Chapter 18 Flashcards
What are the evolutionary and energetic advantages of an operon?
The operon prevents the expression of genes when the products of that gene aren’t needed. It minimizes waste of resources. Found in bacterial cells
Regulatory gene
gene from which the repressor is produced, located some distance from the operon it controls (regulates)
Repressor protein
protein that prevents gene transcription by binding to the operator and blocking RNA polymerase
Corepressor
molecule that cooperates with a repressor protein to switch a repressible operon off
Promoter
part of the DNA strand to which transcription factors and RNA polymerase bind
Operator
the part of the promoter that serves as the binding site for the repressor; the on/off switch of the operon
Gene of operon
the gene(s) whose expression is controlled by the operator sequentially after the promoter
Describe how an inducible operon is different from a repressible operon.
Inducible operons are usually off but can be turned on; repressible operons are usually on, but can be turned off
What is differential gene expression?
the expression of different genes by cells with the same genome
Why is differential gene expression important in multicellular eukaryotic organisms?
it leads to differences between cell types within the body
How do chemical modifications to histones and DNA of chromatin influence chromatin structure and gene expression?
The structural organization of chromatin helps regulate gene expression in several ways; Highly packed heterochromatin cannot be expressed; Chemical modifications to chromatin influence expression
Describe DNA methylation.
the addition of methyl groups (CH3) to certain bases in DNA, can condense chromatin and reduce transcription causing long-term inactivation of genes in cellular differentiation
Describe histone acetylation.
acetyl groups are attached to an amino acid in a histone tail which promotes transcription by opening up the chromatin structure
What are control elements?
segments of noncoding DNA that serve as binding sites for transcription factors
How do control elements influence gene expression?
they give the cell better control of gene expression by requiring additional steps for transcription
Compare and contrast distal and proximal control elements.
Proximal control elements are close to the promoter; A distal control element is far away from a gene
Describe the process by which enhancers and activators encourage gene expression.
An activator protein binds to an enhancer to help initiation of gene transcription; Bound activators come into contact with mediator (helper) proteins through protein-mediated bending of the DNA; The mediator proteins help assemble and position the transcription complex
Describe three mechanisms that occur after transcription that allow for fine-tuning of the gene expression.
A. Alternative RNA splicing can significantly expand the repertoire of a eukaryotic genome depending on which RNA segments are treated as exons and which as introns
B. With mRNA degradation, Each mRNA has a characteristic life span, determined in part by sequences in the 5′ and 3′ UTRs.
C. The length of time each protein functions is regulated by selective degradation; Cells mark proteins for degradation by attaching the protein ubiquitin to them
What is morphogenesis?
The physical processes that give an organism its shape
How does morphogenesis relate to differential gene expression?
It is controlled by differential gene expression; Gene expression orchestrates the developmental programs of animals and leads to the different cell types in a multicellular organism as well as the development of the shape of the organism
What are cytoplasmic determinants?
substances in the egg that influence early development
How do cytoplasmic determinants influence morphogenesis?
They are distributed unevenly in the unfertilized egg; As the zygote divides by mitosis, the daughter cells may contain different cytoplasmic determinants causing them to differentiate into separate cell types as well as giving shape and function
Compare and contrast oncogenes and proto-oncogenes
Proto-oncogenes are genes that are responsible for normal cell growth and division;
Proto-oncogenes can be converted to oncogenes, cancer-causing genes, by viruses such a papilloma or hepatitis viruses
Conversion of a proto-oncogene to an oncogene can lead to abnormal stimulation of the cell cycle and tumor formation
How might proto-oncogenes be converted into oncogenes?
movement of DNA within the genome; amplification of a proto-oncogene; point mutations in the proto-oncogene or its control elements
