Plasma membrane: Composition & Functions

Question 1

What is the role of plasma membrane?

Answer 1

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

Question 2

In eukaryotic cells only…..

Answer 2

compartmentalisation of individual organelles - specific composition for specific reactions

Question 3

lipid bilayer = explain structure

Answer 3

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

proteins are embedded and some carbohydrates

Question 4

Phospholipids

Answer 4

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

Question 5

phosphate group are:

Answer 5

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

Question 6

what are hydrophilic - water repellent in the bilayer?

Answer 6

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

weak hydrophobic interaction between fatty acid tails to form a bilayer

Question 7

What is the fluid mosaic model?

Answer 7

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

Question 8

lipid molecules able yo 2- dimensionally move along

Answer 8

the plane of the bi-layer

Question 9

Phospholipid movements??

Answer 9

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

Question 10

Do proteins usually move?

Answer 10

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

Question 11

Amphiphatic

Answer 11

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

Question 12

Which other molecules are also amphiphatic?

Answer 12

cholesterol
glycolipids

Question 13

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

Answer 13

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

Question 14

Glycolipids :

Answer 14

lipids containing sugars representing their hydrophilic head

Question 15

Which way do sugar groups face

Answer 15

cell exterior (bilayer is asymmetrical)

Question 16

How are membrane protein synthesised?

Answer 16

rough ER

Question 17

other proteins embedded in membrane are exclusively on the _______

Answer 17

cytosolic

Question 18

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

Answer 18

covalently

Question 19

what are the main functions of membrane proteins?

Answer 19

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

Question 20

most membrane proteins are glycoproteisn -

Answer 20

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

Question 21

most membrane proteins are glycoproteisn -

Answer 21

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

Question 22

Trasport Across a cell membrane are

Answer 22

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

Question 23

Two main types of transport

Answer 23

1) passive
2) Active transport

Question 24

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

Answer 24

movement DOWN gradient - reach equilibrium

1) diffusion
2) osmosis
3) facilitated diffusion

Question 25

Diffusion, which molecules?

Answer 25

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)

Question 26

Osmosis

Answer 26

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

Question 27

What is osmotic pressure?

Answer 27

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

Question 28

how can water flow in/out of cells?

Answer 28

through aquaporins (facilitated diffusion)

Question 29

Types of osmosis;

Answer 29

1. isotonic solution
2. hypertonic solution
3. hypotonic solution

Question 30

1. isotonic solution

Answer 30

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

equal

(NORMAL no net water movement)

Question 31

2. hypertonic solution

Answer 31

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

(SHRIVELED - cell loses water)

Question 32

3. hypotonic solution

Answer 32

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

(LYSED/ BURSED - cell gains water)

Question 33

Effect of Osmotic pressure on blood cells

Answer 33

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

Question 34

Facilitated diffusion – Passive transport

Answer 34

DOWN conc via transport proteins

Highly specific

Reversible

No energy (ATP) cost

Question 35

Transport protein;

Answer 35

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

Question 36

Protein channels

Answer 36

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)

Question 37

Protein carrier/transporters – passive transport
(facilitated diff)

Answer 37

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

Question 38

Three transporter types

Answer 38

uniporters, symporters* and antiporters

Uniporter is the only transporter based in passive transport.

Question 39

Symporters and antiporters (

Answer 39

based on cotransport of more than 1 molecule are active transport

against the concentration/electric gradient

Question 40

Symporters and antiporters (

Answer 40

based on cotransport of more than 1 molecule are active transport

against the concentration/electric gradient

Question 41

Active transport

Answer 41

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

Question 42

Common features of transport proteins and enzymes

Answer 42

Specific binding sites for the solute
Can be saturated

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

Catalyse a physical process

Question 43

Protein carrier/transporters – Active transport

Answer 43

based on binding with the molecule - shape complimentary

Question 43

Protein carrier/transporters – Active transport

Answer 43

based on binding with the molecule - shape complimentary

Question 44

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

Answer 44

2
same

Question 45

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.

Answer 45

2
opposite

Question 46

Vesicle Transport - Transport of large macromolecules

Answer 46

Bulk transport requires vesicle transport (endomembranous system)

two main types of transport - endo/exocytosis

Question 47

Endocytosis

Answer 47

> 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

Question 48

Exocytosis

Answer 48

> 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

Question 49

Types of endocytosis

Answer 49

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