Cellular control Flashcards
Although all cells in an organism share the same genes, why does the structure/function of diff. cells vary?
Some genes aren’t expressed- transcribed and used to make a functional protein
What levels can gene expression be controlled?
Transcriptional, post-transcriptional and post-translational
How is gene expression controlled at the transcriptional level?
By altering the rate of transcription of genes. This is controlled by transcription factors.
What are transcription factors?
proteins that bind to DNA and switch genes on or off by increasing/decreasing the rate of transcription
What are activators?
Factors that start transcription
What are repressors?
factors that stop transcription
What does the shape of a transcription factor determine?
Whether it can bind to DNA or not
What can alter the shape of transcription factors?
the binding of molecules like some hormones and sugars
Where do transcription factors bind to in eukaryotes?
specific DNA sites near the start of their target genes
Where do transcription factors bind to in prokaryotes?
operons
What is an operon and what does it consist of?
a section of DNA containing a cluster of structural genes that are all transcribed together, control element, and sometimes a regulatory gene
Structural genes- function
code for useful proteins like enzymes
What do control elements consist of?
a promoter and operator
What is a promoter?
a DNA sequence located before structural genes that RNA polymerase binds to
What is an operator?
a DNA sequence that transcription factors bind to
Regulatory gene- function
codes for an activator or repressor
What does E.coli respire instead of glucose?
lactose
What is the lac operon?
the operon that consists of the genes that produce the enzymes needed to respire lactose
Name the 3 structural genes on the lac operon
lacZ, lacY, and lacA
What do the 3 structural genes in the lac operon code for?
proteins that help E.coli digest lactose e.g. beta-galactosidase and lactose-permease.
Lactose isn’t present- E.coli
1- Regulatory gene (lacI) produces the lac repressor, which is a TF that binds to the operator when lactose isn’t present
2- This blocks transcription because RNA polymerase can’t bind to the promoter
Lactose is present- E.coli
1-Lactose binds to the repressor, changing its shape so it can’t bind to the operator site
2- RNA polymerase begins transcription of the structural genes
What are introns?
In eukaryotic cells, these are sections of DNA that don’t code for amino acids post-transcription.
What are exons?
In eukaryotic cells, these are sections of DNA that do code for amino acids post-transcription.
What happens to introns and exons DURING transcription?
they are copied into mRNA
What are primary mRNA transcripts?
mRNA strands that contain introns and exons
What happens during the post-transcriptional level control?
Introns are removed from primary mRNA transcripts by splicing. Exons are joined together to form mature mRNA. This takes place in the nucleus. The mature mRNA leaves the nucleus for translation.
Why is protein activation needed at the post-translational level control?
some proteins still aren’t functional straight after being synthesised and need to be activated to work.
What is protein activation controlled by?
hormones and sugars
How do some molecules control protein activation?
binding o cell membranes and triggering the production of cAMP inside the cell
What does cAMP do?
it activates proteins inside the cell by altering their 3D structure which could, for example, change an enzyme’s active site, making it more or less active
Activation of PKA by cAMP
When cAMP isn’t bound, PKA’s 4 units are bound together and are inactive.
When cAMP binds. it changes the enzyme’s 3D structure, releasing the active subunits. PKA is now active.
What is PKA?
an enzyme made of 4 subunits
What is a body plan?
the general structure of an organism
What controls the development of a body plan and how?
proteins- they help set up the basic body plan so that everything’s in the right place
What are hox genes?
the genes that code fr the proteins that control the body plan development
Hox genes- Drosophila body plan
2 hox gene clusters control the development. One controls the development of the head and anterior thorax and the other controls the posterior thorax and abdomen.
What are homeobox sequences?
Regions on hox genes that are highly conserved- this means that they have changed very little during the evolution of diff. organisms that possess it
What does the homeobox sequence code for?
a part of the protein called the homeodomain
What does the homeodomain do?
it binds to specific sites on DNA, enabling the protein to work as a transcription factor. the proteins bind to DNA at the start of the developmental genes, activating or repressing transcription and so altering the production of proteins involved in the body plan development.
What is apoptosis?
when some cells die and are broken down
How is a cell broken down after apoptosis is triggered?
1- Enzymes inside the cell break down the cell components
2- The cell shrinks and begins to fragment
3- Phagocytes engulf and digest the cell fragments
Briefly describe the roles of mitosis+differentiation as well as apoptosis in development
mitosis and differentiation create a bulk of body parts and apoptosis refines them by removing unwanted substances
Hands and feet- apoptosis example
when they first develop in humans, their fingers and toes and attached. apoptosis separates them in the cells in the connecting tissue
Tadpoles and frogs- apoptosis example
as tadpoles develop into frogs, their tail cells undergo apoptosis to be removed
Nervous system- apoptosis example
when developing the NS, excess nerve cells are produced. those that aren’t needed undergo apoptosis.
What happens to the genes that control mitosis and apoptosis during development?
they’re switched on and off in appropriate cells so some new cells are produced while some die. the correct body plan is developing.
What can the genes that regulate mitosis and apoptosis do?
respond to internal and external stimuli
What happens to body plan development if an internal stimulus like DNA damage is found?
If detected in the cell cycle, this can cause the expression of genes that cause the cycle to be paused and even trigger apoptosis
What happens to body plan development if an external stimulus is detected?
An example is stress caused by a lack of nutrient availability. This can cause gene expression preventing cells from undergoing mitosis.
Another external stimulus could be a pathogen- this could cause gene expression that leads to apoptosis.
What are changes to the base sequence of DNA called?
mutations
What are the 3 types of mutations?
substitution, deletion and insertion
Substitution mutation
one or more bases are swapped for another base`
Deletion mutation
one or more bases are removed
Insertion mutation
one or more bases are added
What does a mutation in a gene affect of a protein?
It alters its primary structure which could affect its final 3D structure so it doesn’t work properly
It can also cause a protein to not be produced at al
What is frameshift mutation?
When insertion or deletion occurs, the number of bases changes causing a shift in all the base triplets that follow. It changes the way the rest of the sequence is read.
The earlier a frameshift mutation occurs…
the more amino acids affected and the greater the effect of the mutation on the protein
Why do some mutations have a neutral effect?
1- it changes a base in a triplet but the amino acid the triplet codes for doesn’t change e.g. both TAT and TAc code for tyrosine
2- a different amino acid is coded for but it is chemically similar so functions the same way e.g. arginine (AGG) and lysine (ACG)
3- it codes for an amino acid not involved in the protein’s function
How can some mutations have an effect on a protein’s function?
they make it more or less active
If a protein function is affected by a mutation, what effect can it have on the whole organism?
beneficial or harmful
Beneficial mutations
they have an advantageous effect on the organism e.g. increase their chances of survival. these are passed on to future generations by natural selection.
Beneficial mutation- example
some bacterial enzymes break down certain antibiotics. mutations in the gene that codes for these enzymes could make them work on more antibiotics. this antibiotic resistance helps them to survive.
Harmful mutations
- They have a disadvantageous effect on an organism e.g. decrease their chances of survival
- They can also affect whether or not a protein is produced.
Harmful mutation- example (CF)
cystic fibrosis is caused by the deletion of 3 bases in the gene that codes for the CTFR protein. if the protein is mutated, it folds incorrectly and is broken down. this leads to excess mucus production, which affects the lungs of CF sufferers.
