micro exam 1

Select the stain(s) that would be used to successfully stain Mycobacterium species.

Carbolfuchsin

steps of gram staining

Cells must first be fixed to the slide, followed by crystal violet primary stain, then iodine mordant, then ethanol decolorizing, and finally the safranin counterstain. Performing any of these steps out of order will yield results that are neither meaningful nor useful.

numerical aperture (NA) than the oil immersion objective lens.

LOWER

Two students are working together to Gram stain a mix of Gram-positive and Gram-negative cells. One of the students accidentally uses a bottle of water instead of ethanol during the decolorization step. How would this mistake alter the results?

Without the decolorization step involving ethanol, both Gram-positive and Gram-negative cells would appear purple.

Proteins that transport only one kind of molecule down (with) that molecule's concentration gradient are involved in

facilitated diffusion.

Laura has a bacterial infection in her urethra, most likely Escherichia coli. How are the bacteria able to stay attached to the urethra, even during the full force of urination?

fimbriae

Which of the following are steps of the Gram stain?

one must fix cells to the slide surface, stain with crystal violet and iodine decolorize with ethanol, and finally counterstain with safranin.

Which of the following characteristics apply to Gram-positive cells and which apply to Gram-negative cells?

-Gram-positive cell wall is composed of many layers of peptidoglycan, with teichoic acids threaded through it for reinforcement. This supports the cell shape and protects it from physical stresses in the environment. It also holds up to the ethanol wash of the Gram stain, allowing the cells to retain the crystal violet so that they end up purple. -Gram-negative cell wall has very little peptidoglycan (possibly only a single layer) to hold its shape, but it also has an outer phospholipid bilayer containing lipopolysaccharide, which helps protect it from chemical stresses in the environment. Ethanol is able to destabilize phospholipid bilayers so Gram-negative cells decolorize during the ethanol wash and will end up pink at the end of the Gram-stain procedure.

The following statements are characteristics of either passive or active transport through cell membranes. Sort the characteristics into the correct bin.

-Passive transport can occur without the input of energy because molecules are moving down their concentration gradients (from an area of high concentration to an area of lower concentration). This includes simple diffusion, which does not even require a membrane-embedded protein, as well as facilitated diffusion, which does require a membrane protein to help the molecules pass through the phospholipid bilayer. -Active transport requires energy to be added to the system to move molecules against their concentration gradients (from an area of low concentration into an area of higher concentration). This requires the help of membrane-embedded proteins.

Identify the terms and characteristics associated with faryotic cells (such as bacteria) and those associated with eukaryotic cells.

-Prokaryotic cells are small cells. The chromosome is circular and the region of the cytoplasm where it is found is referred to as the nucleoid region. Typically, there are no internal membranes (except in a few types of photosynthetic bacteria) or membrane-enclosed organelles such as mitochondria. The structure of the cell wall is supported by a polysaccharide called "peptidoglycan." -Eukaryotic cells vary greatly in size from very small to quite large. The typical eukaryotic cell has a volume that is nearly 1,000 times greater than that of a typical prokaryotic cell. The chromosomes are linear and are contained in the nucleus of the cell. Eukaryotic cells have numerous membrane-enclosed organelles, including mitochondria.

Which of the following molecules is/are used to make lipopolysaccharide (LPS)?

-o antigen -core polysaccharide -lipid A

The oil immersion objective magnifies at

100X

Oil immersion is used when viewing a specimen using which objective?

100x

the scanning objective lens magnifies at

4x

What properties would you look for in the cell envelope of Gram-negative bacteria that is not present in Gram-positive bacteria?h

A Gram-positive cell envelope consists of a thick layer of peptidoglycan with teichoic acids and a cell membrane.

Which of the following is an example of a differential stain?

A differential stain stains two different kinds of cells differently. The Gram stain is a clinically significant stain that is used to differentiate between Gram-positive and Gram-negative organisms.

Which of the following molecules would the cell be most likely to move through the membrane using the process of efflux?

Antibiotics

Which of the following molecules would NOT be found as part of a bacterial cell's complex cell envelope?

DNA

While performing a Gram stain on a mixed culture, your cell phone rings and you accidently leave the decolorizing solution on too long. What color would you predict your Gram-positive cells to be upon completion of the procedure?

Leaving the decolorizing solution on too long will result in the over-decolorizing of the Gram-positive cells, causing them to lose their purple stain. Upon the addition of the safranin stain, all cells will stain pink.

At the end of microbiology lab, you decide to practice your Gram-staining skills. The teaching assistant has no fresh cultures but says you may use a plate she prepared several weeks ago. You find the correct plate in the refrigerator (labeled B.s. for Bacillus subtilis) and note that the colonies appear raised, dull, and wrinkled. This is just as you recall, so you get to work. After staining, you examine your slide under oil immersion and see that the cells are stained pink. What most likely accounts for this coloring?

Loss of cell wall integrity due to age, and over-decolorization with alcohol, are the two most common reasons why Gram-positive cells may appear Gram-negative. Over-fixing (especially with heat) can also affect cell shape and give erroneous staining results.

Which of the following molecules are the sugars needed for the synthesis of bacterial cell walls?

N-Acetylglucosamine and N-acetylmuramic acid

Why must a cell use energy to bring nutrients into the cell?

Nutrients are usually found in a low concentration outside the cell and must be transported against their concentration gradients. Energy is required whenever something is moved against its concentration gradient.

Lipopolysaccharides are part of the _________ in Gram-negative bacteria.

Outer membrane

Which of the following is NOT a function of the cell membrane?

RNA production

Total magnification is calculated by taking the power of the ocular lens multiplied by the objective.

So, in this case, 10× (ocular lens) times 100× (objective) = 1,000× total magnification.

The structural component of bacterial cell walls is a molecule called peptidoglycan. What two classes of organic molecules are used to create peptidoglycan?

Sugar molecules and amino acids

What is chemotaxis?

The ability to move toward or away from a chemical stimulus

An unknown bacterial sample has been correctly Gram stained and all cells appear pink. Which of the following is possible regarding these cells?

They are Gram-negative and could be Escher. Because all cells appear pink, they are Gram-negative;ichia.

A bacteriologist has Gram stained a mixed sample of unknown bacteria and has decolorized for one minute instead of 20 seconds. Which of the following best predicts the incorrect determination, if any, that will be made following the decolorization?

because of the lengthy decolorization, all Gram-positive cells will be stripped of any crystal violet. Therefore, those cells will be poised to accept safranin upon counterstain. The incorrect result will be that Gram-positives will be incorrectly identified as Gram-negatives.

In a high-quality (and also highly expensive) compound microscope, when the specimen is focused using one objective lens, it remains in focus (or close to focus) when the user switches to another lens. This microscope is therefore considered to be.....

parfocal

The rigid, sugar-like material that makes up the bacterial cell wall is composed of

peptidoglycan.

What type of stain is the Gram stain, and what does it rely on for meaningful results?

the Gram stain is differential because the staining substance interacts differently with different cell walls depending on whether they have just one layer or multiple layers of peptidoglycan.

Which of the following statements correctly describes the structure of the bacterial chromosome?

the bacterial genome contains thousands of genes encoded on several million base pairs of DNA. The bacterial chromosome is supercoiled within the cytoplasm and maintained by DNA-binding proteins.

Some bacteria respond to attractants or repellents (usually chemical in nature) in their environment. This response is called chemotaxis. If the bacterium has one flagellum or more, the bacterium must coordinate its flagellar movement to move toward or away from the stimulus. What is a type of repellent that a bacterium would respond to by moving away?

waste products