B2.1 Membranes and membrane transport

IB BIO

What are all membranes built from?

All membranes are built from phospholipid bilayers.

How do amphipathic phospholipids arrange themselves in a bilayer?

Hydrophilic heads face out and hydrophobic tails face in.

What is the universal structure for plasma membranes and organelles?

Phospholipid bilayers.

In definitions, what term should always be included instead of just "lipids"?

Phospholipid bilayer.

What are integral proteins?

Proteins located inside the membrane with hydrophobic regions embedded, often transmembrane.

What are peripheral proteins?

Proteins located on the outside of the membrane, attached to the surface (often via other proteins).

How is membrane activity related to protein content?

Higher protein content equals higher membrane activity (e.g., 18% in myelin vs. 75% in mitochondria/chloroplasts).

How does the hydrophobic core of the lipid bilayer act as a barrier?

It blocks ions and large polar molecules.

Which types of molecules cross the lipid bilayer easily?

Small non-polar molecules like (O2, CO2, steroid

hormones, cross easily)

How does molecular size affect diffusion speed?

Smaller molecules diffuse faster than large ones.

Is it correct to say the lipid bilayer "repels" water?

No, it is more accurate to say it restricts hydrophilic solutes and favors interactions with themselves.

What is simple diffusion?

The passive net movement of molecules from high to low concentration.

Does simple diffusion require ATP or proteins?

No, no ATP or proteins are required.

What substances can move via simple diffusion?

Small non-polar molecules (O2, CO2) and very small polar molecules (ethanol, urea).

What is a simple way to remember diffusion?

"Downhill, no energy."

What is osmosis?

The net movement of water from a high water potential (low solute concentration) to a region of low water potential (high solute concentration) across a selectively permeable membrane

What are the energy requirements for osmosis?

It is passive, meaning no energy input is required.

What is the function of aquaporins?

They massively increase water permeability (found in kidneys and root hairs).

How should you define osmosis according to exam tips?

Define it using "free water concentration" rather than just "high to low."

What is facilitated diffusion?

The passive movement of ions or polar molecules through selective pores.

What are the characteristics of facilitated diffusion?

It is passive and follows the concentration gradient (down concentration gradient).

What are gated channels in facilitated diffusion?

Channels that open or close in response to signals like voltage or ligands.

How can you conceptually remember the function of protein channels?

Channels are like "doors" that open only for the right "key" (ion)

What is the function of ATP in pump proteins?

ATP is used to push molecules against their concentration gradient.

What is the directionality and specificity of pump proteins?

Pumps work in one direction and each is specific to a particular solute.

What drives transport in pump proteins?

A conformational change in the protein drives transport.

How should you link ATP to solute movement in an exam?

Link ATP hydrolysis to a conformational change, which then leads to solute movement.

What is the effect of saturated tails on membrane fluidity?

Saturated tails make the membrane rigid and less fluid.

What is the effect of unsaturated tails on membrane fluidity and permeability?

Unsaturated tails create kinks, making the membrane more fluid and more permeable.

How do organisms maintain membrane fluidity at different temperatures?

By adjusting the ratios of saturated to unsaturated fatty acids.

What is an example of an organism adapting fatty acid composition for temperature?

Antarctic fish membranes have more unsaturated fatty acids to maintain fluidity in the cold.

What do glycoproteins and glycolipids form when they project outward?

They form the glycocalyx.

What are the main functions of glycoproteins and glycolipids?

They are involved in recognition, adhesion, and the immune response.

What is a specific example of the function of glycoproteins?

They act as ABO blood group antigens.

What is the specific function of glycolipids?

They help the immune system distinguish between self and non-self.

What key term should be used when describing the function of glycoproteins and glycolipids?

Cell-cell recognition.

How does cholesterol affect animal membrane fluidity?

It stabilizes the membrane by reducing extremes of fluidity.

How does cholesterol affect permeability and freezing?

It prevents too much permeability at high temperatures and prevents freezing at low temperatures.

Where is cholesterol positioned within the membrane?

It is positioned between phospholipids with the OH group near the heads.

What provides the "fluid" background in the Fluid Mosaic Model?

the lateral movement of phospholipids within the phospholipid bilayer

How are proteins arranged in the Fluid Mosaic Model?

They are embedded like a mosaic.

What does lateral movement allow for in the membrane?

It allows for flexibility and vesicle formation.

What does the Fluid Mosaic Model explain about the membrane?

It explains membrane flexibility, movement, and vesicle formation.

What is a common analogy for the Fluid Mosaic Model?

Think "icebergs floating in a sea of lipids."

What happens during endocytosis?

The plasma membrane pinches inward to internalize substances.

What happens during exocytosis?

Vesicles fuse with the plasma membrane to release contents outside the cell.

What is required for vesicle fusion and formation?

ATP and the fluidity of the lipid bilayer.

What are the common uses for vesicle transport?

Nutrient uptake, waste expulsion, and neurotransmitter release.

What are examples of endocytosis and exocytosis?

Antibody uptake by the placenta and insulin secretion.

What two processes should you be able to explain clearly for exams regarding membranes?

How cholesterol affects membrane fluidity and the process of vesicle formation

Explain how cholesterol affects membrane fluidity

Cholesterol regulates the fluidity of the Phospholipid bilayer by preventing excessive movement at high temperatures and preventing tight packing at low temperatures.

explain the process of vesicle formation

Vesicle formation involves the membrane folding and pinching off to form vesicles that transport substances into or out of the cell (endocytosis and exocytosis).

What are the Functions of Membrane Proteins?

• Junctions – Serve to connect and join two cells together 

• Enzymes – Fixing to membranes localises metabolic pathways 

• Transport – Responsible for facilitated diffusion and active transport 

• Recognition – May function as markers for cellular identification 

• Anchorage – Attachment points for cytoskeleton and extracellular matrix 

• Transduction – Function as receptors for peptide hormones 

what is Integral protein + function

Channel proteins are a type of integral protein that form pores to allow passive movement of substances across the membrane.