Mastering Biology Chapter 15

What is the function of a spliceosome?

RNA processing

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.

Why is the lac operon said to be an inducible operon?

When allolactose is present, it induces the inactivation of the lac repressor.

How do miRNAs function in controlling gene expression?

by binding to mRNAs and degrading them or blocking their translation

DNA methylation is a mechanism used by eukaryotes to __________.

inactivate genes

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

not transcribed

Enzyme complexes that break down protein are called _____.

proteasomes

Protein-phosphorylating enzymes' role in the regulation of gene expression involves _____.

protein activation

The nuclear membrane's role in the regulation of gene expression involves _____.

regulating the transport of mRNA to the cytoplasm

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

regulatory gene only

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

Jacob and Monod

Regulatory proteins bind to _____.

the operator

Which of the following is an example of post-transcriptional control of gene expression?

the removal of introns and alternative splicing of exon

The operon model describes how bacteria control the production of groups of enzymes. In this model, synthesis of the messenger RNA coding for these enzymes is switched on or off by regulatory proteins. Can you match terms related to operons to their definitions? 1. 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. 2. The ______ is/are arranged sequentially after the promoter. 3. A(n) _______ is a specific nucleotide sequence in DNA that binds RNA polymerase, positioning it to start transcribing RNA at the appropriate place. 4. A(n) ______ for a protein, such as a repressor, that controls the transcription of another gene or group of genes. 5. Regulatory proteins bind to the ______ to control expression of the operon. 6. A(n) ______ is a protein that inhibits gene transcription. In prokaryotes, this protein binds to the DNA in or near the promoter. 7. 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.

1. operon 2. genes of an operon 3. promoter 4. regulatory gene 5. operator 6. repressor 7. inducer

Which of these is a regulatory gene? The figure shows a structure of the lac operon. Letters from A to E mark the definite structures of the operon. Letter A marks the gen before structural genes. Letter B marks the part of the operon, which consists of lacZ, lacY, and LacA genes. Letter C indicates the enzyme, which moves along the operon. Letter D marks the part, named lacl. This part is located before others in the sequence. Letter E indicates the molecule, which can bind to the structure A.

D

Two potential functions that eukaryotic cells perform to regulate transcription are

DNA methylation and histone modification.

The trp and lac operons are regulated in various ways. How do bacteria regulate transcription of these operons? 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: trp operon: tryptophan present lac operon: lactose absent operon is transcribed, but not sped up through positive control: trp operon: tryptophan absent lac operon: lactose present, glucose present operon is transcribed quickly through positive control: lac operon: lactose present, glucose absent

Name the starting molecule from which cDNA is synthesized and the enzyme that does the synthesis.

mRNA ... reverse transcriptase

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? Drag the labels onto the diagram to identify the small molecules and the states of the regulatory proteins. Not all labels will be used.

POSITIVE CONTROL a) Inactive Activator (not glowing, w/o yellow square) b) cAMP c) Active Activator (glowing, w/ yellow square) NEGATIVE CONTROL d) Active Repressor (glowing, w/o yellow square) e) athelose f) Inactive repressor (not glowing, w/ yellow square)