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PMP101 - Health, Disease and Patient > Plasma membrane > Flashcards

Plasma membrane Flashcards

1
Q

What are the main functions of the plasma membrane?

A

Boundary that separates the cell from its surroundings. Found in all cells.
* Internal membranes of organelles allow
compartmentalisation (for a specific
composition → specific reactions/functions)
* It exhibits selective permeability, allowing only specific molecules to pass through
* It plays a key role in interacting with other cells (glycoproteins) & cell signalling
* It provides structural integrity to the cell and protects its contents

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2
Q

What makes up the mosaic part of the fluid mosaic model?

A

▪ Phospholipids,
▪ Glycolipids,
▪ sterols
(cholesterol in
mammalian cells)
▪ various proteins
▪ glycoproteins

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3
Q

What makes up the fluid part of the fluid mosaic model?

A
  • Dynamic, fluid and flexible
    ▪ Phospholipids and proteins move laterally within the layer
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4
Q

What are phospholipids? and what are they composed of?

A
  • Phospholipids (75% lipids of the membrane) and are arranged in two-layer sheets
  • Phospholipids are amphipathic, containing hydrophobic and hydrophilic regions
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5
Q

What are the hydrophilic heads?

A

▪ a phosphate group and a glycerol
▪ Polar, allowing interacting with water

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6
Q

What are the hydrophobic tails?

A

▪ Nonpolar, repelling water and
interacting with other lipid tails
▪ Self-Assembly into the bilayer to
shield water. No energy needed

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7
Q

What can phospholipid fluidity in the membrane lead to?

A

➢Rapid lateral diffusion within the plane (107 times/sec)
➢ Spin in place (rotations – up to 500/sec.)
➢ Flexion (contraction movement)
➢ Very rarely, Flip-flop (side-to-side movement)

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8
Q

What other lipids are there in eukaryotic cell membranes?

A
  • Cholesterol (20%)
  • Glycolipids (5%)
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9
Q

What are the functions of cholesterol?

A

➢ Stabilise the membrane → affecting its
fluidity and stiffness
➢ Improve stability
➢ Reduce permeability ꜜmolecule passage

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10
Q

What are the functions of glycolipids?

A

▪ Sugar groups (hydrophilic) face outwards → asymmetry

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11
Q

What are the two types of membrane proteins?

A

Integral proteins
Peripheral proteins

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12
Q

What are integral proteins?

A

➢ Trans-membrane proteins spanning the membrane
➢ Integral proteins facing only one side

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13
Q

How do integral proteins have ampithatic natures?

A

▪ hydrophobic amino acids lie in the bilayer
▪ hydrophilic regions facing the aqueous environment

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14
Q

What are the functions of membrane proteins?

A

Major functions of membrane proteins
➢Transport of molecules
➢Enzymatic activity
➢As receptors in cell signalling
➢Structural support (linked to cytoskeleton)

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15
Q

What are the functions of glycoproteins?

A

➢Protection from mechanical damage
➢cell-to-cell communication

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16
Q

Describe the conditions of diffusion

A

Movement of small, nonpolar
molecules* that can diffuse
directly through the lipid bilayer
▪ No energy cost
▪ Down their conc. gradient

17
Q

What are small and non polar molecules that diffusion can move?

A

O2, CO2, steroid hormones
+ small uncharged polar molecules like urea and ethanol

18
Q

Describe osmosis

A
  • Movement of water across a cell
    membrane from an area with higher
    water potential (lower solute conc.)
    to an area with lower water
    potential (higher solute conc.)
19
Q

How does water and solute potential differ in osmosis?

A
  • Water potential is inversely proportional to the solute’s concentration
    ▪ as solute concentration increases, water potential decreases.
  • When the solutes are unable to across, osmosis balances solute concentrations, to achieve equilibrium
20
Q

What is an isotonic solution and how does this effect net movement?

A

Isotonic Solution - Solute concentration is equal inside and outside the cell
* No net water movement

21
Q

What is an hypertonic solution and how does this effect net movement?

A

Hypertonic Solution - Solute concentration is higher outside than inside the cell
* Water moves out of the cell → cell shrinkage

22
Q

What is an hypotonic solution and how does this effect net movement?

A

Hypotonic Solution Solute concentration is lower outside than inside the cell
* Water moves into the cell → cell swelling

23
Q

What is facilitated diffusion?

A

The passive movement of molecules down a
concentration gradient (or electric potential) via a
transport protein (transmembrane proteins):
➢ Protein channel
➢ Protein carrier/transporters

24
Q

What molecules apply to facilitated diffusion?

A

➢ Specific ions (e.g. Cl-)
➢ Hydrophilic small molecules (e.g. glucose)
➢ Water facilitated diffusion (via Aquaporins)

25
Q

What are the properties of a protein channel?

A

Form a hydrophilic “tube/corridor” across the membrane
through which specific molecules/ions diffuse
▪ Specific
▪ No molecule-channel interaction
▪ Rapid rate
▪ Can be Gated → open or close in response to signals
(e.g. voltage changes in neurons)

26
Q

What is a uni porter?

A

Uniporter → one molecule/ion interaction at a time
1) The solute interacts with the protein carrier
2) Triggering a change in shape that translocate the
solute across the membrane

27
Q

What are properties of protein carriers in f diffusion?

A

*Uniporter
*specificity
*slower rate than protein channels

28
Q

Describe what makes up 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
    cell/organelle membrane or vesicles
  • To maintain concentration gradients
29
Q

What are the two types of protein carriers in active transport?

A

➢ symporter
➢ antiporter

30
Q

What is a symporter?

A

moving 2 distinct molecules in
the same direction across the cell membrane

31
Q

What is an antiporter?

A

moving 2 molecules in opposite directions across the membrane
✓ E.g. Na+-K+ pump uses the energy of one ATP to pump 3 Na+ out and 2 K+ in

32
Q

What are two main types of vesicle transport? When are they required?

A
  • required in bulk transport
  • Exocytosis
  • Endocytosis
33
Q

What is exocytosis?

A

from inside to outside cell
Transport vesicles (from Golgi) fuse with the
plasma membrane, and release their contents
➢ insulin from pancreatic cells

34
Q

What is endocytosis?

A

Uptake of macromolecules and
large particles (from outside to inside)
* Substances are brought into the cell by
engulfing them in a membrane-bound vesicle

35
Q

What are the three types of ENDOcytosis?

A

➢ Phagocytosis (“cellular eating”)
➢ Pinocytosis (“cellular drinking”)
➢ Receptor-mediated endocytosis

PMP101 - Health, Disease and Patient (20 decks)

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