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Wednesday, June 8, 2011

Tomatoes for Healthy Life

Tomatoes for Healthy Life


Tomato is a deep red pulpy fruit which comes from the Lycopersicon esculentum plant. According to botanical classification, it belongs to the Solanaceae family. Botanically, tomato is considered to be an edible fruit but when it comes to the cooking practices it is largely considered a vegetable. This fruit has originated in South America and has spread all over the world. At present there are at least 7500 different varieties of tomatoes known to us. This fruit is liked because of its tangy taste and is used to prepare a wide range of dishes like jam, sauce, pickles, juice, curries etc.

Nutritional Analysis Tables


100 grams of an edible portion of a ripe tomato has been shown to contain the nutrients in the following proportion.

Nutritional Value of Ripe Tomato
Protein
0.9 g
Fat
0.2 g
Minerals
0.5 g
Fiber
0.8 g
Carbohydrates
3.6 g
Energy
20 Kcal
Calcium
48 mg
Phosphorous
20 mg
Iron
0.64 mg
                                                                     


Vitamins Concentration in Ripe Tomato
Carotene
351 μg
Thiamine
0.12 mg
Riboflavin
0.06 mg
Niacin
0.4 mg
Vitamin C
27 mg
                                                                        

Quantity of Phyto-nutrients in ripe Tomato
Carotene-ß
449 mcg
Carotene-α
101 mcg
Lutein-zeaxanthin
123 mcg
Lycopene
2573 mcg

Nutritional Benefits of Tomatoes


  • Tomatoes provide a lower amount of calories and fats and at the same time they are rich in fiber, vitamins and minerals. An intake of this fruit is recommended to people who are obese and those suffering from higher levels of cholesterol.
  • It is a rich source of phyto-nutrients named lycopene and beta-carotene. Lycopene exists in the cell walls of tomato and acts as an antioxidant protecting the cells and its structures from oxygen free radicals. According to the studies performed by Dr. Edward Giovannucci, Harvard School of Public Health, Cambridge, Massachusetts, this nutrient lycopene, protects us from many kinds of cancers like the prostate cancer.
  • Lycopene prevents heart diseases.
  • Lycopene is associated with the prevention of age-related macular degeneration
  • Cooking practices like heating or frying it in a little bit oil, does not spoil the nutritional value of tomato. Lycopene is fat soluble hence cooking in a little bit of oil, releases this nutrient from the cell walls of tomatoes to a greater extent.
  • Intake of tomatoes helps to maintain the Sodium/potassium balance as they provide a lower concentration of sodium and at the same time are richer in potassium. This in turn regulates the blood pressure and allows the cell to function normally.
  • Tomatoes are richer in two vital vitamins which are Vitamin A and C. Hence they are good for eyes and maintenance of mucus membrane of the skin. They help in developing resistance against infectious agents.
  • It helps in curing the blisters and ulcers of mouth.

These are some of the innumerable health benefits associated with intake of tomatoes. Many nutritional facts are still being researched. It is good to include this vegetable in our daily diet. As cooking practices do not spoil the nutritional value of this fruit it can be preserved in many ways to get the taste of tomatoes all the year round. Some preservation methods have been described below -

Preservation of Tomatoes


Tomatoes can be preserved in various ways so that the flavor, taste and nutritional value are retained. The preservation techniques help us to get the tangy taste of tomatoes even when the price of tomatoes reaches the sky. Various home based methods which increase the shelf life of tomatoes have been discussed below.

The techniques discussed below depend on the kind of tomatoes chosen. Red tomatoes which have a very high content of vitamins have to be plucked from the garden during sunrise. During this time the fruits are still cool as the temperatures are low during the past night. Care should be taken to discard those tomatoes which have any kind of black spots. The tomatoes should be properly cleaned with water and should be kept away from prolonged exposure to sunlight before the preparation as this would spoil the tomatoes.

Preparation of Peeled Tomato Preserves


These peeled tomatoes can be used to prepare sauce all the year round. To prepare this, the tomatoes are gently dipped into hot boiling water for 30 seconds. Soon after this the tomatoes are removed from the cooking pot with the help of a sieve and plunged immediately into cold water for few minutes. This helps to loosen the skin of tomatoes. After this the skin of tomatoes is completely peeled. Clean and dried jars are used to store the peeled tomatoes. Tomatoes are allowed to fit snugly against each other by tapping the bottom of the jar. Lemon juice without the pips is extracted and added to the jars. The amount of lemon juice to be added comes to one coffee/tea-spoonful per half-liter of the jar. The jar is filled up with some amount of hot tomato pulp. The jars are then tightly screwed and allowed for sterilization in hot boiling water for a span of 45 minutes. These jars are allowed to cool and then cleaned and dried. These jars can be stored in a cool dry place and should be consumed within a span of one year.

Preparation of Tomato Pulp


Good tomatoes are chosen and cut into two halves to check for rotten tomatoes. An extractor is used to separate pulp from the seeds and the skin of the tomatoes. As an alternative to an extractor the tomatoes can also be cut into very small pieces and squashed. The seeds and the skin can also be separated with the help of a sieve. These steps can be repeated several times to maximize the yield. The extracted pulp is subjected to pre-heating at low temperature. This pulp is then filled into the jars along with a spoonful of lemon juice. These jars have to be sterilized for a span of 45 minutes.

Preparation of Dried Tomatoes


The tomatoes are cut lengthwise into two halves. The seeds are to be carefully removed using hands or spoons. These pips or seeds can be later sundried and used to grow the next crop of tomato plants. After this the tomatoes are further cut into small and uniform sizes measuring approximately one centimeter in thickness. These tomato pieces are sundried. This technique preserves the tomatoes for a span of three months.

To preserve the tomatoes for more than three months further processing is involved. Water containing a spoonful of salt and preservatives like citric acid powder is boiled. Addition of salt and preservatives prevents the tomatoes from getting blackened during the drying process.

The small pieces of tomatoes and their slices are subjected to the process of blanching. In order to blanch tomatoes, they are put into a clean cloth or a basket and plunged into the above mentioned boiling water for three minutes. Blanching is a preservation technique wherein vegetables are boiled before drying to kill the enzymes which spoil the food. After blanching tomato pieces are drained and then sundried with the help of dryers for at least two and a half days. The dried tomatoes are later gathered and cooled for half an hour in a shady place so that they do not release moisture while packing. These tomatoes are then packed into a polythene bags which are later kept into cardboard boxes containing straw. This protects the tomatoes from dampness and preserves them for one year.

Some other ways by which tomatoes can be preserved are by making a puree, sauce, jam or pickle.

This deep red fruit not only titillates your taste buds but it also encompasses some very wonderful nutritional and medicinal properties. It is a boon for those who want to reduce weight as it can be taken as salad during any time of the day. This fruit has the power to fight against many diseases and at the same time does not lose its nutritional significance upon cooking. With so many advantages associated with this fruit should we not make this a part of our daily diet?


References:


  1. Food and Agriculture Organization of the United Nations (FAO) and the Information Network on Post-Harvest Operations (INPhO) 1998. (2010, Aug 30). Methods for tomato preservation, Retrieved April13, 2011, from http://www.infonet-biovision.org/default/ct/216/farmPlanningAndMarketing.

  1. Gopalan, C. Rama Sastri, B.V. & Balasubramaniam, S.C. (2000). Nutritive value of Indian Foods (Revised by Narasinga, B.S. Pant, K.C. Deosthale, Y.G.). Hyderabad: National Institute of Nutrition.

  1. Tomato nutrition facts. (2010). Retrieved April 13, 2011, from

  1. Khachik, F. Carvalho, L et al. (2002). Chemistry, distribution, and metabolism of tomato carotenoids and their impact on human health. Experimental Biology and Medicine, 227, 845-851.


This article has been inspired from a question asked by Odunlami O Sunday.

Wednesday, March 16, 2011

Osmosis in Living Systems


Osmosis in Living Systems



Osmosis is physical process during which the solvent moves from a region of higher solvent concentration to a region of lower solvent concentration across a semi-permeable or a selectively permeable membrane. This process does not require the input of energy.

When two solutions having a difference in their concentrations are separated by a semi-permeable membrane, the net movement of the solvent takes place from a hypotonic solution (less-concentrated due to lesser amount of salt) to a hypertonic solution (more concentrated due to higher amount of salt). This process of osmosis tries to reduce the concentration gradient between the two solutions.

The pressure that is required to maintain a state of dynamic equilibrium between the two solutions is known as osmotic pressure . At this stage of dynamic equilibrium there is no net movement of solvent across the membrane.



Effect of Osmosis in Plant Cell


•    Hypotonic condition – When a plant cell is placed in a solution containing lower concentration of solute and a higher concentration of water, the cell swells up due to the movement of water into the cell. The cell becomes turgid and the rigid cell wall tries to hold this excess amount of water.
•    Isotonic condition – When the plant cell is placed in a solution of similar concentration, water moves across the cell membrane in both the directions. The net movement of water is zero with no change in the cell size. The cell at this stage is said to be in flaccid condition.
•    Hypertonic solution – When the plant cell is placed in a solution containing higher concentration of solute and a lower concentration of water, the cell shrinks as greater amount of water leaves the cell. The vacuole shrinks and the cytoplasm gets peeled off from the cell wall. The cell is said to be plasmolysed.




Effect of Osmosis in an Animal Cell


Animal cells do not have a rigid cell wall to support the cell membrane. When these cells are placed in a hypotonic solution, the cells absorb water, get swollen and burst. They do not have a capacity to hold water. On the other hand when they are placed in a hypertonic solution the animal cells loose water and shrink. It is very important in animals that the extracellular fluid is maintained at the same concentration as the cell cytoplasm. This balance in concentration is maintained by kidneys which regulate water and salt concentration of the body.

Applications of Osmosis in a Living System


•    Many biological membranes are selectively permeable in nature, that is, they allow only water and small uncharged solute molecules to pass through, whereas they inhibit larger molecules like polysaccharides, proteins etc., from passing across the membrane.
•    A cell adjusts in various salt concentrations due to the semi-permeability of the cell membrane. Osmosis is a most important mechanism by which water gets transported from external environment to internal environment of the cell and vice-versa.
•    In animals, the distribution of nutrients within the body and release of metabolic waste from the body takes place by the process of osmosis. The kidneys are the vital organs of the body which maintain the fluid balance within the organism. Kidneys help in the maintenance of the correct concentration of the plasma within the body.
•    Many water animals adjust to the changes in the water concentrations by the process of osmosis.
•    Our entire ecosystem depends on plants and they absorb water from soil by the process of osmosis. Cells of the root hairs have a concentrated cell sap where as water in soil is a weaker solution. This promotes the absorption of water by the cells of the root hairs.

Wednesday, March 2, 2011

Packaging of DNA into Microscopic Nucleus

Packaging of DNA into Microscopic Nucleus
Human DNA is 2 billion nanometers in length and fits into a small nucleus which is about 2000-6000 nanometers in diameter. DNA passes through various stages to get accommodated within the nucleus. Let us explore the stages of organization of DNA.

Journey of DNA
Central dogma proposed by FrancisCrick in 1958, proves that the information flows from DNA to RNA and then to proteins.

 
Fig1 – Flow of genetic information
The first step of this dogma is the replication where the information within the DNA gets replicated. The second step is transcription wherein the information within the DNA gets copied to RNA. The third step is translation where the information within the RNA is utilized to synthesize proteins.

Packing ratio
It is the ratio obtained by dividing the length of DNA with the length into which it is packaged. The measurement of the packing ratio gives us an idea about the level to which DNA gets condensed. The DNA moves through several hierarchies of organization to obtain different packing ratios.
For example – There are 4.6 x 10^7 bp present in the shortest human chromosome. To obtain the length of DNA the number of base pairs is multiplied with .34nm which is the distance between the two base pairs. The length of DNA so obtained comes to 14,000 µm. The most condensed form of DNA during mitosis measures 2 µm in length. Hence the packing ratio comes to 7000 (14,000/2).

Organization of DNA within prokaryotes -
The prokaryotic organisms lack a well defined nucleus however the DNA is organized with the help of some positively charged groups into a structure named as nucleoid.
The DNA is negatively charged due to the phosphate groups and the repulsion due to this negative charge is counteracted by the association of DNA with positively charged polyamines such as spermine and spermidine. These positively charged groups shield the negative charges of the DNA phosphate groups.
Along with polyamines there are abundant small proteins which give the DNA a compact structure (ex. H-NS). The DNA finally attains a supercoiled structure which gets opened with the help of enzymes like DNA gyrase during replication.

Organization of DNA within eukaryotes
In eukaryotic organisms DNA is present along with some basic proteins in the form of chromosomes within the nucleus and chromatin is a unit of analysis of a chromosome which gives a general idea of the nature of a chromosome

What are Histones?
They are the positively charged basic proteins.They are of 5 major types and contain amino acids residues like lysine and arginine. The five major types are H1, H2A, H2B, H3 and H4.

Formation of nucleosome
The association of the DNA with histone proteins starts from the formation of nucleosomes.
 A neucleosome is a fundamental unit of chromatin which is made up of a histone octamer wrapped around by duplex DNA. The histone octamer acts like a core and consists of two copies of each of these histone proteins H2A, H2B, H3 and H4. This octamer is wrapped around by the duplex DNA which is approximately 147bp in length. During the coiling process DNA takes one full turn and covers ¾ th of the histone octamer in the next turn. Large number of repeating units of neucleosomes forms chromatin. Nucleosomes together with DNA appear like beads on a string. At this stage the DNA is 10nm in diameter and attains a packing ratio of about 6.
 
Fig 1 – Structure of a single neucleosome

Role of Histone 1 or H1-
It holds the DNA which is wrapped around the nucleosome in a proper position. The linker DNA is made up of approximately 20-60 bp and the H1 binds to the linker DNA. This gives the stability to the zig-zagged 30 nm chromatin fiber which is the next level of organization.

Formation of chromatin fiber or solenoid fiber
This stage is seen during interphase in the cell cycle. After the beads on a string stage the DNA coils in such a way that at least 6 nucleosomes are packed per coil. In this stage DNA attains a diameter of 30 nm and this level of organization is known as 30 nm fiber or solenoid fiber. When the chromatin is extracted from isotonic buffers it appears like a 30 nm fiber. At this stage it attains a packing ratio of 10.

Stages after solenoid fiber
Later the solenoid fiber get further coiled and condensed and is organized into loops, scaffolds and domains to obtain cytologically visible threads known as chromatids. The looping is such that the base of the loops is attached to the same protein skeletal work.  Some metallic ions like calcium and copper along with non histone proteins help in the looping process. This increases the packing ratio to about 1000 in interphase chromosomes and about 10,000 in mitotic chromosomes.

 
Fig3 - Levels of organization of DNA

What are non Histone proteins ?
Chromosomal proteins which are not histones are grouped under non histone proteins. They can be acidic, basic or neutral. Their mol. wt varies from 10 KD to many million Daltons.
There are about 750-2000 different kinds of non histone proteins and examples of most abundant ones are Topoisomerases and High mobility group of proteins (HMGs). Functions mostly served by them are
  • Helping in the structural organization of chromatin fibers
  • Maintaining stability of the chromatin fibers
  • Involved in gene regulation 

Histone modifications
The primary structure of all the histone proteins remains the same but they vary from each other due to the chemical modifications which occur at a later stage. Some of these modifications are:
Acetylation:
During this modification, acetyl groups (CH3CO-) are added to the lysine residues of histone proteins. The core of the nucleosomes, is made up of lysine rich N terminal residues of the histone proteins. Being positively charged these residues interact with the negatively charged phosphate groups of the DNA. Enzymes like histone acetyl transferase (HAT) acetylate the lysine residues hence inhibiting their interaction with the phosphate groups of DNA. As a result DNA is inhibited from getting further condensed and this leads to active transcription of the genes.
However enzymes like histone deacetylases (HDACs), remove the acetyl groups from the lysine residues leaving them free to interact with DNA. This interaction helps in further condensation of DNA so that it attains a fully coiled structure which is less exposed to the transcription enzymes.
Phosphorylation :
This modification involves the addition of phosphate groups to serine and threonine residues which makes the chromosomes more compact and prepares them for mitosis and meiosis. 
Methylation:
This modification involves the addition of methyl groups to lysine and arginine residues. Methylation of some residues either stimulates or inhibits gene transcription at that region.

Euchromatin and Heterochromatin
The folding of DNA is not uniform throughout. In some regions the folding is highly compact and intricate giving rise toheterochromatic regions and the others are called euchromatin regions.

Some general characters of heterochromatin
It is densely packed and is found in the regions of chromosomes where there are few or no genes such as
  • Centromeres
  • Telomere
It shows a reduced level of crossing over and replicates during the later stages in the S phase of the cell cycle. It is enriched with transposons  (jumping genes) and other junk DNA. The genes in the heterochromatin are inactive that is they are less transcribed. The transcriptionally active regions are known as euchromatin regions.
Some general characters of euchromatin
Most parts of the chromosomes which are rich in transcriptionally active genes are termed as euchromatin regions.They are made up of loosely packed 30nm fibers. These regions are separated from heterochromatin by insulators. The histone proteins in this region show increased acetylation.

What happens to nucleosomes during transcription?
The neucleosome blocks the promoter region of a gene hence inhibiting the transcription factors from accessing it. During transcription of a gene either the nucleosome is expelled or in some other cases it slides along the DNA so that the transcription factors can bind the promoter region.
A set of proteins remove the neucleosome in front of the DNA to be transcribed and allow the RNA polymerase II (RNAP II) to travel down the DNA. After completion of transcription of that fragment of DNA the proteins replace the necleosome back into its position.

References
Fig1 – http/library.thinkquest.org/C0122429/intro/genetics.htm
Fig2 - http/www.accessexcellence.org/RC/VL/GG/nucleosome.php
Fig3 - http/plantcellbiology.masters.grkraj.org/html/Plant_Cell_Genetics1-Chromosomes.htm

Wednesday, February 16, 2011

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