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Introduction: polarity of the molecule determines its ability to interact with water and dissolve in water YOU CAN DONWLOAD HANDOUTS AS SLIDES FROM: http://www.bristol.ac.uk/phys-pharm/media/teaching/ Chemistry of the Cell. Table salt with water The molecular composition of cells. Four major classes of biomolecules and their essential features: carbohydrates, lipids, amino acids/proteins and nucleotides and nucleic acids. Basic structure of a plasma membrane. Impact of polarity on the functional properties of biomolecules, lipophylicity and hydrophylicity. Na and Cl are charged and can interact with water! Dr. Sergey Kasparov – room E9 The main text for this lecture is: Vander’s Medical Physiology. Some additions from Germann and Stanfield and Cooper’s textbooks Introduction: polarity of the molecule determines its ability to interact with water and dissolve in water REMEMBER: polar, charged molecules dissolve in water! Introduction: polarity of the molecule determines its ability to interact with water and dissolve in water Olive oil with water Water But if oil does not dissolve in water, what does it dissolve in? Oil contains mainly nonpolar molecules! REMEMBER: non-polar, uncharged molecules DO NOT dissolve in water! Introduction: polarity of the molecule determines its ability to interact with water and dissolve in water Fight for the electron: Consider mixing… Table salt with water Olive oil with water + ELECTRONS Ions comprising NaCl are able to interact with water Oil contains mainly nonpolar molecules! Carbon Hydrogen NOT polarised ELECTRONS Carbon Oxygen Polarised 1 Four major classes of biomolecules and their essential features: carbohydrates, lipids, amino acids/proteins and nucleotides/nucleic acids. Carbohydrates… Proteins… are long chains of subunits, called amino acids. are highly polar molecules composed of “carbon atoms and water”. Monosaccharide Disaccharide Glucose GLUCOSE Fructose SUCROSE 1. Are highly polar, well soluble in water. 2. Exist as monomers, dimers and polymers. 3. Important sources of energy, components of cell membranes and the backbone of nucleic acids 4. Glucose is the ONLY source of energy for the brain. 5. Glycogen is abundant most abundant in liver but is also present in muscles. The only brain cells which contain glycogen are called astrocytes. GLYCOGEN 6. There are about 10 “glycogen storage diseases” due to various mutations in enzymes involved in its synthesis and degradation. Polysaccharide Four major classes of biomolecules and their essential features: carbohydrates, lipids, amino acids/proteins and nucleotides and nucleic acids. Lipids… are composed largely of carbon and hydrogen atoms and therefore are nonpolar. All amino acids have the same backbone but different side chains. It is the side chains which actually make all the difference! Amino acids get connected together and form long chains (sometimes > 1000 amino acids). These chains are called PROTEINS 1 Fatty acid Glycerol 2 Triglycerol (fat) 4 Steroid 3 Phospholipid 1. Fatty acids are nonpolar, waterinsoluble molecules. They are used to store energy. 2. Phospholipids have a polar “head” and nonpolar fatty acid “tails”. They are amphipathic. In water they form clusters. In the cells they are the essential component of all membranes. 3. Steroids have 4 cycles of carbon atoms and are important components of plasma membrane and also act as signalling molecules. Phospholipids: the building blocks of cellular membrane Macro-molecular complex protein haemoglobin consists of 4 individual protein chains Phospholipid bi-layer is the key component of all cellular membranes The structure and function of proteins are determined by the amino acid composition. Structural and functional blocks/parts of a protein is often referred to as “domains” (e.g. “catalytic domain” or “regulatory domain”). The key aminoacids which are responsible for the function of a domain are usually conserved throughout evolution. We can trace some of the domains in our proteins back to the yeast cells. 2 Nucleic Acids (DNA and RNA) contain and handle the information in the cell. H RNA = ribonucleic acid DNA = deoxyribonucleic acid The plasma membrane of a cell consists of the phospholipid bi-layer and numerous proteins embedded in it. REMINDER: polar molecules solve well in water. And non-polar … in what? DNA is built of numerous nucleotides connected via phosphoric acid residues Nucleic Acids (DNA and RNA) contain and handle the information in the cell. 1. DNA and RNA are polymer molecules. Their subunits are called nucleotides. 2. Four different nucleotides are found in DNA and RNA (3 are the same in both) 3. Sequence of nucleotides is the genetic code of the cell as it determines the sequence of amino acids in the proteins Other interesting facts about nucleic acids: 1. 2. 3. 4. 5. 6. RNA can not only carry information but also perform functions, similar to proteins: in the ribosome where the proteins are made it is the RNA which obviously joins the amino acids together. There are also “rybozymes” – species of RNA which can attack and destroy other RNAs. Nucleotides give rise to ATP. ATP is the universal energy currency of the cell but also perhaps the most archaic cell-to cell signalling molecule. Viruses have genomes encoded in either DNA or RNA form. Some viruses can use RNA as a template to generate DNA (e.g. information flows in reverse direction). DNA is almost always double-stranded while RNA is usually single-stranded. Because of that RNA often folds on itself forming hairpin-like structures. NOT all the DNA in the cell is located in the nucleus, mitochondria have their own genomes which are different from the main one. In order for a molecule to be inside the lipid bi-layer it needs to … = non-polar, hydrophobic COOH NH2 = polar or charged, hydrophilic Some Functions of (INTEGRAL) Membrane proteins Receptor – detects chemical signals A channel (leak) Anchoring/connecting effect Carriers A gated channel Chemical reactions 3 The Key Points: 1. Polar & charged molecules dissolve in water while non-polar dissolve in oil/fat/lipid media 2. Carbohydrates (sugars) exist as monomers, dimers or polymers. They are polar molecules and are serve as sources of energy and components of other molecules, such as nucleic acids. 3. There are 4 main classes of lipids (fatty acids, triglycerides, phospholipids and steroids). Most lipids are water-insoluble but phospholipids are amphipathic (= have hydrophobic “tails” and hydrophilic “heads”). They are the essential components of all membranes. 4. Proteins are long stretches of amino acids. Their structure and function is determined by the sequence of amino acids. They are responsible for all cellular activities / functions. 5. Nucleic acids (RNA and DNA) are long stretches of nucleotides. There are 4 kinds of nucleotides in RNA and DNA. DNA encodes all the information in the cell and encodes all the proteins while RNA is responsible for the transfer of this information to the places where the proteins are being produced. 6. Some proteins are embedded into the cell membrane. This is possible because their sequences have parts enriched in hydrophobic (non-polar) amino acids. These parts form “membrane-spanning domains”. 4