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PMP-101 > Plasma membrane: Composition & Functions > Flashcards

Plasma membrane: Composition & Functions Flashcards

1
Q

What is the role of plasma membrane?

A

Separates the living cell from its surroundings - essential for all cells

A barrier for contents of the cell from escaping and mixing with other molecules from surrounding environment

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2
Q

In eukaryotic cells only…..

A

compartmentalisation of individual organelles - specific composition for specific reactions

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3
Q

lipid bilayer = explain structure

A

Lipids are arranged in two closely apposed sheets - forming lipid bilayer

proteins are embedded and some carbohydrates

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4
Q

Phospholipids

A

most abundant lipids in plasma membrane - arranged in two-layer sheets
(phosphatidylcholine is MOST abundant)

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5
Q

phosphate group are:

A

hydrophilic- water loving
Heads are arranged outward - exposed to aqueous solutions

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6
Q

what are hydrophilic - water repellent in the bilayer?

A

fatty acid tails - arranged inward, shield water and form a sealed comportment

weak hydrophobic interaction between fatty acid tails to form a bilayer

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7
Q

What is the fluid mosaic model?

A

dynamic and complex structure of plasma membrane

Mosaic (of components) - besides phospholipids, glycolipids, sterols (cholestreol in mammalian cells) and various proteins and glycoproteins

Fluid - dynamic and flexible = viscosity of the lipid bilayer

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8
Q

lipid molecules able yo 2- dimensionally move along

A

the plane of the bi-layer

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9
Q

Phospholipid movements??

A

can lead to
- Rapid lateral diffusion of lipid molecules within the plane of each monolayer
- Spin in place (rotation - up to 500 revolutions per s)
Flexion; contraction movement
Flip-flop; from a side to the other

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10
Q

Do proteins usually move?

A

no - anchored to cytoskeleton
ONLY some proteins can slightly and slowly move driven by the motor proteins

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11
Q

Amphiphatic

A

compounds that are polar and non-polar

hydrophobic regions (non-polar a.a) - often coiled into a helics - lie in the interior of the bilayer

Hydrophilic regions of a.a are exposed to external aqueous environment

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12
Q

Which other molecules are also amphiphatic?

A

cholesterol
glycolipids

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13
Q

Cholesterol - 20% of membrane lipids = modulates the membrane fluidity and improving stability

A

stiffen the membrane ( less flexible and permeable)
Reducing molecules passage

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14
Q

Glycolipids :

A

lipids containing sugars representing their hydrophilic head

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15
Q

Which way do sugar groups face

A

cell exterior (bilayer is asymmetrical)

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16
Q

How are membrane protein synthesised?

A

rough ER

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17
Q

other proteins embedded in membrane are exclusively on the _______

A

cytosolic

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18
Q

how are peripheral membrane proteins attached to membrane lipids or other integral membrane proteins

A

covalently

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19
Q

what are the main functions of membrane proteins?

A

1) transport of molecules
2) enzymatic activity
3) signal transduction/ cell communication
4) structural support / attachment to the extracellular matrix (ECM)

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20
Q

most membrane proteins are glycoproteisn -

A

short chains of sugars linked to a.a (facing extracellular space)

= protect the cell surface from mechanical damage and involved in cell-to-cell communication
- protein glycosylation = post - translational modoficsagtion in rough ER and Golgi appartus

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21
Q

most membrane proteins are glycoproteisn -

A

short chains of sugars linked to a.a (facing extracellular space)

= protect the cell surface from mechanical damage and involved in cell-to-cell communication
- protein glycosylation = post - translational modification in rough ER and Golgi apparatus

22
Q

Trasport Across a cell membrane are

A

selectively permeable -0 regulating traffic molecules and ions in adn out of cells

23
Q

Two main types of transport

A

1) passive
2) Active transport

24
Q

Passive transport ( 3 types) - movement of molecules w/o expenditure energy

A

movement DOWN gradient - reach equilibrium

1) diffusion
2) osmosis
3) facilitated diffusion

25
Q

Diffusion, which molecules?

A

FREE movement of molecules across the lipid bilayer

NO energy (ATP) cost

DOWN gradient concentrations (until equilibrium)

Gases - O2 + CO2
small uncharged polar molecules - urea, ethanol
(many are too large molecules)

26
Q

Osmosis

A

SPONTANEOUS movement (passive transport) of water/ solvent across a semipermeable membrane

DOWN conc

Water potential of a solution is inversely porportional to the solutes concentration

when SOLUTES cannot go across the membrane - osmosis occurs

27
Q

What is osmotic pressure?

A

hydrostatic
pressure required to stop the net flow of water across a membrane separating solutions of different water potentials

28
Q

how can water flow in/out of cells?

A

through aquaporins (facilitated diffusion)

29
Q

Types of osmosis;

A
  1. isotonic solution
  2. hypertonic solution
  3. hypotonic solution
30
Q
  1. isotonic solution
A

a solution with the same concentration of solutes both inside and outside the cell

equal

(NORMAL no net water movement)

31
Q
  1. hypertonic solution
A

a solution that has a higher solute concentration outside the cell than inside

(SHRIVELED - cell loses water)

32
Q
  1. hypotonic solution
A

a solution that has a higher solute concentration inside the cell than outside

(LYSED/ BURSED - cell gains water)

33
Q

Effect of Osmotic pressure on blood cells

A

The movement of water across the plasma membrane determines the volume of an individual cell, which must be regulated to avoid damage to the cell.

changes in osmotic conditions cause cells to swell or shrink rapidly

34
Q

Facilitated diffusion – Passive transport

A

DOWN conc via transport proteins

Highly specific

Reversible

No energy (ATP) cost

35
Q

Transport protein;

A
  • protein channel
  • protein carrier/ transporters (small molecules or ions)
36
Q

Protein channels

A

form a hydrophilic “tube” across the membrane through which specific molecules/ions diffuse (down a concentration gradient)

Do not interact with the molecules, although specific

Move at a very rapid rate

Passive transport (no energy cost)

37
Q

Protein carrier/transporters – passive transport
(facilitated diff)

A

Shift/Transport a single type of molecule (ions or small molecules) across the membrane (not as a channel.

It involves the Interaction with the specific molecule (shape complementarity) that induces a conformational change of the protein to mediate the transport of the molecule
Work at a much slower rate than channels

38
Q

Three transporter types

A

uniporters, symporters* and antiporters

Uniporter is the only transporter based in passive transport.

39
Q

Symporters and antiporters (

A

based on cotransport of more than 1 molecule are active transport

against the concentration/electric gradient

40
Q

Symporters and antiporters (

A

based on cotransport of more than 1 molecule are active transport

against the concentration/electric gradient

41
Q

Active transport

A

Moves substances against their concentration or electrochemical gradients

Requires energy, usually in the form of ATP

Performed by specific proteins embedded in the membranes

Allows for stockpiling

42
Q

Common features of transport proteins and enzymes

A

Specific binding sites for the solute
Can be saturated

Can be inhibited by molecules that resemble the normal “substrate”

Catalyse a physical process

43
Q

Protein carrier/transporters – Active transport

A

based on binding with the molecule - shape complimentary

43
Q

Protein carrier/transporters – Active transport

A

based on binding with the molecule - shape complimentary

44
Q

Symporters moving _ different molecules across the cell membrane ( _____ direction)

A

2
same

45
Q

Antiporter moving _ distinct molecules across the membrane ( ______ directions) E.g. Na+-K+ pump uses the energy of one ATP to pump 3 Na+ out and 2 K+ in.

A

2
opposite

46
Q

Vesicle Transport - Transport of large macromolecules

A

Bulk transport requires vesicle transport (endomembranous system)

two main types of transport - endo/exocytosis

47
Q

Endocytosis

A

> Uptake (from outside to inside) of macromolecules and large particles

  • Invagination of the cell surface to form an intracellular membrane-bounded vesicle containing extracellular fluid
48
Q

Exocytosis

A

> Secretion or excretion (from inside to outside) e.g. insulin (protein hormone) by pancreatic cells

  • Transport vesicles (from Golgi) migrate to the plasma membrane, fuse with it, and release their contents
49
Q

Types of endocytosis

A

1) Phagocytosis (“cellular eating”)
2) Pinocytosis (“cellular drinking”)
3) Receptor-mediated endocytosis

PMP-101 (53 decks)

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