Introduction to Cells CHEMICAL COMPOUNDS IN CELLS

What Are Elements and Compounds?  You are made of many substances.  These substances supply the raw materials that make up your blood, bones, muscles, and more.  They also take part in the processes carried out by your cells.

Elements  An element is any substance that cannot be broken down into simpler substances.  The smallest unit of an element is a particle called an atom.  Any single element is made up of only one kind of atom.

Compounds  Compounds form when two or more elements combine chemically.  Most elements in living things occur in the form of compounds.  The smallest unit of many compounds is a molecule.

What Compounds Do Cells Need?  Many of the compounds in living things contain the element carbon.  Most compounds that contain carbon are called organic compounds.  Compounds that don’t contain carbon are called inorganic compounds.

 Some important groups of organic compounds that living things need are carbohydrates, lipids, proteins, and nucleic acids.  Water is a necessary inorganic compound.  Many of these compounds are found in the foods you eat.

Carbohydrates  Sugars and starches are examples of carbohydrates.  Carbohydrates are energy-rich organic compounds made of the elements carbon, hydrogen, and oxygen.  The food-making process in plants produces sugars.

 Fruits and some vegetables have a high sugar content.  Sugar molecules can combine, forming larger molecules called starches, or complex carbohydrates.  Plant cells store excess energy in molecules of starch.

 Many foods, such as potatoes, pasta, rice, and bread, come from plants and contain starch.  When you eat these foods, your body breaks down the starch into glucose, a sugar your cells can use to get energy.

 Carbohydrates are important components of some cell parts.  For example, the cellulose found in the cell walls of plants is a type of carbohydrate.  Carbohydrates are also found on cell membranes.

Lipids  Lipids are compounds that are made mostly of carbon and hydrogen and some oxygen.  Cell membranes consist mainly of lipids.

 Fats, oils, and waxes are all lipids.  Gram for gram, fats and oils contain more energy than carbohydrates.  Cells store energy from fats and oils for later use.  Foods high in fats include whole milk, ice cream, and fried foods.

Proteins  Proteins are large organic molecules made of carbon, hydrogen, oxygen, nitrogen, and, in some cases, sulfur.  Foods that are high in protein include meat, dairy products, fish, nuts, and beans.  Much of a cell’s structure and function depends on proteins.

 Proteins also make up parts of the organelles within a cell.  A group of proteins known as enzymes speed up chemical reactions in living things.  Without enzymes, the many chemical reactions that are necessary for life would take too long.

Nucleic Acids  Nucleic acids are very long organic molecules.  These molecules consist of carbon, oxygen, hydrogen, nitrogen, and phosphorus.  Nucleic acids contain the instructions that cells need to carry out all the functions of life.  Foods high in nucleic acids include read meat, shellfish, mushrooms, and peas.

 One kind of nucleic acid is deoxyribonucleic acid, or DNA.  DNA is the genetic material that carries information about an organism and is passed from parent to offspring.  This information directs a cell’s functions.

 Most DNA is found in a cell’s nucleus.  The shape of a DNA molecule is described as a double helix.  The double helix forms from many small molecules connected together.  The pattern and sequence in which these molecules connect make a kind of chemical code the cell can “read.”

Water and Living Things  Water plays many important roles in cells.  Most chemical reactions in cells depend on substances that must be dissolved in water to react.  And water itself takes part in many chemical reactions in cells.

 Water also helps cells keep their shape.  A cell without water would be like a balloon without air!

 Water changes temperature slowly, so it helps keep the temperature of cells from changing rapidly – a change that can be harmful.  Water also plays a key role in carrying substances into and out of cells.  Without water, life as we know it would not exist on Earth.

 What’s That Taste? Lab  Homework is pages 28 & 29