Gene Regulation and Expression in Prokaryotes and Eukaryotes Wk11

What are the two main processes that regulate gene expression in response to environmental conditions?

Transcription and Translation.

How does gene expression contribute to multicellularity?

It regulates development and is responsible for differences in cell types.

What are the basic components of gene structure that RNAP binds to?

-10 and -35 elements in the promoter region.

What is feedback inhibition in the context of bacterial gene regulation?

Cells regulate the production of enzymes either by feedback inhibition or gene regulation.

How can proteins be regulated in bacterial gene regulation?

Proteins can be repressed or activated by positive and negative feedback.

What is the operon model in bacterial gene regulation?

It describes how proteins for a metabolic/structural pathway are coded by the same transcript.

What is the function of the regulatory region in an operon?

It acts as an 'on-off switch' for the genes encoding proteins in the same metabolic pathway.

What distinguishes inducible operons from repressible operons?

Inducible operons are normally off and activated by a signal, while repressible operons are normally on and turned off when the end product is available.

What is the role of the lac repressor in the lac operon?

It binds to the operator to block RNAP, preventing transcription until inactivated by lactose.

How does the trp repressor function in the trp operon?

It is activated by tryptophan, binds to the operator, and blocks RNAP, preventing transcription.

What type of pathways do inducible enzymes typically function in?

Catabolic pathways.

What type of pathways do repressible enzymes typically function in?

Anabolic pathways.

What is the role of cyclic AMP receptor protein (CRP) in gene regulation?

It is an activator involved in positive gene regulation.

What happens to the lac operon when lactose is present?

The lac repressor is inactivated, allowing transcription to occur.

What happens to the trp operon when tryptophan levels are high?

The trp repressor is activated, preventing transcription.

What is the significance of multiple transcription factors in gene expression?

They can deliver different levels of expression.

How are genes encoding proteins in the same metabolic pathway organized on the chromosome?

They are grouped together, transcribed together, and regulated together.

What is the difference between the regulation of enzyme production and enzyme activity?

Regulation of production involves gene expression, while regulation of activity involves feedback mechanisms.

What is the main difference in regulation between the trp operon and the lac operon?

The trp operon is repressible (on, turned off when tryptophan is present), while the lac operon is inducible (off, turned on when lactose is present).

What is the function of the structural region in an operon?

It contains the genes that encode the enzymes for a specific metabolic pathway.

What is the role of the operator in an operon?

It is the binding site for repressors that regulate transcription.

What is the outcome of positive gene regulation by CRP in the lac operon?

It enhances the transcription of the lac operon when glucose levels are low.

What are the key differences in gene regulation between eukaryotes and prokaryotes?

Eukaryotes have more complex promoters and regulatory sequences, chromatin structure, and generally lack operons.

What is differential gene expression?

It is the expression of different genes by cells that contain the same genome, leading to differences between cell types.

What role does chromatin structure play in gene regulation?

Chromatin structure can influence gene expression through loops congregating at sites rich in transcription factors and RNA polymerases.

How do chemical modifications to histones and DNA affect gene expression?

They can influence chromatin structure and lead to long-term inactivation of genes, a concept related to epigenetics.

What is the function of transcription factors in eukaryotic gene regulation?

Transcription factors assist RNA polymerase in initiating transcription and can influence chromatin structure.

What is the significance of enhancers in eukaryotic gene expression?

Enhancers are groups of distal control elements that help regulate transcription by interacting with transcription factors.

What are control elements in eukaryotic genes?

Control elements are segments of noncoding DNA that serve as binding sites for transcription factors.

What is the role of the Poly-A signal in eukaryotic transcription?

The Poly-A signal is involved in the termination of transcription and the addition of a Poly-A tail to mRNA.

What are the stages of gene expression that can be regulated in eukaryotic cells?

Regulation can occur at chromatin structure, transcription initiation, RNA processing, and transport to the cytoplasm.

What is the purpose of RNA processing in eukaryotic cells?

RNA processing includes adding a 5' cap and a Poly-A tail, which are necessary for export from the nucleus and translation.

How does DNA topography contribute to gene regulation?

Protein-mediated bending of DNA helps assemble the pre-initiation complex by bringing distal and proximal elements into contact.

What is the pre-initiation complex in eukaryotic transcription?

It is a complex formed by the assembly of general transcription factors, RNA polymerase II, and other proteins at the promoter.

What is the importance of the TATA box in transcription?

The TATA box is a core promoter element that is crucial for the binding of transcription factors and the initiation of transcription.

What is the role of mediator proteins in transcription?

Mediator proteins facilitate the interaction between transcription factors and RNA polymerase, aiding in the regulation of transcription.

What is the significance of the 5' UTR and 3' UTR in mRNA?

The 5' UTR and 3' UTR are untranslated regions that play roles in the regulation of translation and mRNA stability.

What is the function of the 5' cap added during RNA processing?

The 5' cap protects mRNA from degradation and assists in ribosome binding during translation.

What is the role of introns in eukaryotic genes?

Introns are non-coding sequences that are removed during RNA processing, allowing for the coding exons to be joined together.

What is the primary transcript in eukaryotic transcription?

The primary transcript is the initial RNA molecule synthesized from the DNA template before processing into mature mRNA.

How does chromatin modification affect gene availability for transcription?

Chromatin modification, such as DNA unpacking, makes the gene sequences more accessible for transcription factors and RNA polymerase.

What is the significance of RNA polymerase in transcription?

RNA polymerase synthesizes RNA from the DNA template and requires transcription factors for its activity.

What are the three main steps in transcriptional control in eukaryotic cells?

1. Availability of the promoter/gene sequences, 2. Specific binding of transcription factors, 3. Coordination of transcription factors.

What is the role of transcriptional repressors in eukaryotic gene regulation?

Transcriptional repressors inhibit gene expression by preventing the binding of transcription factors or RNA polymerase.

How do activators influence gene expression in eukaryotes?

Activators enhance gene expression by promoting the binding of transcription factors and RNA polymerase to the promoter.

What is the role of the 5' End cap and Poly-A tail in mRNA?

They facilitate export from the nucleus and allow translation.

What is alternative splicing of mRNAs?

It is a process where more than 90% of human protein-coding genes undergo splicing to produce different mRNA variants.

What are miRNAs and their function?

miRNAs are small RNA molecules that regulate gene expression by binding to complementary sequences in mRNA.

What is the estimated impact of miRNAs on human genes?

At least half of human genes may be regulated by miRNAs.

What are siRNAs and how do they function?

siRNAs are similar to miRNAs and block gene expression through RNA interference (RNAi).

What is the function of repressor proteins in relation to mRNA?

Repressor proteins can reversibly bind to mRNA, affecting its stability and translation.

What are the stages in gene expression that can be regulated in eukaryotic cells?

Stages include mRNA degradation, translation, protein processing, and degradation.

What are the four types of post-translational modifications of polypeptides?

1. Proteolysis (cleavage of the peptide chain), 2. Glycosylation (addition of carbohydrates), 3. Phosphorylation (addition of phosphate groups), 4. Addition of signal sequences for transport.

How do cells mark proteins for degradation?

Cells attach ubiquitin to proteins, targeting them for degradation by proteasomes.

What is cell differentiation?

Cell differentiation is the process by which cells become specialized in structure and function.

What is the role of stem cells in the body?

Stem cells are undifferentiated cells that have the potential to become various cell types.

What are cytoplasmic determinants?

Maternal substances in the fertilized egg that influence early cell development.

How do inductive signals influence cell development?

Inductive signals from nearby cells influence gene expression and differentiation during development.

What is the function of enhancers in gene regulation?

Enhancers are DNA sequences that increase the likelihood of transcription of a particular gene.

What is the significance of the albumin and crystallin gene enhancers?

They illustrate how different enhancers can regulate gene expression in different cell types.

What is the relationship between gene expression and developmental programs in animals?

Gene expression orchestrates the developmental programs that lead to the formation of different cell types.

What happens during the process of protein processing?

Chemical modifications of polypeptides occur to convert them into functional proteins.

What is the role of signal sequences in proteins?

Signal sequences direct the transport of proteins to their cellular destinations.

What is RNA interference (RNAi)?

RNAi is a biological process in which RNA molecules inhibit gene expression or translation.

What is the significance of non-coding RNAs in gene expression?

Non-coding RNAs play multiple roles in controlling gene expression and regulating cellular processes.

What is the role of ubiquitin in protein degradation?

Ubiquitin serves as a signal for marking proteins for degradation by the proteasome.

What is the impact of environmental changes on gene expression?

Mechanisms in cells allow for rapid fine-tuning of gene expression in response to environmental changes.

What are homeotic genes responsible for?

They control the final developmental stages and direct the development of body segments or structures.

In which organisms are homeotic genes found?

Homeotic genes are found in many animals, including fruit flies, mice, and humans.

What do Hox genes do?

Hox genes are master regulator genes that are turned on by a cascade of regulatory genes to establish the identity of body segments along the head-tail axis.

What can mutations in Hox genes cause?

Mutations in Hox genes can cause displaced structures and genetic disorders.

How do genetic changes lead to cancer?

Cancer results from mutations to genes that normally regulate cell growth and division, which can be spontaneous or due to environmental influences.

What are proto-oncogenes?

Proto-oncogenes are cellular genes responsible for normal cell growth and division.

What are oncogenes?

Oncogenes are cancer-causing genes that can arise from mutations in proto-oncogenes.

What are some mechanisms that can turn proto-oncogenes into oncogenes?

Mechanisms include point mutations, gene amplification, mutations within control elements, and translocation or transposition.

What role do tumor-suppressor proteins play?

Tumor-suppressor proteins repair damaged DNA, control cell adhesion, and inhibit the cell cycle.

What is the function of the p53 gene?

The p53 gene is a tumor suppressor gene that activates 'suicide' genes to prevent the passing on of mutations and promotes apoptosis.

How prevalent is p53 mutation in human cancers?

The p53 gene is mutated in approximately 50% of all human cancers.

What is Ras in the context of cancer?

Ras is a proto-oncogene that responds to growth factor sensing and is present in about 30% of all human cancers.

What happens in a normal cell cycle-inhibiting pathway involving p53?

In a normal pathway, damaged DNA is not replicated, preventing cell division.

What occurs in a mutant cell cycle-inhibiting pathway?

In a mutant pathway, the inhibitory protein is absent, leading to increased cell division despite DNA damage.

What is the role of the Ras pathway in cell division?

The Ras pathway stimulates the cell cycle, promoting normal cell division.

What happens when there is a mutation in the Ras pathway?

A mutation can lead to Ras being active with or without growth factor, resulting in increased cell division.

What are some environmental influences that can cause gene mutations?

Environmental influences include chemicals, radiation, and some viruses like Epstein Barr.

Can gene mutations be inherited?

Yes, gene mutations can be inherited.

What is the significance of protein kinases in the p53 pathway?

Protein kinases are involved in the signaling pathway that inhibits the cell cycle.

What is the effect of UV light on DNA in the context of cancer?

UV light can cause DNA damage that, if not repaired, can lead to increased cell division and cancer.

How do miRNAs contribute to cancer prevention?

Coordinated miRNAs can help repair DNA and regulate gene expression to prevent cancer.

What is the relationship between embryonic development and cancer?

The gene regulation systems that malfunction during cancer are the same systems involved in embryonic development.

What characterizes a cancerous cell at the DNA level?

At least one active oncogene and the mutation of tumor-suppressor genes.

Why does the incidence of cancer generally increase with age?

Multiple mutations are generally needed for full-fledged cancer.

What are the steps involved in the multistep model of colon cancer development?

1. Activation of ras oncogene; 2. Loss of tumor-suppressor gene APC (or other); 3. Loss of tumor-suppressor gene p53; 4. Additional mutations; 5. Loss of tumor-suppressor gene SMAD4.

What is genomic imprinting?

Genomic imprinting can affect offspring by influencing gene expression based on parental experiences.

What does epigenetic inheritance suggest?

Inheritance is not solely based on DNA sequence but can include epigenetic tags from parents.

How does methylation affect gene expression?

Methylation regulates the expression of parental genes at the start of development.

What happens to genes in highly compacted chromatin?

They are generally not transcribed.

How does histone acetylation affect chromatin structure?

Histone acetylation loosens chromatin structure, enhancing transcription.

What role do DNA control elements play in transcription regulation?

They bind specific transcription factors, enabling activators to contact proteins at the promoter and initiate transcription.

What is the effect of DNA methylation on transcription?

DNA methylation generally reduces transcription.

What is alternative RNA splicing?

A process that allows for the generation of multiple protein variants from a single primary RNA transcript.