Membranes I Flashcards
Why are cell memranes essential?
Act as biological barrier and compartmentalize processes.
What cell structure makes signaling possible?
Cell membrane. Allows for separation of genes from gene products for regulation.
WHat is the average fatty acid tail chain length?
C18
What is the major lipid component of the cell wal;?
Glycerophospholipid
Describe glycerophospholipids.
glycerol-3-phosphate esterified to fatty acids and polar alcohol
which part of the phospholipid allows for its packing in the membrane?
The fatty acid tail
What is the order of the components of phosphatidylcholine?
Choline - phosphate - glycerol - hydrophobic tails
How do sphingolipids differ from phospholipids?
Also major components of then cell membrane, but they are based on lipophilic amino alcohol (sphingosine) rather than glycerol.
What is the main sphingolipid in cell membranes?
Sphingomyelin
How are sphingolipids similar to phosphatidylcholine and phosphatidylethanolamine?
They have similar conformations and charge distributions.
In what cell type is sphingomyelin highly present?
Myelin sheath around nerve cells
What is a ceramide?
A sphingosine attached to a fatty acid.
How do cerebrocides, galactocerebrocides, and gluccocerebrosides differ?
They are all sphingolipids that comprise a ceramide group with different sugars on the head group.
What are the most complex sphingolipids?
Gangliosides
Describe gangliosides.
They are ceramide oligosaccharides that have sugar groups and at least one sialic acid residue
What are the functions of gangliosides?
- primary components of cell surface membranes
- constitute 6% of all brain lipids
- act as receptors for certain pituitary glycoprotein hormones
- act as receptors for certain bacterial cell toxins
- specific determinants of cell-cell recognition
How does cholesterol affect membrane fluidity?
More cholesterol, less fluid (bc less space between phospholipids)
What are the functions of cholesterol?
- substrate used to make steroid hormones (progesterone aldosterone, testosterone)
- substrate used to make vitamin D
- Precursor to bile salts
How is cholesterol classified?
As a sterol due to its branched alipathic side chain (hydrophobic with hydroxy group – branch other than entirely aromatic)
Describe melting point of cell membrane.
Tm. Acyl chains become more flud and disordered, allowing motion.
At what temperature are cell membranes in a gel-like state?
It is gel-like, restricting motion
How can lipids move in the cell membrane?
Laterally (rapid), transverse (slow, facilitated by enzymes flippases)
What factors affect membrane fluidity?
- degree and type of acyl chain unsaturation (double bonds are kinked and allow more fluidity)
- acyl chain length (longer chains are less fluid)
- cholesterol content (rigid ring structure reduces lateral movement – less fluidity)
What is the general composition of biological membranes?
Complex mixture of proteins and lipids, of which varies between cell types and organelle types.
What are the two main classes of memrbane proteins?
Integral and peripheral proteins
How are membrane proteins classified?
Based on how they are separated from the membrane.
Describe integral membrane proteins.
Require detergent to be separated form the membrane
Describe peripheral membrane proteins:
Loosely associated with the membrane and can be easily removed by changing pH or ionic strength
What type of interactions keep integral membranes in the membrane?
Via hydrophobic interactions
Which types of interactions predominate
electrostatic interactions predominate (ionic and hydrogen). Binding to polar lipid heads or integral proteins.
How do some peripheral membranes go to and from the membrane?
Reversibly attached lipid anchor.
Describe lipid anchors.
They are proteins covalently linked to lipids. Some can be reversibly attached from the protein.
What is a lipid anchor switching device?
It alters the affinity of a protein for the membrane, a role in signal transduction pathways in eukaryotes
What are the three main types of lipi anchors?
Prenylation, fatty acylated, glycosylphosphatidylinositol.
Describe prenylation.
iso-prenoid groups attached to protein via thoester linkage (eg. Rab proteins act as taxi cabs)
Describe fatty acyl lipid anchors.
- Myristic acid: myristoylated to N-term gly by amide linkage
- palmitic acid: palmitoylated to cys via thioester linkage and is reversible (e.g. Ras GTPase)
Why are glycosylphosphatidylinositol lipid anchors so complex?
They are involved in cell signaling.
Describe glycosylphosphatidylinositol lipid anchors.
Phosphatidylinositol core is linked to sugars and forms phosphoester bond to phosphoethanolamine which is amide linked to proteins.
How do we know that membranes are more patchy than fluid?
- we have more knowledge of the oligomeric nature of membrane protein structue
- we know pure lipid mixtures form non homogenous patches within vesicles
What is responsible for the assymetry of lipid membranes?
Specific lipid transporter proteins such as flippases
What is the importance of membrane microdomains?
They are important in signaling
In what are lipid rafts enriched.
Cholesterol and sphingolipids.
What types of proteins are lipid rafts enriched in?
Signaling proteins
Why might membranes in lipid rafts differ in thickness?
They might warp the membrane
