19.2 Control Of Gene Expression Flashcards
Housekeeping genes
Genes that code for enzymes that are constantly required
Tissue specific genes
Code for protein based hormones that are only required by certain cells at certain times
Types of regulatory mechanisms
Transcriptional level
Post transcriptional level
Translational level
Post translational level
Transcriptional level
Genes can be turned on and off
Post transcriptional
mRNA can be modified, regulates translation and types of proteins produced
Translational
Translation can be stopped or started
Post translational
Proteins can be modified after synthesis, changes functions
Chromatin remodelling
Heterochromatin - tightly wound DNA
Euchromatin - loosely wound DNA
Transcription is not possible when DNA is tightly wound because RNA polymerase cannot access the genes
Histone modification
Histones can be modified to increase or decrease the degree of packing
Acetylation reduces positive charge on histones - DNA coils less tightly
Methylation makes histones more positive, so DNA coils more tightly
Operon
Group of genes under control of same regulatory mechanism and are expressed at the same time
Lac operon
Group of 3 genes - LacZ, LacY, LacA involved in metabolism of lactose
What enzymes does the lac operon code for?
β galactosidase
Lactose permease
Transacetylase
LacI
Regulatory gene
Codes for repressor protein
What does lac operon do in absence of lactose?
Regulatory gene produces repressor protein constantly
Repressor protein binds to operator
Prevents RNA polymerase binding to DNA and starting transcription
Promoter
Section of DNA that is the binding site for RNA polymerase
