Active vs. Passive Transport

selectively permeable

some substances can pass across them and others cannot

what substances can easily cross the membrane?

small nonpolar hydrophobic molecules

What are some examples of things that can cross the membrane?

- hydrocarbons
- CO2, O2, N2

what substances need assistance in crossing the membrane?

hydrophilic, polar molecules, large molecules, and ions

What are some examples of a substance that needs assistance crossing the membrane?

- sugars
- water

Passive Transport

1. Does not require energy (ATP) from cell
2. Solute is moving with/down concentration gradient
3. High to low concentration
4. Particles move until dynamic equilibrium is reached

dynamic equilibrium

not equal volumes but equal concentrations
still moving but at equal rates

Examples of Passive Transport

diffusion, osmosis, facilitated diffusion

Diffusion

movement of small, nonpolar, hydrophobic particles in a fluid or gas directly across the bilayer

Osmosis

movement of water across the membrane using the aquaporin (protein)

Facilitated Diffusion

movement of small polar or charged molecules across the membrane using an integral protein

What is osmosis an example of?

facilitated diffusion
Osmosis is a type of facilitated diffusion

what are some examples of substances that diffusion moves?

CO2 & O2

Osmosis is the movement of water from _____ solute concentration to _____ solute concentration.

low solute concentration to high solute concentration

What kind of molecules does facilitated diffusion move?

small ions, water, carbohydrates (monosaccharides)

How many categories of transport proteins are there in facilitated diffusion?

What are channel proteins?

Provide a channel for molecules and ions to pass
Hydrophilic
Ex: Aquaporin
Has gated channels that open when a stimulus is being used

What are carrier proteins?

Undergo conformational changes for substances to pass

What is Active Transport?

1. transport of a molecule that requires energy
2. Moves up/against gradient
3. Low to high concentration

What are examples of Active Transport?

- Pumps
- Cotransport
- Exocytosis
- Endocytosis

What energy does active transport require?

ATP

ATP can change shape of the transport protein so it can better move a substance in a process called.....

phosphorylation

What do pumps do?

maintain membrane potential

What is an example of a pump?

Electrogenic pumps

What do electrogenic pumps do?

proteins that generate voltage across membranes which can be used later as an energy source for cellular process

What does the sodium potassium pump do?

moves 3 sodium out of the cell and 2 potassium into the cell

What is a proton pump?

Integral membrane protein pump that builds a proton gradient
- used by plants. fungi, and bacteria
- pumps H+ out of the cell

Cotransport

the coupling of a favorable movement of one substance with an unfavorable movement of another substance

What do plants use cotransport for?

sugars and amino acids

How can sucrose travel into a plant cell against its concentration gradient?

When it is coupled with H+ that is diffusing down its electrochemical gradient

What is bulk transport?

transport of large molecules through exocytosis and endocytosis

What is Exocytosis?

the release of molecules via vesicles that fuse to the membrane, forming a bilayer, then released to the extracellular fluid

What is an example of exocytosis?

nerve cells releasing neurotransmitters; pancreatic cells releasing insulin

What is Endocytosis?

uptake of molecules from vesicles fused from the plasma membrane (opposite of exocytosis)

Examples of endocytosis

phagocytosis, pinocytosis, receptor-mediated endocytosis

Phagocytosis

A type of endocytosis in which a cell engulfs large particles or whole cells

Pinocytosis

The non-specific uptake of liquid particles into a cell by invagination of the plasma membrane and subsequent 'pinching off' a small bit of the extracellular fluid.

receptor-mediated endocytosis

The movement of specific molecules into a cell by the inward budding of membranous vesicles containing proteins with receptor sites specific to the molecules being taken in; enables a cell to acquire bulk quantities of specific substances.

How many categories of transport proteins are there in facilitated diffusion?

Two:
Channel & Carrier