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Unit 1 – Chemical Basis of Life

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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

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 when chemicals react to create new substances reactants
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
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.

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