Cell Bio Quiz 9

Lecture 15 slides 1-20

Cells need to

import nutrients

eliminate waste

regulate ion concentrations

Membrane transport proteins

proteins that transport molecules that can’t pass through the membrane on their own

Simple diffusion

occurs with or without a membrane

the movement of molecules from an area where they are more concentrated to an area
where they are less concentrated without help from any additional molecules

Facilitated transport (or diffusion)

movement of molecules across a membrane with assistance from a transport protein

What affect the rate at which a molecule diffuses across a membrane?

Size and solubility

What moves slowly across membranes?

Large molecules

polar molecules

charged molecules

hydrophilic molecules

they require transporter

What moves rapidly across membranes?

Small molecules

nonpolar molecules

neutral molecules

hydrophobic molecules

diffuse directly across

Each membrane transport protein allows how many molecules?

1 or a few molecules to pass

The two classes of membrane transport are

Channel- discriminate based on size and electric charge

Carriers- discriminate based on a molecule’s ability to bind to a site on the transport protein

Membrane potential

small electrical imbalances at the membrane create a voltage difference

critical for the function of electrically excitable cells

also helps move some ions across the membrane

Passive transport

doesn’t require energy

direction depends on concentration

molecules flow from areas of higher concentration to areas of lower concentration

downhill

Active Transport

requires energy

moves a solute “uphill” against its concentration gradientcarried bout by special types of transporters called pumps

What influences the passive transport of charged solutes?

concentration gradients

membrane potential (charge)

Electrochemical gradient

driving force that determine which way an ion will move across a membrane

Aquaporins

specialized channels that facilitate the flow of water

Osmolarity

the total solute concentration inside a cell
usually higher than the environment

Osmosis

the movement of water from an area of low solute concentration to an area of high solute concentration

Reverse osmosis

water moving across membrane

Water in protozoan, animal cells,, and plant cells

Protozoan- pump water out

Animal cell- pumps ion out

Plant cell- store water

Pumps

actively transport a solute against its electrochemical gradient

three types:

1. Gradient-driven pump

2. ATP-driven pump

3. Light-driven pump

Na-K ATPase

uses ATP to pump sodium out of the cell and potassium into the cell

maintaining membrane potential: this re-polarizes cells

Ca 2+ Pump

pumps Ca2+ out of the cell or into the ER

calcium can bind to proteins and alter their activity

ATPases, so ATP driven

Symport

both molecules move the same direction

the transport molecule moves down the gradient

the co-transported ion moves against the gradient

Antiport

molecules move in opposite directions

Uniport

moves one molecule down its gradient

depends on gradients

Symport, antiport, uniport all use

potential energy from the electrochemcial