Ch. 6 Exam

Question 1

What are the three attributes of a lipid?

Answer 1

1. Fats (triglycerides)
2. Steroids
3. Phospholipids

Question 2

What are the two building blocks found in many lipids?

Answer 2

• Fatty acid: hydrocarbon bonded to a carboxyl (-COOH)
• Isoprene: repetitive 5 carbon units

Question 3

List the three most important types of lipids found in cells.

Answer 3

1. Fats (triglycerides)
2. Steroids
3. Phospholipids

Question 4

What are the structures of fats?

Answer 4

Glycerol linked to 3 fatty acids (triglyceride) by an ester linkage

Question 5

Compare saturated and unsaturated fatty acids.

Answer 5

• Saturated fatty acid chains: single bonds (linear)
  
  • are solid at room temperature (linear fatty acid tails stack tightly
  • Ex: butter, animal fat
• Unsaturated fatty acid chains: 1 or more double bonds (kinks)
  
  • Some saturated lipids have extremely long hydrocarbon tails (waxes) stiff solids at room temperature
  • are liquid at room temperature (kinked fatty acid tails do not stack tightly)
  • Ex: sesame seed oil, olive oil

Question 6

Define a steroid. Give the three examples listed in the notes, and explain them.

Answer 6

• Four-ring structure, differ by functional groups
• Ex: Cholesterol: A hydrophilic hydroxyl group attached to the top ring and an isoprenoid “tail” attached at te bottom
  
  • Plasma membranes in many organisms
• Ex: testosterone and estradiol (hormones) Used to regulate reproductive cycles

Question 7

Describe the 3 components of a phospholipid.

Answer 7

• Glycerol attached to
• 2 hydrophobic fatty “acid tails” (or isoprene tails)
• Phosphate, and charged group “head”

Question 8

Which component of a phospholipid interact with water? (Hint: Which aspect is hydrophilic?)

Answer 8

Phospholipid heads

Question 9

Explain the two structures that phospholipids can form upon contact with water.

Answer 9

• Micelles: heads face the water and tails face each other
• Phospholipid belayers (lipid bilayers): Two layers of phospholipid molecules align

Question 10

List the three functions of a plasma/cell membrane.

Answer 10

• Keep damaging materials out of the cell
• Allow entry of materials needed by the cell
• Facilitate the chemical reactions necessary for life

Question 11

Explain the selective permeability aspect of phospholipid bilayers in regards to molecules.

Answer 11

• Lipid blisters are highly selective
• Phospholipid bilayers have selective permeability
• Small or nonpolar molecules move across phospholipid bilayers quickly
• Charged or large polar substances cross slowly if at all

Question 12

List and explain the four factors that influence the permeability of the cell membrane.

Answer 12

• Number of double bonds between the carbons in the phospholipid’s hydrophobic tail
• Length of the tail
• Number of cholesterol molecules in the membrane
• Temperature

Question 13

(Not a question, just information!) Membrane fluidity decreases with temperature, and when molecules in the bilayer are moving more slowly. Decreased membrane fluidity causes decreased permeability.

Question 14

Do individual phospholipids move throughout the lipid bilayer more, or flip between layers?

Answer 14

• Individual phospholipids can move laterally
  
  • Throughout the lipid bilayer
  • They rarely flip between layers

Question 15

List the three transport mechanisms.

Answer 15

• Passive transport
• Diffusion
• Osmosis

Question 16

Does passive transport require energy?

Answer 16

Does not require an input of energy

Question 17

Define diffusion.

Answer 17

Random movement of molecules from a high concentration to a low concentration

Question 18

Explain osmosis.

Answer 18

• Occurs across a selectively permeable membrane (water passes through other molecules don’t)
• The water tends to equalize the concentration of solutes across a membrane
• Water moves toward the higher concentration gradient

Question 19

Define and explain isotonic, hypotonic, and hypertonic in reference to water movement in/out of a cell.

Answer 19

• Isotonic: equal solute concentration inside cell as outside
  
  • No net movement of water
• Hypotonic: solution with a lower concentration of solutes, than inside of a cell
  
  • Water moves from solution, into cell by osmosis
• Hypertonic: solution with a higher concentration of solutes, than inside of a cell
  
  • Water moves from cell, into solution by osmosis

Question 20

(Not a question, just information!) The plasma membrane is best understood as a fluid- mosaic model. This is because various proteins are inserted into the lipid bilayer, and the fluid mosaic of the phospholipids and proteins makes it look like mosaic that is always shifting around.

Answer 20

(Not a question, just information!) Diffusion and facilitated diffusion are passive transport, they don’t require energy and they’re from a high concentration to a low concentration. Active transport DOES require energy, and is from a low concentration to a high concentration. A good example of active transport used in biology is the sodium- potassium pump.

Question 21

Compare: integral, transmembrane, and peripheral proteins.

Answer 21

• Transmembrane (Integral) proteins are amphipathic integral proteins that span the membrane facing the interior & exterior of a cell
  
  • Involved in the transport of selected ions and molecules across the plasma membrane
  • Able to affect membrane permeability
• Peripheral proteins are found only on one side of the membrane
  
  • Often attached to integral proteins

Question 22

List and define the three types of transport proteins.

Answer 22

1. Channels: proteins which are selective in which molecules pass along a membrane
2. Carrier proteins or transporters: change shape during the transport process moving molecules down a concentration gradient
3. Pumps: are membrane proteins that provide active transport of molecules across the membrane against a concentration gradient (requires energy, ATP)