Unit 1 – Chemical Basis of Life

1. Unit 1 – Chemical Basis of Life Important introductory terminology: • biochemistry • the chemistry of living things • atom • the most basic particle of matter, consisting of a nucleus and electron(s) – e.g. hydrogen atom • element • a substance made up of the same type of atom – e.g. gold • molecule • a particle composed of two or more atoms (atoms can be of the same type or different type) – e.g. water molecule – H2O, nitrogen gas – N2 • compound - substance made up of different type of atoms – e.g. carbon dioxide – CO2

2. Chemical bonds • hold atoms together, some are stronger than others 3 main types of chemical bonds present in living things – covalent, ionic and hydrogen bond: • covalent bond • strongest bond of three types • electrons are shared (e.g. H2)

3. Covalent bond Animation

4. ionic bond • weaker bond than covalent • electrons are not shared • one atom takes one or more electrons from another atom to create ions (anion – a negative ion, cation – a positive ion) • change in charge of these atoms (positive and negative charge) creates an ionic attraction (e.g. NaCl – salt)

5. Ionic Bond animation

6. hydrogen bond • weakest of the three bonds discussed (5% of the strength of a covalent bond), happens because of hydrogen’s poor attraction to electrons • in water, the electrons collect more at the oxygen end of the molecule, giving this end a partial negative charge and the hydrogen end a partial positive charge. • positive end of one water molecule has a weak attraction to the negative end of another water molecule • Give water it’s unique properties, such it’s ability to stay a liquid at a wide range of temperatures, and it’s high boiling point.

7. + + - + hydrogen bonds - + + - - + + - + +

8. hydrogen bonds also hold together the two rungs of the DNA ladder hydrogen bonds

9. Entropy • the natural progress from order to disorder in living things (sometimes thought of as randomness) • Constant supply of energy is needed to combat entropy (in form of food for heterotrophic organisms, or sunlight for autotrophic organisms) • Without a constant supply of energy, living things die and become more random • This energy originates from the sun

10. chemical reaction • when chemicals react to create new substances • reactants • chemicals used up in a chemical reaction • products • chemicals produced in a chemical reaction • anabolism – building of more complex molecules using simpler molecules • catabolism – breaking down of more complex molecules into simpler ones • two types of chemical reactions exist: • exothermic and endothermic

11. exothermic reaction • - release energy into the surroundings when the chemicals react • 2 H2 + O2 2 H2O + energy (heat & light) – Hindenburg reaction • C6H12O6 (glucose) + 6 O2 6 CO2 + 6 H2O+ energy(in the form of ATP, this famous exothermic reaction is called cellular respiration) • endothermic reaction • absorb energy from the surroundings when the chemicals react • e.g. - cold pack containing urea and ammonium chloride – mixed together causes reaction to absorb heat and the chemicals feel cold • e.g. 6 CO2 + 6 H2O + energy (light)  C6H12O6 (glucose) + 6 O2 this famous endothermic reaction is called photosynthesis)

12. Synthesis and Decomposition Reactions • Synthesis Reactions - is when there is a combination of two or more substances and a compound results (also called anabolism) . An example of a synthesis reaction is as follows: A + B --> AB a special type of synthesis reactions occur in living systems, called dehydration synthesis (we will discuss later)

13. Decomposition Reactions is the opposite of synthesis. It is when a compound is broken down into simpler substances (sometimes called catabolism). An example of decomposition is as follows: AB --> A + B a special type of decomposition reaction occur in living systems, called hydrolysis (we will also discuss later)

15. Chapter 2 - Question 1-3, page 39 1. What distinguishes one element from another? • The number of protons in the nucleus 2. Describe the formation of an ionic compound. • In sodium chloride, a sodium atom loses an electron to a chlorine atom. • The opposite charged ions are attracted to each other and form an ionic bond. 3. What is the difference between and ionic bond and a covalent bond? • An ionic bond is formed due to the electrical attraction between oppositely charged ions. • A covalent bond is formed by atoms that share electrons.

16. Questions 4-6 4. Compare and contrast – How does a molecule differ from an atom? • A molecule is made up of two or more atoms held together by a covalent bond. 5. Apply – Explain why a hydrogen atom can become either an ion or part of a molecule. • A hydrogen atom has one unpaired electron in its outer energy level. • The electron can be lost to form an ion or shared to form a covalent bond. 6. Chemistry – A sodium atom has one outer electron, and a carbon atom has four outer electrons. How might this difference be related to the types of compounds formed by atoms of these two elements? • An atom that has a nearly full or nearly empty outer energy level (such as sodium) tends to form ions. An atom in between (such as carbon) tends to share electrons.

17. Questions 1-3, page 43 • How do polar molecules form hydrogen bonds? • The oppositely charged regions of a polar molecule attract other polar molecules, allowing a positively charged hydrogen atom to bond to a negatively charged atom. • What determines whether a compound will dissolve in water? - Compounds that have charges, such as ionic compounds and polar molecules, will dissolve in water • Make a chart that compares acids and bases. - acids donate protons (hydrogen ions) and bases accept them - acids have a pH less than 7, bases have a pH greater than 7

18. Questions 4-5 • Compare and Contrast – How do polar molecules differ from non-polar molecules? How does this affect their interactions? - Polar molecules have charged regions due to an unequal sharing of electrons. Non-polar molecules do not have charged regions because electrons are shared more equally. The charge differences tend to keep the molecules separate. • Connect – Describe an example of cohesion or adhesion that you might observe during your daily life. - Water beading on the surface, water sticking to the side of a glass

19. Question 6 • Cellular Respiration – When sugars are broken down to produce usable energy for cells, a large amount of heat is released. Explain how the water inside the cell helps keep the cell’s temperature constant. • Water has a high specific heat. • Water in a cell can absorb a large amount of energy before its temperature increases.