19.2 Control Of Gene Expression Flashcards
What are housekeeping genes
They are constantly expressed as they code for enzymes necessary for reactions present in metabolic pathways
What are protein based hormones required for
Only required by certain cells at certain times to carry out a short lived response
Coded for by tissue specific genes
Where is the entire genome of an organism present and what does it include
Present in any of its cells that has a nucleus this includes genes that do not need to be expressed by all cells. Genes can be turned on and off
There are a number of different ways in which genes are regulated categorised by the level at which they operate:
Transcriptional - genes 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 is chromatin
Uncondensed DNA in a complex with histones
What are the two types of chromatin
Heterochromotin
Euchromotic
What is Heterochromatin
Is tightly wound DNA causing chromosomes to be visible during cell diversion
Transcription is not possible because RNA polymerase cannot access genes
What is euchromatin
Loosely wound DNA present during interphase . Genes can be freely transcribed allowing protein synthesis to occur
Why does DNA coil around histones
Because they are positively charged and DNA is negatively charged
Histones can be modified to increase or decrease the degree of packing
What does the addiction of acetyl group or phosphate group do to the histones
Reduces the positive charge of histones causing the DNA to coil less tightly allowing certain genes to be transcribed
What does the addition of methyl group do to the histones
Makes the histones more hydrophobic so they bind more tightly to the dna preventing transcription of genes
What does epigenetics mean
Is a term that is increasingly used to describe this control of gene expression by the modification of DNA. It is sometimes used to include all the different ways in which gene expression regulated
What is an Operon
An operon is a group of genes that are under control of the same regulatory mechanism and are expressed at the same time
What are operons more common in
More common in prokaryotes than eukaryotes because of the smaller simpler structure of their genomes
What does regulatory genes in lac operon do
Its located near to the operon and codes for repressor protein that prevents the transcription of the structural genes in the absence of lactose
What is a lac operon
Is a group of three genes involved in the metabolism of lactose
What are the genes making up lac operon
They are structural genes a they code for three enzymes and are transcribed onto a single long molecule of mRNA
What is the role of the operator of the lac operon do
It’s where the repressor protein binds in the absence of lactose
What is down regulation
The binding of the protein in lac operon prevents rna polymerase binding to dna and beginning transcription
What is the role of promoter of the lac operon
Section of dna that is the binding site for rna polymerase to begin transcription
The lac operon when lactose is present
It binds to the repressor protein changing its shape so that it can no longer bind to the operator region
As a result
RNA polymerase cn then bind to the promoter and transcribe the three structural gene and enzymes are synthesised
After the binding of rna polymerase how else can the rate of transcription be increased for the required quantity of enzymes to emotionalise lactose efficiently
Achieved by the binding of another protein (cAMP receptor protein) that i only possible when CRP is bound to cAMP
What happens when cAMP bound to CRP
It leads to an increase in transcription of the lac operon structural genes
The transport of glucose into cells reduced]s campy levels so if both glucose and lactose are present glucose will be metabolised
Post transcription - mRNA processing
Splicing occurs where rna is cut at specific points
- the introns (non coding dna) are removed and the exons 9coding dna)are joined together
Post transcription - mRNA editing
Nucleotide sequence of mRNA is edited by admin, deleting or substituting nucleotides
Results in the synthesis of different proteins that can be produced from a single mRNA molecule or gene
Translational control
What mechanisms regulate the process of protein synthesis
- Degradation of mRNA - more resistant the molecule the longer it will last in cytoplasm
- Binding of inhibitory proteins to mRNA prevents binding to ribosomes and synthesis of protein
- activation of initiation factors aid binding of mRNA to ribosomes and synthesis
Post translational control involves modifications to the protein that have been synthesised this includes:
- addiction of non protein groups
- modifying amino acids and formation of bonds
- folding or shortening of rote is
- modification by cAMP
