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Mol Cell Bio > Prof E. Smythe > Flashcards

Prof E. Smythe Flashcards

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1
Q

What are the properties of plasma membranes?

A
  • Barrier
  • Flexible, self-repairing, continuous
  • Selectively permeable
  • Fluid
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2
Q

When a membrane is very fluid what are the features of its phospholipids?

A
  • Unsaturated (many double bonds)

- Short tails

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3
Q

When a membrane is more rigid what are the features of its phospholipids?

A
  • Saturated (no double bonds, stiff)

- Long

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4
Q

What kind of double bond is usually present in phosolipids?

A

Cis

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5
Q

What are the 4 main types of phospholipids?

A
  • Phosphatidylethanolamine
  • Phosphatidylserine
  • Phosphatidylcholine
  • Sphingomyelin
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6
Q

Which phospholipid has a negative charge?

A

Phosphatidylserine

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7
Q

What is the structure of a phospholipid?

A

Hydrophilic phosphate head and a hydrophobic tail made of 2 fatty acid chains. These are connected by a glycerol molecule.

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8
Q

What is the structure of cholesterol?

A
  • Polar head
  • Rigid steroid ring structure
  • Hydrophobic hydrocarbon tail
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9
Q

What is the function of cholesterol?

A

Packs between phospholipids which locally makes the membrane more rigid/ less permeable

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10
Q

How is bacterial membrane composition more simple?

A
  • No cholesterol

- No sphingomyelin

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11
Q

How are phospholipids amphipathic?

A

Hydrophilic portion and a hydrophobic portion

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12
Q

What 2 structures can phospholipids form in aqueous solutions?

A
  • Bilayer
  • Micelle
    (Energetically favourable to form sealed compartments in order to shield the hydrophobic portion)
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13
Q

What is an integral membrane protein?

A

Directly embedded in the whole bilayer via a hydrophobic domain

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14
Q

What is a peripheral membrane protein?

A
  • Only present on the inner/ outer leaflet of the bilayer. - - Associate non-covalently with integral membrane proteins.
  • Some have a fatty acid modification which can associate with the bilayer.
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15
Q

What is a microdomain?

A

Areas of the plasma membrane which differ because of specialised clusters of proteins/ lipids.

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16
Q

What is a ‘raft’ microdomain?

A
  • Specialised microdomain with a high level of cholesterol and sphingomyelin where the membrane is slightly thicker
  • Allows longer transmembrane proteins to embed
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17
Q

What are the 3 key features of membranes?

A
  • Asymmetric
  • Proteins always have the same orientation
  • Lipid composition of the 2 leaflets of the bilayer is different
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18
Q

What is spectrin?

A
  • Protein which forms mesh cytoskeleton in red blood cells

- Peripheral membrane proteins connect cytoskeleton to the membrane

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19
Q

In what scenarios is membrane asymmetry important?

A
  • Blood groups
  • Coagulation
  • Cell recognition
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20
Q

How is membrane asymmetry important in blood groups?

A

Blood group is determined by the oligosaccharides attached to sphingomyelin and proteins in the red blood cell membrane and to proteins in plasma.

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21
Q

How is membrane asymmetry important in coagulation?

A
  • Phosphatidylserine is the nucleation site for coagulation cascade
  • PS moved from inner leaflet to outer leaflet to trigger clotting
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22
Q

Where is phosphatidylserine usually found in the plasma membrane?

A

Inner leaflet

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23
Q

How is membrane asymmetry important in cell recognition?

A
  • Phosphatidylserine and phosphatidylethanolamine are transferred to outer leaflet in apoptotic cells
  • These are recognised by receptors on macrophages (signal) which can then clear away the apoptotic cells
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24
Q

Which molecules are lipid bilayers highly impermeable to?

A

Polar molecules and ions

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25
Q

What are the different types of transport proteins?

A
  • Channels

- Carriers

26
Q

Which transport proteins mediate passive transport?

A

Channels and carriers

27
Q

Which transport proteins mediate active transport?

A

Carriers (using ATP)

28
Q

What establishes the electrochemical gradient?

A

Membrane potential and ionic concentration differences on each side of the membrane

29
Q

Which transport protein is more efficient?

A

Channels because they only interact weakly with their solute (form an aqueous pore). Carriers directly bind which is slower.

30
Q

What are the features of ion channels?

A
  • Hydrophilic pores
  • Highly specific for their ion
  • Can be open or closed (no energy required)
  • Rapid transport
  • Regulated by ions binding, membrane potentials, ligands
31
Q

What are the ways that active transport can be mediated?

A
  • Co-transport
  • Energy from ATP
  • Energy from light
32
Q

What is symport?

A

Co-transport where both molecules are travelling in the same direction

33
Q

What is antiport

A

Co-transport where molecules are travelling in opposite directions

34
Q

What limits carrier-mediated diffusion?

A

Number of carrier proteins in the membrane

35
Q

What gradient drives transport in mammals?

A

Na+ gradient

36
Q

How is glucose transported into the blood from the lumen of the intestine?

A
  • Co-transport with Na+ into epithelial cell via glucose/Na+ symporter on apical surface
  • Diffuses into blood via carrier protein on basal surface
  • Na+ leaves via Na+/K+ pump (3 Na+ out for 2 K+ in)
  • Tight junctions separate apical and basal carrier proteins
37
Q

What gradient drives transport in bacteria?

A

H+

38
Q

Which enzyme makes sure that there are the same amount of phospholipids in each leaflet?

A

Scramblase

39
Q

Which enzyme ensures that membrane asymmetry is maintained?

A

Flippase

40
Q

What are the flattened sacs of the Golgi and endoplasmic reticulum called?

A

Cisternae

41
Q

What are the functions of the ER?

A
  • Quality control
  • Synthesis of lipids/ proteins
  • Storage
  • Detoxification
42
Q

How is the ER involved in quality control for proteins?

A
  • Associated ribosomes feed the new protein into the ER lumen via a pore as it is translated
  • Chaperone proteins fold the protein
  • If proteins are misfolded they are fed back out and ubiquitinated which marks it for destruction
43
Q

What are the functions of the smooth ER?

A
  • Phospholipid and cholesterol synthesis
  • Steroid hormone production
  • Synthesis and storage of glycerides
  • Synthesis and storage of glycogen
  • Calcium store
44
Q

Where are acinar cells found?

A

Pancreas

45
Q

How are molecules transported from the ER to the Golgi?

A
  • Vesicles bud off and fuse with the Golgi membrane

- Asymmetry of the membrane is maintained

46
Q

What is the role of protein coats in vesicle transport?

A
  • The area of the membrane forming the vesicle is coated with specific peripheral proteins which helps cargo selection
  • Protein coat is discarded before fusion
47
Q

How do vesicles make sure they fuse with the correct target?

A
  • Vesicle membranes contain SNARE proteins (revealed when protein coat is discarded) which are complementary to SNAREs on the target membrane
  • v-SNARE=on vesicle
  • t-SNARE=on target
  • Ensures specifity
48
Q

What are the functions of the Golgi? (3)

A
  • Modification and packaging of secreted proteins (add sugar)
  • Renewal and modification of the plasma membrane
  • Delivery of material to other organelles
49
Q

How do proteins move through the Golgi complex?

A
  • Start at cis face, move through to trans
  • Different sugars/modification added at each cisterna section
  • Sorted at the Trans-Golgi network for secretion, storage etc.
50
Q

What is opsonisation?

A

When bacteria are covered in IGG antibodies

51
Q

Describe the process of phagocytosis.

A
  • Phagocyte receptors recognise IGG proteins on bacteria and bind
  • Pseudopods form (arm projections) using the actin cytoskeleton to engulf the bacteria
  • No change in cell size because membrane is recycled
52
Q

What is the difference between macropinocytosis and phagocytosis?

A

Phagocytosis engulfs solid material whereas macropinocytosis ingests fluids

53
Q

Describe macropinocytosis.

A
  • Non-specific uptake
  • Pathway used by cancer cells to uptake nutrients
  • Actin driven ruffles form in a similar way to phagocytosis
54
Q

What is LDL and what does it do?

A

Low-density lipoprotein

Transports cholesterol around the body

55
Q

How is LDL endocytosed by the clathrin pathway?

A
  • LDL binds to LDL receptors on cell surface
  • Clathrin-coated pit forms (specialised microdomain)
  • Forms clathrin-coated vesicle
  • Coat removed and vesicle fuses with early endosome (has a lower pH which causes the LDL to dissociate from its receptor)
  • Receptor recycled and returned to cell surface
  • LDL hydrolysed in lysosome
56
Q

What is the structure of clathrin?

A
  • Triskelia

- Doesn’t associate directly with the membrane, binds to adaptor proteins

57
Q

How do clathrin-coated vesicles pinch off after formation?

A

Dynamin (GTPase)

58
Q

What are Rab proteins?

A
  • Regulate endocytic transport

- Associate with different organelles to give them identity

59
Q

What are early and late endosomes?

A
  • Early endosome recycles and then matures into late endosome
  • Late endosome sorts material for degradation and directs it to lysosomes
60
Q

What is another name for late endosomes?

A

MVBs= MultiVesicular Body

61
Q

What do lysosomes contain?

A
  • Lipases

- Hydrolases

Mol Cell Bio (7 decks)

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