DO NOW:Review: how can you distinguish

between pro/eukaryotes? Structurally? Environmentally? Both types of organisms seek efficiency, so genes often can be turned on and off.

What kinds of “switches” might control whether genes are on and off for each of these? Do you think they

are the same? What about the response? Explain your response.

GENE CONTROLProkaryotes vs. Eukaryotes

What kind of environment do bacteria live in? How do you think this impacts the way genes get regulated, if at all?

Quick response needed

Have enough?

New stimuli (food?) introduced

Utilize it fast!!!

STOP

QUICK REVIEW IN METABOLIC REGULATION

Allosteric inhibitors – provide feedback inhibition (enzyme regulators)

Product of pathwaysignals continuation ofpath to STOP

Making all these enzymes is wasteful

ALTERNATIVE METHOD…

Gene regulation

Block transcription of genes for ALL enzymes in a pathway,not just enzyme function

Energy efficient

MORE ON GENE REGULATION

Turning genes ON & OFF regulates amt of enzymes present in cell

Example: OFFEnough tryptophan present, bacteria turns

off genes coding for enzymes used to build it

Example: ONSugar lactose enters cell, genes coding for

enzymes to break sugar down turned on

THE OPERON MODEL Operon – group of genes with

related functions

Genes – code for specific proteins Promoter – RNA pol binding site

controls transcription of ALL genes in operon

Single mRNA produced

Operator – binding site of repressor protein (turns off gene)

These 3 make up an operon!

mRNA

enzyme1 enzyme2 enzyme3 enzyme4operator

promoter

EX: REPRESSIBLE OPERON: TRYPTOPHAN

DNATATA

RNApolymerase

tryptophan

repressorrepressor protein

repressortryptophan – repressor proteincomplex

Excess tryptophan present, binds to tryp repressor protein triggering repressor to bind to DNAblocks (represses) transcriptiontend to be anabolic pathways

gene1 gene2 gene3 gene4

conformational change in repressor protein!

1 2 3 4

repressortrpRNApolymerase

trp

trp

trp trp

trp trp

trptrp

trptrp

trp

mRNA

enzyme1 enzyme2 enzyme3 enzyme4operator

promoter

EX: INDUCIBLE OPERON: LACTOSE

DNATATARNApolymerase

repressorrepressor protein

repressorlactose – repressor proteincomplex

lactose

lacrepressor gene1 gene2 gene3 gene4

Lactose present, binds to lac repressor protein & triggers repressor to release DNA

induces transcriptioncatabolic pathways

RNApolymerase

1 2 3 4

lac lac

laclac

laclac

lac

conformational change in repressor protein!

lac

lac

What about Eukaryotes? How are they different? What might the

process have to accommodate for? How might it do this? Eukaryotes often multicellular

Must maintain homeostasis

Coordinate body as a whole Differentiated & specialized cells

Battle changing environment

WHEN DOES GENE CONTROL OCCUR???

1. Packing/unpacking DNA

2. Transcription3. mRNA processing4. Translation5. Protein processing6. Protein degradation

1. DNA PACKINGIf all 46 of your chromosomes were lined up in a

row, your DNA would be over 3 feet long. How can your cells contain this large amount of material when cells are microscopic?

Coils & FoldsDouble helixNucleosomesChromatin fiberLooped domainsChromosomes

from DNA double helix to condensed chromosome

A LITTLE MORE ABOUT NUCLEOSOMES…“Beads on a string”

1st level of DNA packinghistone proteins

8 protein moleculespositively charged amino acids bind tightly to negatively charged DNA

Degree of packing regulates transcriptionTightly packed = no transcription =

genes OFFHeterochromatin – “dark” DNA = tightEuchromatin – “light” DNA = loose

Methylation of DNA (adding -CH3’s) blocks transcription factors no transcription genes OFF!

Acetylation of histones (adding –COCH3’s) unwinds DNA coils loosen transcription genes ON!

2. TRANSCRIPTION INITIATIONControl regions on DNA

Promoter nearby control sequence – “standard” rate

bind RNA pol bind transcription factors

Enhancer distant control sequence – “enhanced” rate

bind activator proteins

TRANSCRIPTION COMPLEX…

ActivatorActivator

Activator

CoactivatorRNA polymerase II

AB F E

HTFIID

Core promoterand initiation

complex

Activator Proteins• regulatory proteins bind to DNA at distant enhancer sites

• increase the rate of transcription

Coding regionT A T A

Enhancer Sitesregulatory sites on DNA distant from gene

Initiation Complex at Promoter binding site of RNA pol

3. POST-TRANSCRIPTIONAL CONTROLAlternate splicing pattern

↑ variation in protein family

4. REGULATION OF MRNA DEGRADATION

Lifespan of mRNA controls amt of protein synthesizedReview: which component on mRNA

determines lifespan?mRNA can last from hrs to weeks!

WHAT IF DEGRADATION IS INTERFERED WITH???

Small interfering RNAs (siRNA)short segments of RNA (21-

28 bases)bind to mRNAcreate sections of double-stranded mRNA

“death” tag for mRNAtriggers degradation

gene “silencing”post-transcriptional controlturns off gene = no protein

ACTION OF SIRNA

siRNAdouble-stranded miRNA + siRNA

mRNA degradedfunctionally turns gene off

mRNA for translation

breakdown

enzyme(RISC)

dicerenzyme

5. CONTROL OF TRANSLATIONBlock initiation of translation

Regulatory proteins attach to 5’ endPrevent attachment of ribosome & initiator tRNA

Synthesis turned OFF

6/7. PROTEIN PROCESSING & DEGRADATION

Protein processingFolding, cleaving, adding sugar

groups, targeting for transportProtein degradation

Ubiquitin – (76 aa’s) “death tag”Proteasome – degradation

machinery

WHAT DARWIN NEVER KNEW… Video – 39:57