Unifying Themes in Biology

As we begin to talk about all the components of life, both on the microscopic and macroscopic level, it is important to understand first the common themes that unify all living things. These are concepts that we will be discussing throughout the semester.

Unifying Themes cont…

• 1. Cellular Structure and Function – All living things are made of one or more cells, highly organized, tiny structures with thin coverings called membranes.

​

• 2. Reproduction – the process by which organisms make more of their own kind from one generation to the next. All living things can reproduce.

​

• 3. Metabolism – the sum of all of the chemical reactions carried out in an organism. An organism must carry out many different chemical reactions in order to obtain and use energy to run the processes of life.

Unifying Themes cont…

• 4. Homeostasis – the maintenance of stable internal conditions in spite of changes in the external environment. All organisms must do this in order to function properly.
• 5. Heredity – the passing of traits from parent to offspring. This is the reason children tend to resemble their parents.

​

• 6. Evolution – change in the inherited traits of species over generations.
• 7. Interdependence – organisms in a biological community live and interact with other organisms. They are interdependent in a biological community.

Chemistry of Life

​

Simple to Complex – Life’s Levels of Organization

Our journey begins here.

To Understand the Big, You’d Better Know the Small

Chemistry and Life

What’s the difference between an atom and a molecule?

​

Atom – smallest unit of matter that cannot be broken down by chemical means.

Molecule – a group of atoms held together by covalent bonds.

​

What makes atoms hold together to form molecules?

​

Covalent Bonds form when two or more atoms share electrons to form a molecule.

Chemistry of Life cont…

• Elements are pure substances made of only one kind of atom.
• A compound is a substance made of the joined atoms of two or more different elements. Examples- When Na, sodium, combines with Cl, clorine, the compound NaCl, sodium cloride (table salt) forms.
• Compounds are represented by chemical formulas that identify the elements and their proportions.

In a simplified yet useful view of an atom, electrons orbit a nucleus composed of protons and neutrons.

​

Protons are positively charged particles, Electrons are negatively charged particles, and Neutrons have no charge.

An ion is an atom or molecule with one or more full positive or negative charges.

​

Atoms and Atomic Structure

Atoms Come in Different Forms Called Isotopes

Isotopes of a given element have the same number of protons but different numbers of neutrons.

Many isotopes are unstable, making them radioactive.

Radioactive isotopes (radioisotopes) play an important role in health, medicine and biological research.

Three isotopes of hydrogen.

Some Atoms are Sociable, Others Aren’t

Atoms “want” (are most stable) to have a filled outer electron shell.

Atoms without a filled outer shell will share electrons with other atoms to accomplish this “goal.”

Filling outer electron shells controls which atom will pair with which others and in what combinations.

Filling Electron Shells

An important rule: the innermost shell holds two electrons; subsequent shells hold 8 electrons.

Water - A Most Important Molecule

Note how bonding fills all outer electron shells.

Ions and Ion Formation

Ionic Bonds

Two oppositely charged ions bind together.

This type of chemical bond is an ionic bond.

Salts are solids held together by ionic bonds.

Ionic bonds are common and important in biology.

Hydrogen Bonding

Oxygen and nitrogen are much more “hungry” for electrons than hydrogen.

The result is a hydrogen bond.

Bonds between nitrogen or oxygen and hydrogen are highly polar.

This allows bonds to form between partially positive and partially negative atoms in different or (in large molecules) the same molecule.

Hydrogen Bonding Gives Water Unique Properties

Relative Bond Strengths

Covalent

Ionic

Hydrogen

>

>

Biological Chemistry Takes Place in Solutions

Molecules are often described as hydrophilic (water-loving) or hydrophobic (water-fearing) on the basis of their solubility in water.

Polar and Non-Polar Covalent Bonding

The polar versus non-polar distinction determines which molecules will dissolve in a particular solute.

For example, sugar dissolves in water, but fat doesn’t.

The general rule is like dissolves like.

The familiar case of oil and water.