Quiz 2

List six functions of proteins.

enzyme catalyst, transport, signal reception, regulation, motility, and support.

A bilayer is associated with

E. phospholipids.

Complementary plays a major role in the structure of

D. DNA.

What is a structural isomer?

6-carbon sugars that contain the same atoms but in different chemical arrangements. they result in distinct sugars with different properties.

How do DNA and RNA differ from one another in composition and function?

DNA: contains the pentose sugar deoxyribose, nucleobases are A, T, C, and G, is a double-stranded helical structure, 5' end to 3', run anti-parallel. RNA: contains the sugar ribose, contains the nucleobases A, U, C, and G, shorter and typical single chain.

The function of a buffer is to

D. stabilize the pH of a solution.

Dehydration synthesis is involved in the synthesis of all of the following except

E. monosaccharides.

Which solution is more acidic, one with a pH of 4 or a pH of 5? What is the concentration of H+ ions in each?

a pH of 4 is more acidic than a pH of 5. pH of 4 has 10^-4 moles per liter and pH of 5 has 10^-5 moles per liter of H+ ions.

Differentiate between an atom, a molecule, and a compound.

an atom is the basic unit of all matter and each element is composed of only one type of atom. atoms consist of protons, neutrons, and electrons. a molecule is two or more atoms joined together by covalent bonds. a molecule is represented by the formula that indicates how many atoms of each type are present. if atoms that make up a molecule are different elements it is a compound. i.e. water is a compound of H+ and O- atoms.

Why is water a good solvent?

it is a good solvent because of its hydrogen bonding and its H+ and O- molecule charges. substances with charges can dissolve in water. non-polar substances can be organized by the presence of water. it is a polar molecule which is in humans and covers the Earth. because of its polar nature and can form hydrogen bonds with all polar molecules.

What is the significance of cellulose?

major structural polysaccharide in plant cell walls.

What are the four levels of protein structure, and what is the distinguishing feature of each?

primary structure: average-sized polypeptide consisting of about 250 amino acids, determined by the amino acid sequence. secondary structure: repeated coiling or folding in localized regions of proteins, results from folding of the various parts of the protein into two major patterns -> helices and sheets. tertiary structure: overall three-dimensional shape of a folded polypeptide, overall shape of the molecule with interactions between R groups superimposed over secondary structures of helices and sheets. Quaternary structure: the specific shape that results from the associations between the chains of polypeptides and proteins in weak bonds, results from several polypeptide chains interacting to form the protein.

Name the major groups of lipids and give an example of each. What feature is common to all lipids?

simple lipids: triglycerides, compound lipids: phospholipids, and steroids: estrogen and testosterone. the single common feature is that they are only slightly soluble in water.

When the pH of a solution changes from 3 to 8, the H+ concentration

A. decreases as the solution becomes more basic.

The primary structure of a protein relates to its

A. sequence of amino acids.

Pure water has all of the following properties except

B. ability to dissolve lipids.

An oxygen atom has an atomic number of 8. It typically forms:

B. two covalent bonds because it contains 6 electrons in its valence shell.

This table indicates the freezing and boiling points of several molecules. Carbon tetrachloride and methane are non-polar molecules. How does the polarity and non-polarity of these molecules explain why the freezing and boiling points for methane and carbon tetrachloride are so much lower than those for water?

Because of the hydrogen bonding between water molecules, much energy is required in the form of heat to break the bonds and convert the liquid into a gas. If there is no hydrogen bonding between molecules, less energy ( a lower temperature ) is required. Further, as the temperature drops, weak hydrogen bonds between water molecules are broken less frequently until a crystalline structure ( ice ) is formed in which hydrogen bonding between molecules is most stable. Molecules that can not form hydrogen bonds between molecules must reach lower temperatures to achieve stability between molecules and form a crystalline structure.

Choose the list that goes from the lightest to the heaviest:

C. electron, proton, atom, molecule.

A shortage of nitrogen (N) would make it most difficult to construct a molecule of

C. enzyme.

What properties of the carbon atom make it ideal as the key atom for so many molecules in organisms?

Carbon is the major building block of all matter because it can form four covalent bonds with other atoms including carbon atoms. Since these bonds can be single, double or triple bonds, with a variety of elements, a wide variety of different molecules can be formed. The bonds can be polar or non polar so a wide variety of molecules with different weak bonding properties can be formed.

A biologist determined the amounts of several amino acids in two separate samples of pure protein. The data are shown. The scientist concluded that protein A and protein B were the same protein. Do you agree with this conclusion? Justify your answer.

No. The amino acids might be arranged differently so the two proteins would be quite different and have different properties.

Microorganisms use hydrogen bonds to attach to surfaces. Many of the cells lose hold of the surface because of the weak nature of these bonds. Contrast the benefits and disadvantages of using covalent bonds as a means of attaching to surfaces.

The weak hydrogen bonds allow the organisms to detach and reattach very quickly and so the organisms can respond very quickly to changing conditions in the environment. Further, very little energy is required to attach and detach from surfaces.

A group of prokaryotes known as thermophiles thrive at high temperatures that would normally destroy other organisms. Yet these thermophiles cannot survive well at the lower temperatures normally found on Earth. Propose an explanation for this observation.

Thermophiles may lack lipids in their cell structures which would allow them to live in high temperatures, but not lower temperatures. Lipids are fats which play a role in temperature, more fats allow more survival in cold temperatures. OR. The enzymes can function well at the high temperatures but function poorly at the lower temperatures.

Show how dehydration synthesis and hydrolysis reactions are related, using an example each.

dehydration synthesis is a chemical reaction that removes the equivalent of one molecule of water and covalently joins subunits together. hydrolysis is used to break down a macromolecule into its subunits by adding water. both involve water and hydrolysis is essentially the reverse reaction. an example: to form a disaccharide, two monosaccharides are joined together by dehydration synthesis reaction between a pair of their hydroxyl groups meanwhile the reaction is reversible so hydrolysis produces the two original monosaccharides.