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