Module 10: V5 - V8 Flashcards
What is an element?
a sequence of DNA
What are transcription factors?
proteins that bind to elements on the DNA strand which either activate or repress transcription
What is an operon?
a sequence of genes following the operator (found in bacteria)
What is the purpose of the trp operon?
producing tryptophan amino acids
How are individual proteins synthesised from the same strand of DNA?
multiple start and stop codons along the length of the DNA strand
When is tryptophan synthesised in bacteria?
when there is no tryptophan present in the external environment
What happens when tryptophan is found in the external environment?
binds to an inactive repressor, thereby activating it resulting in decreased gene expression and synthesis of tryptophan
Is the repressor of the lac operon produced in the active or inactive state?
in the active state
Is the lac operon active when there is lactose present or when there is no lactose present?
when lactose is present
What happens to the lac operon when lactose is present?
allolactose binds to the repressor of the lac operon, thereby inactivating it resulting in transcription of the lac operon
Which type of proteins does the lac operon produce?
permease which allows lactose to be transported into the bacterial cell and β-galactosidase which is used to break down lactose so that it can be used as an energy source
What is tryptophan acting as in the trp operon?
a corepressor
What is allolactose acting as in the lac operon?
an inducer
Are the trp and lac operons examples of negative or positive regulation?
negative regulation
What is the significance of the lac repressor?
a dimer binding to a palindrome sequence
binding results in the formation of a loop in the DNA which prevents the ability of RNA polymerase to transcribe the lac operon
What is combinatorial control?
there are usually several important regulators of a single gene and messages are integrated for a single response
gene activation is synergistic
What does combinatorial control allow E. coli to do when both glucose and lactose is present in the external environment?
allows bacteria to carry out the more efficient process of breaking down glucose so that it can be used as an energy source before breaking down lactose
What is CAP?
a protein that is inactive unless bound to cyclic AMP and is able to bind to the lac operon
binds to a region where it activates the likelihood that RNA polymerase will transcribe
When is there more cAMP in the cell?
when there is less glucose and therefore less ATP
What happens to the lac operon when lactose and glucose is present?
since glucose is present this means that ATP is increased in the cell resulting in decreased cAMP and therefore inactivated CAP -> little lac mRNA synthesised even though the lac repressor is inactive (overridden)
What happens to the lac operon when lactose is present and glucose is scarce?
since glucose is scarce this means that ATP is decreased in the cell resulting in increased cAMP and therefore activated CAP -> abundant mRNA synthesised
What does regulation of gene expression allow cells to have?
different shapes and functions
What are the major differences in regulation of transcription between prokaryotes and eukaryotes?
separation of transcription and translation, chromatin can block RNA polymerase access, ↓ basal transcription, majority of regulation is +ve not -ve, ↑ proteins involved in transcriptional regulation, ↑ transcription factors that control each genes
What are the two aspects of chromatin regulation?
methylation of DNA and histones which causes nucleosomes to pack tightly together
histone acetylation which results in loose packing of nucleosomes
What is a regulatory element?
the DNA sequence that transcription factors bind to
repressors (rare) bind to sequences called silencers
activators bind to sequences called enhancers or enhancer elements
How does gene regulation occur?
activator protein binds the enhancer element -> histone modification / nucleosome remodelling complexes bind -> mediator (co-activator) binds and facilitates binding of the TBP -> other basal transcription factors and RNA pol II bind -> phosphorylation of the CTD of RNA pol II leads to transcription initiation
