Tuesday 7 December 2010
Digestion of Dietary Carbohydrates
Glucose + 2 ADP + 2 NAD+ + 2 Pi ——> 2 Pyruvate + 2 ATP + 2 NADH + 2 H+
The Hexokinase Reaction:
6-Phosphofructo-1-Kinase (Phosphofructokinase-1, PFK-1):
Triose Phosphate Isomerase:
Phosphoglycerate Mutase and Enolase:
Carbohydrates are the main energy source for the human body. Chemically, carbohydrates are organic molecules in which carbon, hydrogen, and oxygen bond together in the ratio: Cx(H2O)y, where x and y are whole numbers that differ depending on the specific carbohydrate to which we are referring. Animals (including humans) break down carbohydrates during the process ofmetabolism to release energy. For example, the chemical metabolism of thesugar glucose is shown below:
|C6H12O6 + 6 O2 6 CO2 + 6 H2O + energy|
Animals obtain carbohydrates by eating foods that contain them, for example potatoes, rice, breads, and so on. These carbohydrates are manufactured by plants during the process of photosynthesis. Plants harvest energy from sunlight to run the reaction just described in reverse:
|6 CO2 + 6 H2O + energy (from sunlight) C6H12O6 + 6 O2|
A potato, for example, is primarily a chemical storage system containing glucose molecules manufactured during photosynthesis. In a potato, however, those glucose molecules are bound together in a long chain. As it turns out, there are two types of carbohydrates, the simple sugars and those carbohydrates that are made of long chains of sugars - the complex carbohydrates.
All carbohydrates are made up of units of sugar (also called saccharide units). Carbohydrates that contain only one sugar unit (monosaccharides) or two sugar units (disaccharides) are referred to as simple sugars. Simple sugars are sweet in taste and are broken down quickly in the body to release energy. Two of the most common monosaccharides are glucose and fructose. Glucose is the primary form of sugar stored in the human body for energy. Fructose is the main sugar found in most fruits. Both glucose and fructose have the same chemical formula (C6H12O6); however, they have different structures, as shown (note: the carbon atoms that sit in the "corners" of the rings are not labeled):
Complex carbohydrates are polymers of the simple sugars. In other words, the complex carbohydrates are long chains of simple sugar units bonded together (for this reason the complex carbohydrates are often referred to as polysaccharides). The potato we discussed earlier actually contains the complex carbohydrate starch. Starch is a polymer of the monosaccharide glucose:
Starch is the principal polysaccharide used by plants to store glucose for later use as energy. Plants often store starch in seeds or other specialized organs; for example, common sources of starch include rice, beans, wheat, corn, potatoes, and so on. When humans eat starch, an enzyme that occurs in saliva and in the intestines called amylase breaks the bonds between the repeating glucose units, thus allowing the sugar to be absorbed into the bloodstream. Once absorbed into the bloodstream, the human body distributes glucose to the areas where it is needed for energy or stores it as its own special polymer - glycogen. Glycogen, another polymer of glucose, is the polysaccharide used by animals to store energy. Excess glucose is bonded together to form glycogen molecules, which the animal stores in the liver and muscle tissue as an "instant" source of energy. Both starch and glycogen are polymers of glucose; however, starch is a long, straight chain of glucose units, whereas glycogen is a branched chain of glucose units, as seen in the illustrations linked below:
Another important polysaccharide is cellulose. Cellulose is yet a thirdpolymer of the monosaccharide glucose. Cellulose differs from starch and glycogen because the glucose units form a two-dimensional structure, withhydrogen bonds holding together nearby polymers, thus giving the moleculeadded stability. Cellulose, also known as plant fiber, cannot be digested by human beings, therefore cellulose passes through the digestive tract without being absorbed into the body. Some animals, such as cows and termites, contain bacteria in their digestive tract that help them to digest cellulose. Cellulose is a relatively stiff material, and in plants it is used as a structural molecule to add support to the leaves, stem, and other plant parts. Despite the fact that it cannot be used as an energy source in most animals, cellulose fiber is essential in the diet because it helps exercise the digestive track and keep it clean and healthy
What is Biochemistry?
A. Biochemistry is concerned with structural chemistry. It seeks to determine the structures of molecules found in living systems in order to understand structure-function relationships.
B. Biochemistry is concerned with chemical change, this is reflected in the stu dy of metabolic pathways
C. Biochemistry is concerned with information which has accumulated through evolution and is preserved in DNA (or sometimes RNA). These nucleic acid sequences code for amino acid sequences, which result in folded proteins. These proteins are often catalysts (enzymes) and some of them are regulated (able to sense the chemical state inside the cell and, in some cases, the outside)
History of biochemistry:
(Proteins - enzymes)
1828 Wohler --> synthesized a biological compound (urea) from ammonium cyanate (an inorganic chemical)! NH4+ NCO-
1897 the Buchner brothers (Eduard and Hans) demonstrated that alcoholic fermentation could occur in a cell-free extract.
1926 J.B. Sumner demonstrated that an enzyme (urease) was a protein and could be crystallized (indicative of fixed molecular structure and purity)
set stage for Perutz and Kendrew's work on X-ray structure of myoglobin and hemoglobin
Nucleic acid polymers (DNA and RNA)
Another series of discoveries surrounding nucleic acids: Miescher; Mendel; Avery, McCarty, and McLeod; Watson and Crick; Hershey and Chase
Distinguishing Characteristics of Living Systems
a. They are complex, that is they are highly organized (cell - nucleus - chromosome - nucleosomes - DNA base pairs - bases). This organization has physical chemical implications.
b. They are capable of self-replication (biochemistry comes from genetics)
c. They can transform energy. Energy is required to create order (G = H -TS)
Implications of Chemistry for Biology
a. There is an underlying simplicity in the molecular organization of cells (similar proteins are found in E. coli and in humans).
b. All living forms have a "common ancestor" (evolution). Biochemists seek a "logical" molecular path upward.
c. Identity (phenotype) of organism is determined by its set of nucleic acids (genotype) and proteins (gene products) and the regulation of their expression (interaction with the environment).
d. There is a molecular economy in living systems; some molecules appear to have an advantage over many others and are used repeatedly (ATP).
Biochemistry refers to the study of the various chemical processes that goes on inside the body of a living organism. A large number of students are opting for this branch of study because of the wide range of job opportunities that this subject presents.
Students can obtain PhD, M.Sc. and even degree certificates in this subject to get a successful career in Biochemistry. The students who have high marks in Plus II level and had Physics, Chemistry and Biology as their optional subjects can go for a degree course in Biochemistry.
A large number of colleges in India offer a B.Sc. degree in Biochemistry. The students who opt for Biochemistry as their main subject can choose subjects like Chemistry, Botany, Zoology and Industrial Microbiology as the subsidiary subjects. Some of the colleges even allow their students to study Biotechnology as the main subject and Biochemistry as the subsidiary subject. The students who have Zoology or Botany as their main subject can also select Biochemistry as their subsidiary subject for a course of B.Sc. degree.
The students can also go for a course in Biochemistry for their M.Sc., M.Phil or Ph.D. degree. The students who score high marks in their B.Sc. degree course in Biochemistry, Zoology, Botany, Biotechnology, etc. can opt for a M.Sc. in Biochemistry and only the students who score greater than 55% in their M.Sc. course can go for an M.Phil or Ph.D. programs that are offered at a limited number of colleges.
There are vast employment opportunities for the students of Biochemistry as they can be absorbed in a number of Research Institutions. They can also work as faculty in the colleges that offer a course in Biochemistry. The students of Biochemistry can also work as Scientists, research officers, research associates, chemical examiners, etc.Scope and importance of Biochemistry.
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