Chapter 6: The Chemistry of Life



Chapter 6: The Chemistry of Life

Section 6.1 Atoms and Their Interactions

I. Elements

A. Natural elements in living things

1. Element = a substance that can’t be broken down into simpler chemical

substances.

2. Four elements make up 96% of the mass of the human body: C, H, O, N

3. Look at page 142, Table 6.1 It shows some common elements, along with their symbols, found in the human body.

B. Trace elements

= elements that play a vital role in maintaining healthy cells, but are needed in very small amounts. (Table 6.1)

II. Atoms: The Building Blocks of Elements

*Atom = the smallest particle of an element that has the characteristics of

that element.

A. The structure of an atom

1. The center of an atom is the nucleus.

2. The nucleus is made up of protons (p+) which are positively charged and neutrons (n0) which are neutral or have no charge.

3. Elements are arranged on the Periodic table according to the number of protons they naturally have. This number is called the atomic number.

4. The region of space surrounding the nucleus contains extremely small, negatively charged particles called electrons (e-). This region is also known as the electron cloud.

B. Electron energy levels (pg. 143, fig. 6.2)

1. Within the electron cloud, there are energy levels which the electrons

move around in.

III. Isotopes of an Element

1. Isotope = atoms of the same element that have the same number of protons, but

a different numbers of neutrons.

2. Scientists refer to isotopes by stating the combined total of protons and

neutrons in the nucleus.

3. For example: Carbon-12 (naturally occurring element)

Carbon-14 (contains 2 more neutrons)

-the nucleus is unstable and tends to break apart and

give off radiation.

IV. Compounds and Bonding

*Compound = a substance that is composed of atoms of two or more

different elements that are chemically combined. Ex: NaCl

*How and why do elements combine? Atoms combine with each other only

when the resulting compound is more stable than the individual atoms.

*For many elements, an atom becomes stable when its outermost energy

level is full.

A. How covalent bonds form

1. Covalent bond = the force between two atoms that share electrons

2. The electrons being shared move around both elements holding them

close together.

3. A molecule is a group of atoms held together by covalent bonds.

Ex: Water (H2O)

4. Examples of covalent bonds:

a. Two hydrogen atoms

b. Two Carbon atoms

B. How ionic bonds form

1. Ionic bond = the attractive force between two ions of opposite charge.

2. Ion = a charged atom that gained or lost electrons.

3. These bonds are less abundant in living things than covalent molecules,

but ions are important in biological processes. Ex: Sodium & potassium pumps conduct nerve impulses

4. Examples of ionic bonds:

a. Table salt NaCl

b. MgS

V. Chemical Reactions

*Chemical reactions occur when bonds are formed or broken, causing

substances to recombine into different substances.

*All the chemical reactions that occur within an organism are referred to as

that organism’s metabolism.

A. Writing chemical equations

1. Basic setup:

Reactants ( Products Na + Cl ( NaCl

2. In chemical reactions, it is important to understand that atoms are

neither created nor destroyed, they are simply rearranged.

VI. Mixtures and Solutions

*Mixture = a combination of substances in which the individual components

retain their own properties. Ex: mixing sand and sugar, salt and pepper

*Solution = a mixture in which one or more substances (solutes) are

distributed evenly in another substance (solvent). In other words, one

substance is dissolved in another and will not settle out of solution.

Ex: sugar and water, food coloring and water

*Organisms have can’t live unless the concentration of dissolved substances

stays within a specific, narrow range.

A. Acids and bases

1. Chemical reactions can only occur when conditions are right. One of the conditions that is very important is the pH of a solution.

2. The pH is a measure of how acidic or basic a solution is.

3. Look on page 150, figure 6.11 for the pH scale

0 to 6 is acidic, 7 is neutral, 8 to 14 is basic

4. An acid is any substance that forms hydrogen ions (H+) in water.

Ex: HCl (H+ + Cl-

5. A base is any substance that forms hydroxide ions (OH-) in water.

Ex: NaOH ( Na+ + OH-

6. If the hydrogen ions equal the hydroxide ions the solution is neutral and

has a pH of 7.

7. So……..

If H+ > HO- then solution is acidic

If H+ < HO- then solution is basic

If H+ = OH- then solution is neutral

Section 6.2 Water and Diffusion

I. Water and Its Importance

A. Water is polar

1. Polar molecule = a molecule with an unequal distribution of charge

2. These molecules have a positive end and a negative end.

3. Polar molecules attract other polar molecules as well as charged ions.

4. Look at page 153, figure 6.12. Water is a polar molecule.

5. When two water molecules come in close contact, the negative oxygen end

is attracted to the other water molecules positive hydrogen end. This

attraction of opposite charges forms a weak bond called a hydrogen bond.

6. Because of waters polarity, it …

-is the universal solvent

-can move up plants by capillary action

B. Water resists temperature changes

1. Water requires more heat to increase its temperature than other liquids.

Why? Because of the hydrogen bonds between each molecule. As

you heat up water, the bonds must be broken to move around.

2. When water cools, it gives off a lot of heat.

3. Because water takes longer to heat up and cool down, it is like an

insulator that helps maintain a steady environment when conditions

fluctuate outside and within our own bodies/cells.

C. Water expands when it freezes

*As water begins to freeze more and more hydrogen bonds are formed and

the water molecules become more spread apart. When this happens as a

piece of ice forms, it becomes less dense than the surrounding liquid

water, therefore, ice floats!

II. Diffusion

A. Early observations: Brownian motion

*In 1827, Scottish scientist Robert Brown used a microscope to observe pollen grains suspended in water. He noticed that the grains moved constantly in little jerks. He did the same with dye in water. Brown had no explanation for the motion, but today we know it as the random motion of atoms and molecules.

B. The process of diffusion

1. Diffusion = the net movement of particles from an area of higher

concentration to an area of lower concentration.

2. Diffusion is a slow process because it relies on the random motion of

atoms and molecules.

3. Three factors affect the rate of diffusion:

a. concentration

b. temperature

c. pressure

C. The results of diffusion

*If you place a drop is food coloring into a glass of water eventually the

glass will be all the same color. However, the water and dye molecules are

still moving. This movement is called dynamic equilibrium.

D. Diffusion in living systems

*Diffusion is one of the methods by which cells move substances in and out

of the cell.

Section 6.3 Life Substances

I. The Role of Carbon in Organisms

*Since carbon has 6 electrons, it has 4 electrons in its outermost energy

level. It is unique because it can potentially form four bonds with other

elements.

*Look at page 157, figure 6.16 for single, double, and triple bonding.

*When carbon atoms bonds to each other, they can form chains or ring

formations.

*Some carbon compounds can have the same chemical formula but have a

different configuration, these compounds are called isomers.

A. Molecular chains

1. Biomolecule = large organic compounds (contains 10’s, 100’s, to 1000’s of carbon atoms)

2. Polymer = a large molecule formed when many smaller molecules bond together

B. The structure of carbohydrates

1. Carbohydrate = a biomolecule composed of carbon, hydrogen, and oxygen that has or can be reduced to a 1:2:1 ratio (C:H:O ratio)

2. Function of carbos.: stores energy for the cell

3. Two types of carbohydrates:

a. Sugars

- A monosaccharide is a simple(small) sugar Ex: glucose & fructose

- A disaccharide is two monosaccharides linked together

Ex: glucose + fructose = sucrose (table sugar) (pg 158, fig. 6.17)

b. Starches

- Starches are polysaccharides. They are polymers composed of

many monosaccharide subunits.

Ex: glycogen & cellulose (pg 159, fig. 6.19)

C. The structure of lipids

1. Lipid = large biomolecules that are made mostly of carbon and hydrogen

with a small amount of oxygen. It can not be reduced to a 1:2:1 ratio.

2. They are insoluble in water because their molecules are Nonpolar and

repel water.

3. Ex: fats, oils, waxes, and steroids

4. Function of lipids: energy storage, insulation, protective coverings

5. Components of a lipid:

a. three fatty acids

b. one glycerol molecule (pg 160, fig. 6.20)

6. Lipids can be saturated, unsaturated, or polyunsaturated.

- Saturated = all of the carbon atoms are single bonded together;

the molecule is now saturated with hydrogen molecules

- Unsaturated = when a double bond exists between two of the

carbon atoms; the molecule now has less hydrogen atoms

- Polyunsaturated = when many double bonds exist between the

carbons; even less hydrogen is present now

D. The structure of proteins

1. Protein = a large, complex polymer composed of carbon, hydrogen, oxygen,

nitrogen, and sometimes, sulfur.

2. Components of a protein: amino acids

3. The amino acids are linked together by covalent peptide bonds.

4. Proteins come in a large variety of shapes and sizes. The number and

order of the amino acids determines its function.

5. Functions of proteins:

a. Gives structures and support Ex: hair, fingernails, horns, hoofs

b. Help muscles contract

c. Transport oxygen in your bloodstream Ex: hemoglobin

d. Provide immunity Ex: antibodies

e. Carry out reactions Ex: enzymes

6. An enzyme is a protein that changes the rate of a chemical reaction.

- Without the help of enzymes, we would not be able to digest our food

fast enough to feed our body.

E. The structure of nucleic acids

1. Nucleic acid = a complex biomolecule that stores cellular information in

the form of a code.

2. Components of a nucleic acid: nucleotides (which have C, H, O, N, & P)

3. A nucleotide is made up of: (page 163, fig. 6.24)

a. sugar

b. nitrogenous base

c. phosphate group

4. Examples:

a. DNA (Deoxyribonucleic acid)

- contains our genetic code (how to make all of our proteins)

b. RNA (Ribonucleic acid)

- takes the code from DNA and actually takes part in making our

proteins

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