Unit 3: Lecture 10

What regulates the exchange of materials with the environment? (1)

Phospholipid bilayer

What other responsibilities does the answer in question 1 have?

1. Physical isolation and protection
2. Structural support
3. Identification

What are the two types of cellular transport?

Passive and active transport

What is the first type of cellular transport (characteristics and subtypes)?

Passive transport:

\-Does NOT use energy

\-Down the gradient (High-> Low)

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1. Simple Diffusion
2. Osmosis
3. Facilitated diffusion

What is the second type of cellular transport (characteristics and subtypes)?

Active transport:

\-Does use cellular energy (usually ATP)

\-Against the gradient (Low-> High)

\

1. Primary (1°)
2. Secondary (2°)
3. Bulk Transport

What is simple diffusion (first type of passive transport)?

\-Concentration gradient present

\-Molecules move from an area of higher concentration to an area of lower concentration

\-Molecules tend to spread out evenly into the available space

What is a concentration gradient?

The concentration of particles is higher in one area than another

Diffusion ends when \___________ is reached.

Equilibrium

When diffusion ends, the solution is now \____________.

Homogenous (spread equally throughout, no longer diffusion)

Are molecules still moving when diffusion ends (equilibrium is reached)?

Yes, molecules are always moving (Brownian motion)

What is solute?

What U put in the solvent!

What is the net (majority of the) movement of passive transport?

High to low (Note: there is movement in all directions)

What does the rate of diffusion refer to?

How fast diffusion is

What is the rate of diffusion controlled by?

1. Molecule diameter (smaller diffuse faster)
2. Temperature (hot = moves faster; cold= move slower)
3. The concentration gradient (steeper concentration gradient = faster)

What does a steeper concentration gradient refer to?

A larger difference

What molecules will freely diffuse through the phospholipid bilayer?

Small uncharged nonpolar molecules (e.g. CO2, O2, NH3, H2O) and lipid-soluble substances (small hydrocarbons and fatty acids [nonpolar])

Why does the molecule that goes through easily have to be nonpolar and small?

Nonpolar b/c majority of the phospholipid bilayer is nonpolar; Small b/c it needs to be able to slip past the phospholipid heads

Why can water freely diffuse through the phospholipid bilayer despite being polar?

It is the exception b/c outside of the cell is 70% of water (majority) where it can leak through the phospholipid bilayer b/c it overwhelms it

Why is CO2 nonpolar?

Symmetry leads to no polarity (even though C and O create a polar bond)

What molecules CANNOT freely diffuse through the phospholipid bilayer?

Water-soluble substances [polar\= partially charged] (e.g. glucose) and ions (fully charged)

What is a real life example of simple diffusion?

Lung air sacs (alveoli) during gas exchange:

\-O2 diffuses into the blood across a membrane

\-CO2 diffuses out of the blood across a membrane

\-Gases can freely leave alveoli to the blood capillaries-> red blood cells-> body)

What is osmosis (second type of passive transport)?

Osmosis- Diffusion of H2O across a semi-permeable membrane

\
\-as the concentration of solute increases the concentration of solvent (H2O) decreases

What direction does water move across a membrane? (Tests will ask you to define osmosis from the context of the solute NOT water)

Down its concentration gradient from *a region of low solute concentration to high*

What does the direction of water movement depend on?

Total dissolved molecules (solutes) in solution

What is concentration?

\# of molecules per 1 L

If one side has 3 molecules per 1 L, while the other side has 8 molecules per 1 L. Which side is more concentrated?

Side with 8 molecules per 1 L

What does the survival of a cell depend on?

Its ability to balance water uptake and loss

Define tonicity.

Ability of a solution to cause a cell to gain or lose water (used to discuss osmolarity of cells)

What is osmolarity?

Total solute concentration of a solution in moles per liter (measures all solutes)

What are the different types of solutions?

Isotonic, Hypotonic, and Hypertonic

How does the tonicity of the bloodstream affect the red blood cells?

Tonicity affects shape

What is a hypotonic solution?

\-Solution with low solute concentration

\-Net movement into cell

\-Animal cells can lyse (burst)

\-Plant cells will be turgid (rigid b/c cell membrane pushes against cell wall)

What is an isotonic solution?

\-Solution with the same conc. of solute

\-No net movement (with every water molecule that enters, another water molecule leaves)

\-Animal cells are normal

\-Plant cells are flaccid

What is a hypertonic solution?

\-Solution with high solute concentration

\-Net movement out of cell

\-Animal cells are shriveled

\-Plant cells are plasmolyzed

Are hypertonic or hypotonic environments ideal for animal cells?

No, it can create osmotic problems for organisms that have cells without rigid walls

Define plasmolysis.

Membrane peels away from the cell wall to stay isotonic by creating a smaller volume

Define osmoregulation.

The control of solute concentrations and water balance, is a necessary adaptation for life

Protist lack cell walls have what type of active mechanism to pump out water in hypotonic environments?

Contractile vacuoles

Define aquaporin?

Membrane proteins in eukaryotic cells that allow passive water transport "plumbing system"

Large hydrophilic molecules require a \_________.

Carrier

Define permeable.

Capable of being permeated or passed through

What is facilitated diffusion (third type of passive transport)?

To help polar/ charged molecules move across the membrane through transport proteins:

1\. Channel proteins

2\. Carrier proteins

What are channel proteins?

Hydrophilic channel for certain molecules or ions by providing long passages that open/close in response to a stimulus (e.g. ion gated channel [ion controls it], aquaporins [facilitate passage of water])

What are carrier proteins?

Bind to solutes and change shape to translocate them across the membrane; specific

What is a chemical gradient?

The concentration gradient for a molecule that wants to move into the cell

What has potential energy in a gradient?

Solute that wants to move from a region of high to low concentration

What is the difference between simple diffusion, osmosis, and facilitated diffusion?

What is diffusing:

1\. Simple diffusion- solute diffusing

2\. Osmosis- solvent diffusing (water)

3\. Facilitated diffusion- polar/ charged diffusion

What is saturation in regards to transporters?

Filled with molecules; reaches a maximum capacity where the rate no longer increases

Why would a cell want to use active transport?

To allow cells to maintain internal solute concentrations that differ from environmental concentrations

What is the difference between primary active transport and secondary (AKA "co-transport")?

Primary: involves the direct hydrolysis of ATP; Secondary: Indirectly uses ATP

What is the most important primary active transport in the body?

Na+/K+ pump (present in most of our tissues); Na+ \= high & K+\=low in extracellular fluid (outside cell); Na+\=low & K+\= high in cytoplasm (inside cells)

How does the most important primary active transport in our body work?

1. Moves Na+ against its concentration gradient by binding it to the Na/K pump which then uses ATP (energy) through phosphorylation
2. K+ binds to the Na/K pump and it is dephosphorylated which changes the shape back to the starting form for K+ to reenter the cell

How do active transport pumps use ATP?

Water hydrolyzes ATP and places one phosphate group onto the pump (phosphorylation)

What does the most important primary active transport in our body create?

Opposing electrochemical (charged) gradients of Na+ and K+

Define membrane potential.

Voltage difference across a cell membrane

What side is negative in charge when considering Na+ and K+?

Cytoplasmic side of the membrane is negative in charge relative to the extracellular side

At physiological pH, what are most proteins?

Negatively charged

Only \______ can create electrochemical gradients?

Ions (charged molecules)

Define electrogenic pump.

A transport protein that generates voltage across a membrane; it helps store energy that can be used for cellular work

What is the primary pump of animal cells?

Na/K pump

What is the primary pump of plants, fungi, and bacteria?

Proton pump (generates voltage across cell membrane, usually powered by ATP)

What is secondary active transport/ cotransport?

Indirectly uses energy to transport against concentration gradient

What drives secondary transport?

Electrochemical gradient

Describe an example of secondary active transport with the proton pump?

1. Primary transport by proton pumps generates H+ gradient
2. H+ gradient drives transport of nutrients into the cell
3. H+/sucrose cotransporter is in use where H+ moves down concentration gradient and sucrose moves up the concentration gradient at the same time

What are the 2 ways glucose can enter a cell?

1. Facilitated diffusion
2. Secondary active transport

What is bulk transport (third type of active transport)?

Large molecules (e.g. polysaccharides and proteins) cross the membrane in bulk via vesicles through endocytosis and exocytosis

What are the three types of endocytosis?

1. Phagocytosis ("cellular eating")
2. Pinocytosis "cellular drinking"
3. Receptor-mediated endocytosis

What organelle performs phagocytosis?

Lysosomes

How do cells take in macromolecules?

Vesicles to form with membranes (vesicle budding and fusion can occur on any membrane)

What is receptor-mediated endocytosis responsible for?

\-Cholesterol uptake

\-LDL/ HDL is "low/high density lipoprotein" particles that carries cholesterol and fat

\-harmful levels of cholesterol can accumulate in the blood if membranes lack HDL receptors