Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Cellular Biology > The Lipid Sea: Open Ocean? > Flashcards

The Lipid Sea: Open Ocean? Flashcards

Lecture 9

You may prefer our related Brainscape-certified flashcards:
AP® Biology flashcards Biology 101 flashcards
1
Q

Describe the fluid mosaic model by Singer and Nicolson.

A

A membrane is two fluid layers of phospholipids, with proteins localized within and on the bilayers. The model is described first as fluid because the lipids and proteins can easily move laterally in the membrane and also as a mosaic because of the presence of proteins within the membrane. Within this model, proteins bob along like bottles in the ocean, moving freely.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are the five physical properties of biomembranes?

A
  1. Stable, yet flexible
  2. Barrier to hydrophilic molecules
  3. Transverse asymmetry (Within a membrane and among organelles)
  4. Fluid
  5. Lateral asymmetry
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Describe the relationship between structure and function of biomembranes.

A

Biomembranes are functionally asymmetric because they are also structurally asymmetric.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Where does lipid flipping often occur?

A

smooth ER

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are the five functions of the smooth ER?

A
  1. Site of synthesis of many phospholipids and sterols.
  2. Involved in detoxification of lipid-soluble drugs and compounds.
  3. Carbohydrate metabolism.
  4. Calcium storage.
  5. Site of lipid droplet formation.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Why does the smooth ER appear smooth (compared to the rough ER)?

A

The smooth ER doesn’t have ribosomes and the rough ER does.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Where are the cones positioned in the bilayer?

A

the inner leaflet, cytosolic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Where are the cylinders positioned in the bilayer?

A

the outer leaflet, exoplasmic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Are lipids randomly distributed to either leaflet?

A

No, active cellular mechanisms determine how lipids are distributed to either leaflet.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Why are cones placed in the cytosolic leaflet?

A

Cones can pack more tightly together, which is useful for membranes that require a tight curve.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What determines the shape and function of a membrane?

A

Shape and location of the lipids

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Are proteins randomly distributed within a bilayer?

A

No, different proteins associated with different lipids. Proteins cannot be randomly replaced, nor can their directions be changed without consequence.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What does functional asymmetry mean in regards to bilayers?

A

Different functions occur on either side of a membrane

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What does structural asymmetry mean in regards to bilayers?

A

This refers to the asymmetric distribution of proteins.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What does transverse asymmetry refer to in regards to bilayers?

A

This refers to the different proportion of different types of phospholipids inside and outside of the cell.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Does phosphatidylcholine fill the volume of a cylinder or a cone?

A

cylinder

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Does phosphatidylethanolamine fill the volume of a cylinder or a cone?

A

cone

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Describe the structure of the smooth ER.

A

network of interconnected tubules

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Where does lipid synthesis begin?

A

at the cytosolic face of the smooth ER

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What is required for lipid synthesis?

A

fatty acids and glycerol

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is the precursor to fatty acids?

A

Acetyl CoA

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

How does Acetyl CoA transition into fatty acids?

A

via cytosolic enzymes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

How are fatty acids modified during lipid synthesis?

A

The OH group is replaced with an S-CoA group to create fatty acyl CoA.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

How is fatty acyl CoA modified during lipid synthesis?

A

Glycerol is added, to create glycerol phosphate, the foundation to attach fatty acids.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What do acyl transferases do during lipid synthesis?

A

take an acyl group from a fatty acid and attach it to glycerol to form diacyl glycerol

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What does a choline phosphotransferase do?

A

adds choline to diacyl glycerol to create phosphatidyl choline

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What makes it possible to synthesize lipids at the cytosolic side and have a bilayer? Why is it necessary?

A

Flippases are necessary because the cytosolic leaflet cannot expand indefinitely and because bilayers need 2 leaflets. They flip a lipid onto the opposing leaflet.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What do flippases do?

A

flip lipids from the cytosolic leaflet to the opposing one, equalizing the number of molecules between leaflets

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

Are flippases able to work on any lipids?

A

No, there are specific flippases for specific lipids.

30
Q

What are the three kinds of movement lipids can do in the plasma membrane?

A

transverse diffusion (flipping)
rotation
lateral diffusion

31
Q

Which is the most prominent glycoprotein in the outer layer of the plasma membrane for mammals?

A

phosphatidylcholine

32
Q

Which layer are the majority of glycolipids present in within the plasma membrane?

A

outer, exoplasmic leaflet

33
Q

Which is the rarest form of movement for lipids through the plasma membrane? Why?

A

Transverse diffusion is rare. It would require the hydrophilic heads to move through the hydrophobic region, which is energetically unfavorable.

34
Q

What is lateral diffusion for lipids in the plasma membrane?

A

when a lipid exchanges place with a neighboring lipid inside the plane

35
Q

Why does phospholipid transverse diffusion occur more frequently in natural membranes than in artificial lipid bilayers?

A

Some membranes have flippases (phospholipid translocators) that catalyze flip-flop of membrane lipids between monolayers.

36
Q

Which membranes have the most flippases?

A

Smooth ER membranes

37
Q

Which molecules can diffuse laterally, proteins or lipids?

A

Trick question! Both can.

38
Q

Which molecules, proteins or lipids, undergo lateral diffusion more quickly? Why?

A

Lipids are faster because they’re smaller. Proteins are much larger and interact with cytoskeletal proteins on the inside of a cell.

39
Q

Which technique demonstrates lateral diffusion of membrane lipids?

A

FRAP (fluorescence recovery after photobleaching)

40
Q

What is the FRAP technique used for?

A

Demonstrating lateral diffusion of membrane lipids and measuring the movements of proteins in the membranes

41
Q

How does membrane fluidity change with temperature?

A

Decreases as temperature drops, increases as it rises

42
Q

What is the transition temperature?

A

Tm is the temperature of the phase transition, at which a lipid bilayer becomes fluid when warmed from a solid gel-like state.

43
Q

What happens if a membrane drops below the Tm value?

A

All functions dependent on mobility or conformational changes of membrane proteins are disrupted, including transport of solutes across the membrane, detection of signals, and cell-to-cell communication.

44
Q

What four factors impact membrane fluidity?

A

temperature
shape of lipid
mixture of lipids
protein content

45
Q

Are all membrane transition temperatures the same?

A

No, depends on the membrane.

46
Q

What does polyunsaturated mean?

A

There are multiple alkenes in the hydrocarbon chain.

47
Q

What does saturated mean?

A

There are no double bonds in the hydrocarbon chain.

48
Q

What do alkenes do to hydrocarbon chains?

A

They add a kink, preventing hydrocarbon chains from packing well.

49
Q

Does the addition of alkenes increase or decrease membrane fluidity?

A

Increases fluidity by forcing the lipids to spread out away from each other by putting kinks in the chain.

50
Q

What influences does the length of the hydrocarbon chains have on fluidity?

A

Long chains decrease fluidity by providing more points of contact with opposing leaflets (feet interact more). Shorter chains increase fluidity.

51
Q

What impact does the presence of cholesterol have on the fluidity of a plasma membrane at low temperature? Why?

A

At low temperature, cholesterol separates hydrocarbon chains from each other and increases fluidity.

52
Q

What impact does the presence of cholesterol have on the fluidity of a plasma membrane at high temperature? Why?

A

At high temperature, cholesterol decreases fluidity. Cholesterol stabilizes the membrane due to cholesterol’s hydroxyl group’s hydrogen bonds with the oxygen in the ester of phospholipids. This increased interaction with cholesterol discourages phospholipid movement.

53
Q

How do organisms that experience frequent temperature transitions achieve set point fluidity for their membranes? Which organisms in particular do this?

A

Homeoviscous adaptation is when poikilotherms (organisms that cannot regulate their internal temperature) experience a drop in temperature, they synthesize unsaturated lipids to maintain fluidity, preventing the membrane from gelling.

54
Q

Describe how fluorescence recovery after photobleaching (FRAP) works for lipids. What does it reveal about plasma membranes?

A
  1. A cell’s surface lipids are labeled with fluorescent probe.
  2. A laser beam bleaches an area of the cell surface.
  3. Fluorescent-labeled molecules diffuse into the bleached area.
  4. After 20 seconds or so, the bleached area disappears.
    This indicates the lipids move laterally.
55
Q

What is the difference between lateral and transverse asymmetry?

A

Lateral asymmetry is the presence of similar lipids clumping within one leaflet. Transverse asymmetry is the difference in lipid content between the two leaflets.

56
Q

Describe how fluorescence recovery after photobleaching (FRAP) works for proteins. What does it reveal about plasma membranes?

A
  1. Membrane proteins are labelled with fluorescent proteins (like GFP).
  2. The cell surface is bleached with a laser.
  3. Over time, some fluorescence returns to the bleached area, but not to it’s original intensity.
    This reveals that proteins are laterally asymmetrical. Some proteins are mobile (moving into the bleached area), and others are immobile (remaining bleached). If proteins were symmetrical, the fluorescence in the bleached area would recover entirely.
57
Q

What restrains lateral mobility in the plasma membrane?

A

Tethering to the cytoskeleton. Membrane proteins are restrained because they interact with protein networks in the cytoplasm or with extracellular structures

58
Q

Describe the compartmentalized fluid model of plasma membrane structure.

A

The lipid is free to move, but cannot leave the area without a gap in the fence formed by transmembrane proteins and the lipids associated with them. Lipids move via hop diffusion.

59
Q

What causes hydrodynamic friction in the compartmentalized fluid model for the plasma membrane?

A

There is low mobility for all lipids in areas with transmembrane proteins, leading to hydrodynamic friction.

60
Q

What is the distance between transmembrane proteins?

A

3-12 nm

61
Q

What is the resolution for the best microscopes?

A

1-2 nm

62
Q

What is the diameter of a transmembrane protein?

A

0.7-3 nm

63
Q

What is the distance between cholesterol-exclusion domains?

A

2-11 nm

64
Q

Which increases fluidity of the plasma membrane more, cis or trans double bonds?

A

Cis. Trans alkenes increase fluidity, but are more able to pack like alkanes.

65
Q

What is an integral membrane protein?

A

Integral membrane proteins are embedded within the lipid bilayer, where they are held in place by the affinity of hydrophobic segments of the protein for the hydrophobic interior of the lipid bilayer. Majority are transmembrane.

66
Q

What is a peripheral membrane protein?

A

Peripheral proteins are much more hydrophilic than integral proteins and are therefore located on the surfaces of the membrane, where they are linked noncovalently to the polar head groups of phospholipids and/or to the hydrophilic parts of other membrane proteins.

67
Q

What are lipid anchored proteins?

A

Lipid-anchored proteins are essentially hydrophilic proteins and therefore reside on membrane surfaces, but they are covalently attached to lipid molecules that are embedded within the bilayer.

68
Q

What is a transmembrane protein?

A

They span both sides of the bilayer and must cross the membrane either once or multiple times.

69
Q

Describe the structure of a transmembrane protein.

A

A hydrophobic region called the transmembrane segment (20-30 amino acids if in an alpha helix) crosses the lipid bilayer. A hydrophilic region that extends to aqueous phase on one or both sides of the bilayer.

70
Q

Why are peripheral membrane proteins peripheral?

A

They lack discrete hydrophobic sequences and don’t penetrate into the lipid bilayer.

71
Q

What binds peripheral membrane proteins?

A

Electrostatic interactions and hydrogen bonding with weak hydrophilic portions of integral proteins and/or with polar head groups of membrane lipids.

Cellular Biology (23 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions