ch 4 cell membrane transport

Question 1

cell membrane structure

Answer 1

• the fluid mosaic model is a bi-layer of phospholipids with proteins inserted into and attached to it.
• fluid bc the phospholipids move around and behave like a liquid.
• mosaic bc there are numerous different types of proteins and carbohydrates associated with it

Question 2

cell membrane structure pt 2

Answer 2

• phospholipids make ideal membranes bc theres water on the inside and outside of cell
• the membrane needs to be able to interact with water on both sides without water rushing into the cell

Question 3

phospholipids

Answer 3

• hydrophilic heads <3 are lipophobic bc fat is dry and dense and POLAR
• hydrophobic (NONPOLAR) tails causing very little water to cross the membrane and make up a bigger portion than the heads so, polar (unequal sharing of electrons) does not cross easily
• plasma membrane is semi-permeable: like dissolves like
• the membrane is mostly nonpolar: hydrophobic tails, lipophilic, equal sharing of electrons
• size: small or nonpolar can freely diffuse across the membrane. large and polar do not cross easily they need a carrier protein to get through it

Question 4

is the cell membrane nonpolar or polar?

Answer 4

nonpolar (equal sharing of electrons)

Question 5

categories of membrane transport

Answer 5

• passive: transport across the membrane does not require energy (HIGHT TO LOW)
• active: transport across the membrane requires energy (LOW TO HIGH)
• moving high to low concentration happens without energy

Question 6

does movement from low to high require energy?

Answer 6

• yes it is active transport
• ex: if you have 10 glucose molecules on the inside of the cell and 3 glucose molecules on the outside of the cell, glucose will move out of the cell passively without energy BUT glucose will move into the cell if energy is used

Question 7

passive transport example:

Answer 7

• a big bag of sand and punch a hole in the bag, the sand will leave bc there is more sand on the inside of the bag than the outside

Question 8

passive transport

Answer 8

• molecules move across membranes from high energy to low energy (HIGH TO LOW)
• energy of a solution depends on solute (being dissolved) concentration. the more solute, the more energy.
• solutes move passively from areas of high concentration to areas of low concentration
• this energy is based on molecules bumping into each other. the more molecules you have, the more likely they are to bump into each other. so, areas with more molecules (high) are areas of high energy.

Question 9

composition of intracellular and extracellular solution

Answer 9

• membrane potential is the difference in charge between the inside and the outside of the cell. so, a membrane potential of -70 millivolts means that the INSIDE of the cell is 70 millivolts more NEG than the outside.
• the main ions that determine the membrane potential for a cell are Na+ and K+
• there is more Na+ OUTSIDE the cell than inside ALWAYS
• there is more K+ inside the cell than outside ALWAYS

Question 10

composition of intracellular and extracellular solution

Answer 10

• how can ion concentration vary in intracellular vs extracellular solutions?
• charged molecules cant cross without help of other proteins–no simple diffusion (passive/no energy/doesnt need a carrier protein/H->L), so ion concentrations dont eventually even out
• so why dont these chemical gradients eventually just even out across the membrane?
• bc these are ions (which have charges). the membrane itself does not have a charge. so ions can only cross the membrane with the help of membrane proteins

Question 11

driving force

Answer 11

• difference in energy across a membrane
• a measure of the factors that determine which direction ions move across the membrane
• naturally pushes from high to low energy
• molecules are subject to three types of driving force: chemical, electrical, electrochemical (combination of chemical and electrical)

Question 12

chemical driving force

Answer 12

• K+ OUT Na+ IN
• concentration gradient
• chemical force never changes bc concentration of ions across membrane never changes
• MOVE K+ OUT and Na+ INSIDE
  chem force wants to KICK K+ out

Question 13

electrical driving force

Answer 13

• opposite charges attract
• affects charged molecules (ions)
• amount of electrical driving force depends on membrane potential
• membrane potential is a difference in electrical potential or voltage across the plasma membrane
• the chemical force is not the only force that controls the movement of these ions, bc they have a charge, and the inside of the cell also has a charge compared to the outside (the membrane potential) Na+ and K+ are pos which means they will be attracted to neg areas and be repelled by pos areas.
• so, the membrane potential is neg, the electrical driving force will attempt to bring Na+ and K+ to inside cell.
• if the membrane potential is pos, the electrical driving force will attempt to push Na+ and K+ out of cell.

Question 14

electrical driving force pt 2

Answer 14

• the more NEG the mem pot is the more Na+ and K+ is gonna be moved in
• the more POS the mem pot is the more likely Na+ and K+ is gonna be KICKED out
• electrical force = voltage
• mem pot at rest is -70millivolts
• intracellular fluid contains more anions (-) than extracellular fluid. most healthy cells have a neg mem pot

Question 15

electrochemical driving force

Answer 15

• determined by the combination of the chemical driving force and the electrical driving force
• equilibrium potential of an ion is the membrane potential at which the electrical driving force on the ion is equal and opposite to the chemical driving force
• ## the electrochemical driving force is the sum total of the chemical force and the electrical force acting on an ion.