Long Answers to - carbon dioxide and ethyl alcohol from sugar. Th...

1 Long Answers to Review Questions Chapter 1

• Using brewer’s yeast in an in vitro reaction, Buchner produced

carbon dioxide and ethyl alcohol from sugar. This discovery paved the way for modern biochemistry because it introduced the idea of enzymes, or catalysts, which can be used to increase the rate of chemical reactions in living organisms.

• Most enzymes are proteins, though sometimes they are RNA

molecules. Enzymes participate in physiologic processes such as aerobic respiration, fermentation, nitrogen metabolism, energy conversion, and programmed cell death.

• Biochemistry is the intersection between chemistry and biology

and aims to study biological processes at the molecular and cellular level. Biochemists attempt to understand the structure and function of biological molecules using hypothesis-driven experiments designed to answer specific biological questions.

• Amino acids, nucleotides, simple sugars, and fatty acids.
• Elements and functional groups, biomolecules, macromolecules

(biopolymers), metabolism, cells, organisms, and ecosystems.

• For a molecule to be considered organic, it must have at least

one carbon atom. Carbon is critical because it can make up to four covalent bonds, so it can serve as the structural backbone for complex organic molecules.

• Energy conversion, coenzymes, information storage, and signaling.
• A nitrogenous base, a five-carbon ribose or deoxyribose sugar, and

one to three phosphate groups.

• Base stacking describes the noncovalent aromatic ring interactions

that take place between the stacked nitrogenous bases of the DNA helix. Hydrogen bonding between complementary base pairs also plays a role in stabilizing the DNA helix.

• Messenger RNA molecules are used as a template for protein

synthesis. Small nuclear RNA plays a role in RNA processing.

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Solutions Manual for Biochemistry, 1e Roger Miesfeld, Megan McEvoy (All Chapters) 1 / 4

• CHAPTER 1  Long Answers to Review Questions

Micro RNA regulates messenger RNA translation and thus gene expression.Ribosomal RNA is contained in ribosomes. Transfer RNA molecules carry amino acids to the ribosome and are required for protein synthesis.

• Mutations in a gene will result in changes to the mRNA transcript. When

the altered mRNA is translated into a protein, the protein can have changes in its amino acid sequence. Addition of the wrong amino acid can lead to protein denaturation (unfolding) or loss of function, resulting in breakdown of biochemical pathways, which can lead to disease or death.

• Gene duplication can lead to new genes or higher survivability of individuals

containing duplicated genes. If doubling the amount of gene product (protein) increases the fitness of an organism, the second copy of the gene is maintained by evolution. However, if no fitness advantages accrue from doubling the amount of gene product, the duplicated gene is free to mutate into another gene that could confer new fitness advantages to an organism.In other cases, this gene could be removed by natural selection if it confers, or is mutated to confer, deleterious qualities to an organism.Biochem_LONG_AN01_001-004v3.0.1.indd 217/08/16 7:16 pm 2 / 4

3 Long Answers to Challenge Problems Chapter 1

• (a) Pyruvate → acetaldehyde + CO

2 (pyruvate decarboxylase).(b) Acetaldehyde + NADH + H + → ethanol + NAD + (alcohol dehydrogenase). (c) Acetaldehyde is a product in (a) and a reactant in (b).

• Buchner (1) used a different strain of yeast than Pasteur

used, (2) prepared the yeast extract using quartz mixed with diatomaceous earth (kieselguhr) rather than glass, and (3) his extract buffer contained glucose, which fortuitously served as the carbon source for fermentation.

• The total number of dodecanucleotides that can be synthesized is

4 12

= 16,777,216.

The total number of tetrapeptides that can be encoded is 20 4 =

160,000.

• Amylose is a polymer of glucose containing α(1→4) glycosidic

bonds that can be cleaved by the human enzyme amylase to produce glucose. However, cellulose is a glucose polymer containing β (1→4) glycosidic bonds that are cleaved by the enzyme cellulase, an enzyme that humans do not have. The reason why horses can digest cellulose is that they have intestinal bacteria expressing cellulase that is secreted into the gut and aids the horse in digestion of plant material.

• Liver cells and skeletal muscle cells both contain insulin receptors,

but only liver cells contain glucagon receptors; skeletal muscle cells do not.

6. mRNA: 5′ – AAAAAAUUUAAAUUU – 3′

Protein: NH

3 + -Lys-Lys-Phe-Lys-Phe-COO −

• Germ-line mutations that occur outside of protein-coding

sequences can persist in the germ line if they do not cause a defect in genome stability or regulation; these are called neutral mutations. However, germ-line mutations that occur Biochem_LONG_AN01_001-004v3.0.1.indd 317/08/16 7:16 pm 3 / 4

• CHAPTER 1  Long Answers to Challenge Problems

in ­protein-coding sequences will be selected against if they alter reproductive rates, and they tend to disappear from the population over long periods of time.

• Paralogous genes are the result of gene duplication and can diverge

within the same species in both structure and function over time, whereas orthologous genes encode proteins with the same structure and function in different species.

• Comparing two amino acid sequences of <20% does not reveal much about

the structure or function of proteins because different amino acid sequences could specify a similar protein structure, or a similar protein function, or ­neither. In contrast, two proteins that are >80% identical at the amino acid level are very likely to have the same structure and function.Biochem_LONG_AN01_001-004v3.0.1.indd 417/08/16 7:16 pm

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