The Chemical Basis of Life

Water is the most abundant molecule found in living organisms.  Most mammals, in fact are approximately 70% water by weight.  About two-thirds of this water is present inside cells.  The other one-third is present outside cells (e.g., in blood plasma or other body fluids).  Why is water so important to cells?

• Water is stored in the cells to be used when the organism gets thirsty.
• Almost all the chemical reactions in life processes occur in solutions with water.
• Water determines which proteins are translated from the cellular DNA.
• The main structural component found in plasma membranes and cell walls is water.

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Each enzyme produced by the body is

• specific-meaning it is only able to catalyze a reaction with a certain molecule.
• immature-meaning it cannot catalyze a reaction until many years later.
• open-meaning it is able to catalyze a reaction with any molecule.
• incomplete-meaning it requires other parts before it is able to bind to a molecule.

Which of the following describes the role that enzymes play in the process of metabolism?

• Enzymes provide the chemical energy that is broken down and released during metabolism.
• Enzymes increase the rate of the chemical reactions carried out during metabolism.
• Enzymes store the chemical energy that is used to construct nucleic acids during metabolism.
• Enzymes carry the genetic instructions required for a cell to initiate metabolism.

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The molecule pictured is a __________ .

• amino acid
• nucleic acid
• carbohydrate
• lipid

All living organisms contain carbon atoms.  Which of the following is an important characteristic of carbon?

• Carbon atoms can bond with many other kinds of atoms to form very stable molecules.
• Carbon atoms can bond with any other atom, but they cannot form bonds with other carbon atoms.
• Carbon atoms are very stable and do not easily form bonds with other atoms.
• Carbon atoms are highly reactive and form unstable bonds with any available atom.

Nucleic acids are one of the four major macromolecules.  The main functions of nucleic acids are to

• store and transport energy and structural components in the cell.
• act as enzymes, cell signals, and structural support for the cell.
• carry genetic material and create structures inside the cell.
• aid in development, the immune system, and blood clotting.

Protein molecules are composed of long chains of __________ .

• ribosomes
• RNA
• amino acids
• DNA

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Organic macromolecules called __________ are insoluble in water, are often found in biological membranes and other waterproof coverings, and have the ability to store energy for extended periods of time.

• carbohydrates
• lipids
• proteins
• nucleic acids

Which reaction is responsible for the production of lipids, when glycerol is joined to three fatty acids?

• dehydration
• hydrolysis
• hydrophilic
• hydrophobic

In living things, dehydration synthesis reactions result in the formation of

• polymers.
• monomers.
• carbon atoms.
• monosaccharides.