19.2Control Of Gene Expression Flashcards
What is transcriptional control
The idea that genes can be turned on or off
What is heterochromatin
Tightly wound DNA causing chromosomes to be visible during cell division
Transcription of genes isn’t possible
What is euchromatin
Loosely wound dna present during interphase
Transcription of genes is possible
What is chromatin remodelling
Protein synthesis occurs during interphase between cell divisions which ensures the proteins necessary for cell division are synthesised in time
It happens to the genes in euchromatin
Why does dna coil around histones
Because histones are positively charged and dna is negative
What is histone modification
When histones are modified to increase or decrease the degree of packing
What will reduce the positive charge of histones
And what does this do
Addition of acetyl groups (acetylation) or phosphate groups (phosphorylation)
It causes dna to coil less tightly allow certain genes to be transcribed
What makes histones more hydrophobic
Addition of methyl groups (methylation)
This makes them bind more tightly to each other causing dna to coil more tightly and prevent transcription
What is Epigenetics
Used to describe the control of gene expression by the modification of dna
Histone modification
What is an operon
Group of genes that are under the control of the same regulatory mechanism and are expressed at the same time
What is the lac operon
A group of 3 genes LacZ LacY LacA They are structural genes as they code for 3 enzymes and they are transcribed onto a single long molecule of mRNA
How is the transcription of the structural genes in the lac operon prevented
A regulatory gene lacI is located near to the operon and codes for a repressor preteen that prevents the transcription in the absence of lactose
Where does the repressor bind in the lac operon and what does it do
The operator
It prevents RNA polymerase binding to DNA and beginning transcription
What is the promoter
Section of dna that is the binding site for rna polymerase
What happens when lactose is present in lac operon
What is this process called
Lactose binds to repressor protein causing it to change shape so it can no longer bind to operator
This means the rna can now bind to promoter and the 3 structural genes are transcribed and enzymes are synthesised
What is the role of cyclic AMP
A protein that binds with rna polymerase to the operator that increase the rate of transcription to produce the required quantity of enzymes
What processes occur in post-transcriptional control
Rna processing
Rna editing
What is rna processing
When the product of transcription (pre - mRNA) is modified forming mature mRNA
How is mRNA modified into mature mRBA
Cap is added to 5’ end and a tail is added to 3’ end - these stabilise mRNA and delay degradation in the cytoplasm
Splicing occurs
What is splicing
Rna is cut at specific points
The introns are removed and the Exxon’s are joined together
What is rna editing
Nucleotide sequence of some mRNA molecules are changed through base addition, deletion or substitution
What are the 3 mechanisms that regulate the process of protein synthesis in translational control
Degradation of mRNA
Binding of inhibitory proteins to mRNA
activation of initiation factors that aid the binding of mRNA
What is teh degradation of mRNA
The more resistant the molecule the longer it will last in the cytoplasm and a greater quantity of protein is synthesised
What does the binding of inhibitory proteins to mRNA do
Prevents it binding to ribosomes and the synthesis of Proteins
What does the activation of initiation factors in translational control do
They aid the binding of mRNA to ribosomes
What are Protein kinases
Enzymes that catalyse the addition of phosphate groups to proteins
This changes the tertiary structure and the function of a protein
They are important regulators of cell activity
What happens in post translational control
Addition Of non-protein groups such as carbohydrate Chains
Modify amino acids and the formation bonds like disulphides bridges
Folding or shortening proteins
Modification by cAMP
