Membrane and Transport

Question 1

How are cell membrane structured?

Answer 1

Cell membrane, or plasma membrane, is the barrier between internal and external environment.
It is formed of phospholipids that stick together thanks to the hydrophobic effect and by the electrostatic interactions.

Question 2

What is the structure of the fatty acids? What types there are?

Answer 2

Fatty acids are molecules structured by a linear chain of carbons and hydrogens with a carboxylic acid at the end.

1. Saturated: C-C single bond
2. Unsaturated: C=C double bond

Types:
I. Fats:
   - store energy
   - triacylglycerol (three fatty acids + glycerol bound by ester bond)
II. Phospholipids/diacylglycerol:
    - two fatty acid + glycerol + phosphate
III. Glycolipids
IV. Sphingomyelin
V. Cerebroside

Question 3

What is the structure of Cholesterol? What is its function?

Answer 3

Cholesterol is a steroid molecule formed by an hydrophobic 4C ring and a short branched hydrocarbon tail.
It is present in animal’s plasma membrane and it affects the fluidity of it.

Question 4

What types of membrane protein there are?

Answer 4

A membrane protein is a protein of which hydrophobic side chains are in contact with the hydrophobic core of the membrane.

1. Transmembrane: span the membrane
   
   • single helix
   • multiple helices
   • barrel of β-strands
2. Membrane-associated: amphipathic protein bound to the membrane
3. Lipid-linked: protein covalently bound to a lipid
4. Protein-attached

Question 5

Give me an overview of the mitochondria.

Answer 5

Mitochondria is the organelle responsible for oxidative phosphorylation, thus the production of ATP.
It has a double plasma membrane, within which there is the intramembraneous space. They posses their own genome, which encode for 13 proteins.

Mitochondrial metabolism is simply the Krebs cycle: PYR is transported inside the mitochondria and the electron that it loose throughout the cycle are taken by the electron transport chain, where ATP is produced due to a pH and chemical difference.

Question 6

What is passive transport? How can molecules perform it?

Answer 6

Passive transport is that type of transport that does not use ATP to move molecules:

1. Simple diffusion: due to entropy, net transport of molecules from a high concentrated area to a low concentrated area.
2. Facilitative transport: larger, more polar or charged molecule can diffuse the membrane only with the help of a carrier protein.
3. Gated channels: transport of molecules from high to low concentration but only upon stimulation by some trigger

Question 7

What is active transport? How can molecules perform it?

Answer 7

Active transport is that transport that needs energy because molecules are transported against their concentration gradients.
1. Primary active transport: energy is directly taken from ATP hydrolysis.
- antiporter: transport of one compound in one direction and the
other in the opposite direction.
- symporter: transport of two compounds in the same direction.
2. Secondary active transport: the flow of one compound down its concentration gradient is used to transport something else against its gradient.
- cotransport: transport of two compounds in the same direction

Question 8

What is meant for multi-drug resistance? How may it be reached?

Answer 8

Multi-drug resistance is the ability of some bacteria to resist to multiple antibiotics. This resistance is mainly caused by a protein that pumps various compounds out of the cell; it is unclear how a pump can transport so many different compounds and how it can recognised drugs from its own metabolite.