Why is the endoplasmic reticulum connected to the nucleus

Ribosomal subunits and mRNA molecules transcribed off genes in the DNA leave the nucleus through pores in the nuclear membrane, enter the cytoplasm, and participate in protein synthesis. Ribosomes attached to mRNA molecules coding for proteins to be secreted from the cell or enter lysosomes attach to receptors on the ER. The ribosomes are tightly attached to the rough ER and contain a tunnel that connects to a pore in the ER called a translocon.

The proteins that are synthesized by the ribosomes can then pass through the translocon and enter the lumen of the ER where they can be transported to other locations within the ER.

Proteins for use within the eukaryotic cell or intended for organelles such as mitochondria, chloroplasts, an d peroxisomes are s ynthesized by mRNA molecules attached to ribosomes in the cytoplasm. The ribosomes small dots were originally called Palade particles. Image made available by James D. The smooth endoplasmic reticulum forms transition vesicles to transfer molecules produced in the rough ER to the Golgi complex. Study the material in this section and then write out the answers to these questions.

Do not just click on the answers and write them out. They are conveyed in vesicles or possibly directly between the ER and Golgi surfaces. It is found fairly evenly distributed throughout the cytoplasm. Smooth ER is devoted almost exclusively to the manufacture of lipids and in some cases to the metabolism of them and associated products.

In liver cells for example smooth ER enables glycogen that is stored as granules on the external surface of smooth ER to be broken down to glucose. Smooth ER is also involved in the production of steroid hormones in the adrenal cortex and endocrine glands. Smooth ER — the detox stop Smooth ER also plays a large part in detoxifying a number of organic chemicals converting them to safer water-soluble products. Large amounts of smooth ER are found in liver cells where one of its main functions is to detoxify products of natural metabolism and to endeavour to detoxify overloads of ethanol derived from excess alcoholic drinking and also barbiturates from drug overdose.

To assist with this, smooth ER can double its surface area within a few days, returning to its normal size when the assault has subsided. The contraction of muscle cells is triggered by the orderly release of calcium ions.

These ions are released from the smooth endoplasmic reticulum. Cytoskeleton — the movers and shapers in the cell. Extracellular Matrix and Cell Adhesion Molecules. Endoplasmic reticulum is an organelle found in both eukaryotic animal and plant cells.

It often appears as two interconnected sub-compartments, namely rough ER and smooth ER. Both types consist of membrane enclosed, interconnected flattened tubes. The rough ER, studded with millions of membrane bound ribosomes, is involved with the production, folding, quality control and despatch of some proteins. While the function of the nucleus is to act as the cell brain, the ER functions as a manufacturing and packaging system.

Structurally, the endoplasmic reticulum is a network of membranes found throughout the cell and connected to the nucleus. For example, some cells, such as prokaryotes or red blood cells, do not have an ER of any kind. Cells that synthesize and release a lot of proteins would need a large amount of ER.

You might look at a cell from the pancreas or liver for good examples of cells with large ER structures. Rough and Smooth There are two basic types of ER. Both rough ER and smooth ER have the same types of membranes but they have different shapes.

Rough ER looks like sheets or disks of bumpy membranes while smooth ER looks more like tubes. Rough ER is called rough because it has ribosomes attached to its surface.