3.E: Biological Macromolecules (Exercises)
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3.1: Synthesis of Biological Macromolecules
Review Questions
Dehydration synthesis leads to formation of
- monomers
- polymers
- water and polymers
- none of the above
- Answer
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C
During the breakdown of polymers, which of the following reactions takes place?
- hydrolysis
- dehydration
- condensation
- covalent bond
- Answer
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A
Free Response
Why are biological macromolecules considered organic?
- Answer
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Biological macromolecules are organic because they contain carbon.
What role do electrons play in dehydration synthesis and hydrolysis?
- Answer
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In a dehydration synthesis reaction, the hydrogen of one monomer combines with the hydroxyl group of another monomer, releasing a molecule of water. This creates an opening in the outer shells of atoms in the monomers, which can share electrons and form covalent bonds.
3.2: Carbohydrates
Review Questions
An example of a monosaccharide is ________.
- fructose
- glucose
- galactose
- all of the above
- Answer
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D
Cellulose and starch are examples of:
- monosaccharides
- disaccharides
- lipids
- polysaccharides
- Answer
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D
Plant cell walls contain which of the following in abundance?
- starch
- cellulose
- glycogen
- lactose
- Answer
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B
Lactose is a disaccharide formed by the formation of a ________ bond between glucose and ________.
- glycosidic; lactose
- glycosidic; galactose
- hydrogen; sucrose
- hydrogen; fructose
- Answer
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B
Free Response
Describe the similarities and differences between glycogen and starch.
- Answer
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Glycogen and starch are polysaccharides. They are the storage form of glucose. Glycogen is stored in animals in the liver and in muscle cells, whereas starch is stored in the roots, seeds, and leaves of plants. Starch has two different forms, one unbranched (amylose) and one branched (amylopectin), whereas glycogen is a single type of a highly branched molecule.
Why is it impossible for humans to digest food that contains cellulose?
- Answer
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The β 1-4 glycosidic linkage in cellulose cannot be broken down by human digestive enzymes. Herbivores such as cows, buffalos, and horses are able to digest grass that is rich in cellulose and use it as a food source because bacteria and protists in their digestive systems, especially in the rumen, secrete the enzyme cellulase. Cellulases can break down cellulose into glucose monomers that can be used as an energy source by the animal.
3.3: Lipids
Review Questions
Saturated fats have all of the following characteristics except:
- they are solid at room temperature
- they have single bonds within the carbon chain
- they are usually obtained from animal sources
- they tend to dissolve in water easily
- Answer
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D
Phospholipids are important components of ________.
- the plasma membrane of animal cells
- the ring structure of steroids
- the waxy covering on leaves
- the double bond in hydrocarbon chains
- Answer
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A
Free Response
Explain at least three functions that lipids serve in plants and/or animals.
- Answer
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Fat serves as a valuable way for animals to store energy. It can also provide insulation. Waxes can protect plant leaves and mammalian fur from getting wet. Phospholipids and steroids are important components of animal cell membranes, as well as plant, fungal, and bacterial membranes.
Why have trans fats been banned from some restaurants? How are they created?
- Answer
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Trans fats are created artificially when hydrogen gas is bubbled through oils to solidify them. The double bonds of the cis conformation in the hydrocarbon chain may be converted to double bonds in the trans configuration. Some restaurants are banning trans fats because they cause higher levels of LDL, or “bad” cholesterol.
3.4: Proteins
Review Questions
The monomers that make up proteins are called ________.
- nucleotides
- disaccharides
- amino acids
- chaperones
- Answer
-
C
The α helix and the β -pleated sheet are part of which protein structure?
- primary
- secondary
- tertiary
- quaternary
- Answer
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B
Free Response
Explain what happens if even one amino acid is substituted for another in a polypeptide chain. Provide a specific example.
- Answer
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A change in gene sequence can lead to a different amino acid being added to a polypeptide chain instead of the normal one. This causes a change in protein structure and function. For example, in sickle cell anemia, the hemoglobin β chain has a single amino acid substitution—the amino acid glutamic acid in position six is substituted by valine. Because of this change, hemoglobin molecules form aggregates, and the disc-shaped red blood cells assume a crescent shape, which results in serious health problems.
Describe the differences in the four protein structures.
- Answer
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The sequence and number of amino acids in a polypeptide chain is its primary structure. The local folding of the polypeptide in some regions is the secondary structure of the protein. The three-dimensional structure of a polypeptide is known as its tertiary structure, created in part by chemical interactions such as hydrogen bonds between polar side chains, van der Waals interactions, disulfide linkages, and hydrophobic interactions. Some proteins are formed from multiple polypeptides, also known as subunits, and the interaction of these subunits forms the quaternary structure.
3.5: Nucleic Acids
Review Questions
A nucleotide of DNA may contain ________.
- ribose, uracil, and a phosphate group
- deoxyribose, uracil, and a phosphate group
- deoxyribose, thymine, and a phosphate group
- ribose, thymine, and a phosphate group
- Answer
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C
The building blocks of nucleic acids are ________.
- sugars
- nitrogenous bases
- peptides
- nucleotides
- Answer
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D
Free Response
What are the structural differences between RNA and DNA?
- Answer
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DNA has a double-helix structure. The sugar and the phosphate are on the outside of the helix and the nitrogenous bases are in the interior. The monomers of DNA are nucleotides containing deoxyribose, one of the four nitrogenous bases (A, T, G and C), and a phosphate group. RNA is usually single-stranded and is made of ribonucleotides that are linked by phosphodiester linkages. A ribonucleotide contains ribose (the pentose sugar), one of the four nitrogenous bases (A,U, G, and C), and the phosphate group.
What are the four types of RNA and how do they function?
- Answer
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The four types of RNA are messenger RNA, ribosomal RNA, transfer RNA, and microRNA. Messenger RNA carries the information from the DNA that controls all cellular activities. The mRNA binds to the ribosomes that are constructed of proteins and rRNA, and tRNA transfers the correct amino acid to the site of protein synthesis. microRNA regulates the availability of mRNA for translation.