How genes are controlled
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How Genes are Controlled. Muse 2009. CONTROL OF GENE EXPRESSION. 0. 11.1 Proteins interacting with DNA turn prokaryotic genes on or off in response to environmental changes. Gene expression is the overall process of information flow from genes to proteins

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How genes are controlled

How Genes are Controlled

Muse 2009


How genes are controlled

CONTROL OF GENE EXPRESSION


How genes are controlled

0

11.1 Proteins interacting with DNA turn prokaryotic genes on or off in response to environmental changes

  • Gene expression is the overall process of information flow from genes to proteins

    • Mainly controlled at the level of transcription

    • A gene that is “turned on” is being transcribed to produce mRNA that is translated to make its corresponding protein

    • Organisms respond to environmental changes by controlling gene expression


How genes are controlled

0

11.1 Proteins interacting with DNA turn prokaryotic genes on or off in response to environmental changes

  • An operon is a group of genes under coordinated control in bacteria

  • The lactose (lac) operon includes

    • Three adjacent genes for lactose-utilization enzymes

    • Promoter sequence where RNA polymerase binds

    • Operator sequence is where a repressor can bind and block RNA polymerase action


How genes are controlled

0

11.1 Proteins interacting with DNA turn prokaryotic genes on or off in response to environmental changes

  • Regulation of the lac operon

    • Regulatory gene codes for a repressor protein

    • In the absence of lactose, the repressor binds to the operator and prevents RNA polymerase action

    • Lactose inactivates the repressor, so the operator is unblocked


How genes are controlled

0

11.1 Proteins interacting with DNA turn prokaryotic genes on or off in response to environmental changes

  • Types of operon control

    • Inducible operon (lac operon)

      • Active repressor binds to the operator

      • Inducer (lactose) binds to and inactivates the repressor

    • Repressible operon (trp operon)

      • Repressor is initially inactive

      • Corepressor (tryptophan) binds to the repressor and makes it active

    • For many operons, activators enhance RNA polymerase binding to the promoter (ie NAC)


How genes are controlled

0


How genes are controlled

OPERON

0

Regulatory

gene

Promoter Operator

Lactose-utilization genes

DNA

mRNA

RNA polymerase

cannot attach to

promoter

Active

repressor

Protein

Operon turned off (lactose absent)

DNA

RNA polymerase

bound to promoter

mRNA

Protein

Enzymes for lactose utilization

Lactose

Inactive

repressor

Operon turned on (lactose inactivates repressor)


How genes are controlled

0

OPERON

Regulatory

gene

Promoter Operator

Lactose-utilization genes

DNA

mRNA

RNA polymerase

cannot attach to

promoter

Active

repressor

Protein

Operon turned off (lactose absent)


How genes are controlled

0

DNA

RNA polymerase

bound to promoter

mRNA

Protein

Enzymes for lactose utilization

Lactose

Inactive

repressor

Operon turned on (lactose inactivates repressor)


How genes are controlled

0

Operator

Gene

Promoter

DNA

Active

repressor

Active

repressor

Tryptophan

Inactive

repressor

Inactive

repressor

Lactose

trp operon

lac operon


11 2 differentiation results from the expression of different combination genes

0

11.2 Differentiation results from the expression of different combination genes

  • Differentiation involves cell specialization, in both structure and function

  • Differentiation is controlled by turning specific sets of genes on or off


11 3 dna packing in eukaryotic chromosomes helps regulate gene expression

0

11.3 DNA packing in eukaryotic chromosomes helps regulate gene expression

  • Eukaryotic chromosomes undergo multiple levels of folding and coiling, called DNA packing

    • Nucleosomes are formed when DNA is wrapped around histone proteins

      • “Beads on a string” appearance

      • Each bead includes DNA plus 8 histone molecules

      • String is the linker DNA that connects nucleosomes

    • Tight helical fiber is a coiling of the nucleosome string

    • Supercoil is a coiling of the tight helical fiber

    • Metaphase chromosome represents the highest level of packing

  • DNA packing can prevent transcription


11 3 dna packing in eukaryotic chromosomes helps regulate gene expression1

0

11.3 DNA packing in eukaryotic chromosomes helps regulate gene expression

Animation: DNA Packing


How genes are controlled

0

Metaphase

chromosome

Tight helical fiber

(30-nm diameter)

DNA double helix

(2-nm diameter)

Linker

“Beads on

a string”

Nucleosome

(10-nm

diameter)

Histones

Supercoil

(300-nm diameter)

700 nm


11 4 in female mammals one x chromosome is inactive in each somatic cell

0

11.4 In female mammals, one X chromosome is inactive in each somatic cell

  • X-chromosome inactivation

    • In female mammals, one of the two X chromosomes is highly compacted and transcriptionally inactive

    • Random inactivation of either the maternal or paternal chromosome

    • Occurs early in embryonic development and all cellular descendants have the same inactivated chromosome

    • Inactivated X chromosome is called a Barr body

    • Tortoiseshell fur coloration is due to inactivation of X chromosomes in heterozygous female cats


How genes are controlled

0

Early embryo

Two cell populations

in adult

Cell division

and random

X chromosome

inactivation

Orange

fur

Active X

X chromosomes

Inactive X

Inactive X

Allele for

orange fur

Black fur

Active X

Allele for

black fur


11 5 complex assemblies of proteins control eukaryotic transcription

0

11.5 Complex assemblies of proteins control eukaryotic transcription

  • Eukaryotic genes

    • Each gene has its own promoter and terminator

    • Are usually switched off and require activators to be turned on

    • Are controlled by interactions between numerous regulatory proteins and control sequences


11 5 complex assemblies of proteins control eukaryotic transcription1

0

11.5 Complex assemblies of proteins control eukaryotic transcription

  • Regulatory proteins that bind to control sequences

    • Transcription factors promote RNA polymerase binding to the promoter

    • Activator proteins bind to DNA enhancers and interact with other transcription factors

    • Silencers are repressors that inhibit transcription

  • Control sequences

    • Promoter

    • Enhancer

      • Related genes located on different chromosomes can be controlled by similar enhancer sequences


11 5 complex assemblies of proteins control eukaryotic transcription2

0

11.5 Complex assemblies of proteins control eukaryotic transcription

Regions on the DNA called enhancers control genes that may be quite

distant.

Enhancer binding proteins may have multiple controls built into them

Animation: Initiation of Transcription


How genes are controlled

Enhancers

Promoter

0

Gene

DNA

Activator

proteins

Transcription

factors

Other

proteins

RNA polymerase

Bending

of DNA

Transcription


11 6 eukaryotic rna may be spliced in more than one way

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11.6 Eukaryotic RNA may be spliced in more than one way

  • Alternative RNA splicing

    • Production of different mRNAs from the same transcript

    • Results in production of more than one polypeptide from the same gene

    • Can involve removal of an exon with the introns on either side

Animation: RNA Processing


How genes are controlled

0

Exons

4

1

3

2

5

DNA

4

1

3

2

RNA

transcript

5

RNA splicing

or

4

1

2

1

5

3

2

mRNA

5


11 7 small rnas play multiple roles in controlling gene expression

0

11.7 Small RNAs play multiple roles in controlling gene expression

  • RNA interference (RNAi)

    • Prevents expression of a gene by interfering with translation of its RNA product

    • Involves binding of small, complementary RNAs to mRNA molecules

    • Leads to degradation of mRNA or inhibition of translation

  • MicroRNA

    • Single-stranded chain about 20 nucleotides long

    • Binds to protein complex

    • MicroRNA + protein complex binds to complementary mRNA to interfere with protein production


11 7 small rnas play multiple roles in controlling gene expression1

0

11.7 Small RNAs play multiple roles in controlling gene expression

Anti-sense RNA and snRNAi

Animation: Blocking Translation

Animation: mRNA Degradation


How genes are controlled

0

Protein

miRNA

1

miRNA-

protein

complex

2

Target mRNA

4

3

Translation blocked

OR

mRNA degraded


11 8 translation and later stages of gene expression are also subject to regulation

0

11.8 Translation and later stages of gene expression are also subject to regulation

  • Control of gene expression also occurs with

    • Breakdown of mRNA

    • Initiation of translation

    • Protein activation

    • Protein breakdown


How genes are controlled

0

Folding of

polypeptide and

formation of

S—S linkages

Cleavage

Disulfide

bonds

Active form

of insulin

Initial polypeptide

(inactive)

Folded polypeptide

(inactive)

Quartenary structure


11 9 review multiple mechanisms regulate gene expression in eukaryotes

0

11.9 Review: Multiple mechanisms regulate gene expression in eukaryotes

  • Many possible control points exist; a given gene may be subject to only a few of these

    • Chromosome changes (1)

      • DNA unpacking

    • Control of transcription (2)

      • Regulatory proteins and control sequences

    • Control of RNA processing

      • Addition of 5’ cap and 3’ poly-A tail (3)

      • Splicing (4)

    • Flow through nuclear envelope (5)


11 9 review multiple mechanisms regulate gene expression in eukaryotes1

0

11.9 Review: Multiple mechanisms regulate gene expression in eukaryotes

  • Many possible control points exist; a given gene may be subject to only a few of these

    • Breakdown of mRNA (6)

    • Control of translation (7)

    • Control after translation

      • Cleavage/modification/activation of proteins (8)

      • Breakdown of protein (9)


11 9 review multiple mechanisms regulate gene expression in eukaryotes2

0

11.9 Review: Multiple mechanisms regulate gene expression in eukaryotes

  • Applying Your KnowledgeFor each of the following, determine whether an increase or decrease in the amount of gene product is expected

    • The mRNA fails to receive a poly-A tail during processing in the nucleus

    • The mRNA becomes more stable and lasts twice as long in the cell cytoplasm

    • The region of the chromatin containing the gene becomes tightly compacted

    • An enzyme required to cleave and activate the protein product is missing


How genes are controlled

11.9 Review: Multiple mechanisms regulate gene expression in eukaryotes

0

  • Applying Your KnowledgeFor each of the following, determine whether an increase or decrease in the amount of gene product is expected

    • The mRNA fails to receive a poly-A tail during processing in the nucleus ---------

    • The mRNA becomes more stable and lasts twice as long in the cell cytoplasm ++++++

    • The region of the chromatin containing the gene becomes tightly compacted --------

    • An enzyme required to cleave and activate the protein product is missing +++++ feedback


11 9 review multiple mechanisms regulate gene expression in eukaryotes3

0

11.9 Review: Multiple mechanisms regulate gene expression in eukaryotes

Animation: Protein Degradation

Animation: Protein Processing


How genes are controlled

NUCLEUS

0

Chromosome

DNA unpacking

Other changes to DNA

Gene

Gene

Transcription

Exon

RNA transcript

Intron

Addition of cap and tail

Splicing

Tail

mRNA in nucleus

Cap

Flow through

nuclear envelope

mRNA in cytoplasm

CYTOPLASM

Breakdown of mRNA

Broken-

down

mRNA

Translation

Polypeptide

Cleavage / modification /

activation

Active protein

Breakdown

of protein

Broken-

down

protein


How genes are controlled

NUCLEUS

Chromosome

DNA unpacking

Other changes to DNA

Gene

Gene

Transcription

Exon

RNA transcript

Intron

Addition of cap and tail

Splicing

Tail

mRNA in nucleus

Cap

Flow through

nuclear envelope


How genes are controlled

mRNA in cytoplasm

CYTOPLASM

Breakdown of mRNA

Broken-

down

mRNA

Translation

Polypeptide

Cleavage / modification /

activation

Active protein

Breakdown

of protein

Broken-

down

protein


11 10 cascades of gene expression direct the development of an animal

0

11.10 Cascades of gene expression direct the development of an animal

  • Role of gene expression in fruit fly development

    • Orientation from head to tail

      • Maternal mRNAs present in the egg are translated and influence formation of head to tail axis

    • Segmentation of the body

      • Protein products from one set of genes activate other sets of genes to divide the body into segments

    • Production of adult features

      • Homeotic genes are master control genes that determine the anatomy of the body, specifying structures that will develop in each segment


11 10 cascades of gene expression direct the development of an animal1

0

11.10 Cascades of gene expression direct the development of an animal

Animation: Cell Signaling

Animation: Development of Head-Tail Axis in Fruit Flies


How genes are controlled

0

Eye

Antenna

Leg

Head of a normal fruit fly

Head of a developmental mutant


How genes are controlled

Egg cell

Egg cell

within ovarian

follicle

0

Protein

signal

Follicle cells

Gene expression

1

“Head”

mRNA

Cascades of

gene expression

2

Embryo

Body

segments

3

Gene expression

Adult fly

4


Dna microarrays test for the transcription of many genes at once

0

DNA microarrays test for the transcription of many genes at once

  • DNA microarray

    • Contains DNA sequences arranged on a grid

    • Used to test for transcription

      • mRNA from a specific cell type is isolated

      • Fluorescent cDNA is produced from the mRNA

      • cDNA is applied to the microarray

      • Unbound cDNA is washed off

      • Complementary cDNA is detected by fluorescence


How genes are controlled

0

DNA microarray

Actual size

(6,400 genes)

Each well contains DNA

from a particular gene

mRNA

isolated

1

Unbound

cDNA rinsed

away

4

Reverse transcriptase

and fluorescent DNA

nucleotides

Nonfluorescent

spot

Fluorescent

spot

cDNA applied

to wells

3

cDNA made

from mRNA

2

cDNA

DNA of an

expressed gene

DNA of an

unexpressed gene


Global transcription analysis

Global transcription analysis


How genes are controlled

0

11.12 Signal transduction pathways convert messages received at the cell surface to responses within the cell

  • Signal transduction pathway is a series of molecular changes that converts a signal at the cell’s surface to a response within the cell

    • Signal molecule is released by a signaling cell

    • Signal molecule binds to a receptor on the surface of a target cell


How genes are controlled

0

11.12 Signal transduction pathways convert messages received at the cell surface to responses within the cell

  • Relay proteins are activated in a series of reactions

  • A transcription factor is activated and enters the nucleus

  • Specific genes are transcribed to initiate a cellular response

Animation: Overview of Cell Signaling

Animation: Signal Transduction Pathways


How genes are controlled

Signaling cell

0

Signaling

molecule

Plasma

membrane

1

Receptor

protein

2

3

Target cell

Relay

proteins

Transcription

factor

(activated)

4

Nucleus

DNA

5

Transcription

mRNA

New

protein

6

Translation


How genes are controlled

CLONING OF PLANTS AND ANIMALS

Hello Dolly!


11 14 plant cloning shows that differentiated cells may retain all of their genetic potential

0

11.14 Plant cloning shows that differentiated cells may retain all of their genetic potential

  • Most differentiated cells retain a full set of genes, even though only a subset may be expressed

    • Evidence is available from

      • Plant cloning

        • A root cell can divide to form an adult plant

      • Animal limb regeneration

        • Remaining cells divide to form replacement structures

      • Involved dedifferentiation followed by redifferentiation into specialized cells


How genes are controlled

0

Root of

carrot plant

Single

cell

Cell division

in culture

Root cells cultured

in nutrient medium

Plantlet

Adult plant


11 15 nuclear transplantation can be used to clone animals

0

11.15 Nuclear transplantation can be used to clone animals

  • Nuclear transplantation

    • Replacing the nucleus of an egg cell or zygote with a nucleus from an adult somatic cell

    • Early embryo (blastocyst) can be used in

      • Reproductive cloning

        • Implant embryo in surrogate mother for development

        • New animal is genetically identical to nuclear donor

      • Therapeutic cloning

        • Remove embryonic stem cells and grow in culture for medical treatments

        • Induce stem cells to differentiate


How genes are controlled

0

Donor

cell

Reproductive

cloning

Nucleus from

donor cell

Implant blastocyst in

surrogate mother

Clone of

donor is born

Remove

nucleus

from egg

cell

Add somatic cell

from adult donor

Grow in culture

to produce an

early embryo

(blastocyst)

Therapeutic

cloning

Remove embryonic

stem cells from

blastocyst and

grow in culture

Induce stem

cells to form

specialized cells


How genes are controlled

0

Donor

cell

Nucleus from

donor cell

Add somatic cell

from adult donor

Grow in culture

to produce an

early embryo

(blastocyst)

Remove

nucleus

from egg

cell


How genes are controlled

0

Reproductive

cloning

Implant blastocyst in

surrogate mother

Clone of

donor is born

Therapeutic

cloning

Induce stem

cells to form

specialized cells

Remove embryonic

stem cells from

blastocyst and

grow in culture


Reproductive cloning has valuable applications but human reproductive cloning raises ethical issues

0

Reproductive cloning has valuable applications, but human reproductive cloning raises ethical issues

  • Cloned animals can show differences from their parent due to a variety of influences during development

  • Reproductive cloning is used to produce animals with desirable traits

    • Agricultural products

    • Therapeutic agents

    • Restoring endangered animals

  • Human reproductive cloning raises ethical concerns


How genes are controlled

0

CAT1 CC


11 17 connection therapeutic cloning can produce stem cells with great medical potential

0

11.17 CONNECTION: Therapeutic cloning can produce stem cells with great medical potential

  • Stem cells can be induced to give rise to differentiated cells

    • Embryonic stem cells can differentiate into a variety of types

    • Adult stem cells can give rise to many but not all types of cells

  • Therapeutic cloning can supply cells to treat human diseases

  • Research continues into ways to use and produce stem cells


How genes are controlled

0

Blood cells

Adult stem

cells in bone

marrow

Nerve cells

Cultured

embryonic

stem cells

Heart muscle cells

Different types of

differentiated cells

Different culture

conditions


How genes are controlled

THE GENETIC BASIS OF CANCER


11 18 cancer results from mutations in genes that control cell division

0

11.18 Cancer results from mutations in genes that control cell division

  • Mutations in two types of genes can cause cancer

    • Oncogenes

      • Proto-oncogenes normally promote cell division

      • Mutations to oncogenes enhance activity

    • Tumor-suppressor genes

      • Normally inhibit cell division

      • Mutations inactivate the genes and allow uncontrolled division to occur


11 18 cancer results from mutations in genes that control cell division1

0

11.18 Cancer results from mutations in genes that control cell division

  • Oncogenes

    • Promote cancer when present in a single copy

    • Can be viral genes inserted into host chromosomes (src, ras)

    • Can be mutated versions of proto-oncogenes, normal genes that promote cell division and differentiation

    • Converting a proto-oncogene to an oncogene can occur by

      • Mutation causing increased protein activity

      • Increased number of gene copies causing more protein to be produced

      • Change in location putting the gene under control of new promoter for increased transcription


11 18 cancer results from mutations in genes that control cell division2

0

11.18 Cancer results from mutations in genes that control cell division

  • Tumor-suppressor genes

    • Promote cancer when both copies are mutated


How genes are controlled

0

Proto-oncogene DNA

Multiple copies

of the gene

Mutation within

the gene

Gene moved to

new DNA locus,

under new controls

New promoter

Oncogene

Hyperactive

growth-

stimulating

protein in

normal

amount

Normal growth-

stimulating

protein

in excess

Normal growth-

stimulating

protein

in excess


How genes are controlled

0

Mutated tumor-suppressor gene

Tumor-suppressor gene

Normal

growth-

inhibiting

protein

Defective,

nonfunctioning

protein

Cell division not

under control

Cell division

under control


11 19 multiple genetic changes underlie the development of cancer

0

11.19 Multiple genetic changes underlie the development of cancer

  • Four or more somatic mutations are usually required to produce a cancer cell

  • One possible scenario for colorectal cancer includes

    • Activation of an oncogene increases cell division

    • Inactivation of tumor suppressor gene causes formation of a benign tumor

    • Additional mutations lead to a malignant tumor


How genes are controlled

0

Colon wall

1

2

3

Increased

cell division

Growth of polyp

Growth of malignant

tumor (carcinoma)

Cellular

changes:

DNA

changes:

Oncogene

activated

Second tumor-

suppressor gene

inactivated

Tumor-suppressor

gene inactivated


How genes are controlled

0

Chromosomes

4

mutations

1

mutation

2

mutations

3

mutations

Normal

cell

Malignant

cell


11 20 faulty proteins can interfere with normal signal transduction pathways

0

11.20 Faulty proteins can interfere with normal signal transduction pathways

  • Path producing a product that stimulates cell division

    • Product of ras proto-oncogene relays a signal when growth hormone binds to receptor

    • Product of ras oncogene relays the signal in the absence of hormone binding, leading to uncontrolled growth


11 20 faulty proteins can interfere with normal signal transduction pathways1

0

11.20 Faulty proteins can interfere with normal signal transduction pathways

  • Path producing a product that inhibits cell division

    • Product of p53 tumor-suppressor gene is a transcription factor

    • p53 transcription factor normally activates genes for factors that stop cell division

    • In the absence of functional p53, cell division continues because the inhibitory protein is not produced


How genes are controlled

Growth factor

0

Receptor

Target cell

Hyperactive

relay protein

(product of

ras oncogene)

issues signals

on its own

Normal product

of ras gene

Relay

proteins

Transcription

factor

(activated)

DNA

Nucleus

Transcription

Translation

Protein that

Stimulates

cell division


How genes are controlled

0

Growth-inhibiting

factor

Receptor

Relay

proteins

Nonfunctional transcription

factor (product of faulty p53

tumor-suppressor gene)

cannot trigger

transcription

Transcription

factor

(activated)

Normal product

of p53 gene

Transcription

Translation

Protein absent

(cell division

not inhibited)

Protein that

inhibits

cell division


Lifestyle choices can reduce the risk of cancer

0

Lifestyle choices can reduce the risk of cancer

  • Carcinogens are cancer-causing agents that damage DNA and promote cell division

    • X-rays and ultraviolet radiation

    • Tobacco

  • Healthy lifestyle choices

    • Avoiding carcinogens

    • Avoiding fat and including foods with fiber and antioxidants

    • Regular medical checkups


How genes are controlled

0


Wrap up and review

Wrap up and Review

  • Bacteria arrange multiple genes into operons and control promoters with repressors and activators.

  • Eukaryotes have multiple ways to control genes.


How genes are controlled

0

A typical operon

Regulatory

gene

Promoter

Operator

Gene 1

Gene 2

Gene 3

DNA

Switches operon

on or off

Encodes repressor

that in active form

attaches to operator

RNA

polymerase

binding site


How genes are controlled

0

Whole Organism Cloning

Early embryo

resulting from

nuclear trans-

plantation

Clone

of donor

Surrogate

mother

Nucleus from

donor cell


How genes are controlled

0

Therapeutic cloning

Embryonic

stem cells

in culture

Specialized

cells

Early embryo

resulting from

nuclear trans-

plantation

Nucleus from

donor cell


How genes are controlled

Gene

regulation

0

(a)

prokaryotic

genes often

grouped into

is a normal gene that

can be mutated to an

in eukaryotes

may involve

when

abnormal

may lead to

operons

oncogene

controlled by

protein called

can cause

are

switched

on/off by

(b)

(c)

in active

form binds to

(d)

(e)

(f)

(g)

are proteins

that promote

occurs in

can produce

multiple mRNAs

per gene

female

mammals

transcription


You should now be able to

0

You should now be able to

  • Explain how prokaryotic gene control occurs in the operon

  • Describe the control points in expression of a eukaryotic gene

  • Describe DNA packing and explain how it is related to gene expression

  • Explain how alternative RNA splicing and microRNAs affect gene expression

  • Compare and contrast the control mechanisms for prokaryotic and eukaryotic genes


You should now be able to1

0

You should now be able to

  • Distinguish between terms in the following groups: promoter—operator; oncogene—tumor suppressor gene; reproductive cloning— therapeutic cloning

  • Define the following terms: Barr body, carcinogen, DNA microarray, homeotic gene; stem cell; X-chromosome inactivation

  • Describe the process of signal transduction, explain how it relates to yeast mating, and explain how it is disrupted in cancer development


You should now be able to2

0

You should now be able to

  • Explain how cascades of gene expression affect development

  • Compare and contrast techniques of plant and animal cloning

  • Describe the types of mutations that can lead to cancer

  • Identify lifestyle choices that can reduce cancer risk


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