Chapter 3 - the living units

Question 1

What percentage of cholesterol makes up the plasma membrane and its function?

Answer 1

20%
- stiffen the membrane and decrease water solubility

Question 2

What are the different types of proteins in the cell membrane?

Answer 2

integral - protrude from one side

peripheral - are not embedded in the membrane - attached on integral proteins

transmembrane - protrude from both sides

Question 3

What are the 6 tasks of the membrane?

Answer 3

1) transportation
2) receptors for reactions
3) enzyme activity
4) cell-cell recognition
5) cell-to-cell joining
6) attachment to the cytoskeleton and ECM - maintain cell shape, fix protein locations, cell movements

Question 4

What is the function and location of carbohydrates?

Answer 4

help with cell recognition
- on integral proteins

Question 5

what is the function of integral proteins?

Answer 5

• most are transmembrane
• is hydro- and hydra- philic
• transport, enzyme, receptors

Question 6

what is the function of peripheral proteins?

Answer 6

• attached to integral proteins
• cell-to-cell connections

Question 7

what are glycocalyx?

Answer 7

consists of sugars (carbs) sticking out
- include glycoproteins and glycolipids
- help in cell-to-cell recognition

Question 8

what are the 3 types of intercellular junctions?

Answer 8

tight, desmosomes, and gap

Question 9

what is the function of tight junctions?

Answer 9

• Integral proteins molecules and adjacent cells fuse together creating 2 fluid filled compartments
• Prevent molecules from passing through the extracellular space and resist movement in membrane
• Keeps digestive enzymes and microorganisms from the intestines from leaking into the blood stream

Question 10

what is the function of desmosomes?

Answer 10

• Bind together through linker proteins (cadherins) that extend from the plaques
• Help keep cells from tearing apart
• Keratin filaments (intermediate filaments) extend from the cytoplasmic side to anchor onto the plaque of the other side.
• In skin and heart muscles

Question 11

What is the function of gap junctions?

Answer 11

• The plasma membranes are connected by hollow cylinders called connexons
• Different gap junctions are composed of different transmembrane proteins, which determine which molecules and ions can pass through
• Found in excitable tissues: heart, smooth muscle

Question 12

What are the types of passive transport?

Answer 12

• simple diffusion
• facilitated diffusion
• osmosis

Question 13

what are the types of active transport

Answer 13

• primary and secondary active transports
• endocytosis (phago, Pino, receptor mediated) vesicular trafficking and exocytosis

Question 14

explain simple diffusion.

Answer 14

substances diffusion directly into the lipid bilayer. The molecules are small nonpolar (gases, steroid hormones, and fatty acids)

Question 15

explain the 2 types of facilitated diffusion.

Answer 15

carrier mediated
- transporting polar molecules like sugars and amino acids that are too large. The shape of the protein changes shape.

channel mediated - leakage (always open) and gated channels (chemical or electrical signal)
- transports ions through water filled channels from one side of the membrane to the other.

Question 16

explain osmosis. 3 points

Answer 16

Water diffuses across plasma membranes (even though water is polar, it is so small that some molecules can sneak past nonpolar phospholipid tails)
through specific water channels called aquaporins (A Q P s)
- Osmosis occurs whenever the solute concentration differs on the two sides of a membrane

Osmolarity: total concentration of all solute particles in a solution - Water concentration varies with number of solute particles because solute particles displace water molecules

Question 17

explain primary active transport.

Answer 17

• hydrolysis of ATP
• protein changes shape to pump the solute across the membrane

Question 18

explain secondary active transport and the 2 types.

Answer 18

• concentration gradient is the source of energy created by primary AT

symport - moves 2 substances at once through the same protein
antiport - moves 2 substances across the membrane in opposite directions

Question 19

what are the types of endocytosis?

Answer 19

phagocytosis, pinocytosis, receptor-mediated endocytosis, vesicular trafficking

Question 20

explain the difference between phagocytosis and pinocytosis.

Answer 20

Phago: engulfs large or solid materials
- Pseudopods form and flow around the particle (phagosome)
- Ex. Macrophages
Ingesting and disposing bacterial and foreign substance.

Pino: engulfs very small volume of extracellular fluid containing dissolve molecules
- Fuses with endosomes
- Added back through exocytosis

Question 21

explain what receptor mediated endocytosis is.

Answer 21

engulfs particles attached to receptors before endocytosis occurs.

• Engulfs ligands to be injected into the cells, the separate from the receptor, so that the receptors can join the membrane again and the ligand can join the lysosomes. The lysosomes break down the ligand and disperse it out to function throughout the cell.

Question 22

explain what vesicular trafficking is.

Answer 22

Moves substances from one area (or organelle) in the cell to another.

Question 23

explain what exocytosis is.

Answer 23

• Mechanism by which substances are moved from the cell interior to the extracellular space as a secretory vesicles (vesicle migrating to the plasma) fuses with the plasma membrane

Question 24

What are the factors effecting speed of diffusion?

Answer 24

• concentration gradient: greater the difference, more collisions occur
• molecular size
• temperature

Question 25

explain facilitated diffusion.

Answer 25

Binds to carrier proteins or moves through water-filled channel proteins (Glucose, amino acids, ions).

Question 26

explain hydrostatic and osmotic pressure

Answer 26

Hydrostatic pressure: the back pressure exerted by water against the cell wall

Osmotic pressure: the tendency of water to move into the cell by osmosis

Question 27

What is tonicity and what are the 3 types

Answer 27

Tonicity—the capability of a solution to modify the volume of cells by altering their water content

Isotonic solution has same osmolarity as inside the cell, so volume remains unchanged

Hypertonic solution has higher osmolarity than inside cell, so water flows out of cell, resulting in cell shrinking

Hypotonic solution has lower osmolarity than inside cell, so water flows into cell, resulting in cell swelling