Biology questions (First Level)?

1. Water is a polar molecule (that is, it is held together by polar covalent bonds). As a consequence …

A. Oxygen has a partial negative charge, because its protons pull electrons toward it.

B. Hydrogen has a partial positive charge, because its one proton has little pull on the electrons compared to oxygen.

C. Hydrogen bonds form between the partially negatively charged oxygens of one water molecule and the partially positively charged hydrogens of another.

D. All of the choices are correct.

2. Many hydrogen atoms (in the gas phase) are placed in a vial. Some collide at an angle that allows them to react with each other, and H2 (gas) is formed. The reaction 2H --> H2 releases energy overall. What type of bond forms between the hydrogen atoms?

A. Covalent, because the electrons are shared between atoms that have an equal number of protons (and thus equal electronegativity).

B. Polar covalent, because the electrons are shared between atoms that have very different atomic numbers (& numbers of protons) and so have different electronegativities.

C. Ionic, because one atom will completely transfer an electron to the other atom.

D. Hydrogen bond, because the bond is forming between hydrogen atoms.

3. According to the Watson-Crick model, DNA is a double-stranded molecule that consists of two single-stranded polymers. What holds the two single-stranded polymers together to form the double-stranded form of the molecule?

A. Weak bonds (van der Waals forces) between the stacked bases, and hydrogen bonds between A and T, and G and C.

B. Hydrogen bonds between A and G, and T and C.

C. Covalent bonds between A and G, and T and C.

D. Covalent bonds between A and T, and G and C.

4. Stanley Miller and his colleagues showed that the building blocks of life could have evolved on early Earth from inorganic components. What is thought to be the next step toward life?

A. The formation of DNA

B. The formation of the cell

C. The formation of proteins

D. The formation of RNA

5. Within a double-stranded DNA molecule, the 2 single-stranded polymers are described as 'antiparallel'. What does this mean?

A. 'Antiparallel' doesn't refer to the orientation of the strands, but to the angle of the hydrogen bonds between the bases.

B. 'Antiparallel' means the strands run in opposite directions, but side by side.

C. 'Antiparallel' means the two strands don't run exactly parallel to each other because of the twisting of the helix.

D. 'Antiparallel' means the two strands never achieve an orientation that allows them to be exactly side-by-side.

6. It has been hypothesized that early life consisted of an “RNA world”—a world before DNA. Which of the following does not support this hypothesis?

A. Retroviruses have an enzyme that catalyzes the synthesis of DNA from RNA.

B. Protein enzymes catalyze the great majority of reactions in living cells.

C. Ribozymes catalyze formation of peptide linkages.

D. Adding a short RNA sequence to a mixture of nucleotides causes formation of RNA polymers 7 million times faster than without the short sequence.

E. An artificial ribozyme catalyzes assembly of short RNAs into a longer molecule that is a copy of itself.

7. The ΔG of ATP hydrolysis is negative and the change in entropy is positive. The reaction, therefore,

A. requires energy.

B. is endergonic.

C. is exergonic.

D. will not reach equilibrium.

E. decreases the disorder in the system.

8. The phosphorylation of glucose to glucose-6-phospate has a ΔG of +4.0 kcal/mol. If hexokinase is added to speed up the rate of this reaction, the ΔG will

A. increase.

B. decrease.

C. stay the same.

D. increase, but only with an increase in enzyme amount.

E. decrease, but only with a decrease in enzyme amount.

9. In the presence of alcohol dehydrogenase, the rate of reduction of acetaldehyde to ethanol increases as the concentration of acetaldehyde is increased. Eventually, the rate of the reaction reaches a maximum, at which point further increases in the concentration of acetaldehyde have no effect. Why?

A. All the alcohol dehydrogenase molecules are bound to acetaldehyde molecules.

B. At high concentrations of acetaldehyde, the activation energy of the reaction increases.

C. At high concentrations of acetaldehyde, the activation energy of the reaction decreases.

D. The enzyme is no longer specific for acetaldehyde.

E. At high concentrations of acetaldehyde, the change in free energy of the reaction decreases.