2. control of gene expression Flashcards
What are housekeeping genes?
genes that code for enzymes necessary for reactions present in metabolic pathways
What are tissue-specific hormones?
affect specific tissues- protein based hormones (required for growth and development of an organism or enzymes), only required by certain cells at certain times to carry out a short lived response.
what is gene regulation?
entire genome of an organism is present within every prokaryotic cell, and all eukaryotic cells that contain a nucleus.
this includes genes not required by the cell- the expression of genes and the rate of synthesis of protein products (like enzymes and hormones) has to be regulated
genes can be turned on or off
bacteria can respond well to changes in the environment- express genes only when the products are needed, prevents vital resources being wasted.
gene reg similar in prokaryotic and eukaryotic cells- diff stimuli and eukaryotic produces more complex responses.
What are the ways in which genes are regulated?
transcriptional- can be turned on and off
Post-transcriptional- mRNA can be modified which regulates translation and the types of proteins produced
translational- translation can be stopped or started
post-translational- proteins can be modified after synthesis which changes their functions
What are the mechanisms that can affect the transcription of genes?
chromatin remodelling- DNA is long molecule, wound around histones in eukaryotic cells to pack into nucleus = chromatin.
heterochromatin- tightly wound DNA- chromosomes visible during cell division
euchromatin- loosely wound DNA, present during interphase
tightly wound DNA cannot be replicated, DNA polymerase cannot transcribe it.
protein synthesis occurs during interphase- regulation as ensures proteins are synthesised and prevents the energy- consuming process of protein synthesis when cells are actually dividing.
Histone modification- negative DNA coils around histones as they are positive.
addition of acetyl groups (acetylation) or phosphate groups (phosphorylation) = reduces + charge= DNA coils less tight.
addition of methyl groups (methylation) = histones more hydrophobic = bind more tightly to each other, causing DNA to coil more tightly/
What is epigenetics?
describe the control of gene expression by the modification of DNA
how does the lac operon work?
in prokaryotic cells
operon- group of genes controlled by the same regulatory mechanism and are expressed at the same time
lac= lactose- if there is a lack of glucose, prokaryotes can activate the lac opperon to use lactose to make energy
structural genes- genes that code for proteins not involved in DNA regulation- there are 3 in the lac operon- lac Z, Y, A
they make 3 enzymes that metabolise lactose…
1. beta galactosidase
2. lactose permease
3, lactose transacetylase
regulatory genes- lac I- the genes that code for proteins involved in DNA regulation- codes for repressor protein- stops the transcription of the 3 structural genes to make the enzymes
operator- DNA sequence right next to promotor- where the repressor protein is
promotor- DNA sequence where the RNA polymerase will bind
Lac I triggers repressor protein this happens when glucose is present, binds to operator region, blocking the promotor region, meaning RNA polymerase cannot bind. lactose binds to repressor protein, repressor protein changes shape and can no longer bind to operator, RNA polymerase can now bind to promotor, transcription can happen,
made more efficient by cAMP receptor protein binds to cAMP, binds to RNA polymerase to upregulate it and make transcription more efficient
the RNA polymerase, CRP, cAMP complex, now moves along to lac Z, Y and A, making the enzymes to break down lactose and use it in respiration to release energy
glucose reduces the conc of cAMP, cannot form complex with CRP, complex breaks down and cycle begins again
transcriptional factors controlling gene expression
can turn genes on and off by altering conditions, allowing RNA polymerase to bind
prokaryotic= lac operon
eukaryotic= histone modification and chromatin remodelling
chromatin remodelling- DNA is long molecule, wound around histones in eukaryotic cells to pack into nucleus = chromatin.
heterochromatin- tightly wound DNA- chromosomes visible during cell division
euchromatin- loosely wound DNA, present during interphase
tightly wound DNA cannot be replicated, DNA polymerase cannot transcribe it.
protein synthesis occurs during interphase- regulation as ensures proteins are synthesised and prevents the energy- consuming process of protein synthesis when cells are actually dividing.
histone modification- change how tightly wound the DNA is
addition of acetyl groups (acetylation) or phosphate groups (phosphorylation) = reduces + charge= DNA coils less tight.
addition of methyl groups (methylation) = histones more hydrophobic = bind more tightly to each other, causing DNA to coil more tightly
post-transcriptional factors and gene modification- modifying mRNA
pre-mRNA goes through splicing to remove introns, this needs to then be transported to ribosome for translation, protected by cap (modified nucleotide) to the front and tail of adenine added to back to protect and stabilise it= mature mRNA, this mRNA can then go through RNA editing- diffe3rent versions of the mRNA to create proteins with different functions
alternative splicing- a regulated process that results in a single gene coding for multiple proteins
what are introns and exons?
introns- DNA sequences that do not code for proteins, they are removed through gene splicing- even though they may not be useful to code for that protein, they are exons for other proteins
exons- DNA sequences that code for proteins
What is pre-mRNA?
contains both introns and exons- not ready for translation
RNA splicing will be used to remove introns
translational level of gene control
deciding whether we want translation to go ahead or not- do we want the protein to be made
how do we stop translation?
- degrade mRNA
- inhibitory proteins binding to mRNA- stops mRNA binding to ribosome
how do we start translation?
- activate initiation factors- allow mRNA to bind to ribosome, activation of these factors done through phosphorylation- add a phosphate group to proteins to activate them, controlled by protein kinases - activated my cAMP
post-translational control of gene expression
modifying the protein, can happen in golgi apparatus
- can add non-protein groups to it- glycoprotein, carbohydrate chain
- modify amino acids to form specific bonds- change amino acid to cysteine to form disulphide bridges
- change or affect protein fold- tertiary or quaternary structure
- modification by cAMP- cAMP binds to CRP, this complex can bind to RNA polymerase to upregulate its activity for transcription and translation of structural genes, or, cAMP activate kinesis which go on to phosphorylate and activate other enzymes and proteins
what are homeobox genes?
regulatory genes- genes that code for proteins involved in DNA replication
180 base pairs long
the code for the homeodomain- part of a regulatory protein
they control the development- positioning of body parts- the pax6 gene is a homeobox gene that codes for eye development. mutation may mean abnormal development
they are highly conserved in plants, animals, fungi- you will find the same types of homeobox genes in all 4 types of organism
they reg mitosis and apoptosis (programmed cell death- feutus webbed fingers break down before birth)
hox genes- homeobox genes only found in animals- 39 arranged in 4 clusters
