Phospholipid Structure and Function

12 Questions

What is the top half of the phospholipid bilayer called?

Outer leaflet

Which type of molecules are phospholipids?

Amphipathic

According to the Fluid Mosaic Model, membranes are described as:

Fluid structures with embedded proteins

What technique allows visualization of membrane surfaces according to the text?

Freeze fracture (electron microscopy)

The Davson-Danielli model initially proposed that membranes consist of:

Two layers of proteins with a phospholipid layer in between

What is the most abundant type of lipid in the plasma membrane?

Phospholipids

What type of movement is described when a phospholipid changes places with the other leaflet?

Flip flop movement

Which type of membrane protein is primarily hydrophobic and extends into the hydrophobic portion of the lipid bilayer?

Integral membrane protein

What is required to move substances from one side of the membrane to another?

Transport protein

What is the main driving force behind diffusion of molecules across a membrane?

Concentration gradient

What term describes the net movement of water across a selectively permeable membrane in response to a concentration gradient?

Osmosis

Which type of membrane carbohydrate is more commonly bonded to proteins and serves as signals to the immune system?

Glycoprotein

Study Notes

Phospholipids and Membrane Structure

Phospholipids have a hydrophobic tail and a hydrophilic head, making them amphipathic molecules.
They are the most abundant lipids in the plasma membrane, forming a bilayer in water.
The bilayer consists of two layers: the outer leaflet and the inner leaflet.

The Fluid Mosaic Model

The fluid mosaic model describes a biological membrane as a fluid structure with a mosaic of various proteins embedded in it.
The model was developed from the Davson-Danielli model (1935), which showed phospholipids sandwiched between two layers of proteins.
Freeze-fracture electron microscopy provided evidence for the fluid mosaic model.

Fluidity of Membranes

Phospholipids in the plasma membrane can move within the bilayer.
Lateral movement refers to the movement of phospholipids within the same leaflet.
Flip-flop refers to a phospholipid changing places with another in the opposing leaflet, which is a rare event.

Membrane Proteins

Integral membrane proteins extend into the hydrophobic portion of the bilayer and are primarily hydrophobic.
Peripheral membrane proteins are loosely bound to the surface of the membrane and are easy to remove.

Membrane Protein Function

Biological membranes are semipermeable, allowing some substances to pass through while others cannot.
Transport proteins are necessary to move substances from one side of the membrane to the other.
Membrane proteins can have enzymatic activity, participate in signal transduction, and act as receptors.
They can also be involved in cell-cell recognition, intercellular joining, and attachment to the cytoskeleton and extracellular matrix.

Membrane Carbohydrates

Membrane carbohydrates can be covalently bonded to lipids (forming glycolipids) or proteins (glycoproteins).
Glycoproteins and glycolipids are important for cell surface identity, cell adhesion, and recognition by the immune system.

Membrane Asymmetry

Biological membranes have distinct inside and outside faces.
The asymmetrical distribution of protein, lipids, and associated carbohydrates is determined during membrane construction by the ER and Golgi apparatus.

Membrane Transport

Passive transport involves the diffusion of substances across a biological membrane without energy input.
Diffusion is the random movement of molecules from regions of high concentration to regions of low concentration.
Osmosis is the net movement of water across a selectively permeable membrane in response to a concentration gradient.
Tonicity refers to the ability of a surrounding solution to cause a cell to lose or gain water, depending on the concentration of solutes that cannot cross membranes.