Biology - Module 3 Mastering Bio Part 2

Use this model of a eukaryotic transcript to answer the following question.E = exon and I = intron5' UTR E1 I1 E2 I2 E3 I3 E4 UTR 3'Which components of the previous molecule will also be found in mRNA in the cytosol?

5' UTR E1 E2 E3 E4 UTR 3

The direction of synthesis of an RNA transcript is _____.

5' —> 3'

Transcription begins at a promoter. What is a promoter?

A site in DNA that recruits the RNA Polymerase

Where does translation of secreted proteins?

Ribosomes in the rough ER

What happens to the expression of the lacI gene if lactose is not available in the cell?

There is no change—the lacI gene is constitutively expressed. The lacI gene is expressed regardless of the presence of lactose. Only the structural genes of the lac operon are affected by the presence or absence of lactose.

What is the function of the lacZ gene?

This gene encodes an enzyme, b-galactosidase, which cleaves lactose into glucose and galactose. The lacZ gene encodes b-galactosidase, a key enzyme in lactose metabolism. When lactose is present in the cell, the cell expresses lacZ and metabolizes lactose.

What is the process called that converts the genetic information stored in DNA to an RNA copy?

Transcription

Where does the translation of cytoplasmic proteins happen?

ribosome

The process, performed by the ribosome, of reading mRNA and synthesizing a protein is called ________.

translation The process of translation, or protein synthesis, is a crucial part of the maintenance of living organisms. Proteins are constantly in use and will break down eventually, so new ones must always be available. If protein synthesis breaks down or stops, then the organism dies.

A particular triplet of bases in the template strand of DNA is 5-AGT-3. What would be the corresponding codon for the mRNA that is transcribed?

3-UCA-5

Which of the following statements best defines the term operon?

An operon is a region of DNA that codes for a series of functionally related genes under the control of the same promoter. This arrangement of genes is common in bacteria. For example, genes involved in lactose metabolism are clustered in the lac operon of E. coli, and genes involved in tryptophan metabolism are in the trp operon.

What determines which base is to be added to an RNA strand during transcription?

Base pairing between the DNA template strand and the RNA nucleotides

Which of the following terms best describes the relationship between the newly synthesized RNA molecule and the DNA template strand?

Complementary Because the template strand determines the nucleotides to be added to the RNA strand, using the same complementarity rules of the DNA, they will be complementary to each other.

The operon model of the regulation of gene expression in bacteria was proposed by _____.

In 1961 Jacob and Monod proposed the operon model of gene regulation.

________ of translation always happens at the start codon of the mRNA.

Initiation

Which of the following processes correctly describes alternative RNA splicing?

It can allow the production of proteins of different sizes and functions from a single mRNA.

How does the transcription of structural genes in an inducible operon occur?

It starts when the pathway's substrate is present.

Once researchers identified DNA as the molecule responsible for transmitting heritable traits, they asked how information was transferred from the DNA in the nucleus to the site of protein synthesis in the cytoplasm. Which of the following statements correctly describes the mechanism of information transfer in eukaryotes that accomplishes this task?

Messenger RNA is transcribed from a single gene and transfers information from the DNA in the nucleus to the cytoplasm, where protein synthesis takes place.

Which of the following conditions is most likely to cause the lactose operon to be transcribed?

The cyclic AMP and lactose levels are both high within the cell.

In an experimental situation, a student researcher inserts an mRNA molecule into a eukaryotic cell after she has removed its 5 cap and poly-A tail. Which of the following processes would you expect her to find to have occurred?

The molecule is digested by enzymes because it is not protected at the 5 end.

Which of the following statements best describes the promoter of a protein-coding gene?

The promoter is a nontranscribed region of a gene. The promoter is the regulatory region of a protein-coding gene at which RNA polymerase must bind to initiate transcription—it is not transcribed into the RNA.

Transcription in eukaryotes requires which of the following molecules in addition to RNA polymerase?

several transcription factors

Spliceosomes are composed of _____.

small RNAs and proteins

The RNA that has an amino acid attached to it, and that binds to the codon on the mRNA, is called a _________.

tRNA

Sort each description by the type of RNA it describes. Drag each item to the appropriate bin.

tRNA - has amino acids covalently attached - contains an anticodon mRNA - specifies the amino acid sequence for a protein - contains exons rRNA - is a component of ribosomes - is the most abundant form of RNA The cell uses three different types of RNAs to build proteins. rRNA is part of the ribosome, which is the site of protein synthesis. mRNA carries the genetic information from the DNA; the information specifies the sequence of amino acids in the new protein. tRNA interprets the information from the mRNA and brings the appropriate amino acids to the ribosome.

Which of the following terms associated with transcription describe regions of nucleic acid? A. terminator B. gene C. RNA polymerase D. promoter

terminator gene promoter The gene itself, the promoter, and the terminator are all DNA deoxyribonucleic acid) sequences. The RNA (ribonucleic acid) that is produced is another. The RNA polymerase enzyme that performs transcription is a protein and therefore not a nucleic acid.

Which of the following results would occur if the repressor of an inducible operon were mutated so that it could not bind the operator?

the continuous transcription of the operon's genes

Which of the following choices represent mRNA molecules that could be produced from the primary RNA transcript by alternative RNA splicing? (In each choice, the yellow part on the left represents the 5' cap, and the yellow part on the right represents the poly-A tail.)

Alternative RNA splicing produces different mRNA molecules from the same primary RNA transcript. During alternative RNA splicing, all introns are removed, and some exons may also be removed. The removal of different exons produces different mRNA molecules, which are then translated into different proteins. Alternative RNA splicing can greatly expand the number of proteins produced from the same gene.

There is a mutation that is found in E. coli in the repressor that results in a molecule known as a super-repressor because it represses the lac operon permanently. Which of the following characteristics would you expect to observe in such a mutant?

It cannot bind to the inducer.

What happens to RNA polymerase II after it has completed transcription of a gene?

It is free to bind to another promoter and begin transcription.

Which of the following statements best describes the significance of the TATA box in the promoters of eukaryotes?

It is the recognition site for the binding of a specific transcription factor

The genetic code is redundant. What is meant by this statement?

More than one codon can specify the addition of the same amino acid.

Under which conditions are the lac structural genes expressed most efficiently?

No glucose, High lactose When glucose is absent and lactose levels are high, the lac structural genes are expressed the most efficiently. Without glucose, cAMP is produced and CAP can stimulate transcription of the structural genes. In the presence of lactose, the repressor does not bind to the operator and therefore does not block transcription.

Where does transcription and RNA processing happen?

Nuclear envelope

What molecule binds to promoters in bacteria and transcribes the coding regions of the genes?

RNA Polymerase

During which step of the replication-transcription-translation process does each type of RNA first play a role? Drag each item to the appropriate bin. (Not every bin has to be filled.)

Replication - none Transcription/RNA processing - mRNA Translation - tRNA - rRNA The understanding that genetic information flows in one direction, from DNA to RNA to protein, became known as the central dogma of biology. The replication-transcription-translation pathway is connected with the DNA→RNA→protein flow of information. During replication, a faithful copy of a DNA molecule is made. During transcription, the DNA "message" is copied onto a molecule of mRNA. During translation, the information carried in the mRNA is transferred to molecules of tRNA to build a protein on the ribosomes.

Use the table to sort the following ten codons into one of the three bins, according to whether they code for a start codon, an in-sequence amino acid, or a stop codon.

Start/methionine - AUG Stop - UAA - UAG - UGA Amino Acid the rest of the codon table

_________ of translation happens when the ribosome hits a stop codon on the mRNA.

Termination

During RNA processing a(n) _____ is added to the 3' end of the RNA

a long string of adenine nucleotide

The RNA segments joined to one another by spliceosomes are _____.

exons

The _________ is/are arranged sequentially after the promoter.

genes of an operon

RNA processing converts the RNA transcript into _____.

mRNA

A(n) ________ is a protein that inhibits gene transcription. In prokaryotes, this protein binds to the DNA in or near the promoter.

repressor

Regulatory proteins bind to _____.

the operator Transcription is inhibited when a regulatory protein binds to the lac operon operator.

How does the primary transcript in the nucleus of a eukaryotic cell compare to the functional mRNA?

the primary transcript is larger than the mRNA

Life as we know it depends on the genetic code: a set of codons, each made up of three bases in a DNA sequence and corresponding mRNA sequence, that specifies which of the 20 amino acids will be added to the protein during translation. Imagine that a prokaryote-like organism has been discovered in the polar ice on Mars. Interestingly, these Martian organisms use the same DNA → RNA → protein system as life on Earth, except that there are only 2 bases (A and T) in the Martian DNA, and there are only 17 amino acids found in Martian proteins. Based on this information, what is the minimum size of a codon for these hypothetical Martian life-forms?

5 bases In the most general case of x bases and y bases per codon, the total number of possible codons is equal to xy . In the case of the hypothetical Martian life-forms, is the minimum codon length needed to specify 17 amino acids is 5 (25 = 32), with some redundancy (meaning that more than one codon could code for the same amino acid). For life on Earth, x = 4 and y = 3; thus the number of codons is 43, or 64. Because there are only 20 amino acids, there is a lot of redundancy in the code (there are several codons for each amino acid)

Which of the following enzymes converts ATP to cAMP?

Adenylyl cyclase Adenylyl cyclase converts ATP to cAMP, which helps CAP bind and facilitates binding of RNA polymerase to the lac promoter.

Which statements about the modification of chromatin structure in eukaryotes are true? Select all that apply. A. Methylation of histone tails in chromatin can promote condensation of the chromatin. B. DNA is not transcribed when chromatin is packaged tightly in a condensed form. C. Some forms of chromatin modification can be passed on to future generations of cells. D. Acetylation of histone tails is a reversible process. E. Deacetylation of histone tails in chromatin loosens the association between nucleosomes and DNA. F. Acetylation of histone tails in chromatin allows access to DNA for transcription.

All but E

Suppose an experimenter becomes proficient with a technique that allows her to move DNA sequences within a prokaryotic genome. If a researcher moves the promoter for the lac operon to the region between the beta galactosidase (lacZ) gene and the permease (lacY) gene, which of the following results would be most likely?

Beta galactosidase will not be produced.

True or false? The mechanism by which glucose inhibits expression of the lac structural genes is known as catabolite stimulation, whereas the mechanism by which lactose stimulates expression of the lac structural genes is known as allosteric regulation.

False The process by which lactose binds to the lac repressor and inactivates it by causing it to change shape is known as allosteric regulation. However, the process by which glucose causes cAMP levels in the cell to drop, thereby preventing CAP from stimulating expression of the lac structural genes, is known as catabolite repression.

You are studying a bacterium that utilizes a sugar called athelose. This sugar can be used as an energy source when necessary. Metabolism of athelose is controlled by the ath operon. The genes of the ath operon code for the enzymes necessary to use athelose as an energy source. You have found the following: The genes of the ath operon are expressed only when the concentration of athelose in the bacterium is high. When glucose is absent, the bacterium needs to metabolize athelose as an energy source as much as possible. The same catabolite activator protein (CAP) involved with the lac operon interacts with the ath operon. Based on this information, how is the ath operon most likely controlled?

Metabolism of the sugar athelose in this hypothetical system is controlled by an operon that exhibits both positive control and negative control. Transcription of the ath operon is turned on when athelose is present (negative control), and sped up when the bacterium runs out of glucose and must rely on athelose for energy (positive control).

DNA does not store the information to synthesize which of the following?

Organelles

Place the events in the transcription of a gene in their proper order from left (first event) to right (last event).

RNA polymerase binds promoter -> RNA polymerase transcribes gene -> RNA polymerase reaches terminator -> RNA polymerase exits gene, RNA is released

For a repressible operon to be transcribed, which of the following conditions must occur?

RNA polymerase must bind to the promoter, and the repressor must be inactive.

Which of the following statements best describes the termination of transcription in prokaryotes?

RNA polymerase transcribes through the terminator sequence, causing the polymerase to separate from the DNA and release the transcript.

What name is given to the process in which pre-mRNA is edited into mRNA?

RNA processing

Which one of the following statements about RNA processing is correct?

Ribozymes may function in RNA splicing.

Polypeptides are assembled from _____.

amino acids

Amino acids are attached to tRNA by enzymes called ________.

aminoacyl-tRNA synthetase

Which of the following processes would result from a mutation that deactivates a regulatory gene of a repressible operon in an E. coli cell?

continuous transcription of the structural gene controlled by that regulator

Translation occurs in the _____.

cytoplasm

Where does the attachment of an amino acid to tRNA happen?

cytoplasm

Most repressor proteins are allosteric. Which of the following molecules binds with the repressor to alter its conformation and therefore affect its function?

inducer

When taken up by a cell, which of the following molecules binds to a repressor so that the repressor no longer binds to the operator?

inducer

A(n) _______ is a specific small molecule that binds to a bacterial regulatory protein and changes its shape so that it cannot bind to an operator, thus switching an operon on.

inducer An operon is made up of a promoter and the genes of the operon. The promoter, which includes an operator, is the stretch of DNA where RNA polymerase binds. Regulatory proteins bind to the operator. The genes of the operon code for a related set of proteins. A regulatory gene located away from the operon codes for a protein that controls the operon.

According to the central dogma, what is the intermediate molecule involved in the flow of information in a cell that should go in the blank?DNA → ________ → Proteins

mRNA

During RNA processing a(n) _____ is added to the 5' end of the RNA.

modified guanine nucleotide

In the presence of a regulatory protein the lac operon is _____.

not transcribed The regulatory protein of the lac operon is a repressor.

Where does the formation of ribosomal subunits happen?

nucleus

Regulatory proteins bind to the ________ to control expression of the operon.

operator

A(n) _________ is a stretch of DNA consisting of an operator, a promoter, and genes for a related set of proteins, usually making up an entire metabolic pathway.

operon

A(n) _________ is a specific nucleotide sequence in DNA that binds RNA polymerase, positioning it to start transcribing RNA at the appropriate place.

promoter

A(n) _________ codes for a protein, such as a repressor, that controls the transcription of another gene or group of genes.

regulatory gene

Which of these is NOT a component of the lac operon?

regulatory gene only The regulatory gene, while not a part of the operon, plays a role in regulating the expression of the genes of the operon

What name is given to the process in which a strand of DNA is used as a template for the manufacture of a strand of pre-mRNA?

transcription

What name is given to the process in which the information encoded in a strand of mRNA is used to construct a protein?

translation

What is allosteric regulation?

In allosteric regulation, a small molecule binds to a large protein and causes it to change its shape and activity. Allosteric regulation is an important mechanism for changing enzyme activity, as well as for changing the function of some gene repressors and activators.

It is possible for a cell to make proteins that last for months; hemoglobin in red blood cells is a good example. However, many proteins are not this long-lasting; they may be degraded in days, hours, or even minutes. What is the advantage of short-lived proteins

Short-lived proteins enable the cells to control their activities precisely and efficiently.

Drag the labels to the appropriate bins to identify the step in protein synthesis where each type of RNA first plays a role. If an RNA does not play a role in protein synthesis, drag it to the "not used in protein synthesis" bin.

Transcription/RNA processing - mRNA - snRNA - pre-mRNA Translation - rRNA - tRNA Not used in protein synthesis - RNA primers In eukaryotes, pre-mRNA is produced by the direct transcription of the DNA sequence of a gene into a sequence of RNA nucleotides. Before this RNA transcript can be used as a template for protein synthesis, it is processed by modification of both the 5' and 3' ends. In addition, introns are removed from the pre-mRNA by a splicing process that is catalyzed by snRNAs (small nuclear RNAs) complexed with proteins. The product of RNA processing, mRNA (messenger RNA), exits the nucleus. Outside the nucleus, the mRNA serves as a template for protein synthesis on the ribosomes, which consist of catalytic rRNA (ribosomal RNA) molecules bound to ribosomal proteins. During translation, tRNA (transfer RNA) molecules match a sequence of three nucleotides in the mRNA to a specific amino acid, which is added to the growing polypeptide chain. RNA primers are not used in protein synthesis. RNA primers are only needed to initiate a new strand of DNA during DNA replication.

Sort the statements into the appropriate bins depending on whether or not each operon would be transcribed under the stated conditions.

operon is not transcribed - lac operon: lactose absent - trp operon: tryptophan present operon is transcribed, but not sped up through positive control - la operon: lactose present, glucose present - trp operon: tryptophan absent operon is transcribed quickly through positive control - lac operon: lactose present, glucose absent The trp operon is regulated through negative control only. When tryptophan is present, the operon genes are not transcribed. The lac operon is regulated through both negative control and positive control. Negative control:When lactose is absent, the repressor protein is active, and transcription is turned off.When lactose is present, the repressor protein is inactivated, and transcription is turned on. Positive control:When glucose is absent, another regulatory protein (CAP) binds to the promoter of the lac operon, increasing the rate of transcription if lactose is present.