Difference between C3 and C4 Cycles of Photosynthesis in Plants


C3 vs C4 Cycles of Photosynthesis

Similarities and Differences between C3 and C4 Cycles: A Comparison Table
(Calvin Cycles Vs Hatch and Slack Cycle)

Photosynthesis is one of the vital events in the earth in which the green plants fix the energy from the sunlight and synthesis nutrients with carbon dioxide and water. Almost all living things on earth, either directly or indirectly, depend on photosynthesis for energy. The process of photosynthesis in plants is completed in two major pathways, a light dependent ‘Light Reaction’ and a light independent ‘Dark Reaction’. In the light reaction, the chlorophyll molecules in the plants absorb energy from sunlight and synthesize energy rich chemical molecules such as ATP and reduced coenzymes (NADPHH+). In the dark reaction, this energy rich molecules are used up for the synthesis of carbohydrates from carbon dioxide. The first describe dark reaction pathway, better known as Calvin cycle (Melvin Calvin who discovered this pathway), is called C3 cycle. For a considerable period of time, the Calvin cycle (C3 cycle) was thought to be the only dark reaction pathway in plants. Later, a new pathway of dark reaction called Hatch and Slack pathway or C4 cycle was described in some plants. Both these cycles (C3 and C4 cycles) show many similarities and differences. The present post describes the similarities and differences between C3 cycle and C4 cycle of the dark reaction of photosynthesis.

Similarities between C3 cycle and C4 cycle

Ø  Both C3 and C4 cycles are pathways of dark reaction of photosynthesis.

Ø  Both are light independent reactions.

Ø  Both C3 and C4 cycle requires energy from ATP or reduced coenzymes.

Ø  Both C3 and C4 plants accept carbon dioxide to perform dark reaction.

Ø  End products of C3 and C4 cycle are similar.

Ø  Both C3 and C4 cycle requires RuBP and RUBISCO to complete the pathway.

Difference between C3 cycle and C4 cycle:

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biological chemistry

Chemical Bonds Involved in Protein Structure and Conformation


bonds stabilizing protein structure

Bonds involved in Protein Structure
(Bonds Stabilizing the Primary, Secondary, Tertiary and Quaternary Structure of Proteins)

Proteins are the polymers of amino acids. Amino acids are joined together by a special type of covalent bond (peptide bond) to form linear structures called polypeptides. The polypeptides are then folded into specific structures to form the functional conformation of the protein. The folding of proteins into specific shapes and conformations are assisted and stabilized by many types of bonds in them. Some of these bonds are strong bonds whereas others are weak interactions. Important types of bonds involved in protein structure and conformation are Peptide bonds, Ionic bonds, Disulfide bonds, Hydrogen bonds and Hydrophobic Interactions. The current post describes the importance of each of these bonds and their role in the functional conformation of the protein.

What are the different types of bonds present in a protein?

Ø  Typically, proteins possess the following FIVE types of bonds.

(1).    Peptide bond

(2).   Ionic bond

(3).   Disulfide bond

(4).   Hydrogen bond

(5).   Hydrophobic Interactions

(1). Peptide Bond

Ø  Peptide bond definition: a covalent bond formed between the carboxylic group of one amino acid and the amino group of another amino acid.

Ø  Peptide bond is a strong covalent bond with high bond dissociation energy.

Ø  It is formed by the joining of two amino acid residues during protein synthesis.

Ø  The carboxylic group (- COOH) of one amino acid combine with the amino group (-NH2) of another amino acid to form the peptide bond.

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biological chemistry

Classification of Proteins Based on Structure and Function

protein classification

Classification of Proteins

Proteins are important macromolecules of the cells, formed by the polymerization of amino acids according to the sequence of genetic code in the mRNA. Proteins are the mode of expression of the genetic information. They perform a variety of duties in the cells such as they act as the structural components of cells, enzymes, hormones, pigments, storage proteins and some toxins in the cells. The proteins are classified into many categories based on different criterions.

Criterion for the classification of proteins:

Ø  Proteins are classified based on the following THREE criterions:

                             (I).     Classification based on STRUCTURE of Protein

                            (II).    Classification based on COMPOSITION of Protein

                           (III).    Classification based on FUNCTIONS of Proteins

(I). Classification of Proteins based on the Structure of Proteins

Ø  Based on the structure, proteins are classified into 3 groups.

(A).   Fibrous Proteins

(B).   Globular Proteins

(C).   Intermediate Proteins

(A). Fibrous Proteins

Ø  They are linear (long fibrous) in shape.

Ø  Secondary structure is the most important functional structure of fibrous proteins.

Ø  Usually, these proteins do not have tertiary structures.

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biological chemistry

Biological Importance of Water


biological functions of water

Biological Importance of Water

Water is the mother liquid of all forms of life. The essentiality of water for living systems is quite evident as without water, there is no life. No other substance on earth is abundant as water. All aspects of cell structure and functions are adapted to the physical and chemical properties of water. The following are the important biological significance or importance of water in the living system.

(1).  Water is a ‘universal solvent’.

(2).   Water can dissolve most of the biologically important molecules.

(3).  It is the solvent of life. The life originated in water and adapted to survive only in the presence of water.

(4).  About 70 to 90% of a cell occupies water.

(5).  Water acts as a medium for the diffusion of molecules in the cell.

(6).  Osmotic concentration of cell is maintained by water and dissolved solutes.

(7).  The turgidity of the cell is maintained by the water.

(8).  Translocation of inorganic and organic compounds in the living system takes place through the water.

(9).  Carbohydrates, the product of photosynthesis, in plants are transported through the water.

(10).  Water is the source of H+ ions for photosynthesis.

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biological chemistry

Physical and Chemical Properties of Water and its Biological Significance


biological significance of water

Physical and Chemical Properties of Water and its Biological Significance

Water is the most abundant substance in the living system. Water makes up about 70% or more of the weight of almost all organisms. The life has originated in remote past in the aqueous environment. The properties (both physical and chemical) of water enabled it as the ‘solvent of life’. The water possesses some unusual physical and chemical properties. These ‘unusual properties’ are responsible making water as the ‘solvent of life’. The present post describes the Physical, Chemical and Unusual Properties of Water. We will also discuss the importance or significance of these properties of water in the biological system.

The unusual properties of water are mainly due to three factors:

(A).  The small size of water molecules

(B).  The polarity of water molecules

(C).  The formation of hydrogen bonds between adjacent water molecules

Most important physio-chemical and unusual properties of water can be summarized into the following heads:

(1).  Solvent properties of water

(2).  High heat capacity of water

(3).  High heat of vaporization

(4).  High heat of fusion

(5).  Density and freezing properties

(6).  High cohesion, adhesion and surface tension of water

(7).  Water acts as a reactant

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