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BIO-330: Cell Biology > Exam 2 > Flashcards

Exam 2 Flashcards

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1
Q

What are the roles of the cell membrane in a cell’s daily activities for survival and function?

A

-protection
-encloses inside of cell from outside environment
-regulate transport of substances inside and out of the cell
-receives chemical messages from other cells
-cell mobility

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2
Q

What do “fluid” and “mosaic” refer to in the fluid-mosaic model of the cell membrane?

A

Fluid = due to flexibility and lateral movement of the membrane

Mosaic = the array of proteins, lipids, and macromolecules present in the membrane

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3
Q

What supports the current fluid-mosaic model?

A

Freeze-fracture technique
Electron microscopy
Human and Mouse cell mixed proteins

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4
Q

How might the membrane of an epithelial cell in the intestines be different than the membrane of a neuron?

A

Epithelial: may be more permeable, contain greater proteins in absorption, such as aquaporins, glucose, ions, lipids, etc.

Neuron: have more of a focus on sodium channels, especially voltage-gated sodium channels to aid in the generation of an action potential

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5
Q

Why is a liposome energetically favorable?

A

maximizes hydrogen bonding and nonpolar interactions

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6
Q

If a drug was added to a cell that inhibited scramblase activity, what is expected to happen?

A

the phospholipid bilayer would grow asymmetrically, with more lipids on the cytosolic side of the ER membrane

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7
Q

What allows a “flip-flop” to occur more easily in a cell membrane?

A

Flippases

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8
Q

In what way do water molecules organize themselves?

A

in a way to maximize hydrogen bonding between the hydrogen of one and the oxygen of another

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9
Q

Why do membrane lipids form bilayers in water?

A

they are amphipathic

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10
Q

Where does membrane synthesis occur?

A

ER

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11
Q

What are two ways in which the cytosolic monolayer is different from the non-cytosolic monolayer?

A

glycolipids on exterior surface - these don’t get flipped

specific phospholipids are flipped to the cytosolic side, while some remain on exterior surface

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12
Q

What is a flippase?

A

proteins that aid in “flipping” specific phospholipids to cytosolic monolayer

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13
Q

What are Glycolipids and an example of a function in a membrane?

A

Lipid + Carb

adhesion, cell signaling, identification
Act as receptors on the surface of RBCs (help determine blood group)

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14
Q

Why is non-cystolic a better term than exterior?

A

gets confusing in the case of a vesicle that leaves from a membrane-bound organelle, where the “exterior” is really the cytosolic face (as it is facing the cytosol of the cell)

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15
Q

TRUE OR FALSE: Phosphatidylserine is normally found in the extracellular face of the cell membrane

A

FALSE - it is normally found in the intracellular face (cytosolic face)

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16
Q

Why do cells need fluid membranes?

A

so they can adjust fluidity at different temperatures (not be stuck and unable to move)

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17
Q

What helps keep membranes fluid and why?

A

Unsaturated fatty acids

cholesterol - for more structure

holds together lipids at high temps
acts to spread out lipids at low temps, keeping them from solidifying

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18
Q

How do organisms change their membrane composition to match environmental temperatures to keep membrane fluid?

A

changes in fatty acid composition (unsaturated = more fluid in lower temps, saturated = viscous in higher temps

cholesterol provides greater structure and acts as a “temperature buffer”

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19
Q

How do the properties of lipids, and the lipid composition of the membrane, influence membrane fluidity?

A

Saturated fatty acid = more rigid, less fluid
Longer fatty acid chains = more rigid, less fluid
membrane proteins = can promote clustering of lipids or disrupt it (increasing fluidity)

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20
Q

Give a biological example of when a cell would benefit from changing its membrane fluidity

A

If temperatures drop, cholesterol and unsaturated hydrocarbon tails allow for the membrane to stay fluid and not become “stuck” because of the lower temperature (and unable to move)

e.g. antifreeze protein properties in fish

21
Q

Name examples of lipids and what they have in common

A

Phospholipids
Triglycerides
Glycolipids
Steroids

In Common: energy storage, transport, communication, nonpolar

22
Q

When will a protein associate with the membrane?

A

At the region where protein is nonpolar

23
Q

What structure provides structural stability and strength to a cell membrane?

A

Cell Cortex (actin network)

24
Q

What is a human disease that results from a problem with proteins in the cell cortex?

A

Hereditary elliptocytosis

25
Q

What is a Detergent?

A

amphipathic molecules that are able to isolate membrane proteins from the lipid bilayer (e.g. SDS)

26
Q

Name 10 specific membrane proteins and their functions

A

Insulin receptor
Aquaporin
GLUT4
Voltage-gated ion channels
Na/K Pump
Rhodopsin
Glycoprotein
Gap junction

27
Q

What is an example of a toxin or disease that impacts cell membrane integrity?

A

cystic fibrosis - chloride becomes trapped in cells and unable to be transported out, leading to water unable to hydrate the cellular surface. This leads the mucus covering the cells to become thick and sticky

28
Q

What types of molecules can cross the membrane through simple diffusion?

A

water, oxygen, carbon dioxide, nitrogen, glycerol, ethanol

29
Q

What is the difference between passive and active transport and 3 examples of each?

A

Passive = no energy required, down a concentration gradient
-Aquaporins with water
-GLUT4
-Nicotinic Acetylcholine receptor

Active = energy required, against concentration gradient
-Na/K pump
-Bacteriorhodopsin
-Sodium-glucose transporter

30
Q

What would happen if a red blood cell is placed in a beaker of hypertonic (high salt) solution?

A

The RBC would begin to shrink and shrivel for water will follow the solute - moving from the area of high free water concentration (i.e. RBC) to low free water concentration (i.e. the solution). Thus, this leads to the RBC to shrink for it is rapidly losing water to the overwhelming solute concentration

31
Q

What are the relative concentrations inside and outside of the cells for the following:

Na
K
Ca
Glucose

A

INSIDE:
Na = 10
K = 140
Ca = 0.0001
Glucose = 0-20

OUTSIDE:
Na = 142
K = 4
Ca = 2.4
Glucose = 90

32
Q

What is the typical pH inside and outside of a cell?

A

Inside = 7.0
Outside = 7.4

33
Q

What does it mean if the red line shows an increase from -60mV to +40mV?

A

Sodium is entering the cell

34
Q

What is true of voltage-gated ion channels?

A

-contain a voltage-sensing domain
-found in neurons, muscles, and in many other types of cells

35
Q

What forces are responsible for substances moving into the cell?

A

-concentration of the substance
-charges in the cytosol
-charges of the substrate

36
Q

What is the role of ATP hydrolysis in the Na/K pump and how it leads to the active transport of sodium and potassium?

A

ATP is hydrolyzed into ADP and a free phosphate group. This phosphate phosphorylates on the pump to allow it to “shift in shape” and expose the 3 sodium ions toward the outside of the cell

37
Q

What is meant by the resting membrane potential of a cell?

A

electrical potential difference across the plasma membrane when cell is not in an excited state

38
Q

Why is the inside of a cell negative compared to the outside?

A

more cations are leaving the cell than entering, leaving more anions within the cell, but the Na/K pump helps to retain the resting membrane potential

39
Q

Why are Coupled Transporters a different form of active transport from ATP-driven pumps?

A

EXAMPLE: sodium-glucose transporters

active transport because the passive movement of sodium WITH its gradient can drive the movement of glucose AGAINST its gradient…ATP is not used and sodium’s gradient provides the energy

40
Q

What two forces contribute to setting the equilibrium potential for a given ion? How do these relate to the Nernst potential equation?

A

Concentration and Electrical gradient

concentration gradient = ion inside/ion outside

41
Q

What structural feature allows an ion channel to sense voltage?

A

the voltage sensing domain

42
Q

Describe the process of action potential generation, including the role of the neurotransmitter, its receptor, the voltage-gated sodium and potassium channels, and sodium & potassium ions.

A

-ACh neurotransmitter acts as a ligand for the ACh receptor (AChR) in the neuromuscular junction, allowing for it to become activated.

-Once activated, the AChR is able to open (from the “key”) and allow for an influx of sodium ions to flow inside of the cell.

-The influx of sodium ions depolarizes the cell to become more positive. Once this hits the threshold of about -40mV (from a resting membrane potential of -80mV), an “all or nothing” response occurs where the voltage-gated sodium channels are able to open and allow for hyperpolarization of the cell.

  • The action potential is created and leads to a chain reaction, which may then move down the axon of neurons. The sodium channels then become inactivated and close as the cell repolarizes
  • The cell begins to lose K+ from inside (as they begin to repel the like charges of sodium) which begins to repolarize the cell until the resting membrane potential is hit (after overshooting)
43
Q

What is a ligand-gated channel?

A

Integral protein that allows the passage of select ions when a ligand, or “key of sorts,” activates the channel, such as through a neurotransmitter

44
Q

How is a ligand-gated channel different from a voltage-gated channel?

A

voltage-gated requires a threshold to be hit before opening

ligand-gated requires a ligand to open

45
Q

Why can’t an action potential move backward?

A

The previous sodium channels begin to close, making the chain reaction move forward to the open sodium channels down the axon.

46
Q

You are deep in a remote tropical rainforest when you discover a new species of spider after it has bitten you. The toxin immediately begins blocking voltage-gated sodium channels in peripheral neurons. What symptoms might you expect from this bite and why?

A

-Paralysis, because of the inability to create action potential as the sodium channels are blocked to allow for depolarization of the cell (and hyperpolarization through these voltage-gated sodium channels)

-Pain, muscle weakness

47
Q

How does active and passive transport work together to move glucose from the intestinal lumen into the bloodstream (discuss two different proteins that move glucose and their locations in a cell)?

A

ACTIVE: Sodium-glucose transporters allow for the active transport of sodium and glucose into the intestinal epithelium from the intestinal lumen as a “symport”
-passive movement of sodium with its gradient can drive the movement of glucose against its concentration gradient (energy from the Na gradient drives transport of glucose)

PASsIVE: GLUT4 allows for the passive transport (as a uniport) of glucose from the intestinal epithelium into the bloodstream.

48
Q

Why must free edges be avoided?

A

they leave bonds unsatisfied

BIO-330: Cell Biology (6 decks)

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