Elements in Living Cells

The most abundant element in cells include  hydrogen (H), followed by carbon (C), oxygen (O), nitrogen (N), phosphorous (P), and sulfur (S). These elements are the macronutrients, and they account for about 99% of the dry weight of cells.

Some elements called as micro nutrients or trace elements as they are required only in small amounts by the cell. These elements  include sodium (Na), potassium (K), magnesium (Mg), zinc (Zn), iron (Fe), calcium (Ca), molybdenum (Mo), copper (Cu), cobalt (Co), manganese (Mn), or vanadium (Va).  These  are essential to the function of many biochemical reactions, and, therefore, are essential to life.

Molecules in Cell

“Molecules in cell” by Openstax is licensed under CC BY 4.0

Living organisms also contain inorganic compounds mainly water and salts .Inorganic compounds do not contain carbon. Carbon oxides and carbonates are exceptions; they contain carbon but are considered inorganic because they do not contain hydrogen. Inorganic compounds account for about 1%–1.5% of the mass of a living cell.

Water accounts for about 70% of a cell’s weight,

Cells contain four major families of small organic molecules. The small organic molecules of the cell are carbon-based compounds  whose molecular weights  range  from 100 to 1000 and contain up to 30 or  more carbon atoms. They are usually found free in solution and have many different fates. They molecules  can  be as  monomers  or they can join to form polymeric  macromolecules  like the proteins, nucleic acids, and polysaccharides.

Some of these molecules act as energy sources and some of them  are broken down and transformed into other small molecules through various intracellular metabolic pathways. Many small molecules have more than one role in the cell. Small organic molecules are much less abundant than the organic macromolecules.  They constitute   only about one-tenth of the total mass of organic matter in a cell . The four major small organic molecule of the cell include the sugars, the fatty acids, the amino acids, and the nucleotides .

Significant Functional Groups in molecules of the cell

“Functional groups “ by Openstax is licensed under CC BY 4.0

The symbol R in the table stands for “residue” and represents the remainder of the molecule. R might symbolize just a single hydrogen atom or it may represent a group of many atoms.

Macromolecules

Carbon chains form the skeletons of most organic molecules and functional groups combine with this chain to form biomolecules. As these biomolecules are  large they are called  macromolecules. Biological macromolecules are formed by linking together a  number of identical, or very similar, smaller organic molecules. Cells contain four main groups of carbon-containing macromolecules:. They are  polysaccharides, proteins, lipids, and nucleic acids. The

 Carbohydrates

These are abundant biomolecule on earth and are abundant in terrestrial ecosystem. They are  primarily combination of carbon and water. They have the empirical formula (CH₂O)_n, where n is the number of repeated units. These molecules are regarded as “hydrated” carbon atom chains in which water molecules attach to each carbon atom, leading to the term “carbohydrates.”

Functions of carbohydrates include;

• They are food sources.

• These molecules parts of nucleic acids  that store and transmit genetic information (i.e., DNA and RNA).

• They  impart strength to various structural components of organisms (e.g., cellulose and chitin), and

• They are the primary source of energy storage as starch and glycogen.

Carbohydrates in biochemistry,  are often called saccharides, derived from the Greek word sakcharon, meaning sugar, although not all the saccharides are sweet. Carbohydrates are classified as  Monosaccharides , Disaccharides and Polysaccharides.

Monosaccharides, or simple sugars. 

These  are the building blocks (monomers) for the synthesis of polymers or complex carbohydrates, They are classified based on the number of carbons in the molecule. In general they are named using a prefix that indicates the number of carbons and the suffix –ose, which indicates a saccharide; for example, triose (three carbons), tetrose (four carbons), pentose (five carbons), and hexose (six carbons) .  D-glucose , a hexose , is the most abundant monosaccharide in nature. Other very common  hexose monosaccharides are galactose, used to make the disaccharide milk sugar lactose, and the fruit sugar fructose.

“Monosaccharides “ by Openstax is licensed under CC BY 4.0

Monosaccharides with four or more carbon atoms are typically more stable when they adopt cyclic, or ring, structures. These ring structures result from a chemical reaction between functional groups ,carbonyl group and a relatively distant hydroxyl group. Glucose, for example, forms a six-membered ring

“Monosaccharides “ by Openstax is licensed under CC BY 4.0

Disaccharides

Two monosaccharide molecules f may chemically link together by a covalent bond called glycosidic bond  to form a disaccharide. Glycosidic bonds form between hydroxyl groups of the two saccharide molecules,

 

$$\text{monosaccharide—OH}+\text{HO—monosaccharide}⟶\underset{\text{disaccharide}}{\underbracket{\text{monosaccharide—O—monosaccharide}}}$$ 

Examples of  disaccharides are

Maltose : the grain sugar maltose, made of two glucose molecules;

Lactose: the milk sugar lactose, made of a galactose and a glucose molecule; and t

Sucrose : the table sugar sucrose, made of a glucose and a fructose molecule

.“Common disaccharides” by Openstax is licensed under CC BY 4.0

Polysaccharides

Polysaccharides are non sweet carbohydrates . They are also called glycans. They are large polymers composed of hundreds of monosaccharide monomers, linked  together by glycosidic bonds..  They are not soluble in water.

Polysaccharides are very diverse in their structure. The most biologically important polysaccharides are starch, glycogen, and cellulose.

Cellulose : consists of a linear chain of glucose molecules and is a common structural component of cell walls in plants and other organisms.

Glycogen  :   branched polymers; glycogen is the primary energy-storage molecule in animals and bacteria,

Starch :  branched polymer Plants primarily store energy in starch.

The orientation of the glycosidic linkages in these three polymers is different as well and, as a consequence, linear and branched macromolecules have different properties.

Other structural polysaccharides.

Examples of these types of structural polysaccharides are N-acetyl glucosamine (NAG) and N-acetyl muramic acid (NAM)

found in bacterial cell wall peptidoglycan. Polymers of NAG form chitin, which is found in fungal cell walls and in the exoskeleton of insects.

“Polysccharides “ by Openstax is licensed under CC BY 4.0

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