b2 3
TRANSCRIPT
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Unit B2 & 3: Cell Biology (Cell Compounds & Biological Molecules)
Students who have fully met the prescribed learning outcomes (PLO’s)
are able to:B2 •Describe the characteristics of water and its role in biological systems. •Describe the role of water as a solvent,
temperature regulator, and lubricant.•Describe how the polarity of the water molecule results in hydrogen bonding
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As well as…..
B3• Describe the role of acids, bases and
buffers in biological systems in the human body.
• Differentiate among acids, bases, and buffers.
• Describe the importance of pH to biological systems in the human body.
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So let’s get started….
B1: Water/H2O
Water makes up 60 (women) to 70 (men) % of the weight of most living organisms including all of us.
-Not an organic molecule, i.e. does NOT contain carbon.
-Water is an inorganic, polar molecule.
-Bonds between Hydrogen and Oxygen are covalenti.e. they consist of pairs of shared electrons to
become stable. -
+ +
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Water: a polar molecule
• Electrons are shared unevenly • They spend more time orbiting
oxygen than hydrogen. • This results in a slight positive
charge on the hydrogen side and a slight negative charge on the oxygen side, therefore making H2O a polar molecule.
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Note that the average electron density around the oxygen atom is about 10x that around the hydrogen atoms.
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• http://programs.northlandcollege.edu/biology/Biology1111/animations/hydrogenbonds.html (H2O animation)
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Association of Two Water Molecules
• Hydrogen bonds form between adjacent water molecules
• The covalent bonded positively charged H is attached to the negatively charged O by a H-bond.
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Provincial Diagrams!!
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• The water will dissociate (separate) into ions (the bonds break when energy is supplied).– E.g. H2O H+ + OH- (hydroxide ion)
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B2: Properties/Roles of H2O
• Because of its polarity and H-bonding, H2O has properties/roles beneficial to life.
• 1) Universal Solvent (Dissolving Agent)
• The chemical reactions in our bodies occur in an environment where water
is the solvent.
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• Due to its polarity, water molecules surround and breaks apart molecules.
• As a result, the ions and molecules move around, collide and cause reactions to occur.
• Water will then transport these ions and facilitate chemical reactions outside and inside cells.
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Example of this ….• Blood circulating dissolved ions, and molecules,
causing reactions involving oxygen and carbon dioxide to be picked up and transported to and from tissues and lungs; blood circulating nutrients and ions to tissue cells and removing waste
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http://www.coolschool.ca/lor/BI12/unit1/U01L02.htm (Check out Solvent animation)
• 2) Temperature Regulator
– The many H-bonds cause water to absorb/store large amounts of heat or release heat (energy) slowly, therefore protecting cells from rapid temperature change.
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3.) Lubricant
• Lubricates cell parts and reduces friction.
– E.g. Tears, saliva, alveoli and pleural membranes in lungs, synovial joints.
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B3: Chemical Facts: Introduction
1.) Dissociation-Separating/breaking apart molecules; frequently in polar molecules.
E.g. H-O-H H+ + OH- (Water) lost e- gain e-
2.)Acids and Bases -Acids and bases are a way of classifying compounds based upon what
happens to them when they are placed in water.
AcidsMolecules that dissociate in H2O, releasing hydrogen ions (H+ ). E.g. HCl (in H2O) H+ + Cl-(hydrochloric acid)
BasesMolecules that release more hydroxide ions (OH-) in H2O or take up hydrogen ions (H+).E.g. NaOH (in H2O) Na+ + OH- (sodium hydroxide)
or HCO3- + H+ H2CO3 (bicarbonate ion) (carbonic acid)
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3.) pH:• A scale (-log[H+]) that measures the [H+] (hydrogen ion
concentration).• Indicates the strength of an acid or basic/alkaline solution.
[H+] acidic [OH-]basic/alkaline
0 7 14• Less than 7 = an acid• Greater than 7 = a base/alkaline• 7 = Neutral
• pH scale runs in increments of 10.E.g. 1x10-4 [H+] = pH 4 (acidic) 1x10-7 [H+] = pH 7 (neutral), such as
water 1x10-9 [H+] = pH 9 (basic/alkaline)
Animations of pHhttp://www.purchon.com/chemistry/ph.htm http://www.johnkyrk.com/pH.html
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acidic neutral basic
pH = <7 pH = 7 pH = >7
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4.) Strengths• The strength of an acid depends on the
[H+] ions and the strength of a base depends on the [OH-] ions.
• Therefore, the stronger the acid, the greater the [H+]; the stronger the base, the greater the [OH-].
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5.) Importance of pH to Biological Systems
• In plant and animal cells, pH needs to be maintained within a narrow range to facilitate all chemical reactions. Animals must also control the pH of blood within a narrow range.
• pH that is too acidic or basic causes proteins and enzymes to denature, – i.e. their 3-D shape and biological properties
are destroyed and all chemical reactions, active transport, gas exchange, digestion, protein synthesis, cell replication, nerve transmission etc. will NOT occur. (See B11)
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6.) Buffers
Slight changes in pH can be harmful. A buffer will minimize changes in [H+] and/or [OH-] by taking up excess H+ or OH- or donating H+ or OH-. (A substance that acts as a hydrogen ion "sponge" and prevents drastic changes in pH when acid is added.)
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• Buffers functions to neutralize the pH of a solution/maintain a constant pH by combining with either H+ or OH- ions.
• They are helpful since many reactions can occur only at pH’s which are not too acidic or basic. – E.g. HCO3
- + H+ H2CO3 (using up excess H+) or– H2CO3 + OH- HCO3
- (using up excess OH-)
• We have buffers in our blood, i.e. hemoglobin. Hb picks up and transports excess H+ in the reaction with carbonic anhydrase.
Buffers
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Buffers Cont.• We have buffers in our blood, i.e. hemoglobin. Hb picks up and
transports excess H+ in the reaction with carbonic anhydrase.– E.g. H2O + CO2 H2CO3 HCO3- + H+
• (carbonic acid) (bicarbonate ion)
Hb + H+ HHb • (reduced Hb)
During exercise we produce lots of CO2, HCO3- and therefore lots of H+. The Hb in our blood accepts the H+ (acts as a buffer resulting in HHb) causing blood pH to decrease, i.e. becoming less acidic. (See C9 and 10)