Changes in Matter

Chapter Eighteen: The Chemistryof Living Systems

• 18.1 The Chemistry of Carbon

• 18.2 Protein, Fats, and Nucleic Acids

Investigation 18B

• How does a DNA molecule carry information?

The Structure of DNA

18.2 Proteins, fats and nucleic acids

• Proteins, fats, and nucleic acids are complex molecules, containing thousands of individual atoms in a single molecule.

• Nucleic acids found in DNA are at the core of genetics, an active area of scientific research.

• Fats are large molecules that take much longer to break down.

18.2 Fats

• Fats are high-energy molecules that plants and animals use to store energy.

• A fat molecule has a two-part structure.

18.2 Proteins

• Proteins are basic molecular building blocks of cells and all parts of animals.

• Proteins are among the largest organic molecules.

Why is the shape of aprotein important?

18.2 Saturated and unsaturated fats

• In a saturated fat, carbon atoms are surrounded by as many hydrogen atoms as possible.

• An unsaturated fat has fewer hydrogen atoms than it could have.

18.2 Enzymes

• Thousands of chemical reactions are going on in your body each second, involving thousands of chemicals.

• Catalysts help control chemical reactions.

• You can think of catalysts as helper molecules that allow a reaction to proceed in many small steps instead of all at once.

18.2 Enzymes

• Enzymes are special proteins.

18.2 Enzymes• Enzymes allow your body to initiate chemical reactions at a low

temperature and to control the rate of reactions.

The body has thousands of different enzymes.Each one is specific and matched with its target molecule.

18.2 DNA and nucleic acids

• Cells must continually create the proteins they need.

• In the process called protein synthesis, proteins are made using the instructions found in DNA molecules.

Where does the energy needed for this process come from?

18.2 DNA and nucleic acids

• DNA is a nucleic acid .• A DNA molecule is put

together like a twisted ladder.

*This model shows a short piece of the flattened DNA ladder. A DNA molecule is usually twisted and much longer.

18.2 DNA

• Each side of the ladder is made of:– 5-carbon sugars

called deoxyribose – and phosphate

groups.

18.2 DNA

• There are four nitrogen bases in two matched pairs.

18.2 DNA and amino acids• The assembly of proteins is coded by a certain

sequence of nitrogen bases.• The sequence: thymine + thymine + adenine

would code the amino acid leucine.

What sequence stops the assembly of proteins?Can you name the bases involved?

18.2 DNA and replication• When an organism reproduces, the DNA

molecule is able to make exact replicas of itself.

18.2 DNA and replication• Special enzymes play a role when DNA copies

itself:– Helicase enzymes untwist the DNA helix.– Ligase enzymes unzip the DNA.– Polymerase enzymes rebuild nitrogen bases on the

open strands.

18.2 DNA and reproduction• Changes in DNA are called mutations.

• Mutations lead to new proteins, and the resulting changes in living organisms are passed on in successive generations.

Health Connection

Good Fats vs. Bad Fats

• We need a reasonable amount of fat in our diets.

• Fat helps support cell function and helps our bodies absorb vitamins.

• But a diet too high in certain fats can lead to many health problems, including obesity, diabetes, and heart disease.

Activity

• A nutrition label shows the amount of calories, fat, cholesterol, carbohydrates, protein, and several vitamins and minerals in one serving of the food.

• The exact amount of each nutrient a person needs depends on gender, age, activity level, and weight.

The Scoop on Nutrition Labels