Biology Chapter 18: Gene Expression Regulation

Questions and Answers

Why are all genes not 'on' all the time in E. coli?

The E. coli turns on the genes only when it needs enzymes to produce the amino acid tryptophan, and since it does not need this all the time, it turns off the genes to save energy and not overproduce tryptophan.

What are the two main ways of controlling metabolism in bacterial cells?

Gene regulation and enzyme regulation

Is feedback inhibition in E. coli regulating tryptophan synthesis positive or negative inhibition?

Negative inhibition

What is a promoter?

A site where RNA polymerase can bind to DNA and begin transcription. Signup and view all the answers

What is the operator and what does it do?

The operator is a segment of DNA that acts as the 'switch' for the group of functionally related genes, located between the promoter and enzyme-coding genes. Signup and view all the answers

What is an operon?

The combination of the operator, promoter, and the genes they control. Signup and view all the answers

List the three components of an operon and explain the role of each one.

(1) Promoter: where RNA polymerase binds; (2) Operator: acts as the switch for the genes; (3) Genes of Operon: the genes that are transcribed and translated into proteins. Signup and view all the answers

How does a repressor protein work?

It binds to the operator and blocks the attachment of RNA polymerase to the promoter, preventing genes from being transcribed. Signup and view all the answers

What are regulatory genes?

Regulatory genes are located away from the operon, have their own promoter, and can influence the operon. Signup and view all the answers

Distinguish between inducible and repressible operons and provide one example of each.

Repressible operons are usually ON but can be inhibited by a small molecule; inducible operons are usually OFF but can be stimulated by a small molecule. Signup and view all the answers

What is a corepressor? Give an example.

A small molecule that cooperates with a repressor protein to switch an operon off; tryptophan is an example. Signup and view all the answers

What is CAP and how does it work?

Catabolite Activator Protein; cAMP binds to CAP, which then attaches to the lac promoter to increase the chances of RNA polymerase binding. Signup and view all the answers

Explain why CAP binding and stimulation of gene expression is positive regulation.

It facilitates the binding of RNA polymerase to the promoter, increasing the rate of transcription. Signup and view all the answers

Describe the relationship between glucose supply, cAMP, and CAP.

Low glucose increases cAMP, activating CAP and leading to more lac mRNA synthesis; high glucose decreases cAMP, inactivating CAP and reducing lac mRNA synthesis. Signup and view all the answers

How can both repressible and inducible operons be negative regulators?

Both operons are switched off by the active form of the repressor protein. Signup and view all the answers

What does beta-galactosidase do?

It catalyzes the hydrolysis of lactose. Signup and view all the answers

What does differential gene expression mean?

Different genes are expressed by cells with the same genome. Signup and view all the answers

What percentage of the genes of a typical human cell is expressed at any given time?

20% Signup and view all the answers

What is the common control point of gene expression for all organisms?

Transcription. Signup and view all the answers

Distinguish between heterochromatin and euchromatin.

Heterochromatin is highly condensed and its genes are not usually expressed; euchromatin is less condensed and its genes are easier to express. Signup and view all the answers

What occurs in histone acetylation and how does it affect gene expression?

Acetyl groups attach to the histone tails' lysines, making gene expression more probable. Signup and view all the answers

What is DNA methylation and what role may it play in gene expression?

DNA methylation is the process where methyl groups are added to histone tails, causing chromatin to condense and thus likely turning genes off. Signup and view all the answers

Where can DNA methylation be found and how can it be reversed?

DNA methylation can be found in unexpressed and inactivated genes; it can be reversed by removing methyl groups. Signup and view all the answers

What is the result of heavy methylation of the inactive mammalian X chromosome?

That X chromosome will not express its genes, and all other daughter gametes with it will also have this methylation. Signup and view all the answers

What is genomic imprinting and how is it maintained?

Genomic imprinting is gene expression specific to the maternal or paternal allele; it is maintained by cell division passing on methylation patterns. Signup and view all the answers

What is epigenetic inheritance?

Epigenetic inheritance refers to traits inherited due to factors other than nucleotide sequences. Signup and view all the answers

How do enhancers and activators interact with transcription factors to affect gene expression?

Activators bind to enhancers, causing DNA to bend and attract transcription factors, allowing RNA to attach and transcribe. Signup and view all the answers

What has been found regarding functionally related genes in eukaryotes compared to prokaryotes?

In eukaryotes, functionally related genes are often scattered over different chromosomes, with each gene having its own promoter. Signup and view all the answers

What is a plausible mechanism for the coordination of gene expression in eukaryotes?

Signal molecules bind to protein receptors on the plasma membrane. Signup and view all the answers

How can alternative RNA splicing result in different proteins from the same initial RNA transcript?

Alternative RNA splicing produces different mRNA molecules from the same primary transcript, allowing for different proteins. Signup and view all the answers

Explain posttranscriptional control in regulating mRNA degradation.

Nucleotide sequences in the untranslated region affect how long mRNA remains intact; translation cannot occur without a poly-A tail and 5' cap. Signup and view all the answers

Compare mRNA degradation in eukaryotes and prokaryotes.

Prokaryotes have mRNA degrade soon after being synthesized; eukaryotes can take hours, days, or weeks to degrade. Signup and view all the answers

Summarize the steps of mRNA degradation.

It begins with shortening of the poly-A tail, followed by removal of the 5' cap, and then nucleases degrade the mRNA. Signup and view all the answers

How are proteins targeted for degradation?

Proteins tagged with ubiquitin are recognized and degraded by proteasomes. Signup and view all the answers

What is the role of noncoding RNAs?

They regulate gene expression at mRNA translation and chromatin configuration. Signup and view all the answers

What is a microRNA (miRNA) and its two modes of action?

A single-stranded and small RNA that can bond with mRNA to degrade it or block its translation. Signup and view all the answers

What is siRNA, and how is it similar and different from microRNA?

Small interfering RNAs are similar in size and function to miRNAs but have different precursor molecules. Signup and view all the answers

What three processes lead to the transformation of a zygote into an organism?

Cell division, cell differentiation, and morphogenesis. Signup and view all the answers

What occurs in cell differentiation and morphogenesis?

Cell differentiation is when cells become specialized; morphogenesis is when cells acquire their shape. Signup and view all the answers

What are cytoplasmic determinants?

Maternal substances in the egg that influence early development. Signup and view all the answers

What are inductive signals?

Signals from other embryonic cells that cause changes in target cells through signal transduction pathways. Signup and view all the answers

What is meant by determination in embryonic cells?

Determination refers to the events leading to observable differentiation in a cell. Signup and view all the answers

What process ensures that all tissues and organs of an organism are in their characteristic places?

Pattern formation, which arises from cytoplasmic determinants and inductive signals. Signup and view all the answers

What is controlled by homeotic genes?

The development of pattern formation in the late embryo, larva, and adult stages. Signup and view all the answers

What mechanism is involved in the beginning of tumor growth?

Oncogenes promote cancer; proto-oncogenes are normal versions that stimulate cell growth. Signup and view all the answers

What are three mechanisms for converting a proto-oncogene to an oncogene?

Movement of DNA, amplification of proto-oncogene, and point mutations in a control element. Signup and view all the answers

What are the functions of tumor-suppressor genes?

Repair DNA, control cell adhesion, and inhibit the cell cycle. Signup and view all the answers

Describe the double whammy that results from mutation of p53.

Mutated p53 leads to no activation of p21 and no genes turned on for DNA repair or apoptosis. Signup and view all the answers

What is a polyp?

A small benign growth. Signup and view all the answers

What is an adenoma?

A larger benign growth. Signup and view all the answers

What is carcinoma?

A malignant tumor. Signup and view all the answers

Study Notes

Regulation of Gene Expression in Prokaryotes and Eukaryotes

Genes are not continuously active; E. coli activates genes for tryptophan production only when needed to conserve energy.
Bacterial metabolism is controlled primarily through gene regulation and enzyme regulation.

Feedback Inhibition

E. coli employs negative feedback inhibition for tryptophan synthesis, reducing production when in excess.

Operon Structure and Function

Promoter: Binding site for RNA polymerase to initiate transcription.
Operator: DNA segment that acts as a switch, located between the promoter and enzyme-coding genes.
Operon: Combination of promoter, operator, and genes, regulated by repressor proteins which prevent transcription.

Repressor Proteins and Gene Regulation

Repressor proteins bind to operators, blocking RNA polymerase and preventing transcription.
Regulatory genes exist separately from operons and have their own promoters; an example includes the TATA box.
Inducible operons are typically off but can be activated by small molecules, while repressible operons are usually on and can be repressed by specific molecules.

cAMP and CAP in Gene Expression

CAP (Catabolite Activator Protein) enhances RNA polymerase binding to the promoter when activated by cAMP.
Low glucose levels increase cAMP, promoting lac mRNA synthesis; high glucose reduces cAMP, decreasing lac mRNA production.

Gene Expression and Chromatin Modification

Gene expression is primarily controlled at the transcription level, and chromatin structure influences this regulation.
Heterochromatin is tightly packed and less active in gene expression, whereas euchromatin is loosely packed and more active.
Histone acetylation increases gene expression likelihood by loosening DNA structure.
DNA methylation typically suppresses gene expression by condensing chromatin.

Epigenetics and Gene Regulation

Epigenetic inheritance refers to traits passed on without changes to the DNA sequence, illustrated by differences in identical twins.
Enhancers and activators interact to stimulate transcription factors and promote RNA polymerase binding.

mRNA Regulation

Prokaryotes degrade mRNA quickly (minutes), while eukaryotes take longer (hours to weeks).
Degradation steps include shortening the poly-A tail, removing the 5' cap, and action by nucleases.
Noncoding RNAs and microRNAs regulate gene expression during translation.

Cell Differentiation and Development

Cell differentiation leads to specialized functions, while morphogenesis gives cells their shape.
Cytoplasmic determinants are unevenly distributed maternal substances influencing early development.
Inductive signals from embryonic cells direct changes via signal transduction pathways.

Homeotic Genes and Tumor Suppression

Homeotic genes guide pattern formation in embryos.
Oncogenes are mutated proto-oncogenes leading to cancer; mechanisms for conversion include DNA movement, gene amplification, and mutations.
Tumor-suppressor genes, like P53, repair DNA and control cell adhesion and signaling; P53 mutations lead to loss of cell cycle regulation and repair mechanisms.

Cancer Types

Polyp: Small benign growth.
Adenoma: Larger benign growth.
Carcinoma: Malignant tumor.

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Explore the intricate mechanisms of gene expression regulation in E. coli through this flashcard quiz. Understand how metabolic needs dictate when genes are activated or turned off, thus conserving energy and resources. This quiz covers key concepts from Chapter 18 of your biology curriculum.