Enzymes are potent catalysts because they:
dramatically lower the activation energy for the reactions they catalyze.
Which of the following is true of the binding energy derived from enzyme-substrate interactions?
It is used to hold functional groups in optimal orientations for reactions to occur.
The concept of "induced fit" refers to the model that says:
substrate binding induces a conformational change in the enzyme, which can enhance binding of substrate enzyme and/or brings functional groups into proper orientation for the rapid change of substrate to product.
For an enzyme that follows Michaelis-Menten kinetics, which of the following statements about a plot of vo vs. [S] is false?
At very high [S], the velocity curve approaches a horizontal line that intersects the y-axis at Km.
Which of these statements about enzyme-catalyzed reactions is false?
The activation energy for the catalyzed reaction is the same as for the uncatalyzed reaction, but the equilibrium constant is more favorable in the forward direction for the enzyme-catalyzed reaction.
Which of the following statements about allosteric control of enzymatic activity is false?
Negative allosteric effectors compete with substrates for their binding sites.
A metabolic pathway proceeds according to the scheme R->S->T->U->V->W. A regulatory enzyme, X, catalyzes the first reaction in the pathway, R-> S. Which of the following is most likely correct for this pathway?
The last product, W, is likely to be a negative regulator of X, leading to feedback inhibition.
Which of the following describes how trypsinogen is converted to trypsin?
Proteolysis of trypsinogen forms trypsin.
Enzyme X exhibits maximum enzyme activity at pH = 7.0. X shows a sharp decrease in activity as the pH drops below 6.4. One likely interpretation of this pH activity is that:
a critical His residue on the enzyme is involved in the catalysis
Which one of the following is true of the pentoses found in nucleic acids, DNA, and RNA?
The pentoses are always in the B-furanose form.
In double-stranded DNA, cytosine typically base-pairs with:
Which of the following is not true of naturally occurring DNA?
The ratio of A+T/G+C is constant for all natural DNAs.
In naturally occurring double-stranded DNA:
the two strands have complementary sequences
B-form DNA in vivo has a _____-handed helix, is ______ A in diameter, with a rise of _____ A per base pair.
right; 20; 3.4
Which of the following is a palindromic sequence?
Double-stranded regions of RNA:
can form between two complementary regions of the same single strand of RNA.
When double-stranded DNA is heated at neutral pH, which change occurs?
The hydrogen bonds between A's and T's break.
In living cells, nucleotides and their derivatives can serve as:
carriers of metabolic energy
intracellular signaling molecules
precursors for nucleic acid synthesis
all of the above
Triple-helical DNA structures can result from Hoogsteen interactions. These interactions are primarily:
hydrogen bonds involving the bases.
The biological role of restriction enzymes is to:
degrade foreign DNA that enters a cell
Certain restriction enzymes produce cohesive (sticky) ends. This means that they:
make a staggered double-strand cut, leaving ends with a few nucleotides of single-stranded DNA protruding.
In the laboratory, recombinant plasmids are commonly introduced into bacterial cells by:
transformation-heat shock of the cells incubated with plasmid DNA in the presence of CaCl2.
A PCR reaction mixture needs to contain all of the following except:
heat-stable Restriction Endonuclease
Which of the following statements about the polymerase chain reaction (PCR) is false?
DNA is amplified at many points within a cellular genome.
Which of the following statements about type II restriction enzymes is false?
They cleave and ligate DNA.
The E. coli recombinant plasmid pBR322 has been widely utilized in genetic engineering experiments. pBR322 has all of the following features except:
a number of palindromic sequences near the EcoRI site, which permit the plasmid to assume a conformation that protects newly inserted DNA from nuclease degradation.
Which of the following statements regarding plasmid cloning vectors is correct?
The copy number of plasmids may vary from a few to 10-20 to possibly several hundred within a cell depending on the plasmid.
base stacking of double stranded complementary bases that occur in DNA and RNA