Cellular control Module 6 Flashcards
What do all cells in an organism carry?
The same genes
How come the structure and function of different cells varies if they all have the same genes?
Not all genes in a cell are expressed (transcribed and used to make functional proteins), they are selectively switched on and off
What does cells having different gene expression lead to?
Different proteins made
Different cell structure and processes
What levels can gene expression (and therefore protein synthesis) be controlled at?
Transcriptional
Post-transcriptional
Post-translational
How can gene expression be controlled at transcriptional level?
Altering the transcription of genes
This is controlled by transcription factors
What are transcription factors?
Proteins which bind to DNA and switch genes on/off by increasing or decreasing the rate of transcription
Factors which increase rate = activators
Factors which decrease rate = repressors
What determines whether a transcription factor can bind to DNA or not?
The shape, can be altered by hormones and sugars
Meaning the amount of certain molecules in an environment or cell can control translation
In eukaryotes where do transcription factors bind to?
Specific DNA sites near the start of the target genes
In prokaryotes where do the transcription factors bind to?
The operon
What’s an operon?
A section of DNA which 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 the control elements consist of?
Promoter (a DNA sequence located before the structural genes that RNA polymerase binds to) An operator (a DNA sequence that transcription factors bind to)
What does the regulatory gene do?
Codes for an activator or repressor
For an example of example of an operon, explain the lac operon in E.coli?
The lac operon has 3 structural genes which lacZ, lacY and lacA which produce proteins which allow the bacteria to digest lactose (including B-galactosidase and lactose permease)
Lactose not present:
The regulatory gene prodcues the lac repressor, which is a transcription factor which binds to operator site when there’s no lactose present. This blocks transcription because RNA polymerase can’t bind to the promoter
Lactose present:
When lactose is present, it binds to the 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 is E.coli?
Bacterium that respires glucose, but it can use lactose if glucose isn’t available
The genes that produce the enzyme needed to respire lactose are found on the operon, called the lac operon
What is edited at post-transcriptional level?
mRNA
What’s an intron?
Section of DNA which doesn’t code for amino acids?
What’s an exon?
Section of DNA which does code for amino acids
What’s happens in transcription in relation to introns and exons?
Introns and exons are both copied into mRNA forming primary mRNA transcripts
Then in a process called splicing, the introns are removed and the exons join together, forming mature mRNA strands, this occurs in the nucleus
The mature mRNA then leaves the nucleus for the next stage of protein synthesis (translation)
Why do some proteins need to activated?
They aren’t functional straight after they have been synthesised
What is protein activation controlled by?
Molecules eg. hormones and sugars
How does protein activation work?
Molecules such as hormones or sugars bind to the cell membrane, triggering the production of cyclic AMP within the cell
Cyclic AMP then activates proteins within the cell, by altering their 3D strucuture
What is PKA?
An enzyme made of 4 subunits
How does cyclic AMP activate PKA?
When cyclic AMP isn’t bonded the 4 units are held together and it’s inactive
However, when cyclic AMP binds, it causes a change in the enzymes 3D structure, releasing the active subunits, PKA is now active
What the body plan of an organism?
The general structure, it’s controlled by proteins created from hox genes
What are similar hox genes found in, and what does this mean?
Found in animals, plants and fungi, meaning body development is controlled in a similar way
What are homeobox sequences?
Regions in hox genes which are highly conserved, so have changed very little in the evolution of different organisms
How do hox genes control development?
Homebox sequences code for a part of the protein called the homeodomain
The homedomain binds to specific sites on DNA, enabling the protein to work as transcription factor
The protein binds 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’s apoptis?
Programmed cell death
What are the steps of apoptis?
Enzymes in 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 shrinks and breaks into fragments
The cell fragments are engulfed by phagocytes and digested
Bried description how a body part is formed?
Mitosis and differentiation provide the bulk of body parts, apoptosis then refines them by removing unwanted structures
Eg digits on hands and feet formed via this
What happens during development to the genes that control apoptosis and mitosis?
Switched on/off in appropriate cells
What internal stimulus can the genes that regulate apoptosis respond to?
DNA damage
What external stimulus can the genes that regulate apoptosis respond to?
Attack from a pathogen
Any change to the base (nucleotide) sequence is know as a?
Mutation
3 types of mutation?
Substitution
Deletion
Insertion
What’s substitution?
One or more bases are swapped for another
What’s deletion?
Where one or more bases are removed
What’s insertion?
Where one or more bases are added
What do mutations do?
Change in the order of DNA bases, will change the order of amino acids and therefore the primary structure of the protein formed
This may change the final 3D shape of the protein, so it doesn’t work properly
Why can a mutation have a neutral affect on a protein?
Mutation has changed a base in a triplet, but the amino acid that that triplet codes for doesn’t change, as some amino acids are coded for by more than 1 triplet
Mutation produces a triplet code which codes for a different amino acid, however it’c chemically similar to the original so it functions like the original
The mutated triplet codes for an amino acid not involved in the proteins function
Mutations with beneficial effects?
Bacterial enzymes break down certain antibiotics, mutations in the genes could allow them to break down a wider range of antibiotics
Mutations with harmful effects?
cycstic fibrosis can be caused by deletion of bases in genes which code for CFTR protein, leads to excess mucus production
