Membranes & Transport Unit 3

Question 1

What does a selectively permeable membrane allow, and what phenomenon does it allow for?

Answer 1

Allows organisms to maintain different internal conditions in comparison to outer conditions, transport different solutes, and allows for compartmentalisation

Question 2

What are five(5) functions of the biological membrane?

Answer 2

1. Selective permeability
2. Aids in anchoring cell to the ECM and other cells
3. Sites of energy transduction processes
4. Area for enzymatic activities
5. Membranes function in communication from outside the cell to inside

Question 3

What three(3) macromolecules are present within the membrane?

Answer 3

Lipids, carbohydrates, & proteins

Question 4

What two(2) lipids are present in the membrane and describe them?

Answer 4

Phospholipids- form a bilayer that is fluid, not rigid

Sterols- keep inner fluid at an ideal viscosity when facing extremes in weather ex. extreme heat or cold

Question 5

What are the two(2) different types of proteins in the membrane?

Answer 5

Peripheral- associated only w/ hydrophilic face of the membrane
Integral- spanning the entirety of the membrane

Question 6

What is osmosis?

Answer 6

The diffusion of water across a membrane that does not allow solutes in the water to pass

Question 7

What determines the direction of osmotic movement by water, and what direction does it flow?

Answer 7

It is the number of dissolved particles that determines the direction of water, water moves in the direction of the higher solute concentration

Question 8

What is osmotic pressure?

Answer 8

The pressure needed to attain osmotic equilibrium w/ a pure solvent

Question 9

What are the hypotonic, isotonic, & hypertonic names for animal and plant cells?

Answer 9

• Hypotonic (to much water) Lysed, Turgid
• Isotonic (equilibrium) Normal, Flaccid
• Hypertonic (lack of water) Shrivelled, Plasmolyzed

Question 10

What happens to animal and plant cells during a hypotonic situation?

Answer 10

Animal cells burst (unhealthy)

Plant Cells push back reaching equilibrium (healthy)

Question 11

What are the three(3) types of particle transport across membranes?

Answer 11

Simple diffusion, facilitated diffusion, & active transport

Question 12

Define simple diffusion (passive transport).

Answer 12

Movement across a membrane down a gradient w/o the need for a transport protein, no energy input

Question 13

Define active transport.

Answer 13

Requiring energy to move solutes across a membrane against a gradient

Question 14

Define facilitated diffusion.

Answer 14

Movement across a membrane, down a gradient with the aid of a transport protein

Question 15

What are the two(2) proteins involved in facilitated diffusion movement?

Answer 15

Channel proteins- some open all times, some gated that open & close by mechanical disturbance, binding of a lignand, or voltage
Carrier proteins- undergo conformational change during transport

Question 16

What is a aquaporin?

Answer 16

Water channels in the plasma membrane that increase the membranes permeability to water; water therefore passes across the plasma membrane by both simple & facilitated diffusion

Question 17

What is the important pump in animal cells involved in active trasnport?

Answer 17

Sodium & potassium pump, release three Na, uptake two K

Question 18

What is Endocytosis?

Answer 18

Vesicular uptake of material from the cell surface or the extracellular environment

Question 19

What are the three(3) different types of Endocytosis?

Answer 19

Phagocytosis, pinocytosis, & receptor mediated endocytosis

Question 20

Describe phagocytosis.

Answer 20

Uptake of a material too bulky to fit through a transport protein such as a food particle (envelops particle)

Question 21

Plants don’t have a Na K pump, but what do they have?

Answer 21

A proton pump that removes a H+ atom called a ATPase

Question 22

What system is phagocytosis also involved in?

Answer 22

The immune system

Question 23

What is pinocytosis?

Answer 23

Nonspecific uptake of extracellular fluid and solutes

Question 24

What is receptor mediated cytosis?

Answer 24

Uptake of molecules bound to a receptor in the plasma membrane

Question 25

How does cholesterol get into cells?

Answer 25

Endocytosis

Question 26

What is Exocytosis?

Answer 26

The vesicular removal of molecules to the extracellular fluid

Question 27

Why does there need to be a balance of Endo and Excocytosis

Answer 27

To balance nutrients/uptake in and out of cell

Question 28

What happens when phospholipids are placed into water?

Answer 28

They spontaneously form bilayers, this is due to thermodynamic reasons.

Question 29

What are the three(3) different types of lipid permeability, and what types of molecules do they allow in?

Answer 29

High permeability-hydrophobic molecules like CO2, O, & N
Medium permeability- small, uncharged polar molecules H2O, glycerol
Low permeability (almost 0)- large uncharged, polar molecules glucose, sucrose, nucleosides

Question 30

What role do carbohydrates have in the membrane?

Answer 30

Oligosaccharides components of glycoproteins and glycolipids in the membrane

Question 31

What is a phospholipid (of the kind we have been discussing in this course)? What features make phospholipids amphipathic molecules?

Answer 31

A phospholipid is a molecule containing two fatty acid chains esterified to glycerol, a phosphate group bound to the third carbon of glycerol, and a polar head group (charged or uncharged) bound to the phosphate group. Phospholipids are amphipathic molecules because the fatty acyl chains are hydrophobic, while the head group is hydrophilic.

Question 32

What role does cholesterol play in the membranes of mammals such as ourselves? What role does it play in the membranes of invertebrates living in a northern lake?

Answer 32

Cholesterol in our membranes restrains the movement of the fatty acid chains and decreases membrane fluidity. In the membranes of invertebrates at high temperature cholesterol would have the same function, but at lower temperature would reduce fatty acid interactions and lower the phase transition temperature of the membrane, keeping the membrane fluid.

Question 33

In what ways are biological membranes asymmetric?

Answer 33

Biological membranes are asymmetric in the following ways:
• lipid composition – different membrane lipids can be found in each
leaflet of a membrane
• protein composition – each side of a membrane has different peripheral
proteins associated with it, and integral membrane proteins have different domains facing opposite side of a membrane
Membranes and Transport - 11
• carbohydrate composition – glycolipids and glycoproteins hold their carbohydrate moieties toward the exterior of the cell

Question 34

How does water diffuse across a lipid bilayer? How does water diffuse across the plasma membrane of a typical cell?

Answer 34

Water molecules can diffuse across a lipid bilayer by travelling between the membrane lipids. Water molecules diffuse across the plasma membrane of a typical cell by the same route, but also through water channels in the membrane called aquaporins.

Question 35

What is a concentration gradient? What is an electrical gradient? What is an electrochemical gradient?

Answer 35

Gradients are differences in magnitude across a distance.
• concentration gradient – a difference in the concentrations of a solute
between two regions
• electrical gradient – a difference in electrical charge between two
regions
• electrochemical gradient – a sum of both the concentration gradient and
the electrical gradient for a given ion; it will determine the direction in which the ion will diffuse; its direction is determined by the concentration difference of that ion (across a membrane, let’s say), and the total number of positive and negative charges, from any source, on either side of the membrane.

Question 36

The oligosaccharide part of a plasma membrane glycoprotein faces the outside of the cell. What compartment did this oligosaccharide face when the glycoprotein was synthesized in the rough ER? When the glycoprotein was present in the membrane of a transport vesicle?

Answer 36

the ER lumen; the lumen of the vesicle