Health Sciences I - Lecture 1: The Ingredients of Life PDF

Lecture 1: The Ingredients of Life Dr Isabel Hwang Division of Education School of Biomedical Sciences [email protected] E-mail: [email protected] Office number: 3943 6795 Copyright © 2024 The Chinese University of Hong Kong (viewing right is offered to CU...

Lecture 1: The Ingredients of Life Dr Isabel Hwang Division of Education School of Biomedical Sciences [email protected] E-mail: [email protected] Office number: 3943 6795 Copyright © 2024 The Chinese University of Hong Kong (viewing right is offered to CUHK students in MEDF1011 only) 1  LECTURE OUTLINE Part 1 Why certain elements are essential to human functions Major intracellular and extracellular ions (solutes) in plasma and their physiological functions How to represent concentrations in plasma and blood samples Life depends on water molecules and hydrogen bonds Surface tension and its biomedical uses Relationship between surface tension and surfactants Part 2 Major macromolecules important for human life (carbohydrates and proteins) Copyright © 2023 The Chinese University of Hong Kong 2 Learning outcomes ⚫ Identify major intracellular and extracellular elements (or their ionic form) and state their major functions in the body ⚫ Recall the normal physiological concentrations of important ions (solutes) in plasma/serum ⚫ Define molarity with a formula and a common physiological unit ⚫ Define hydrogen bonding and describes its function(s) in human body ⚫ Summarise how life depends on water molecules with examples ⚫ Recall concept and medical uses of surface tension in meniscus formation ⚫ Summarise the physiological roles of pulmonary surfactant ⚫ Describe how a deficiency in pulmonary surfactant leads to newborn respiratory distress syndrome (NRDS) ⚫ List major classes of organic molecules that are important to life ⚫ Identify the different types of bonds that form carbohydrates and proteins ⚫ Define the 4 levels of protein structure with examples ⚫ Identify the additional bonds that stabilize the structure of polypeptide chain ⚫ Differentiate between fibrous and globular proteins with examples 3 Micro-module 1 on Blackboard 4 A case of low potassium (K+) level (hypokalemia) Sex: Male Age: 50 Medical history: no chronic illness ❖ He had waited for many hours in Prince of Wales Hospital before he could see a medical doctor in the A&E unit Clinical examination Plasma measurement Acute onset of muscle weakness [Na+] = 140 mmol/L (normal: 135- (more prominent in the lower limbs) 145 mmol/L) Dry tongue [K+] = 2.5 mmol/L (normal: 3.5-5.0 Low urine output mmol/L) Fatigue 5 What is the difference between blood and plasma? Is one of the key components of the circulatory system including the heart and blood vessels (lectures 6 & 7). Blood is composed of formed elements (cells and cell fragments) suspended in a liquid called plasma, which is mostly water. Plasma (55-60% of blood volume) Can decrease with dehydration in the heat and during exercise Contains water, inorganic salts and proteins Buffy coat (95% of a living organism is made up of these 4 elements Element Important Physiological importance electrolyte for this course Calcium (Ca) Ca2+ Nerve impulse, muscle contraction, blood clotting, structure of bone Carbon (C) Principal element in organic compounds such as carbohydrates and proteins Chlorine (Cl) Cl− Major extracellular anion (negatively charged ion, counter ion of Na+) Hydrogen (H) H+ Component of all organic compounds, important for acid and base balance Iron (Fe) Component of haemoglobin (form structure of the haem) Nitrogen (N) Component of amines, amino acids, and nucleic acids Oxygen (O) Necessary life functions (cellular respirations) Phosphorus (P) Component of adenosine triphosphate (ATP): the body’s chemical form of energy Potassium (K) K+ Major intracellular cation (positively charged ion), nerve impulse Sodium (Na) Na+ Major extracellular cation, fluid balance, blood pressure, nerve impulse 9 9 Compounds Substances contain atoms of more than one kind are joined together by chemical bonds. Formula given for convenience and to reduce labor of writing E.g. Sodium Chloride (NaCl) Common names for lay people is called table salt Elements not always in equal proportions E.g. Carbon dioxide (CO2) Exhaled waste product of cellular respiration Respiratory stimulant found on anesthetic machines 10 Common name used in medicine & healthcare practice 0.9% sodium chloride (NaCl) – Common name in medicine is called normal saline or physiological saline which is a sterile (free from micro- organism), non-pyrogenic (free from fever-causing substances) solution for fluid and electrolyte replenishment – Classified as volume expander and electrolyte replacement (Lecture 8) for intravenous infusion (drip) Expression of concentration: 0.9% NaCl = 0.9g NaCl in 100ml H2O 11 The structure of the atom and its atomic symbol Atom forms the smallest particle of an element that retains the characteristics of that element – Is made up of subatomic or elementary particles such as protons, neutrons and electrons – Protons and neutrons have equal mass, but the mass of the electrons is negligible The atomic symbol The atomic number is the number of the protons an atom contains and it is given as a subscript before the element symbol The mass number is the sum of the number of protons and neutrons and it is given as a numerical superscript before the element symbol 12 Chemical bonding Ionic bonds Covalent bonds Formed by transfer of electrons Formed by sharing of electrons Involve the formation of oppositely charged ions that attract each other Ionic compounds tend to have high Covalent compounds tend to have low melting points and are soluble in polar melting points and dissolve in non-polar solvents such as water solvents such as alcohol E.g. NaCl E.g. H2O, O2, CO2 An excess of protons (+) or electrons (−) in an atom or molecule creates ions that are positively or negatively charged. Positively charged ions such as sodium (Na+) and called cations; negatively charged ions such as chloride (Cl−) or many proteins are called anions. 13  Implications forhealth Implications for health Hypernatremia is a condition when plasma/serum Na+ ion level is higher than normal. Na+ (and Cl−) ions attract water Substances that have polar or ionized groups (e.g. NaCl) dissolve in Na+ (and Cl−) ions retain water water by being electrically attracted to the polar water water molecules Na+ affects water balance (i.e. blood volume) Na+ indirectly affects blood pressure called mean arterial pressure, MAP, lectures 6 & 7) 14 Hydrogen bonding Are weak attractive forces that exist between polar molecules. A polar molecule is a molecule in which A non-polar molecule does not have the one end of the molecule is slightly positive, charges present at the end of the molecule while the other end is slightly negative When two polar molecules are in close contact, an electrical attraction may form between them Water is attracted to other water molecules by hydrogen bonds Rule: Like charges repel each other and unlike charges attract 15 Hydrogen bonding Other examples of hydrogen bonds occurs in proteins and deoxyribonucleic acid (DNA) Dotted lines ( ) represent hydrogen bonds formed 16 Molecular formula and structural formula Molecular formula = the number of each of the atoms present in a molecule Structural formula = the number of each of the atoms present and their structural arrangement Compounds can have same molecular formula, but different structural formula and they are called isomers E.g. glucose, fructose and galactose -D-Glucose (cyclic) – In ileum, fructose and galactose are subsequently converted into glucose as only glucose can be used as a source of energy 17  Molecular mass The molecular mass of a compound is the sum of the relative atomic masses of the elements that make up a compound. E.g. Glucose (C6H12O6) Leads us to another level of concept called molarity (mmol/L) which is an expression of concentration. Please refer to micro-module 7 for the practice examples to represent concentrations in a plasma sample 18 Application of molarity in medicine Commonly used to express concentrations of substances – dissolved in blood, plasma, serum, intravenous fluids or solutions of drugs The concentrations of solutes (substances dissolved in a liquid) are key to their ability to produce physiological function(s). 19 What is a solute? A solute is a substance that can be dissolved into a solution by a solvent. A solvent is a substance in which a solute is dissolved Solutes can be classified as non-electrolytes or electrolytes Non-electrolytes Electrolytes Mostly organic Mostly inorganic Do not dissociate in water Dissociate in water into particles called ions E.g. NaCl → Na+ + Cl− No charged particles created Charged particle created E.g., glucose, lipids, creatinine, and E.g. Na+, K+, Cl−, H+, and some urea proteins 20 Practice example: To calculate the molarity of NaCl in a plasma sample Molarity (mmol/L or mM) is the concentration measured in number of moles of solute per volume of solution – A mole (mol) of a compound is the amount of the compound in grams equal to its molecular mass Practice example: If we dissolve 0.9 g of NaCl powder into 100 ml (= 0.1L) of pure water, what will be the molarity of the dissolved solution containing dissociated Na+ and Cl− ions? Molecular (molar) mass of NaCl = (atomic mass of Na + atomic mass of Cl) = (23 + 35.5) = 58.5 No. of moles of NaCl powder = mass / molecular mass = 0.9g / 58.5 gmol-1 = 0.015 mol Molarity of NaCl = number of moles/volume = 0.015/ 0.1 mol/L = 0.15 mol/L or 0.15 M or 153 mmol/L 21 Life depends on water molecules Life is established on water-based or aqueous solutions that are quite similar to dilute seawater in terms of ionic composition. Is the most abundant Is a good physiological Acts as a substance found in human solvent for both lubricant body and comprises about electrolytes and non- 60% of the total body weight electrolytes, i.e. dissolves things well Is required for a variety Provides an optimal of metabolic processes medium in which that are necessary for cells can function survival Is the major transport component of the Breaks down food body particles into smaller components in the digestive system Aids in thermoregulation Provides cushioning 22 Surface tension A term used to describe the observation that the surface of a liquid behaves as though tense as a consequence of forces of cohesion Cohesion Adhesion Forces of attraction between Forces of attraction between dissimilar like molecules molecules E.g. water droplets E.g. attraction between molecules of a liquid and the glass of the container in which they are held Cohesive and adhesive Concave Convex forces lead to the formation of meniscus which is the bending of the liquid surface 23 Meniscus formation and manometer reading A meniscus is a curve in the upper surface of a liquid when it touches the surface of the container Water Mercury Adhesive forces > cohesive forces → Cohesive forces > adhesive forces → bowl-shaped (concave) meniscus dome-shaped (convex) meniscus ❖ Measured at the center of the meniscus, ✓ the bottom of a concave meniscus or ✓ the top of a convex meniscus A Manometer is a device in which pressure is measured by means of a vertical column of fluid – E.g. Measurement of arterial blood pressure with a mercury sphygmomanometer; Measurement of central venous pressure (CVP) with a saline manometer Reference: Page 61-62. Chapter 4, Basic Concepts in Biomedical Sciences I 24 Surfactants improves lung function by reducing surface tension The lungs are made up of alveoli which are air sacs, the site of gaseous exchange Each alveolus is lined with a film of alveolar fluid. 300-500 millions alveoli in the lungs Rich blood supply of capillaries 3 types of cells Type I alveolar Type II alveolar cells Alveolar cells macrophages Make up wall of Secrete surfactant Role for alveoli, site of to lower surface immune system gaseous tension of the exchange alveolar fluid Reference: https://www.ncbi.nlm.nih.gov/books/NBK557542/ 25 Surfactants reduces surface tension in the lungs Alveoli are lined with pulmonary surfactant that act as a film to keep alveoli open by reducing the cohesive forces between water molecules Surfactant lubricates the alveoli and allowing them expand without over-stretching and to get smaller without collapsing Produced by type II alveolar cells (A) (B) Without surfactants, solid arrows With surfactant coating, broken represent strong attractive forces that arrows represent reduced tension leads to alveolar collapse leading to lung stability Source of image: Fathi-Azarbayjani A., Jouyban A., BioImpacts, 2015, 5(1), 29-44 26 Newborn Respiratory Distress Syndrome (NRDS) Newborn RDS is a life-threatening breathing disorder of premature newborns which commences at (or soon after) birth — Most seen in babies before 28th week The alveoli collapse in the newborn’s lungs and do not remain open due to absence or insufficient production of surfactant — Surfactants are normally produced between 34th and 36th week of pregnancy Management: Breathing support Artificial surfactant 27 Organic molecules of living organisms Organic molecules are substances that contain carbon and accounts for 18% of the body weight Aliphatic Cyclic Alcohols, aldehydes, ketones, Exhibits characteristic smell- carboxylic acids and amines aromatic Most components of the diet are not only organic but polymers which are chains of similar units called monomers (building blocks) Components of the diet can be divided into 7 groups Carbohydrate Proteins Lipids s Vitamins Minerals Water Fiber 28 Macromolecules are synthesized and broken down within the cell Dehydration (condensation) – Removes the equivalent of a water molecule to link molecular units – Builds macromolecules from smaller subunits Hydrolysis – Adds the equivalent of a water molecule to break apart macromolecules Dehydration synthesis is the reverse of hydrolysis 29 Carbohydrates Contains carbon, hydrogen and oxygen atoms The presence of the polar hydroxyl (-O-H) groups makes carbohydrates soluble in water It has a general formula of Cn(H20)n or (CH2O)n and a typical ratio of C, H and O as 1: 2: 1 3 classes: 1. Monosaccharides 2. Disaccharides 3. Polysaccharides (one sugars) (double sugars) (complex sugars) Examples of one sugar (C6H12O6): The most abundant monosaccharide in the body is glucose, which is stored in cells in the form of polysaccharide glycogen 30 Oligosaccharides: more than one mono- saccharide linked together Monosaccharides can be linked together via dehydration synthesis Disaccharides: two monosaccharides linked together Too large to pass through plasma membrane Sucrose Maltose Lactose Glucose + Fructose Glucose + Glucose Glucose + Galactose Digested by sucrase Digested by maltase Digested by lactase 31  Polysaccharides store energy Glycogen is highly branched polysaccharide composed of thousands of glucose subunits and is the major carbohydrate storage form in body Hydrolysis of glycogen, as occurs during periods of fasting, leads to release of the glucose monomers into the blood Preventing blood glucose from decreasing to dangerously low levels 32 Reference: Page 160-161. Chapter 7, Basic Concepts in Biomedical Sciences I 32 Proteins Long chains (polymers) of subunits called amino acids Amino acids – Are linked by covalent bonds (peptide bonds) via dehydration – Contain amino group and carboxyl group – Can act as either acid or base The general structure of amino – All identical except for “R group” which represents a acids H atom or chain of C atoms with H atoms attached Protein No of polypeptide Non-protein Function chains component Hemoglobin 4 Heme pigment Carries O2 in blood Myoglobin 1 Heme pigment Store O2 in muscle Insulin 2 None Hormonal regulation Blood group proteins 1 Carbohydrate Produces blood types Lipoproteins 33 1 Lipids Transports lipids in blood 33  A total of 20 amino acids Amino acids are linked by peptide bonds Peptide- up to 10 amino acids Polypeptide- longer chains Proteins- >100 amino acids 34 34 Peptide bonds builds amino acid chain 35 A protein can have 4 levels of structure Increase in complexity Primary Secondary Tertiary Quaternary structure structure structure structure The amino acid sequence 3-D arrangement of backbone atoms in space 3-D arrangement ✓ The amino acid of all the atoms in sequence causes the space polypeptide to assume 3-D arrangement a particular shape of subunit chains ✓ The shape of a protein 36 determines its specific function 36 Primary structure The amino acid sequence determined by the cell’s Secondary structure genetic information Results from coiling or folding of Any slightest change in the polypeptide this sequence affects the Coiling results in a helical protein’s ability to structure called an alpha helix function Folding may lead to a structure called a pleated sheet Coiling and folding result from Tertiary structure hydrogen bonding between certain areas of the polypeptide Is the overall three- chain dimensional shape of a protein Quaternary structure Tertiary structure Are two or more polypeptide generally results from chains (subunits) associated interactions between the together R groups of the various Collagen is an example of a amino acids protein with quaternary Disulfide bridges are structure 37 covalent bonds that Its triple helix gives great further strengthen the strength to connective tissue, protein’s shape bone, tendons, and ligaments 37 Additional bonds to hold the polypeptide chain Disulfide bond (S-S) between the two sulfur molecules of two cysteine amino acids are formed Hydrophobic interactions result when two non-polar side chains are close to each other Globular Fibrous Ball-shaped Rope-like Functional Structural Enzymes Keratin provides impermeability on Plasma proteins (albumin) the epidermis (skin’s outer layer) Erythrocyte (red blood cell) pigment hemoglobin Collagen (toughness of the skin) Elastin (elasticity of the skin) Fibrinogen (protein precursor of fibrin) 38 38 Relevant reading: Basic Concepts in biomedical sciences I Chapter 1, Expressing numbers in SI units Chapter 3, The physical world and basic chemistry Chapter 7, Biological molecules and food 39 39  End of this lecture Copyright © 2024. The Chinese University of Hong Kong (reading access is only allowed for students in MEDF1011) 40