Question 1

TAT is a codon for the amino acid tyrosine (Tyr).If a mutation changes TAT to TAC,a ________-point mutation has occurred.

Accepted Answer

The answer of TAT is a codon for the amino...

Question 2

CASE HISTORY
In San Francisco, a 3-year-old boy named Luke was admitted to the hospital after an abrupt onset of fever and a generalized seizure. The boy's cerebrospinal fluid was normal, and he had a normal chest radiograph, but his white blood cell count was 20,000/mm3 (normal is 5,000-10,000), with 85% polymorphonuclear leukocytes (PMns). Luke's blood culture revealed bacteremia (bacteria in the blood). The bacteria were identified as "nontypeable" Haemophilus influenzae bacteria. The nontypeable H. influenzae strain was beta-lactamase-positive (expressed an enzyme to inactivate penicillin G, ampicillin, and amoxicillin) but proved sensitive to cefixime, a third-generation cephalosporin.
The diagnosis surprised the boy's two fathers. They showed the doctor Luke's full record of immunizations and booster shots, including the standard DTaP (diphtheria, tetanus, and pertussis), hepatitis B, pneumococcus, and Haemophilus influenzae b (Hib). Why was Luke not protected by the Hib vaccine? The doctor explained that the Hib vaccine protected only from H. influenzae type b, the most common virulent strain-but not the only virulent strain. Six strains, or serotypes, a through f, are "typed" based on the type of polysaccharide capsule surrounding the cell envelope. The Hib vaccine targets capsule type b. But some variant strains of H. influenzae, called "nontypeable," lack a capsule. These strains can be identified on the basis of other properties, such as enzyme activities, but they are unaffected by the vaccine. Fortunately, after seven days of intravenous antibiotic, Luke recovered fully.
The H. influenzae strain infecting Luke was beta-lactamase positive. Would the cell be likely to express the gene for this enzyme at all times? Describe one mechanism by which the cell could regulate the expression of this enzyme.

Accepted Answer

The answer of CASE HISTORY
In San Francisco, a 3-year-old boy...

Question 3

Why might the insertion or deletion of three base pairs in a gene be less harmful than the insertion or deletion of only one or two base pairs?

Accepted Answer

The answer of Why might the insertion or deletion of...

Question 4

Transcription of genes starts at regions of the genome called ________.

Accepted Answer

The answer of Transcription of genes starts at regions of...

Question 5

CASE HISTORY
Tina,a 33-year-old store clerk from Peoria,Illinois,had her first dental exam in five years.She told the hygienist that her gums hurt and that stains appeared on her pillow where her jaw had rested.She also told the hygienist that she did not smoke or drink.
The hygienist found that Tina's gums were swollen and bled upon probing.The gums had receded from Tina's teeth,forming pockets about 5 mm deep,and X-rays revealed some loss of bone.
Tina then saw the dentist,who told her she had periodontitis,inflammatory disease of the gums and bone supporting the teeth.Periodontitis is caused by dental plaque,a biofilm of mixed bacterial species that grow on the teeth.Without regular oral hygiene,the biofilm grows beneath the gum and eventually causes loss of teeth.
Tina expressed surprise,as she thought that only elderly people suffered gum disease.The dentist asked her again whether she smoked,perhaps two packs a day.Tina denied smoking that much,but admitted to one pack a day.The dentist told her that smoking is a common factor in early gum disease,as are diabetes and genetic susceptibility.Under predisposing conditions,many different kinds of bacteria can cause gum disease.
To determine the bacterial species causing Tina's periodontitis,the dentist ordered a DNA test.The DNA test works by polymerase chain reaction (PCR),a technique in which a short piece of DNA is amplified (copied many times),making it possible to read the sequence of DNA base pairs.The DNA sequence reveals the bacterial species.Tina's DNA test revealed Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans,two Gram-negative anaerobes that are sensitive to metronidazole and amoxicillin,respectively.
The DNA test enabled the dentist to target the most effective antibiotics for Tina's condition.The dentist also enrolled Tina in a smoking cessation program.
Following amplification of the bacterial DNA from Tina's sample,one of the ways the bacteria involved may be identified is via sequencing of the amplified fragment of DNA.Explain how this process works and how it can be used to identify bacteria.

Accepted Answer

The answer of CASE HISTORY
Tina,a 33-year-old store clerk from Peoria,Illinois,had...

Question 6

An enzyme that cuts the DNA phosphodiester backbone at a particular DNA sequence is called a ________.

Accepted Answer

The answer of An enzyme that cuts the DNA phosphodiester...

Question 7

A protein that affects the expression of many different genes is known as a ________.

Accepted Answer

The answer of A protein that affects the expression of...

Question 8

CASE HISTORY
In Wichita,Kansas,a 20-year-old college student named Lillian visited the college health practitioner for a routine gynecological exam.Lillian's periods had been regular,but she recently noted some spotting between periods.Her last menstrual period was four weeks prior.The practitioner asked Lillian whether she was sexually active.Lillian reported two male partners within the past six months.She reported no vaginal discharge,dyspareunia (painful intercourse),genital lesions,or sores.Her breast,thyroid,and abdominal exam were within normal limits,as were her vital signs-blood pressure: 118/68,pulse: 74,respiration: 18,temperature: 37.1°C (98.6°F).
The genital exam revealed normal vulva and vagina.The practitioner found no cervical motion pain and no uterine or adnexal tenderness (areas that include and surround the fallopian tubes and ovaries).But Lillian's cervix appeared inflamed and bled easily,with a purulent discharge coming from the cervical os (opening).
The practitioner performed nucleic acid amplification tests (NAATs)for Chlamydia trachomatis and Neisseria gonorrhoeae.Within a day,the NAAT results were positive for Chlamydia and negative for N.gonorrhoeae.Wet-mount microscopy revealed no pathogens but many WBCs (white blood cells).The diagnosis was confirmed as chlamydia infection,an infection reportable to the Centers for Disease Control and Prevention (CDC).
The practitioner prescribed doxycycline to clear up the infection.To curtail transmission,the practitioner asked Lillian to identify all her sexual partners for partner notification.Lillian recalled a third partner seven months earlier.The practitioner also recommended use of condoms to decrease further infections.
Doxycycline is an antibiotic that binds to the bacterial ribosome.How does this antibiotic interfere with the creating of proteins in bacterial cells?

Accepted Answer

Doxycycline binds to the 30S subunit of the bacterial ribosome, preventing the binding of aminoacyl-tRNA to the A site of the ribosome, thereby inhibiting the elongation of the peptide chain during translation. This ultimately interferes with the creation of proteins in bacterial cells, which are essential for bacterial survival and replication.

Question 9

Proteins that assist the folding of newly formed proteins are known as ________.

Accepted Answer

The answer of Proteins that assist the folding of newly...

Question 10

Is the mRNA shown a model of a bacterial mRNA or a eukaryotic mRNA? Please explain your rationale.

Accepted Answer

The answer of Is the mRNA shown a model of...

Question 11

During Sanger DNA sequencing,in addition to normal dNTPs used in cellular DNA synthesis,small amounts of modified DNA polymerase substrates are added to the reaction.How do these modified monomers differ from the normal dNTPs?

Accepted Answer

The answer of During Sanger DNA sequencing,in addition to normal...

Question 12

In a two-component signal transduction system the response regulator activity is altered via phosphorylation.This is an example of

Accepted Answer

The alteration of response regulator activity via phosphorylation is an example of posttranslational control since it modifies the structure and activity of the protein after it has been synthesized. Choices A through C are not applicable since they involve changes that occur prior to protein synthesis.

Question 13

If DNA polymerase misincorporates a base,leading to a mismatch,how do repair enzymes distinguish the parental and daughter DNA strands to specifically fix the daughter strand?

Accepted Answer

The answer of If DNA polymerase misincorporates a base,leading to...

Question 14

Two common levels of regulation of protein activity are transcriptional control and posttranslational control.Please discuss the differences between the two in terms of speed of response and energy efficiency.

Accepted Answer

The answer of Two common levels of regulation of protein...

Quiz 8: Bacterial Genetics and Biotechnology