3.4.3 - Cell Differentiation Flashcards
How Can Stem Cells Become Specialised?
Through differential gene expression, where only certain genes in the DNA of a the stem cell are activated and get expressed.
Describe The Steps Of Differentiation
(6 Points)
~ Some genes are activated, some aren’t.
~ mRNA is transcribed from the active genes.
~ mRNA is then translated to form proteins.
~ These proteins modify the cell, determining the cell structure and control cell processes.
~ As these proteins continue to modify the cell, the cell gets increasingly specialised.
~ These changes are irreversible.
What Controls Gene Expression?
Transcription factors.
What Are Transcription Factors?
Proteins that bind to DNA and activate or deactivate genes by increasing or decreasing the rate of transcription.
What Are Activators?
(2 Points)
~ Transcription factors.
~ Increase the rate of transcription, by helping RNA polymerase bind to the DNA and begin transcription.
What Are Repressors?
(3 Points)
~ Transcription factors.
~ Decrease the rate of transcription, by preventing RNA polymerase from binding.
~ They stop transcription.
What Do Transcription Factors Bind To If It Is A Eukaryotic Cell?
Promotor region of a gene.
What Do Transcription Factors Bind To If It Is A Prokaryotic Cell?
Operons.
What Is An Operon?
Section of DNA.
The Operon Is A Section Of DNA, What Does This Contain?
(3 Points)
~ Cluster of structural genes that are transcribed together.
~ Control elements, including a promotor region and an operator region.
~ Sometimes regulatory genes, coding for activators and repressors.
Describe The Lac Operon
(4 Points)
~ Found in some bacteria, like E. coli.
~ Controls the production of the enzyme lactase.
~ Has 3 structural genes -> lacZ, lacY and lacA, produce proteins which help the bacteria digest lactose.
~ Regulatory gene lacl coding for the lac repressor protein.
What Does Lactase Do?
(2 Points)
~ Breaks down the substrate lactose so that it can be used as an energy source in the bacterial cell.
~ Helps bacteria avoid wasting energy and materials.
Describe What Happens When Lactose Is Not Present
(5 Points)
~ Regulatory gene is transcribed and translated to produce lac repressor protein.
~ The lac repressor binds to the operator region.
~ Due to the presence of the lac repressor, RNA polymerase cannot bind to the promoter region.
~ No transcription takes place.
~ No lactase enzyme is synthesised.
Describe What Happens When Lactose Is Present
(4 Points)
~ Lactose binds to the repressor, changing its shape so that it can no longer bind to the operator site.
~ RNA polymerase is able to bind to the promotor region and transcription of the structural genes can take place.
~ mRNA from all 3 structural genes is translated.
~ Enzyme lactase is produced to break down lactose and use it for energy.
