Biology

Learninsta presents the core concepts of Biology with high-quality research papers and topical review articles.

Lipids and its Various Types

The term lipid is derived from greek word lipos, meaning fat. These substances are not soluble in polar solvent such as water but soluble in non-polar solvents such as benzene, ether, chloroform. This is because they contain long hydrocarbon chains that are non-polar and thus are hydrophobic. The main groups of compounds classified as lipids are triglycerides, phospholipids, steroids and waxes.

Triglycerides

Triglycerides are composed of single molecule of glycerol bound to 3 fatty acids. These include fats and oils. Fatty acids are long chain hydrocarbons with a carboxyl group at one end which binds to one of the hydroxyl groups of glycerol, thus forming an ester bond. Fatty acids are structural unit of lipids and are carboxylic acid of long chain hydrocarbons. The hydrocarbon can vary in length from 4 – 24 carbons and the fat may be saturated or unsaturated.

In saturated fatty acids the hydrocarbon chain is single bonded (Eg. palmitic acid, stearic acid) and in unsaturated fatty acids (Eg. oleic acid, linoleic acid) the hydrocarbon chain is double bonded (one/two/three). In general solid fats are saturated and oils are unsaturated, in which most are globules.

Lipids are molecules that contain hydrocarbons and make up the building blocks of the structure and function of living cells. Examples of lipids include fats, oils, waxes, certain vitamins (such as A, D, E and K), hormones and most of the cell membrane that is not made up of protein.

The Four Main Groups of Lipids Include:

• Fatty acids (saturated and unsaturated)
• Glycerides (glycerol-containing lipids)
• Nonglyceride lipids (sphingolipids, steroids, waxes)
• Complex lipids (lipoproteins, glycolipids)

A lipid is any of various organic compounds that are insoluble in water. They include fats, waxes, oils, hormones, and certain components of membranes and function as energy-storage molecules and chemical messengers.

Fats and lipids are an essential component of the homeostatic function of the human body. Lipids contribute to some of the body’s most vital processes. Lipids are fatty, waxy, or oily compounds that are soluble in organic solvents and insoluble in polar solvents such as water.

Examples of lipids include fats, oils, waxes, certain vitamins (such as A, D, E and K), hormones and most of the cell membrane that is not made up of protein. Lipids are not soluble in water as they are non-polar, but are thus soluble in non-polar solvents such as chloroform.

The main difference between lipids and fats is that lipids are a broad group of biomolecules whereas fats are a type of lipids. Fat is stored in the adipose tissue and under the skin of animals. It is mainly used as an energy-storage molecule in the body. Most steroids in the body serve as hormones.

Lipids are an important part of the body, along with proteins, sugars, and minerals. They can be found in many parts of a human: cell membranes, cholesterol, blood cells, and in the brain, to name a few ways the body uses them.

Within the body, lipids function as an energy reserve, regulate hormones, transmit nerve impulses, cushion vital organs, and transport fat-soluble nutrients. Fat in food serves as an energy source with high caloric density, adds texture and taste, and contributes to satiety.

Most people have high levels of fat in their blood because they eat too much high-fat food. Some people have high fat levels because they have an inherited disorder. High lipid levels may also be caused by medical conditions such as diabetes, hypothyroidism, alcoholism, kidney disease, liver disease and stress.

Lipids play diverse roles in the normal functioning of the body: they serve as the structural building material of all membranes of cells and organelles. they provide energy for living organisms – providing more than twice the energy content compared with carbohydrates and proteins on a weight basis.

The body uses three main nutrients to function – carbohydrate, protein, and fat. These nutrients are digested into simpler compounds. Carbohydrates are used for energy (glucose). Fats are used for energy after they are broken into fatty acids.

Learninsta presents the core concepts of Biology with high-quality research papers and topical review articles.

Carbohydrates and its Types

Carbohydrates are organic compounds made of carbon and water. Thus one molecule of water combines with a carbon atom to form CH₂O and is repeated several (n) times to form (CH₂O)_n where n is an integer ranging from 3-7. These are also called as saccharides. The common term sugar refers to a simple carbohydrate such as a monosaccharide or disaccharide that tastes sweet are soluble in water (Figure 8.7).

Monosaccharides – The Simple Sugars

Monosaccharides are relatively small molecules constituting single sugar unit. Glucose has a chemical formula of C₆H₁₂O₆. It is a six carbon molecule and hence is called as hexose.

All monosaccharides contain one or two functional groups. Some are aldehydes, Eg: glucose and are referred as aldoses; other are ketones, Eg: Fructose and are referred as Ketoses.

Disaccharides

Disaccharides are formed when two monosaccharides join together. An example is sucrose. Sucrose is formed from a molecule of α-glucose and a molecule of fructose. This is a condensation reaction releasing water. The bond formed between the glucose and fructose molecule by removal of water is called glycosidic bond. This is another example of strong, covalent bond.

In the reverse process, a disaccharide is digested to the component monosaccharide in a hydrolysis reaction. This reaction involves addition of a water (hydro) molecule and splitting (lysis) of the glycosidic bond.

Polysaccharides

These are made of hundreds of monosaccharide units. Polysaccharides also called “Glycans”. Long chain of branched or unbranched monosaccharides are held together by glycosidic bonds. Polysaccharide is an example of giant molecule, a macromolecule and consists of only one type of monomer. Polysaccharides are insoluble in water and are sweetless. Cellulose is an example built from repeated units of glucose monomer (Figure 8.6).

Depending on the function, polysaccharides are of two types – storage polysaccharide and structural polysaccharide.

Starch

Starch is a storage polysaccharide made up of repeated units of amylose and amylopectin. Starch grains are made up of successive layers of amylose and amylopectin, which can be seen as growth rings. Amylose is a linear, unbranched polymer which makes up 80% of starch. Amylopectin is a polymer with some 1, 6 linkages that gives it a branched structure.

Test for Starch

We test the presence of starch by adding a solution of iodine in potassium iodide. Iodine molecules fit nearly into the starch helix, producing a blue-black colour.

• Test on potato
• Test on starch at varied concentrations
• Starch – iodine reaction

Celluloses

Cellulose is a structural polysaccharide made up of thousands of glucose units. In this case, β-glucose units are held together by 1, 4 glycosidic linkage, forming long unbranched chains. Cellulose fibres are straight and uncoiled. It has many industrial uses which include cellulose fibres as cotton, nitrocellulose for explosives, cellulose acetate for fibres of multiple uses and cellophane for packing (Figure 8.7).

Chitin

Chitin is a homo polysaccharide with amino acids added to form mucopolysaccharide. The basic unit is a nitrogen containing glucose derivative known as N-acetyl glucosamine. It forms the exoskeleton of insects and other arthropods. It is also present in the cell walls of fungi (Figure 8.8).

Test for Reducing Sugars

Aldoses and ketoses are reducing sugars. This means that, when heated with an alkaline solution of copper (II) sulphate (a blue solution called benedict’s solution), the aldehyde or ketone group reduces Cu²⁺ ions to Cu⁺ ions forming brick red precipitate of copper(I) oxide.

In the process, the aldehyde or ketone group is oxidised to a carboxyl group (-COOH). This reaction is used as test for reducing sugar and is known as Benedict’s test. The results of benedict’s test depends on concentration of the sugar. If there is no reducing sugar it remains blue.

• Sucrose is not a reducing sugar
• The greater the concentration of reducing sugar, the more is the precipitate formed and greater is the colour change.

Other Sugar Compounds

Learninsta presents the core concepts of Biology with high-quality research papers and topical review articles.

Primary and Secondary Metabolites

Most plants, fungi and other microbes synthesizes a number of organic compounds called as metabolites which are intermediates and products of metabolism. The term metabolite is usually restricted to small molecules. It can be catergorized into two types namely primary and secondary metabolites based on their role in metabolic process (Figure 8.4).

Primary Metabolites

Are those that are required for the basic metabolic processes like photosynthesis, respiration, protein and lipid metabolism of living organisms.

Secondary Metabolites

Does not show any direct function in growth and development of organisms.

Organic Molecules

Organic molecules may be small and simple. These simple molecules assemble and form large and complex molecules called macromolecules. These include four main classes – carbohydrates, lipids, proteins and nucleic acids. All macromolecules except lipids are formed by the process of polymerisation, a process in which repeating subunits termed monomers are bound into chains of different lengths. These chains of monomers are called polymers.

A primary metabolite is a kind of metabolite that is directly involved in normal growth, development, and reproduction. A secondary metabolite is typically present in a taxonomically restricted set of organisms or cells (plants, fungi, bacteria, etc).

The main difference between primary metabolites and secondary metabolites is that primary metabolites are directly involved in primary growth development and reproduction whereas secondary metabolites are indirectly involved in metabolisms while playing important ecological functions in the body.

Some common examples of primary metabolites include: ethanol, lactic acid, and certain amino acids. In higher plants such compounds are often concentrated in seeds and vegetative storage organs and are needed for physiological development because of their role in basic cell metabolism.

Examples of primary metabolites include proteins, enzymes, carbohydrates, lipids, vitamins, ethanol, lactic acid, butanol, etc. Some examples of secondary metabolites include steroids, essential oils, phenolics, alkaloids, pigments, antibiotics, etc.

Examples of secondary metabolites include antibiotics, pigments and scents. Secondary metabolites are produced by many microbes, plants, fungi and animals, usually living in crowded habitats, where chemical defense represents a better option than physical escape.

Metabolites are intermediate end products of metabolism. Primary metabolites are essential for the proper growth of microorganisms. Secondary metabolites are formed near the stationary phase of growth and are not involved in growth, reproduction and development.

The antibiotics are defined as “the complex chemical substances, the secondary metabolites which are produced by microorganisms and act against other microorganisms”. Those microorganisms which have capacity to produce more antibiotics can survive for longer time than the others producing antibiotics in less amount.

Definition:
A primary pollutant is an air pollutant emitted directly from a source. A secondary pollutant is not directly emitted as such, but forms when other pollutants (primary pollutants) react in the atmosphere.

Secondary metabolites are compounds that are not required for the growth or reproduction of an organism but are produced to confer a selective advantage to the organism. For example, they may inhibit the growth of organisms with which they compete and, as such, they often inhibit biologically important processes.

Learninsta presents the core concepts of Biology with high-quality research papers and topical review articles.

Water Importance and its Properties

Water is the most abundant component in living organisms. Life on earth is inevitably linked to water. Water makes up 70% of human cell and upto 95% of mass of a plant cell (Figure 8.2).

Chemistry of Water

Water is a tiny polar molecule that can readily pass through membranes. Two electronegative atoms of oxygen share a hydrogen bonds of two water molecule. Thus, they can stick together by cohesion and results in lattice formation (Figure 8.3).

Properties of Water

• Adhesion and Cohesion Property
• High Latent Heat of Vaporisation
• High Melting and Boiling Point
• Universal Solvent
• Specific Heat Capacity

Water is very important to the human body. Every one of your cells, organs and tissues use water to help with temperature regulation, keeping hydrated and maintaining bodily functions. In addition, water acts as a lubricant and cushions your joints. Drinking water is great for your overall health.

Our bodies use water in all the cells, organs, and tissues, to help regulate body temperature and maintain other bodily functions. Because our bodies lose water through breathing, sweating, and digestion, it’s crucial to rehydrate and replace water by drinking fluids and eating foods that contain water.

Your body uses water to sweat, urinate, and have bowel movements. Sweat regulates body temperature when you’re exercising or in warm temperatures. You need water to replenish the lost fluid from sweat. You also need enough water in your system to have healthy stool and avoid constipation.

Uses of Water

• For Drinking
• For Cleaning Dishes
• For Cooking
• For Watering Plants
• For Washing Clothes
• For Bathing
• For Generation of Hydroelectricity
• For Washing Car

It is said that too much consumption of water can lead to fluid overload in the body and imbalance in the body. Excess water can lead to lower sodium levels in the body, which may further lead to nausea, vomiting, cramps, fatigue, etal. This condition is known as hyponatremia.

It’s important to drink enough water during the day, however, it can be disruptive if you drink directly before bed. Avoid drinking water or any other fluids at least two hours before sleeping to prevent waking up at night.

Water helps your kidneys remove waste from your blood. If you don’t get enough water, that waste – along with acids – can build up. That can lead to your kidneys getting clogged up with proteins called myoglobin. Dehydration can also lead to kidney stones and urinary tract infections.

Eliminating food and water intake for a significant period of time is also known as starvation. Your body can be subject to starvation after a day or two without food or water. At that time, the body starts functioning differently to reduce the amount of energy it burns. Eventually, starvation leads to death.

Learninsta presents the core concepts of Biology with high-quality research papers and topical review articles.

Cell Division and its Difference Phases

Amitosis (Direct Cell Division)

Amitosis is also called direct or incipient cell division. Here there is no spindle formation and chromatin material does not condense. It consist of two steps: (Figure 7.2).

Karyokinesis:

• Involves division of nucleus.
• Nucleus develops a constriction at the center and becomes dumbell shaped.
• Constriction deepens and divides the nucleus into two.

Cytokinesis:

• Involves division of cytoplasm.
• Plasma membrane develops a constriction along nuclear constriction.
• It deepens centripetally and finally divides the cell into two cells.

Example:
Cells of mammalian cartilage, macronucleus of Paramecium and old degenerating cells of higher plants.

Drawbacks of Amitosis

• Causes unequal distribution of chromosomes.
• Can lead to abnormalities in metabolism and reproduction.

Mitosis

Mitosis occurs in shoot and root tips and other meristematic tissues of plants associated with growth. The number of chromosomes in the parent and the daughter (Progeny) cells remain the same so it is also called as equational division.

Closed and Open Mitosis

In closed mitosis, the nuclear envelope remains intact and chromosomes migrate to opposite poles of a spindle within the nucleus (Figure 7.3). Example: Many single celled eukaryotes including yeast and slime molds. In open mitosis, the nuclear envelope breaks down and then reforms around the 2 sets of separated chromosome. Example: Most plants and animals.

Mitosis is divided into four stages prophase, metaphase, anaphase and telophase (Figure 7.6).

Prophase

Prophase is the longest phase in mitosis. Chromosomes become visible as long thin thread like structure, condenses to form compact mitotic chromosomes. In plant cells initiation of spindle fires takes place, nucleolus disappears. Nuclear envelope breaks down. Golgi apparatus and endoplasmic reticulum disappear.

In animal cell the centrioles extend a radial array of microtubules (Figure 7.4) and reach the poles of the cell. This arrangement of microtubules is called an aster. Plant cells do not form asters.

Metaphase

Chromosomes (two sister chromatids) are attached to the spindle fires by kinetochore of the centromere. The spindle fires are made up of tubulin. The alignment of chromosome into compact group at the equator of the cell is known as metaphase plate.

This is the stage where the chromosomal morphology can be easily studied. Kinetochore is a DNA-Protein complex present at the centromere where microtubules are attached. It is a trilaminar disc like plate.

Anaphase

Each chromosome splits simultaneously and two daughter chromatids begin to migrate towards two opposite poles of a cell. Each centromere splits longitudinally into two, freeing the two sister chromatids from each other. When sister chromatids separate the actual partitioning of the replicated genome is complete.

APC (Anaphase Promoting Complex) is a cluster of proteins that induces the breaking down of cohesion proteins which leads to the separation of chromatids during mitosis (Figure 7.5). This it helps in the transition of metaphase to anaphase.

Telophase

Two sets of daughter chromosomes reach opposite poles of the cell and mitotic spindle disappears. Division of genetic material is completed during karyokinesis, followed by cytokinesis (division of cytoplasm). Nucleolus and nuclear membranes reforms. Nuclear membrane form around each set of chromosomes. Now the chromosomes decondense.

In plants, phragmoplast are formed between the daughter cells. Cell plate is formed between the two daughter cells, reconstruction of cell wall takes place. Finally cells are separated by the distribution of organelles, macromolecules into two newly formed daughter cells.

Cytokinesis

Cytokinesis in Animal Cells It is a contractile process. The ring consists of a bundle of microfilaments assembled from actin and myosin. This firil generates a contractile force, that draws the ring inward forming a cleavage furrow in the cell. This it divides the cell into two.

Cytokinesis in Plant Cell

Division of the cytoplasm often starts during telophase. In plants, cell plate grows from centre towards lateral walls. Phragmoplast contains microtubules, actin filaments and vesicles from golgi apparatus and ER. Microtubule of the pharagmoplast move to the equator, fuse to form a new plasma membrane and the materials which are placed there becomes new cell wall.

The first stage of cell wall construction is a line dividing the newly forming cells called a cell plate. The cell plate eventually stretches right across the cell forming the middle lamella. Cellulose builds up on each side of the middle lamella to form the cell walls of two new plant cells.

Significance of Mitosis

Exact copy of the parent cell is produced by mitosis (genetically identical).

1. Genetic stability:
Daughter cells are genetically identical to parent cells.

2. Growth:
As multicellular organisms grow, the number of cells making up their tissue increases. The new cells must be identical to the existing ones.

3. Repair of Tissues:
Damaged cells must be replaced by identical new cells by mitosis.

4. Asexual Reproduction:
Asexual reproduction results in offspring that are identical to the parent. Example Yeast and Amoeba.

5. Flowering Plants:
In flowering plants, structure such as bulbs, corms, tubers, rhizomes and runners are produced by mitotic division. When they separate from the parent, they form a new individual.

The production of large numbers of offsprings in a short period of time, is possible only by mitosis. In genetic engineering and biotechnology, tissues are grown by mitosis (i.e. in tissue culture).

6. Regeneration:
Arms of star fish.

Meiosis

In Greek meioum means to reduce. Meiosis is unique because of synapsis, homologous recombination and reduction division. Meiosis takes place in the reproductive organs. It results in the formation of gametes with half the normal chromosome number.

Haploid sperms are made in testes; haploid eggs are made in ovaries of animals. In flowering plants meiosis occurs during microsporogenesis in anthers and megasporogenesis in ovule. In contrast to mitosis, meiosis produces cells that are not genetically identical. So meiosis has a key role in producing new genetic types which results in genetic variation.

Stages in Meiosis

Meiosis can be studied under two divisions i.e., meiosis I and meiosis II. As with mitosis, the cell is said to be in interphase when it is not dividing.

Meiosis I:
Reduction Division

Prophase I:
Prophase I is of longer duration and it is divided into 5 substages – Leptotene, Zygotene, Pachytene, Diplotene and Diakinesis (Figure 7.7).

Leptotene:
Chromosomes are visible under light microscope. Condensation of chromosomes takes place. Paired sister chromatids begin to condense.

Zygotene:
Pairing of homologous chromosomes takes place and it is known as synapsis. Chromosome synapsis is made by the formation of synaptonemal complex. The complex formed by the homologous chromosomes are called as bivalent (tetrads).

Pachytene:
At this stage bivalent chromosomes are clearly visible as tetrads. Bivalent of meiosis I consists of 4 chromatids and 2 centromeres. Synapsis is completed and recombination nodules appear at a site where crossing over takes place between non-sister chromatids of homologous chromosome. Recombination of homologous chromosomes is completed by the end of the stage but the chromosomes are linked at the sites of crossing over. This is mediated by the enzyme recombinase.

Diplotene:
Synaptonemal complex disassembled and dissolves. The homologous chromosomes remain attached at one or more points where crossing over has taken place. These points of attachment where ‘X’ shaped structures occur at the sites of crossing over is called Chiasmata.

Chiasmata are chromatin structures at sites where recombination has been taken place. They are specialised chromosomal structures that hold the homologous chromosomes together.

Sister chromatids remain closely associated whereas the homologous chromosomes tend to separate from each other but are held together by chiasmata. This substage may last for days or years depending on the sex and organism.

Diakinesis:
Terminalisation of chiasmata, homologous chromosomes become short and condensed. Nucleolus and nuclear envelope disappears. Spindle fires assemble.

Metaphase I

Spindle fires are attached to the centromeres of the two homologous chromosomes. Bivalent (pairs of homologous chromosomes) aligned at the equator of the cell known as metaphase plate. The random distribution of homologous chromosomes in a cell in Metaphase I is called independent assortment.

Anaphase I

Homologous chromosomes are separated from each other by shortening of spindle fiers. Each homologous chromosomes with its two chromatids and undivided centromere move towards the opposite poles of the cells. The actual reduction in the number of chromosomes takes place at this stage. Homologous chromosomes which move to the opposite poles are either paternal or maternal in origin. Sister chromatids remain attached with their centromeres.

Telophase I

Haploid set of chromosomes are present at each pole. The formation of two daughter cells, each with haploid number of chromosomes takes place. Nuclei reassembled. Nuclear envelope forms around the chromosome and the chromosomes becomes uncoiled. Nucleolus reappears.

In plants after karyokinesis, cytokinesis takes place by which two daughter cells are formed by the cell plate between 2 groups of chromosomes known as dyad of cells (haploid). The stage between the two meiotic divisions is called interkinesis which is short-lived.

Meiosis II:
Equational Division

This division is otherwise called mitotic meiosis because it resembles mitosis. Since it includes all the stages of mitotic divisions.

Prophase II

The chromosome with 2 chromatids becomes short, condensed, thick and becomes visible. New spindle develops at right angles to the cell axis. Nuclear membrane and nucleolus disappear.

Metaphase II

Chromosome arranged at the equatorial plane of the spindle. Microtubules of spindle gets attached to the centromere of sister chromatids.

Anaphase II

Sister chromatids separate. The daughter chromosomes move to the opposite poles due to shortening of spindle fires. Centromere of each chromosome split, allowing to move towards opposite poles of the cells holding the sister chromatids.

Telophase II

Four groups of chromosomes are organised into four haploid nuclei. The spindle disappears. Nuclear envelope, nucleolus reappear. After karyokinesis, cytokinesis follows and four haploid daughter cells are formed, called tetrads.

Signifiance of Meiosis

• This maintains a definite constant number of chromosomes in organisms.
• Crossing over takes place and exchange of genetic material leads to variations among species.
• These variations are the raw materials to evolution.
• Meiosis leads to genetic variability by partitioning different combinations of genes into gametes through independent assortment.
• Adaptation of organisms to various environmental stress.

Difference Between Mitosis in Plants and Animals