Lecture 5 Membrane Biology

Saturated vs Unsaturated

Role of fatty acids in membrane structure Fatty acids are hydrophobic and can therefore position themselves away from aqueous environments in the cell which results in the spontaneous lipid formation.Relationship of fatty acid saturation levels on membrane fluidity Maintaining fluidity within a certain range is very important. Being fully saturated (no double bonds) means the acids align very close together and as a result the membrane is less fluid. However the more unsaturation the more fluid the membrane will be. Desaturation is caused by a double bond in the carbon chain.

Relationship of temperature on membrane fluidity If membrane is too fluid then there will be too much ion transfer, membrane will fall apart. If it isnt fluid enough then ETC will stop and the cell will die which is why its important to maintain fluidity.

Saturated vs Unsaturated Fats Saturated No double bonds. Unsaturated Double bonds which causes a kink in the tail.

Role of Desaturases in Fatty Acid Biosynthesis Acids are synthesized through a biosynthetic pathway in a totally linear form and then desaturase introduces double bonds.

Relationship of Bacterial Desaturase Expression vs Temperature At high temperature, low abundance and vice-versa.

Role of size and charge in movement of molecules across biological membranes Molecules small and uncharged can get through semi permeable membranes. Bigger size of molecules and charge can impede movement across membranes which is why sometimes proteins are needed.

Characteristics of transmembrane proteins that enable them to interact with hydrophobic core of membrane Alpha Helices, Hydrogen bonding that gives rise to the alpha helical structure minimizes the charges of the protein backbone which lets it interact with the hydrophobic tails. Membrane has a part of protein which is made up of non-polar amino acids, about 17-20 amino acids.

Factors Influencing Simple and Facilitated Diffusion Simple diffusion is influenced by a concentration gradient. Facilitated diffusion operates under the same principles but uses pores or channels specific to molecules to let one molecule through at a time.

Transport against a concentration gradient (Active Transport) Moving from a region of low concentration to higher requires energy because it goes against free energy change. Consists of a the transmembrane domain which is 100s of variations of molecule specific domains and the ATP binding cassette which is purple and binds ATP and uses the energy for transport.

ABC Transporter Transmembrane Domain, the part that transports the molecule. ATP binding cassette, binds to the ATP and uses its energy to fuel the transport.

Genetics Underlying Cystic Fibrosis

Cystic Fibrosis caused by a homozygous recessive disease. (If both parents are heterozygous for it a child has a chance of getting two mutant copies of CFTR). It is a defect in CFTR (an ABC transporter). Leads to problems with lungs and gastrointestinal tract. Cilia and mucus stay wet due to CFTR but with CF, CFTR cannot pump chloride out and the lung tissue sticks together so gas exchange is inhibited. The mutant form of CFTR will never make it to the membrane because of the chaperone proteins quality control system.