Untitled Deck

Question 1

Describe the types of transport across membranes.

Answer 1

There are two types of transport: passive transport, which occurs down the concentration gradient, and active transport, which occurs against the concentration gradient.

Question 2

Define facilitated diffusion.

Answer 2

Facilitated diffusion is a passive process where molecules move down their concentration gradient with the help of specific proteins or channels.

Question 3

How does the concentration gradient affect the rate of diffusion?

Answer 3

The rate of diffusion is directly proportional to the concentration gradient; as the gradient increases, the rate of diffusion increases.

Question 4

Explain the energy changes associated with moving molecules down a concentration gradient.

Answer 4

Moving molecules down a concentration gradient releases energy, resulting in a negative change in free energy (ΔG).

Question 5

What is the permeability of biomembranes to sugars?

Answer 5

Biomembranes appear permeable to sugars, but this permeability is facilitated by helper molecules rather than simple diffusion.

Question 6

Describe the effect of metabolic inhibitors on diffusion.

Answer 6

Metabolic inhibitors have no effect on both simple and facilitated diffusion.

Question 7

How does facilitated diffusion differ from simple diffusion?

Answer 7

Facilitated diffusion involves specific proteins or channels to assist the movement of molecules, while simple diffusion does not require such assistance.

Question 8

Define passive transport in the context of concentration gradients.

Answer 8

Passive transport is the movement of molecules down their concentration gradient without the use of energy.

Question 9

What types of molecules are membranes generally impermeable to?

Answer 9

Membranes are generally impermeable to large uncharged molecules such as amino acids and glucose, as well as small, polar-charged molecules (ions).

Question 10

Explain the significance of Fick’s law in diffusion.

Answer 10

Fick’s law states that the rate of diffusion is linear as the concentration of the solute increases, indicating a direct relationship between concentration and diffusion rate.

Question 11

Describe the role of helper molecules in diffusion.

Answer 11

Helper molecules facilitate the diffusion of substances across membranes, particularly for those that cannot pass through the lipid bilayer easily.

Question 12

How does active transport differ from passive transport?

Answer 12

Active transport requires energy to move molecules against their concentration gradient, while passive transport does not require energy and moves molecules down their gradient.

Question 13

What happens to ΔG when moving molecules up a concentration gradient?

Answer 13

Moving molecules up a concentration gradient consumes energy, resulting in a positive change in free energy (ΔG).

Question 14

Identify the types of molecules that membranes are permeable to.

Answer 14

Membranes are permeable to gases (O₂, CO₂, N₂), lipids, and small, polar, neutral molecules such as urea.

Question 15

Explain the concept of saturation in facilitated diffusion.

Answer 15

In facilitated diffusion, the rate of transport saturates as the concentration of the solute increases, indicating that all available transport proteins are occupied.

Question 16

Describe the process of passive transport in cells.

Answer 16

Passive transport occurs when a cell moves particles across a membrane without using energy, allowing particles to go down their concentration gradient.

Question 17

Define diffusion in the context of cellular transport.

Answer 17

Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration.

Question 18

How does osmosis differ from diffusion?

Answer 18

Osmosis is the diffusion of water across a selectively permeable membrane, while diffusion refers to the movement of any type of particles.

Question 19

Explain the importance of regulating water flow through the plasma membrane.

Answer 19

Regulating water flow is crucial for maintaining homeostasis within a cell.

Question 20

What are the two models for facilitated diffusion?

Answer 20

The two models for facilitated diffusion are the pore (channel) model and the carrier model.

Question 21

Describe the role of the phospholipid bilayer in membrane transport.

Answer 21

The phospholipid bilayer consists of hydrophobic fatty acid sides and hydrophilic phosphoric sides, allowing only non-polar or small polar molecules to pass through.

Question 22

How do carrier ionophores function in facilitated diffusion?

Answer 22

Carrier ionophores, like valinomycin, transport impermeable species across the membrane by carrying them.

Question 23

What is the structural feature of Gramicidin A?

Answer 23

Gramicidin A is a pentadecapeptide with a specific sequence of amino acids, including D-amino acids, that forms a pore in the membrane.

Question 24

Explain the significance of concentration gradients in passive transport.

Answer 24

Concentration gradients drive passive transport, as particles naturally move from areas of higher concentration to areas of lower concentration.

Question 25

Define the term ‘selectively permeable membrane’.

Answer 25

A selectively permeable membrane allows certain substances to pass through while blocking others, crucial for maintaining cellular homeostasis.

Question 26

Describe the process of formylation in relation to membrane proteins.

Answer 26

Formylation involves the insertion of proteins into the membrane with the N-terminal facing inwards, leading to the formation of a beta-helix structure.

Question 27

Define the structure and function of gramicidin.

Answer 27

Gramicidin is a transmembrane ionophore that forms a pore in the membrane, allowing ions to pass through, with non-polar side chains facing the membrane and polar parts facing inwards.

Question 28

How does the selectivity of gramicidin compare to other ion channels?

Answer 28

Gramicidin has poor selectivity but primarily functions as a sodium ion channel.

Question 29

Compare the rates of transport for gramicidin and valinomycin.

Answer 29

Gramicidin transports ions at a rate of 10⁷ ions/molecule/sec, while valinomycin transports ions at a rate of 10⁴ ions/molecule/sec.

Question 30

What are ionophores and their role in ion transport?

Answer 30

Ionophores are molecules, often small antibiotics or synthetics, that facilitate the movement of ions across membranes, acting as carriers or channels.

Question 31

Describe the structural features of valinomycin that contribute to its function.

Answer 31

Valinomycin has alternating ester and ether peptide bonds, with inwardly facing carbonyls that coordinate potassium ions octahedrally, allowing it to be freely permeable in membranes.

Question 32

How does the permeability of valinomycin vary among different ions?

Answer 32

Valinomycin’s permeability is ranked as Rb⁺ > K⁺ > H⁺&raquo_space; Na⁺&raquo_space; Mg²⁺, indicating it preferentially carries potassium ions.

Question 33

Explain the models for facilitated diffusion.

Answer 33

There are two models for facilitated diffusion: pores (channels) like potassium channels and aquaporins, and carriers (uniporters) like valinomycin and GLUT1.

Question 34

What is facilitated diffusion and how does it function?

Answer 34

Facilitated diffusion is the passive transport of materials across the membrane using transport proteins, allowing specific molecules to cross without energy input.

Question 35

Describe the role of GLUT1 in facilitated diffusion.

Answer 35

GLUT1 is a protein carrier that facilitates the transport of glucose across the cell membrane, functioning as a uniporter.

Question 36

Describe the role of proteins in facilitated diffusion.

Answer 36

Proteins act as channels or carriers that help specific molecules move across the cell membrane without the need for energy.

Question 37

Explain the concept of passive transport.

Answer 37

Passive transport is the movement of substances across a cell membrane without the use of energy, relying on concentration gradients.

Question 38

What is the relationship between facilitated diffusion and osmosis?

Answer 38

Both facilitated diffusion and osmosis are forms of passive transport, but osmosis specifically refers to the movement of water across a semipermeable membrane.

Question 39

Describe the process of osmosis.

Answer 39

Osmosis is the diffusion of water molecules through a selectively permeable membrane from an area of lower solute concentration to an area of higher solute concentration.

Question 40

How does facilitated diffusion contribute to cellular function?

Answer 40

Facilitated diffusion allows cells to efficiently take up essential nutrients and remove waste products without expending energy.