BIO 1140 Lecture 3

What is hereditary spherocytosis?

A genetic disease causing hemolytic anemia(red blood cells get destroyed before body can replace them).

What are symptoms of anemia?

Fatigue, dizziness, hair loss, and yellowing of the eyes.

What causes hereditary spherocytosis at the cellular level?

Defective proteins that connect the membrane to the cytoskeleton (e.g., spectrin, ankyrin).

How are red blood cells affected in this disease?

They lose their flexible biconcave shape and become spherical.

Why is the normal RBC shape important?

It allows cells to pass through narrow capillaries.

What supports the plasma membrane?

The cell cortex (a network of actin filaments and proteins).

What is the plasma membrane made of?

A thin lipid layer with embedded proteins and surface carbohydrates.

What is the glycocalyx?

A carbohydrate (sugar) coating on the cell membrane.

What are all cell membranes made of?

Lipids and proteins.

How are membrane lipids arranged?

In a lipid bilayer (two layers).

What does amphipathic mean?

Having both a hydrophilic (water-loving) head and hydrophobic (water-fearing) tail.

What lipids are found in the plasma membrane?

Phospholipids, cholesterol, and glycolipids.

Which is the main membrane lipid?

Phospholipids.

What is phosphatidylcholine?

A common phospholipid in cell membranes.

What makes up its hydrophilic head?

Choline + phosphate group.

What makes up its hydrophobic tails?

Two fatty acids (14–24 carbons).

What links the head and tails?

Glycerol.

What is the difference between saturated and unsaturated fatty acids?

• Saturated: no double bonds

• Unsaturated: contain double bonds

How are phospholipids arranged in the membrane?

Hydrophilic heads face water; hydrophobic tails face inward away from water.

Why do phospholipids form a bilayer in water?

They spontaneously arrange to keep hydrophobic tails away from water.

Why does the lipid bilayer form a closed structure?

To prevent hydrophobic tails from being exposed to water.

Why is this structure stable?

It minimizes contact between water and hydrophobic tails.

What does it mean that the membrane is fluid?

Lipids and proteins can move within the membrane.

What does membrane flexibility mean?

It can bend without breaking.

How can phospholipids move?

Rotate, move sideways, and flip layers (with enzymes like flippases).

How do membrane proteins move?

They move laterally within the membrane.

What factors affect membrane fluidity?

Temperature and lipid composition.

How does temperature affect fluidity?

Higher temperature increases fluidity.

How does cholesterol affect the membrane?

It makes the membrane more rigid (less fluid).

How do unsaturated fatty acids affect fluidity?

Increase fluidity due to double bonds.

How does fatty acid length affect fluidity?

Shorter chains increase fluidity.

Where are new membrane phospholipids made?

On the cytosolic side of the smooth ER.

How are lipids distributed in the ER membrane?

Randomly between both layers.

What happens to membranes in the Golgi?

They are modified and specific lipids are redistributed.

How are membranes delivered to their destination?

By vesicles budding from the Golgi and fusing with target membranes.

What does membrane asymmetry mean?

The two layers have different lipid compositions.

Where are glycolipids found?

Only on the outer (non-cytosolic) layer.

Is membrane asymmetry maintained during transport?

Yes, each layer keeps its orientation.

What happens to cytosolic vs non-cytosolic layers during transport?

Cytosolic layer stays facing the cytosol; the other faces outside or organelle lumen.

What are the main functions of the cell membrane?

• Cell signaling

• Transport

• Cell growth and movement

• Cell adhesion

• Cell recognition

What do membrane proteins do?

Carry out most membrane functions.

What are the main types of membrane protein functions?

• Enzymes

• Receptors

• Anchors

• Transporters

• Ion channels

What are the two main types of membrane proteins?

• Integral proteins

• Peripheral proteins

What types fall under integral proteins?

Transmembrane, monolayer-associated, and lipid-linked proteins.

How are peripheral proteins attached?

They attach to membrane proteins or lipids (not embedded in the bilayer).

Is the distribution of membrane proteins symmetrical?

No, it is asymmetrical (different on each side).

How do transmembrane proteins span the membrane?

Usually as alpha helices.

Why are alpha helices used?

They protect the hydrophilic backbone while exposing hydrophobic side chains to the lipid bilayer.

Where are membrane proteins made?

On ribosomes attached to the rough ER.

Where are they first inserted?

Into the ER membrane.

What is a single-pass transmembrane protein?

A protein that crosses the membrane once.

What characterizes single-pass proteins?

One hydrophobic region spanning the bilayer.

What is a multi-pass transmembrane protein?

A protein that crosses the membrane multiple times.

What structures do multi-pass proteins form?

Channels or receptors.

How are channels structured in the membrane?

Amphipathic alpha helices form channels with:

• Hydrophilic sides facing inward

• Hydrophobic sides facing the lipid bilayer

How can we observe membrane fluidity?

By staining membrane proteins.

How do membrane proteins move in the bilayer?

They move laterally (sideways).

Can membrane protein movement be restricted?

Yes.

What can restrict protein movement in the membrane?

• Physical barriers

• Binding to the extracellular matrix

• Binding to proteins on other cells

• Binding to the cell cortex

How do tight junctions affect membrane proteins in gut cells?

They prevent mixing of proteins between different regions of the membrane.

Where are carbohydrates located on the cell membrane?

On the outer surface of the cell.

What is the glycocalyx?

A carbohydrate (sugar) coating on the cell surface.

What are the functions of the glycocalyx?

Cell adhesion and cell recognition.

How do neutrophils recognize infection sites?

Their surface carbohydrates are recognized by endothelial cells.

What happens after neutrophils are recognized?

They stick to endothelial cells and then migrate to the infection site.