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Flashcards in Cell membrane Deck (51)
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1
Q

What are some of the main functions of the plasma membrane?

A

It separates the living cell from its surroundings
It is involved in cell recognition and messaging
It controls cell’s internal environment (selective permeability)

2
Q

What are functions common to membranes in general?

A

They define compartments (organelles) inside the cell

They are involved in metabolic processes

3
Q

What did Langmuir discover ?

A

That the fatty acids in phospholipids are oriented vertically with polar group in water

4
Q

What did Gorter and Grendel find in 1925 ?

A

That red blood cells were covered by a bilayer of phospholipids

5
Q

What did Davson and Danielli propose in 1935?

A

The sandwich model: phospholipid bilayer lies between two layers of globular proteins

6
Q

What model did Singer and Nicolson propose in 1972?

A

The fluid mosaic model: the membrane is a mosaic of proteins dispersed within the bilayer, with only the hydrophilic regions exposed to water

7
Q

How do phospholipids move within the bilayer?

A

They move laterally (most of the time)

Flip-flop (rarely)

8
Q

What has an influence on membrane fluidity?

A

Saturation of fatty acids

Presence of cholesterol (in animals)

9
Q

How do fatty acids influence membrane fluidity?

A

Membranes rich in unsaturated fatty acids are more fluid that those rich in saturated fatty acids

10
Q

How does cholesterol influence membrane fluidity?

A

It reduces phospholipids movement & membrane fluidity at moderately high temperatures
Maintains membrane fluidity at low temperatures by preventing tight packing

11
Q

What determine most of the membrane’s specific functions ?

A

Proteins

12
Q

What is the role of carbohydrates on the plasma membrane ?

A

They are involved in cellular recognition

13
Q

Why is the plasma membrane selectively permeable ?

A

In order to regulate molecular traffic

14
Q

Do polar or non-polar molecules cross the lipid bilayer the most easily and why ?

A

Non-polar (hydrophobic) molecules

They can dissolve in the lipid bilayer

15
Q

What are the three transport mechanisms that allow to control molecular traffic ?

A

Passive transport (No ATP needed)
Active transport
Bulk transport

16
Q

What are the two types of passive transport?

A

Simple diffusion

Facilitated diffusion

17
Q

What is diffusion ?

A

The tendency for molecules to spread out evenly into the available space
Molecules diffuse DOWN ther concentration gradient

18
Q

What is osmosis ?

A

The diffusion of water across a selectively permeable membrane ( from the region of lower solute concentration to the region of higher solute concentration)

19
Q

What is tonicity ?

A

The ability of a solution to cause a cell to gain or lose water

20
Q

What is an isotonic solution ?

A

The solute concentration in solution = to that inside the cell (no net water movement accross the plasma membrane)

21
Q

What is an hypertonic solution ?

A

The solute concentration in solution > than that inside cell (cell loses water)

22
Q

What is an hypotonic solution ?

A

Solute concentration in solution < than that inside cell (cell gains water)

23
Q

What is osmolarity ?

A

The total concentration of all solutes

24
Q

In what units is osmolarity measured ?

A

In Osmoles (Osm)

25
Q

What are examples of solutions isosmotic to the humain body ?

A
Saline solution (0.9% NaCl) 
5% glucose solution
26
Q

How is called the control of water balance in an organism ?

A

Osmoregulation

27
Q

What happens to a plant in a hypotonic solution ?

A

The cell swells until the wall opposes uptake

The cell is now turgid (firm)

28
Q

What happens to a plant in a isotonic solution ?

A

No net movement of water into the cell

The cell becomes flaccid (limp), and the plant may wilt

29
Q

What happens to a plant in a hypertonic solution ?

A

Plant cells lose water

Membrane pulls away from the wall (plasmolysis)

30
Q

What happens during facilitated diffusion ?

A

Transport proteins speed up the passive movement of molecules across the plasma membrane

31
Q

What to transport proteins might be used ?

A
Carrier proteins (permease) 
Channel proteins
32
Q

What does a channel protein ?

A

It provides corridors that allow a specific molecule or ion to cross the membrane

33
Q

What does a carrier protein ?

A

It undergoes a subtle change in shape that translocates the solute-binding site across the membrane

34
Q

Why is facilitated diffusion considered passive ?

A

Because the solute moves down its concentration gradient

35
Q

What does active transport ?

A

It moves substances against their concentration gradient

36
Q

What are characteristics of active transport ?

A

it is performed by specific integral membrane proteins

It requires energy, usually in the form of ATP

37
Q

What is an example of active transport ?

A

The sodium-potassium pump (Na+/K+-ATPase)

38
Q

What do ion pumps create ?

A

They create a membrane potential (a voltage difference across a membrane)

39
Q

How is the mmbrane potential created ?

A

By differences in the distribution of positive and negative ions

40
Q

How are called transport proteins that generate voltage across a membrane (such as ion pumps) ?

A

electrogenic pumps

41
Q

What is the main electrogenic pump of animal cells ?

A

The Na - K pump

42
Q

The main electrogenic pump of plants, fungi, and bacteria ?

A

The proton pump

43
Q

How can the membrane potential (voltage across membrane) be used

A

This energy can be used for cellular work ( ATP synthesis and cotransport )

44
Q

When does cotransport occur ?

A

When the active transport of a solute indirectly drives transport of another solute

45
Q

To what end do plants commonly use the gradient of hydrogen ions generated by proton pumps ?

A

To drive active transport of nutrients into the cell

46
Q

How do large molecules, such as polysaccharides and proteins, cross the membrane ?

A

In bulk via vesicules

47
Q

What are the two types of bulk transport ?

A

Endocytosis

Exocytosis

48
Q

How does endocytosis work ?

A

THe cell takes in macromolecules by forming vesicles from the plasma membrane

49
Q

What are the three types of endocytosis ?

A

Phagocytosis : the cell engulfs particle by forming vacuole
Pinocytosis : cell takes in extracellular fluid in vesicle

Receptor-mediated endocytosis: cell acquires bulk quantities of specific substance (ligands) that may not be highly concentrated in extracellular fluid

50
Q

How does exocytosis work ?

A

The transport vesicles migrate to the membrane, fuse with it, and release their contents

51
Q

How do many secretory cells use to export their products ?

A

Exocytosis