BI226 Study Guide - Permease, Lac Operon, Operon

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salmondeer718

11 Apr 2013

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Inducible: enzymes produced only when specific chemicals are present. Constitutive: enzymes that are produced continuously, regardless of the chemical makeup of the environment. Negative control: gene expression occurs unless it is shut off by some form of a regulator molecule. Positive control: transcription occurs only if a regulator molecule directly stimulates rna production. Enzymes responsible for lactose metabolism are inducible, and lactose serves as the inducer. Regulatory region is almost always upstream of the gene cluster it controls. Regulatory region is known as the cis-acting site. This site binds molecules that control transcription of a gene cluster. Actions at the site determine whether or not the genes are transcribed into rna and whether the corresponding enzymes or other protein products are synthesized from the mrna. (can turn on or turn off transcription). Made up of three structural genes and a regulatory region.

Related Questions

3. Assume that in a bacterial species you discover a cluster ofthree genes (A, B, and C) that accountfor the enzymatic production of a cellulose-like carbohydrate (clc)that is needed as a component of its cell wall. When there issufficient clc is in the cell, the three enzymes are notsynthesized. However, when more clc is needed, the three enzymesare abundantly produced. This cluster of genes appears to be undercoordinate control because deletion of a distant gene (R)results in constitutive expression of all three genes even whenexcess clc is present. When mutations (P^-) occur in a region upstream ofgene A, no synthesis of the three enzymes occurs even whenclc levels are extremely low. Mutations (O ^-)that occur right next to the P ^- mutationsresult in constitutive expression of all three genes even when clcis present at high levels.

(a) Do the three genes (A, B,and C) behave as if they were part of an operon?

(b) What type of control (positive or negative)seems likely to control the production of the three enzymes?

(c) What is the most likely function of theprotein produced from gene R?

(d) Do you expect that clc is an inducer,inhibitor, or corepressor?

(e) You discover that clc binds to the proteinmade from gene R. What is the most likely effect of this binding?(Hint: will it cause the R protein to bind DNA or fall off ofthe DNA?)

(f) Where do you think protein R binds?(Hint: P region or O region ?)

sapphirebeaver902

QUESTION 10

If you can drink milk as an adult, it means that you have inherited a mutation in the promoter of your lactase gene (the gene that encodes the enzyme you need to break down lactose). Predict the effect of this mutation:

		The mutation changes the number of domains in the enzyme, which makes it work more efficiently
		The mutation changes the amino acid sequence of the lactase protein
		The mutation increases the number of copies of the lactase gene that will be found in your genome
		The mutation changes whether the lactase sequence is found in an intron or exon
		The mutation affects the expression of the lactase gene

1.2 points

QUESTION 11

A competitive inhibitor is decreasing the activity of an enzyme. Predict the effect of adding more substrate to the reaction.

		The substrate will increase the reaction rate by binding to the allosteric site
		The substrate will increase the reaction rate by competing with the inhibitor for the active site
		The reaction rate will not change unless the inhibitor can be removed
		The enzyme adjusts its shape so that the substrate, but NOT the competitive inhibitor, can bind
		The substrate will bind to the competitive inhibitor and block its ability to bind to the enzyme

1.2 points

QUESTION 12

What determines where in the genome a transcription regulator will bind?

		Transcription regulators bind to the 5' UTR region of a gene
		Regulators bind via complementary base-pairing to certain DNA molecules
		Covalent bonds form between the transcription regulator and the atoms of the DNA backbone
		Every eukaryotic gene has a different transcription regulator that will bind to the 5' end of the gene
		Transcription regulators bind to specific DNA sequences via multiple weak non-covalent interactions

1.2 points

QUESTION 13

What is the basic premise of cell theory?

		DNA -> RNA -> protein
		All cells arise from pre-existing cells
		DNA provides the complete instructions to create a cell
		The identity of a cell is determined through gene expression patterns
		All cells contain the same four basic macromolecules

1.2 points

QUESTION 14

What is the benefit of using BOTH the lac activator and the lac repressor to control gene expression?

		Using both an activator and repressor enables cells to more accurately determine the amount of lactose available in the environment
		Enzymes to digest lactose are only made when energy is low and lactose is available
		The activator can override the inhibition of the lac operon by the repressor
		The repressor can control the enhancer, while the activator can control the promoter
		When neither the lac activator or repressor is present, expression of the lac operon is too high

1.2 points

QUESTION 15

What is the histone code used for?

		Phosphorylation and acetylation of DNA affect its ability to be compacted
		Changes to the sequence of DNA change whether DNA will wrap around histone proteins
		Covalent modifications of histones affect the ability of the transcription initiation complex to form
		Histones provide the codon sequences needed for translation to occur
		The histone code affects which amino acids will get added to a polypeptide

1 DNA sequences found in introns provide [A] amino acid sequence information.

[B] regulatory information.
[C] no known useful information.

[D] structure for the gene.
[E] alternative DNA splicing possibilities.

3. The TATA box is a(n)
[A] sequence close to the promoter region of many genes.
[B] square-shaped sequence.
[C] enhancer consensus sequence.
[D] activator sequence necessary for proper translation.
[E] None of the above

5. Regarding genes and gene expression, which of the following is not a difference between prokaryotes and eukaryotes
[A] Eukaryotic DNA does not contain a TATA box close to the initiation site as does prokaryotic DNA.

[B] In eukaryotes, RNA polymerase requires

'transcription factors'or initiation.

[C] Prokaryotic genes are often grouped together in

operons.

[D] In eukaryotes, the regulation of several genes at once requires common control elements in each of the genes.
[E] There is a diversity of eukaryotic polymerases that is reflected in the diversity of eukaryotic promoters.

10) In eukaryotic cells, a repressor

[A] is made of DNA.
[B] binds to the enhancer region to block transcription. [

C] is located both upstream and downstream from the promoter.
[D] binds to the operator to block RNA polymerase.

[E] binds to a silencer to reduce transcription rates.

Coordinated regulation of genes in eukaryotic cells [A] is the result of positioning the same regulatory sequence in front of each gene.
[B] results from all of those genes being under the control of one promoter.

[C] occurs because related genes all have the same

operons.
[D] occurs because enhancers cause DNA to bend.

BI226 Study Guide - Permease, Lac Operon, Operon

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