Understanding Prokaryotic Genes

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1

A segment of prokaryotic DNA that binds transcription factors, usually as repressors that prevent transcription, are best known as __________.

Operators

CORRECT

Promoters

0

Exons

0

Enhancers

0

Untranslated regions

0

Explanation

The correct answer is operator. In most operons, repressors bind operators to prevent transcription of downstream genes.

Promoters are sequences of DNA upstream of genes that usually promote transcription by recruiting polymerases and other transcription factors. Enhancers are distant DNA sequences that promote transcription, whereas exons are the coding segments of a gene.

2

Which of the following is true of Rho-dependent transcription termination in prokaryotes?

Rho unwinds the DNA-RNA helix at the transcription bubble

CORRECT

Rho is a nuclease that terminates transcription by cutting template DNA

0

Rho uses GTP as a source of energy

0

Rho attaches to a Rho recognition site on the DNA template

0

None of the other answers

0

Explanation

Rho attaches to a Rho recognition site on the mRNA strand and uses ATP to move along the mRNA strand towards RNA polymerase. When RNA polymerase pauses at the terminator, Rho unwinds the DNA-RNA hybrid. RNA polymerase, Rho, and the newly synthesized mRNA are released.

3

Prokaryotic genes are often grouped together based on function. What are these groups of genes called?

Operons

CORRECT

Operator sequences

0

Promoter sequences

0

Clusters

0

Linked genes

0

Explanation

Bacteria organize some of their genes into operons. Operons contain genes of a similar function grouped together, and these genes are all transcribed together. For example, the lac operon involves the three genes required for breaking down lactose. There is no point in only transcribing one or two of the three genes since they are all required to break down lactose. Thus, they are under the control of a single operator and are all transcribed when the operator is active.

4

Which of the following technological advances allows for the creation of a “recombinant plasmid”?

Restriction endonucleases

CORRECT

cDNA libraries

0

Sanger sequencing

0

Watson-Crick base pairing

0

Viral vectors

0

Explanation

Restriction Endonucleases, or otherwise known as restriction enzymes, allows biologist to “cut and paste” different DNA sequences together. The use of restriction endonucleases is critical for the creation of recombinant plasmids. Viral vectors is incorrect, as viral vectors are useful in the application of recombinant DNA plasmids, delivery to host cell, but not in forming.

5

When a repressor binds to the __________, the LacZ gene does not get expressed.

operator

CORRECT

promoter

0

gene

0

terminator

0

Explanation

The region of a gene where activator/repressors bind in prokaryotic organisms is called an operator. The protein that's bound to the operon strongly influences the level of gene expression.

6

What is the main difference between prokaryotic and eukaryotic genes?

Prokaryotic genes only have exons, but eukaryotic genes have exons and introns

CORRECT

Prokaryotic genes are not replicated, and only transcribed to RNA to then become protein

0

Prokaryotes have one large gene, but eukaryotes have many smaller genes

0

Prokaryotes do not have gene regulatory sequences, but eukaryotes do

0

Eukaryotes stores genes together in operons, but prokaryotes do not

0

Explanation

The correct answer is that prokaryotes only have exons, whereas eukaryotes have exons and introns. As a result, in eukaryotes, when mRNA is transcribed from DNA, the introns have to be cut out of the newly synthesized mRNA strand. The exons, or coding sequences, are then joined together. Prokaryotes do not have to process their mRNA to this extent.

7

What is the function of RNA polymerase in prokaryotes?

Transcribe RNA from a DNA template

CORRECT

Replicate DNA during cell division

0

Repress transcription by binding operators

0

None of the other answers

0

Translate RNA to protein

0

Explanation

The correct answer is transcribe RNA from a DNA template. RNA polymerases are DNA-dependent, meaning that they require a DNA template; however, the new daughter strand that they create is composed of RNA. This RNA will then be translated into a functional protein by prokaryotic ribosomes.

8

Bacterial plasmids can __________.

All of these

CORRECT

carry antibiotic resistance genes

0

transfer between bacterial cells

0

be present in multiple copies

0

integrate into the bacterial genome

0

Explanation

Plasmids are small pieces of DNA that are not part of a bacteria's genome. The genes contained on plasmids are not necessary for proper function of the bacteria. However, bacterial plasmids can carry genes to confer antibiotic resistance, and commonly do. Plasmids can be transferred between bacteria via conjugation, and can be integrated into their genomic DNA.. Plasmids are usually present in more than one copy per cell.

9

A mutation in the bacterial cell escherichia coli makes it unable to break down the sugar lactose. Which of the following is not a potential mutation that could result in this phenotype?

A mutation in the region DNA polymerase binds to in the promoter

CORRECT

A frameshift mutation in the LacZ coding region

0

A mutation in the operator that blocks the activator from binding

0

A point mutation in the LacZ gene that abolishes enzyme activity

0

Explanation

DNA polymerase is not involved in the process of transcription. The incorrect answer could be corrected if it was rewritten as "a mutation in the promoter region where the RNA polymerase binds to."