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All genes are not "on" all the time. Using the metabolic needs of E. coli, explain why not. |
E. coli live in very fickle environments. If an E. coli in the human gut is lacking an amino acid, it will turn the gene that makes it on. If the human ate a meal rich in that amino acid, it turns that gene off, and does not use up excess resources. |
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What are the two main ways of controlling metabolism in bacterial cells? |
1) regulation of enzyme activity. 2) regulation of enzyme production. |
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Promoter |
Region of DNA where RNA polymerase can bind. |
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Operator |
It is the "on-off" switch controlling a cluster of functionally related genes. |
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What is an operon? |
A segment of DNA that consists of three parts: the operator, the promoter, and the genes being controlled. |
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How does a repressor protein work? |
Repressor proteins bind to the operator and block attachment of RNA polymerase 2 to the promoter. |
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What are regulatory genes? |
A gene that produces repressor proteins. |
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What is an inducible operon? |
An operon that is usually off, but can be induced to turn on by interaction between moleces and regulatory proteins. |
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What is an example of an inducible operon? |
The LAC operon |
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What is a repressible operon? |
An operon that is usually on, but can be inhibited when a molecule, like tryptophan binds to a regulatory protein. |
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What is an example of the repressible operon? |
TRP operon |
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How is the LAC operon similar to the TRP operon? |
Both are in prokaryotes and each have a promoter, operator, and genes. Also, the operon contributes to different methods of conserving energy. |
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How is the LAC operon different from the TRP operon? |
LAC operon acts as an inducible operon; TRP operon acts as a repressible operon. |
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What happens when a repressor is bound to the operator? |
RNA polymerase cannot bind; transcription does not occur. |
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What is CAP? |
It is a catabolite activator protein. |
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How does CAP work? |
CAP assumes its active shape and attaches to the DNA molecule later upstream which increases RNA polymerase’s affinity to the promoter. |
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Explain why CAP binding and stimulation of gene expression is positive regulation |
The attachment of CAP stimulates gene expression, and thus protein translation |
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Describe the relationship between the glucose supply, cAMP, and CAP |
When glucose levels degrease, there are high levels of cAMP, which turn on CAP. |
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How can both repressible and inducible operons be negative regulators? |
1) Repressible operons are negative regulators because tryptophan activates regulatory proteins which does not allow RNA polymerase to bind to the promoter region. This decreases protein yield. 2) In inducible operons, if glucose is increased, CAP unbinds and genes are expressed less. |
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Differential gene expression |
expression of different genes by cells with same genome. |
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What percentage of the genes typical of human cells is expressed at any given time? |
20% |
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What is the common control point of gene expression for all organisms? |
Transcription |
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Heterochromatin |
Highly condensed, usually not expressed. |
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Euchromatin |
Not very condensed, expressed. |
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Histone acetylation |
acytyl groups (-COCH3) is attached to histone tails. This causes a looser structure and encourages expression |
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DNA methylation |
addition of methyl groups to DNA. It discourages gene expression |
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Genomic imprinting |
the passing down of methylation patterns |
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How is genomic imprinting maintained, give an example? |
Specialized tissues keep a chemical record during embryonic development. Methylation regulates expression of paternal or maternal alleles of genes. |
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Epigenetic inheritance; give an example |
inheritance of traits transmitted by mechanisms not directly involved in nucleotide sequence. Enzymes that modify chromatin structure are an example. |
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In prokaryotes, functionally related genes are usually clustered in a single operon. What has been found to be the case in eukaryotes? |
There are no operons in eukaryotes. Genes coding for the enzymes of particular metabolic pathways are usually on different chromosomes. |
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How can alternative RNA splicing result in different proteins derived from the same initial RNA transcript? |
Different sequences are treated as exons and introns. |
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Postranscriptional control includes regulation of mRNA degradation. Explain how this affects translation. |
Depending on how long it takes for mRNA to degrade, translation can last from a few minutes, to weeks. |
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How can proteins be activated, processed, and degraded? |
Proteins are degraded by the attachment of ubiquiton. Some cell surface proteins must be transported to proper destinations to work. |
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How are proteins targeted for degradation, give an example. |
Ubiquitin tag is attached. An example is the recycling of cyclin to allow healthy cell cycle. |
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What role does noncoding RNA play? |
It plays an important role in the regulation of gene expression by molecules such as miRNA. |
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What three processes lead to the transformation of a zygote into the organism? |
Cell division, cell differentiation, and morphogenesis. |
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Cell differentiation |
Cells become specialize in structure and function |
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Morphogenesis |
Physical processing that gives an organism its shape |
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Distribution of cytoplasmic determinants |
Substances in the mother’s egg in the cytoplasm are not evenly distributed, so when cell division occurs, these cytoplasmic determinants are not equally divided. |
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Different inductive signals |
Depending on what cells surround other cells, different inductive signals are released. |
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What process ensures that all tissues and organs of an organism are in their characteristic places? |
Pattern formation, position information |
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Where do the molecular cues that control the process of pattern formation and position information? |
Cytoplasmic determinants, inductive signals |
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Homeotic genes |
genes that regular pattern formation in late embryo, larva, and adults |
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Oncogenes |
cancer causing genes |
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Proto-oncogenes |
normal genes |
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What mechanism is involved in the beginning of tumor growth? |
The failure of cells to respond to control mechanisms of a cell |
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What are three mechanism for converting a proto-oncagene to an oncogene |
1) movement of DNA within genome 2) amplification of proto-oncogenes 3) point mutations in proto-oncogene |
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Describe the negative effects of a mutated p53 gene |
1) DNA cannot be repaired 2) cancer forms |
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