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BIOLOGY-FY > S1-L6: The Plasma Membrane > Flashcards

S1-L6: The Plasma Membrane Flashcards

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1
Q

Define a phospholipid

A

-lipids with phosphate group (PO4 2-) covalently bonded to glycerol backbone instead of fatty acid

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2
Q

Describe the following groups as part of phospholipid:

(figure 1)

1-Phosphate
2-Fatty acid

A

1-polar/ soluble in water (hydrophilic)/ head

2-non-polar/ insoluble in water (hydrophilic)/ tail

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3
Q

How are cell membranes organised in water?

A

-phospholipids organise themselves to keep hydrophilic “heads wet” AND hydrophobic “tails dry”

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4
Q

Describe the “bilayer” (figure 2)

A
  • composed of 2 layers of lipids organised as sheet
  • v. thin membrane (7-8 nm) with flexible yet sturdy barrier
  • ->fluid mosaic model best explains it’s structure
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5
Q

Describe the fluid mosaic model? (figure 3)

A
  • 2D liquid which restricts lateral diffusion of membrane components
  • regions with membrane that contain lipid rafts/ proteins AND glycoproteins
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6
Q

What is the basic composition of cell membranes?

A
  • phospholipids- 75%
  • cholesterol- 20%
  • Polar glycolipids in external layer- 5%
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7
Q

Outline and describe “cholesterol” (figure 4)

A
  • steroid lipid
  • ->made up of ringed C structure with floppy C-chain AND hydrophilic hydroxyl (OH) group-useful structural lipid for membranes- lipid rafts
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8
Q

What is the effect of “fluidity” in terms of cell membranes?

A

-allows movement of membrane components needed for cell movement/ growth/ division/ secretion AND cellular junction formation

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9
Q

How do cholesterol molecules affect fluidity?

A
  • neighbouring lipid molecules swap places 10 million times per/sec
  • cholesterol immobilises first few hydrocarbon groups of phospholipid molecules
  • ->makes lipid bilayer less deformable AND decreases it’s permeability to small water-soluble molecules
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10
Q

State what glycolipids are and their use

A
  • lipid covalently attached to oligosaccharide
  • forms part of cell membrane AND glycocalyx
  • determines ABO blood group
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11
Q

What is a “glycocalyx”? (figure 7)

A
  • many membrane proteins are glycoproteins containing associated oligosaccharide
  • ->form glycocalyx
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12
Q

Outline the uses of the glycocalyx

A
  • required for detection of “self” in immunity
  • aids in cell-cell adhesion (stick to each other)
  • makes red blood cell’s slippery AND protects GI from drying out
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13
Q

List the functions of the phospholipid bilayer

A
  • regulates what enters AND exits cell
  • altering pH AND charge
  • involved in cell recognition
  • major role in cell signalling-like from hormones
  • has enzymatic functions
  • aids in cell linking AND cross-talk
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14
Q

Different types of cell membrane proteins (figure 8)

A
  • transporters
  • anchors
  • receptors
  • enzymes
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15
Q

Explain how the cell membrane is selectively permeable:

1-Permeable
2-Impermeable
3-Slightly permeable

(figure 9)

A

1-lipid bilayer permeable to non-polar molecules like O2/ CO2 AND hormones
2-impermable to ions AND large molecules like Na+ & glucose
–>need trans-membrane channel AND carrier proteins
3-to small permeable uncharged polar molecules
–>like water

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16
Q

What is the link between gradients and membrane permeability and it’s consequent effect?

A
  • selective permeability allows cell to build conc gradient
  • ->exmple: O2 and Na+ more conc in extracellular fluid
  • ->opposite true for K+ AND CO2
  • pH can be regulated
  • electrical gradients built–>inside of cell more (-)- this creates membrane potentials
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17
Q

Outline the different types of membrane transport (refer to figure 10)

A
  • transport can be classed in to 3 types:
  • ->passive: diffusion/ osmosis/ facilitated diffusion
  • ->active: primary/ secondary
  • ->vesicular: endocytosis/ phagocytosis/ pinocytosis/ transcytosis
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18
Q

What is passive transport?

A

-no cellular energy used as substances move down their own conc. gradient

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19
Q

State the different types of passive transport

A
  • diffusion via lipid bilayer
  • channel mediated facilitated diffusion
  • carrier mediated facilitated diffusion
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20
Q

Explain how ionic gradients (K+) can create potential difference across a membrane

A
  • only K+ able to leave cell–>diffuses out & down chemical gradient
  • as K+ leaves cell inside becomes more (-)
  • separation of charges occurs
  • ->creates potential difference across membrane
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21
Q

What is “equilibrium potential”?

A
  • potential gradient across membrane to maintain conc gradient
  • ->i.e: electrical potential needed to stop on diffusion down chemical gradients
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22
Q

How may channel mediated facilitated diffusion occur?

A
  • can be gated
  • may be timed/signal regulated
  • refer to figure 11
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23
Q

What is carrier mediated facilitated diffusion dependent on?

A
  • subject to transport maximum AND saturation

- refer to figure 12

24
Q

How may facilitated diffusion be regulated (in relation to diabetes)?

A
  • selective permeability can be regulated to maintain homeostasis
  • ->Example: hormone insulin- via it’s receptor up-regulates glucose transporters
  • diabetic patients may lack ability to up-regulate GluT
25
Q

Outline what osmosis is and its relation to facilitated transport (figure 13)

A
  • diffusion of water through semi-permeable membrane

- diffusion through lipid bilayer occurs through specific transmembrane protein channels- aquaporins

26
Q

Define the following types of solution:

1-Hypertonic

2-Hyopotonic

A

1-Higher conc of solution outside–> water leaves

2-lower conc of solution outside–>water comes in

27
Q

How may red blood cells be destroyed? (refer to figure 14)

A

-RBC’s for transfusion destroyed by hypertonic AND hypotonic solutions

28
Q

What are most intravenous (administering in to veins) solutions like?

A
  • most intravenous solution isotonic

- ->0.9% saline OR 5% dextrose

29
Q

What is active transport and it’s importance in the body?

A
  • involves expenditure (use) of energy from hydrolysis of ATP
  • ->used to transport essential ions against their conc gradient
  • ->helps maintain tonicity/volume AND charge
30
Q

Outline the two types of active transport

A
  • primary–> uses energy stored from hydrolysis of ATP

- secondary–> uses energy stored by ionic conc. gradient

31
Q

Describe primary active transport

A
  • movement against conc. gradient (mainly ions)
  • ATP changes shape of carrier proteins–>pumps substances across
  • ->cells typically use 40% of their generated ATP this way
32
Q

What is a common example of primary active transport AND why does it have to work non-stop?

A
  • most common example is sodium-potassium pump (figure 15)

- must work non-stop due to passive leaking

33
Q

How does the Na+-K+ pump work?

A
  • 3Na+ bind/ ATP hydrolysed (via ATPase)
  • 2K+ bind/ P released
  • 2K+ enters
34
Q

Briefly explain what secondary active transport (Co-transport) is

A
  • form of a. transport across biological membrane in which transporter protein couples movement of ion (typically Na+ OR H+) down it’s electrochemical gradient
  • ->to uphill movement of another molecule/ion against a conc/electrochemical gradient
  • ->this gradient made by primary a. transport
35
Q

Define the terms “symport” and “antiport”

A
  • symport: where molecules travel in same direction –>used for Ca2+ regulation & H+ regulation
  • antiport: where molecules go in opposite directions
36
Q

Secondary active transport example (refer to figure 17)

A
  • Na used to drive glucose transport across membrane

- primary active transport then recycles Na via Na-K pump

37
Q

What is Vesicular transport and it’s use?

A
  • used for endocytosis-bringing substances in to cell &
  • ->exocytosis- expelling from cell
  • used for inter-organelle transport
  • both use ATP
38
Q

Outline what endocytosis can further be classified in to

A

-receptor mediated endocytosis/ phagocytosis/ pinocytosis

39
Q

What is receptor mediated endocytosis used for?

A

-for LDL/ some vitamins/ proteins and hormone uptake

40
Q

Define the term “Cathrin”

A

-protein for enriching membrane domains

41
Q

State the process of Receptor Mediated endocytosis (figure 18)

A

1-Binding: receptor-ligand complex forms
2-Lateral diffusion- clathrin coated pit binds to it
3-Invagination- process of being turned inside out
–>molecule moves from outside to inside
4-Vesicle formation- vesicle is coated (2)
5-Uncoating
6-Unocated vesicle fuses with early endosome AND ligand released in to endosome
7- vesicle transport to late endosome for digestion
–>receptors transported to cell surface membrane for recycling
–>transcytosis occurs- ejection of certain macromolecules other side of cell

42
Q

Outline what phagocytosis is

A

-engulf large particles like worn out cells AND bacteria –>carried out by macrophages AND neutrophils

43
Q

State the process of phagocytosis (figure 19)

A

1-microbe becoming phagocyte
-cell movement in direction to decreasing in conc
2-ingestion of microbe to phagocyte
3-phagosome formation
4-phagosome fusion with lysosome to form a phagolysome
5-digestion of ingested microbe by enzyme
6-residual body containing indigestible material formation
7-waste material discharge

44
Q

Briefly explain what Bulk Phase endocytosis is (figure 20)

A
  • small droplets of extracellular fluid taken in
  • no receptors needed
  • all solutes in extracellular fluid brought in (non-selective)
  • occurs in most cells BUT especially absorptive cells in intestines AND kidneys
45
Q

In appropriate detail outline what exocytosis is

A
  • used to transport material out of cell
  • is exhibited by all cells BUT v. important in:
  • ->secretory cells- digestive enzymes AND hormones
  • ->nerve cells- neurotransmitter
46
Q

What is transcytosis?

A
  • combination of endo AND exocytosis
  • substances passed through a cell
  • common in endothelial cells which line blood vessels
47
Q

Cell-to-Cell: What happens at the synapse (including exocytosis)?

A

1-action potential depolarises axon terminal
2-depolarisation opens voltage-gated Ca2+ channels AND Ca2+ enters cell
3-Calcium entry triggers exocytosis of synaptic vesicle content
4-neurotransmitter diffuses across synaptic cleft AND binds with receptors on postsynaptic cell
5-neurotransmitter binding initiates response in postsynaptic cell

48
Q

What are the different types of cell junctions?

A

-tight junctions/ adherens junctions/ desmosomes/ hemidesmosomes/ gap junctions

49
Q

Outline the functions of the following junctions:

1-Tight junctions
2-Adhering junctions
3-Gap junctions

A

1-prevent substance movement
2-maintain cellular respiration
3-allows movement of substances

50
Q

Explain what tight junctions are and how they work with reference to figure 22

A
  • formed by fusion of integral proteins of adjacent cells
  • ->prevent anything passing through extracellular space between them
  • ->E.G: cells lining digestive tract
  • bar movement of dissolved materials through space between epithelial cells
  • no intercellular space where tight junction
  • long tight junction protein rows form complex meshwork
51
Q

Outline and describe Adherens junctions (figure 23)

A
  • plaque which attaches to membrane proteins & microfilaments of cytoskeleton
  • often form adhesion belts
  • resist separation in contractile activities like peristalsis (involuntary constriction & intestine muscle relaxation)
  • ->creates wave-like movements which push canal content forward
52
Q

In appropriate detail outline what desmosomes (figure 24) AND hemidesmosomes (figure 25) are

A
  • anchoring junctions held together by linker protein filaments- called cadherins
  • ->OR integrins extending from button like thickenings called plaques
  • distribute tension AND prevent tearing
  • ->like skin/ heart muscle
53
Q

Describe gap junctions

A
  • adjacent cells connected by hollow to cylinders (connexons) made of trans membrane proteins
  • found in electrically excitable tissues for synchronisation –> like heart AND smooth muscle
54
Q

Cell to Cell junction- Intercalated disk example used:

1-What is an Intercalated disk?

A

1-Junction between two cardiomyocytes (cells composing heart muscle)

55
Q

2-Using the example, outline what mechanical coupling is

A
  • small gap (0.2 um) between membranes of adjacent cells which filled with connective tissue
  • ->this firmly binds 2 adjacent cells together
  • ->cells bound together more strongly at certain points-desmosomes
56
Q

3-Explain what electrical coupling is

A
  • longitudinal (length wise up-down) segments contain specialised regions where membranes of adjacent cells come v. close together
  • ->in nexus (gap junction) regular arrays of proteins-connexins
  • ->these form large channels which allow passage of ions + other small molecules between cells
57
Q

What are the two important roles of intercalated discs?

A
  • act firmly to bind adjacent cells together (mechanical coupling)
  • also allow electrical coupling between adjacent cells

BIOLOGY-FY (12 decks)

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