Microbiology practice test 3

How many genes are estimated to be present in the human genome?

20,000 (as opposed to the 4300 in prokaryotes)

Put the events of RNA sequencing in the correct order: 1. Extra adenine nucleotides are added to the end of the RNA strand, forming a tail 2. Segments of the RNA that do code for the protein are reconnected 3. A modified guanine nucleotide is added to the beginning of the RNA strand as a cap 4. Segments of the RNA strand that do not actually code for the protein are removed. 5. The completed messenger RNA (mRNA) leaves the nucleus A. 3, 4, 2, 1, 5 B. 4, 1, 2, 3, 5 C. 5, 3, 1, 2, 4 D. 1, 2, 3, 4, 5

A. 3, 4, 2, 1, 5

The names for the stages of transcription and translation are identical except for... A. Binding B. Elongation C. Termination D. None of the above

A. Binding applies to transcription; initiation applies to translation. (It's a dumb difference but he will ask you this.)

A mutation that results in a completely different protein due to nucleotide insertions OR deletions would be a... A. Frameshift mutation B. Missense mutation C. Silent mutation D. Substitution mutation

A. Frameshift mutation

Where does translation take place? A. Ribosomes in the cell cytoplasm B. Ribosomes in the cell nucleus C. The Golgi apparatus D. The plasma membrane

A. Ribosomes in the cell cytoplasm

Which of the following statements about DNA replication is correct? A. The leading strand is built continuously, and the lagging strand is built in pieces B. The leading strand is one of the strands of parental DNA C. The lagging strand is built continuously D. DNA ligase helps assemble the leading strand E. The lagging strand is one of the strands of parental DNA

A. The leading strand is built continuously, and the lagging strand is built in pieces (The leading and lagging strands are the new strands of DNA made during DNA replication. The leading strand is built continuously, and the lagging strand is built in pieces.)

During translation, the ribosome will translate the mRNA molecule until... A. The ribosome reaches a stop codon B. The sigma factor gives the signal for a small ribosomal subunit to attach to a mRNA molecule C. The RNA polymerase releases the mRNA polymer and detaches from the DNA D. The DNA ligase completes the process of joining the Okazaki fragments together to form a single unified strand

A. The ribosome reaches a stop codon (B happens during the first stage of translation, not the last. C and D happen during transcription and DNA replication respectively.)

Although blunt-ended DNA fragments are more difficult to join back together than are sticky ends, blunt ends have an advantage in that... A. They can be recombined with blunt fragments produced by different restriction enzymes B. Once joined to another blunt-ended fragment, the DNA can never be cut again C. They form many more hydrogen bonds than sticky-ended fragments D. Blunt-ended fragments can be used to make recombinant DNA between two different species

A. They can be recombined with blunt fragments produced by different restriction enzymes (Blunt-ended fragments are non-specific and can be joined to any other blunt-ended fragment, regardless of the restriction enzymes used.)

What is the function of the high temperature step in PCR (polymerase chain reaction)? A. To break hydrogen bonds for strand separation B. To deactivate DNA polymerase to pause synthesis C. To activate the DNA polymerase D. To facilitate DNA synthesis E. To allow primers to bind complementary sequences

A. To break hydrogen bonds for strand separation

When different phage particles infect the bacteria and are passed on before the cell dies during the lytic cycle, the cell is performing... A. Transduction B. Transformation C. Translation D. Transcontinentalism

A. Transduction

What type of mutation causes skin cancer? A. Ultraviolet radiation B. Chemical mutagens C. Inherited genes D. All of the above

A. Ultraviolet radiation (Technically skin cancer can also be hereditary--but the INITIAL cause is generally UV radiation)

What are the products of transcription? A. tRNA and mRNA B. rRNA and mRNA C. tRNA and rRNA D. tRNA, mRNA, and rRNA

A. tRNA and mRNA

Which of the following does NOT play a role in translation? A. Ribosomes B. DNA C. tRNA D. Amino acids E. Anticodon

B. DNA (DNA contains the instructions for making proteins, but these instructions are transcribed to RNA before translation occurs.)

Which enzyme breaks the hydrogen bonds during replication? A. DNA polymerase B. DNA helicase C. Stabilizing proteins D. RNA helicase

B. DNA helicase (DNA polymerase synthesizes DNA molecules from deoxyribonucleotides. Stabilizing proteins form new bonds with DNA, they don't break existing ones. RNA helicases do exist, but they relate to RNA and do not interfere with the hydrogen bonds of DNA.)

Which of the following statements about DNA replication is NOT true? A. DNA polymerase builds a new strand by adding DNA nucleotides one at a time B. DNA ligase adds nucleotides to the lagging strand C. Because the two strands of parental DNA run in opposite directions, the new strands must be made in different ways D. The lagging strand is made of a series of pieces that must be joined together to make a continuous strand E. None of the above, all of these are correct

B. DNA ligase adds nucleotides to the lagging strand (DNA ligase seals the gaps between segments of DNA in the lagging strand; it does not add nucleotides to the lagging strand)

In which direction does the replication fork move? A. It moves ahead of the unzipped DNA B. It moves ahead of the newly synthesized DNA C. It moves from the double-stranded DNA to the single-stranded DNA D. It moves towards the stabilizing proteins

B. It moves ahead of the newly synthesized DNA

The joining of two DNA strands or other molecules by a phosphate ester linkage is called... A. Hybridization B. Ligation C. Transformation D. Translation

B. Ligation

DNA encodes _____, which then encodes ______. A. Proteins, RNA B. RNA, proteins C. Genes, RNA D. Proteins, genes

B. RNA, proteins

Which enzyme is produced chiefly by certain bacteria, for the purpose of cleaving DNA molecules at or near a specific sequence of bases? A. DNA helicase B. Restriction endonuclease C. Ligase D. Polymerase

B. Restriction endonuclease

What role do restriction enzymes serve in the prokaryotes that produce them? A. They are involved in bacterial apoptosis or cell suicide B. They destroy viral DNA C. They provide a means by which different prokaryotic species can share genes D. They play a role in DNA synthesis during reproduction

B. They destroy viral DNA (Specifically, they destroy any viral DNA that might otherwise harm the bacterium or archaeon.)

In the laboratory, recombinant DNA technologists use restriction enzymes... A. To destroy pathogenic bacteria within a human cell B. To cut specific genes from one organism for the purpose of inserting the genes into the DNA of another organism C. Only as a last resort D. As genes

B. To cut specific genes from one organism for the purpose of inserting the genes into the DNA of another organism

A recipient cell takes up donor DNA, which aligns with complementary bases and results in recombination between donor DNA and recipient DNA. What is the name of this process? A. Conjugation B. Transformation C. Transduction D. Translation

B. Transformation

If you want to clone genes from eukaryotes, you cannot put a eukaryotic gene into a bacterium and expect to get a good protein because the introns will NOT be removed by the bacterium. What do you need in order to successfully complete this process? A. mRNA B. cDNA C. tRNA D. microRNA

B. cDNA (You'll need reverse transcriptase as well as cDNA, which can be cloned into plasma.)

Why are plasmids so important to bacteria?

Because nearly all plasmids that are used to deliver DNA contain genes for antibiotic resistance.

When analyzing the results of a cloning experiment, the insert is cloned into a vector containing a lacΖ sequence encoding the α-peptide, a functional subunit of the β-galactosidase enzyme. Empty vectors will be ______ and vectors containing the DNA insert that disrupts the lacZ sequence will be ______.

Blue; white.

What is the molecule that seals the gaps between the pieces of DNA in the lagging strand? A. DNA polymerase B. RNA polymerase C. DNA ligase D. Messenger RNA

C. DNA ligase (DNA ligase seals the gaps between the pieces of DNA in the lagging strand, turning it into a continuous strand.)

How are restriction enzymes named? A. Restriction enzymes are usually named after the scientist that discovers them B. The naming of a restriction enzyme involves several letters corresponding to an amino acid and a Greek letter implying the type of organism on which they act C. Each is named with letters referring to the genus, species, and strain of the source prokaryote and a Roman numeral denoting the order of its discovery D. Restriction enzymes are usually titled according to the nucleotide sequence of the restriction site upon which they act

C. Each is named with letters referring to the genus, species, and strain of the source prokaryote and a Roman numeral denoting the order of its discovery

Hybridization is the process of... A. Genetic alteration of a cell via direct uptake and incorporation of exogenous genetic material from its surroundings through the cell membrane to perform B. Categorizing RNA and DNA by using an electrical field to push separable molecules through a gel that contains small pores C. Forming a double stranded nucleic acid from joining two complementary strands of DNA or RNA D. Inserting two different species into a host organism to produce new genetic combinations

C. Forming a double stranded nucleic acid from joining two complementary strands of DNA or RNA (A is transformation, B is gel electrophoresis, and D is genetic engineering)

Double-stranded DNA fragments are separated by size using... A. PCR B. Northern blotting. C. Gel electrophoresis. D. Restriction analysis.

C. Gel electrophoresis

What are the three types of substitution mutations? A. Silent, frameshift, and deletion B. Frameshift, insertion, and deletion C. Missense, nonsense, and silent D. Missesnse, nonsense, and frameshift

C. Missense, nonsense, and silent

What type of substitution mutation occurs when a single nucleotide is replaced which results in a stop codon being produced, which causes a shortening of the protein? A. Missense mutation B. Silent mutation C. Nonsense mutation D. Frameshift mutation

C. Nonsense mutation

Which enzyme binds to the strand at the site of the primer and adds complementary base pairs to the strand during replication? A. Helicase B. Ligase C. Polymerase III D. Polymerase I

C. Polymerase III

Which of the following enzymes transcribes DNA? A. DNA polymerase B. DNA ligase C. RNA polymerase D. Transcriptase

C. RNA polymerase

Which of the following processes synthesizes a new strand of DNA from a template strand? A. Translation B. Transcription C. Semiconservative replication D. Meiosis

C. Semiconservative replication (DNA replication is literally THE only answer here that makes sense. Just saying.)

How do stabilizing proteins work on the DNA? A. They bind to the double-stranded DNA B. They use ATP to break the hydrogen bonds C. They bind to the single-stranded DNA D. They form the replication fork

C. They bind to the single-stranded DNA

What action do restriction enzymes employ? A. They inhibit DNA from being transcribed B. They glue two pieces of DNA back together C. They cut DNA D. They facilitate the production of hydrogen bonds

C. They cut DNA (To clarify: restriction enzymes work by cutting DNA at sites with very specific nucleotide sequences.)

Which of the following occurs during the elongation stage of transcription? A. RNA polymerase moves along the DNA until it reaches a terminator sequence, at which point the mRNA polymer detaches from the DNA B. The ribosome moves along the mRNA molecule linking amino acids and forming a polypeptide chain C. Transcription factors unwind the DNA strand and allow RNA polymerase to transcribe only a single strand of DNA into the single stranded RNA polymer mRNA D. The sigma factor gives the signal for a small ribosomal subunit to attach to a mRNA molecule

C. Transcription factors unwind the DNA strand and allow RNA polymerase to transcribe only a single strand of DNA into the single stranded RNA polymer mRNA

Which of the following does NOT occur during RNA processing? A. Adenine nucleotides are added to the end of the RNA strand, forming a tail B. Segments of RNA that do code for the protein are reconnected C. mRNA attaches to the small subunit of a ribosome D. Segments of the RNA strand that do not actually code for the protein are removed. E. A modified guanine nucleotide is added to the beginning of the RNA strand as a cap

C. mRNA attaches to the small subunit of a ribosome (mRNA attaches to the small subunit of a ribosome at the beginning of TRANSLATION.)

In which of the following organisms would you most likely find a plasmid? A. A human B. A cow C. An E. coli bacterium D. All of the above

D. All of the above. (Plasmids, or genetic structures in a cell that can replicate independently of the chromosomes, ARE mostly found in bacteria and protozoa....BUT bacteria also live in the bodies of other organisms. So by extension, plasmids could be found in other organisms because they reside in the plasmids inside the bacteria.)

The strand that serves as the template for transcription is called the ________ strand. The strand that is not transcribed is called the ________ strand. A. Coding, anticoding B. Sense, coding C. Anticodon, antisense D. Antisense, sense

D. Antisense, sense (The sense strand may also be referred to as the coding strand.)

Which of the following statements concerning sticky-ended fragments is TRUE? A. Sticky-ended fragments have the ability to join any other sticky fragment, regardless of whether or not it is complementary B. Sticky-ended fragments will never be more than two nucleotide bases long C. The sticky-ended fragments are much harder to join together than blunt-ended fragments D. Complementary sticky-ended fragments were likely cut by the same restriction enzyme

D. Complementary sticky-ended fragments were likely cut by the same restriction enzyme (Sticky-ended DNA fragments cut by the same restriction enzyme will always be complementary to one another. Sticky-ended fragments cut by two different restriction enzymes will most likely be different and thus not complementary to one another.)

Which of the following is responsible for building new strands of DNA? A. The lagging strand B. The leading strand C. Parental DNA D. DNA polymerases

D. DNA polymerases

Which of the following is NOT a mutagen? A. Nitrous acid B. Ultraviolet C. Ethidium bromide D. E. coli

D. E. coli. (Nitrous acid and ethidium bromide are chemical mutagens; ultraviolet is a radiation mutagen)

Which enzyme joins together Okazaki fragments? A. Okazakase B. Helicase C. Gyrase D. Ligase

D. Ligase (Helicase unzips the DNA, Gyrase unwinds and rewinds the DNA coils, and okazakase does not exist)

All restriction sites are palindromic. What does this mean? A. It means that the restriction sites are the same for both prokaryotes and eukaryotes B. It means that a restriction site may be targeted by any of the restriction enzymes C. The restriction sites are always five nucleotide base pairs in length D. The nucleotide sequences at the restriction sites are the same when read forward or backward

D. The nucleotide sequences at the restriction sites are the same when read forward or backward

Which of the following ensures that the single strands of DNA do not come back together? A. Opposite polar charges B. The DNA helicase C. The replication fork D. The stabilizing proteins

D. The stabilizing proteins

During translation, what happens as the ribosome moves along the mRNA molecule? A. The mRNA is released as the polypeptide chain forms B. A new tRNA molecule recognizes the next codon sequence on the mRNA, and attaches to the antisense strand C. mRNA turns into rRNA as soon as the stop codon is reached D. The tRNA in the first site is released, and the tRNA in the second site is translocated to the first

D. The tRNA in the first site is released, and the tRNA in the second site is translocated to the first

Which of the following statements about mRNA is correct? A. mRNA binds directly to amino acids during translation B. Segments of mRNA that code for protein are removed before translation C. mRNA is transcribed from DNA in the cytoplasm D. mRNA moves from the nucleus to the cytoplasm following RNA processing

D. mRNA moves from the nucleus to the cytoplasm following RNA processing (mRNA undergoes RNA processing in the nucleus and then moves to the cytoplasm for translation.)

What is cDNA?

DNA synthesized from a single stranded RNA (mRNA or microRNA) template in a reaction catalyzed by reverse transcriptase. Its chief use is to clone eukaryotic genes in prokaryotes.

Which of the following events occurs during transcription? A. A cap is added to the RNA molecule B. Those segments of the RNA strand that do not actually code for the protein are removed C. mRNA binds to a ribosome in the cytoplasm D. The message in mRNA is translated into a protein E. A molecule of RNA is formed based on the sequence of nucleotides in DNA

E. A molecule of RNA is formed based on the sequence of nucleotides in DNA (During transcription, RNA nucleotides line up with their complementary DNA partners, transcribing the information in DNA into RNA.)

Bacteria mutate faster than eukaryotic organisms chiefly because... A. Bacteria reproduce by cell division, which is faster than any of the reproductive methods utilized by eukaryotes B. Bacteria die off faster than eukaryotes, and quick mutation is a survival mechanism C. Bacteria need to adapt as more and more antibiotic and antibacterial drugs and substances are created, a threat not faced by eukaryotes D. A and B E. All of the above

E. All of the above

True or false: bacterial cells must be physically touching before conjugation in order for it to be successful.

False. Conjugation is the genetic transmission through direct contact between cells, achieved by the sex pilus--the pilus is a flagella-like structure and can "reach," so the cells do not need to be on top of each other.

True or false: the terms "gene" and "DNA" are interchangeable.

False. Only the fragment of DNA that has the particular concrete meaning to synthesize a specific molecule makes up the gene, NOT the whole piece of DNA.

Where does reverse transcriptase come from?

From HIV and other similar viruses.

Why can't the primary transcript in eukaryotes be used for translation?

In prokaryotes, the transcription and translation occur in the cytoplasm whereas in eukaryotes, transcription occurs in the nucleus and translation occurs in the cytoplasm.

How many double-stranded DNA molecules do eukaryotes have per chromosome?

One

They may sound alike, but there is a key difference between the operon and the operator. What is it?

Operons are multiple genes that are a part of a single gene expression unit, while the operator controls the transcription of the operon.

Name some examples of gene products.

Proteins, ribosomal RNA, and transfer RNA

How does gel electrophoresis sort longer DNA fragments from shorter ones?

Shorter molecules move faster and migrate farther than longer ones because shorter molecules migrate more easily through the pores of the gel.

What is the purpose of DNA replication?

The purpose of DNA replication is to produce two identical copies of a DNA molecule. This is essential for cell division during growth or repair of damaged tissues. DNA replication ensures that each new cell receives its own copy of the DNA.