Cellular control (6) Flashcards
How does DNA play a part in the variation in structure and function of cells?
Not all the genes in a cell are expressed- they are selectively turned on or off. Because cells show different gene expressions, different proteins are made and these proteins modify the cell- they determine the cell structure and control cell processes.
At what levels can gene expression be controlled?
- transcriptional level
- post-transcriptional level
- post-translatory level
How can gene expression be controlled at the transcriptional level?
This can be done by altering the rate of transcription of genes.
What are transcription factors, activators, and repressors?
They are 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 factors affect the action of transcription factors?
The shape of a transcription factor determines whether it can bind to DNA or not, and can sometimes be altered by the binding of some molecules, like hormones and sugars.
This means that the amount of certain molecules in an environment or a cell can control the synthesis of some proteins by affecting transcription factor binding.
What are structural genes?
Most structural genes code for useful proteins like enzymes
Where do transcription factors bind?
In eukaryotes transcription factors bind to specific DNA sites near the start of their target genes- the genes that they control the expression of.
In prokaryotes control of gene expression often involves transcription factors binding to operons.
What is an operon?
An operon is a section of DNA that contains a cluster of structural genes, that are transcribed together, as well as control elements and sometimes a regulatory gene.
What are control elements?
Promoter - A DNA sequence located before the structural gene that RNA polymerase binds to
Operator - A DNA sequence that transcription factors bind to
What is a regulatory gene?
A regulatory gene codes for an activator or a repressor
What is the lac operon in E. coli?
- it is a bacteria that respires glucose but it can use lactose if glucose is unavaliable
- the genes that produce the enzymes needed to respire lactose are fdound on an operon called the lac operon
- the lac operon has 3 structural genes lacZ,Y and A which produce proteins that hlep the bacteria digest lactose.
What happens in the lac operon if lactose is not present?
The regulatory gene produces the lac repressor, which is a transcription factor that bind to the operator site when there’s no lactose present. This blocks transcription because RNA polymerase cannot bind to the prometer
What happens in the lac operon if lactose is present?
When lactose is present, it binds to the repressor, changing the repressor’s shape so that it can no longer bind to the operator site. RNA polymerase can now begin transcription of the structural genes.
What are introns?
introns are regions of DNA that do not code for amino acids.
What are exons?
exons are regions of DNA that code for amino acids.
What are primary mRNA transcripts?
During transcription the introns and exons are both copied into mRNA. mRNA strands containing introns are called primary mRNA transcripts.
How are introns removed from primary mRNA?
They are removed by a process called splicing where introns are removed and exons joined, forming mature mRNA. (takes place in nucleus)
How do some molecules work to activate proteins?
Some work by binding to cell membranes and triggering the production of cyclic AMP inside the cells.
How does cAMP work to activate proteins?
It activates proteins inside the cell by altering their three dimensional structure. e.g changing enzyme active site shape to make it more or less effective.
How does cAMP activate protein kinase A?
- PKA is an enzyme made of four subunits
- when cAMP isn’t bound, the four units are bound together and are inactive.
- When cAMP binds, it causes a change in the enzyme’s 3D structure, releasing the subunits- PKA is now active.
What is a body plan?
A body plan is the general structure of an organism, that are arranged in a particular way.
What are Hox genes?
They are the genes that code for the proteins that control body plan development.
What are homeobox sequences?
They are regions on hox genes which are highly conserved.
How do Hox genes control development?
- Homeobox sequences code for a part of the 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?
apoptosis is programmed cell death
What are the steps in apoptosis?
- enzymes inside the cell break down important cell components such as proteins in the cytoplasm and DNA in the nucleus
- as the cell’s contents are broken down it begins to shrink and breaks up into fragments
- the cell fragments are engulfed by phagocytes and digested
How is apoptosis a part of mitosis?
Apoptosis refines the parts created from mitosis by removing the unwanted structures.
How is development and apoptosis linked?
During development, genes that control apoptosis and gens that control mitosis are switched on and off in appropriate cells. This means that some cells die, whilst some new cells are produced and the correct body plan develops.
What is an internal stimulus that can regulate apoptosis?
An internal stimulus could be DNA damage. If DNA damage is detected during the cell cycle, this can result in the expression of genes which cause the cycle to be paused and can even trigger apoptosis.
What is an external stimulus that can trigger apoptosis?
An external stimulus, such as stress caused by a lack of nutrient avaliability could result in gene expression that prevents cells from undergoing mitosis. Gene expression which leads to apoptosis being triggered can also be caused by an external stimulus such as attack by a pathogen.
What is a mutation?
A mutation is a rare random change in base sequence of DNA
What are the three types of mutation?
Substitution
Deletion
Insertion
Why can sometimes mutations be neutral?
- the base change doesn’t affect the amino acid produced due to the degenerate nature of the genetic code.
- the mutation produces a chemically similar amino acid so functions like the original
- the mutation affects an amino acid that is not involved with protein function.
Why can sometimes mutations be beneficial?
They can have an advantageous effect on an organism, increasing its chance of survival.
Why can sometimes mutations be harmful?
They can affect a protein’s function to make it worse. These types of mutations have a disadvantageous effect on survival.
How can mutations have an effect on whether or not a protein is produced?
If a mutation occurs at the start of a gene so that RNA polymerase can’t bind to it and begin transcription, the protein coded for by the gene won’t be made. THe loss of production of a protein can have harmful effects.
