Chapter 2 Lecturer 3.pptx

Valence shell: An atom’s outermost occupied shell Atoms are most stable when their valence shells are occupied Atoms can donate, steal, or share electrons to arrive at exactly the right number The exact strategy will depend in part on its electronegativity Electronegativity measures the atom’s abili...

Valence shell: An atom’s outermost occupied shell Atoms are most stable when their valence shells are occupied Atoms can donate, steal, or share electrons to arrive at exactly the right number The exact strategy will depend in part on its electronegativity Electronegativity measures the atom’s ability to attract electrons on a scale of 0 to 4 For example: Oxygen has high electronegativity compared to Sodium Elements with high electronegativity tend to strip electrons away from those with lower values Elements with moderate electronegativity often share electrons Whether electrons are shared or stolen, the transfer of electrons from one atom to another creates a chemical bond Chemical bond is an attractive force that hold atoms together Three types of chemical bonds that are important in Biology Ionic bond: One atom transfers electrons to another atom Covalent bond: Atoms share electrons Hydrogen bond: Made by partial charges on adjacent polar molecules Please open this link to understand more about chemical bonds, remember that in our course we only discuss three: Ionic, covalent, and hydrogen bonds Ionic and Covalent Bonds, Hydrogen Bonds, van der Waals - 4 types of Chemical Bonds in Biology (youtube.com) Ionic bond Covalent bond: a. Non-polar & b. Polar Hydrogen bond You can also see the attached link for further explanation about hydrogen bonds: https://www.youtube.com/watch?v=RSRiywp9v9w Water is essential to life - Not an ordinary fluid Properties of water: 1. Water is cohesive and adhesive Cohesion is the tendency of water molecules to stick together. Cohesion also contributes to the observation that you can sometimes fill a glass to the brim, yet water doesn’t flow over unless it is disturbed. Water has a high surface tension (The tendency Adhesion: The tendency to form hydrogen bonds with substances other than water When water soaks into a paper towel, it adheres to the molecules that make up the paper towel 2. Many substances dissolve in water Water is a solvent: A chemical in which other substances (solutes) dissolve Scientists divide chemicals into two categories based on their affinity to water: Hydrophilic substances: Water-loving. They dissolve in water e.g. sugar, salt… Hydrophobic substances: Water-fearing. They do not dissolve in water 3. Water regulates temperature Water has the ability to resist temperature changes A lot of heat is required to evaporate water Water’s resistance to temperature changes explains why coastal climates tend to be mild 4. Water expands when it freezes In liquid water, hydrogen bonds are constantly forming and breaking, and the water molecules are relatively closer together Ice crystal: Hydrogen bonds are stable and molecules are locked into a roughly hexagonal shell 5. Water participates in life’s chemical reactions In a chemical reaction: Two or more molecules swap their atoms, to yield different molecules You can watch the video in the attached link to learn more about water properties: Properties of Water | Hydrogen Bonding in Water | Biology | Biochemistry (youtube.com) Cells have an optimum pH One of the most important substances dissolved in water is one of the simplest H+ ions Each Hydrogen atom is stripped of its electron Too much or two little H+ can ruin the shape of your critical molecules inside the cell, rendering them nonfunctional At any time, about one in a million water molecules spontaneously breaks into two pieces: H2O H+ ion + OH- ion The number of Hydrogen ions equal to the number of Hydroxide ions Acid: A chemical that adds H+ ion to a solution, making the concentration of H+ ions exceed the concentration of OHions A pH scale expresses acidity or alkalinity This scale is used to measure how acidic or basic a solution is The scale ranges from 0–14 with 7 representing a Neutral solution such as pure water. An Acidic solution has a pH lower than 7, whereas an Alkaline or Basic solution has a pH greater than 7 Cells Contain Four Major Types of Organic Molecules Organisms are composed mostly of water and organic molecules Organic Molecules - chemical compounds that contain both carbon and hydrogen Plants and other autotrophs will produce their own organic molecules, whereas heterotrophs, including humans will obtain their building blocks from food The four most abundant types of organic molecules in organisms are Carbohydrates, Lipids, Proteins, and Nucleic Acids. Organic molecules consist of a carbon backbone and a Functional Group that will determine the physical, chemical, and solubility properties of the specific compound Organic molecules consisting of almost entirely of Carbon and Hydrogen are called Hydrocarbons e.g. Methane (CH4) Many organic compounds also include other essential elements: Oxygen, Nitrogen, Phosphorus and Sulfur All organisms – from bacteria to plants to humans, consist largely of the four types of organic compounds: carbohydrates, proteins, nucleic acids, and lipids Large molecules are composed of smaller subunits Proteins, nucleic acids, and some carbohydrates all share a property in common – they are Polymers Polymers are chains of small molecular subunits called monomers A polymer is made up of monomers that are linked together In between the monomers there are small groups of atoms called functional groups These functional groups participate in the reactions that create life’s large organic Cells use a chemical reaction called dehydration synthesis (condensation reaction) to link monomers into polymers In this reaction, a protein called an enzyme removes an –OH group (hydroxyl group) from one molecule and a hydrogen atom from another, forming H2O Dehydration means that water is lost The reverse reaction, called hydrolysis, breaks the covalent bonds that link monomers In hydrolysis, enzymes use atoms from water to add a hydroxyl group to one molecule Carbohydrates include Simple sugars and Polysaccharides Candy, sugary fruits, cereal, potatoes, pasta, bread are rich in carbohydrates Carbohydrates are organic molecules that consist of carbon, hydrogen and oxygen, often in proportion 1:2:1 These are the simplest of the four main types of organic compounds Two main groups: Simple Carbohydrates (sugars) and Complex Carbohydrates The smallest carbs are called monosaccharides They usually contain five or six carbon atoms C:H:O = 1:2:1 Simple Carbohydrates (Sugars): monosaccharides, disaccharides - fructose and glucose both have the formula C6H12O6 Complex Carbohydrates: oligosaccharides (glycoproteins), polysaccharides/complex carbohydrates: cellulose, chitin, starch, glycogen Glossary of terms Electronegativity Chemical bond Ionic bond Covalent bond Hydrogen bond Cohesion Surface tension Adhesion Hydrophilic substances Hydrophobic substances Acid Base Neutral solution Alkaline solution Organic Molecules Hydrocarbons Polymers Dehydration synthesis Hydrolysis Carbohydrates