what are housekeeping genes
genes that code for proteins that are constantly required such as enzymes
what are tissue specific genes
genes that code for proteins that are only required by certain cells at certain times to carry out a short lived response such as peptide hormones
when can genes be turned on or off
depends on when they are needed
why is it important that genes are only expressed when products are needed
it prevents vital resources being wasted
why is gene regulation required for multicellular organisms
so they can respond to changes in their internal and external environment and so their cells can specialise and work in a coordinated way
what are 4 stages of gene regulation
- transcriptional = genes can be turned on or off
- post-transcriptional = mRNA can be modified which regulates translation and the types of proteins produced
- translational = can be stopped/started
- post-translational = proteins can be modified after synthesis which changes their function
what is DNA wound around that makes it packed inside the nucleus (since its too long)
histone proteins
what is DNA/histone complex called
chromatin
what is heterochromatin
tightly wound DNA causes chromsomes to be visible during cell division
what is euchromatin
loosely wound DNA present during interphase.
why is transcription of genes not possible when DNA is tightly wound
RNA polymerase cant access the gene
why can the genes in euchromatin be transcribed
RNA polymerase can access the gene
why does protein synthesis not occur during cell division but occur during interphase
- ensures proteins necessary for cell division are synthesised in time.
- prevents complex and energy consuming protein synthesis from occuring when cells are actually dividing
how does DNA coil around histones
histones are positively charged and DNA is negatively charged due to their phosphate groups
how can histones be modified
to increase/decrease degree of packing
what does acetylation and phosphorylation do
it reduces the positive charge on the histones making them more negative - DNA coils less tightly allowing certain genes to be transcribed
heterochromatin
–>euchromatin
what does methylation do
mkaes the histone proteins hydrophobic so they bind more tightly to eachother causing DNA to coil more tightly preventing transcription of genes
euchromatin –> heterochromatin
what is epigenetics
controlling gene expression by modifying DNA
what are transcription factors
proteins or non coding RNA that act in the nucleus to control which genes in a cell are turned on or off. they slide along part of a DNA molecule and bind to their specific promoter regions. they aid/inhibit attachment of RNA polymerase to DNA and activate or suppress transcription of the gene
what is the difference between structural and regulatory genes
structural genes encode protein or RNA that build cell structures or act as functional enzymes.
regulatory genes encode proteins that control the expression of other genes
what is an operon
a group of genes that are under the control of the same regulatory mechanism and are expressed at the same time.
why is an operon common in prokaryotes
due to its smaller and simpler genome
why is an operon an efficient way of saving resources
if certain gene products arent needed then all of the genes involved in their production can be switched off
what is the preffered substrate of E.coli and what can be used instead if its in short supply
glucose. if in short supply lactose is used instead
