Unit B2.1: Membrane Structure

Outline how the phospholipid bilayer is formed

Phospholipids form bilayer in water. Hydrophilic phosphate/glycerol heads are attracted to the water. Hydrophobic fatty acids tails remain on bilayer's inside, because they aren't attracted to water

Outline the structure of phospholipids

Two fatty acid chains and a phosphate are bonded to a glycerol molecule. The fatty acids tails are hydrophobic and nonpolar. The phosphate head is charged and hydrophillic. Because of this, phospholipids are amphipathic.

What does selectively permeable mean?

Cell membrane allows certain substances through while others cannot

Why are plasma membranes selectively permeable

A cell must exchange materials with its surroundings, a process that's controlled by the plasma membrane. This regulates the cell's molecular traffic

Be specific on what makes plasma membranes/ lipid bilayer selectively permeable

the hydrophobic molecules, such as hydrocarbons, can dissolve in the lipid bilayer and pass through the membrane rapidly. However, polar/charged molecules, like sugars, don't cross easily

What's the key thing to remember about the permeability of the phospholipid bilayer

Like substances mix with like substances

What are transport proteins

Allow the passage of hydrophillic substances across the membrane

Are transport proteins specific for the substances they move (name an example)

Yes. Glucose is transported into the liver via a carrier protein, which won't transport fructose (it's a structural isomer)

How do carrier proteins work

The bind to molecules and change shape to shuttle them across the membrane

How do channel proteins work

They have a hydrophillic channel that certain molecules or ions can use as a tunnel

Examples of transport proteins

Carrier proteins and channel proteins

Example of channel protein

Aquaporins, which facilitate the passage of water

What are integral proteins

They are proteins that are permanently attached to the plasma membrane. They penetrate into the center of the phospholipid bilayer

Outline the sections of an integral protein

A hydrophobic section (with the fatty acids) that anchors the protein within the bilayer, and two hydrophillic sections (one at each surface of the bilayer)

Two things that integral proteins can be (in regards to the bilayer)

Transmembrane or partially penetrate the bilayer

three examples of integral proteins

Channels, glycoproteins, and protein pumps

What are peripheral proteins

Proteins that are temporarily attached to one side of the membrane

Where and how to peripheral proteins attach to the membrane

They attach to the membrane surface or to integral proteins, through electrostatic interactions. The charged peripheral proteins are attracted to the charged sections of the integral proteins and phosphate heads

Are peripheral proteins hydrophillic

YES

Examples of peripheral proteins

Receptors or enzymes

How are carbohydrate chains attached to membrane proteins and phospholipids (name the process)

Glycosylation

Where are carbohydrates of glycoproteins and glycolipids located

On the outside surface of the cell

Explain how cell to cell adhesion works

The carbohydrates of glycoproteins and glycolipids can form an extracellular matrix with the glycoproteins and glycolipids of neighbouring cells, leading to stable cell to cell adhesion

What does the extracellular matrix provide

Structural support for nieghbouring cells, and a role in the formation of tissues

How does cell recognition work on the plasma membrane

The carbohydrate chains that form on glycoproteins and glycolipids have specific chains allowing the immune system to recognize the cells as self

How do glycoproteins and glycolipids work as antigens

If the carbohydrate chain is not recognized as self by the immune system

What are anitgens

Substances which stimulate an immune response and the production of antibodies

Two important functions of the membrane

Cell to cell adhesion and cell recognition

Distinguish between saturated and unsaturated fatty acids (in terms of properties)

Triglycerides with saturated fatty acids have higher melting points than those with unsaturated fatty acids

How are the phospholipids in the cell membrane fluid

They are not in a fixed position and they move around

What affects the fluidity of the membrane

The types of fatty acids present in the phospholipids

What do saturated fatty acids contribute to the membrane

because they're closely packed (straight chains), they have higher melting points, decreasing the fluidity of the membrane and make it stronger at higher temps

What do unsaturated fatty acids contribute to the membranes

They have lower melting points and aren't closely packed, making the membrane more fluid

Outline the relationship between temperature and fatty acid composition in steelhead trout

As the temp decreases, the concentration of unsaturated fatty acids increases in the tissues of the trout. At low temp, the high concentration of the unsaturated fatty acids makes the membrane fluid in trout. At warmer temps, higher concentration of saturated fatty acids keeps the membrane strong

What does cholesterol do

Regulates the fluidity of cell membranes in animal cells

What does cholesterol do at higher temps

Reduces fluidity and melting point of phospholipids, making stable membrane

What does cholesterol do at lower temps

Maintains fluidity of membrane

Where is cholesterol located

cell membrane, between phospholipids

What makes cholesterol locate between fatty acid tails

Most of the cholesterol molecule is hydrophobic and is located between the fatty acids tails, whereas the hydroxyl group is hydrophillic and forms a hydrogen bond with the phosphate of a phospholipid

Tissues

Group of cells that work together to carry out a function. The cells in the tissue must be able to adhere to each other to carry out function

What is cell to cell adhesion

To process by which a cell uses a combination of an extracellular matrix and cell adhesion molecules (CAMs) to adhere to other cells

CAMs

Range of proteins used in different cell junctions

What is cell to cell adhesion required for

Development and maintenance of tissues, cell-cell communication and cell regulation

Cell junctions

Proteins complexes used to provide adhesion between animal cells

4 types of cell junctions

Tight, gap, adherons, and desmosomes

Tight junctions

Form seal between cells, preventing leakage

Gap junctions

Channels between cells that allow molecules to pass between cells, allowing cell-cell communication

Adherons junctions

Use protein complexes to connect cells together

Desmosomes

Use protein complexes to form strong connections between cells, providing tissues with structural integrity