W09 L1 - Cell Membranes Flashcards

Flashcards based on lecture notes about cell membranes, their composition, and functions.

What are the learning objectives for this lecture?

Describe the functions of the cell membrane, understand its composition (lipids and proteins), understand the asymmetry of the membrane, and understand amphipathic molecules.

What are some important functions of cell membranes?

Compartmentalization, receiving information/signaling, cell-to-cell interactions, capacity for cell movement/expansion/division, and structural support.

According to the core textbook, what is the significance of membranes?

Without membranes, there would be no cells, and there would be no life.

What is the difference in membrane structure between prokaryotic and eukaryotic cells?

Prokaryotic cells (bacteria) have only the plasma membrane, while eukaryotic cells have both the plasma membrane and membrane-enclosed organelles.

How do the membranes surrounding organelles contribute to their function?

They aid their function by keeping the contents separate and giving them distinct functions.

How does the structure of the inner mitochondrial membrane aid in its function?

The inner membrane of mitochondria is highly folded into cristae, which enhances the productivity of the mitochondria for respiration.

Which organelles form part of the endomembrane system?

The endoplasmic reticulum, the Golgi apparatus, the lysosome, and endosomes.

Do plant cells have a plasma membrane?

Plant cells also have a plasma membrane, in addition to the cellulose cell wall.

What are the various functions of the cell membrane?

Defining boundaries, aiding organelle function, import/export of small molecules and ions, signal detection, cell-cell interactions, interactions with the extracellular matrix, structural support, and enabling cell movement/expansion/division.

What are the two main components of cell membranes?

Lipids and proteins.

What is the approximate thickness of the lipid bilayer?

Approximately 5 nanometers.

What does it mean for phospholipids to be amphipathic?

They have a hydrophilic head and a hydrophobic tail.

What is the hydrophilic head of phosphatidylcholine made of?

Choline and phosphate.

What are the hydrophobic tails of phospholipids made of?

Hydrocarbon chains originating from fatty acids.

This configuration is energetically favorable because those phospholipids will …?

They come together.

When is a hydrocarbon chain considered saturated?

When there are no carbon-carbon double bonds in the hydrocarbon tail.

What is the difference between trans and cis configurations in unsaturated phospholipids?

The hydrogen atoms are on opposite sides, or on the same side, of a double bond.

How do unsaturated hydrocarbon chains affect membrane fluidity?

Unsaturated chains have a kink, preventing tight packing and increasing membrane fluidity.

Name some other examples of amphipathic molecules?

Phosphatidylserine, cholesterol, and glycolipids.

Where is cholesterol found?

Only found in animal cells.

How does cholesterol affect membrane fluidity?

It makes the membrane more rigid and less permeable.

What processes depend on membrane fluidity?

Cell signaling and protein diffusion.

How membrane fluidity is important in molecular trafficking?

Proteins and other cargo will get delivered around the cell through vesicles.

How do phospholipids spontaneously assemble into bilayers?

Hydrophilic heads pointing outwards towards water and hydrophobic regions protected in the core.

What drives phosopholipids to join together?

The hydrophobic effect.

Besides bilayers, what other structures can amphipathic molecules form?

Liposomes and micelles.

What are liposomes often used for?

Drug delivery.

What is a micelle?

Micelles are amphipathic molecules that have one hydrocarbon tail and this conical shape.

What is meant by membrane asymmetry?

It means that the outer and inner layers of the membrane have different compositions.

Which lipids enrich which leaflet of the membrane?

The outer leaflet faces the outside of the cell and is enriched in phosphatidylcholine and glycolipids, whilst the inner leaflet faces the cytosol and is enriched in phosphatidylethanolamine and phosphatidylserine.

What role do sugar molecules that protrude from the cell play?

Act as markers for the cell and may have roles in the immune respone

Where does membrane asymmetry originate?

In the endoplasmic reticulum (ER).

What is the role of scramblases in the ER?

They catalyze the transfer of phospholipids in either direction.

Which organelle is responsible for membrane asymetry?

The Golgi apparatus.

What is the role of flippases?

They catalyze the transfer of phosphatidylethanolamine and phosphatidylserine to the cytosolic phase.

What are the two distinct types of membrane proteins?

Integral and peripheral membrane proteins.

What is the difference between integral and peripheral membrane proteins?

Integral proteins span one or both layers, while peripheral proteins do not enter the bilayer.

What kind of interactions do the proteins use?

Integral proteins use hydrophobic interactions, while peripheral proteins use non-hydrophobic interactions.

How do detergents help remove hydrophobic proteins?

Detergents will form micelles around the membrane proteins and remove them.

What is the difference between SDS and Triton X detergents?

SDS is a strong ionic detergent that denatures proteins, while Triton X is a milder non-ionic detergent that allows for functional studies.

How can peripheral proteins be removed?

Tweak the salt concentration or pH to preserve the interactions between the integral protein and the peripheral protein and therefore remove it from the bilayer.

What structures can transmembrane proteins use to span the membrane?

Single alpha helix, multiple alpha helices, or beta barrels.

What structures do monolayer associated proteins use?

Amphipathic alpha helices or lipid links.

What are GPI anchors?

They are linkages between a protein and a specific type of phospholipid called phosphatidylinonosol

How do peripheral proteins interact with integral proteins?

Interacting with transmembrane proteins through weak non-covalent interactions.

Why will hydrophobic amino acids protrude into lipid part of the membrane?

To protrude out into the core of the membrane

What are examples of proteins that enable movement across membranes?

Transporters and channels.

How can proteins provide structural support through membranes?

They can be anchored to the extracellular matrix or the cytoskeleton.

Membranes do what in terms of what can enter and exit?

They also determine what gets in and out.

To what are membranes permeable?

Small, uncharged molecules (O2, CO2, H2O) and hydrophobic molecules.

What are some molecules membranes are not permeable to?

They are impermeable to large and charged molecules.

What are the two types of proteins facilitating transport across the membrane?

Channel proteins and transporter proteins.

What determines a channel protein's configuration?

They can either be open or closed based upon ligand binding, voltage changes or mechanotransduction.

What is transporter specificity?

Transporters are highly specific for their cargo.

What are the two types of transport?

Passive and active transport.

What is an active transport?

Transporters that use the energy from ATP hydrolysis to pump molecules against their concentration gradient.

Example of a pump through active transport

The sodium-potassium pump.

What determines the movement of charged molecules?

Concentration gradient and membrane potential (electrochemical gradient).

When there is a build up of positive ions on the outside of the cell?

Electrochemical gradient.

What kind of pumps are available in the lysosome?

Proton pumps.

What kind of material are available in Nucleus?

Transporters that carry nucleotides in.

Takeaway for macromolecules in lipids are …?

Lipids and proteins.

Phospholipids

Proteins in bilayers are mainly…?

What are bilayers called that have both hydrophilic and hydrophobic regions?

Amphipathic

Membrane proteins are necessary for allowing …?

The organelle has a unique function.

Where can you get more details on the discussed topics?

The Essential Cell Biology textbook.

What enables it to pass through the hydrophobic amino acids to protrude into the bilayer

Alpha helices and beta barrels.

What do you call a transmembrane protein with both hydrophilic and hydrophobic regions?

Amphipathic

How to molecules pass through channel proteins?

They move through the membrane and down the concetration gradient, in an open configuration

When molecules pass through membranes down their concentration gradient, what is this called?

Passive transport.

Because of being highly specific, molecules can pass …?

Down their concentration gradient, so passive transport.

Why can't ions pass through the membrane easily?

Because they like to interact with the water

Generally speaking, what is the charge of the inside and outside of cell when pertaining to charge?

Inside the cell is - and outside of the cell is +