Deck 7: The Blueprint of Life, From Dna to Protein

Question 1

A graduate student is trying to identify the gene coding for an enzymefound in a bacterial species that degrades trinitrotoluene (TNT). Thestudent is frustrated to find that the organism does not produce theenzyme when grown in nutrient broth, making it difficult to collectthe mRNA needed to help identify the gene. What could the studentdo to potentially increase the amount of the desired enzyme?

Answer 1

Inducible enzymes are those that are only synthesized in the presence of their specific substrate molecules. In contrast, the constitutive enzymes are continuously synthesized because they are utilized by the basic metabolic pathways.
In the given case, the organism is not producing the enzyme when grown in the normal culture media. Means, the enzyme might be inducible.
So, the student should try growing the organism in the presence of trinitrotoluene (TNT) enzyme. The genomic expression is also influenced by the environmental conditions. So, the student should try growing the organism in both the aerobic and anaerobic conditions. TNT might also be used as a terminal electron acceptor, if that is the case, the student should try eliminating the nitrogen sources and grow the organism in the presence of TNT.

Question 2

The study of protein synthesis often uses a cell-free system where cells are ground with an abrasive to release the cell contents and then filtered to remove the abrasive. These materials are added to the system, generating the indicated results:
What is the best interpretation of these observations?

Answer 2

The two important steps in protein synthesis are "transcription and translation." During protein synthesis, mRNA (messenger RNA) is synthesised under the direction of DNA (deoxyribonucleic acid).
The message carried by the DNA is read by the mRNA, this process is called "transcription," it takes place in the nucleus. " Translation" of the message in the mRNA takes place with the aid of transfer RNA or tRNA.
The term "RNase" refers to the enzymes that digest RNA. From the given results, it can be observed that the protein is only produced in the absence of RNase. This indicates that the protein synthesis requires RNA.

Question 3

Replication is the process of duplicating double-stranded DNA. Transcription is the process of copying the information encoded in DNA into RNA. Translation is the process of interpreting the information carried by messenger RNA in order to synthesize the encoded protein.
How does the 5? end of a DNA strand differ from the 3? end?

Answer 3

DNA is an asymmetrical double helix molecule that has two strands running in opposite directions. One end of a strand of DNA has a free phosphate group (P). This end of the strand is the 5' end, while the other end of the strand, designated the 3' end, is marked by a free hydroxyl group (OH).
The strands are connected by hydrogen bonds that form between base pairs on each strand. One strand is oriented in the 5' to 3' direction, and its complement is oriented in the 3' to 5' direction.

Question 4

All of the following are involved in transcription except

A) polymerase.
B) primer.
C) promoter.
D) siga factor.
E) uracil.

Question 5

Explain what the term semiconservative means with respect toDNA replication.

Question 6

A student wants to remove the introns from a segment of DNA coding for protein X. Devise a strategy to do this.

Question 7

Replication is the process of duplicating double-stranded DNA. Transcription is the process of copying the information encoded in DNA into RNA. Translation is the process of interpreting the information carried by messenger RNA in order to synthesize the encoded protein.
What are the base-pairing rules?

Question 8

All of the following are involved in DNA replication except

A) polysome.
B) gyrase.
?
C) polymerase.
D) primase.
E) primer.

Question 9

What is an origin of replication?

Question 10

Replication is the process of duplicating double-stranded DNA. Transcription is the process of copying the information encoded in DNA into RNA. Translation is the process of interpreting the information carried by messenger RNA in order to synthesize the encoded protein.
If the nucleotide sequence of one strand of DNA is 5? ACGTTGCA 3?, what is the sequence of the complementary strand?

Question 11

All of the following are directly involved in translation except

A) promoter.
B) ribosome.
C) start codon.
D) stop codon.
E) tRNA.

Question 12

Why are primers required in DNA replication but not in transcrip­tion?

Question 13

DNA replication begins at the origin of replication and then proceeds bidirectionally, creating two replication forks. DNA polymerases synthesize DNA in the 5? to 3? direction, using one strand as a template to generate the complementary strand.
Why is a primer required for DNA synthesis ?

Question 14

Using the DNA strand shown here as a template, what will be the sequence of the RNA transcript?
5? GCGTTAACGTAGGC 3?
??
Promoter 3? CGCAATTGCATCCG 5?

A) 5? GCGUUAACGUAGGC 3?
B) 5? CGGAUGCAAUUGCG 3?
C) 5? CGCAAUUGCAUCCG 3?
D) 5? GCCUACGUUAACGC 3?

Question 15

What is polycistronic mRNA?

Question 16

DNA replication begins at the origin of replication and then proceeds bidirectionally, creating two replication forks. DNA polymerases synthesize DNA in the 5? to 3? direction, using one strand as a template to generate the complementary strand.
How does synthesis of the lagging strand differ from that of the leading strand?

Question 17

A ribosome binds to the following mRNA at the site indicated by the dark box. At which codon will translation likely begin?
5? ? GCCGGAAUGCUGCUGGC

A) GCC
B) GGC
C) AUG d) AAU

Question 18

Explain why knowing the orientation of a promoter is critical when determining the amino acid sequence of an encoded protein.

Question 19

DNA replication begins at the origin of replication and then proceeds bidirectionally, creating two replication forks. DNA polymerases synthesize DNA in the 5? to 3? direction, using one strand as a template to generate the complementary strand.
Eukaryotic chromosomes often have multiple origins of replication. Why would this be the case?

Question 20

Which of the following statements about gene expression is false?

A) More than one RNA polymerase can be transcribing a specific gene at a given time.
B) More than one ribosome can be translating a specific transcript at a given time.
C) Translation begins at a site called a promoter.
D) Transcription stops at a site called a terminator.
E) Some amino acids are coded for by more than one codon.

Question 21

What is the function of a sigma factor?

Question 22

Gene expression involves transcription and translation. RNA polymerase synthesizes RNA in the 5? to 3? direction, using one strand of DNA as a template. Ribosomes move along the resulting mRNA in the 5? to 3? direction, synthesizing protein. tRNAs carry specific amino acids, thereby acting as keys to the genetic code.
How does a promoter dictate which DNA strand is used as the template?

Question 23

An enzyme used to synthesize the amino acid tryptophan is most likely

A) constitutive.
B) inducible.
C) repressible.
D) a and b.

Question 24

What is the fate of a protein that has a signal sequence?

Question 25

Gene expression involves transcription and translation. RNA polymerase synthesizes RNA in the 5? to 3? direction, using one strand of DNA as a template. Ribosomes move along the resulting mRNA in the 5? to 3? direction, synthesizing protein. tRNAs carry specific amino acids, thereby acting as keys to the genetic code.
What is the role of tRNA?

Question 26

Under which of the following conditions will transcription of the lac operon occur?

A) Lactose present/glucose present
B) Lactose present/glucose absent
C) Lactose absent/glucose present
D) Lactose absent/glucose absent
E) a and b

Question 27

Explain how some bacteria sense the density of cells in their own population.

Question 28

Gene expression involves transcription and translation. RNA polymerase synthesizes RNA in the 5? to 3? direction, using one strand of DNA as a template. Ribosomes move along the resulting mRNA in the 5? to 3? direction, synthesizing protein. tRNAs carry specific amino acids, thereby acting as keys to the genetic code.
Could two mRNAs have different nucleotide sequences and yet code for the same protein? Explain your answer.

Question 29

All of the following are characteristics of eukaryotic gene expression except

A) 5? cap is added to the mRNA.
B) a poly A tail is added to the 3? end of mRNA.
C) introns must be removed to create the mRNA that istranslated
D) the mRNA is often polycistronic.
E) translation begins at the first AUG.

Question 30

Compare and contrast regulation by a repressor and an activator.
Repressors bind to the operator (downstream of the promoter), blocking the progress of RNA polymerase.

Question 31

Eukaryotic pre-mRNA must be processed, which involves capping, polyadenylation, and splicing. In eukaryotic cells, the mRNA must be transported out of the nucleus before it can be translated in the cytoplasm. Eukaryotic mRNA is monocistronic.
What is an intron?

Question 32

Which of the following statements is false?

A) A derivative of lactose serves as an inducer of the lac operon.
B) Signal transduction provides a mechanism for a cell to sense the conditions of its external environment.
C) Quorum sensing allows bacterial cells to sense the density of like cells.
D) An example of a two-component regulatory system is the lactose operon, which is controlled by a repressor and an activator.
E) An ORF is a stretch of DNA that may encode a protein.

Question 33

Explain why it is sometimes difficult to locate genomic regions that encode a protein.

Question 34

Eukaryotic pre-mRNA must be processed, which involves capping, polyadenylation, and splicing. In eukaryotic cells, the mRNA must be transported out of the nucleus before it can be translated in the cytoplasm. Eukaryotic mRNA is monocistronic.
Would a deletion of two base pairs have a greater consequence if it occurred in an intron or in an exon?

Question 35

Quorum sensing and two-component regulatory systems allow a cell to respond to changing environmental conditions. The expression of some genes changes randomly, increasing the chances of survival of at least a subset of a cell population under varying environmental conditions.
Explain how certain bacteria "sense" the density of cells.

Question 36

Quorum sensing and two-component regulatory systems allow a cell to respond to changing environmental conditions. The expression of some genes changes randomly, increasing the chances of survival of at least a subset of a cell population under varying environmental conditions.
Describe antigenic variation.

Question 37

Quorum sensing and two-component regulatory systems allow a cell to respond to changing environmental conditions. The expression of some genes changes randomly, increasing the chances of survival of at least a subset of a cell population under varying environmental conditions.
In quorum sensing, why might a bacterium synthesize more than one type of signaling molecule?

Question 38

Enzymes can be constitutive, inducible, or repressible. A repressor blocks transcription when it binds to an operator. An activator enhances transcription when it binds to an activator-binding site. The lac operon, a model for regulation, is controlled by a repressor, an activator, and inducer exclusion.
Explain the difference between a constitutive enzyme and an inducible enzyme.

Question 39

Enzymes can be constitutive, inducible, or repressible. A repressor blocks transcription when it binds to an operator. An activator enhances transcription when it binds to an activator-binding site. The lac operon, a model for regulation, is controlled by a repressor, an activator, and inducer exclusion.
Explain how glucose represses the lactose operon.

Question 40

Enzymes can be constitutive, inducible, or repressible. A repressor blocks transcription when it binds to an operator. An activator enhances transcription when it binds to an activator-binding site. The lac operon, a model for regulation, is controlled by a repressor, an activator, and inducer exclusion.
Why would it be advantageous for a cell to control the activity of an enzyme as well as its synthesis?

Question 41

RNA interference uses short strands of RNA to locate specific RNA transcripts destined for destruction.
What is the role of miRNA and siRNA in regulation of gene expression?

Question 42

Sequencing methods are rapid, but analyzing the data and extracting the pertinent information is difficult.
What is an open reading frame?

Question 43

Sequencing methods are rapid, but analyzing the data and extracting the pertinent information is difficult.
Describe two things that you can learn by searching a computerized database for sequences that have similarities to a newly sequenced gene.

Question 44

Sequencing methods are rapid, but analyzing the data and extracting the pertinent information is difficult.
There are characteristic differences in the nucleotide sequences of the leading and lagging strands. Why might this be so?