The control of gene expression
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The Control of Gene Expression. Chapter 11. Cloning. Researchers clone animals by nuclear transplantation A nucleus of an egg cell is replaced with the nucleus of a somatic cell from an adult In reproductive cloning, the embryo is implanted in a surrogate mother

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The Control of Gene Expression

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The control of gene expression

The Control of Gene Expression

Chapter 11


Cloning

Cloning

  • Researchers clone animals by nuclear transplantation

    • A nucleus of an egg cell is replaced with the nucleus of a somatic cell from an adult

  • In reproductive cloning, the embryo is implanted in a surrogate mother

  • In therapeutic cloning, the idea is to produce a source of embryonic stem cells

    • Stem cells can help patients with damaged tissues


Cloning1

Donorcell

Nucleus fromdonor cell

Implant blastocystin surrogate mother

Clone of donoris born(REPRODUCTIVEcloning)

Removenucleusfrom eggcell

Add somaticcell fromadult donor

Grow in culture to producean early embryo (blastocyst)

Remove embryonic stem cells from blastocyst andgrow in culture

Induce stemcells to formspecialized cellsfor THERAPEUTICuse

Cloning


Gene regulation

Gene Regulation

  • The process by which genetic information flows from genes to proteins is called gene expression

  • A gene is turned ‘on’ is being transcribed into specific protein molecules, a gene that is turned ‘off’ is not actively being transcribed

  • The turning off and on of transcription is the main way in which gene expression is regulated


Gene expression

Gene Expression

  • E. coli was first first studied because it does not require intercellular gene expression

  • Found that the bacterium changes its gene expression according to its environment

  • Gene expression is controlled by several parts

    • Promoter-before the gene, where the RNA polymerase attaches and starts transcription

    • Operator- between the promoter and the gene, determines whether the RNA polymerase can attach


Gene expression1

Gene Expression

  • Regulatory Gene- turns off transcription by turning off and on the operator

  • Genes for related enzymes are often controlled together by being grouped into regulatory units called operons

  • Regulatory proteins bind to control sequences in the DNA and turn operons on or off in response to environmental changes


Gene expression2

OPERON

Regulatorygene

Promoter

Operator

Lactose-utilization genes

DNA

mRNA

RNA polymerasecannot attach topromoter

Activerepressor

Protein

OPERON TURNED OFF (lactose absent)

DNA

RNA polymerasebound to promoter

mRNA

Protein

Inactiverepressor

Lactose

Enzymes for lactose utilization

OPERON TURNED ON (lactose inactivates repressor)

Gene Expression


Gene expression in eukaryotes

Gene Expression in Eukaryotes

  • Cell differentiation results from selective gene expression

  • Different types of cells make different kinds of proteins

  • Different combinations of genes are active in each type


Gene expression in eukaryotes1

Gene Expression in Eukaryotes


Cell differentiation

Root ofcarrot plant

Plantlet

Cell divisionin culture

Single cell

Adult plant

Root cells cultured in nutrient medium

Cell Differentiation

  • Most differentiated cells retain a complete set of genes

    • In general, all somatic cells of a multi-cellular organism have the same genes


Cloning2

Cloning

  • Common in plants

    • Manufactured like in the carrot cells

    • Natural like in cuttings or in runners in bamboo

  • The first mammalian clone, a sheep named Dolly, was produced in 1997

    • Dolly provided further evidence for the developmental potential of cell nuclei


Applications of cloning

Applications of Cloning

  • Piglet clones might someday provide a source of organs for human transplant

  • Adult stem cells can also give rise to differentiated cells

    • Harder to culture than embryonic stem cells

    • Give rise to only a limited range of cell types, in contrast with embryonic stem cells


Applications of cloning1

Liver cells

Culturedembryonicstem cells

Nerve cells

Heart muscle cells

Different cultureconditions

Different types ofdifferentiated cells

Applications of Cloning


Gene regulation in eukaryotes

DNAdoublehelix(2-nmdiameter)

Histones

“Beads ona string”

Nucleosome(10-nm diameter)

Tight helical fiber(30-nm diameter)

Supercoil(200-nm diameter)

700nm

Metaphase chromosome

Gene Regulation in Eukaryotes

  • A chromosome contains a DNA double helix wound around clusters of histone proteins

  • DNA/ histone (8) complex is called nucleosome

  • DNA further ‘supercoils’

  • DNA packing tends to block gene expression


Chromosome inactivation

Chromosome Inactivation

  • In females, one X chromosome per somatic cell is inactivated early in embryonic development

    • So coiled it cannot be read

  • The inactivation is inherited by its decedents

  • A female that is heterozygous for genes on the X chromosome has cells that express different alleles

    • Calico cat


Regulation of eukaryotic transcription

Regulation of Eukaryotic Transcription

  • Regulate by making DNA more or less available for transcription

  • Regulatory proteins

    • Have more than prokaryotic organisms

  • Each gene has its own promoter and other control sequences

  • Transcription factors facilitate correct attachment of RNA polymerases

    • Enhancers and silencers bind to DNA

  • Coordinated effort to transcribe RNA


Regulation of eukaryotic transcription1

Enhancers

Promoter

Gene

DNA

Activatorproteins

Transcriptionfactors

Otherproteins

RNA polymerase

Bendingof DNA

Transcription

Regulation of Eukaryotic Transcription


Rna splicing

Exons

DNA

RNAtranscript

RNA splicing

or

mRNA

RNA Splicing

  • Once RNA is transcribed, the introns are spliced out

  • With-holding splicing or the way an RNA is spliced may be a way for regulating gene expression

  • Can get more than one polypeptide from one gene


Regulation during translation

Regulation During Translation

  • Breakdown of mRNA

    • Enzymes in the cytoplasm break mRNA down quickly

  • Initiation of Translation

    • There are many proteins involved in the start of photosynthesis

  • Protein Activation

    • After translation polypeptides may need alteration to become functional (folding etc.)

  • Protein Breakdown

    • Selective breakdown of proteins after translation


Gene regulation1

Chromosome

DNA unpackingOther changes to DNA

GENE

TRANSCRIPTION

GENE

Exon

RNA transcript

Intron

Addition of cap and tail

Splicing

Tail

Cap

mRNA in nucleus

NUCLEUS

Flowthroughnuclear envelope

mRNA in cytoplasm

CYTOPLASM

Breakdown of mRNA

Translation

Broken-down mRNA

Polypeptide

Cleavage/modification/activation

ACTIVE PROTEIN

Breakdownof protein

Broken-down protein

Gene Regulation

  • Each stage of eukaryotic expression offers an opportunity for regulation

    • The process can be turned on or off, speeded up, or slowed down

  • The most important control point is usually the start of transcription


Genetic control of embryonic development

Eye

Antenna

Head of a normal fruit fly

Leg

Head of a developmental mutant

Genetic Control of Embryonic Development

  • Experiments in the embryonic development of fruit flies have shown the relationship between gene expression and development

  • A cascade of gene expression involves genes for regulatory proteins that affect other genes

    • It determines how an animal develops from a fertilized egg

    • Problems with gene expression can lead to mutations


Head tail polarity in the fruit fly

FERTILIZATION AND MITOSIS

ZYGOTE

EGG CELL

WITHIN

OVARIAN

FOLLICLE

Egg cell

Egg protein signaling follicle cells

1

Translation of “head” mRNA

EMBRYO

Follicle cells

Gradient of regulatory protein

Gene expression in follicle cells

4

Follicle cell protein signaling egg cell

2

Gene expression

Gradient of certain other proteins

Localization of “head” mRNA

5

3

Gene expression

Body segments

“Head” mRNA

6

Head-Tail Polarity in the Fruit Fly


Signal transduction pathways

SIGNALING CELL

Signal

molecule

1

Plasma

membrane

Receptor

protein

2

TARGET CELL

Signal Transduction Pathways

  • Cell-to-cell signaling

    • Important for development

    • Coordination of cellular activities

  • A signal-transduction pathway that turns on a gene

  • The signaling cell secretes the signal molecule

  • The signal molecule binds to a receptor protein in the target cell’s plasma membrane


Signal transduction pathways1

SIGNALING CELL

Signal

molecule

1

Plasma

membrane

Receptor

protein

2

3

TARGET CELL

Relay

proteins

4

Transcription factor (activated)

Signal Transduction Pathways

  • Binding activates the first relay protein, which then activates the next relay protein, etc.

  • The last relay protein activates a transcription factor


Signal transduction pathways2

SIGNALING CELL

Signal

molecule

1

Plasma

membrane

Receptor

protein

2

3

TARGET CELL

Relay

proteins

4

Transcription factor (activated)

NUCLEUS

DNA

5

Transcription

mRNA

New

protein

6

Translation

Signal Transduction Pathways

  • The transcription factor triggers transcription of a specific gene

  • Translation of the mRNA produces a protein


Developmental genes

Developmental Genes

  • Homeotic Genes- A master control gene that determines the identity of a body structure of a developing organism, by controlling the developmental fate of groups of cells

    • Contain nucleotide sequences called homeoboxes

    • Are similar in many kinds of organisms

    • Arose early in the history of life


Developmental genes1

Fly chromosomes

Mouse chromosomes

Fruit fly embryo (10 hours)

Mouse embryo (12 days)

Adult fruit fly

Adult mouse

Developmental Genes

  • Fruit flies and mice have similar homeotic genes (colored boxes)

  • The order of homeotic genes is the same

  • The gene ordercorresponds toanalogous bodyregion


The genetic basis of cancer

The Genetic Basis of Cancer

  • Escape from the control mechanisms that normally limit their growth and development

    • Due to changes in genes that affect expression of other genes

  • Oncogene-gene that causes cancer

  • Proto-oncogene- a normal gene with the potential to become an oncogene

  • A mutation can change a proto-oncogene into an oncogene

    • An oncogene causes cells to divide excessively


Mutations and cancer

Proto-oncogene

DNA

Multiple copies of the gene

Gene moved tonew DNA locus,under new controls

Mutation within the gene

Oncogene

New promoter

Hyperactivegrowth-stimulatingprotein in normalamount

Normal growth-stimulatingproteinin excess

Normal growth-stimulatingproteinin excess

Mutations and Cancer


Mutations and cancer1

Mutated tumor-suppressor gene

Tumor-suppressor gene

Normalgrowth-inhibitingprotein

Defective,nonfunctioningprotein

Cell divisionunder control

Cell division notunder control

Mutations and Cancer

  • Mutations that inactivate tumor-suppressor genes have similar effects


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