Chapter 3 The Molecules of Cells By Dr. Par Mohammadian Overview: -Carbon atom -Functional Groups -Major Biomolecules

Life’s molecular diversity is based on the properties of carbon –Cell consists mostly of carbon-based molecules –Organic chemistry: Study of carbon compounds Carbon: –It has four electrons in an outer shell that holds eight –Carbon can share its electrons with other atoms to form up to four covalent bonds

The simplest organic compounds are hydrocarbons –These are organic molecules containing only carbon and hydrogen atoms –The simplest hydrocarbon is methane

The unique properties of an organic compound depend not only on its carbon skeleton but also on the atoms attached to the skeleton –These atoms are called functional groups Functional groups are the groups of atoms that participate in chemical reactions –Hydroxyl groups are characteristic of alcohols –The carboxyl group acts as an acid Functional groups help determine the properties of organic compounds

Most of the large molecules in living things are macromolecules called polymers (e.g. proteins, DNA) –Polymers are long chains of smaller molecular units called monomers –A huge number of different polymers can be made from a small number of monomers Cells make a huge number of large molecules from a small set of small molecules

Cells link monomers to form polymers by dehydration synthesis Polymers are broken down to monomers by the reverse process, hydrolysis

There are four categories of large molecules in cells BIOLOGICAL MOLECULES –Carbohydrates –Lipids –Proteins –Nucleic acids

Carbohydrates include Carbohydrates –Small sugar molecules in soft drinks –Long starch molecules in pasta and potatoes Monosaccharides are the simplest carbohydrates Monosaccharides are simple sugars The monosaccharides glucose and fructose are isomers –Their atoms are arranged differently

The most common disaccharide is sucrose, common table sugar –It consists of a glucose linked to a fructose –Sucrose is extracted from sugar cane and the roots of sugar beets Simple sugars and double sugars dissolve readily in water –They are hydrophilic A disaccharide is a double sugar Disaccharides –It is constructed from two monosaccharides Disaccharides are joined by the process of dehydration synthesis

Complex carbohydrates are called polysaccharides Polysaccharides –They are long chains of sugar units –They are polymers of monosaccharides These large molecules are polymers of hundreds or thousands of monosaccharides linked by dehydration synthesis Starch and glycogen are polysaccharides that store sugar for later use Cellulose is a polysaccharide in plant cell walls

Lipids are hydrophobic Lipids –They do not mix with water –Examples: fats and steroids Fats are lipids whose main function is energy storage –They are also called triglycerides A triglyceride molecule consists of one glycerol molecule linked to three fatty acids

The fatty acids of unsaturated fats (plant oils) contain double bonds –These prevent them from solidifying at room temperature Saturated fats (lard) lack double bonds –They are solid at room temperature

Phospholipids are a major component of cell membranes Waxes form waterproof coatings Steroids are often hormones Phospholipids, waxes, and steroids are lipids with a variety of functions

Steroids are very different from fats in structure and function Steroids –The carbon skeleton is bent to form four fused rings Cholesterol: your body produces other steroids

Proteins are involved in –cellular structure –movement –defense –transport –communication Mammalian hair is composed of structural proteins Enzymes regulate chemical reactions PROTEINS Proteins are essential to the structures and activities of life

Each amino acid consists of –A central carbon atom bonded to four covalent partners –an amino group –a carboxyl group –A side group that is variable among all 20 All proteins are constructed from a common set of 20 kinds of amino acids The Monomers: Amino Acids

Cells link amino acids together by dehydration synthesis Proteins as Polymers –The resulting bond between them is called a peptide bond Your body has tens of thousands of different kinds of protein –The arrangement of amino acids makes each one different

A protein, such as lysozyme, consists of polypeptide chains folded into a unique shape –The shape determines the protein’s function –A protein loses its specific function when its polypeptides unravel Overview: A protein’s specific shape determines its function

A protein’s primary structure is its amino acid sequence Secondary structure is polypeptide coiling or folding produced by hydrogen bonding Tertiary structure is the overall shape of a polypeptide Quaternary structure is the relationship among multiple polypeptides of a protein

A protein’s shape is sensitive to the surrounding environment What Determines Protein Structure? –Unfavorable temperature and pH changes can cause a protein to unravel and lose its shape –This is called denaturation

Nucleic acids such as deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) serve as the blueprints for proteins They ultimately control the life of a cell NUCLEIC ACIDS Nucleic acids are information-rich polymers of nucleotides Nucleic acids are polymers of nucleotides

–Each nucleotide is composed of a sugar, phosphate, and nitrogenous base (RNA has A, C, G and instead of T, it has uracil (U). Each DNA nucleotide has one of the following bases –Adenine (A) –Guanine (G) –Thymine (T) –Cytosine (C)