M6 S1 : Cellular Control Flashcards
Why do the structure and function of different cells vary when all cells in an organism carry the same genes (DNA)?
Not all the genes in a cell are expressed (transcribed to make a useful protein) they are selectively switched on and off. As cells show different gene expressions, different proteins are made and these modify the cells. They determine the cell structure and control processes (including expression of more genes which produce more proteins).
How can gene expression (and therefore protein synthesis) be controlled?
- Transcriptional level
- Post-transcriptional level
- Post/translational level
What is a transcription factor?
Proteins that bind to DNA and switch genes on and off by increasing and decreasing the rate of transcription.
What are the 2 types of transcription factors?
- Activators : Factors that start transcription.
- Repressors : Factors that stop transcription.
How is gene expression controlled by transcriptional level control?
Gene expression controlled by altering the rate of transcription of genes (increased transcription produces more mRNA, which can be used to make new proteins.
What affects whether a transcription factor can bind to DNA or not?
The shape, it can sometimes be altered by the binding of some molecules (like hormones and sugars). This means the amount of some molecules in an environment or a cell can control the synthesis of some proteins by affecting transcription factor binding.
How do transcription factors bind to DNA in eukaryotes?
They bind to specific DNA sites near the start of their target genes (these are the genes that control the expression of).
How do transcription factors bind to DNA in prokaryotes?
Binds to the operon.
What is an operon?
A section of DNA that contains a cluster of structural genes that are all transcribed together, control elements and sometimes a regulatory gene.
What are structural genes?
They code for useful proteins, such as enzymes?
What are control elements?
It includes a promoter (a DNA sequence located before the structural genes that RNA polymerase binds to) and an operator (a DNA sequence that transcription factors bind to). The regulatory gene codes for an activator or repressor.
Why and how does E coli bacterium respire lactose when it is and isn’t present?
When glucose is not available, E coli can respire lactose. The genes that produce the enzyme needed to respire lactose are found on an operon called the lac operon. It has 3 structural genes lacZ lacY lacA, which produces proteins that helps digest enzymes (including B-galactosidase and lactose permease).
When lactose is not present : The regulatory gene lacl produces lac repressor (transcription factor) that binds to operator site where no lactose present. This blocks transcription as RNA polymerase can’t bind to promoter.
When lactose is present : It binds to lac repressor, changing the repressors shape, so it can no longer bind to the operator site. RNA polymerase can now begin transcription of the structural genes.
what are introns?
Sections of DNA that don’t code for amino acids.
What are exons?
Sections of DNA that do code for amino acids.
What is post-transcriptional level control?
Control of the gene expression after genes have been transcribed. After transcription mRNA in eukaryotic cells is edited. This is because the genes in eukaryotic DNA contain sections that do not code for amino acids (introns) as well as exons.
During transcription both introns and exons copied into mRNA. mRNA strands containing introns and exons are called primary mRNA transcripts (pre-mRNA). Splicing removes introns from primary mRNA strands, exons are joined together forming mature mRNA strand. This happens in the nucleus, it then leaves nucleus for next stage of protein synthesis.
What is mature mRNA?
When introns are removed from a primary mRNA strand, and the exons join together.
What are primary mRNA transcripts?
mRNA strand containing introns and exons.
Why don’t prokaryotes produce mRNA directly from DNA without splicing?
No need for splicing as there are no introns in prokaryotic DNA.
What is post-translational level control?
As some proteins aren’t functional straight after they have been synthesised (after translation). They need to be activated to work (become a functional protein). Like protein synthesis, protein activation is controlled by molecules like hormones and sugars
What is cAMP and how does it control protein activation?
Some molecules control protein activation by binding to cell membranes and triggering the production of cyclic AMP (cAMP) inside the cell. cAMP activates proteins inside the cell by altering their 3D structure (like altering 3D structure of the active site in an enzyme,making it more or less active.
How does cAMP activate PKA (protein kinase A)?
PKA is an enzyme that has 4 subunits. When cAMP is not bound , the 4 subunits are inactive. The then cAMP binds and changes the shape of enzyme’s 3D structure, releasing the active subunits. PKA is now active.
What is a body plan? How is it controlled?
The general structure of an organism.
What controls the development of a body plan?
Proteins help set up the basic body plan so that everything is in the right place (e.g. legs grow where legs should grow). The proteins that control the body plan are coded for by genes called Hox genes.
What are homeobox sequences in Hox genes?
Regions on the Hox gene that are highly conserved. This means it has changed very little during the evolution of different organisms that have the homeobox sequence.
Complete the sentence :
_______ Hox genes are found in animals, plants and fungi, which means body plan is controlled in a _______ way in flies, mice, humans, etc.
Similar
How do Hox genes control development?
Homeobox sequences code for part of a protein called the homeodomain. The homeodomain binds to specific sites on DNA, enabling the protein to act as a transcription factor. The protein binds to DNA at the start of the developmental genes, activating or repressing transcription, so altering the production of proteins involved in the body plan.
What is apoptosis?
Some cells die and break down as a normal part of development. This is a highly controlled process called apoptosis (programmed cell death).
What is the process of apoptosis?
- Enzymes inside the cell break down cell components (e.g. proteins, DNA).
- The cell shrinks and begins to fragment.
- Phagocytes engulf and digest the cell fragments.
What are the roles of mitosis and apoptosis in development?
Mitosis and differentiation create the bulk of the body parts and then apoptosis refines the parts by removing unwanted structures.
During development, the genes that control mitosis and the genes that control apoptosis are switched on and off in appropriate cells. This means new cells are produced while some cells die, creating the body plan.
What are some examples of how mitosis and apoptosis control development?
- When hands and feet first develop in humans, the digits (fingers and toes) are connected. They are only separated when cells in the connecting tissues undergo apoptosis.
- When tadpoles develop into frogs, their tails are removed by apoptosis.
- During the development of the nervous system, an excess of nerve cells are produced. Nerve cells that are not needed undergo apoptosis.
What are the responses of genes that regulate the cell cycle and apoptosis? What are the examples?
The genes that regulate the progression through a cell cycle (cells undergoing mitosis) and apoptosis can respond to both internal and external stimuli :
- An internal stimuli can be DNA damage. If DNA damage is detected in the cell cycle, it can result in the expression of genes that cause the cycle to be paused, and can even trigger apoptosis.
- An external stimuli can be a stress caused by a lack of nutrient availability, which can result in the gene expression that prevents cells from undergoing mitosis.
- An external stimulus (like an attack from a pathogen) can trigger gene expression which leads to apoptosis.
