Chapter 8 Manipulating Proteins, DNA, and RNA Manipulating Proteins, DNA, and RNA.
Definitions Gene – sequence of DNA that is expressed as a protein (exon) Genes are coded –DNA...
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Transcript of Definitions Gene – sequence of DNA that is expressed as a protein (exon) Genes are coded –DNA...
Definitions
• Gene – sequence of DNA that is expressed as a protein (exon)
• Genes are coded– DNA →RNA→Protein→Trait
• Transcription – rewritting DNA into RNA which is needed for a gene to be expressed as a protein
• Operon – a sequence of DNA that will turn transcription on and off
Parts of an Operon• Regulatory gene
– Repressor
• Promoter
Operator
Structural Genes
Parts of an Operon
• Promoter – site where RNA polymerase attaches to begin transcription
• Operator – on/off switch– Repressor will attach turning off transcription– If repressor doesn’t fit into operator, RNA
polymerase can transcribe structural genes– Transcription occurs
Operator/Repressor
• Lock n’ Key arrangement
Inducible Operon
• Transcription is normally off
• Repressor is active – Fits into operator turning off transcription
• Inducer– Molecule from the environment – Attaches to the repressor – Changes the shape of the repressor making it
inactive.
• Inducible Operon– Repressor is active
• RNA polymerase can not attach to promoter
• No proteins are translated (synthesized)
• Inducer needs to be present to start transcription
• i.e. inducer is lactose
Transcription is on• The end proteins
produced are enzymes
• i.e. lactase
• Operon is off– Repressor is
active– Transcription
does not occur
• Operon is on– Inactive
repressor– Proteins
(enzymes) are made
Regulatory Gene makes an active repressor
Inducible Animation Lac Operon
• Transcription is normally off
• Repressor is active (fits into operator)
• Need an outside molecule from environment to inactivate repressor
• Inducer has the role of inactivating repressor
• Proteins produced through transcription are enzymes.
• Enzymes break down inducer.
• Inducer is absent which makes repressor active again.
Repressible Operon
• Transcription is normally on
• Repressor is inactive– Repressor does not fit into the operator
• CoRepressor is needed to stop transcription– COREPRESSOR is the end protein produced
by transcription– Structural protein used by the cell
End product = corepressor
Tryptophan is the corepressor
Repressible Operon AnimationTrpytophan Operon
• Inactive repressor
• The build up of the end product turns off transcription
• Usually makes structural proteins– Proteins needed for cell function
• When structural proteins are used up by the cell; the corepressor is absent
• Transcription will turn on again.