Exam 2 Flashcards
Antibiotics that weaken the peptidoglycan cell wall make a bacterium more prone to
Osmotic lysis
Many bacteria adapt to adverse environmental conditions by modifying the composition of their cell membranes. For example, the membranes of bacteria subjected to heat stress often contain high levels of which of these compounds?
Saturated fatty acids
Active transport is required for bacterial cells to
Transport solutes against their concentration gradient
Tetracycline is an antibiotic that works by binding to the 30S subunit of bacterial ribosomes, thus inhibiting protein synthesis. This drug is able to cross the cell membrane because
As a weak base, it can cross the membrane in its uncharged form
A- Bond hydrolyzed by lysozyme.
B- N-acetylglucosamine
C- Penicillin inactivates the enzyme that generates this bond.
D- This amino acid is not found in proteins.
E- Vancomycin prevents crosslinking by inhibiting this process.
F- N-acetylmuramic acid
BFDECA
Cells of a normally rod-shaped bacterium (e.g., Bacillus subtilis) that have completely lost the ability to produce the MreB protein would mostly likely be
Coccoid shaped
Bacteria exposed to quinolone-type antibiotics rapidly become unable to
Carry out normal gene expression, condense and package their chromosomes, replicate their DNA
Order the following events as they occur from beginning to end during DNA replication in a dividing cell.
A- Replisomes synthesize daughter chromosomes bidirectionally
B- Daughter cells separate
C- Terminator site is replicated
D- DNA @ origin unzips and replication forks form
E- Septum forms
- DNA @ origin unzips and replication forks form
- Replisomes synthesize daughter chromosomes bidirectionally
- Terminator site is replicated
- Septum forms
- Daughter cells separate
Which of the following is true of the newly synthesized daughter chromosomes?
Each chromosome contains one parental and one newly synthesized DNA strand.
The cell envelope of a Gram-negative cell, such as Escherichia coli or Vibrio cholerae, contains which of the following? (Select all that apply.)
A. an inner cytoplasmic membrane
B. porins
C. a thick peptidoglycan cell wall
D. a thin peptidoglycan cell wall
E. an outer membrane
ABDE
The outbreak was caused by the now infamous E. coli strain O157:H7. The “O” in this designation refers to an antigen on which of the following molecules?
Lipopolysaccharide
How does ToxR respond to pH and temperatures characteristic of the human gut environment?
Binding to the promoters of genes involved in virulence
Engineering principles employed by synthetic biologists include all except which of the following?
DNA sequences encoding random peptides
You want to develop a similar system that can respond to carbon monoxide. What gates and switches would you need to ensure the E. coli only fluoresce in the presence of CO?
A toggle switch to turn the gfp gene on or off and two NOT gates to repress or allow fluorescence depending on environment
Label the four specified parts of the genetic toggle switch.
A Neither repressor 1 nor GFP is made. No fluorescence.
B Repressor 2 inhibits transcription from promoter 2.
C Repressor 1 inhibits transcription from promoter 1.
D Repressor 2 is not made. GFP will fluoresce.
BCAD
BioBricks is a term used to describe which of the following?
Connectible pieces of DNA
What function does the targeted endonuclease Cas9 from Streptococcus pyogenes perform in the CRISPR-Cas9 system?
Breaking the double-stranded target DNA
First, CRISPR-Cas9 is used to target and remove the mutant gene. Second, naturally occurring repair enzymes will add the wild-type gene into the gap left from the site where the mutant gene was removed. Which of these bacterial repair mechanisms would most likely be responsible for repairing the DNA when used to edit bacterial genes?
RecA recombination repair
The CRISPR system
Is a type of immunity that directs degradation of foreign DNA upon repeat exposure.
Why do so many upstream regulatory elements have inverted repeats?
Many regulatory elements form dimers where each binds a repeat site and binding can cause a conformational change
Describe similarities and differences of regulation by activators vs repressors
Both- Bind at or near the promoter and encourage or prevent RNAP binding.
Repression- Binds operator to prevent transcription. If a repressor binds an operator, an inducer must bind to release the repressor (induction). Without a corepressor, the repressor binds weakly, releasing the corepressor releases repressor (derepression)
Activation- Transcription is stimulated by contacting the RNAP at a promoter. Without the inducer, the activator binds weakly, releasing the inducer releases the activator.
Why is there a biphasic growth curve if both glucose and lactose are present in the media?
There is a growth delay after glucose is gone while the lac operon is being expressed.
How does regulation of a catabolic pathway compare to that of an anabolic pathway?
Catabolic- Ligand binding would activate the pathway because the enzyme is induced when the substrate is present.
Anabolic- Ligand binding would repress the pathway because a product doesn’t need to be made if it’s present.
Describe the different types of regulation that occur at the trp operon.
The repressor only binds if tryptophan binds it. If there is high trp-tRNA, the P-independent terminator will form.
