Unit 4 - Ch 14 - Gene Regulation Flashcards
Types of Genes (3)
Constitutive
Inducible
Repressible
Constitutive genes
genes that are always “on” (being transcribed and translated)
- producing proteins needed for basic life functions => enzymes in glycolysis
- however, not all expressed at the same rate
Inducible genes
genes that are normally “off” (not being transcribed or translated)
- may be turned on, usually by a chemical signal
- usually for catabolic functions
Repressible Genes
genes that are normally “on”
- may be turned off to save cellular energy, usually by a chemical signal
- usually associated with anabolic activity
Operon
Gene complex in prokaryotes consisting of a group of structural genes with related functions plus the closely linked DNA sequences responsible for controlling them.
Lac Operon components (in order)
An inducible operon
Components
- Repressor Gene – produces repressor protein; always “on”
- Promoter – RNA polymerase binds to the DNA; start transcription
- Operator – structural gene swithch
- Structural Gene –series of genes in a metabolic pathway
Control of Lac Operon when lactose is present
lactose binds to the repressor protein and inactivates it so it does not bind to the operator and structural genes are transcribed and translated
Control of Lac Operon when lactose is absent
repressor binds to the operator and blocks RNA polymerase
- no transcription or translation of structural genes occurs
Trp Operon
A repressible operon
- synthesizes tryptophan in prokaryotes
Trp Operon components (in order)
- Repressor Gene – produces repressor protein (constitutive)
- Promoter – RNA polymerase binds, transcription start
- Operator – repressor binds here
- Structural Gene – genes needed to synthesize tryptophan
Control of Trp Operon with Tryptophan present
repressor protein is activated; binds to operator
- blocks transcription
Control of Trp Operon with Tryptophan absent
repressor protein cannot bind to operator
- RNA polymerase transcribes the structural genes
In Eukaryotes gene regulation occurs where?
Nucleus
Cytoplasm
Two major types of nuclear gene regulation
Transcriptional Control
Posttranscriptional Control
Transcriptional Control. Involves (4)
producing mRNA in the nucleus of eukaryotes. Involves:
a. Chromosome organization
b. DNA methylation
c. Multiple gene copies – more RNA is produced
d. UPEs/Enhancers
Posttranscriptional Control. Involves (2)
mRNA has been formed, is still in the nucleus. Involves:
a. mRNA processing
– introns and exons are initially transcribed - introns are removed - exons are retained in mature transcript
b. mRNA transport – rate is controlled via nuclear pores
Two major types of Cytoplasmic gene regulation
Translational Control
Posttranslational Control
Translational Control
Determines how long / often mRNA is translated.
Often influenced by chemical signals in the cytoplasm.
Posttranslational Control. Involves (2)
A protein has been produced. Involves:
a. Polypeptide Modification – often involves phosphorylation of a protein to activate it’s activity (consumes ATP)
b. Polypeptide Degredation – Selective degradation targets specific proteins for destruction by proteasomes - terminal amino group AA often impacts protein longevity
Chromosome organization as part of Transcriptional Control
Euchromatin is transcribed while Heterochromatin is not.
heterochromatin: appears dense in micrographs
euchromatin: appears spread out
DNA methylation
– of cytosine nucleotides
- methylated DNA is inaccessible to transcription
- inactivates the DNA - basis for barr body inactivation
UPE’s / Enhancers
Upstream Promoter Elements
DNA sequences that enhance the amount of mRNA produced
