Chapter 5: The Molecules of Life Life is carbon-based.Why? Why not some other element? Organic molecules:Most carbon-based molecules. Inorganic molecules:Non carbon-based molecules. Examples: Water (H 2 O) Ammonia (NH 3 ) Oxygen (O 2 ) Hydrogen (H 2 ) Sodium chloride (NaCl) etc. These molecules have many different shapes and sizes.

Carbon may also bond with other elements. Hydrocarbons:Molecules composed of carbon and hydrogen only. Many hydrocarbons are important fuels. Examples:Propane (C 3 H 8 ) Butane (C 4 H 10 ) Octane (C 8 H 18 ) Acetylene (C 2 H 2 ) Other common elements in organic molecules: Oxygen (O) and nitrogen (N)

Functional group(s):A specific group of atoms in a molecule with a specific structure. Each of these groups has specific function that is predictable. Examples of Functional Groups on next slide 

Five Important Functional Groups

Hydrophilic : Means “water-loving”. Hydrophilic molecules attract water molecules. Hydrophilic molecules are polar. Hydrophobic : Means “water–hating”. Hydrophibic molecules do not attract water molecules. Hydrophobic molecules are non- polar.

Biomolecules range in size from a few to millions of atoms. (That’s atoms per molecule !). Monomers:Are small molecular units. Large biomolecules are composed of many monomers connected together. So monomers are the building blocks of larger molecules. Polymers: Are long chains of linked monomers. There are nearly 50 different monomers in living things. The diversity of life’s polymers is vast.

THESE LARGE BIOPOLYMERS ARE CLASSIFIED INTO 4 MAIN GROUPS: Carbohydrates Lipids Proteins Nucleic Acids

Processes that Build Up and Break Down Polymers Dehydration Synthesis : Connecting two monomers by removing an –OH from one monomer and an –H from the other monomer. The –OH and the –H link to make a molecule of water. Hydrolysis: Separating two monomers by adding a molecule of water to the region of the bond between them. Basically this process is the opposite of dehydration synthesis.

CARBOHYDRA TES

Are organic compounds made of sugar molecules. Contain carbon, hydrogen, and oxygen in 1: 2: 1 ratio. So…the molecular formula is a multiple of CH 2 O. The molecular core is usually a carbon skeleton in a ring shape. Are important sources of energy.

CARBOHYDRATES: MONOSACCHARIDES Are simple sugars that contain one sugar unit. Examples: glucose, fructose, ribose. Found in many sweet foods. Glucose’s structure: straight chain and ring. Have a structural formula of a ring: A simplified representation: Sugars (esp. glucose) are main fuel for cell work.

A Ball and Stick Model of Glucose:

CARBOHYDRATES: DISACCHARIDES Double sugars made from two monosaccharides. Most common is sucrose which is composed of glucose and fructose. Found in plants (sap, etc.) Can be used for energy immediately or stored for later.

Sucrose: The Most Common Disaccharide

The Synthesis of Two Different Disaccharides:

CARBOHYDRATES: POLYSACCHARIDES Long chains composed of monosaccharide monomers (usually glucose). Starch: plants store excess sugar in this form.. Glycogen: animals store excess sugar in this form in muscles and liver. Cellulose: found in plant cells, involved in protection of cells, and plant structure (rigidity) Humans cannot digest cellulose but use it as fiber. Some animals can use cellulose for energy.

LIPIDS

A class of hydrophobic compounds. Can act as a boundary and they help contain aqueous solutions. Involved in transmission of chemical signals in cells. Store energy for cells/organisms. Lipids include fats and steroids. Can provide insulation for organs.

LIPIDS: FATS (TRIGLYCERIDES) A fat consists of a 3-carbon backbone called glycerol. 3 fatty acid molecules are attached to the glycerol. This is called a triglyceride. Some fats are solid at room temp (animal fat) and others are liquids at r.t. (plant oils). Some fats are saturated and others are unsaturated. Diets rich in saturated fat may be unhealthy.

A ball and stick model of glycerol   The structural formula for glycerol

Saturated Fats : All 3 fatty acids contain the maximum number of hydrogen atoms. In other words there are only single bonds between the carbon atoms and hydrogen atoms. UnSaturated Fats : Contain less than the maximum numbers of hydrogen atoms in one or more of its fatty acid chains. This is a result of one or more double bonds between carbon atoms. Unsaturated fats with more than one double bond b/w adjacent carbons are referred to as polyunsaturated.

Two Fatty Acids:

A fat molecule (triglyceride):

The Formation of a Fat Molecules via Dehydration Synthesis:

LIPIDS: STEROIDS Their carbon skeleton consists of 4 fused rings. They are classified as lipids because they are hydrophobic. Some serve as chemical signals such as the sex hormones testosterone, progesterone, and estrogen. Some are involved in membrane function like cholesterol. Excessive levels of cholesterol can be a problem in humans.

Steroid Structure - 4 Examples:

More Examples of Steroids

PROTEINS

PROTEIN FUNCTIONS (THE IMPORTANCE OF PROTEIN) Proteins are responsible for nearly all the day-to-day functions of cells. Proteins form cell structures. Proteins take part in cell defenses (immune systems) Proteins control chemical reactions in cell (enzymes) Proteins are involved in intracellular and extracellular communication.

PROTEIN STRUCTURE Proteins are polymers constructed from 20 different kinds of amino acid building blocks (monomers). Chains of amino acids (usually > 100) are called polypeptides. Several polypeptides are wrapped together in a specific 3-D shape to form a protein.

Basic Amino Acid Structure :

The 20 Amino Acids:

The connecting of two amino acids or the forming of a polypeptide chain:

Formation of a peptide bond b/w 2 Amino Acids

A protein is composed of multiple chains of amino acid (monomers). The specific sequence and number of amino acids affects the proteins structure and function. Connecting Amino Acid Monomers:

A Chain of Amino Acids

The specific 3-D shape of a protein has everything to do with its function!

FACTORS THAT INFLUENCE A PROTEIN’S SHAPE The Amino Acid sequence and the A.A. sidegroups that form bonds with each other resulting in a specific 3-D shape. The surrounding environment which is usually aqueous (hydrophilic). Temperature pH

DENATURATION OF A PROTEIN The unraveling of a protein resulting in a change in protein shape. This can be caused by a change in temperature, pH, or some other factor w/in the surrounding environment of a protein.

Some Protein Shapes; Note 3-D Structure:

ENZYMES

Enzymes are catalysts composed of protein. They facilitate chemical reactions in cells. They do this by lowering the activation energy required to start a chemical reaction. Enzymes can be re-used many times. Without enzymes, cell reactions would require higher cell temperatures. This would damage the cell. The lock-key model, enzyme-substrate model, and induced-fit model describe how enzymes work. Enzyme structure is essential to function. Many enzyme names end in “-ase”.

Enzymes lower the energy (activation energy) needed to start a reaction:

Some Models of How Enzymes Work :

The Induced-Fit Model of enzyme action:

A model of anabolic (building up) enzyme action:

A model of a catabolic (breaking down) enzyme:

Digestive Enzymes in Action