Medical Biology Lecture Notes (University of Mosul) PDF

University of Mosul College of Medicine Lecture: (2) Subject/year: Medical Biology / 1st year Lecturer: Inaam A. Abdulhameed Department : Anatomy Date:17/11/2024 The AIM of this lecture is To understand the structure and the functions of molecular components of living organi...

University of Mosul College of Medicine Lecture: (2) Subject/year: Medical Biology / 1st year Lecturer: Inaam A. Abdulhameed Department : Anatomy Date:17/11/2024 The AIM of this lecture is To understand the structure and the functions of molecular components of living organisms. Intended learning outcomes: By the end of this lecture the student will be able to: 1. Determine the functions of water in living organsms. 2. Summarize the structure of the pH scale and the importance of buffers to biological systems. 3. Describe the four major types of biological molecules. 4. Understand the functions of the four major types of molecules.  The Molecular Composition of Cells  Cells are composed of water, inorganic ions, and organic molecules.  Water is the most abundant molecule in cells, accounting for 70% or more of total cell mass.  Functions of water in the body:  Water is the primary building block of cells.  It regulates our internal body temperature by sweating and respiration.  The carbohydrates and proteins that our bodies use as food are metabolized and transported by water in the bloodstream.  It assists in flushing waste mainly through urination.  Acts as a shock absorber for brain, spinal cord, and fetus.  Forms saliva.  Lubricates joints.  Acids and Basses Acids are substances that dissociate in water, releasing hydrogen ions (H+). For example, an important inorganic acid is hydrochloric acid (HCl), which dissociates in this manner: Bases are substances that either take up hydrogen ions (H+) or release hydroxide ions (OH−). For example, an important base is sodium hydroxide (NaOH), which dissociates almost completely in this manner:  pH scale The pH scale is used to indicate the acidity and basicity of a solution.The pH scale ranges from 0 to 14, with 0 being the most acidic and 14 being the most basic. A solution at pH 7 (neutral pH).  Buffers A buffer refers to a solution that resists changes in pH when small amounts of an acid or a base are added. Buffers are crucial in maintaining stable pH levels in biological systems, which is essential for proper cellular function and metabolic processes.  The inorganic ions The inorganic ions of the cell, including sodium (Na+), potassium (K+), magnesium (Mg2+), calcium (Ca2+), phosphate (HPO42-), chloride (Cl-), and bicarbonate (HCO3-), constitute 1% or less of the cell mass. These ions are involved in a number of aspects of cell metabolism, and thus play critical roles in cell function.  Organic Compounds: In biology, “organic” refers to a molecule that contains carbon (C) and hydrogen (H) and is usually associated with living organisms. Organic molecules are classified into four types: 1. carbohydrates 2. lipids 3. proteins 4. nucleic acids Biological molecules tend to be very large and are built of repeating units of smaller molecules. These small subunits that make up larger biological molecules are called monomers. 1- Carbohydrates Carbohydrates are almost universally used as an energy source for living organisms, including humans. In some organisms, such as plants and bacteria, carbohydrates have a structural function. They are made up of carbon, hydrogen and oxygen. The ratio of hydrogen to oxygen atoms in a molecule usually 2:1. Carbohydrates are classified into three subtypes: monosaccharides, disaccharides, and polysaccharides. - Monosaccharides Monosaccharides consist of only a single sugar molecule and are commonly called simple sugars. The most common monosaccharide, and the one that our bodies use as an immediate source of energy, is glucose. Other common monosaccharides are fructose, found in fruits, and galactose, which is found in milk. - Disaccharides Two monosaccharides can form a covalent bond between them to form a disaccharide sugar. Three important disaccharides are also found in living things: maltose, sucrose, and lactose. - Polysaccharides A long chain of monosaccharides linked by covalent bonds is known as a polysaccharide. Starch, glycogen , and cellulose are examples of polysaccharides. Starch is the stored form of sugars in plants Glycogen is the form in which glucose is stored in the human liver. 2- Lipids Lipids are diverse in structure and function, but they have a common characteristic: They do not dissolve in water. They contain little oxygen and consist mostly of carbon and hydrogen atoms. Lipids perform many different functions in a cell: 1. Cells store energy for long-term use in the form of fats. 2. Lipids are the building blocks of many hormones. 3. Lipids are an important constituent of all cellular membranes. Lipids include fats, oils, waxes, phospholipids, and steroids. - Fats and Oils The most familiar lipids are called the triglycerides. You may commonly know these as fats and oils. The term triglyceride refers to the three-part structure of the molecule. Triglycerides are formed when one glycerol molecule reacts with three fatty acid molecules. A fatty acid is a carbon-hydrogen chain that ends with the acidic group — COOH. Fatty acids are either saturated or unsaturated. ⦁ Saturated fatty acids have no double bonds between the carbon atoms. The chain is saturated with all the hydrogens it can hold , and they are solid at room temperature. ⦁ Unsaturated fatty acids have double bonds in the carbon chain wherever the number of hydrogens is less than two per carbon , and they are liquid at room temperature. - Phospholipids The phospholipid molecule is similar to a fat except that the third fatty acid is replaced by a phosphate group. The phosphate end of the molecule will dissolve in water and is said to be hydrophilic (“likes water”). The fatty acid end of the molecule repels water and is called hydrophobic (“fears water”). Phospholipids are a major component of the cell membranes. - Steroids Steroids are lipids that have an entirely different structure from those of fats. Steroid molecules have a backbone of four fused carbon rings. One example of a steroid is cholesterol. Cholesterol is a component of an animal cell’s plasma membrane and is the precursor of several other steroids, such as the sex hormones estrogen and testosterone. 3- Proteins Proteins are macromolecules with amino acid subunits.There are 20 kinds of amino acids. One protein differs from another by the number and arrangement of the 20 different amino acids. The primary structure of a protein is a long chain made of many amino acids. The long chain of amino acids twists and folds on itself to produce the final shape of a protein  Proteins are of primary importance in the structure and function of cells. Some of their many functions in humans include:  Support: Some proteins are structural proteins. Keratin, for example, makes up hair and nails. Collagen lends support to ligaments, tendons, and skin.  Enzymes: Enzymes bring reactants together and thereby speed chemical reactions in cells.  Transport: Channel and carrier proteins in the plasma membrane allow substances to enter and exit cells. Some other proteins transport molecules in the blood of animals; hemoglobin in red blood cells is a complex protein that transports oxygen.  Defense: Antibodies are proteins. They combine with foreign sub stances, called antigens. In this way, they prevent antigens from destroying cells.  Hormones: Hormones are regulatory proteins. They serve as intercellular messengers that influence the metabolism of cells. The hormone insulin regulates the content of glucose in the blood and in cells. The presence of growth hormone determines the height of an individual.  Motion: The contractile proteins actin and myosin allow parts of cells to move and cause muscles to contract. 4- Nucleic acids Nucleic acids are key macromolecules in the continuity of life. They carry the genetic blueprint of a cell and carry instructions for the functioning of the cell. The two main types of nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). DNA is the genetic material found in all living organisms. The other type of nucleic acid, RNA, is mostly involved in protein synthesis. DNA and RNA are made up of monomers known as nucleotides. Each nucleotide is made up of three components: a nitrogenous base, a pentose (five-carbon) sugar, and a phosphate group.  The nucleotides in DNA contain the sugar deoxyribose, and the nucleotides in RNA contain the sugar ribose. There are four different types of bases in DNA: adenine (A), thymine (T), guanine (G), and cytosine (C).In RNA, the base uracil (U) replaces the base thymine. DNA is double-stranded, with the two strands twisted about each other in the form of a double helix. RNA molecules are single- stranded. To summarize: - Water is the most abundant molecule in living organisms.Water serves a number of essential functions in the body. - The pH scale reflects whether a solution is acid or basic (alkaline). - Buffers help cells and organisms maintain a constant pH. - Carbohydrates, lipids, proteins, and nucleic acids are organic molecules with specific functions in cells  Lets check our knowlege Choose the best answer for each question. 1- An example of a polysaccharide used for energy storage in humans is a. cellulose. b. cholesterol. c. glycogen. D. Starch 2-Saturated and unsaturated fatty acids differ in the a. number of carbon-to-carbon double bonds. b. consistency at room temperature. c. number of hydrogen atoms present. d. All of these are correct. References and recommended further readings: 1. Madder, S., S., and Windelelspecht, M., Human biology, 17th ed. Mc Graw – hill, USA, 2023. 2. Sylvia S. Madder, Biology, 6th ed. Mc Graw-Hill Education, USA,1999.