Exam 1 MCs

The three main branches in the phylogenetic "tree" of life are:

Bacteria, Archaea and Eukaryotes

There is much interest in using bacteriophages to kill the bacteria that cause infectious diseases in
humans. Which of the following is a valid concern about such therapy?

The virus preparation might be contaminated with a few live bacterial cells

In a biological context, which of the following describes a strong bond?

Electron sharing between atoms with an electronegativity difference less than 1.6

Bacteria can vary the lipids they use in their membrane, depending on the temperature. The goal is
to keep the membrane from melting but not allowing it to get so solid that proteins cannot move around. How would the membrane of a psychrotroph growing at 28ºC compare to the membrane of the same organism growing at 5ºC?

It would have more cis-unsaturated lipids at 5ºC

Which type of microscope uses special prisms to make a thin specimen appear pseudo-3-dimensional?

Differential Interference Contrast

In Pasteur's famous experiment that finally disproved spontaneous generation, bacteria grew:

only in media that came in contact with other bacteraia

Weak bonds are caused by:

charge interactions

A phosphodiester bond is important in the structure of

RNA

Single-celled photosynthetic organisms with nuclei and without cell walls

algae

Which type of microscope is the best to use for viewing viruses attached to human host cells?

Scanning electron microscope

Which of the following is true about a condensation reaction?

It generally requires energy input

Mycolic acids cause mycobacteria to

resist chemical damage

Which type of microscopy would be most suitable for examining the 3-dimensional appearance of
magnetosomes inside a bacterial cell?

Electron cryotomography

A C-C (carbon-carbon) bond in molecule A undergoes a random charge fluctuation. As molecule A comes close to a C-C bond in molecule B, what will happen to molecule B?

A dipole will be induced ichi will weakly attract molecule B to molecule A

What makes passive transport “passive”?

It is unable to concentrate a solute against a chemical gradient

Which of the following microscopes depends on the phenomenon of photon drag to differentiate
between structures with different refractive index?

Phase contrast

Which of the following would not require enzyme catalysis?

Rotation of prolines R-group by 180 degrees

In an environment that was isotonic to the cell’s cytoplasm, what effect would penicillin have on logarithmic phase Gram-negative rod-shaped cells?

The cells would lose their rod shape

A hallmark of type 3 secretion system is

Secretion only one contact has been made with a host cell membrane receptor

The purpose of osmoprotectants accumulating within bacterial cells is

prevent the cytoplasm from shriveling up in a hyperosmotic environment

E. coli cells are able to chemotax towards a nutrient attractant (ATR). How?

By sensing ATR concentration every few milliseconds and keeping a “memory” of it

Which structure below most accurately represents a porin

E

The protein coat of an endospore

is deposited between the membranes of the forming endospore and the mother cell

Given their particular lifestyle, thermophilic bacteria must have evolved specialized mechanisms
to guard against

denaturation of their enzymes

Why does the PTS (phosphotransferase system) use a phosphorelay mechanism?

To sense the available carbohydrate and regulate cell responses accordingly

Which of the following is not a way to store bacterial cultures long-term?

Agar plates, refrigerated

The structure indicated by the arrow is most important for

DNA transfer

In the United States, swimming beaches are periodically tested for bacterial counts. In Indiana, a
beach is closed if the bacterial titer exceeds 125 bacteria per 100 mL. Which of the following would be
the best way to determine this titer?

Membrane filtration and plating

What is the role of the periplasmic binding protein in ABC uptake systems?

It blocks reverse transport of the solute

The purpose of an enrichment culture is to

allow better growth of one type of bacteria than others from an environmental sample

Which of the following statements about enzymes is INCORRECT?

Enzymes lower the free energy of a reaction

The luciferase reaction is not routinely used to obtain an accurate bacterial titer. Why not?

The amount of ATP produced per cell is not constant

Much of the bacterial cell membrane is made of lipids. Where do lipids come from during bacterial metabolism?

They are built from glycerol and acetyl-CoA

Which of the following is NOT a function of capsules or slime layers?

motility

Compare the two cultures represented by the growth curves at right. Which of the following conclusions can you make?

Culture B has the higher growth rate

You suspect a patient has a blood infection caused by a bacterium, and you need to get a titer of bacteria from the patient's blood. How would you do that most effectively?

Use a Petroff-Hauser chamber to estimate the titer

Which of the following statements about enzyme inhibitors is correct?

An allosteric inhibitor functions even at a much lower concentration than the substrate