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

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.

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. -

+ +

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.

Note that the average electron density around the oxygen atom is about 10x that around the hydrogen atoms.

• http://programs.northlandcollege.edu/biology/Biology1111/animations/hydrogenbonds.html (H2O animation)

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.

Provincial Diagrams!!

• The water will dissociate (separate) into ions (the bonds break when energy is supplied).– E.g. H2O H+ + OH- (hydroxide ion)

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.

• 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.

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

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.

3.) Lubricant

• Lubricates cell parts and reduces friction.

– E.g. Tears, saliva, alveoli and pleural membranes in lungs, synovial joints.

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)

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

acidic neutral basic

pH = <7 pH = 7 pH = >7

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-].

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)

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.)

• 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

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)