Bio 2.11 Gene regulation

How were all cells in the body produced?

By repeated mitosis from the original zygote. All somatic cells have the same DNA.

If all cells have the same DNA, why are they different?

Because of gene regulation different genes are turned on in different cell types.

What is gene regulation?

Mechanisms that turn some genes on and keep others off.

What is gene expression?

The process of going from DNA—→RNA—> protein.

What does genes being turned on/off mean?

On:Gene—>mRNA—>protein is being made

Off: the gene is transcribed into mRNA—> protein is not made

What does gene expression allow cells to do?

Make the right proteins at the right place and time so they can respond to the environment.

What is crucial for normal cell function?

Proper control over which genes are active at any moment.

Why does gene regulation matter?

Because cells do not use all their genes all the time. Turning genes on/off lets organisms grow, metabolize, and adapt to environment changes.

What does gene regulation allow?

Cell specialization neurons, red blood cells, muscle cells.

If blood cells and skin cells have the same DNA, why are they different?

They express different combinations of genes.

How do cells become different during development?

Each group of cells activates different genes as the embryo grows. Each cell type ends up with a unique pattern of gene activity.

Why must bacteria regulate their genes?

To save energy and resources only making proteins when needed. This gives them a survival advantage.

What allows bacteria to adjust to environmental changes?

Changing which genes are turned on/off-this is essential for metabolism

What is an operan?

A cluster of related genes+ their control sequences that are turned on/off together.

How does a bacterium know if lactose is present?

The lac operon:three lactose digesting genes grouped together controlled as one unit.

What does the promoter do?

Site where RNA polymerase binds to begin transcription.

What is the operator?

A DNA switch that turns transcription on or off depending on whether a repressor protein is bound.

How does the repressor work in the lac operon?

Repressor binds operator—> transcription OFF

-RNA polymerase can’t start making mRNA

What happens when lactose is present?

1) Lactose binds to the repressor

2) Repressor changes shape

3) Repressor can’t bind operator

4)Operator turns ON—>enzymes for lactose digestion are made

Why does the lac operon turn on all three genes at once?

Because bacteria need all lactose-digesting enzymes together-it”s efficient

What happens if the lac operator is mutated so the repressor can’t bind?

The operon is ALWAYS on

— the cell constantly makes lactose digesting enzymes

— this wastes energy when lactose isn’t present (disadvantage)

Why do eukaryotes need more complex gene regulation than bacteria?

Because eukaryotes (especially multicellular ones) have many specialized cell types,so they need elaborate control systems to decide which genes are active in each cell.

Why do prokaryotes need less regulation?

They’re single-called and don’t have specialized cells like neurons or red blood cells, so simpler gene control is enough.

Why does eukaryotic gene expression have many regulation points?

The path from gene—> protein is long,giving many opportunities to switch the process on/off, slow it, or speed it up.

How does DNA packing affect gene expression?

Tightly packed DNA blocks RNA polymerase-Gene is OFF

Loosely packed DNA=gene more accessible-ON

What long term way can cells use DNA packing?

To permanently inactivate certain genes.

What is X-chromosome inactivation?

In female mammals, one X chromosome in each cell becomes highly compacted and turned off early in development.

Why do female cells form patches expressing different alleles?

Because each embryonic cell randomly inactivated either the maternal or paternal X, and all it’s descendants keep that choice.

What is the most important control point in eukaryotic gene regulation?

Starting transcription (deciding whether RNA polymerase can begin)

What does RNA polymerase need to start transcription in eukaryotes?

Transcription factors (helper proteins)

What are transcription factors?

Proteins that help the RNA polymerase bind the promoter and start transcription.

What are enhancers?

Noncoding DNA sequences that transcription factors bind to in order to increase transcription.

What are silencers?

DNA sequences where repressor proteins bind to turn transcription OFF.

Which is more common in eukaryotes,activators or repressors?

Activators,because most eukaryotic genes stay OFF unless needed.

What do activators do?

Activators turn genes ON by helping RNA polymerase bind to the promoter and start transcription.

What do repressors do?

Repressors turn genes OFF by binding to DNA and blocking transcription.

What must happen before mRNA leaves the nucleus?

It must be processed into mature mRNA.

Three main steps of RNA processing?

1) Addition of cap and tail

2)Removal of introns

3) Splicing together exons

What are introns and exons?

Introns-Noncoding segments of RNA that are cute out and removed

Exons-the coding regions that remain and are spliced together

Alternative to RNA splicing?

The cell can splice the same RNA in different ways,producing different mRNAs (and different proteins) from the same gene.

Why is alternative splicing important?

Allows one gene to produce multiple polypeptides.

How does gene controlling mRNA lifetime regulate gene expression?

Longer-lasting mRNA=more protein made.

Shorter-lasting mRNA=less protein made

What are microRNAs?

A small single stranded RNA molecules that do NOT code for proteins but regulate gene expression.

How do microRNAs work?

They pair with complementary mRNA sequences,forming a complex that either destroys the mRNA or blocks its translation.

What is RNA interference?

Gene expression blocking caused by siRNAs binding to destroying mRNA.

Can translation be regulated?

Yes-cells can block or allow translation of specific mRNAs as another control point

What is protein activation?

Some proteins are made as inactive precursors and become a tube only after being cut or chemically modified

Example of a protein needing activation?

Insulin-made as a longer inactive polypeptide that must be chopped into pieces to become active.

How does protein breakdown regulate gene expression?

Cells selectively destroy proteins to control how long they remain active.

What is the final opportunity for regulating gene expression?

Post-translation control activating,modifying,or destroying proteins after they are made.

Why do multicellular organisms need cell-to cell communication?

To let different cells coordinate their activities and respond to environmental signals.

How can cells communicate with each other?

By producing and secreting signal molecules such as hormones.

What happens when a signal molecule reaches a target cell?

It binds to a receptor protein on the targets cell membrane.

What is a signal transduction pathway?

A series of molecular steps that converts an external signal into a specific internal response.

What does the final delay in protein do?

Activates a transcription factor.

What happens after transcription is triggered?

The mRNA is translated into a protein.

How can a signal molecule from one cell alter gene expression in a target cell without entering this cell?

By binding to a receptor protein on the target cell’s membrane and triggering a signal transduction pathway that activates transcription factors.

What are homeotic genes?

Master control genes that regulate groups of other genes, determining which body parts form in which locations.

Why are homeotic genes important?

They organize the body plan during embryonic development.

What controls homeotic gene activation during development?

Cell-to cell signaling using chemical signals that coordinate which genes turn on in each region of the embryo.

What happens if a homeotic gene is mutated?

Body parts may form in the wrong places.

What major discovery was made about homeotic genes across different species?

Similar homeotic genes exist in almost all eukaryotes examined -yeast,plants,worms, frogs chickens, mice, and humans.