Biological Molecules: Properties and Functions PDF

BIOLOGICAL MOLECULES: THEIR PROPERTIES AND FUNCTIONS BIOMOLECULES are chemical molecules that play an important role in living system. Generally, these follow the same laws of nature like other chemical molecules. However, biomolecules have specific functions, especially in a living system where th...

BIOLOGICAL MOLECULES: THEIR PROPERTIES AND FUNCTIONS BIOMOLECULES are chemical molecules that play an important role in living system. Generally, these follow the same laws of nature like other chemical molecules. However, biomolecules have specific functions, especially in a living system where they commonly act as a building materials. They are arranged from smaller and simpler molecules, called subunit, until they form a more complex structure called Macromolecules. It is important that we understand the basis of how these biomolecules functions. The human body is composed of biochemical about 80% of which is water and inorganic salts. The remaining are organic biomolecules composed of four types: carbohydrates, lipids, proteins and nucleic acids.  CARBOHYDRATES are biomolecules that are naturally polymeric in nature. They are composed of simple repeating units called monosaccharides. These monosaccharides are of three kinds: glucose, fructose and galactose. Glucose is very important because its structure permit them to be converted into a molecule called pyruvate. Pyruvate is the source of energy in the body. So without glucose, the body has limited supply of energy for it to barely survive. Two types of complex carbohydrates are the source of glucose in the body. Dietary starch and dietary glycogen. Simple carbohydrates can also be sources of glucose such as milk sugar and honey. Starch is of plant material and glycogen is present in meat. Structurally, monosaccharides are polar molecules, and hence, very soluble in water.. Their metabolism inside the body is also determined by its reactivity with enzymes called carbohydrases which react specifically with the structure of carbohydrates. A number of enzymes is responsible for the conversion of glucose molecules to pyruvate molecules. Pyruvate will then be converted to Acetyl Coenzyme A by oxidation process. Acetyl Coenzyme A will then enter a biological process called the Krebs' Cycle. The Krebs’ Cycle and glycolysis will then produce molecules called nicotinamide adenine dinucleotide (NAD) and flavine adenine dinucleotide(FAD) that will enter a process called the Electron Transport Chain (ETC). This whole process will produce molecules called adenosine triphosphate (ATP) and guanosine triphosphate (GTP). It is the ATP and GTP molecules that will undergo change to produce energy. The conversion of glucose to energy is summarized by figure 2.3 LIPIDS on the other hand, are biomolecules which are structurally diverse, unlike carbohydrates. But they do share a common feature based on their structures. LIPIDS ARE ALL NON-POLAR MOLECULES. Because of this, lipids are generally non-soluble in water but are soluble in non-polar solvents like ether and other organic solvents. The structural diversity of lipids classifies them into five different groups: energy-storage lipids, membrane lipids, messenger lipids, emulsification lipids and protective-coating lipids ENERGY-STORAGE LIPIDS – This type of lipid is also known as TRIACYL GLYCEROL (TAG). Though they are all structurally similar, TAGs are classified as FATS and OILS. There are four components: A GLYCEROL molecule, which serves as a platform molecule, and three FATTY ACIDS connected to the glycerol molecule. The difference between fats and oils is the structural feature of the three fatty acid molecules attached to the glycerol molecule. In fats, the fatty acid molecules are predominantly unsaturated fatty acids. While in oils, the fatty acid molecules are predominantly saturated fatty acids. Fats will be solid while oils will be liquid at room temperature. In terms of food source, oils are obtained from plant sources while fats are obtained from animal sources (except for fish: fishes are good sources of oils, especially deep ocean fishes like cods, tunas and mackerels). Fats and oils are stored in special cells in the body called adipocytes. These cells are present in adipose tissues present in the inside lining of the skin, in tissues lining and supporting the internal organs and in specialized structures called lipoproteins. Lipoproteins are very important in the transport of TAGs inside the body. MEMBRANE LIPIDS – membrane lipids, as the term implies, are lipids that are components of cellular membranes. This includes cell membrane and membrane of cellular organelles. There are several types of membrane lipids depending on the structure: glycerophospholipids, sphingophospholipids, sphingoglycolipids and cholesterol. Each of this type are structurally diverse. CHOLESTEROL is a membrane lipid that is imbedded inside the lipid bilayer. The cholesterol molecules inside the lipid bilayer give plasticity to the layer and give it a non-rigid property that allows it to be flexible. This flexibility allows the cell to expand or shrink as conditions inside and outside the cell changes. Excessive deposits in the arteries results in a condition known as arteriosclerosis and narrows the passageway of blood. This results in a disease known as hypertension and can lead to brain stroke and myocardial infarction (heart attack). MESSENGER LIPIDS – messenger lipids are cholesterol derivative that function as agents that deliver biological signals that trigger a tissue or organ to perform its functions. They are called hormones. Other types of hormones are made up of proteins which will be discussed later. Lipid hormones are of two principal types: steroid hormones (cholesterol derivative) which are composed of sex hormones and adrenocorticoid hormones; eicosanoids(a derivative of the 20-carbon fatty acid known as arachidonic acid) which are composed of leukotrienes, thromboxanes and prostaglandins Sex hormones are produced by the sex glands: the testes in males and the ovary in females. There are three major groups of sex hormones, one group for male and two groups for females. Androgens are the male sex hormones. The primary androgen hormone is testosterone. Testosterone controls the secondary male characteristics in male like the widening of shoulders, deepening of voice and development of facial hair. In females the two groups are estrogens and progestins. Estrogens control the secondary female characteristics like widening of the hips and enlargement of the breasts. The primary estrogen hormone of females is estradiol. Progestins are the pregnancy hormones. These hormones prepare the female body for carrying and developing fetus in her uterus. The primary progestin hormone is progesterone. The balance of estradiol and progesterone controls the menstrual cycle in females. The other steroid hormones are the adrenocorticoid hormones which are produced by the adrenal glands. There are two types of adrenocorticoid hormones: mineralocorticoid hormones and glucocorticoid hormones. Mineralocorticoids, as the name implies, control the balance of minerals in the body, specifically sodium ions (Na+) and potassium ions (K+). The major mineralocorticoid hormone is aldosterone. Glucocorticoids on the other hand control glucose metabolism and counteract inflammation. The major glucocorticoid hormone is cortisol. The eicosanoids, unlike the steroid hormones, are hormone-like substances and cannot be considered as true hormones. This is due to the fact that they are not transported in the blood stream as true hormones do. Nevertheless they are still messenger substances since they send signals to tissues to start or stop their functions. There are three major types of eicosanoids: prostaglandins,thromboxanes and leukotrienes. In the human body prostaglandins regulate bodily functions such as body temperature, inhibition of gastric juice secretion, increases mucus layer in the stomach, smooth muscle regulation and intensifying pain during injuries and other diseases. Thromboxanes promote the formation of blood clots. Leukotrienes on the other hand, promote inflammation and sensitivity responses to allergens. EMULSIFICATION LIPIDS – also called bile acids, these are lipids produced in the liver that converts dietary fats into micelles such that they become soluble in the aqueous environments of the stomach and intestines. This conversion allows enzymes to act on lipids so that they can be digested and absorbed in the digestive tract. Two important type of bile acids are cholic acids and deoxycholic acids. PROTECTIVE-COATING LIPIDS – also known as biological waxes, these lipids form a protective layer in the outer surface of plants and animals. They protect the plant or animal from water and serve lubricant function. In plants, they are found specifically in the outer layer of leaves. Other plants have waxes in their stems and flowers. In animals, they are found under the skin being produced by the sebaceous glands making the skin pliable and prevent dryness. They also protect the hair of mammal and feathers of birds. In mammals, aside from the sebaceous glands, wax is also produced in the ears. Earwax is known as It protects the ears from water and insects. PROTEINS are biomolecules that comprise most of the substances found in the body. They are biological polymers composed of 20 standard amino acids and several other non-standard amino acids. The non-standard amino acids are actually just derivatives of the 20 standard amino acids found in all living things. The 20 standard amino acids are subdivided into two large groups: Polar amino acids and Non-polar amino acids. NUCLEIC ACIDS are molecules, which just like proteins, are polymeric in nature. The units that make up the polymer molecule are called nucleotides and are actually made up of three simpler subunits: a sugar molecule, a phosphate group and a nitrogenous base. There are two types of nucleic acids depending on the sugar molecule and the nitrogenous base they contain: Ribonucleic Acid (RNA) and Deoxyribonucleic Acid (DNA). Although they are made up of different components, the primary structure basically is the same: the nucleic acids are connected in such a way that the sugar molecule of one nucleotide is connected to the phosphate group of another nucleotide in a straight chain form forming a sugar-phosphate backbone and the nitrogenous base jutting out of the backbone. Both DNA and RNA are composed of this primary structure. The difference is that RNA is smaller, single stranded and forms a variety of shape while DNA is much larger, double stranded and forms a double helix. Another difference is the sugar present: deoxyribose in DNA and ribose in RNA. The last difference is the combination of bases. Both DNA and RNA contain cytosine, guanine and adenine. But for DNA, it contains thymine and for RNA, it is uracil. RNA has five different types: messenger RNA, transfer RNA, ribosomal RNA, small nuclear RNA, and heterogeneous nuclear RNA. Each one of these has different shapes and performs different functions. While DNA carries the genetic traits of each individual, RNA performs the duty of protein synthesis. DNA is located in the nucleus of the cell. They are combined with a protein called histones to form a structure called chromosomes.Its double stranded structure allows it to self-duplicate in a complex process called DNA replication. This process allows an individual to pass its traits from generation to generation. RNA on the other hand creates proteins that the body needs in order for it to continue life processes. The process is simplified according to the following steps: Step 1: TRANSCRIPTION 1. In the cell nucleus, a portion of the DNA, called a gene is copied with the base uracil replacing the base thymine in the copying process resulting in the production of an RNA strand called heterogeneous nuclear RNA (hnRNA) 2. The hnRNA strand is then converted to messenger RNA (mRNA) by another RNA called the small nuclear RNA (snRNA). The mRNA now carries a base sequence called a code that will assemble a particular protein according to the gene copied from the DNA template. Step 2. TRANSLATION 1. The mRNA then leaves the nucleus towards the cytoplasm and attaches itself with a cellular organelle called ribosome. The ribosome is a complex structure formed by a type of RNA called ribosomal RNA (rRNA) and different protein structures. Once the mRNA is attached to the ribosome, the code it is carrying is now ready to be translated by another type of RNA called transfer RNA (tRNA). It is the tRNA that will carry the amino acids to be assembled in the ribosome. 2. The amino acids are then carried one by one by the tRNA in order of the sequence according to the code carried by the mRNA. Step 2. TRANSLATION 1. As the amino acids are being carried towards the rRNA, they are now assembled to finally form a protein that is encoded by the mRNA. 2. As the assembly is finished, the ribosome then leaves the mRNA and another ribosome attaches itself to the mRNA. But mRNA utilization is so efficient that many ribosomes attach themselves to a single mRNA strand at the same time producing a considerable amount of the same protein. This process is called polysomal protein synthesis. A polysome is a complex of several ribosomes attached to a single mRNA at the same time.