Cellular control Flashcards
What varies between genes and why
Structure and function as not all genes in a cell are expressed (selectively switched on or off).
Why do cells show a different gene expression
Different proteins are made that modify the cell and determine structure and processes
What level can gene expression be controlled
The transcriptional, post-transcriptional and post-translational level
Transcription factors control gene expression at what level
Transcriptional level
How can gene expression be controlled
By altering the rate of transcription of genes
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 activators
Factors that increase the rate of transcription
What are repressors
Factors that decrease the rate of transcription
What does the shape of a transcription factor determine
Whether it can bind to DNA or not and can be altered by the binding of some molecules
In Eukaryotes where do transcription factors bind to specific DNA sites
Near the start of their target genes - the genes they control the expression of
In Prokaryotes where do transcription factors bind to specific DNA sites
Binding to operons
What is an operon
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 do structural genes code for
Useful proteins such as enzymes
What do regulatory genes code for
An activator or repressor
What do control elements include
A promoter and 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
Process of the Lac operon in E.coli when lactose is not present
1) The regulatory gene (lacl) produces the lac repressor, which is a transcription factor that binds to the operator site when there is no lactose present.
2) This blocks transcription because RNA polymerase can’t bind to the promoter
Process of the Lac operon in E.coli when lactose is present
Lactose binds to the repressor, changing its shape so it can no longer bind to the operator site. RNA polymerase can now begin transcription of the structural genes
What is the lac operon and what is involved
1) E coli respires glucose or lactose if no glucose is available
2) The genes that produce the enzymes needed to respire lactose are found on an operon called the lac operon
3) The structural genes lacZ, lacY and lacA produce proteins (beta-galactosidase and lactose permease) to help digest lactose
What level is mRNA edited
Post-transcriptional level
What are introns
In eukaryotic DNA sections that don’t code for amino acids
What are exons
Sections of DNA that do code for an amino acid.
During transcription what is copied into mRNA
Both introns and exons
What are mRNA strands containing introns and exons
Primary mRNA transcripts (pre mRNA)
How and where are introns removed from primary mRNA
Splicing - introns are removed and exons joined forming mature mRNA strands taking place in the nucleus
What is protein activation controlled by
Molecules such as hormones or sugars
What is cAMP
Cyclic AMP - a secondary messenger relaying the message from the control molecule
How can cAMP activate a protein
Molecules bind to cell membranes triggering the production of cAMP inside the cell. It then activates proteins inside the cell by altering their 3D structure. This can change the active site making it more or less active.
How does cAMP activate protein kinase A (PKA)
1) PKA is an enzyme made of four subunits
2) When cAMP isn’t bound, the four units are bound together and are inactive
3) 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 that are arranged in a particular way
What controls the development of a body plan
Proteins as they help to set up the basic body plan so everything is in the right place
What are the proteins that control body plan coded by
Hox genes
How can you tell if body plan development is controlled in a similar way from species to species
Similar hox genes are found
What are homeobox sequences
They are highly conserved (changed very little from evolution) and code for a part of the protein called the homeodomain. This binds to specific sites on DNA enabling the protein to work as a transcription factor. This happens at the start of developmental genes, activating or repressing transcription altering the production of proteins involved in the development of the body plan.
What is apoptosis
Programmed cell death
Once apoptosis is triggered how is the cell broken down
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
How does apoptosis and mitosis/differentiation work together
Mitosis and differentiation create the bulk of body parts and then apoptosis refines he parts removing unwanted structures
What is an internal stimulus
Factors located inside the body that are detected and cause a response such as DNA damage
What is an external stimulus
Changes to conditions outside of the body, or in general, information from outside the body that our senses detect such as stress from lack of nutrient availability
What does an internal stimuli mean for genes
Expression of the genes which causes the cycle to be paused and can trigger apoptosis
What does an external stimuli mean for genes
It could result in gene expression that prevents cells from undergoing mitosis. This can also lead to apoptosis being trigged.
What is substitution
One or more bases are swapped for another
What is deletion
One or more bases are removed
What is insertion
One or more bases are added
What is duplication
Sections get duplicated on a chromosome
What is translocation
A section of one chromosome breaks off and joins another non-homologous chromosome
What is inversion
A section of chromosome breaks off, is reversed and then joins back onto the chromosome
What is a mutation
A change to the base sequence of DNA
What are neutral mutations
The base of a triplet changes but the amino acid dose not change as some amino acids are coded for by more than one triplet.
The mutation could code for a different amino acid that is chemically similar so functions the same
The mutated triplet codes for an amino acid not involved with the proteins function
What is a beneficial mutation
They have advantages on an organism such as increasing chance of survival such as enzymes working in antibiotics on a larger range of bacteria
What is a harmful mutation
They have disadvantageous effects on an organism such as decreasing their survival chances. An example is cystic fibrosis is a result of a deletion of three bases producing excess mucus
