Cellular Control Flashcards
At what levels can gene expression be controlled at?
- The transcriptional level
- The post transcriptional level
- The post-translational level
What controls gene expression at the transcriptional level?
Transcription factors
What are transcription factors?
Proteins that bind to DNA and switch genes on or off by increasing or decreasing the rate of transcription.
What are the 2 types of transcription factors?
- Activators
- Repressors
What do activators do?
they increase the rate of transcription
What do repressors do?
They decrease the rate of transcription
What determines whether a transcription factor can bind to DNA or not?
The shape of the transcription factor
In eukaryotes, where do transcription factors bind?
They bind to specific DNA sites near the start of their target genes.
In prokaryotes, where do transcription factors bind?
To operons
What is an operon?
A cluster of structural genes that are transcribed together, and also control elements and sometimes a regulatory gene.
What do the control elements include?
- A promoter
- An operator
What is a promoter?
A DNA sequence located before the structural genes that RNA polymerase binds to
What is an operator?
A DNA sequence that transcription factors bind to
What does the bacteria E.coli typically respire?
Glucose
What can the bacteria E.coli respire if glucose isn’t available?
Lactose
Where are the genes that produce the enzymes needed to respire lactose found?
On an operon called the Lac Operon.
What happens when lactose isn’t present?
- The regulatory gene produces the lac repressor.
- The lac repressor is a transcription factor that binds to the operator site when there’s no lactose present.
- This blocks transcription because RNA polymerase can’t bind to the promoter
What happens when lactose is present?
- Lactose binds to the repressor.
- This changes the repressor’s shape so that the repressor can no longer bind to the operator site.
- RNA polymerase can now begin the transcription of the structural genes.
what structural detail of a polypeptide is altered by gene mutations?
the base sequence
how is it possible for a mutation to have no effect on the protein produced from that gene?
- Some triplets code for the same amino acid, so the amino acid sequence isn’t altered.
- Some alternative amino acids will not alter the shape of the protein.
- The mutation may occur in the intron.
How could a mutation alter the protein so that it no longer performs its correct function in the cell?
- An insertion or deletion may result in a frameshift mutation.
- All triplets downstream will be different.
- The protein will have a different sequence of amino acids.
- The tertiary structure of the protein will be different.
What do regulatory genes do?
code for proteins that control the expression of structural genes.
What do the structural genes do?
codes for a protein that has a function within a cell
How can transcription be controlled in eukaryotes?
- Hormone enters a cell and binds to a transcription factor.
- The transcription factor will then be activated and will bind to a promoter.
- This will allow RNA polymerase to bind to the promoter.
How can gene expression be regulated after transcription?
- The primary mRNA is modified.
- Introns are removed to make mature mRNA.
- Alternative splicing can produce different versions of mRNA.
Why are fruit flies chosen for research into genes controlling the development of the body plan?
- There’s less ethical concerns
- Low cost
- Rapid reproduction rate
- The genetics of fruit flies is well understood.
- They have a simple body plan
Why are mice usually used or research into genes controlling the development of the body plan, despite there being some ethical concerns?
- low cost
- share some genes with humans
- more than one species is needed to demonstrate the conservation of base sequences.
do species that have diverged recently share a similar base sequence?
Yes
Why do non-coding regions of DNA show more variation?
Because they are not selected against
Do homeobox genes enable proteins to work as transcription factors?
Yes
What does RNA polymerase do?
makes RNA via transcription
What does DNA polymerase do?
Allows for DNA replication, where 2 polypeptide strands are produced.
What is programmed cell death?
Apoptosis
What do hox genes do?
They determine the identity of embryonic body regions along the anterior-posterior axis (i.e. the head-tail axis)
What is a homeobox gene?
A homeotic gene that initiates transcription and controls the development of the body plan.
Why has there been little change by mutation in homeobox genes?
Because these genes are very important so any mutations are likely to be lethal
What is the relationship between regulatory genes and structural genes?
Regualatory genes control the expression of structural genes
How is gene expression regulated at the post-translational level?
- Certain molecules, like hormones, bind to cell membranes and trigger the production of cAMP inside the cell.
- cAMP then activates proteins inside the cell by altering their 3D structure.
- Altering the 3D structure can change the active site of an active site, making it more or less active.
How does cAMP activate PKA?
- cAMP binds to PKA and causes the shape of the enzymes 3D structure to change, releasing the active subunits.
- PKA is now active
What are the 3 main ways a mutation can occur?
- Substitution
- Insertion
- Deletion
What can form frameshift mutation?
Insertion and deletion
