a much slower rate than lipids (due to larger size)

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21
Q

Types of protein movement in membranes

A

1) Highly directional manner
2) Simply drifting in the membrane

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22
Q

Non-moving Proteins

A

Many membrane proteins do not move as they are bound/fixed by the ECM or cytoskeleton

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23
Q

What does the fluidity of a membrane depend on?

A

Composition AND temperature

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24
Q

> # Unsaturated Phospholipids =

A

Increase in fluidity (close packing is not as possible)

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25
Unsaturated phospholipids solidify at...
Lower temperatures --> Lower freezing point
26
> # saturated phospholipids =
Decrease in fluidity (closer packing is possible)
27
Saturated phospholipids solidify at...
Higher temps --> Higher freezing point
28
Cholesterol
A bulky molecule wedged between phospholipids in a membrane
29
Effects of cholesterol under high temp
Restricts movement of phospholipids (decreases fluidity)
30
Effects of cholesterol under low temp
Prevents close packing of phospholipids (causes freezing point to decrease) (increases fluidity)
31
Cholesterol is known as a...
"Fluidity buffer" : Resists changes in membrane fluidity that can be caused by changes in temp --> Cholesterol has a "dual effect"
32
Membranes must be ____ to work properly
Fluid: --> Allows membranes to be permeable and allows for proteins to move in membrane where needed
33
Membrane that is too fluid:
Cannot support protein function
34
Membrane that is too rigid:
1) Changes permeability 2) Can make enzymes inactive if they require movement
35
Extreme environments pose a serious threat as...
It can affect membrane fluidity (make it either too fluid or too rigid)
36
Plants have a _____ amount of unsaturated phospholipids because...
GREATER This prevents their membranes from freezing in winter when temperature get very cold
37
2 main types of membrane proteins:
1) Peripheral proteins 2) Integral proteins
38
Integral Proteins
Proteins that penetrate the hydrophobic interior of the membrane --> Sit IN the membrane
39
Transmembrane Proteins
Extend through the entirety of the membrane (poke out on both sides) --> Make up the majority of integral proteins
40
Transmembrane proteins have 2 types of _________
DOMAINS --> Hydrophobic domain = inside bilayer --> Hydrophilic domain = poking outside of membrane
41
Hydrophilic Domain
= "loops" of protein poking out of the membrane
42
Hydrophobic Domain
= region of protein inside the membrane (mainly alpha-helix structure)
43
Peripheral Proteins
Proteins that are loosely bound to the surface of the membrane --> NOT inserted into membrane: works WITH the membrane
44
Peripheral proteins are often loosely bound to the membrane through...
Association with exposed regions of integral proteins
45
"Sidedness" of Membranes
Membranes are asymmetrical: they have distinct inside and outside faces
46
Faces of Membrane
Inside Face = cytoplasmic side Outside Face = extracellular side
47
Asymmetrical Membrane Landscape
Composition of membranes (proteins, lipids, carbs.) is different for inner and outer layers
48
Functions of Membrane (2)
1) Cell-cell recognition and COMMUNICATION 2) Transport: Regulating what goes in and out of the cell
49
Selective Permeability
Allows some substances to cross the membrane more easily than others EX: Polar molecules either can't pass or pass through membrane very slowly
50
Common Membrane Proteins (6)
1) Transport/"channel" proteins 2) Enzymes 3) Intercellular Joinings (Linkers) 4) Cell-Cell Recognition (glycoproteins) 5) Signal Transduction (Receptors) 6) Proteins attached to ECM or cytoskeleton (structural support proteins)
51
Transport Proteins
Span the membrane to create a hydrophilic channel that polar molecules/ions can travel through --> UNI-Directional
52
Transport proteins are specific to...
the substrate is moves/translocates
53
Membrane Enzymes
Proteins that carry out enzymatic activities in the membrane (sometimes these enzymes create a chain of reactions) --> No transport
54
Intercellular Connection Proteins
Proteins such as linkers that tether certain cellular regions together (to form JUNCTIONS)
55
Cell-Cell Recognition Proteins
Identification tags: Mainly glycoproteins that are specifically recognized by membrane proteins on other cells --> Brief tethering (don't bind permanently): They bind to recognize and then release
56
Signal Transduction Proteins
Receptors: Accept a chemical messenger (signal) and then relay the message into the cell (transduction)
57
Proteins that bind to ECM/Cytoskeleton
Structural support proteins: --> Coordinate extra- and intra- cellular changes --> Help to maintain cell shape --> Stabilize the location of some other membrane proteins
58
Extra Cellular Matrix (ECM)
Helps the cell to adhere and communicate: network of fibers and materials outside of cell
59
ECM Components
1) Collagen 2) Proteoglycans 3) Fibronectin 4) Integrins
60
Collagen
Most abundant glycoprotein --> Found in ECM
61
Proteoglycans
Small core proteins with many carbohydrate chains covalently attached
62
Fibronectin
Attaches the ECM to integrins
63
Integrins
Membrane proteins that bind to the ECM on the outside and the cytoskeleton on the inside --> *Transmit signals between inside and outside cellular environment

BIO 202 (33 decks)

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