Chapter 16 Flashcards
(23 cards)
Define gene regulation
Mechanisms/systems that control expression of genes
- Differentiate between environmental induction of gene expression and tissue-specific gene expression.
Expression due to environmental factors vs genes who only express a function in a certain tissue/cell type
structural genes
DNA sequence that encodes a protein that functions in metabolism or biosynthesis or that has a structural role in the cell
- Define operon. Do prokaryotes have operons? Eukaryotes?
A group of bacterial structural genes that are transcribed together, along with their promoter and additional sequences that control their transcription. Yes, no
- Draw the structure of an operon and label: structural genes, promoter, operator, operon
- Define regulator gene and regulator protein. How is this related to an operon?
Regulator gene-
Gene associated with an operon in bacterial cells that encodes a protein or RNA molecule that functions in controlling the transcription of other genes.
regulator protein
Protein produced by a regulator gene that binds to another DNA sequence and controls the transcription of other genes.
HOW IS THIS RELATED TO AN OPERON?
- Differentiate between positive and negative control with respect to operons
- Negative: regulator protein is a repressor; repressor binds to DNA and turns transcription off
- Positive: regulator protein is an activator; activator binds to DNA and stimulates transcription
- Differentiate between inducible and repressible operons
- Inducible: Transcription is off unless something turns it on (induces transcription)
- Repressible: Transcription is on unless something turns it off (represses transcription)
- Define a negative inducible operon
- Regulator protein is a repressor- off unless something turns it on
- Since transcription is off, the repressor must be made in an active state, so that it can repress the
operon
- Explain how a negative inducible operon functions in the presence and absence of an inducer
Presence- can’t bind to operator, doesn’t work
Absence- Bound to operator, no transcription
- Define a negative repressible operon
- Regulator protein is a repressor- on unless something turns it off
- Since transcription is on, the repressor must be made in an inactive state, so that it is not
repressing—it would have to be activated to repress the operon
- Explain how a negative repressible operon functions in the presence and absence of a product
Presence- operon turned off
Absence- Kept on
- Be able to describe how the lac operon works
The lacI gene is always expressed. Without lactose, LacI binds to the promoter, preventing RNA polymerase from binding. This means that lacZ and lacY can’t be expressed.
- β-gal mutants (lacZ-):
no β-gal produced
- Describe how the lac operon can also be under positive control using catabolite repression
- In addition to being a negative inducible operon, the lac operon also has positive control exerted
on it - This positive control is termed catabolite repression
- Regulator protein is an activator (positive control)
- bacteria prefer to use glucose over other sugars
- when glucose is present, genes that metabolize other sugars (such as lactose) are repressed
- CAP = Catabolite Activator Protein
- List the 2 requirements for maximum transcription of the lac operon
- Lactose present
- Low glucose levels
- Permease mutants (lacY-):
no permease produced
- Regulator gene mutation (lacI-):
no regulator (repressor) produced
o lacIs (superrepressor):
cannot be inactivated—always represses
- Promoter mutation (lacP-):
RNA polymerase can’t bind
- Operator mutation (lacOc):
repressor can’t bind to operator
regulatory genes
DNA sequence that encodes a protein or RNA molecule that interacts with other DNA sequences and affects transcription or translation of those sequences
regulatory elements
regulatory element
DNA sequence that affects the transcription of other DNA sequences to which it is physically linked
