Cellular Control Flashcards
(19 cards)
What 3 levels can gene expression be controlled at?
Transcriptional, post transcriptional and post translational
How can gene expression be controlled at transcriptional level?
Transcription can be controlled by rate of transcription which can be controlled by transcription factors
Factors that increase transcription are called activators, factors that decrease transcription are called repressors
What are transcription factors?
They are proteins that bind to the DNA and switch gene on or off by either inceasing or decreasing the rate transcription.
Why is the shape of the transcription factor importanat?
The shape determines whether it can bind to DNA or not. The shape can be altered by binding of molecules in the cell therefore the amount of molecules can affect synthesis of some proteins by affecting transcription factors binding.
In eukaryotes, how do transcription factors function?
They bind to the specific DNA site at the start of the target gene
In prokaryotes, how do transcription factors function?
They bind to operons which are sections of DNA that contain a cluster of structural genes (code for proteins), control elements (include a promoter and operator) and sometimes a regulatory gene which codes for an activator or a repressor
Describe the lac operant in E.coli.
- E.coli is a bacteria that respires glucose but uses lactose if glucose is not present
- the genes that are needed to respire lactose are found on lac operan
- the lac operon has 3 structural genes: lacZ lacY and lacA
When lactose is not present the regulatory gene produces repressor which is the transcription factor. It binds to the operator site with blocks transcription becasue RNA polymerase cant bind to the promoter. When lactose is present it binds to the repressor which changes the shape so it can no longer bind to operator site. RNA polymerase transcription begins
How can gene expression be controlled at post transcription level?
In eukaryotes, introns which are genes that dont code for amino acids are removed from primary mRNA strands, which contains introns and exons, by a processes called slicing. It resulted in mature mRNA being formed of just exons and this mRNA leaves the nucleus for the next stage of protein synthesis
Introns are genes that dont code for DNA, exons are genes that do. When both are in a mRNA strand it is called a primary mRNA
How can gene expression be controlled at a post translational stage?
It can be controlled by protein activation.
After translations proteins still need to be activated by molecules such a s hormones or sugars. The molecules bind to the membrane of the protein to stimulate cAMP inside the cell. CAMP actives the protein by altering the 3D shape e.g altering shape of active site can make enzyme more or less active.
How does cAMP activate protein kinase A at post translational level?
- when protein kinase A is not active it has 4 subunits all together
- when cAMP binds, the sub units separate becsue the enzymes 3D structure is changed
What is a body plan?
General structure of an organism
What are Hox genes?
What is a homeobox sequence?
Genes that code for proteins that control body plan development.
They are found in animal, plants and fungi which suggests that body plan is controlled in a similar way
Hox genes have regions called homeobox sequences which are highly converges sequences of DNA that have not changes much through evolution
How do Hox genes control development?
Homeobox sequences code for part of a protein called homeodomain. The homeodomain binds to specific part of DNA allowing the protein to work as a transcription factor. The protein bind to DNA at the start of developmental genes and they activate or repressor transcription and so altering the production of proteins involved in making the body plan
What is apoptosis?
Programmed cell death
- Enzymes in the cell break down components e.g proteins in cytoplasm and DNA in nucleus
- Once contents are broken down cell begins to shrink and breaks up into fragments
- Cell fragments are engulfed and digested by phagocytes
How are apoptosis and mitosis involved in the development of a body plan?
Gene control switches on and off apoptosis genes in appropriate cells so some die while some new ones are produced by mitosis.
What internal and external stimuli can regulate apoptosis?
Internal: DNA damage, if ther is DNA damage detected the process can be paused and apoptosis can be triggered
External: stress caused by lack of nutrients avlibabity could result in gene expression that prevents cells from undergoing mitosis
What is a mutation?
What are the three types?
Any change to the base sequence
Substitution: bases are swapped
Deletion: a base is removed
Addition/insertion: base added
Why might a mutation have a neutral effect on a protein?
The amino acid the triplet is coding for doesnt change because some amino acids have more than one triplet code
The new amino acid the triplet codes for is chemically similar
The mutated triplet code is not involved with the proteins function
What are some beneficial effects of mutations?
They increase chance of survival fo r teh organism e.g bacterial resistance
