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IMMS Lectures > Membrane ultrastructure and function 14.10.22 > Flashcards

Membrane ultrastructure and function 14.10.22 Flashcards

1
Q

What is a cell?

A
  • Cell-specific functions
  • Growth and division: cell cycle
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2
Q

What is in the nucleus?

A

Genome:
- Instructions
- Inherited disease
- Cancer

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3
Q

What is the smooth ER?

A
  • NO ribosomes
  • Site of lipid synthesis
  • Some drug metabolism
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4
Q

What is the golgi body?

A
  • Mediates protein sorting to specific sites
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5
Q

What is the Rough ER?

A
  • Studded with ribosomes
  • Site of protein synthesis
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6
Q

What is a ribosome?

A

Translate mRNA into protein

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7
Q

What are microtubules?

A

Give structure to cell

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8
Q

What is the plasma membrane?

A
  • Keeps stuff in and out
  • Selectively permeable
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9
Q

What are mitochondria?

A
  • TCA cycle
  • oxidative phosphorylation
  • Maternal inheritance only
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10
Q

What are lysosomes?

A

Cell’s dustbin

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11
Q

What is endocytosis?

A

Energetic process to absorb/engulf molecules into a cell. Some extracellular fluid is usually engulfed too along with the molecule e.g. a portion of the membrane is invaginated to form a membrane bound vesicle called an endosome
* Occurs in neutrophils & macrophages - they implement phagocytosis (eating)
whereby they engulf entire cells/macromolecules to form a phagosome
* Pinocytosis (drinking) - bringing in dissolved solutes
* Receptor mediated - specific, found in depressed areas (coated pits) - allows the cell
to get the molecules it needs. Ligands bind to receptor, this complex is engulfed -
releasing the ligand into the cytosol (fluid portion of the cytoplasm outside the cell
organelles)

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12
Q

What is exocytosis?

A

Vesicle from the golgi apparatus, fuse with the plasma cell membrane, resulting in the expulsion of waste or the secretion of enzyme/hormones.

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13
Q

What type of things can be inside the phospholipid bilayer?

A
  • Cholesterol (charged)
  • Integral or intrinsic proteins e.g. ion channels
  • Peripheral (extrinsic) protein
  • Hydrophilic head
  • Hydrophobic tail

contains; glycolipids: communication, joins cells to form
tissues + stability, glycoproteins: for cell to cell recognition + acts as receptors,
cholesterol: maintains fluidity in membrane

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14
Q

What is the membrane permeability?

A
  • Selective permeability
  • The fluidity is modified by cholesterol and temperature
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15
Q

What is the membrane freely permeable to?

A
  • Water: aquaporins (small channels for water)
  • Gases: CO2, N2, O2
  • Small uncharged polar molecules: Urea, ethanol
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16
Q

What is the membrane impermeable to?

A
  • Ions: Na+, K+, Cl-, Ca2+
  • Charged Polar molecules: ATP, Glucose-6-phosphate
  • Large uncharged polar molecules: Glucose
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17
Q

What does simple diffusion transport?

A
  • Blood gases, water
  • Urea, free fatty acids
  • Ketone bodies
18
Q

What is facilitated diffusion?

A
  • The movement of solutes from a region of their high concentration to a region of their low concentration through protein channels
  • This continues until dynamic equilibrium is reached. e.g. Glucose - protein assisted which is regulated by insulin. Voltage gate channels activated by action potentials
  • no real energy expended
19
Q

What is active transport?

A
  • The movement of solutes from a region of low concentration to a
    region of high concentration against the concentration gradient.
  • Both transmembrane carrier protein and ATP is required. e.g Na/K ATPase pump (sodium out and potassium into cell) - going against chemical and electrical gradients
  • This is primary example
20
Q

What is secondary active transport?

A

Secondary: sodium, glucose chain. Transports sodium and glucose across membrane. Energy not used directly it is derived from Na/K ATPase as lots of sodium out of cell so now high to low and means sodium can go down its gradient and take glucose with it

21
Q

What is an osmotic drag?

A

When water also moves through the membrane with it.

22
Q

What examples of ion channels?

A
  • Put a channel in and ions can move in and out without having to interact with the membrane
  • E.g. Voltage-gated and “Leak” channels
  • Can also have pino-/phago-cytosis that are large molecules transported through vesicles.
23
Q

Why are membranes and membrane proteins needed?

A
  • Cell polarisation
  • Compartmentalisation which allows cell to set up: ion gradients, diffusion, membrane potential
  • Tightly regulated
  • Disease disrupts this: heart disease, kidney failure
    These processes are tightly regulated and diseases can set in
24
Q

What is the membrane potential?

A

(Em = membrane potential)
- Potential difference across the cell membrane generated by different ion concentrations
- Potassium is the major determinant of Em
- Stable in most cells but sensitive to ionic imbalance
- When ions can’t diffuse anymore = equilibrium

25
Q

What is the membrane potential?

A
  • Extracellular fluid potential = 0mV
  • Membrane potential is that on intra-cellular membrane
  • Composed of various individual diffusion potentials
26
Q

What does hyperpolarised mean?

A

When we take away positive from inside the cell, the intra-cellular becomes more negative e.g. K+

Or more rarely when negative ions move into the cell e.g. Cl-

27
Q

What does depolarised mean?

A

When positive ions move into the cell e.g. Na+, Ca2+

28
Q

How do we measure the diffusion potential?

A

The Nernst equation
Eion = (RT/zF)ln ionE/ionI
Log ration of the intracellular ion concentration and extracellular concentration
First part of equation = describes ion diffusion work done
Second part of equation (zFV) describes the electrical work done

29
Q

How does permeability determine membrane potential?

A
  • Ion conductance (permeability) is a key determinant of Em
  • Permeability dependent on: channel numbers, and channel gating (open or close)
  • If we change the ion permeability, it will change the membrane potential.
30
Q

Describe the K+ diffusion potential

A
  • Major role in K+ homeostasis
  • Renal failure
  • If we raise the extracellular potassium and what happens is the membrane potential becomes less negative and more positive so starts to depolarise.
    Clinically called hyperkalaemia
  • If we decrease the extracellular potassium then the membrane potential becomes more negative
    Clinically called hypokalaemia
31
Q

What is Ischaemia?

A
  • Can’t produce ATP anymore
  • The K ATP channel opens too early so potassium can leak out when it shouldn’t
  • So depolarisation occurs
  • So the fast sodium channels can’t open anymore so sodium and calcium enter very slowly.
32
Q

What does the epithelia require?

A
  • polarisation of plasma membrane
  • The epithelial permits cell-specific function
  • It can strongly adhere to neighbours - tight junctions
33
Q

What do tight junctions do?

A

Occluding: tight junctions help seal cells together in an epithelial sheet to prevent
leakage of molecules between them

34
Q

What are gap junctions?

A

Communicating: gap junctions - allows the passage of small water-soluble ions and molecules

35
Q

How do actin filaments provide anchoring?

A

Actin filaments: enable cell to cell adhesion through adherens
junctions (ADHERENS JUNCTION JOINS ACTIN BUNDLE IN ONE CELL TO A
SIMILAR BUNDLE IN ANOTHER CELL - HELPS KEEP CELLS TOGETHER) & cell to matrix (external to cell) adhesion through adherens junctions too.

36
Q

How do intermediate filaments provide anchoring?

A

INTERMEDIATE FILAMENTS; enable cell to cell adhesion through desmosomes
(cell surface adhesion proteins + intracellular keratin cytoskeletal filaments - they
resist shearing forces & JOIN THE INTERMEDIATE FILAMENTS IN ONE CELL
TO THOSE IN A NEIGHBOUR) & cell to matrix adhesion through focal adheren
junctions. HEMIDESMOSOMES; anchor intermediate filaments in a cell to the basal lamina

37
Q

What are cell receptors?

A

Gateway to intracellular signals: Examples; open a channel, activate a intracellular enzyme, induce second messenger (peptide hormone binds to receptor) & migrate nucleus to receptor-ligand complex

38
Q

What is an example of an enzyme linked receptor?

A

e.g. tyrosine kinase - transfers a phosphate group from ATP to a protein in a cell thus acts like an on/off switch,

39
Q

What is an example of an ion channel linked receptor?

A

participate in rapid signalling events found in electrically active cells
like neurons, also referred to as ligand gated ion channels,

40
Q

What is a G-protein coupled receptor?

A

sense molecules outside the cell and activate inside signal transduction pathways to ultimately illicit a cellular response

41
Q

What environmental changes can alter the membrane function?

A
  • pH
  • Calcium concentrations
  • temperature (too cold: proteins slow down, too hot: proteins denature)

IMMS Lectures (21 decks)

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