Cell Membrane

Cell Membrane: Structure and Functions

1.

Discuss the composition and structure of cell membranes ( membrane lipids, protein, carbohydrate, fluid mosaic model)

The cell membrane consists of phospholipid bilayer (phosphotidyl serine, phosphotidyl inositol, phosphotidyl choline, and phosphotidyl ethanolamine) as well as cholesterol, proteins (integral proteins, peripheral proteins, lipid-anchored proteins) and carbohydrates (glycolipids and glucoproteins). Cell membrane is represented as fluid mosaic model which is considered as 2-dimentional liquid where all lipids and protein molecules diffuse more or less easily. Plasma membrane consists of structures and domains classified as protein-protein complexes, lipid rafts and pickets and fences formed by the actin-based cytoskeleton. 2.

Discuss the following features of biological membranes on relation to membrane lipids: a. Membrane fluidity b. Selective permeability permeabilit y c. Self-sealing Self-seali ng capability d. Asymmetry

Membrane fluidity is the movement of the viscous lipid-bilayer of the cell membrane. It is affected by increase in temperature, saturation, presence of cholesterol, length of fatty acids and types of fatty acids present. Selective permeability of the cell membrane is a property of being freely permeable to water and oil-soluble substances while allowing much slower passage of polar solutes; In terms of self-sealing capacity, when the lipid bilayer is damaged, the endoplasmic reticulum and golgi complex synthesize phospholipids and transport these to the cell membrane to seal the damaged part. The cell membrane is asymmetric. The inner layer is composed mostly of phosphatidyl ethanolamine, serine and inositol, while the outer membrane is primarily composed of phosphatidyl chloline and sphingomyelin. 3.

Differentiate Differentiat e integral protein protein and peripheral protein in cell membrane. Discuss the different roles of membrane proteins

The integral proteins penetrate the lipid-bilayer thus have domains that protrude from both ECF and cytoplasm. Peripheral proteins are located entirely on the outside either on ECF or cytoplasm. They interact with signaling molecules and growth factors. the integral proteins are mainly for the transport of molecules. 4.

What are the major membrane proteins proteins in erythrocyte membranes? What are their functions?

In the erythrocytes, the usual proteins found in the cell membrane are spectrin, ankyrin, band 4.1, glycophorin, band 3, actin and band 4.2. These functions as cytoskeletons to maintain membrane stability, transport molecules, act as receptors, signal cascade and communication with other cells.

5.

Describe the membrane assembly

The cell membrane constituents are synthesized in the golgi complex and endoplasmic reticulum through a series of biochemical reactions. The vesicles then transport the synthesized biomolecules on the cell membrane. 6.

What is signal hypothesis?

The signal hypothesis is a major mechanism whereby proteins that insert into a membrane are synthesized by a membrane bound ribosome. The first 13 to 36 amino acids are synthesized termed as peptides are recognized by a signal recognition particle that draws the ribosome to the membrane surface by interaction with docking proteins. 7.

What is the significance of biological membranes in relation to the following: a. Transport b. Neural transmission c. Receptor interaction

The movement of substance across the membrane can either be passive (occurring without theinput of cellular energy) or active transport requiring the cell to spend energy in transporting it. Nerve signals are transmitted by action potential which occurs at the nodes. Salsatory conduction is an action potential that happens from node to node. Receptors are activated by binding to extracellular signal molecules and ligands.