Sec 6- Membranes Flashcards

Unit II- Life of a Cell

1
Q

What are plasma membranes made of?

A

Phospholipids and proteins

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2
Q

Membrane Proteins

A
  • Membrane proteins that interact with molecules outside of the cell are called receptors.
  • They are improtant for cell-to-cell signaling.
  • Viruses can take advantage of these receptors and bind to (and enter) our cells.
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3
Q

What is the function of membrane proteins?

A
  • Anchor the cell to the ECM
  • Transport substances across the membrane
  • Catalyze enzymatic reactions near the cell surface
  • Receive information from other cells in the form of chemical or electrical signals
  • Serve as identification tag
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4
Q

What is the movement of molecules across the Plasma Membrane?

A

For metabolism to work, a cell must keep its internal composition stable- even when conditions outside are greatly different.

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5
Q

What is selective permeability?

A

Membrane property that allows some substances, but not others, to cross.

  • Nonpolar, small molecules easily cross
  • Ions and/or large molecules can’t cross
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6
Q

What is concentration?

A

The number of molecules or per unit volume of a fluid.

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7
Q

What is the concentration gradient?

A

Difference in concentration of a substance between adjoining regions of fluid.

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8
Q

What is passive transport?

A

Substance moving down its concentration gradient drives it across a cell membrane.

  • Requires no direct energy input
  • Diffusion (including osmosis)
  • can be through the phospholipids directly or through a transport protein (pore)
  • Molecules will move down it’s own concentration gradient until equilibrium is reached.
  • This movement is independent of other molecules and their concentration gradients.
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9
Q

What is active transport?

A

A transport protein use energy, usually from ATP, to pump a substance across a cell membrane against its concentration gradient (pump).

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10
Q

What is diffusion?

A

Molecules and ions tend to follow their own concentration gradient and fdiffuse into an adjoing region in which they are less concentrated.

  • net movement of molecules from a region of higher concentration to a region of lower concentration
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11
Q

What is diffusion rate?

A

How quickly a particular solute diffuses through a particular solution depends on various factors:
1. size
2. temp
3. steepness of the conc. gradient
4. solvent density
5. pressure
6. distance travelling

  • Diffusion rate across a membrane is also influenced by:
    1. solubility (nonpolar vs polar/ion)
    2. surface area of membrane
    3. thickness of membrane
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12
Q

Osmosis

A

Net diffusion of water molecules across a selectively permeable membrane between two fluids with different water concentrations.

  • Passive transport
  • water molecules tend to diffuse in response to its own concentration gradient
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13
Q

What is tonicity?

A

Describes relative concentrations of solutes in fluids separated by a selectively permeable membrane.

  • Hypertonic solution
  • Hypotonic solution
  • Isotonic solution
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14
Q

What is a hypertonic solution?

A

Has a higher concentration of solute/stuff.
Has a low concentration of water.

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15
Q

What is a hypotonic solution?

A

Has a lower concentration of solute.
Has a high concentration of water.

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16
Q

What is an isotonic solution?

A

Has an equal concentration of solute/stuff.
Has an equal concentration of water.

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17
Q

What is osmosis?

A

Osmosis is the diffusion of water across a membrane from the region with a higher water concentration (low solute concentration = hypotonic) toward the region with a lower water concentration (high solute concentration = hypertonic).
Osmosis will continue until the two fluids are isotonic.

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18
Q

What happens when a cell is not in an isotonic solution?

A

Cells burst or shrink.
Ex: RBCs
Maintain the tonicity of extracellular fluids is an improtant part of homeostasis.

19
Q

What is paramecia?

A

Paramecia are single-celled organisms that live in freshwater environments (ponds).

  • They are surrounded by a hypotonic environment that they can’t control.
  • They have contractile vacuoles, which actively pump water tot he outside of the cell.
  • Otherwise they would burst because water continuously rushes in through osmosis!
20
Q

How does osmosis affect plant cells?

A

Cells lose turgor pressure in hypertonic solutions (when not being watered).

  • Hypertonic- water goes out of cell
  • Isotonic- plant cell is healthy
  • Hypotonic- vacuole is full of water
21
Q

What are the different membrane crossing mechanisms?

A
  1. Directly- Gases and small nonpolar molecules can diffuse across a lipid bilayer.
  2. Transport proteins- Most other moluecules and ions cross only with the help of transport proteins, which gives a cell or membrane-enclosed organelle control over which substances enter and exit.

  • Water crosses membranes both ways
22
Q

What are the two types of transport proteins?

A
  1. Channel proteins
  2. Carrier proteins
    * Each type of transport protein moves one (or sometimes two) specific molecule(s) across a membrane.
23
Q

What are channel proteins?

A
  • Barrel shaped proteins
  • Makes a tunnel through the plasma membrane
  • Always passive transport
24
Q

What are carrier proteins?

A
  • Carrier proteins undergo conformational changes
  • Passive or active depending on concentration gradient
25
Q

What is passive transport: Facilitated Diffusion?

A
  • Passive transport is when no energy is needed to transport.

  • Glucose from the blood enters RBCs through a carrier protein.
  • No energy is required because glucose moves down its concentration gradient.
  • The RBC adds a phosphate group to the glucose once it enters the cell to maintain the concentration gradient.
26
Q

What is passive transport in osmosis?

A

Aquaporins are channel proteins specific for water.

  • Water molecules move down their concentration gradient.
27
Q

What is active transport: Calcium Pump?

A

Requires a direct input of ATP.

  • Moves against the concentration gradient.
  • Muscle cells have calcium pumps to keep the calcium levels low in the cytosol.
28
Q

What is active transport: Sodium-Potassium Pump?

A

Uneven exchange: Two K^+ enter for every three N^+ exiting.

  • In all animal cells
  • Creates an electrical potential; more positive outside than inside of the cell.
  • Membrane potential
  • Electrochemical gradient
29
Q

WHat is active transport: Cotransport?

A

The sodium concentration gradient that is established by the sodium-potassium pump can be used to transport glucose into a cell (hitches a ride) against its concentration gradient.

30
Q

What are the different types of transport proteins?

A
  • Uniporter: one molecules or ion
  • Symporter: two different molecules/ions in same direction
  • Antiporter: two different molecules/ions in different direction
31
Q

How does the membrane trafficking of larger molecules?

A

Patches of membrane constantly move to and from the cell surface as vesicles that fuse with or pinch off from the plasma membrane.

  • The lipid bilayer reseals itself when the membrane is disrupted.
  • Molecules move across the lipid bilayer by exocytosis and endocytosis.
  • Exocytosis and endocytosis require energy (active transport).
32
Q

What is active transport: Exocytosis?

A

Ex:
* Expelling waste from the cell
* Releasing ECM proteins
* Neurotransmitter release into synaptic cleft

33
Q

What is active transport: Endocytosis?

A

Two types:
1. Phagocytosis (eating)
2. Pinocytosis (drinking)

34
Q

What is phagocytosis?

A
  • Macrophages and other white blood cells engulf particles such as microbes or cellular debris
  • Amoebas engulf food, like algae
35
Q

What are receptor-mediated endocytosis?

A
  • Example is the removal of “bad” cholestrerol from the blood (LDL)
  • Viruses take advantage of cell receptors to enter cells
36
Q

Diffusion

A
  • Active
  • Phospholipids
  • Small molecules
37
Q

Osmosis

A
  • Passive
  • Phospholipids
  • Water
38
Q

Facilitated Diffusion

A
  • Passive
  • Proteins
  • Glucose
39
Q

(Facilitated) Osmosis

A
  • Passive
  • Proteins
  • Water
40
Q

Active Uniporter

A
  • Active
  • Proteins
  • Calcium
41
Q

Symporter

A
  • Active/Passive
  • Proteins
  • Glucose and sodium
42
Q

Antiporter

A
  • Active
  • Proteins
  • Sodium-potassium
43
Q

Exocytosis

A
  • Active
  • Vesicle
  • Waste disposal
44
Q

Endocytosis

A
  • Active
  • Vesicle
  • “Bad” cholesterol into cell, Macrophages eating bacteria, Fluid intake

  • Phagocytosis
  • Pinocytosis