Cell Membrane ( Plasma Membrane), Prokaryotic & Eukaryotic Cell Membrane.

Plasma Membrane

cell membrane ( plasma membrane ) and its components

All living things are composed of one cell or more than one cells ( the basic structural unit of life). If we talk about plasma membrane it is also known as cell membrane/cytoplasmic membrane & historically known as the plasmalemma. Cell membrane, which is a thin layer, present in all cells, it serve as a barrier which separates the inner cell environment to outside. It contains a bilayer (two layers of phospholipids with cholesterols) made up of a lipid which is semipermeable. Plasma membrane/cell membrane regulates the transport of materials which are entering and existing the cell.

plasma membrane

Note: This membrane contains membrane proteins, including integral proteins that( span the membrane &  serve as membrane transporters(, and the peripheral proteins which is loosely attached to the outer (peripheral) side of the cell membrane, which acts as an enzymes to facilitate interaction with the cell's environment.

Why Plasma membrane called selectively permeable membrane?

Plasma/cell membrane is also known as selectively permeable as it only allows specific molecules such as (water, gaseous molecules) to pass directly. It restrict/stops the flow of other molecules towards the both sides.

cholesterol, protein, phospholipids, side chains

What are the components of Cell/Plasma Membrane?

1.     lipids (phospholipids and cholesterol),
2.     proteins,
3.     and
4.     carbohydrate groups that are attached to some of the lipids and proteins.

Note: A phospholipid is a lipid which is made up of glycerol, two fatty acid tails, and a phosphate-linked head group.

A single phospholipid contain a head which is “hydrophilic” in nature, and a non-polar tail which is “hydrophobic” in nature. As shown in figure.

Hydrophobic , Hydrophilic parts of cell membrane 

Main functions of the cell membrane

·       work as a selective permeable membrane.

·       It regulates the exchange of materials between inner and outer environment the cell.

·       Intra-cellular communication

·       Active Transport.

·       Endocytosis.

·       Exocytosis:

·       Protect the integrity of interior cell.

·       Maintain the shape of a cell.

What is Eukaryotic Cell membrane?

Eukaryotes are the organisms whose cells are composed of a membrane-bound nucleus. All the animals, Plants, and fungi and many unicellular organisms are eukaryotes in nature. Eukaryotic cells contain membrane-bound organelles i.e.

• ·     nucleus,
• ·       (ER) endoplasmic reticulum,
•              &
• ·       Golgi apparatus.

 Eukaryotes may be unicellular eukaryotes or multicellular eukaryotes. Prokaryotes are typically unicellular. Unicellular eukaryotes are sometimes known as protists. Eukaryotes can reproduce both by asexually (mitosis) and sexually (meiosis) & gametes fusion (fertilization). Eukaryotic cells are organisms that range from microscopic single cells ( picozoans), to animals (blue whale), or plants ( coast redwood). Eukaryotes have a nucleus in their cells. It is derived from the Greek word (Eu, means "well" or "good") and (karyon, means "nucleus"). Many organelles are present in eukaryotes. Mitochondrion is commonly known as  "powerhouse of the cell’’. Mitochondria have their own DNA, which is similar to the bacterial DNA. Eukaryotic cell membrane is composed of a phospholipid bilayer with proteins & cholesterol which is embedded in it. Main difference between the prokaryotes and eukaryotes is only a “nucleus” and other some membrane-bound organelles that's are only presents in eukaryotes.

eukaryotic cell membrane(plasma membrane)

What is Prokaryotic Cell membrane?

A prokaryote is s single cell organism that lack nucleus in their cells & other membrane-bound organelles. Word prokaryote comes from an Ancient Greek word (Pró) means “before” and karyon means “nucleus”.

prokaryotic plasma membrane ( cell membrane )

According to scientists, Prokaryotes are evolved before the eukaryotes, that’s why they lack nuclei ( nucleus), and other organelles. Prokaryotes are asexual. They are reproducing by the binary fission process without any fusion of gametes.

Prokaryotic cell structure

1.     Flagellum

2.     Cell membrane: It surrounds the cell's cytoplasm & it regulates the flow of substances/materials in and out of the cell.

3.     Cell wall: ( that protects the bacterial cell & maintain it’s shape).

4.     Cytoplasm: (A gel-like structure/substance that is composed mainly of water which contains some enzymes, cell components, salts and various organic molecule.

5.     Ribosome: these are cell structures which are responsible for protein production.

6.     Nucleoid:  It is an area of cytoplasm, contains the prokaryote's single DNA molecule.

7.     Glycocalyx (only in some types of prokaryotes): It is a glycoprotein-polysaccharide covering which surrounds the cell/plasma membrane.

8.     Cytoplasmic inclusions: In inclusions, structures like ribosomes and larger masses are scattered in the cytoplasmic matrix.

Prokaryotic cells have four basic shapes

·       Bacilli – is a bacterium having cylindrical shapes called rod or a bacillus (Plural, bacilli).

·       Vibrio – comma like structure.

·       Spiral bacteria – Some rods which are twist into spiral shapes & are called spirilla (singular, spirillum).

·       Cocci – is a bacterium having a spherical or ovoid shape, called a coccus (Plural, cocci). e.g. Streptococcus, Staphylococcus.

·       The Archaeon-Haloquadratum has a flat square like shaped cells.

Function of cell wall in Prokaryotes

Prokaryotic cells, like other cells, have a plasma membrane. It controls what is entering in the cell and leaving out the cell. It is also a site for many metabolic reactions (cellular respiration and photosynthesis), take place in the cell/plasma membrane.

Prokaryotic cells lacks an organized nucleus & other membrane-bound organelles. The prokaryotic DNA is present in the central part of the cell which is called the nucleoid. The prokaryotic cell wall acts as an extra layer of protection, which helps to maintain cell’s shape, and prevents it from dehydration.

Do prokaryotes have any mitochondria in it?

First of all, you should know about the Prokaryotes. They lack mitochondria & some researchers have suggested that the mitochondria might be actually one of the reasons that eukaryotic cells are typically larger than the prokaryotic cells & more varied in their structures and shape.

Is Plasma Membrane/Cell membrane present in Prokaryotes?

It is an important Question that all the prokaryotes have plasma membranes, ribosomes, cytoplasm, DNA, a cell wall, & lack the membrane-bound organelles.

Prokaryotes have any chloroplasts in it?

Answer is No, prokaryotes don’t have any chloroplasts as it consists of lipid membrane.

How Prokaryotes make their ATP ? As they Lack mitochondria.

As mitochondria are absent in prokaryotes, so (ADENOSINE TRIPHOSPHATE) ATP is not synthesized. Prokaryotes have specific enzymes for production of ATP in their cell cytoplasm. They use the (electron transport chain) system on their cell/plasma membrane to produce ATP.

prokaryotic and eukaryotic cell (plasma membrane)