13. Describe the internal structures of prokaryotic cell. Cytosol and Cytoplasm. Nonmembranous organelles: Ribosomes, Mesosomes. Nucleoid.

Cytosol vs Cytoplasm

Cytosol is the intra-cellular fluid that is present inside the cells. Once the process of eukaryotes starts, the fluid is separated by the cell membrane from the organelles (mitochondrial matrix) and the other contents that float about in the cytosol. Cytosol is the part of the cytoplasm that is not held by any of the organelles in the cell. On the other hand, cytoplasm is the part of the cell which is contained within the entire cell membrane. It is the total content within the cell membrane other than the contents of the nucleus of the cell. All the cell organelles in eukaryotic cells are contained within the cytoplasm. The central, granular mass in the cytoplasm is the endoplasm while the surrounding lucid layer is known as the cell cortex or the ectoplasm. It is in the cytosol that all the metabolic chemical reactions of prokaryotes take place. On the contrary large scale cellular activities including glycolis, cell division and other metabolic paths take place in the cytoplasm. Cytoplasm is the gelatin-like, semi-transparent liquid that fills the cell. It contains the mitochondrion, golgi apparatus, vacuoles, plastids, cell wall and the endoplasmic reticulum. The major components in cytosol are concentration gradients, protein complexes, protein compartments and cytoskeletal sieving. Even though none of these components are alienated by cell membranes still they don’t mix as numerous levels of union confine definite molecules to distinct locales inside the cytosol. On the other hand, cytoplasm is made of three chief elements including the cytosol, the cell organelles and the inclusions. The vital composition of cytosol comprises of a lot of water, dissolved ions, large water soluble molecules, smaller minute molecules and proteins. The combination of diminutive molecules is an excessively complicated solution involving each and every molecule that is required in metabolism. Cytoplasm on the other hand is made of water up to 80%. Other substances present in the cytoplasm are nucleic acids, enzymes, lipids, non-organic ions, amino acids, carbohydrates, and lightweight molecular compounds. Other than these, cytoplasm also contains salts and nutrients in a dissolved state which helps to get the water components easily absorbed by the cell. The cytoplasm is an excellent conductor of electricity. Moreover, the presence of cytoplasm within the cell helps the various materials to navigate all around within the cell with the help of cytoplasmic streaming.

The ribosome is a large and complex molecular machine, found within all living cells, that serves as the primary site of biological protein synthesis (translation). Ribosomes link amino acids together in the order specified by messenger RNA (mRNA) molecules. Ribosomes consist of two major subunits—the small ribosomal subunit reads the mRNA, while the large subunit joins amino acids to form a polypeptide chain. Each subunit is composed of one or more ribosomal RNA (rRNA) molecules and a variety of proteins. A ribosome is made from complexes of RNAs and proteins and is therefore a ribonucleoprotein. Each ribosome is divided into two subunits: the smaller subunit binds to the mRNA pattern, while the larger subunit binds to the tRNA and the amino acids. Ribosomes from bacteria, archaea and eukaryotes (the three domains of life on Earth) differ in their size, sequence, structure, and the ratio of protein to RNA. The differences in structure allow some antibiotics to kill bacteria by inhibiting their ribosomes, while leaving human ribosomes unaffected. The ribosomal subunits of prokaryotes and eukaryotes are quite similar. The unit of measurement is the Svedberg unit, a measure of the rate of sedimentation in centrifugation rather than size, and this accounts for why fragment names do not add up (70S is made of 50S and 30S). Prokaryotes have 70S ribosomes, each consisting of a small (30S) and a large (50S) subunit. Eukaryotes have 80S ribosomes, each consisting of a small (40S) and large (60S) subunit.

Mesosomes are folded invaginations in the plasma membrane of bacteria. These structures are invaginations of the plasma membrane observed in gram-positive bacteria that have been chemically fixed to prepare them for electron microscopy. Initially, it was thought that mesosomes might play a role in several cellular processes, such as cell wall formation during cell division, chromosome replication, or as a site for oxidative phosphorylation. Mesosomes are the infoldings in the plasma membrane, these are rich in enzymes that helps to perform functions like cellular respiration,DNA replication, secretion of glycocalyx and cell division(most important function; it increases the surface area of the cell membrane.

The nucleoid (meaning nucleus-like) is an irregularly-shaped region within the cell of a prokaryote that contains all or most of the genetic material.^[1] In contrast to the nucleus of a eukaryotic cell, it is not surrounded by a nuclear membrane. The genome of prokaryotic organisms generally is a circular, double-stranded piece of DNA, of which multiple copies may exist at any time. The length of a genome widely varies, but generally is at least a few million base pairs. A genophore is the DNA of a prokaryote. It is commonly referred to as a prokaryotic chromosome. The term "chromosome" is misleading for a genophore because the genophore lacks chromatin. The genophore is compacted through a mechanism known as supercoiling, whereas a chromosome is additionally compacted via chromatin. The genophore is circular in most prokaryotes, and linear in very few. The circular nature of the genophore allows replication to occur without telomeres.^[ Genophores are generally of a much smaller size than Eukaryotic chromosomes. A genophore can be as small as 580,073 base pairs (Mycoplasma genitalium). Many eukaryotes (such as plants and animals) carry genophores in organelles such as mitochondria and chloroplasts. These organelles are very similar to true prokaryotes.