Cellular control Flashcards
What are transcription factors?
Proteins that bind to DNA and switch genes on or off by increasing or decreasing the rate of transcription. Factors that increase the rate are called activators and those that decrease the rate are called repressors.
What are the different levels of gene control?
Transcriptional- lac operon and transcriptional factors in eukaryotes
Post-transcriptional level- the editing of primary mRNA and the removal or introns to produce mature mRNA
Post-translational level- the activation of proteins by cyclic AMP
What is an operon?
A section of DNA that contains a cluster of structural genes (code for useful proteins) that are transcribed together, as well as control elements and sometimes a regulatory gene (codes for an activator or repressor).
What is E.coli?
A bacterium that respires glucose, but it can use lactose if glucose isn’t available.
The lac operon in E.coli: Where are the genes that produce enzymes needed to respire lactose found?
On an operon called lac operon
The lac operon in E.coli: What structural genes does the lac operon have?
lacZ, lacY, lacA, which produce proteins that help bacteria digest lactose
The lac operon in E.coli: What happens when lactose is not present?
The regulatory gene (lacL) produces the lac repressor which is a transcription factor that binds to the operator site when no lactose is present.
This blocks transcription because RNA polymerase can’t bind to the promoter.
The lac operon in E.coli: What happens when lactose is present?
Lactose binds to the repressor, changing the repressor’ shape so that it can no longer bind to the operator site.
RNA polymerase can now begin transcription of the structural genes.
Post-transcription level: What are introns?
The sections of eukaryotic DNA that don’t code for amino acids.
Post-transcription level: What are exons?
All the bits of DNA that do code for amino acids
Post-transcription level: What happens to introns and exons during transcription?
Introns and exons are both copied into mRNA. mRNA strands containing introns and exons are called primary mRNA transcripts (or pre-mRNA).
Post-transcription level: What happens to primary mRNA strands?
Introns are removed from primary mRNA strands by a process called splicing- introns are removed and exons joined, forming mature mRNA strands. This takes place in the nucleus.
Post-transcription level: What happens to the mature mRNA?
Then leaves the nucleus for the next stage of protein synthesis (translation).
Post-translation level: What do some proteins need after they have been synthesised?
Some proteins aren’t functional straight after they have been synthesised- they need to be activated to work (to become a functional protein).
Protein activation is controlled by molecules e.g. hormones and sugars.
Post-translation level: How do some molecules work in protein activation?
Work by binding these molecules to cell membranes and triggering the production of cyclic AMP (cAMP) inside the cell.
Post-translation level: What does cAMP do?
Activates proteins inside the cell by altering their three-dimensional (3D) structure.
For example, altering the 3D structure can change the activate site of an enzyme and make it more or less reactive.
Post-translation level: How does cAMP activate protein kinase A (PKA)?
- PKA is an enzyme made of 4 subunits.
- When cAMP isn’t bound, the 4 units are bound together and are inactive.
- When cAMP binds, it causes a change in the enzyme’s 3D structure, releasing the active subunits- PKA is now active.
What is a body plan?
The general structure of an organism .
What controls the development of a body plan?
Proteins- they help set up the basic body plan so everything is in the right place, e.g. the legs grows where the legs should grow.
What are the proteins that control body plan development coded by?
Genes called Hox genes. e.g. two Hox gene clusters control the developement of the Drosophila body plan- one controls the development of the head and anterior thorax and the other controls the development of the posterior thorax and abdomen.
What do Hox genes have?
Regions called homeobox sequences, which are high conserved- this means that these sequences have changed very little during the evolution of different organisms that posses these homeobox sequences.
How do Hox genes control the development?
- Homeobox sequences code for a part of a protein called the homeodomain.
- The homeodomain binds to specific sites on DNA, enabling the protein to work as a transcription factor.
- The proteins bind to DNA at the start of developmental genes, activating or repressing transcription and so altering the production of proteins involved in the development of the body plan.
What is apoptosis?
When some cells die and break down as a normal part of development- this is a highly controlled process.
What happens once apoptosis has been triggered?
The cell is broken down in a series of steps:
1) Enzymes inside the cell break down important cell components such as proteins in the cytoplasm and DNA in the nucleus.
2) As the cell’s contents are broken down it begins to shrink and breaks up into fragments.
3) The cell fragments are engulfed by phagocytes and digested.
