Chapter 7: Membrane Stucture and Function

Question 1

Define phospholipids.

Answer 1

A Phospholipid is a type of liquid molecule, made of a phosphate group and a fatty acid tail, that is a major component of cell membranes. The phospholipid bilayer has both hydrophobic and hydrophillic regions, allowing the cell membrane to be selectively permiable.

Question 2

In phospholipids, the phosphate group is the ________ region, and the fatty acid tain is the _________ region.

Answer 2

hydrophillic, hydrophobic

Question 3

When a molecule is _____, it means that is has both a hydrophobic region and a hydrophillic region.

Answer 3

Amphipathic

Question 4

Define the fluid mosaic model.

Answer 4

The currently accepted model of cell membrane structure.

Fluid = The cell membrane is not solid but is a gel like consistency, therefore not covalently bonded.

Mosaic = Proteins and Cholesterol imbedded within the membrane.

Question 5

Name and define the two kinds of movement of phospholipids.

Answer 5

Lateral Movement: When lipids and proteins shift sideways

Flip-Flop: When proteins and lipids switch sides of the membrane (rare).

Question 6

Membranes are held together by _______ interactions.

Answer 6

Hydrophobic

Question 7

Describe speed of lipid movement vs speed of protein movement.

Answer 7

• Lipid movement is always rapid, switching positions 10000000x per second
• Proteins move more slowly than lipids, or are immobile because they are are larger than lipids.

Question 8

In membrane fluidity, what is the importance of fatty acid tails being unsaturated vs saturated?

Answer 8

• The presence of unsaturated fatty acid tails increases membrane fluidity by introducing kinks that prevent tight packing of phospholipids
• The presence of saturated fatty acid tails decrease membrane fluidity by promoting close packing of phospholipids

Question 9

What is the importance of cholesterol within the animal cell membrane?

Answer 9

At lower temperatures, cholesterol acts as a fluidity buffer by inserting itself through the tails, preventing the phospholipids from packing too closely together.

At higher temperatures, Cholesterol helps to pack the phospholipids more closely together, reducing membrane fluidity to prevent excessive fluid intake.

Question 10

________ molecules dissolve in the lipid bilayer and pass through rapidly, while ________ molecule do NOT cross the membrane easily.

Answer 10

Nonpolar, polar

Question 11

Define osmosis.

Answer 11

The diffusion of water, from lower solute concentration to higher solute concentration, across a semi-permeable membrane.

Question 12

Define diffusion.

Answer 12

The movement of particles from high concentration to low concentration of any substance so that they spread out into the available space.

Question 13

In osmosis, water diffuses from _______ regions to _______ regions, because the higher concentration of solute _____ the free floating molecules from the lower side.

Answer 13

Hypotonic, Hypertonic, Attracts

Question 14

What is tonicity? Describe the three terms used to characterize tonicity.

Answer 14

Tonicity: The ability of a solution to cause a cell to lose or gain water.

Isotonic: Concentration of the solute is the same inside and outside; overall mass is the same.

Hypertonic: Concentration of the solute increases overtime in percent mass; loses water.

Hypotonic: Concentration of the solute decreases overtime in percent mass; gains water.

Question 15

What are the six major functions of membrane proteins?

Answer 15

1. Transport
2. Enzymatic Activity
3. Signal Transduction
4. Cell-to-cell Recognition
5. Intercellular Joining
6. Attachment to the cytoskeleton and extracellular matrix

Question 16

Describe the first major function of membrane proteins: Transport.

Answer 16

Membrane proteins form a channel between the membrane to allow polar molecules to successfully transport through the membrane rather than getting stuck in the hydrophillic region of the membrane.

Question 17

Describe the second major function of membrane proteins: Enzymatic Activity.

Answer 17

Enzymes are used to speed up chemical reactions in the cell and are made up of mostly proteins.

Question 18

Describe the third major function of membrane proteins: Signal Transduction.

Answer 18

Proteins in the membrane act as a receptor for receiving signals. The signaling molecule may cause the protein to change shape, allowing it to relay the message to the inside of the cell, usually by binding to a cytoplasmic protein.

Question 19

Describe the fourth major function of membrane proteins: Cell-to-cell Recognition.

Answer 19

Glyco-proteins serve as an ID tag that are specifically recognized by membrane proteins of other cells, allowing them to bond.

Question 20

Describe the fifth major function of membrane proteins: Intercellular Joining.

Answer 20

Membrane proteins of adjacent cells may hook together in various kinds of junctions, such as gap junctions or tight junctions. Longer lasting bonds than cell-to-cell recognition

Question 21

Describe the sixth major function of membrane proteins: Attachment to the cytoskeleton and Extracellular matrix.

Answer 21

Microfilaments or other elements of the cytoskeleton may be noncovalently bound to the menbrane proteins, heping to maintain cell shape and stabalizes location of certain membrane proteins.

Proteins bound to the ECM molecules can coordinate extracellular and intracelular changes.

Question 22

Name and describe the two types of membrane proteins.

Answer 22

Intergral Proteins: Proteins that are firmly embedded within the lipid bilayer of the cell membrane. They are also considered transmembrane proteins, meaning they span the membrane.

Peripheral Proteins: Proteins that are loosely associated with the membrane surface, and only extend partway into the hydrophobic interior

Question 23

How do transport proteins facilitate diffusion?

Answer 23

By forming a channel between the membrane to allow polar molecules to successfully transport through the membrane rather than getting stuck in the hydrophillic region of the membrane.

Question 24

Compare and contrast channel proteins vs carrier proteins.

Answer 24

Channel Proteins…
- Work like tunnels or pipes in the membrane that allow specific ions to go through.
- Are more efficent and helps to speed the process of crossing the membrane.
- Work like open gates.

Carrier Proteins…
- Grab onto molecules on one side, rotates its self to face the other side, and releases the molecule to the other side.
- Work like revolving doors.

Question 25

What are aquaporins?

Answer 25

A type of channel protein specific for facilitated diffusion of water.

Question 26

Define the two types of transport in which substances move across a cell membrane.

Answer 26

Passive Transport:
- Goes WITH the flow, requires NO extra energy because it follows the natural movement of molecules from areas of high concentration to areas of low concentration.

Active Transport:
- Goes AGAINST the flow and requires extra energy because it moves molecules from areas of low concentration to areas of high concentration AGAINST their natural gradient.

Question 27

What is simple diffusion vs. facillitated diffusion?

Answer 27

• Simple Diffusion: Small, uncharged molecules do not need help getting through the membrane.
• Facillitated Diffusion: Larger, charged molecules that need help from specific proteins that act like doors that open and close to only let specific molecules in.

Question 28

What is membrane potential?

Answer 28

The voltage difference across a membrane.

Question 29

How do ion pumps maintain a membrane potential?

Answer 29

By actively transporting ions across the cell membrane against their concentration gradients. This process requires the use of energy in the form of ATP.

Question 30

Why is there a difference in electrical charge on the inside of a cell membrane vs the outside of a cell membrane?

Answer 30

A difference in electrical charge on the inside vs outside is due to the unequal distribution of positive and negative ions.

Question 31

What is an electrogenic pump?

Answer 31

A transport protein that generates voltage across a membrane

Question 32

The main electrogenic pump of animal cells is called the ________. The main electrongenic pump of plants, fungi, and bacteria is called a __________.

Answer 32

sodium-potassium pump, proton pump

Question 33

What is the function of the sodium potassium pump?

Answer 33

Its primary function is to actively transport sodium ions (Na+) out of the cell and potassium ions (K+) into the cell, against their respective concentration gradients. This process requires the break down of ATP to provide energy for the pump’s activity.

Question 34

Describe the steps of the sodium potassium pump.

Answer 34

1. The pump’s shape attracts sodium ions, and grabs three sodium ions from inside the cytoplasm and puts them in the pump to bind.
2. The binding of the three sodium ions takes a phosphate group from ATP and attaches it to the pump (ATP is now ADP).
3. The attachment of a phosphate group signals the pump to change shape and close the door facing inside the cell and opens the door facing outside the cell for the three sodium ions to be released.
4. While the cell is open to the outside, its new shape attracts potassium ions and causes two outside potassium ions to go inside the pump and bind.
5. The binding of the potassium ions causes the pump to release the phosphate group.
6. The loss of the phosphate group restores the original shape open to the cytoplasm and it regains its attraction for sodium ions again, causing the potassium to be released into the cytoplasm.
7. Process repeats.

Question 35

Define cotransport.

Answer 35

Cotransport in cells involves the simultaneous movement of two molecules or ions across the cell membrane, with one molecule or ion providing the energy needed for both to be transported (like catching a ride).

Question 36

Name and describe the two kinds of bulk transport for larger molecules.

Answer 36

Exocytosis: EXpelling things OUT of the cell by releasing substances stored in vesicles into the external environment (like sending packages out).

Endocytosis: taking things IN, like materials from its external environment by englufing them with its membranes and forming vesicles (putting it in a bubble).

Question 37

Name and describe the three kinds of Endocytosis.

Answer 37

Phagocytosis: When certain specialized cells, called phagocytes, engulf and digest large particles or pathogens, such as bacteria, dead cells, or cellular debris. (Cell eating)

Pinocytosis: When cells take in extracellular fluid and dissolved solutes by engulfing them into small vesicles (pinosomes) formed by folding of the cell membrane. (Cell drinking)

Receptor-mediated endocytosis: When cells internalize specific molecules from the external environment (the cell “grabs” a specific molecules, and binds to them to form vesicles).