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Control over GenesControl over Genes
Chapter 15Chapter 15
Skin CancerSkin Cancer
Basal Cell CarcinomaBasal Cell Carcinoma
Squamous Cell CarcinomaSquamous Cell Carcinoma
Malignant MelanomaMalignant Melanoma
Changes in DNA Changes in DNA Trigger CancerTrigger Cancer
Ultraviolet Ultraviolet
radiation can radiation can
cause breakscause breaks
In-text figurePage 238
Gene ControlGene Control
Which genes are expressed in a Which genes are expressed in a cell depends upon:cell depends upon:
• • Type of cellType of cell
• • Internal chemical Internal chemical conditionsconditions
• • External signalsExternal signals
• • Built-in control systemsBuilt-in control systems
Mechanisms of Gene ControlMechanisms of Gene Control
Controls related to transcriptionControls related to transcription
Transcript-processing controlsTranscript-processing controls
Controls over translationControls over translation
Post-translation controlsPost-translation controls
Regulatory ProteinsRegulatory Proteins
Can exert control over gene Can exert control over gene
expression through interactions with:expression through interactions with:
–DNADNA
–RNARNA
–New polypeptide chainsNew polypeptide chains
–Final proteinsFinal proteins
Control MechanismsControl Mechanisms
Negative controlNegative control– Regulatory proteins slow Regulatory proteins slow
down or curtail gene activity down or curtail gene activity
Positive controlPositive control
– Regulatory proteins promote Regulatory proteins promote
or enhance gene activitiesor enhance gene activities
Chemical ModificationsChemical Modifications
Methylation of Methylation of DNA can DNA can inactivate genesinactivate genes
Acetylation of Acetylation of histones allows histones allows DNA unpacking DNA unpacking and transcriptionand transcription
Figure 15.2Figure 15.2Page 240Page 240
Gene Control in ProkaryotesGene Control in Prokaryotes
No nucleus separates DNA No nucleus separates DNA
from ribosomes in cytoplasmfrom ribosomes in cytoplasm
When nutrient supply is high, When nutrient supply is high,
transcription is fasttranscription is fast
Translation occurs even before Translation occurs even before
mRNA transcripts are finishedmRNA transcripts are finished
The Lactose OperonThe Lactose Operon
gene 1 gene 2 gene 3
lactose operon
regulatory gene
transcription,translation
operator
operator
promoter
repressor protein
Figure 15.3aFigure 15.3aPage 241Page 241
Low LactoseLow Lactose
Repressor binds to Repressor binds to
operatoroperator
Binding blocks promoterBinding blocks promoter
Transcription is blockedTranscription is blocked
Figure 15.3bFigure 15.3bPage 241Page 241
High LactoseHigh Lactose
gene 1operator operatorpromoter
mRNA RNA polymerase
lactose
allolactose
Figure 15.3cFigure 15.3cPage 241Page 241
Lac-Operon AnalogyLac-Operon AnalogyLike an elephant that likes to sit on a Like an elephant that likes to sit on a railroad track blocking the train.railroad track blocking the train.The only thing that the elephant likes The only thing that the elephant likes better than to sit on his spot on the track better than to sit on his spot on the track is peanuts.is peanuts.If peanuts are available, the elephant If peanuts are available, the elephant leaves the track and eats the peanuts. leaves the track and eats the peanuts. While he is gone the train can proceed While he is gone the train can proceed down the track until the elephant goes down the track until the elephant goes back to sit on the track after eating all the back to sit on the track after eating all the peanuts.peanuts.
Controls in Eukaryotic CellsControls in Eukaryotic Cells
Control of transcriptionControl of transcription
Transcript processing controlsTranscript processing controls
Controls over translationControls over translation
Controls following translationControls following translation
Most Genes Are Turned OffMost Genes Are Turned Off
Cells of a multicelled organism Cells of a multicelled organism rarely use more than 5-10 percent rarely use more than 5-10 percent of their genes at any given timeof their genes at any given time
The remaining genes are The remaining genes are selectively expressedselectively expressed
Homeotic GenesHomeotic Genes
Occur in all eukaryotesOccur in all eukaryotes
Master genes that control Master genes that control development of body partsdevelopment of body parts
Encode homeodomains (regulatory Encode homeodomains (regulatory proteins)proteins)
Homeobox sequence can bind to Homeobox sequence can bind to promoters and enhancerspromoters and enhancers
X Chromosome X Chromosome InactivationInactivation
One X inactivated in One X inactivated in
each cell of femaleeach cell of female
Creates a “mosaic” Creates a “mosaic”
for X chromosomesfor X chromosomes
Governed by Governed by XISTXIST
gene gene
Figure 15.6Figure 15.6Page 245Page 245
HormonesHormones
Signaling moleculesSignaling molecules
Stimulate or inhibit activity in target Stimulate or inhibit activity in target cellscells
Mechanism of action variesMechanism of action varies
– May bind to cell surfaceMay bind to cell surface
– May enter cell and bind to regulatory May enter cell and bind to regulatory proteinsproteins
– May bind with enhancers in DNAMay bind with enhancers in DNA
Vertebrate HormonesVertebrate Hormones
Some have widespread effectsSome have widespread effects
– Somatotropin (growth Somatotropin (growth
hormone)hormone)
Others signal only certain cells Others signal only certain cells
at certain timesat certain times
– Prolactin stimulates milk Prolactin stimulates milk
production production
PhytochromePhytochrome
Signaling molecule in plantsSignaling molecule in plants
Activated by red wavelengths, Activated by red wavelengths, inactivated by far-red wavelengthsinactivated by far-red wavelengths
Changes in phytochrome activity Changes in phytochrome activity influence transcription of certain influence transcription of certain genesgenes
Controlling the Cell CycleControlling the Cell Cycle
Cycle has built-in checkpointsCycle has built-in checkpoints
Proteins monitor chromosome Proteins monitor chromosome structure, whether conditions favor structure, whether conditions favor division, etc.division, etc.
Proteins are products of checkpoint Proteins are products of checkpoint genesgenes
KinasesKinases
Growth factors Growth factors
OncogenesOncogenes
Have potential to induce cancerHave potential to induce cancer
Mutated forms of normal genesMutated forms of normal genes
Can form following insertions of Can form following insertions of
viral DNA into DNA or after viral DNA into DNA or after
carcinogens change the DNAcarcinogens change the DNA
Cancer CharacteristicsCancer Characteristics
Plasma membrane and Plasma membrane and
cytoplasm alteredcytoplasm altered
Cells grow and divide abnormallyCells grow and divide abnormally
Weakened capacity for adhesionWeakened capacity for adhesion
Lethal unless eradicatedLethal unless eradicated
ApoptosisApoptosis
Programmed cell deathProgrammed cell death
Signals unleash molecular weapons Signals unleash molecular weapons
of self-destructionof self-destruction
Cancer cells do not commit suicide Cancer cells do not commit suicide
on cue on cue