Cell membrane systems are important in intracellular division of labour. They allow compartmentalization and therefore efficiency through locations of multi-enzyme pathways.
1.Reverse pinocytosis (endocytisis) releases contents of vesicle into the extracellular environment.
2.Plasmamembrane
3.Lysosome contains hydrolytic enzyme which may digest ingested materials, redundant organelles(autophagy)or whole cells (autolysis).
4.Trans Golgi network separated products ready for inclusion in secretory vesicles or in lysosomes.
5.Cisternae stack of Golgi ‘processes’ molecules often by adding or modifying carbohydrate ‘signals’ which direct the molecules to the correct cellular compartment.
6.Cis Golgi network collects sacs from the E.R. Any misdirected molecules, e.g. components, are returned to the endoplasmic reticulum.
7.Protein synthesis at ribosomes on E.R. Newly-synthesized protein carries a ‘signal’ which ensures that the protein will enter the cisterna ready to be packaged within a sac and delivered to the Golgi apparatus.
8.Messenger DNA carries coded message from nucleus to ribosomes.
9.Nucleolus is the site of manufacture of ribosomal subunits. It disperses in preparation for nuclear division, and is reassembled at the end of telophase.
10.Nucleoplasm contains a variety of solutes, including nucleoside triphosphate for DNA synthesis, and the enzyme complex (DNA polymerase) which regulates DNA replication and repair.
11.Nucleus contains coded information for protein synthesis as a series of genes on the chromosomes.
12.Chromatin is the genetic material, containing he coded information for protein synthesis in the cell. It is composed of DNA bound to basic proteins celled Histones. The DNA and histone are organized into nucleosomes. During nuclear division the chromatin condenses to from the chromosomes, and the chromatin containing DNA which is being ‘expressed’ (transcribed into mRNA) becomes visible as more loosely-coiled threads called euchromatin.
13.Endocytic contains product for export, e.g. mucoprotein rom goblet cell, trypsinogen from pancreatic acinar cells and complex carbohydrates for plant cell wall synthesis. The endoplasmic reticulum (E.R.) has a wide range of other functions:
13.1 Synthesis of lipids, e.g. reassembly of fats in gut epithelium.
13.2 Steroid synthesis, e.g. in cells which secrete steoid hormones.
13.3 Control of ---------concentration in skeletal muscle cells. 12 and 3 all occur on smooth E.R.
13.4 Surface for enzyme systems, e.g.the oxidizing system which detoxifies alcohol and other drugs in the liver.
14. Product molecules re moved through the stack in a precisely defined sequence.
15. Endoplasmic reticulum ‘buds off’ membranous sacs containing products of its metabolism. These products include proteins nd lipids and may be for export ------
Or for use within the cell--------
16 Cisterna is an enclosed space within the membranes of the E.R.
17 Nuclear envelope is a double membrane, the outer of which is continuous with the E.R.
18 Nuclear pore can regulate the entry (e.g. ribosomal proteins) and exit (e.g. ribosomal subunits, messenger RNA) of molecules to and from the nucleus.