How a Cell Interacts with its Environment

Question 1

carrier protein

Answer 1

bind a substance and change shape to carry it through the membrane

Question 2

simple diffusion

Answer 2

very small substances that are lipid-soluable can cross directly through the plasma membrane

ex) oxygen, carbon dioxide, alcohol

Question 3

channel-mediated diffusion

Answer 3

small molecules that are hydrophilic must be transported through proteins across the membrane

protein channels act as pores that permit the selective movement of these small water-soluable molecules

ex) ions and water (through aquaporins)

Question 4

facilitated diffusion

Answer 4

molecule binds to binding site of the protein carriers, then the protein carrier changes shape and shifts the molecule to the other side of the membrane (conformational change) uses the concentration gradient to move the molecule (high to low)

• larger (cant fit through protein channels), hydrophilic (glucose and amino acids)
  ex) glucose, needs to bind to a carrier protein’s binding site which changes shape and allowed to be transported across the plasma membrane

Question 5

active transport

Answer 5

molecules that don’t have a favorable concentration gradient (low to high), these molecules bind to a protein carrier and energy (ATP) must be used to transport the molecules across

• moves ions from a low concentration to a high concentration using ATP (energy)
• can saturate and can be inhibited
  ex) ATPase, moves ions of sodium and potassium

Question 6

endocytosis/exocytosis

Answer 6

very large molecules (ex, proteins, neurotransmitters)

endocytosis: “enters” the cell, plasma membrane forms a pocket and substances enters the pocket which then gets pinched off to form a vesicle
exocytosis: “exits” the cell, secretory vesicle fuses with the plasma membrane and excretes the substances to the extracellular fluid

Question 7

carrier protein

Answer 7

bind a substance and change shape to carry it through the membrane

Question 8

Fick’s law of diffusion

Answer 8

Rate of diffusion =

= (surface area x concentration gradient​) / membrane thickness​

Question 9

endocytosis/exocytosis

Answer 9

very large molecules (ex, proteins, neurotransmitters)

endocytosis: “enters” the cell, plasma membrane forms a pocket and substances enters the pocket which then gets pinched off to form a vesicle
exocytosis: “exits” the cell, secretory vesicle fuses with the plasma membrane and excretes the substances to the extracellular fluid

Question 10

autocrine signaling

Answer 10

• > local communication
• > neurotransmitter acts back on the same cell that released it

Question 11

paracrine signaling

Answer 11

• > local communication
• > adjacent or local cell communication rather than going into the blood

Question 12

gap junctions

Answer 12

a quick way for cells to communicate with other cells, is having a direct transfer of small molecules through connecting “tunnels” or bridges called gap junctions

this requires 2 specialized proteins (connexons) to connect

only small ions and small molecules can pass

Question 13

4 factors that can affect channel-mediated diffusion

Answer 13

• concentration gradient
• molecule size
• charge (the protein channels are charged and only let in specific charged particles like water and sodium)
• number of channels (more channels means more particles can pass at the sametime)

Question 14

6 factors that affect the rate of simple diffusion

Answer 14

• surface area
• liquid soluabililty
• size of substance
• thickness of plasma membrane
• concentration gradient
• membrane composition