Chemicals of Life

Chemical Basis of Life• principles of

chemistry help to understand biology

• organisms are bags of chemicals

• function of organisms & parts of organisms are determined by– way chemicals are

arranged• compounds &

molecules formed by chemicals

• structure determines function

• Structure Function

long handle to hold easiermade of wood to be strongblunt metal end to hit nailscurved, claws to pull out nails

Chemistry• chemicals give cells properties

• these properties are called life

• Hierarchy

• Chemicalsorganellescellstissuesorgansorganisms

Matter• all living things are made of

matter

–anything that occupies space & has mass

• matter is composed of elements

Elements• substances which cannot be decomposed

into simpler substances by chemical means

• 92 naturally occurring elements

• 25 elements are found in living things

• 96%-H, O, C & N• 4%-Ca, P, K & S• Trace elements-Fe, Mg, Mn (manganese) & I

– essential– cannot live without them

Periodic Table

Atoms• elements are composed of atoms

• only one kind of atom for each element

– smallest units of matter that retainproperties of an element

Sub-atomic Particles• Protons• Electrons• Neutrons

–different elements have different numbers of sub-atomic particles

–put together differently in different atoms

–chemical & physical differences of elements are due to these differences

Sub-Atomic Particles• Protons

– one positive charge

– found in nucleus of atom

• Neutrons– no charge

– found in nucleus of atom

• Electrons– one negative charge

– orbit nucleus

Periodic Table• atom’s structure

determines how element it comprises forms compounds & molecules

• key to this can be found by knowing number of sub-atomic particles an element possess

• found in Periodic Table of the Elements

atomic number-number in upper left corneratomic number-number in upper left corneratomic weight or mass number-number atomic weight or mass number-number located on bottomlocated on bottom

Atomic Number• gives number of

protons in atom

• Helium

• Atomic Number = 2

–has 2 protons

Mass Number• number of neutrons +

number of protons• He = 4• variant forms of elements

can exist• some atoms of an

element may have different mass numbers

• these are isotopes– same number of

protons & electrons; different number of neutrons

Number of Electrons• net charge of atom = zero• each proton has one

positive charge• each electron has one

negative charge• neutrons have no charge• to be neural atom must

have same number of electrons as protons

atom of helium with 2 protons has 2 electrons

ChallengeQuestion• How many protons does Sulfur

have?

• How many electrons?

• Why?

Chemical Properties• arrangement of electrons

determines chemical properties of atom

• electrons orbit around nucleus• found at different energy levels-

shells• each shell accommodates a

specific number of electrons

Electron Shells• innermost shell-2 • 2nd & 3rd-8• number of electrons in

outermost shell determines chemical properties of atom

• those with shells that are not full will interact with other atoms & participate in chemical reactions

• those with full shells do not interact-inert

Electron Shells• H-one electron in outer most shell

– very reactive• C, N, & O

– highly reactive since outer shells are incomplete

• He– inert or nonreactive-outer shell is full

Challenge Question

• Is Chlorine reactive or not reactive?

• How can you tell?

Atom Interactions-Chemical Bonds• when atom with incomplete outer shell

reacts with another atom with incomplete outer shell they can interact or form a bond

• Share

• Donate

• Receive electrons

• in this way both atoms can have a complete outer shell

Types of Chemical Bonds• Covalent Bonds

–share electrons

• Ionic–give or receive

electrons

Sodium & Chloride

Ionic Bonding

Covalent Bonds• 2 atoms with incomplete shells

• share electrons

• so at any one time one atom has a completed outer shell

• molecules are formed

In Class Exercise• Pretend you are an atom

• Take the number of your birth month as your atomic number

• Determine the configuration of electrons in your valence shell

• Find another atom that you might interact with to form ions or new molecules

• Demonstrate-draw on board

Chemical Reactions• elements combine to make molecules &

compounds• 2 H2 + O2 2H2O• 2 molecules of H react with one

molecule of O (reactants) to form 2 molecules of water (product)

• arrow indicates direction of reaction• two sides of equation on either side of

arrow must balance

Water• single most important

constituent of body

• life on Earth depends on unusual structure & nature of water

Importance of Water• Organisms consist mostly of water

– 2/3rds total body weight of humans

• Biochemistry is a wet chemistry– biological molecules do not

react chemically unless in solution

• Water is an important reactant– nearly all chemical reactions in

body occur in water• Foods are digested to building

blocks by decomposition reactions called hydrolysis– involves addition of water

• When large molecules form from smaller ones, water is removed in dehydration synthesis or condensation reactions

Water Structure• 2 H atoms attached

covalently to one O2 molecule• sharing of electrons is not

equal• oxygen pulls more on

electrons than hydrogen • electrons spend more time

near oxygen than hydrogen• unequal sharing produces-

polar bond• bond in which two atoms

involved have an equal pull on electrons-nonpolar

Water Structure• O2 attracts electrons more strongly than H-

giving water an asymmetrical distribution of charge

• result-V-shape

• H end has positive charge

• Oxygen end has negative charge

• water has 2 poles-polar

• polarity results in weak electrical attractions between neighboring water molecules

Polarity of Water• Polarity results in weak

electrical attraction between neighboring water molecules

• slightly positive Hs in one water molecule attract slightly negatively charged O2 in another water molecule

• opposite electrical charges attract

• water molecules attract each othermaking water kind of sticky

• these weak attractions-hydrogen bonds– weaker than covalent or

ionic bonds

Polarity, H Bonding & Water’s Properties

• cohesive nature

• ability to moderate temperature

• ice floating

• universal solvent properties

Dissociation• compounds formed by ionic

bonds will ionize or dissociate in water

• dissociation produces cations (+) & anions (-)

• aqueous solution containing anions & cations will conduct electrical currents

• cations move to negative side have + change

• anions move to positive side having – charge

• soluble inorganic molecules whose ions will conduct an electrical current in solution are electrolytes– NaCl

• NaCl + H2ONa+ + Cl-

Acids & Bases• H+ & OH- are in solution at all times• H2O <-------> H+ + OH- -reversible

reaction• some compounds add more hydrogen ions• others remove them• compounds that donate hydrogen ions-

acid• HClH+ + Cl-

• acidic solution is one that has more H+ than OH-

Acids & Bases• compound that accepts or

removes hydrogen ion is a base

• NaOHNa+ +OH-

• basic solution-one that has more OH- than H+

pH scale• pH = potential hydrogen• scale developed-1909

by Dane Soren Sorensen– beer brewer looking

for way to check acidity of beer

• describes how acidic or basic a solution is

• scale ranges from 0-14• 0 = most acidic• 14 = most basic• 7=neutral

pH• at neutral pH• H+ = OH-

• pH < 7 is acidic• pH > 7 is basic or alkaline

Buffers• pH of blood ranges

between 7.35-7.45• value must be maintained

in narrow range• even small change can

lead to severe metabolic consequences

• biological fluids contain buffers– substances that resist

changes in pH by accepting H+ when in excess & donating H+

when depleted