Download Fats and Proteins

BIOLOGY – Activity
Modeling Fats and Proteins
Period 1 2 3 4 5 6 7 8
Date: _____________
Station # _____
Names _____________________
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INTRODUCTION
Lipids are a class of chemical compound composed mostly of carbon and hydrogen
atoms with very little oxygen. Common examples of lipids are fats, oils and waxes. Generally
these compounds are not soluble in water. On a molecular basis, all fats are somewhat similar.
Just as carbohydrates are composed of monosaccharide molecules, fats are composed of
smaller molecules. The smaller molecules in fats are called glycerol and fatty acid. There are
many different fatty acids but they are all similar in several ways. As with all molecules, a
molecular formula can be written for a fatty acid by counting the numbers of different atoms
and inserting those numbers as subscripts next to the corresponding symbol for the atom. For
example, the molecular formula for palmitic acid is C16H32O2.
Proteins also consist of many smaller molecules joined together. These smaller
molecules are called amino acids. Like many complex carbohydrates, proteins are polymers
made of smaller units called monomers. In carbohydrates, the monomers are simple sugars
whereas in proteins the monomers are amino acids. There are about 20 different amino acids so
there are thousands of different proteins.
OBJECTIVE
To determine the molecular characteristics of fats and proteins
MATERIALS
scissors
paper models of fatty acids and amino acids
glue
cardstock
PROCEDURE
Fats
Using the diagram provided:
1. What elements are present in glycerol? _________________________________
2. Are there elements in glycerol not found in carbohydrates? _________________
3. What is the molecular formula for glycerol? ______________________________
4. What is the ratio of H to O atoms in glycerol? ____________________________
5. Is the ratio of H to O in glycerol the same as in carbohydrates? _______________
6. What elements are present in all fatty acids? ______________________________
7. What is the molecular formula for butyric acid? ___________________________
8. What is the molecular formula for caproic acid? ___________________________
9. What is the ratio of H to O atoms in fatty acids? ___________________________
10. Is the ratio of H to O atoms the same in all fatty acids? _____________________
Notice that the end of the butyric acid molecule contains oxygen atoms in a special
arrangement of carbon and hydrogen called a carboxyl group as shown below.
11. Is the carboxyl group present in all fatty acids shown ? ___________________
A fat molecule consists of one glycerol molecule and three fatty acid molecules joined
together. Cut out the models of the glycerol and three fatty acid molecules by cutting along the
solid lines only. Next, cut along the dotted lines to remove the –H and –OH groups from each
of the paper molecule models. Join each –H you removed with an –OH.
12. What substance is formed when the –H and –OH are joined? ________________
Construct a fat molecule by joining the glycerol model you cut out with the three fatty acid
molecules. Production of a fat molecule is a chemical reaction. A chemical shorthand way of
expressing the formation of a fat is shown below.
Glycerol + fatty acids
fat +
water
Glue your fat molecule and all your water molecules on the card stock provided.
13. How many water molecules are formed when one fat molecules if produced?
__________
Many different kinds of fats exist in living things. The wide variety of fats are formed by
different combinations of fatty acid molecules.
14. What molecule remains the same in all fats? ______________________________
Proteins
Carbohydrates consist of many monosaccharides joined together while fats consist of glycerol
and fatty acid molecules joined together. Proteins also consist of many small molecules joined
together. In proteins, these smaller molecules are called amino acids. Examine the structural
formulas and corresponding models for the four amino acids on the diagram provided. Notice
the element nitrogen ( symbol N ) is present in all amino acids.
15. Is nitrogen present in fats and carbohydrates? ___________________________
16. What is the molecular formula for glycine? _____________________________
17. What is the molecular formula for alanine? ______________________________
18. Are the molecular formulas the same for all amino acids? ___________________
19. What end arrangement of atoms is present in
amino acids that are also present in fatty acids? _________________________
Another end arrangement of atoms in amino acids consists of a nitrogen atom and two
hydrogen atoms. This arrangement is called an amino group and is shown below.
20. Is the amino group present in all amino acids? _______________
A protein is composed of many amino acids joined together. Cut out the models of the four
amino acid molecules provided by cutting on the solid lines only. Next, cut along the dotted
lines to remove the –H and –OH groups from each of the paper models. Now join the 4 amino
acid models together in this order: valine - threonine – alanine - glycine. Also join the –H and
-OH units to each other and glue all your molecules to the card stock provided. Label the
molecules you have glued to the card stock and staple the card stock to the back of this packet.
Chemists can express the joining of these amino acids as follows:
valine + threonine + alanine + glycine
protein + water
21. How many molecules of water formed when you combined the
four amino acid molecules?
_____________
ANALYSIS
1. Dehydration means loss of water and synthesis means putting together. Explain
why the chemical process of building fats and proteins is called a dehydration
synthesis.
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2. What are the two types of molecules needed to form a fat molecule?
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3. What type of molecule is needed to from a protein?
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4. How does a glycerol molecule differ from a carbohydrate molecule?
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5. How does a fatty acid molecule differ from a carbohydrate molecule?
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6. How do amino acid molecules differ from fatty acid molecules?
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7. How are amino acids and fatty acids similar?
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8. How might a human muscle protein differ chemically from a cow muscle protein?
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9. Molecules of carbohydrates, fats and proteins can undergo a process called
condensation or hydrolysis ( hydro means water and lysis means to break apart ).
This process occurs when water molecules are used by cells to break apart the
subunits of polymers. For example, 3 water molecules are used to break a fat
down into the glycerol and the three fatty acids of which it was composed. What
part of the water molecule, -H or –OH, is reattached to the glycerol molecule
when a fat undergoes hydrolysis?
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10. How many water molecules must be used in the hydrolysis of a protein that
consists of 35 amino acids?
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Complete the table below by filling in YES or NO
Glycerol
carbon present
hydrogen present
oxygen present
nitrogen present
2:1 ratio between
H and O
has a carboxyl
group
has an amino
group
join to form
proteins
join to form
fats
Fatty acid
Amino acid