Download Section 18.2

Changes in Matter
Chapter Eighteen: The Chemistry
of Living Systems
• 18.1 The Chemistry of Carbon
• 18.2 Protein, Fats, and Nucleic Acids
Investigation 18B
The Structure of DNA
• How does a DNA molecule carry information?
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 a
protein 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
The Scoop on Nutrition Labels
• 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.