Biochemistry - Eukaryotes
Animals, plants, fungus, and slime moulds are all examples of eukaryotes. Each eukaryotic cell has a plasma membrane surrounding it, a membrane-bound nucleus, and a variety of other unique subcellular organelles. These membrane-bound organelles each play a distinct purpose and contain a particular combination of proteins and other substances. Although several organelles and features are unique to animal and plant cells (such chloroplasts, vacuoles, and cell walls in plant cells versus lysosomes in animal cells), both have the same basic structure.

Biochemistry - Bacterial Flagella 
Many bacterial cells feature one or more flagella, which are tail-like extensions. Chemotaxis is the term for the ability of bacteria to move across the extracellular medium by rotating their flagella in the direction of attractants and away from repellents. Both bacterial flagella and eukaryotic cilia and flagella are made of the protein flagellin (53 kDa subunit), which is different from tubulin.

Additionally, bacterial flagella rotate as opposed to bend. About six flagella protrude from various locations on the cell surface of an E. coli bacteria. Flagella are little, 10 mm long, helical filaments with a diameter of 15 nm. According to electron microscopy, the flagellar filament consists of 11 subunits arranged in two helical turns, giving it the appearance of an 11-bladed propeller with a hollow centre when viewed end-on. New flagellin subunits are added to the end of the flagellum that faces away from the cell, and these new subunits diffuse across the central core of the flagellum. The flagellar motor is located at its base in the plasma membrane and is a complex assembly of about 40 proteins. A passage of protons through certain proteins in the flagellar motor causes the flagella to rotate. The F0F1-adenosine triphosphatase (ATPase), which produces adenosine triphosphate (ATP), also has a proton-driven motor.

Biochemistry - Bacterial Cell Walls

​Most prokaryotes have a hard cell wall that is 3–25 nm thick to shield it from osmotic pressure and mechanical damage. Peptidoglycan, a combination of oligosaccharides and proteins, makes up the cell wall. The linear chains of alternate N-acetylglucosamine (GlcNAc) and N-acetylmuramic acid (NAM) connected b1-4 make up the oligosaccharide component. A tetrapeptide containing d-amino acids is linked to the lactic acid group on NAM by an amide bond. Other short peptides form covalent cross-links between adjacent parallel peptidoglycan chains via the tetrapeptide side-chains. The peptidoglycan cell wall's strength and rigidity are a result of the considerable cross-linking in the structure. A unique target for the action of some antibiotics, such as penicillin, is provided by the presence of d-amino acids in the peptidoglycan, which renders the cell wall resistant to the activity of proteases, which act on the more frequently present l-amino acids. Penicillin weakens the cell wall by blocking the enzyme that creates the covalent cross-links in the peptidoglycan. The lysozyme enzyme, found in tears, mucus, and other bodily secretions, can hydrolyze the b1-4 glycosidic bond between NAM and GlcNAc. 

Depending on whether they accept the Gram stain, bacteria can be categorised as either Gram-positive or Gram-negative. Gram-positive bacteria, like Bacillus polymyxa, have a cell wall that surrounds their plasma membrane that is thick (25 nm), whereas Gram-negative bacteria, like E. coli, have a cell wall that is thinner (3 nm) and have a second outer membrane. Due to porin proteins, which create pores in the lipid bilayer, this outer membrane is much more permeable to the passage of relatively large molecules (molecular weight >1000 Da) than the plasma membrane. The periplasm, which is a region where the cell's secreted proteins are located, lies between the outer membrane and the cell wall.

Biochemistry - Prokaryotes
The most abundant and widespread organisms on Earth are prokaryotes, which are so named because they lack a distinct, membrane-bound nucleus. The bacteria (or eubacteria) and the archaea are two distinct but related groups that make up the prokaryotes (or archaebacteria). Early in Earth's history, these two different prokaryotic groupings split apart.

Prokaryotic cell makeup
Prokaryotes typically have one of three basic shapes: spherical (cocci), rod-like (bacilli), or helically coiled, and range in size from 0.1 to 10 mm (spirilla). A prokaryotic cell, like all cells, is surrounded by a plasma membrane that completely encloses the cytoplasm and keeps the cell isolated from its surroundings. A lipid bilayer with proteins makes up the plasma membrane, which is 8 nm thick. The membrane subcellular organelles that distinguish eukaryotes from prokaryotes are absent. The macromolecules [enzymes, messenger ribonucleic acid (mRNA), transfer RNA (tRNA), and ribosomes], chemical substances, and ions required for cellular metabolism are found in the aqueous cytosol. The prokaryotic "chromosome," which consists of a single circular DNA molecule condensed into a substance known as the nucleoid, is also found in the cytosol.

Biochemistry - the history and development of cells
​Despite the enormous diversity of living systems, all creatures on Earth exhibit remarkable molecular uniformity, proving that they have a common origin and have undergone evolution. At least 3.8 billion years ago, life initially appeared, yet it is still unknown how the first cell and life itself arose. Experiments have demonstrated that in the circumstances believed to exist in the early Earth's atmosphere, the so-called prebiotic epoch, simple organic molecules can synthesise and spontaneously polymerize into macromolecules. The ability of the macromolecules to self-replicate, as seen with modern nucleic acids, and to catalyse other reactions, as seen with ribonucleic acid (RNA), was the next crucial step (Section G1). The first cell is thought to have developed as a result of the self-replicating RNA being enclosed in a membrane made of phospholipids (Section E1), thereby insulating the cell's interior from its surroundings. Thus, the enclosed macromolecules would have continued to function as a single unit, able to self-replicate and undergo additional development to give rise to the variety of life forms observed on Earth today. An evolutionary path from a common ancestral cell to the cells and animals of today can be inferred by examination of the deoxyribonucleic acid (DNA) sequences of organisms. Bacteria, archaea, and eukaryotes are the three main divisions or domains of the living world. The bacteria, which include cyanobacteria, Escherichia coli (E. coli), and the Bacillus species as well as living in or on larger organisms, are the prokaryotes most frequently found in soil, water, and other environments (photosynthetic blue-green algae). The sulphur bacteria and the methanogens are among the uncommon archaea, although some can also be found in less harsh conditions like salt brines, hot acid springs, and the depths of the ocean.