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Biology Honors Cambridge > C4: Cell Membranes and Transport > Flashcards

C4: Cell Membranes and Transport Flashcards

1
Q

Why are cells small?

A

They need a high surface area to volume ratio to be efficient at taking in nutrients and removing waste.

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2
Q

What is the fluid mosaic model?

A

a model that explains various characteristics regarding the structure of cell membranes

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3
Q

What are intracellular membranes?

A

membranes inside the cell that form compartments within the cell (EX: mitochondria, lysosome, nucleus)

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4
Q

How wide are phospholipids

A

roughly 7nm

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5
Q

Who first correctly outlined the fluid mosaic model, and when?

A

Singer and Nicolson in 1972

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6
Q

What is a phospholipid monolayer?

A

a structure formed when phospholipids are spread over the surface of water, forming a single layer with the hydrophilic phosphate heads in the water and the hydrophobic fatty acid tails sticking away from the water

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7
Q

What is a micelle?

A

sphere with hydrophilic phosphate heads facing out and hydrophobic fatty acid tails facing in (used to deliver materials to specific locations)

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8
Q

Why do the enzymes in lysosomes need to be compartmentalised?

A

Otherwise, they would break down most of the cellular components.

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9
Q

What factors affect the fluidity of membranes?

A
  • saturation of phospholipids
  • length of the fatty acid tails
  • temperature
  • cholesterol
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10
Q

How does phospholipid saturation affect membrane fluidity?

A

The more unsaturated they are, the more fluid the membrane.

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11
Q

How does the length of the fatty acid tails affect membrane fluidity?

A

The more short they are, the more fluid the membrane.

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12
Q

How does temperature affect membrane fluidity?

A

The higher the temperature, the more fluid the membrane.

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13
Q

What are the two types of proteins in cell membranes?

A

intrinsic/integral (embedded in the membrane) and extrinsic/peripheral (on the outer or inner surface of the membrane)

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14
Q

What are transmembrane proteins?

A

proteins that span the entire membrane

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15
Q

What are transport proteins?

A

intrinsic/integral proteins that provide hydrophilic channels for certain molecules and ions to pass through the membrane

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16
Q

What are the types/functions of proteins?

A

Junctions, Enzymes, Transport, Recognition, Anchorage, Transduction

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17
Q

How can phospholipids act as signaling molecules?

A

They can move about in the bilayer and activate other molecules such as enzymes.

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18
Q

How can phospholipids activate receptors?

A

Some can be hydrolyzed and release small, water-soluble, and glycerol-related molecules that can diffuse through the cytoplasm and bind to specific receptors.

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19
Q

What is the function of cholesterol in the cell membrane?

A

regulating the membrane’s fluidity and preventing the membrane from breaking

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20
Q

What does the hydrophobic region of cholesterol do?

A

helps prevent ions and polar molecules from passing through the membrane (just like hydrophobic fatty acid tails of phospholipids)

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21
Q

What are the three main parts of a cholesterol molecule?

A
  1. the hydroxyl group (—OH) makes the head polar and hydrophilic (they are attracted to the phosphate heads of phospholipid molecules)
  2. carbon rings make up the main body structure of the molecule, and this classifies cholesterol as a steroid
  3. non-polar hydrophobic tails are at the end (attracted to the hydrophobic tails of phospholipids in the center of the membrane)
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22
Q

What do the carbohydrate chains projecting out from glycolipids and glycoproteins do?

A

They form hydrogen bonds with water molecules to help stabilize the membrane structure.

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23
Q

What can some glycolipids and glycoproteins aid in?

A

cell-to-cell recognition (receptor molecules)

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24
Q

What are the three major groups of receptors?

A
  1. Signalling receptors (they recognize messenger molecules, and once they bind, a series of chemical reactions is triggered inside the cell)
  2. Endocytosis-related receptors (they bind to molecules that are going to be engulfed by the cell membrane)
  3. Binding receptors (they are involved in binding cells to other cells in tissues and organs in animals)
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25
Q

What is cell signaling?

A

the process by which messages are sent to cells

26
Q

Explain the basic stages of a cell signaling pathway.

A
  1. a stimulus or signal is received by a receptor
  2. transduction occurs (signal is converted to a “message” that can be passed on)
  3. the “message” is transmitted to an effector (a target that carries out a response)
  4. an appropriate response is made
27
Q

Why is cell signaling important?

A

allows organisms to respond to their environment

28
Q

How are receptors triggered to send a message?

A

The signal brings a small change in the shape of the receptor.

29
Q

What is a ligand?

A

signaling molecule that binds to a receptor

30
Q

What substance picks up the message passed to the inside of the cell by the receptor?

A

G protein

31
Q

What messengers get released after the G protein?

A

secondary messengers

32
Q

Explain how a signal goes through amplification after the secondary messengers are released.

A

Enzymes are activated by the secondary messengers, which will then further activate more enzymes.

33
Q

What is a signaling cascade?

A

the sequence of events that is triggered by the G protein

34
Q

What are the other ways in which a receptor molecule can alter the activity of a cell? (other than activating G protein and signaling cascade)

A
  1. open an ion channel (change in membrane potential)
  2. act directly as a membrane-bound enzyme
  3. act as an intracellular receptor when the signal passes straight through the cell membrane
35
Q

What is diffusion?

A

the net movement of a substance from a region of higher concentration to a region of lower concentration (due to random motion of molecules or ions)

36
Q

What factors affect the rate of diffusion?

A
  • “steepness” of concentration gradient
  • temperature
  • surface area
  • properties of the molecules or ions
37
Q

What kind of molecules can easily pass through the phospholipid bilayer via simple diffusion?

A

small, non-polar, and uncharged molecules

38
Q

What kind of molecules cannot pass through the phospholipid bilayer via simple diffusion?

A

large, polar, and charged molecules

39
Q

What is facilitated diffusion?

A

diffusion that takes place through transport proteins

40
Q

What two factors affect the rate at which facilitated diffusion takes place?

A
  1. the number of channels present
  2. whether the channels are open or not
41
Q

What is osmosis?

A

the net movement of water molecules from a region of higher water potential to a region of lower water potential

42
Q

What is water potential (ψ)?

A

the tendency of water molecules to move from one place to another

43
Q

How do you increase water potential?

A

by adding more pressure

44
Q

How do you decrease water potential?

A

by adding more solutes

45
Q

What must be true for cells to maintain homeostasis?

A

the water potential is equal to the solute potential

46
Q

What is tonicity?

A

a term that describes the ability of a surrounding solution to cause a cell to gain or lose water

47
Q

Explain what happens to animal cells in hypertonic, hypotonic, and isotonic solutions.

A
  • cells shrink in a hypertonic solution
  • cells swell in a hypotonic solution
  • cells are normal in an isotonic solution
48
Q

Explain what happens to plant cells in hypertonic, hypotonic, and isotonic solutions.

A
  • cells go through plasmolysis in a hypertonic solution
  • cells are turgid in a hypotonic solution
  • cells are flaccid in an isotonic solution
49
Q

What is the term that describes a cell bursting?

A

lyse

50
Q

What is incipient plasmolysis?

A

the point at which pressure potential has just reached 0 and plasmolysis is about to occur

51
Q

What is active transport?

A

the transport of molecules or ions across a membrane against a concentration gradient by using energy (ATP)

52
Q

What does the sodium-potassium pump do?

A

pumps three Na+ ions out of the cell while allowing two K+ ions into the cell (this causes the inside of the cell to become more negative than the outside of the cell)

53
Q

Why is the sodium-potassium pump important?

A
  1. necessary for nerve cells to respond to stimuli and transmit impulses
  2. maintains osmotic equilibrium and membrane potential in cells
  3. maintains blood pressure and controls cardiac contractions
54
Q

What is bulk transport?

A

the process by which large quantities of molecules are transported across membranes

55
Q

What is endocytosis?

A

the process by which cells engulf substances by wrapping the cell membrane around them (forms vesicles)

56
Q

What is phagocytosis?

A

the uptake of solid material by phagocytes (cell eating)

57
Q

What is pinocytosis?

A

the uptake of liquid by small vesicles (cell drinking)

58
Q

What is receptor-mediated endocytosis?

A

the uptake of specific molecules that is triggered by receptors on the cell membrane

59
Q

What is exocytosis?

A

the process by which materials are removed from cells

60
Q

How does exocytosis occur?

A

vesicles containing the substance needing to be released fuse with the cell membrane and releases the substance out of the cell

Biology Honors Cambridge (7 decks)

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