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PHYSL212 > Cell Physiology > Flashcards

Cell Physiology Flashcards

1
Q

Describe the trilaminar appearance of the Plasma membrane

A

The membrane consists of two layers of phospholipids with embedded proteins. A light space consisting of the lipid fatty tails is sandwiched between the phosphate heads of each layer.

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2
Q

What is the structure of the phospholipid?

A

Hydrophilic, phosphate-containing head.
Glycerol backbone.
Hydrophobic fatty acid chain tails.

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3
Q

How would you describe the hydrophilicity or hydrophobicity of the phospholipid molecule?

A

Amphipathic

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4
Q

How does the micelle differ from the phospholipid bilayer?

A

The micelle phospholipids contain only one fatty acid tail and therefore form a conical shape or sphere.

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5
Q

How does a saturated fatty acid differ from an unsaturated fatty acid?

A

Unsaturated: double bond present.
Saturated: no double bonds present.

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6
Q

What is the structure of cholesterol?

A

A steroid ring structure (3 cyclohexanes and 1 cyclopentane) with a hydrophobic branch off the pentane and a hydrophilic hydroxy group off the left-most cyclohexane. It is amphipathic,

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7
Q

Why is the plasma membrane fluid?

A

Random, rapid lateral movements of phospholipids and proteins.
Rotation of lipids and flexing.
Very rarely flip-flopping

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8
Q

How is the mobility of membrane proteins restricted?

A

Associations with the cytoskeleton, other proteins, and cellular matrix.

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9
Q

How is the PM a mosaic?

A

Many different types of macromolecules.

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10
Q

What affects the fluidity of the membrane?

A

Unsaturated phospholipids have kinks in their tails that cause an increase in fluidity.
Heat increases fluidity.
Cholesterol increases fluidity by fitting between phospholipids.

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11
Q

Why is asymmetry essential in the plasmas membrane?

A

The faces of proteins likely facilitate different functions based on their location.
Carbohydrates are only on outward-facing surfaces.
The outer and inner halves of the PM have different phospholipid content.

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12
Q

What are the two mechanisms of intercellular communication?

A

Direct communication: Gap junctions.

Indirect communication: Chemical messengers (hormones, etc.)

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13
Q

What is signal transduction?

A

The sequence of events between the binding of a messenger to the receptor and the production of a cellular response.

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14
Q

What are the three properties of receptors?

A

Specificity, saturation, affinity.

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15
Q

What two places can receptors be in? What is the name for both locations?

A

Plasma membrane: transmembrane protein.

Intracellular: cytosolic, nuclear.

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16
Q

What messengers bind to intracellular receptors?

A

Lipid-soluble chemical messengers (ie, steroid hormones)

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17
Q

What are transcription factors?

A

Alters the transcription of mRNA by binding to a response element, which is a specific sequence of DNA near the beginning of a gene.
TFs alter the rate of protein synthesis.

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18
Q

What messengers bind to transmembrane receptors?

A

Water-soluble chemical messengers (cannot cross PM).
Bind on the extracellular surface.
Channel, enzyme, or g-protein-linked receptors as well.
ie) hormones, NTs, paracrine/autocrine compounds.

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19
Q

What is the first messenger?

A

An extracellular chemical messenger that binds to a specific membrane receptor.

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20
Q

What is the second messenger?

A

substances that enter or are generated in the cytoplasm of a cell in response to the binding of the first messenger to a receptor.

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21
Q

What is protein kinase?

A

An enzyme that phosphorylates another protein.

22
Q

What are g-proteins?

A

On the cytosolic surface of PM,
Bind guanosine nucleotides (GDP, GTP).
3 subunits: alpha, beta, gamma.
The link between G-protein coupled receptor and an effector protein.

23
Q

What does the alpha-subunit do?

A

Binds guanosine nucleotides.

24
Q

How does the g-protein inactivate?

A

GTPase of a-subunit produces Pi and G-GDP.

25
Q

What are the three types of G-proteins?

A
  1. Affect ion-channels (open or close)
  2. Stimulate enzymes (activate)
  3. Inhibit enzymes (deactivate)
26
Q

Describe the action of g-proteins on an ion channel

A
  1. the First messenger binds to a receptor, causing a conformational change.
  2. The change causes the affinity of alpha-subunit for GTP to increase; GDP will dissociate and GTP will bind to the alpha subunit.
  3. GTP-bound alpha-subunit dissociates from beta and gamma sub-units as a result and moves to ion channel.
  4. The ion channel opens or closes as the alpha-subunit binds.
27
Q

Describe the action of g-proteins on enzymes

A
  1. the First messenger binds to a receptor, the affinity of alpha for GTP increases, causing GDP to dissociate and GTP to bind to alpha.
  2. alpha dissociates from beta and gamma, moves to the enzyme.
  3. Gs protein will stimulate the enzyme, Gi will inhibit.
  4. This alters the production of a second messenger in the cytosol.
28
Q

What is cAMP?

A

Cyclic adenosine monophosphate and acts as a second messenger.

29
Q

How does cAMP act as a second messenger?

A

Gs proteins activate Adenylyl cyclase, which converts ATP into cAMP.
2. cAMP then activates cAMP-dependant protein kinase, which phosphorylates a protein that will induct a cellular response.

30
Q

How is cAMP recycles?

A

Phosphodiesterase breaks cAMP down into AMP.

31
Q

Why is calcium a good second messenger?

A

Active transporters maintain a low calcium concentration in the cytoplasm; minimal amounts of calcium cause an exponential cellular change.

32
Q

How does calcium act as a second messenger?

A
  1. the First messenger binds to a receptor.
  2. Receptor is a ligand-gated calcium channel OR released a g-protein to activate an ion channel.
  3. cytosolic calcium is increased.
  4. Cytosolic calcium activates calcium calmodulin.
  5. Calcium calmodulin alters the activity of enzymes to phosphorylate a protein to make a cellular response.
33
Q

What is phagocytosis?

A

Pseudopodia form around a large extracellular molecule and entrap inside a lipid-soluble phagosome, which is transported through the cytoplasm and to the lysosome to be digested.

34
Q

What is Pinocytosis?

A

Pseudopodia engulf non-specific solutes and package inside vesicles to be delivered to the lysosome.

35
Q

What is receptor-mediated endocytosis?

A

Ligand bind to receptor-coated dimples in the PM. Clathrin proteins form a coated pit and the receptors and ligands are entrapped in a vesicle. Clathrin is released from the vesicle as the vesicle reaches the endosome.

  1. Receptors are recycled to the membrane.
  2. Ligands are transported to their desired destination.
36
Q

What is exocytosis?

A

Secretory vesicle carries contents to the plasma membrane via linking proteins; empties contents by secretion into the ECF.

37
Q

What is the function of exocytosis?

A

To secrete membrane-impermeable molecules synthesized by the cell.
Release waste products that cannot be digested by the cell.
Add components to the plasma membrane.

38
Q

What is transcytosis?

A

Endocytosis directly to exocytosis, to move a specific molecule through several cells or layers to reach a certain destination.
Often in epithelial cells heading to blood.

39
Q

What are the four types of transport?

A
  1. Simple diffusion.
  2. Channel-mediated.
  3. Carrier-mediated.
  4. Activate transport.
40
Q

What is simple diffusion?

A

Passive movement of the molecule through PM and does not require energy and is lipid-soluble.

  1. Is small.
  2. Moves in high to low concentration.
41
Q

What factors influence the rate of simple diffusion?

A
  1. Magnitude of driving force (concentration gradient).
  2. Membrane surface area.
  3. Membrane permeability: lipid-soluble, nonpolar, small, specific shape, increased temperature, thin membrane.
42
Q

What is a chemical driving force?

A

Concentration gradient; molecules move passively in the direction of the driving force. (High to Low).

As the size of the gradient increases, the rate of transport increases

43
Q

What is the electrical driving force?

A

Membrane potential: differences in electrical potential or voltage across the cell membrane (caused by charge separation).

Ion experiences attractive or repulsive forces depending on membrane potential.

44
Q

What is the electrochemical driving force?

A

The net sum of both the electrical driving force and chemical driving force (via vector addition).

45
Q

What are the characteristics of channel proteins?

A
  1. Usually multimeric proteins.
  2. Spans PM layer.
  3. Substrate specific.
  4. Has an opened and closed state.
  5. Can move solutes very rapidly.
  6. Can function as a receptor.

Characterized by its gating and selectivity.

46
Q

What is the channel selectivity filter?

A

The narrowest part of the conduction pathway through the pore of the channel that discriminates between different ionic species.

47
Q

What are the four types of channel-gated proteins?

A
  1. Voltage-gated.
  2. Ligand-gates (extracellular)
  3. Ligand-gates (intracellular)
  4. Stretch-activated.
48
Q

What are the characteristics of transporter proteins?

A
  1. Monomeric or multimeric (passive or active)
  2. Span PM
  3. Substrate specific.
  4. Activity can be regulated.
  5. May couple the movement of solutes.
  6. May move substrate uphill against a gradient.
  7. Usually slower than channels.
49
Q

What is primary active transport?

A

Na/K Pump, where the energy source is ATP.

Maintains membrane potential, (Na concentrated outside, K concentrated inside).
Contribute to controlling of cell volume.

50
Q

What is secondary active transport?

A

The energy source is the electrochemical gradient.
Couples movement of one substance down its gradient with that of another against its gradient.

The gradient is then restored by primary active transport., maybe electroneutral or electrogenic.

PHYSL212 (7 decks)

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