Endoplasmic reticulum (ER), in biology, a continuous membrane system that forms a series of flattened sacs within the cytoplasm of eukaryotic cells and serves multiple functions, being important particularly in the synthesis, folding, modification, and transport of proteins .

Main. The endoplasmic reticulum (ER) is the largest membrane-bound organelle in eukaryotic cells and performs a variety of essential cellular functions, including protein synthesis and processing, lipid synthesis, and calcium (Ca2+) storage and release.

The ER is the largest organelle in the cell and is a major site of protein synthesis and transport, protein folding, lipid and steroid synthesis, carbohydrate metabolism and calcium storage [1–7].

There are two types of endoplasmic reticulum: rough endoplasmic reticulum (rough ER) and smooth endoplasmic reticulum (smooth ER). Both types are present in plant and animal cells. The two types of ER often appear as if separate, but they are sub-compartments of the same organelle.

Both rough ER and smooth ER have the same types of membranes but they have different shapes. Rough ER is called rough because it has ribosomes attached to its surface. The double membranes of smooth and rough ER form sacs called cisternae. Protein molecules are synthesized and collected in the cisternal space/lumen.

Introduction on Rough and Smooth Endoplasmic Reticulum

Function of SER and RER Smooth endoplastic reticulum helps in manufacture hormones and lipid molecules. It transport the hormones and lipid molecules to the cell and the organisms.

The most basic difference between RER and SER is the presence of ribosomes….Difference between Smooth and Rough Endoplasmic Reticulum.

Smooth endoplasmic reticulum (SER), meshwork of fine disklike tubular membrane vesicles, part of a continuous membrane organelle within the cytoplasm of eukaryotic cells, that is involved in the synthesis and storage of lipids, including cholesterol and phospholipids, which are used in the production of new cellular …

Smooth ER consists of a long network of a folded, tube-like structure. You can think of it like a pipeline with a lot of twists and turns. The interior of the smooth ER is called the lumen, which is enclosed by a phospholipid membrane, just like the membrane that encloses the entire cell.

Ribosomes have two main functions — decoding the message and the formation of peptide bonds. These two activities reside in two large ribonucleoprotein particles (RNPs) of unequal size, the ribosomal subunits. Each subunit is made of one or more ribosomal RNAs (rRNAs) and many ribosomal proteins (r-proteins).

A ribosome, formed from two subunits locking together, functions to: (1) Translate encoded information from the cell nucleus provided by messenger ribonucleic acid (mRNA), (2) Link together amino acids selected and collected from the cytoplasm by transfer ribonucleic acid (tRNA).

There are two types of ribosomes, free and fixed (also known as membrane bound). They are identical in structure but differ in locations within the cell. Free ribosomes are located in the cytosol and are able to move throughout the cell, whereas fixed ribosomes are attached to the rER.

70S Ribosomes The “S” stands for svedbergs, a unit used to measure how fast molecules move in a centrifuge.

Explanation: Ribosomes are bound to the endoplasmic reticulum, creating rough endoplasmic reticulum in eukaryotes, while in prokaryotes ribosomes are distributed in the matrix of cell. Both types of ribosomes are the sites of protein synthesis.

All prokaryotes have 70S (where S=Svedberg units) ribosomes while eukaryotes contain larger 80S ribosomes in their cytosol. The 70S ribosome is made up of a 50S and 30S subunits. Ribosomes play a key role in the catalysis of two important and crucial biological processes.

sedimentation coefficient

Ribosome Structure and Composition. Ribosomes are composed of ribosomal RNA (rRNA) and protein. The 30S subunit contains 16S rRNA and 21 proteins; the 50S subunit contains 5S and 23S rRNA and 31 proteins. The two subunits combine during protein synthesis to form a complete 70S ribosome about 25nm in diameter.

Answer. Answer: The S in the ribosomal subunits stand for sevdberg units named so in honour of the scientist Theador Svedberg and represent the different sedimentation rates of the ribosomes during centrifugation. While the larger subunit sediments at 50S and the smaller at 30S together they sediment at 70S.

Eukaryotic ribosomes are also known as 80S ribosomes, referring to their sedimentation coefficients in Svedberg units, because they sediment faster than the prokaryotic (70S) ribosomes. Both subunits contain dozens of ribosomal proteins arranged on a scaffold composed of ribosomal RNA (rRNA).

Ribosomes contain two different subunits, both of which are required for translation. The small subunit (“40S” in eukaryotes) decodes the genetic message and the large subunit (“60S” in eukaryotes) catalyzes peptide bond formation.

A Svedberg unit (represented as S or sometimes Sv) is a non-Système Internationale unit for sedimentation rate. The sedimentation rate is a measure of how quickly a particle sediments from a solution or suspension under the induced gravitational field of a centrifuge.

A Svedberg unit (symbol S, sometimes Sv) is a non-SI metric unit for sedimentation coefficients. The Svedberg unit offers a measure of a particle’s size indirectly based on its sedimentation rate under acceleration (i.e. how fast a particle of given size and shape settles to the bottom of a solution).

Theodor Svedberg

The same way an eukaryotic ribosome has a large sub-unit that sediments at 60s, a small one that sediments at 40s, but the whole structure sediments at 80s, not 100s. Essentially the sedimentation coefficient serves to normalize the sedimentation rate of a particle by the acceleration applied to it.

Synopsis of Eukaryotic Ribosome Assembly. Ribosomes are the molecular machines that translate the genetic information from the intermediary mRNA templates into proteins [1]. Eukaryotic 80S ribosomes comprise two unequal subunits that contain four different rRNAs and around 80 r-proteins (Figure 1).

The two subunits of 80S ribosomes are 60S and 40S. Ribosomes are molecular machines, which catalyze the translation of genetic information into proteins. They consist of two unequal subunits (small subunit and large subunit), both of which are large assemblies consisting of ribosomal RNA (rRNA) and ribosomal proteins.

While viruses do not have their own ribosomes—they hijack the ribosomes of the human cell to make more virus—it may be possible to exploit the unique methods by which viruses take over the human ribosomes to create novel anti-viral drugs.

All viruses contain nucleic acid, either DNA or RNA (but not both), and a protein coat, which encases the nucleic acid. Some viruses are also enclosed by an envelope of fat and protein molecules. In its infective form, outside the cell, a virus particle is called a virion.