Unit 1 - The Living Cell Membrane

Question 1

What is the cell membrane? Why is it important?

Answer 1

• The cell membrane is a flexible envelope that holds cytoplasm and organelles in place
• Regulates what enters and leaves the cell
• Is dynamic, only found in living cells
• It is important b/c if this thin membrane does not function properly, cellular processes fail and cells die

Question 2

What is the role of the CFTR protein?

Answer 2

• It is a membrane transport protein that pumps chloride out of the cells that line the lung and intestinal tract into the mucus lining
• This results in an electrical gradient across the membrane and leads to the movement of sodium ions in the same direction as chloride ions

Question 3

What is Cystic Fibrosis?

Answer 3

• A genetic disease
• Caused by a mutation to the gene that codes for the CFTR protein
• Mutant CFTR results in water being retained in the cells, instead of moving by osmosis out into the mucus lining to keep it moist
• Causes a thick buildup of mucus in the body, leading to numerous other health issues such as trouble breathing

Question 4

What happens when Cholera bacteria produce a toxin/protein? What does this result in?

Answer 4

1. Inactivated certain proteins that pump Na + ions into the cell
2. Opened channels in the membrane that are normally closed, allowing Cl- ions to escape from inside the cell into the small intestine

This results in:
- Ionic imbalance = there is a gradient, instead of having a higher Na+ and Cl- inside the cells, this now exists in the lumen of the intestine
- Through osmosis, this reversal ion gradient caused water to be pulled out of the cells and into the intestine, resulting in diarrhea, dehydration

Question 5

Describe the Fluid Mosaic Model

Answer 5

• Composed of lipids, proteins, carbohydrates
• The lipid molecules exist in a double layer called a bilayer and these molecules may vibrate/flex back and forth/spin/move sideways/exchange place within the same half of the bilayer
• Main lipid component = phospholipids
• Membranes also have an assortment of proteins
• Many of the lipid/protein components of some membranes have carbs linked to them, forming glycolipids and glycoproteins, which face the outside of the cell

Question 6

What does membrane asymmetry refer to?

Answer 6

• Refers to the fact that the composition of proteins and other components of the internal layer of the membrane bilayer differ from the external layer
• Each layer performs different functions
• Glycolipids and carbohydrate groups attach to proteins on the external side of the membrane for communication and cell recognition while components of the cytoskeleton bind to protein on the internal side of the membrane, for cellular structure

Question 7

What is a phospholipid?

Answer 7

• A type of amphipathic lipid (water-hating + loving)
• Head = hydrophilic and made of a modified alcohol (ex: choline) and a phosphate group along w/ glycerol
• Tail = hydrophobic, made of two fatty acids

Question 8

Why do phospholipid bilayers form?

Answer 8

• Because of the tendency for the fatty acids to aggregate together while the polar heads associate w/ water

Question 9

What 4 factors maintain the fluidity of the cell membrane?

Answer 9

1. Temperature - high temp = too fluid, low temp = gel-like state, right temp = oil-like viscosity
2. Unsaturated fatty acid tails - presence of double bonds create kinks that prevent solidification
3. Fatty acid length - the longer they are, the more intermolecular forces, cannot be longer than 18 C atoms
4. Cholesterol - prevents the membrane from solidifying in cold temps and maintains its structure in high temps

Question 10

What are the two major categories of membrane proteins?

Answer 10

1. Integral proteins - inserted into the membrane and span the entire membrane
2. Peripheral proteins attached to the surface of membrane (not embedded)

Question 11

What are the functions of proteins in the cell membrane?

Answer 11

1. Transportation
2. Enzymatic activity
3. Cell recognition
4. Signal reception and transduction

Question 12

What are the functions of the cell membrane?
1. Provide a barrier - hydrophobic environment prevents most substances from entering the cell
2. Gatekeeping - opens and closes paths through the membrane
3. Receptor sites - provide a binding site for chemical messengers (like hormones) to induce cell activity
4. Transport - transport proteins, aid the movement of particles across the membrane, and control what enters/exits
5. Structural Support - proteins are attached as microfilaments to maintain cell shape
6. Catalyze biological reactions - proteins present on the surface of the membrane assist in chemical reactions