The Chemistry

of Life

Why do we study chemistry?

Chemistry is the foundation for Biology!

The World of Elements About 25 elements are essential for life

4 elements make up about 96% of living matter carbon (C) hydrogen (H) oxygen (O) nitrogen (N)

6 elements make up most of the remaining 4% sodium (Na) magnesium (Mg) phosphorus (P) sulfur (S) potassium (K) calcium (Ca) (iron … Fe)

C

H

P SNa Mg

K Ca

N OCarbsLipidsProteinsNucleic acids

PhospholipdsNucleic acids

BonesNerve impulses

Nerve impulses

ProteinsNucleic acids

CirculationDigestionImmune systems

Nerve impulsesMuscles

Elements & their valence shellsElements in the same column have the same valence & similar chemical properties

Chemical reactivity Atoms want to have a full or complete valence shell Two ways to achieve this:

◦Gain/lose electrons◦Share electrons

–

This tendency drives chemical reactions…

and creates bonds

Bonds in Biology Weak bonds:

◦ hydrogen bonds◦ Attraction between + and -

◦ hydrophilic & hydrophobic interactions◦ Interactions with H2O

◦ van derWaals forces◦ ionic

Strong bonds:◦ covalent

◦ sharing electrons

Hydrogen bond

Covalent bond

I’m feeling bonded to you

Nonpolar covalent bond Pair of electrons are shared equally by 2 atoms

◦Example: hydrocarbons = CxHx ◦Methane (CH4)

balanced, stable,good building block

Lots of energyto release

Lots of storedenergy

Will become the structural

basefor carbohydrates & lipids

* ENERGY *

Polar covalent bond Pair of electrons are shared UNequally by 2 atoms◦Example: water = H2O ◦Oxygen has a stronger “attraction” for the electrons◦ Has a higher electronegativity

◦Water is a polar molecule◦ + vs – poles◦ Leads to many interesting properties

of water …

H

H

Oxygen

–

–

–

–+

+

Hydrogen bonds Found between polar molecules involving H◦Example: water◦Attraction between positive H in one H2O to negative O in another H2O

◦Can also occur wherever an –OH exists in a large molecule

Weak bond◦Common in biology

HO

H

H bonds

Let’s take a look at water … the elixir of life!

Why study water? All life occurs in water◦It’s found inside & outside the cell

The Chemistry of Water H2O molecules form H-bonds with each other◦+H attracted to –O◦Creates a “sticky” molecule

The Chemistry of Water Special properties of water

◦Cohesion & adhesion◦ Surface tension, capillary action

◦Good solvent◦ Many molecules dissolve in H2O

◦Lower density as a solid◦ Ice floats!

◦High specific heat◦ Water stores heat

◦High heat of vaporization◦ heats & cools slowly

Ice .. Ice, Baby ….

Cohesion & Adhesion Cohesion

◦H bonding between H2O molecules◦Water is “sticky”

◦ Surface tension

Adhesion◦H bonding between H2O & other substances◦ Capillary action◦ Meniscus

Think: Adhesive

tape

How does H2O move towards the top of tree?

Transpiration works with cohesion & adhesion

Water is the solvent of life Polarity makes H2O a good solvent◦Polar H2O molecules surround + and – ions

What dissolves in water? Hydrophilic

◦Substances have attraction to H2O◦polar or nonpolar??

What doesn’t dissolve in water? Hydrophobic

◦Substances that don’t have an attraction to H2O

◦polar or nonpolar??

I’m feeling kinda fatty

…

The special case of ice Most substances become more dense as a solid, but not water◦Ice floats!◦H bonds form a crystal

And this hasmade all the difference!

Specific heat H2O resists changes in temperature◦High specific heat◦Takes a lot to heat it up◦Takes a lot to cool it down

H2O moderates temperatures on Earth

Specific heat& climate

Important for me too -

outside & inside my body

Specific heat Amniotic fluid acts as a temperature buffer for a developing fetus

Heat of vaporization Amount of energy required to turn a substance from liquid to gas

Evaporative cooling

Organisms rely on heat of vaporization to remove body heat

Ionization of water & pH Water ionizes

◦H+ splits off from H2O, leaving OH-◦ If [H+] = [OH-], water is neutral◦ If [H+] > [OH-], water is acidic◦ If [H+] < [OH-], water is basic

pH scale◦Measures [H+]◦How acidic or basic a solution is◦0 7 14 H2O H+ +

OH–

pH Scaletenfold changein H+ ions

pH1 pH210-1 10-2

10 times less H+

pH8 pH710-8 10-7

10 times more H+

pH10 pH810-10 10-8

100 times more H+

10–1

H+ IonConcentration

Examples of Solutions

Stomach acid, Lemon juice1

pH100 Hydrochloric acid0

10–2 2

10–3 Vinegar, cola, beer3

10–4 Tomatoes410–5 Black coffee, Rainwater5

10–6 Urine, Saliva6

10–7 Pure water, Blood7

10–8 Seawater8

10–9 Baking soda910–10 Great Salt Lake1010–11 Household ammonia1110–12 Household bleach12

10–13 Oven cleaner13

10–14 Sodium hydroxide14

Buffers & Cellular Regulation pH of cells must be kept ~7

◦ pH affects shape of molecules◦ Shape of molecules affects function

Control pH by buffers◦ H+ reservoir

◦ Donates H+ when [H+] falls◦ Absorbs H+ when [H+] rises

100

1

2

3

4

5

6

7

8

9

3Amount of base added

Bufferingrange

4 52

pH

AnyQuestions?

Homework Pick any specific terrestrial or aquatic animal and list the ways that water is important to its survival.

Relate your list to the properties discussed today.◦ Cohesion & adhesion◦ Good solvent◦ Lower density as a solid◦ High specific heat◦ High heat of vaporization◦ pH