BIOL 1010 Lecture Notes - Lecture 13: Lac Operon, Operon, Polysome

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lRegulation of Gene Expression and Mutation

October 23, 2014

Structure of a Gene:

Transcription is very important when determining whether a gene is expressed, especially

in prokaryotic cells. In eukaryotic cells, translation and transcription occur in different

areas (separated by a membrane). In prokaryotic cells, these processes occur in one area

simultaneously because there are no membranes present.

Major Question: What controls gene transcription in bacterial cells?

The Operon:

The bacterial genome consisting of cistrons (genes) is transcribed into polygenic mRNA.

This causes the formation of polyribosome and direct translation into a polypeptide. All

genes have the same promoter and operator, which coordinate the control of the process.

*Eukaryotic cells do not have operons. Protein synthesis requires energy (ATP and GTP).

A cell will not make proteins it doesnt need.

Ex. The Metabolism of Lactose

Lactose gets broken down into glucose and Galactose (Metabolic Pathway).

The enzyme β-galactosidase breaks down the lactose ring.

Induction is the process that occurs when lactose is added to a growth medium, which

causes the concentration of this enzyme to increase rapidly.

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The Lactose Operon:

Structural Genes:

Lac Z – β-galactosidase

Lac Y – permease

Lac A – transacetylase

Binding of the Lactose Repressor Protein to the Operator blocks Transcription

of the Operon

Regulator Genes:

Lac I – repressor

Regulatory Proteins:

• Undergo a conformational change upon binding a small molecule (ligand)

that decreases or increases its affinity (binding) for DNA

• Proteins that undergo a conformational change upon binding a ligand, are

called allosteric proteins

DNA

mRNA

Protein

Active

repressor

RNA

polymerase

RNA

made

lacZ

lacl

Regulatory

gene Operator

Promoter

5¢

3¢

THE OPERON

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Document Summary

Transcription is very important when determining whether a gene is expressed, especially in prokaryotic cells. In eukaryotic cells, translation and transcription occur in different areas (separated by a membrane). In prokaryotic cells, these processes occur in one area simultaneously because there are no membranes present. The bacterial genome consisting of cistrons (genes) is transcribed into polygenic mrna. This causes the formation of polyribosome and direct translation into a polypeptide. All genes have the same promoter and operator, which coordinate the control of the process. A cell will not make proteins it doesn(cid:495)t need. Lactose gets broken down into glucose and galactose (metabolic pathway). The enzyme -galactosidase breaks down the lactose ring. Induction is the process that occurs when lactose is added to a growth medium, which causes the concentration of this enzyme to increase rapidly. Binding of the lactose repressor protein to the operator blocks transcription.

Related Questions

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.

QUESTION 1

How is a bone marrow transplant able to treat someone with leukemia?

		The donor blood contains antibodies that destroy cancer cells
		Donor blood contains stem cells that regenerate cells in the immune system
		Bone marrow contains induced pluripotent stem cells that turn into red blood cells
		Bone marrow contains tumor supressor genes that slow down leukemia growth
		Bone marrow contains pluripotent human embryonic stem cells

1.2 points

QUESTION 2

What would happen if siRNAs designed to target mRNA from an oncogene were introduced into cancer cells?

		Increased genomic instability would result from adding foreign nucleic acids
		New mutations would arise in the oncogene
		The oncogene would be converted back into a proto-oncogene
		The siRNAs would compete with the oncogene's active site
		Production of the oncogene protein would decrease

1.2 points

QUESTION 3

What is the purpose of chromatin-remodeling enzymes in human cells?

		The enzymes control the rate of translation of an mRNA transcript
		The enzymes add phosphate or methyl groups to histone tails
		The enzymes slide nucleosomes farther apart or closer to each other
		The enzymes send damaged proteins to the proteasome for degradation
		The enzymes cause DNA looping to occur

1.2 points

QUESTION 4

If you wanted to resurrect the mammoth, how would you do it?

		Use somatic cell nuclear transfer to insert the mammoth genome into the egg of an elephant
		Use transcription factors to re-program adult cells from elephants into mammoth cells
		Change the gene expression patterns of elephants to increase production of mammoth genes
		Use siRNAs to decrease expression of elephant-specific genes in an elephant embryo

1.2 points

QUESTION 5

How is eukaryotic transcription initiated?

		RNA polymerase is recruited to the start codon by transcription factors
		RNA polymerase begins transcription at the enhancer sequence
		RNA polymerase is activated by binding to GTP
		An initiator tRNA binds to the ribosome
		A complex of proteins forms at the promoter of a gene

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

BIOL 1010 Lecture Notes - Lecture 13: Lac Operon, Operon, Polysome

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