microbiology chapter 7

How many nucleotides are in a codon?

3

Without changing the sequence or the orientation of the sequence(s), which is/are complementary to the sequence 5' AGGCUAAC 3'?

3' TCCGATTG 5'

There are ____ codons to code for 20 possible amino acids

61

The report that genes direct the synthesis of proteins was first made by:

Beadle and Tatum.

True or False A codon consists of 2 nucleotides

False

What is the number of tRNA molecules that may be associated with translation?

Fewer than 64

Which may be or is an RNA molecule?

GGGCCCA AND GCCCUUA

Why is it a good idea for a bacterial cell to be able to use glucose FIRST as an energy source (until it is depleted), THEN switch to lactose?

Glucose is an easier compound to break down and obtain energy from than lactose AND for conservation of energy: why use the energy to make the enzymes for breaking down lactose when glucose doesn't need any extra enzymes for breakdown?

Which is not true of RNA?

It contains both uracil and thymine

Does the presence of introns/exons in eukaryotic cells provide more potential diversity in gene products (proteins) than is possible in prokaryotic cells?

It does. Exons/introns can be spliced together in different ways post-transcription to yield different mRNAs (and therefore, different proteins). Bacteria lack this system.

RNA transcript:

It is formed using the DNA minus strand as a template. It has the same 5'-3' orientation as the DNA positive strand. The template starts at the promoter region.

Which is FALSE about the RNA transcript?

It is made in short fragments that are then stitched together

Which is true about DNA replication?

It is semiconservative. It starts at an origin of replication. It is bidirectional. It requires RNA primers. ALL ANSWERS ARE CORRECT!

Which is true about prokaryotic (bacterial) RNA polymerase?

It is used during transcription

RNA:

It is usually single-stranded. It functions in the cytoplasm. It contains ribose. It is a component of ribosomes.

The amino acid that is placed first during translation in bacteria, mitochondria, and chloroplasts is:

N-formyl-methionine

Cells are often ground up with abrasive to get to their internal enzymes/molecules, followed by removal of the abrasives. Here are three situations and three outcomes. What is the correct interpretation of the results? In situation #1, radioactive amino acids are added to cell material, and radioactive proteins are produced. In situation #2, radioactive amino acids, cell material, and the enzyme DNAse (degrades DNA) are added together. Radioactive proteins are still produced. In situation #3, the ground-up cell material is allowed to sit for 24 hours before radioactive amino acids and DNAse are added to it. No radioactive protein is produced. What is the most likely interpretation?

Natural RNAses present in the ground-up material will degrade any existing mRNAs in that 24-hour interval. Added DNAses break down DNA so that new RNAs are not synthesized. This will lead to a loss of capability to translate protein in the last scenario.

Which of the following is/are true of DNA replication?

Nucleotides are added to the 3' end.

When E. coli is placed in a medium containing both glucose and lactose, why does cell growth stop temporarily when the glucose is used up?

Once glucose is depleted, the cell must use the lactose; before it can do this, it must express the lac operon and synthesize the enzymes needed to use lactose, which takes time.

RNA is characterized by which one of the following features?

Ribose

What structure is indicated by: 10A, 15T, 3G, 7C?

Single-stranded DNA

Which pair is INCORRECT?

Splicing—removal of introns from prokaryote mRNA following transcription.

True or false? Antisense RNA is the complement of the plus strand and may be useful in inhibiting translation.

True

If a DNA triplet is AGT, the mRNA codon would be ______ and the tRNA anticodon would be ______.

UCA; AGU

For synthesis of an inducible enzyme to occur:

a compound must bind to the repressor

A regulatory protein binds to the operator in a strand of DNA, blocking transcription. The protein is

a repressor

Activators:

are allosteric proteins AND are involved in positive control

ribozymes:

are self-catalytic RNA AND suggest that nucleic acids evolved before proteins.

Repressors

bind or do not bind to the operator depending on their shape (conformation) AND are involved in negative control

Negative control means a regulator molecule is:

bound, and transcription is inhibited OR removed, and transcription starts.

GCCCAAAG is a molecule of:

cannot tell as written

AUG:

codes for methionine AND determines the reading frame.

A stop codon:

codes for no amino acid.

The placement of the amino acid during translation is determined by the:

complementarity of the codon-anticodon

True or False: Adenine binds to thymine via three hydrogen bonds.

false

True or false: DNA replication is usually unidirectional.

false

Post-translational modification may include:

folding of the protein, often with the aid of chaperones AND removal of the signal sequence.

The simultaneous regulation of many bacterial genes is:

global control

The 3' end of DNA:

has a hydroxyl group attached to the number 3 carbon of deoxyribose

The two strands of DNA are bonded to one another by:

hydrogen bonds

The molecules that bind to a repressor and cause it to no longer bind to the operator are called:

inducers

Some segments of the precursor mRNA in eukaryotes are non-coding and are called

introns

Quorum sensing

involves the production and monitoring of signaling molecules AND is used by bacteria to sense the density of cells within their population

The lac operon:

is an example of negative control

The lac operon:

is an example of negative control.

The lagging strand:

is formed during DNA replication because of the antiparallel nature of DNA.

CAP

is involved in positive control AND works in conjunction with cAMP.

Glucose:

is preferentially used over lactose in E. coli as a result of catabolite repression AND glucose levels are the inverse of cAMP levels

The E-site:

is responsible for the release of the tRNA.

The P-site:

is the peptidyl site on the ribosome

Why is the position of the first AUG after the ribosome binding site critical?

it establishes the reading frame

The regulatory protein

may inhibit or enhance transcription

The ribosomes:

move along the mRNA in a 5'-3' direction AND provide a platform that brings the amino acids into a favorable position for joining

DNA polymerases:

move in a 3' to 5' direction on the template DNA.

The DNA site to which the repressor protein binds is the:

operator

The set of genes in bacteria that are linked together and transcribed as a single unit is referred to as a(n):

operon

The specific sequence of nucleotides in the DNA to which the RNA polymerase binds is the:

promoter region

Transcription begins at the ______ and ends at the ______, while translation begins at the ______ and ends at the ______.

promoter; terminator; start codon; stop codon

The genetic code has more than one codon for some amino acids. This is an example of

redundancy

Operon(s) in bacteria

refers to a group of genes that are controlled in a coordinated manner AND involve polycistronic mRNA

The term antiparallel:

refers to the opposite orientation of the two strands in DNA

The transcription terminator:

results in a hairpin loop structure in RNA AND results in the polymerase falling off the DNA template.

DNA replication is:

semiconservative

Bacteria use ______ attached to the polymerase to direct RNA polymerase to promoters; eukaryotic cells use ______ that attach directly to the DNA first instead.

sigma factors; transcription factors

Which molecule carries an anticodon?

tRNA

All of the following are true about DNA sequence analysis EXCEPT

the (−) strand of DNA is used.

When E. coli is grown in medium containing both glucose and lactose:

the cells grow fastest initially when glucose is available

True or False: Ribozymes are non-protein molecules with catalytic activity.

true

True or False: The anticodon determines which amino acid is linked to its tRNA.

true

True or False: The minus strand of DNA serves as the template for RNA production.

true

True or false: Ribozymes are non-protein molecules with catalytic activity.

true

True or false: The genetic code is nearly universal.

true

RNAi:

uses short pieces of single-stranded RNA to direct the degradation of specific RNA transcripts

A drug that inhibits the activity of bacterial DNA gyrase ______ be a good antibiotic because ______.

would; it would selectively inhibit bacterial DNA synthesis due to differences between bacterial/human gyrase

A graduate student is trying to isolate bacterial mRNA for an enzyme that will degrade trinitrotoluene (TNT). She's frustrated to find that the enzyme isn't produced when the bacterium in question is grown on nutrient agar. What might she do to solve the problem and obtain the mRNA?

Add TNT to the agar—this will drive synthesis of the enzyme to degrade it, leading to production of the mRNA the student is looking for

The scientists responsible for the idea that RNA can act as a catalyst were:

Altman and Cech.

Which tasks must a bacterial cell accomplish in order to multiply?

DNA duplication, RNA synthesis, protein synthesis

How can some bacteria sense the density of cells in an environment?

Detecting the concentration of a signaling molecule.

Which of the following is an example of phase variation?

E. coli producing pili for attachment to epithelial cells.

Cells are often ground up with abrasive to get to their internal enzymes/molecules, followed by removal of the abrasives. Here are two situations and two outcomes. What is the correct interpretation of the results? In situation #1, radioactive amino acids are mixed with ground-up cell material. Radioactive proteins are produced. In situation #2, radioactive amino acids AND the enzyme RNAse (an enzyme that degrades RNA) are mixed with ground-up cell material. No radioactive proteins are produced.

The mRNA from the cell can be used to make proteins with the radioactive amino acids in the first situation. In the second situation, the mRNA is destroyed by the RNAse before it can be translated into protein containing the radioactive amino acids.

One end of a strand of DNA is different from the other end. True False

True

Which of the following is INCORRECT?

Transcription is the conversion of DNA into RNA.