Lecture 5 to 6: Structure and Function of Large Biological Molecules PDF

Student will be able to explain: 1. Describe that Macromolecules are polymers built from monomers. 2. Describe that Carbohydrates is the Structural and Functional Molecules of Life. Page 66 – 72 The Molecules of Life...

Student will be able to explain: 1. Describe that Macromolecules are polymers built from monomers. 2. Describe that Carbohydrates is the Structural and Functional Molecules of Life. Page 66 – 72 The Molecules of Life All living things are made up of four classes of large biological molecules: Carbohydrates, Lipids, Proteins, and Nucleic Acids. Macromolecules are large molecules composed of thousands of covalently connected atoms. Large biological molecules exhibits unique properties from the orderly arrangements of their atoms. A polymer is a long molecule consisting of many similar building blocks. These small building-block molecules are called monomers. Three of the four classes of life’s organic molecules are polymers.  Carbohydrates  Proteins  Nucleic acids  Lipids: Not big enough to be considered as macromolecules Page 66 The Synthesis and Breakdown of Polymers Dehydration : It occurs when two monomers bond together through the loss of a water molecule (Fig 5.2 a); One monomer provides a Hydroxyl (˗OH), while the other provides a Hydrogen (˗H). Hydrolysis: Polymers are disassembled to monomers by hydrolysis (addition of water), a reaction that is essentially the reverse of the dehydration reaction (Fig 5.2 b). ✓ eg. Digestion (Break down) and Protein building using Enzymes. Page 67 Concept 5.2: Carbohydrates serve as fuel and building material Carbohydrates include sugars and the polymers of sugars. The simplest carbohydrates are Monosaccharides, or single sugars. Carbohydrate macromolecules are Polysaccharides, polymers composed of many sugar building blocks. Sugars: Monosaccharides have molecular formulas that are usually multiples of CH2O Glucose (C6H12O6) is the most common monosaccharide. Monosaccharides are classified by ✓ The location of the carbonyl group (as Aldose or Ketose). ✓ The number of carbons in the carbon skeleton. Apart from Hexoses (6C); Pentoses (5C) and Trisoses (3C) are also common. Page 68  Sugars drawn as linear skeletons, in aqueous solutions many sugars form rings. Monosaccharides serve as a major fuel for cellular work, Eg. Breakdown of Glucose molecules into series of reactions, by the process of Cellular Respiration. It is also a raw material for synthesis and building molecules such as Amino acids and Fatty acids. When not utilized these monomers are incorporated into Disaccharides or Polysaccharides. Page 69  Disaccharides is formed when a dehydration reaction joins two monosaccharides. Covalent bond between two monosaccharide is called a Glycosidic linkage. o Eg. Plants transport these carb from leaves to roots as Sucrose (Fig. 5.5 b). o Lactose in milk is formed from joining Glucose molecule with Galactose molecule. Page 69  Polysaccharides (Polymers of Sugars) have storage and structural roles. The structure and function of a polysaccharide are determined by its sugar monomers and by the positions of its glycosidic linkages. 1 – Storage Polysaccharides: ❑ A – Starch, a storage polysaccharide of plants, consists entirely of glucose monomers. Plants store starch as granules within Chloroplasts and other Plastids. The simplest form of starch is Amylose (unbranched) and Amylopectin (some what branched). Page 70 Figure 5.6 Page 70 ❑ B – Glycogen is a storage polysaccharide in animals. Humans and other vertebrates store glycogen mainly in Liver and Muscle cells. Hydrolysis of glycogen in these cells releases glucose when the demand for sugar increases. In animals, glycogen storage gets depleted in about a day, unless they are replenished by consumption of food and low carb diet results in weakness and fatigue. 2 – Structural Polysaccharides: ❑ A – Cellulose: This polysaccharide is a major component of the tough wall of plant cells. Like starch, cellulose is a polymer of glucose, but the glycosidic linkages differs. The difference is based on two ring forms: Alpha () and Beta (). Page 71  Polymers with  glucose are helical (see Fig 5.6a and 5.7b Starch). Polymers with  glucose are straight (see Fig 5.6c Fig 5.7c Cellulose). Parallel cellulose molecules are held together and grouped into units called Microfibrils, which form strong building materials for plants and for humans in making paper and cotton. In Human, cellulose is not a nutrient but is a part of healthful diet. Page 71  Cellulose in human food passes through the digestive tract as insoluble fiber. Some microbes use enzymes to digest cellulose. Many herbivores, from Cows and Termites, have symbiotic relationships with these microbes. N- acetylglucosamine ❑ B – Chitin, its and another structural polysaccharide found as the exoskeleton of Arthropods. Chitin also provides structural support for the cell walls of many fungi. Page 72 Concept 5.3: Lipids are a diverse group of hydrophobic molecules Lipids are the one class of large biological molecules that do not form polymers. Lipids is having little or no affinity for water. Lipids are hydrophobic because they consist mostly of hydrocarbons, which form non-polar covalent bonds. The most biologically important lipids are fats, phospholipids, and steroids. 1 – Fats Components Fats are constructed from two types of smaller molecules: Glycerol and Fatty acids. 1) Glycerol is a three-carbon alcohol with a hydroxyl group attached to each carbon. 2) Fatty acid consists of a carboxyl group attached to a long carbon skeleton. Page 72  Fats separate from water because water molecules form hydrogen bonds with each other and exclude the fats. In a fat, three fatty acids are joined to glycerol by an ‘Ester linkage’, creating a Triacylglycerol, or Triglyceride. The fatty acids in a fat can be all the same or of two or three different kinds. Page 73  Fatty acids vary in length (number of carbons) and in the number and locations of double bonds. Saturated fatty acids have the maximum number of hydrogen atoms possible and no double bonds. Unsaturated fatty acids have one or more double bonds. Page 73  Fats made from saturated fatty acids are called Saturated fats and are solid at room temperature. Most animal fats are saturated Eg. Lard (Pig fat) and Butter (Dairy product). Plant fats (Olive) and fish fats (Cod liver) are usually Unsaturated fats. A diet rich in saturated fats may contribute to Cardiovascular disease through plaque deposits. Hydrogenation is the process of converting Unsaturated fats to Saturated fats by adding Hydrogen (Hydrogenating Vegetable Oils) Eg. Peanut butter and Margarine (Trans-unsaturated Fats). The major function of fats is energy storage. Humans and other mammals store their fat in Adipose cells. Adipose tissue also cushions vital organs and insulates the body. ‫وسائد األعضاء الحيوية‬ ‫يعزل الجسم‬ Page 74 2 – Phospholipids In a Phospholipid, two fatty acids and a phosphate group are attached to glycerol. The two fatty acid tails are hydrophobic, but the phosphate group and its attachments form a hydrophilic head. When phospholipids are added to water, they self- assemble into a bilayer, with the hydrophobic tails pointing toward the interior. The structure of phospholipids results in a bilayer arrangement found in cell membranes. Phospholipids are the major component of all cell membranes. Page 74 Page 74 3 – Steroids Steroids are lipids characterized by a carbon skeleton consisting of four fused rings. Cholesterol, an important steroid, is a component in Cholesterol animal cell membranes and acts as precursor for sex C27H46O hormones. Although cholesterol is essential in animals, it is synthesized in the liver and as well as can be obtained from diet High levels in the blood may contribute to Atherosclerosis Page 75 Concept 5.4: Proteins include a diversity of structures, resulting in a wide range of functions Proteins account for more than 50% of the dry mass of most cells. Protein functions include - Structural support, Storage, Transport, Cellular communications, Movement, and Defense against foreign substances Human protein are diverse in nature and 10’s of 1000’s of different protein are derived from the set of 20 amino acid. The bond between amino acids is called peptide bond, so polymer chain is called as polypeptide. They fold and coil into specific 3D structures. Page 75 An Overview of Protein Functions Page 76 An Overview of Protein Functions Page 76 Amino Acid (AA) Monomer Amino acids are organic molecules with carboxyl and amino groups. Amino acids differ in their properties due to differing side chains, called R groups. At the center of the amino acid is a asymmetric carbon atom called Alpha (α) carbon. The 4 different partners of amino acid monomers are 1) Amino Group 2) Carboxyl Group 3) Hydrogen Atom, and 4) Variable Group, Symbol R (also called side chain, differ with each amino acid) Page 75 Amino Acid Polymers Amino acids are linked by peptide bonds. A polypeptide is a polymer of amino acids. Polypeptides range in length from a few to more than a 1000’s of AA monomers. Each polypeptide has a sequence of amino acids, with a carboxyl end (C-terminus) and an amino end (N-terminus). In a polypeptide, the chemical nature of the molecule as a whole is determined by the kind and sequence of side chains. Page 78 Protein Structure and Function The specific activities of proteins results from their intricate 3D architecture. A functional protein consists of one or more polypeptides precisely twisted, folded, and coiled into a unique shape. The sequence of amino acids determines a protein’s three-dimensional structure. A protein’s structure determines its function. The function of a protein usually depends on its ability to recognize and bind to some other molecule. Many protein are roughly spherical (globular protein), while other are shaped like long fibers (fibrous protein). Page 78 Concept 5.5: Nucleic acids store, transmit, and help express hereditary information The amino acid sequence of a polypeptide is programmed by a unit of inheritance called a gene. Genes are made of DNA, a nucleic acid made of monomers called nucleotides. The Roles of Nucleic Acids There are two types of nucleic acids 1) Deoxyribonucleic acid (DNA) and 2) Ribonucleic acid (RNA) DNA provides directions for its own replication (separation). DNA directs synthesis of messenger RNA (mRNA) and, through mRNA, controls protein synthesis. Protein synthesis occurs on Ribosomes and this process is called Gene expression. Page 84  GENE EXPRESSION DNA → RNA → PROTEIN In a eukaryotic cell, DNA in the nucleus programs protein production in the cytoplasm by dictating synthesis of messenger RNA (mRNA). Prokaryotic cell lack nuclei but still use mRNA to convey message from the DNA to ribosomes and other amino acid sequences. Page 84 – 85 The Components of Nucleic Acids Each nucleotide consists of a nitrogenous base, a pentose sugar, and one Nucleic acids are polymers called polynucleotides. or more phosphate groups. Each polynucleotide is made of monomers called The portion of a nucleotide without the nucleotides. phosphate group is called a nucleoside. Each nitrogenous base has one or two rings that include nitrogen atoms. Page 85  There are two families of nitrogenous bases ❖ Pyrimidines include Cytosine (C), Thymine (T), and Uracil (U). ❖ Purines include Adenine (A) and Guanine (G). Thymine is found only in DNA, and Uracil only in RNA; the rest are found in both DNA and RNA. The sugar in DNA is deoxyribose; and in RNA, it is ribose. The only difference between these two sugars is that deoxyribose lacks an oxygen atom on the second carbon in the ring; hence the name deoxyribose. A nucleoside with at least one phosphate attached to the 5’C of the sugar builds up as monophosphate, more often called a nucleotide. Page 86  The nitrogenous bases in DNA pair up and form hydrogen bonds. This is called complementary base pairing. Page 86  RNA molecule, by contrast exist as single strands (single helix). Complementary base pairing can occur creating a 3D shape necessary for its function eg. Transfer RNA (tRNA). tRNA, brings required amino acid molecules to the ribosome during the synthesis of a polypeptide. A tRNA molecule is about 80 nucleotides in length. Note in RNA, Adenine (A) pairs with Uracil (U); and Thymine (T) is not present in RNA. RNA molecule are more variable in shape and very versatile. Biologist, consider that RNA may have preceded DNA as the carrier of genetic information in early forms of life. Page 86  Types of RNA Messenger RNA (mRNA), carries instruction for polypeptide synthesis to ribosome. Transfer RNA (tRNA), carries amino acids to the ribosome and matches them to the coded mRNA. Ribosomal RNA (rRNA), forms protein polymer chain.  the end ☺