Cell membrane - Composition Flashcards
observation and composition
Electron microscopy has shown that each cell is surrounded by a plasma membrane that delimits and defines its cell boundaries;Specialized proteins such as channels and transporters contribute to the creation and maintenance of ionic gradients which in turn generate trans-membrane electrical potentials. Finally, surface receptors are able to transfer information from the extracellular environment through the multiple modes of signal transduction.
The thickness of the membrane in the photo is about 10 nm and it appears as a sandwich in which a lighter layer is interposed between two darker layers.
Today we know that this is due to the double layer organization of the main lipid components of the membrane: the phospholipids.
explain the FLUID MOSAIC model and the dynamic of the cell membrane
The fluid mosaic model describes the cell membrane as a tapestry of several types of molecules (phospholipids, cholesterols, and proteins) that are constantly moving. This movement helps the cell membrane maintain its role as a barrier between the inside and outside of the cell environments.
The lipids in this double barrier can move in three different forms: lateral diffusion, flexion, rotation and flip flop
composition- lipids
composed by PHOSPHOLIPIDS, COLESTEROL is GLYCOLIPIDS
what is the function of MICELLES and LIPOSSOMES?
MICELLES are a single layer of lipid molecules that arrange themselves in a spherical form in aqueous solutions. Its very useful to increase the contact area and facilitate the lipid absorption in intestine.
LIPOSSOME are a double layer of lipid molecules that contains a water soluble molecule inside, very useful for transport of water soluble molecules (like drugs)
these forms are energetic advantageous because the polar part interacts with the water from the liquid compartments.
explain what LIPID RAFTS are
Lipid rafts are functional membrane microdomains containing sphingolipids (with long tails), cholesterol and proteins. These regions are characterized by highly ordered and tightly packed lipid molecules. Lipid rafts influence membrane fluidity and membrane protein trafficking, thereby regulating neurotransmission and receptor trafficking
And what about the CARBOHYDRATES?
They are attached to extracellular side os proteins to form glycocalyx structures. It confers mechanical and chemistry protection to the membrane and also temporary adhesions to another cells.
Talk about the protein structures
α-helix and β-pleated sheet are the most common secondary structures in proteins.
The alpha-helix has a helix shape because of the interactions of the polar residue with hydrogen because theres no water inside the membrane.
The beta pleated is a very rigid structure and consist of beta strands (β-strands) connected laterally by at least two or three backbone hydrogen bonds, forming a generally twisted, pleated sheet.
what is HYDROPATHY INDEX?
In biochemistry, the hydropathy index is used to know the hydrophilic or hydrophobic (polarity) character of the protein. It’s measured by the energy required to transfer a segment of a protein from a solvent to water.
what are the PROTEINS of the membrane?
INTEGRAL PROTEIN (transmembrane protein): water soluble part outside and hydrophilic helix. membrane transport
PERIPHERAL PROTEIN: attached with a single layer or a integral protein
ATTACHED WITH A PROTEIN: contains acyl group and prenilic group
explain the difference between
PHOSPHOLIPIDS
COLESTEROL and
GLYCOLIPIDS
PHOSPHOLIPIDS can be divided in two groups:
-phosphoglycerids (phosphate group+glycerol+ fat acid) they are the principal component of the eukaryotic cell plasmatic membrane
-sphingolipids (sfingosin+ fat acids)
both have a polar head and two apolar tails
the saturation can influence the fluidity of the membrane
CHOLESTEROL
Cholesterol functions to immobilise the outer surface of the membrane, reducing fluidity. It makes the membrane less permeable to very small water-soluble molecules that would otherwise freely cross. It functions to separate phospholipid tails.
GLYCOLIPIDS
Glycolipids are lipids (sphingolipids) with a carbohydrate attached by a glycosidic (covalent) bond.
Their role is to maintain the stability of the cell membrane and to facilitate cellular recognition, which is crucial to the immune response and in the connections that allow cells to connect to one another to form tissues.
