Biochemistry:The Chemistry of Living Things

Everything in the universe is composed of ATOMS, the basic building blocks of matter

How small is an atom? The thickness of a piece of paper is about 1 million atoms.

CHALLENGE:What does an atom look like? Draw a picture of an atom to the best of your ability.

What is Matter?

YES we can! It has only been in the last 2 decades that we can see them, using the most powerful electron microscopes in the world.

These are carbon atoms (within a sheet of graphite)

Can We See Atoms?

Over the past 200 years, scientists have conducted many experiments that provide evidence of an atom’s properties.

We have developed several atomic models based on this.

ORBITAL MODEL

BOHR MODEL

ELECTRON CLOUD MODEL

Atomic StructureAn atom is composed of two regions:

1. NUCLEUS

- Contains PROTONS (+) and NEUTRONS (0), which are held together by the “strong force”

2. ELECTRON CLOUD

- Where the electrons (-) are found; but we don’t know exactly where they are because they’re “zipping” around constantly at the speed of light

Electron cloud (negatively charged)

Nucleus (positively charged)

Electron Cloud Model of the Atom

Atomic ChargeAn atom has an overall charge of zero (neutral), because it has an equal number of protons & electrons

But an atom doesn’t always stay neutral.

Electrons can be lost or gained between atoms, resulting in:

IONS, which are charged particles,

such as Na+ or Cl-

How Do Atoms Differ?The identity of an atom is determined by the number of protons

The Periodic Table is arranged by the number of protons in each element.

# of protons = ATOMIC NUMBER

The Periodic Table of Elements

• Elements are pure substances that can’t be broken apart by chemical means and are composed of identical atoms.

• There are more than 100 elements

• The first 92 are found in nature, but the rest are man-made (particle physics)

• Some elements are unstable and radioactive Example: Uranium

What is an Element?

• Two or more elements can bond together

to form molecules and compounds

Examples of molecules & compounds:– Water H20– Carbon Dioxide CO2

– Oxygen Gas O2

– Glucose C6H12O6

– Sodium Chloride NaCl– Limestone CaCO3

– Propane C3H8

Combining Elements

There are three basic types of bonds:

1. IONIC BOND: Electrons are transferred from metals to nonmetals

metal ions lose electrons, and nonmetal ions gain electrons

This type of bond is very strong and results in solid crystal structures, such as NaCl (table salt)

Types of Bonding

2. COVALENT BOND: Electrons are shared between two or more nonmetals

This type of bond is weaker than ionic bondsand results in compounds that are gases or liquids,

such as H2O and CO2

Bonding, continued

3. HYDROGEN BOND: Occurs between water molecules, because water is POLAR which means that a part of the molecule is positively charged, while another part is negatively charged

NONPOLAR molecules have no charge

Bonding, continued

When water molecules are next to each other, they line up in a certain way because the Hydrogens (+) are attracted to the Oxygens (-), which creates hydrogen bonds

• Water is one of the most unique molecules known to man and also one of the most important to living organisms.

• Not only does water exist in nature in all three states of matter (solid, liquid, gas), it also covers 75% of the earth and makes up approximately 78% of the human body.

• Water has special properties, due to the hydrogen bonding between its molecules.

Properties of Water

• Cohesion is an attractive force between particles of the same kind

• Cohesion between water molecules creates surface tension on the top layer of the water, causing it to behave as an elastic sheet.

• Example: water bugs are able to “walk on water” because they are light and have long legs to distribute their weight along the surface tension.

What is Cohesion?

Examples of Cohesion

• Adhesion is the attraction between molecules of two different substances

• Water molecules will form hydrogen bonds with many other materials (such as glass, soil, plant stems, paper)

• This results in capillary action, where water molecules move through a substance quickly, or “climb” up a thin tube against gravity

What is Adhesion?

Examples of Adhesion

A split celery stalk is placedinto two different cups of water with food coloring.

Water molecules can move upwards against gravity, through thin tubes of xylem tissue in the stem.

This is how plants are able to transport water from their roots up to their leaves.

Example of capillary action:

• Water is called the “Universal Solvent” because of its polar nature; it can dissolve many other polar substances

• “Like dissolves Like”

• Pure water cannot dissolve nonpolar substances, such as:– Oils and fats– Plastic, Gasoline– Sand & Glass– Certain metals, like pure Gold & Silver

Water as a Solvent

Water cannot dissolve…

Olive oil

Gasoline

• Water is very resistant to changes in temperature; it takes a lot of energy to heat up or cool down

• Specific heat: How much heat energy is required to raise the temperature of 1 gram of a substance by 1°C

• Example: When you place a pot of water on the stove, the average time for it to begin to boil is 5 to 10 minutes – that’s a long time!

Water’s Specific Heat

• Water is an essential substance in all living things because of its ability to:

1. Resist temperature changes2. Move through materials

quickly3. Dissolve many substances

• These properties allow an organism to maintain homeostasis, which is the cell’s stable internal environment

Water and Homeostasis

STOP HERE

• SOLUTION: a homogeneous mixture in

which the particles are very small and well-mixed Example: salt water

• SOLUTE: the substance being dissolved Example: salt

• SOLVENT: the substance doing the dissolving Example: water

Solutions

AcidsACIDS: produce H+ ions in water

–Acids taste sour–Acids are corrosive to metal–pH lower than 7

Examples:• LEMON JUICE• VINEGAR• HYDROCHLORIC ACID

BasesBASES: produce OH- ions in water

–Bases taste bitter–Bases are slippery–Also called “alkaline”–pH higher than 7

Examples:• AMMONIA• BAKING SODA• LYE (in soaps)• BLEACH

The pH Scale

INDICATOR: a chemical that changes color in the presence of an acid or a base

– pH paper:• Turns a range of colors, must compare

tothe color chart to determine pH

– Litmus paper:• Turns red = acid• Turns blue = base

– Phenophthalein: turns pink in a base

– Natural indicators: red cabbage juice

– Electronic pH meters: very precise

Measuring pH

• Controlling the pH level in living cells is very important in maintaining homeostasis

• Most cells function only within a very narrow pH range

Example: blood pH is 6.8 – 7.8

• Control of pH is accomplished with buffers made by the body

Controlling pH