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ESA2 Emily > M+R > Flashcards

M+R Flashcards

0
Q

What is an additional function present in a mitochondrial membrane but not in others?

A

Energy conservation by oxidative phosphorylation

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1
Q

List the 5 general functions of biological membranes

A
  1. Continuous highly selective permeability barrier
  2. Allow control of enclosed chemical environment
  3. Communication between cells and environment
  4. Recognition by signalling molecules, adhesion proteins and immune surveillance
  5. Signal recognition (electrical and chemical)
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2
Q

What are the constituent parts and percentages of membranes?

A

40% lipid
60% protein
1-10% carbohydrate dry weight

When hydrated, 20% of total membrane weight is water

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3
Q

What lipids are found in membranes and which is predominant?

A

The predominant lipid is phosphotidylcholine with the head group containing choline. Other polar head groups include: amines, amino acids and sugars
There are also plasmalogens such as sphingomyelin (which is the only phospholipid NOT based on glycerol)
There are also glycolipids and cholesterol

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4
Q

What is most common length of a fatty acid chain?

A

C16-18

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5
Q

Why are fatty acid chains kinked?

A

They contain unsaturated side chains (double bonds) on cis formation, which which kink the chains and reduce phospholipid packing

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6
Q

Which membrane phospholipid is not based on glycerol?

A

Sphingomyelin (a plasmalohen)

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7
Q

What different head groups can a glycolipid have?

A

Cerebroside (contains sugar monomers)

Ganglioside (contains oligosaccharides)

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8
Q

What percentage does cholesterol contribute to the total plasma membrane lipid level?

A

45%

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9
Q

What two structures can be formed by amphipathic molecules in water?

A

Micelles

Bilayers (favoured for phospholipids and glycolipids)

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10
Q

How are bilayers formed in water?

A

Spontaneously by VDW forces of attraction between hydrophobic tails.
Further cooperative stabilisation by non-covalent forces and hydrogen bonding and electrostatic interaction between hydrophilic groups and water.

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11
Q

Are lipid bilayers permeable to ions and polar molecules?

A

No.

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12
Q

How do lipids move in bilayers?

A
  1. Intra chain motion
  2. Fast axial rotation
  3. Fast lateral diffusion within plane of bilayer
  4. Flip flop movement from one half of bilayer to other (exchange)
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13
Q

What is the function of unsaturated double bonds in fatty acid side chains?

A

Disrupt hexagonal packing of phospholipids to increase membrane fluidity

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14
Q

Protein content of membranes can vary. How much protein is present in myelin?

A

18%

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15
Q

Protein content of membranes can vary. How much protein is present in mitochondria?

A

75%

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16
Q

How do proteins move in bilayers?

A

Conformational change
Fast axial rotation
Fast lateral diffusion

NO FLIP FLOP

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17
Q

Why do membrane proteins have restrictions on mobility?

A

Lipid mediated effects of proteins moving into cholesterol poor regions
Membrane associations
Association with membrane proteins e.g. Cytoskeleton

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18
Q

What are the two ways that a membrane protein may be situated in the membrane bilayer

A 
Deeply embedded (integral) 
Associated with the surface (peripheral)
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19
Q

How do peripheral membrane proteins bind to the surface?

A

Electrostatic and hydrogen bind interactions

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20
Q

How are peripheral membrane proteins removed from the surface of the bilayer?

A

Changes in pH or ionic strength

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21
Q

Which part of the bilayer do integral proteins interact with?

A

Hydrophobic region

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22
Q

How are integral membrane proteins removed from the membrane?

A

By agents competing for non-polar interactions in the bilayer
Cannot be removed by manipulating pH or ionic strength alone

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23
Q

Why is it important to have asymmetrical orientation of membrane proteins?

A

For recognition and signalling
Allow for direct receptor sites and effector interaction domains appropriately.
Also for cellular economy, since random orientation would lead to half receptor sites not being active if facing wrong way!

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24
Q

Explain the use of erythrocytes membrane ghosts in analysing the plasma membrane

A

Erythrocytes ghosts are prepared by osmotic haemolysis, which causes cytoplasmic components to be released.
Analysis shows there is over 10 major proteins involved in the membrane. The major proteins are 1,2,3,4.1,4.2,5,6,7 etc and are released when treated with high ionic strength or changing pH.

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25
Q

Since erythrocyte membranes can be disrupted by changing pH or ionic strength, what kind of proteins are present? Where are they situated?

A

They are peripheral proteins and are located on cytoplasmic face since they are susceptible to proteolysis when cytoplasmic face is available only.

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26
Q

Describe why flip flop cannot occur in glycoproteins

A

Highly hydrophilic nature of extracellular extracellular carbohydrate groups locks orientation to prevent flip flop

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27
Q

Most membrane proteins of an erythrocyte are peripheral proteins. Which two are not (are integral) and why?
How else are they classified?

A

3 and 7
They can only be dissociated from the membrane by detergents.
Glycoproteins

28
Q

What are membrane carbohydrate groups important?

A 
Cellular recognition (allowing tissues to form) 
Immune recognition
29
Q

Describe the erythrocyte cytoskeleton

A

Network of spectrin and actin molecules
Spectrin is long and floppy and comprising of two subunits which wind together to form an Antiparallel heterodimer. Two heterodimers come together to form head-to-head associations which form a heterotertramer of a2b2.
The rods are crosslinked to networks by short actin protofilaments and band 4.1 and addutin molecules, which interact at end of spectrin rods.
The spectrin-actin complex then is attached to membranes by adapter proteins

30
Q

What are the adapter proteins used in attaching the spectrin-actin network to the membrane in an erythrocyte cytoskeleton?

A

Ankyrin (Band 4.9)
Link spectrin (Band 4.1)
Band 3 protein
Glycophorin A

31
Q

What is the effect of attaching integral membrane proteins to the cytoskeleton?

A

Restricts lateral mobility of the membrane protein

32
Q

Describe the condition hereditary spherocytosis

A

Spectrin levels get depleted by 40-50%, causing cells to become round and more easy to lyse. The erythrocytes are cleared by the spleen.
Shortened in vivo survival of erythrocytes and inability for bone marrow to increase erythropoiesis to meet new demand leads to haemolytic anaemia.

Another form of this disease is when mutated cytoskeleton elements with dysfunctional binding sites for other components are expressed.

33
Q

Explain hereditary elliptocytosis

A

Defect in spectrin molecule, meaning it cannot form heterotetramers.
This results in fragile elliptoid cells.

Treatment with cytochalasain drugs caps the end of the growing end of the polymerising actin filaments to alter deformability

34
Q

In membrane protein biosynthesis, if positive residues are positioned at side A then which side passes into the lumen (A or B?)

A

B. The side opposite to the side possessing the possible residue. In this example, A or B can either be N terminus or C terminus.

35
Q

What mechanism controls multiple transmembrane domain insertion?

A

Series of start stop transfer sequences within primary sequence. Stabilisation is assisted by lumenal binding proteins (which are related to heat shock proteins)

36
Q

Explain post-translational processing

A

Nascent chain is processed as it passed from ER and from cis to trans Golgi. New protein then passes along the secretory pathway in a vesicle until fusing with the plasma membrane when the proteins are released.

37
Q

What is the role of cholesterol in the plasma membrane?

A

Cholesterol stabilises membrane structure. The is a hydrophilic hydroxyl group on the planar conjugated ring structure of the cholesterol near the bilayer which hydrogen bonds to ester oxygens of adjacent phospholipids .
At high temperatures, cholesterol reduces movement of fatty acid side chains at a given temperature to enhance phospholipid packaging and reduce membrane fluidity.
At low temperatures, normally phospholipids would pack together into crystalline form, which reduces membrane fluidity. Cholesterol counteracts that by intercalating with phospholipid molecules to reduce ability to form ordered, packed crystals and increase membrane fluidity.

38
Q

Why may one phospholipid travel a lot slower than another phospholipid?

A

Movement depends on size and whether the phospholipid is associated with a peripheral protein, which would cause motion to be restricted.

39
Q

What kind of molecule can diffuse across the hydrophobic domains of the lipid bilayer?

A

Non polar molecules

Rate of passive transport increases linearly with increasing concentration gradient.

40
Q

What is the role of transport systems in membranes?

A

Maintaining intraceolualr pH
Maintaining ionic composition
Regulation of cell volume
Concentration of metabolic fuels and building blocks
Extrusion of waste products of metabolic and toxic substances
Generation of ionic gradients necessary for electrical excitability of nerve and muscle

41
Q

Which protein is responsible for transport of Cl- ions?

A

Band 3 protein
It does not just form a Cl- selective pore, but carries out a specific exchange of Cl- for hydrogen carbonate ions which are essential to the function of the erythrocyte.

42
Q

Name the facilitated diffusion methods

A

Protein pores
Carrier molecules
Protein flip flop (thermodynamically unlikely)

43
Q

Give examples of gated pores in membranes

A 
Ligand gated ion channels 
Voltage gated ion channels 
Gap junctions (connexin)- which are closed when cellular calcium concentration rises above 10um or the cell becomes acidic
44
Q

What determines whether a transport mechanism will need energy (active) or be passive transport?

A

Free energy change which is determined by concentration gradient for transported species and electrical potential across membrane bilayer.

45
Q

Explain the principles behind active transport

A

To overcome unfavourable chemical or electrical gradients, movement to the transported ion or molecule must be coupled to a thermodynamically favourable reaction.
Free energy required to drive transport can come either directly or indirectly from hydrolysis of ATP, electron transport, or light.

46
Q

Name 3 co-transport systems

A

Symport: Na-glucose cotransporter in small intestine and kidney. Entry of sodium provides energy for entry of glucose
Antiport: Na-Ca- exchange provides inward flow of sodium ions down its concentration gradient up concentration gradient
Antiport: Na-H- exchange is an inward flow of sodium down a concentration gradient, leading to alkalisation of cell by removing hydrogen ions.

47
Q

What is the role of the Na-K ATPase pump?

A

Forms Na and K gradients

Drives secondary active transport processes such as: ion homeostasis, intra cellular calcium ion concentration and pH

48
Q

Why must calcium concentration in cells be maintained?

A

Toxic to cells

49
Q

What pump involved in a resting calcium concentration has a high affinity but low capacity?

A

PMCA Plasma membrane Ca2+ ATPase

SERCA Sarco/endoplasmic reticulum Ca2+ ATPase

50
Q

What pump involved in a resting calcium concentration has a low affinity but high capacity?

A

Na-Ca exchanger (NCX)

51
Q

What pump involved in a resting calcium concentration buffers potentially damaging calcium ions by operating at high calcium ion concentration.

A

Mitochondrial Ca2+ uniports

52
Q

What happens to NCX under normal conditions and in depolarised cells?

A

Normally, 3 Na+ are exchanged for 1 Ca2+
This makes it electrogenic with current flowing in direction of Na+ gradient.
When the cell is depolarised normal flow is inhibited so that mode of operation reverses so that calcium is brought into the cell. This means that is mechanism is used in depolarisation of cardiac myocytes when generating an action potential and can also cause toxicity in periods of ischameia.

53
Q

Cellular pH is controlled by activity of a variety of plasma membrane transporters. Name them.

A 
Na-K ATPase 
Na-H exchanger 
Na-Cl-HCO3-H co transporter (coupled cation and anion exchange)
Na-HCO3 co transporter 
Anion exchange
54
Q

Which ion transporters regulating cellular pH are most common, present in most cells?

A

Na-H exchanger
Anion exchanger

They are what causes the pH to move away from its set point.

55
Q

Why is electroneutral transport used in cell volume regulation?

A

Allows ions to be transported without effect on membrane potential. Cells extrude ions in response to swelling and shrinking and water follows.

56
Q

What mechanisms are in place to resist cell swelling?

A

Conductive and cotransport systems which utilise the efflux of osmotically active ions

Influx for resistance to cell shrinkage

57
Q

Give an example of when there is a concerted action of transporters to reach a physiological endpoint.

A

Bicarbonate reabsorption in the proximal tubule of the kidney and sodium ion reabsorption together together allows regulation to be achieved.

Under normal conditions, the kidney reabsorbs all bicarbonate filtered into the proximal tubule. The main reason for doing it is to retain base for pH buffers

58
Q

Almost all Na+ appearing in glomerular filtrate is reabsorbed from kidney nephron. Driving force is low intracellular Na+ concentration. Why?
Several transport mechanisms are used in different areas. What are these areas?

A

Low sodium ion concentration is due to Na-K-ATPase activity in tubular cells.
Points of transport systems in the nephron are thick ascending limb, distal convoluted tubule and cortical collecting duct.

59
Q

Describe the action of a diuretic of your choice.

A

In thick ascending limb:
Loop diuretics are used to block Na-K-Cl cotransporter (NKCC2). This cotrasnporter normally brings in Na+ and K+ with Cl-.

60
Q

Why may a diuretic be used?

A

Fluid loss is required to treat oedema or hypertension. Mechanism is to block a sodium ion reabsorber mechanism with diuretic drugs to increase sodium ion excretion and produce hyperosmotic urine and therefore excrete water.

61
Q

What is approx total amount of aqueous volume in a 70kg man?

A

40L of water

62
Q

What proportion of the fluid is intra and extracellular?

A 
25L intracellular
15L extracellular (5L of which is blood volume and 3L is plasma. Remaining is interstitial fluid and small amount is lymph, cerebrospinal fluid and eye fluid).
63
Q

What is the consequence of an increase in permeability of blood capillaries to plasma proteins?

A

Movement of albumin from circulation into interstitial fluid leads to oedema because of increased interstitial, and decreased intravascular, colloid osmotic pressure.

64
Q

How is glucose uptake from blood different in adipose, brain, liver and skeletal muscle different from intestinal kidney and epithelial cells?

A

Glucose concentration gradient favours uptake. Glucose enters by facilitated transport down glucose concentration gradient via glucose transporters. GLUT1-7 receptors show different properties to suit needs of individual tissues.

65
Q

How does insulin stimulate glucose uptake into adipose and skeletal muscle tissue?

A

Recruits GLUT4 from internal vesicular membranes to the plasma membrane to increase transport capacity.

66
Q

Why does glucose not efflux from cells when circulating concentration falls after absorptive period after a meal?

A

Glucose is rapidly converted to glucose-6-phosphate on entering the cell. This means intracellular glucose concentration never rises high enough to reverse the gradient

67
Q

What other metabolites use sodium gradient for their uptake into cells against concentration gradient?

A

Amino acids use it

ESA2 Emily (8 decks)

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