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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
Q

Unsaturated phospholipids solidify at…

A

Lower temperatures
–> Lower freezing point

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26
Q

> # saturated phospholipids =

A

Decrease in fluidity (closer packing is possible)

27
Q

Saturated phospholipids solidify at…

A

Higher temps

–> Higher freezing point

28
Q

Cholesterol

A

A bulky molecule wedged between phospholipids in a membrane

29
Q

Effects of cholesterol under high temp

A

Restricts movement of phospholipids

(decreases fluidity)

30
Q

Effects of cholesterol under low temp

A

Prevents close packing of phospholipids
(causes freezing point to decrease)

(increases fluidity)

31
Q

Cholesterol is known as a…

A

“Fluidity buffer” : Resists changes in membrane fluidity that can be caused by changes in temp

–> Cholesterol has a “dual effect”

32
Q

Membranes must be ____ to work properly

A

Fluid:

–> Allows membranes to be permeable and allows for proteins to move in membrane where needed

33
Q

Membrane that is too fluid:

A

Cannot support protein function

34
Q

Membrane that is too rigid:

A

1) Changes permeability
2) Can make enzymes inactive if they require movement

35
Q

Extreme environments pose a serious threat as…

A

It can affect membrane fluidity (make it either too fluid or too rigid)

36
Q

Plants have a _____ amount of unsaturated phospholipids because…

A

GREATER

This prevents their membranes from freezing in winter when temperature get very cold

37
Q

2 main types of membrane proteins:

A

1) Peripheral proteins
2) Integral proteins

38
Q

Integral Proteins

A

Proteins that penetrate the hydrophobic interior of the membrane

–> Sit IN the membrane

39
Q

Transmembrane Proteins

A

Extend through the entirety of the membrane (poke out on both sides)

–> Make up the majority of integral proteins

40
Q

Transmembrane proteins have 2 types of _________

A

DOMAINS

–> Hydrophobic domain = inside bilayer

–> Hydrophilic domain = poking outside of membrane

41
Q

Hydrophilic Domain

A

= “loops” of protein poking out of the membrane

42
Q

Hydrophobic Domain

A

= region of protein inside the membrane

(mainly alpha-helix structure)

43
Q

Peripheral Proteins

A

Proteins that are loosely bound to the surface of the membrane

–> NOT inserted into membrane: works WITH the membrane

44
Q

Peripheral proteins are often loosely bound to the membrane through…

A

Association with exposed regions of integral proteins

45
Q

“Sidedness” of Membranes

A

Membranes are asymmetrical: they have distinct inside and outside faces

46
Q

Faces of Membrane

A

Inside Face = cytoplasmic side

Outside Face = extracellular side

47
Q

Asymmetrical Membrane Landscape

A

Composition of membranes (proteins, lipids, carbs.) is different for inner and outer layers

48
Q

Functions of Membrane (2)

A

1) Cell-cell recognition and COMMUNICATION

2) Transport: Regulating what goes in and out of the cell

49
Q

Selective Permeability

A

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
Q

Common Membrane Proteins (6)

A

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
Q

Transport Proteins

A

Span the membrane to create a hydrophilic channel that polar molecules/ions can travel through

–> UNI-Directional

52
Q

Transport proteins are specific to…

A

the substrate is moves/translocates

53
Q

Membrane Enzymes

A

Proteins that carry out enzymatic activities in the membrane (sometimes these enzymes create a chain of reactions)

–> No transport

54
Q

Intercellular Connection Proteins

A

Proteins such as linkers that tether certain cellular regions together (to form JUNCTIONS)

55
Q

Cell-Cell Recognition Proteins

A

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
Q

Signal Transduction Proteins

A

Receptors:

Accept a chemical messenger (signal) and then relay the message into the cell (transduction)

57
Q

Proteins that bind to ECM/Cytoskeleton

A

Structural support proteins:

–> Coordinate extra- and intra- cellular changes
–> Help to maintain cell shape
–> Stabilize the location of some other membrane proteins

58
Q

Extra Cellular Matrix (ECM)

A

Helps the cell to adhere and communicate: network of fibers and materials outside of cell

59
Q

ECM Components

A

1) Collagen
2) Proteoglycans
3) Fibronectin
4) Integrins

60
Q

Collagen

A

Most abundant glycoprotein

–> Found in ECM

61
Q

Proteoglycans

A

Small core proteins with many carbohydrate chains covalently attached

62
Q

Fibronectin

A

Attaches the ECM to integrins

63
Q

Integrins

A

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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