Lecture 8 - Membrane Transport & Cell Respiration

How of thick is the plasma/cell membrane?

5-6nm

What is the plasma membrane?

An amphipathic phospholipid bilayer

What is the plasma membrane composed of?

Hydrophobic and Hydrophillic cores

Which part of the plasma membrane is the non-polar part?

Hydrophobic core

Which part of the plasma membrane is the polar part?

Hydrophillic core

Which part of the phospholipid is water loving (hydrophilic)?

Head group

Which part of the phospholipid is water fearing (hydrophobic)?

Fatty acid tails

True or False: Phospholipids cannot differ in head groups

False

Which part of the phospholipid is the functional group?

The head

True or False: Different lipid composition in different organelles happen for different cellular functions

True

True or False: Phospholipids can't differ in Fatty Acid tails

False

What are the different types of fatty acid tails?

Saturated and Unsaturated

Which fatty acid group has double bonds in the tail?

Unsaturated FA

What does fluidity of lipids depend on?

The length and saturation of hydrocarbon chains

What does butter consists of?

Saturated lipids

What does beeswax consists of?

Saturated lipids with long hydrocarbon tails

What does safflower oil consists of?

Unsaturated lipids

What is cholesterol and important component of?

The plasma membrane

What FA molecule makes up micelle?

Single FA chains

How is micelle packed in water?

In a circle

What FA molecule makes up the lipid bilayer?

Double FA

How is the lipid bilayer packed in water

In a straight line with tails opposite each other

How are liposomes delivered in drug delivery?

They placed into micelle which is then taken in the lipid bilayer

Membranes are:

1. Flexble

2. Repairable

3. Expandable

Membrane flexibility means that ___________________.

cells can change their shape

Membrane repairability means that _______________________.

lipids move to reform a continuous surface

Membrane expandability means that ________________________.

cells increase surface area by adding new membrane lipids

Lipids form micelle and bilayers in _________________.

solution

In micelle and bilayers, the hydrophilic heads of lipids _____________; and the hydrophobic heads of lipids ______________.

face out towards the water; face in away from the water

What is the foundation of cellular membranes?

Lipid bilayers

True or False: The membrane bilayer is not fluid

False

What is the fluidity of the layer caused by?

motions of lipid molecules

What does membrane fluidity affect?

cellular function (endocytosis, exocytosis, membrane signaling, transport etc.)

Is the plasma membrane static?

No

How isn't the plasma membrane static?

Phospholipids are in constant lateral motion, but rarely flip to the other side of the bilayer

What affects membrane fluidity?

1. Membrane composition

2. Temperature

What affects membrane composition?

1. Saturated vs. Unsaturated fatty acids

2. Chain length of the fatty acid tails

3. Cholesterol

Lipid bilayer with short and unsaturated hydrocarbon tails have a ___________________________________.

higher permeability and fluidity

Lipid bilayer with long and saturated hydrocarbon tails have a ___________________________________.

lower permeability and fluidity

What is the higher ratio of unsaturated fatty acids a result of?

Double bonds pushing neighbouring phospholipids aside

Less packed =

more fluid

What is the higher ratio of saturated fatty acids a result of?

Phospholipids packing closely

How does increased temperature affect membrane fluidity?

It causes a sharp transition from a more rigid membrane to a more fluid one

How does decreased temperature affect membrane fluidity?

It causes a sharp transition from a fluid membrane to a more rigid one

What is desaturase?

An enzyme that catalyzes the formation of double bonds to create an unsaturated FA to increase membrane fluidity

When do orgnanisms increase the expression of desaturase?

To add more unsaturated FA to their membrane when more fluid membrane is needed

Higher temp ____________ fluidity of membrane.

increases

Why does higher temp make the membrane more fluid?

To overcome the temperature effect, organisms need lower fluidity by increasing saturated FA (SFA) and lowering desaturase

Lower temp ____________ fluidity of membrane.

decreases

Why does lower temp make the membrane less fluid?

To overcome the temperature effect, organisms need more fluidity by increasing unsaturated FA (UFA) and lowering desaturase

How do organisms maintain optimum fluidity for the function of the membrane?

Organisms adjust FA composition at different temps

Which organisms are high in pre-formed EPA/DHA?

Ocean algae, phytoplankton, fish-eat algae, organisms that consume sunlight and CO2

Where are organisms high in pre-formed EPA/DHA found?

In the cold, in whole cells, oil in flesh

Which organisms are high in omega 6?

Canola plant, sunflower, organisms that consume sunlight and CO2

Where are organisms high in omega 6 found?

In the semi-cold, leaves/seeds

Which organisms are high in saturates?

Farm raised animals, pork & beef, organisms that eat grass and grains

Where are organisms high in saturates found?

In warm blooded breeds, body fat

Which organisms are very high in saturates?

Milk fat and butter

Where are organisms very high in saturates found?

In items hard at cold temp, milk fat

Which organisms survive better in the cold?

Organisms with more YFAs in their membranes

How does cholesterol maintain fluidity at lower temp?

By reducing packing opportunities (relative to non-cholesterol condition)

How does cholesterol maintain fluidity at higher temp?

By reducing phospholipid movement (relative to non-cholesterol condition)

Cholesterol has a ________________ effect on Cholesterol on membrane fluidity

bidirectional

Membrane composition _________, _________________________ and ___________________________________.

varies, is complex and dynamic, is essential to function

What model is the bilayer membrane considered to be?

The fluid mosaic model

Membranes consider a diversity of ____________ and _____________

protein, lipid

What is the purpose of freeze-fracture preparations?

They allow biologist to view membrane proteins

What is the first step in freeze-fracture preparations?

Fracturing the cell

Explain fracturing the cell

Striking frozen cells with a knife to split the lipid bilayer

What is the second step in freeze-fracture preparations?

Separating the parts

Explain the purpose of separating the parts

It must be done to prepare for transmission electron microscopy

What is the third step in freeze-fracture preparations?

Microscopy

What happens in microscopy?

Puts and mounds in the membrane interior are observed

What is the fourth step in freeze-fracture preparations?

Interpretation

Explain the free-fracture preparation interpretation

Image supports fluid-mosaic model of membrane structure

What does the semi-permeable membrane act as a barrier to?

Water soluble (polar) molecules

Charged ions

Charged molecules

Large molecules

What can readily pass through the semi-permeable membrane with the concentration gradient?

Hydrophobic (nonpolar) molecules like O2, CO2, N2

What molecules have the highest permeability?

Small, nonpolar molecules (O2, CO2, N2)

What molecules have the second highest permeability?

Small, uncharged molecules (H20, glycerol)

What molecules have the third highest permeability?

Large, uncharged polar molecules (Glucose, sucrose)

What molecules have the lowest permeability?

Small ions (Cl-, K+, Na+)

What is passive (simple) diffusion?

Movement of substances from high concentration towards low concentration

How does passive diffusion occur?

Spontaneously (ΔG < 0, ΔS > 0)

What does passive diffusion not require?

Transporters or energy

What are the steps involved in the process of diffusion across a lipid bilayer?

1. Separation of solutes

2. Diffusion

3. Equillibrium

What process is an example of passive diffusion?

Osmosis

What is osmosis?

The diffusion of water, based on solute concentration across a selective permeable membrane

What direction does osmosis occur?

From a region of lower solute concentration (higher water concentration) to a region of higher solute concentration (lower water concentration).

A selectively permeable membrane must allow __________ to pass, but not _____________________.

water, solute molecules

Hypertonic:

Solute concentration is high relative to the comparison solution

Hypotonic:

Solute concentration is lowrelative to the comparison solution

Isotonic:

Comparison solutions have the same solute concentration

What happens when the outside solution is hypertonic to the inside?

Shrinkage (Net flow of H20 OUT of vesicle)

What happens when the inside solution is hypertonic to the outside?

What happens when the outside solution is hypotonic to the inside?

Swelling/bursting (Net flow of H20 INTO vesicle)

What happens when the inside solution is hypotonic to the outside?

What happens when the outside solution is isotonic to the inside?

No change

Tonicity in plant and animal cells:

How do polar, charge molecules and large molecules get across the membrane?

Through facilitated diffusion