cellular control Flashcards
why is that all organisms carry the same genes but the structure and function of different cells varies ?
- this is because not all genes are expressed(transcribed and used to make functional protein)- they are selectively switched on or off . because cells show different gene expression , different proteins are made and modify the cell - they determine the cell structure and control the cell process.
what are the different levels gene expression can be controlled at ?
transcriptional, post transcriptional and post translational level.
how can gene expression be controlled at transcriptional level ?
by altering the rate of transcription of genes. eg increased transcription produces more mrna , which can be used to make more protein.
how is transcriptional level altering the rate of transcription of genes controlled ?
its controlled by transcription factors - they are protein that bind to dna and switch genes on or off by increasing or decreasing the rate of transcription.
whats an activator?
factors that increase the rate of transcription
whats an repressor ?
factors that decrease the rate of transcription.
what does the shape of a transcription factor determine and what does that mean?
shape of a transcription factor determines weather it can bind to dna or not and it can sometimes be altered by binding of other mollecules such as hormones this means that the amount of certain molecules in an certain enviorment or cell can control the synthesis os some protein by affecting transcription factor binding.
transcription factors - what happenes in eukaryotes
transcription factors bind to specific dna sites near the start of the target genes-the genes they control the expression of.
transcription factors - what happens in prokaryokes
the control of the gene expression often incoves transcription factors binding to operons.
what’s an operon?
An operon is a section of a DNA that contains a cluster of structural genes , that are transcribed together as well as control elements and sometimes a regulatory gene.
whats a structural gene ?
its a gene that codes for a useful proteins such as enzymes
what are the control elements? - define promotor and operator
a control element include promoter ( a dna sequence located before the structural genes that rna polymerase binds to ) and an operator (a dna sequence that the transcription factors bind to)
whats a regulatory gene?
its a gene that codes for an activator and a repressor
give an example of an operon?
- Ecoli is a bacterium that respires glucose, but it can use lactose if glucose isn’t available.
- the genes that produce the enzymes needed to respire lactose are found on an operon called a lac operon.
- the lac operon has three structural genes – lacZ , lacy and lacA , which produce proteins that help bacteria digest lactose.
lactose not present
- then the regulatory gene (lacl) produces a lac repressor which is a transcription factor that binds to the operator site when theres no lactose present. this blocks transcription because RNA polymerase cant bind to the promoter.
lactose is present
- it binds to the repressor changing the repressors shape so that it can no longer bind to the operators site
- Rna polymerase can now begin transcription of structural genes.
where is mrna edited ?
at post transcriptional level
how is mrna edited at post transcriptional level?
- genes in eukaryotic DNA contain sections that don’t code for amino acids.
- these sections of DNA are called introns. All the bits that do code for amino acids are called exons.
- during the transcription the introns and exons are both copied into mrna. mrna strands containing intons and exons are called primary mrna transcript.
- introns are removed from the primary mRNa strands by a process called splicing-introns are removed and exons joined ,forming mature mRNA strands. this takes place in the nucleus.
- the mature mRNA then leaves the nucleus for the next stage of protein synthesis(translation).
when some proteins are not activated to be synthesised what happenes?
- then camp activates some proteins.
- protein activation is controlled by molecules such as hormones some of the molecules work by binding to cell membrane and triggering the production of cyclic AMP inside the cell.
- Camp then activates proteins inside the cell by altering their three dimensional structure.
- for eg : altering the 3d structure can change the active site of an enzyme.
how does camp activate protein kinase a (PKA)
- 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 active subunits - PKA is now active.
whats a mutation
mutations are changes to the base sequence of DNA
what are the types of mutations :
- substitution
- insertion
- deletion
subsitution
its when one or more bases are swapped for another eg: ATGCCT becomes ATTCCT
DELETION
its when one or more bases are removed eg: ATGCCT BECOMES ATCT
INSERTION
one or more babes are added eg ATGCCT TO ATGACCT
what effect can a mutation have
- neutral
- beneficial
- harmful
what does having aneutral effect on a proteins function mean
- neutral affect on protein function wont affect the organism overall.
- the mutation change a base in a triplet, but the amino acid that the triplet codes for doesn’t change. this happens because some amino acids are coded by more than one triplet. EG: TAT and TAC code for tyrosine , so if TAT is changed to TAC the amino acid wont change.
- the mutation produces a triplet that codes for different amino acids but the amino acid is chemicaly similar to the original so its functions are like the original amino acid.
- however some mutations may change proteins structure and make it less active.
what are the mutations with beneficial effect
- they increase its chance of survivaleg some bacterial enzymes breakdown certain antibodies. mutations in the genes that code for these enzyes could make them work on a wider range of antibiotics. this is a beneficial to bacteria because antibiotic resistance can help them to survive.
what are the mutations with harmful effects
decreases its chance of survival
eg cystic fibross can be caused by deletion of three babes in the gene that codes for CFTR (ystic fibrosis transmembrane condunctane regulator) protein. the mutated CFTR protein folds incorrectly sp its broken down . this leads to excess mucus production, which affects the lungs of cf sufferes.
whats a body plan
its a general structre of an organism
what controls the development of a body plan
proteins control the development of body plans - they help set up the basic body plan so that everything is in its right place : eg legs grow where they are meant to grow
what’s an hox genes
its the proteins that control body plan development are coded by genes called hox genes , similar hox genes are found in huumans , animals ,plants , and fungi which means body plan is controlled in a similar way.
whats an homeobox sequence
they are the hox genes regions - which are highly conserved - this means that these sequences have changed very little during the evolution of different organisms that possess these homeobox sequence.
how do hox genes control development?
- hoxgenes code for a part of protein called the homeodomain.
- the homeodomain binds to specific sits on dna, enabling the protein to work as a transcriptional factor.
- the proteins bind to dna at the start of development genes, activating or repressing transcription and so altering the production of proteins involved in the development of the body plan.
what are the two main feautures involved in development of a body plan?
- apoptosis
- mitosis
how is apoptosis involved in the development of a body plan?
- some cells die and breakdown as a normal part of the development.
- this is highly controlled process called apoptosis / programmed cell death.
how is the cell broken down once apoptosis is triggered ?
1- enzymes inside the cell break down important cell components such as proteins in the cytoplasm amd dna in the nucleus..
2-as the cells content are broken down it begins to shrink and breaks up into fragments.
3-the cell fragments are engulfed by phagocytes and digested.
how is mitosis involved in the development of a body plan ?
mitosis and differentiation create the bulk of body parts and then apoptosis refines the parts by removing the unwanted structures.
-during development, genes that control apoptosis and genes that control mitosis are switched on and off in appropriate cells. this means that some cells die, whilst some new cells are produced and correct plant develops.
how can genes that regulate apoptosis and the cell cycle can respond to stimuli ? - internal and external - give examples
- an internal stimulus could be a dna damage. if the dna damage is detected during cell cycle, this can result in the expression genes which cause the cycle to be paused and can even trigger apoptosis.
- an external stimulus, such as stress caused by a lack of nutrient avalibility, could result in a 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.
