BIOL 2112 Chapter Notes - Chapter 5: Hydrophile, Fibril, Cell Membrane
10 May 2018
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Lecture 6 – Polymers, Carbohydrates, and Lipids
1) A. Three polymeric macromolecules are synthesized by the dehydration reaction (or
dehydration synthesis). Describe the mechanism of a dehydration reaction. In cells,
these processes are facilitated by enzymes, specialized macromolecules that speed up
chemical reactions. The reaction connecting monomers is a good example of dehydration
reaction – a reaction in which two molecules are covalently bonded to each other with the
loss of a water molecule. When a bond forms between two monomers, each monomer
contributes part of the water molecule that is released during the reaction (one monomer
provides a hydroxyl group while the other provides a hydrogen). B. What is the reverse
process of dehydration synthesis? Provide an example. Polymers are disassembled to
monomers by hydrolysis – the bond between monomers is broken by the addition of a
water molecule, with a hydrogen from water attaching to one monomer and the hydroxyl
group attaching to the other. C. Which of the four classes of macromolecules are
synthesized with the dehydration reaction? Proteins, carbohydrates, lipids. 2) The
glucose molecule is one of the most important organic molecules on earth. A. What type
of monomer is glucose? Monosaccharides B. Is glucose a ketose or an aldose? Why?
Depending on the location of the carbonyl group, a sugar is either a ketose or an aldose.
Glucose is an aldose. C. Describe the structure of glucose in an aqueous environment
(i.e. the cell). In aqueous solution, glucose molecules form rings because they are the
most stable form of these sugars under physiological conditions. 3) A. What is the term
for the covalent bond formed between two glucose monomers? A disaccharide consists
of two monosaccharides joined by a glycosidic linkage, a covalent bond formed between
two monosaccharides by a dehydration reaction. B. When two glucose molecules bond
together, which carbons are the most common sites for covalent bond formation?
Bonding of two units of glucose forms maltose. The 1-4 glycosidic linkage joins the
number 1 carbon of one glucose to the number 4 carbon of the second glucose. 4) When
glucose is ingested, it is either broken down immediately for cellular energy or it is
stored. A. How are glucose monomers stored? Both plants and animals store sugars for
later use in the form of storage polysaccharides. Plants store starch, a polymer of glucose
monomers, as granules within cellular structures known as plastids. Synthesizing starch
enables the plant to stockpile surplus glucose. Animals store a polysaccharide called
glycogen, a polymer of glucose that is like amylopectin but more extensively branched.
Vertebrates store glycogen mainly in liver and muscle cells. B. What is the function of
storage polysaccharides? Because glucose is a major cellular fuel, starch represents
stored energy. C. How do these macromolecules differ between plants and animals?
Plants store starch, animals store glycogen. 5) A. What is the structural difference
between starch and cellulose? Like starch, cellulose is a polymer of glucose with a 1-4
glycosidic linkages, but the linkages within the two polymers differ. When glucose forms a
ring, the hydroxyl group attached to the number 1 carbon is positioned either below or
above the plane of the ring. These two ring forms are called alpha (
) and (
) beta
respectively. In starch, all the glucose monomers are in the
configuration. In cellulose,
all of the glucose monomers are in the
configuration. B. How is a cellulose micro fibril
so strong? Cellulose in never branched, and some hydroxyl groups on its glucose
monomers are free to hydrogen bond with the hydroxyls of other cellulose molecules lying
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Document Summary
Lecture 6 polymers, carbohydrates, and lipids: a. Three polymeric macromolecules are synthesized by the dehydration reaction (or dehydration synthesis). In cells, these processes are facilitated by enzymes, specialized macromolecules that speed up chemical reactions. The reaction connecting monomers is a good example of dehydration reaction a reaction in which two molecules are covalently bonded to each other with the loss of a water molecule. When a bond forms between two monomers, each monomer contributes part of the water molecule that is released during the reaction (one monomer provides a hydroxyl group while the other provides a hydrogen). Polymers are disassembled to monomers by hydrolysis the bond between monomers is broken by the addition of a water molecule, with a hydrogen from water attaching to one monomer and the hydroxyl group attaching to the other. 2) the glucose molecule is one of the most important organic molecules on earth.
