Phases of mitosis. Mitosis consists of four basic phases: prophase, metaphase, anaphase, and telophase. Meiosis is a process where a single cell divides twice to produce four cells containing half the original amount of genetic information. These cells are our *** cells – sperm in males, eggs in females. During meiosis one cell divides twice to form four daughter cells. There are six stages within each of the divisions, namely prophase, prometaphase, metaphase, anaphase, telophase and cytokinesis.

Guanosine triphosphate (GTP) is a guanine nucleotide containing three phosphate groups esterified to the sugar moiety. GTP functions as a carrier of phosphates and pyrophosphates involved in channeling chemical energy into specific biosynthetic pathways. GTP is involved in energy transfer within the cell. For instance, a GTP molecule is generated by one of the enzymes in the citric acid cycle. This is tantamount to the generation of one molecule of ATP, since GTP is readily converted to ATP with nucleoside-diphosphate kinase (NDK).

Binomial Nomenclature.

The Wobble hypothesis proposes that normal base pairing can occur between nitrogen bases in positions 1 and 2 of the codon and the corresponding bases (3 and 2) in the anticodon. Actually, the base 1 in anticodon can form non-Watson-Crick base pairing with the third position of the codon. The wobble effect is an effect caused by the redundancy found in the genetic code. Each amino acid is coded for by a 3 nucleotide sequence on the mRNA. ... Thus, each amino acid can be coded for by more than one codon. For any amino acid, the first 2 nucleotides in the codon are always identical.

Factors affecting the rate of Imbibition

• Nature of imbibant:Different types of organic substances have different imbibing capacities. Proteins have a very high imbibing capacity, starch has less capacity and cellulose is the weakest imbiber. That is why proteinaceous pea seeds swell more on imbibition than starchy wheat seeds
• Temperature:The rate of imbibition increases with the increase in temperature.
• Concentration of the solute: Increase in concentration of the solute decreases imbibition due to a decrease in the diffusion pressure gradient between the imbibant and the liquid being imbibed.
• Surface area of imbibant:The imbibition will be greater when the surface area of imbibant is larger.

Synapsis (also called syndesis) is the pairing of two homologous chromosomes that occurs during meiosis. It allows matching-up of homologous pairs prior to their segregation, and possible chromosomal crossover between them. Synapsis takes place during prophase I of meiosis. Chiasmata is the point of contact, the physical link, between two (non-sister) chromatids belonging to homologous chromosomes. The chiasmata become visible during the diplotene stage of prophase I of meiosis, but the actual "crossing-overs" of genetic material are thought to occur during the previous pachytene stage.

The cell cycle is a 4-stage process consisting of Gap 1 (G1), Synthesis, Gap 2 (G2) and mitosis. An active eukaryotic cell will undergo these steps as it grows and divides. After completing the cycle, the cell either starts the process again from G1 or exits the cycle through G0.

Cofactors are not proteins but rather help proteins, such as enzymes, although they can also help non-enzyme proteins as well. Examples of cofactors include metal ions like iron and zinc.

A peptide bond is a chemical bond formed between two molecules when the carboxyl group of one molecule reacts with the amino group of the other molecule, releasing a molecule of water (H2O). This is a dehydration synthesis reaction (also known as a condensation reaction), and usually occurs between amino acids. 

Glycosidic bonds are the covalent chemical bonds that link ring-shaped sugar molecules to other molecules.

The phosphodiester bond is the linkage between the 3' carbon atom of one sugar molecule and the 5' carbon atom of another, deoxyribose in DNA and ribose in RNA.

The mechanism by which an enzyme binds with the substrate to forward the reaction of producing products can be explained by Lock and key hypothesis and Induced fit mechanism.
Lock and Key hypothesis: This hypothesis was putforth by Emil Fischer in 1894. Enzyme has a special site called as active site. the conformation of this active site corresponds to the shape of the substrate which fits into the active site.  Enzyme is the lock and substrate is the key. A particular substrate can only fit into active site of the enzyme to form the enzyme substrate complex. (ES complex) This intermediate complex is later broken to form enzyme and the products. Enzyme undergoes no change but helps in forwarding the reaction. This is called as lock and key hypothesis.


Induced-Fit mechanism: In this mechanism, the substrate wraps over the enzyme bringing about the change in the enzyme molecule. Here substrate determines the final shape of the enzyme. ES complex is formed after bnding. ES complex breaks to give rise to enzyme and products. Enzyme undergoes no change. Exactly to say the active site is modified during Enzyme-Substrate complex formation.

Many proteins are actually assemblies of multiple polypeptide chains. The quaternary structure refers to the number and arrangement of the protein subunits with respect to one another. Examples of proteins with quaternary structure include hemoglobin, DNA polymerase, and ion channels.

The most exciting aspect of chemistry deals with isolating thousands of compounds, small and big, from living organisms, determining their structure and if possible synthesising them.

If one were to make a list of biomolecules, such a list would have thousands of organic compounds including amino acids, sugars, etc. For reasons that are given in topic Metabolic basis for living, we can call these biomolecules as metabolites. In animal tissues, one notices the presence of all such categories of compounds shown in Figure 1. These are called primary metabolites. However, when one analyses plant, fungal and microbial cells, one would see thousands of compounds other than these called primary metabolites, e.g. alkaloides, flavonoides, rubber, essential oils, antibiotics, coloured pigments, scents, gums, spices. These are called secondary metabolites

Eukaryotic cells contain many membrane-bound organelles. An organelle is an organized and specialized structure within a living cell. The organelles include the nucleus, ribosomes, endoplasmic reticulum, Golgi apparatus, vacuoles, lysosomes, mitochondria, and, in plants, chloroplasts. Mitochondria are double- membrane-bound structures. The membrane of a mitochondrion is divided into the inner and outer membranes, distinctly divided into two aqueous compartments – outer and inner compartments.

Centromere is a constriction present on the chromosomes where the chromatids are held together.

Chromosomes are divided into four types based on the position of the centromere.

(i) Metacentric chromosome

The chromosomes in which the centromere is present in the middle and divides the chromosome into two equal arms is known as a metacentric chromosome. During anaphase, they appear V-Shaped.

(ii) Sub-metacentric chromosome

The chromosome in which the centromere is slightly away from the middle region is known as a sub-metacentric chromosome. In this, one arm is slightly longer than the other. During anaphase, they appear L-Shaped.
(iii) Acrocentric chromosome

The chromosome in which the centromere is located close to one of the terminal ends is known as an acrocentric chromosome. In this, one arm is extremely long and the other is extremely short. During anaphase, they appear J-Shaped.

(iv) Telocentric chromosome

The chromosome in which the centromere is located at one of the terminal ends is known as a telocentric chromosome. During anaphase, they appear i-Shaped.

Singer and Nicolson proposed the fluid mosaic model of plasma membrane. 
The plasma membrane is composed of a lipid bilayer.
The lipid molecules are arranged in such a way that their polar head are towards the outer side and the hydrophobic tails are on the inner side.
This arrangement of lipid molecules ensures that the non-polar tail of hydrocarbons does not come in contact with the aquatic environment present.
The proteins are of two types. Integral proteins which are either partially or totally embedded in the lipid bilayer and peripheral proteins which are present on the surface of the membrane.
The quasi fluid nature of lipid enables the lateral movements of proteins within the lipid bilayer.
The fluid nature of the membrane enables functions such as cell growth, secretion, endocytosis, cell division and formation of the intercellular junction.

Characteristics of Kingdom Monera:

(i) Kingdom Monera are one-celled without an organized nucleus. Examples: bacteria and blue-green "algae."

(ii) They are found in almost every imaginable habitat; in air, soil, and water and in extreme temperatures and harsh chemical environments.

(iii) There are no membrane bound "organelles".

(iv) Reproduction by asexual method.

(v) Monerans show either autotrophic or heterotrophic nutrition.

(vi) Cell wall may be present or absent.

Characteristics of Kingdom Protista:

1. This group includes many kinds of unicellular eukaryotic organisms such as unicellular algae, protozoans and unicellular fungi. 
2. They are found where there is moisture.
3. They are single celled, but many live in a colonial setting (more or less independently). 
4. Many are unicellular, but some are multicellular (Algae and fungus-like protists).
5.  Some can live in very harsh environments.
6. Reproduction can be sexual (conjugation), asexual (binary fission), or a combination of both.
7. Some of these organisms use appendages, such as hair-like cilia (e.g. Paramecium) or whip-like flagellum (e.g. Euglena).
8. Their mode of nutrition can be autotrophic or heterotrophic.