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physiology > cell membranes > Flashcards

cell membranes Flashcards

1
Q

What are membranes

A
  • Selectively permeable barriers
  • Maintain constant internal environment
  • Enclose cell contents
  • Internal organelles often have different environments to the cytosol
  • Very thin (7-10nm
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2
Q

What is a phospholipid bilayer

A

it is a Dynamic structure

able to move freely around

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3
Q

what is a phospholipid and describe its structure

A

•Amphiphilic – both hydrophilic and hydrophobic parts
•Polar head; negatively charged phosphate group
•Non polar tail; no charge
•Phospholipids ‘self-assemble’ to create the bilayer
-Tails exist as saturated or unsaturated
•Double bond creates a kink in the fatty acid chain of the tail

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4
Q

what is saturated and unsaturated bonds

A
  • Saturated – single bonds only

* Unsaturated – at least one double bond

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5
Q

what does high conc of saturated and unsaturated acids form

A
  • Higher concentrations of unsaturated acids promote membrane fluidity
  • Higher concentration of saturated fatty acids reduce cell membrane fluidity
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6
Q

two main types of carbohydrates

A
  • glycolipids

- glycoproteins

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7
Q

three main roles of carbohydrates

A

-Maintain membrane stability and cell protection (glycocalyx)
•Aid cell-cell adhesion (cell adhesion molecules)
•Facilitate cell recognition

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8
Q

what is cholesterol and describe its structure

A

-Is a lipid. Approximately 20% of membrane lipid is cholesterol.
•Also has polar and non polar regions
•Wedges itself between the phospholipid tails
•Can migrate and even ‘flip’ between the membrane layer

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9
Q

what are the two main types of proteins

A
  • integral

- peripheral

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10
Q

what are the different functions that proteins serve

A

•Serve different functions: enzymes, carrier proteins, channel proteins, receptors, cell adhesion, recognition

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11
Q

what is integral membrane protein

A
  • Firmly inserted into the membrane
  • Span the bilayer of the membrane
  • Transmembrane portion is hydrophobic
  • Extracellular and cytosolic portions are hydrophilic
  • Carrier proteins and channels are integral protein
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12
Q

what is peripheral membrane protein

A

-Loosely attached to membrane

•May be removed easily from the membrane with minimal disruption

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13
Q

what is membrane fluidity affected by

A
  1. Extreme temperatures (hot or cold)
  2. Concentration of unsaturated fatty acids
  3. Cholesterol levels
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14
Q

what happens to the membrane fluidity at low temps

A

-Less kinetic energy
•Phospholipids pack together
•Membrane less fluid

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15
Q

what happens to the membrane fluidity at high temps

A

-More kinetic energy
•Phospholipids tend to move further away
•Membrane more fluid

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16
Q

what happens to the membrane fluidity when there is an addition of cholesterol

A

-Maintains fluidity by preventing lipids from getting too close or too far apart from each other

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17
Q

are the proportions of the individual components the same in membranes of different cell-types?

A
  1. Reb Blood cell – equal amounts of lipid and protein and a small amount of carbohydrate
  2. Nerve cells – higher amounts of lipid in cell membranes (80% lipid)
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18
Q

what is passive transport

A

-Moves down a concentration (electrochemical) gradient

•Uses inherent kinetic energy

19
Q

what are the three types of passive transport

A
  • Three types:
  • Simple diffusion
  • Facilitated diffusion
  • Osmosis
20
Q

what is active transport

A
  • Moves against a concentration (electrochemical) gradient
  • Has directionality
  • Requires a specific carrier protein
  • Needs an external energy source
21
Q

what are the two types of active transport

A
  • Two types:
  • Primary
  • Secondary (Symport, Antiport)
22
Q

simple diffusion in plasma membrane

A
  • Small, uncharged, non polar molecules
  • O2, CO2, NO, urea
  • No metabolic energy required
  • Uses kinetic energy (natural motion)•No specificity
  • Rate of diffusion proportional to concentration gradient
23
Q

facilitated diffusion in plasma membrane

A

Small, polar molecules
•H2O, Glucose, Na+
•Uses specific integral proteins (carrier proteins)
•Rate of diffusion proportional to concentration gradient BUT also on one other factor..

24
Q

rate of diffusion in facilitated diffusion

A

The rate of diffusion reaches a plateau (transport maximum; Tm) in facilitated diffusion as carrier proteins become fully occupied

25
Q

what is osmosis

A

Net movement of water down a concentration gradient

26
Q

osmosis in plasma membrane

A

-Water highly polar, but small amounts can ‘sneak’ through the membrane unaided
•Water moves freely and reversibly through specific protein channels called Aquaporins
•Bulk movement of water is facilitated

27
Q

what is active transfer mechanisms

A

Utilises external energy sources and specific carrier proteins (pumps)
Allows cells to be very specific about which substances move in and out of the cell
No pump, no transport

28
Q

what is primary active transport and how does it work

A
  • Movement of Na+ and K+ uses the Na+/K+ ATPase pump
  • Maintaining ion concentration differences inside the cell are crucial
  • Hydrolysis of ATP results in phosphorylation of the pump
  • Results in conformational change of pump
  • Causes transport of 3Na+ out and 2K+ in to the cell (against their concentration gradients)•Other examples include calcium and hydrogen pumps
29
Q

what is secondary active transport and how does it work

A

Movement of a substance (against its concentration gradient) is coupled to ion movement (down it’s concentration gradient)
•The energy used for secondary active transport comes from the electrochemical gradient across the membrane
•Example: Na+/Glucose transport

30
Q

what are the two types of transfers called in secondary active transport

A
  • symport

- antiport

31
Q

what is symport in secondary active transport

A

-transported substances move in the same direction

•Na+/Glucose transporter

32
Q

what is antiport in secondary active transport

A

-transported substances move in opposite direction

•Na+/Ca2+ exchanger – uses the Na electrochemical gradient to transport Ca2+ out of the cell

33
Q

what two process transfer large molecules

A
  • endocytosis (into the cell)

- exocytosis (out of the cell)

34
Q

what is endocytosis

A

Moves large molecules into the cell (ingestion / uptake)

35
Q

what are the 3 types of endocytosis

A

-Phagocytosis
•Pinocytosis
•Receptor-mediate

36
Q

what is exocytosis

A

Moves large molecules out of the cell (excretion / secretion

37
Q

what is exocytosis used for

A
  • Hormone secretion
  • Neurotransmitter release
  • Mucous secretion
38
Q

what are vesicles

A

-Bubble-like, membranous sacs
•Made of a phospholipid bilayer containing fluid
•Transport bubble
•Protects substances being transported

39
Q

what is phagocytosis (endocytosis) and what is it used for

A
  • ‘cell eating’
  • Ingestion of large particles by specialised cells (phagocytes; in the immune system)
  • Macrophages
  • Certain white blood cells
  • Used for removing bacteria and debris
  • When a particle (e.g. bacteria) binds to a phagocyte, the cell membrane wraps itself around the particle
  • Resulting in a phagosome containing the particle
40
Q

what is pinocytosis (endocytosis)

A
  • ‘cell-drinking’
  • Occurs in most cells
  • Process used to take in extracellular fluid with dissolved substances
  • Droplet enters the cell and fuses with an endosome (sorting vesicle
41
Q

what is receptor mediated (endocytosis)

A
  • Main mechanism for specific uptake of macromolecules
  • Very selective method
  • Uptakes substances (hormones, cholesterol) found in small amounts •Receptors for this are specific membrane proteins
  • Some viruses can hijack this route and enter our cell
42
Q

how does endocytosis work and in depth exocytosis

A

…

43
Q

how does exocytosis work

A
  • Substances to be moved out of the cell e.g. (Hormones, Waste products, Neurotransmitters)
  • Process is stimulated by a cell-surface signal that results in a cascade of events:
  • Substance is enclosed in a vesicle
  • Transported to plasma membrane
  • Vesicle attaches to ‘docking’ sites on the membrane
  • Vesicle •Transported to plasma membrane
  • Fuses with membrane and ejects substance

physiology (7 decks)

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