13 Lecture Animation Ppt

Sylvia S

. Mad

er

Copyright © The McGraw Hill Companies Inc. Permission required for reproduction or display

PowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor

BIOLOGY10th Edition

Regulation of Gene Activity

Chapter 13: pp. 233 - 248

1

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

regulator gene promoter operator structural genes

DNARNA polymerase

RNA polymerase cannot bind to promoter.

mRNA

enzymesinactive repressor

a. Tryptophan absent. Enzymes needed to synthesize tryptophan are produced.

DNA

inactive repressor

b. Tryptophan present. Presence of tryptophan prevents production of enzymes used to synthesize tryptophan.

tryptophan

active repressor

5 3

2

Outline

Prokaryotic Regulation trp Operon lac Operon

Eukaryotic Regulation Chromatin Structure Transcriptional Control Posttranscriptional Control Translational Control Posttranslational Control

Genetic Mutations Cancer

3

Prokaryotic Regulation

Bacteria do not require the same enzymes all the time

Enzymes are produced as needed Francois Jacob and Jacques Monod (1961)

proposed the operon model to explain regulation of gene expression in prokaryotes

Operon is a group of structural and regulatory genes that function as a single unit

4

Prokaryotic Regulation: The Operon Model

Operon consist of three components Promoter

DNA sequence where RNA polymerase first attaches Short segment of DNA

Operator DNA sequence where active repressor binds Short segment of DNA

Structural Genes One to several genes coding for enzymes of a metabolic

pathway Translated simultaneously as a block Long segment of DNA

Animation

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6

Repressible Operons: The trp Operon

The regulator codes for a repressor

If tryptophan (an amino acid) is absent:

Repressor is unable to attach to the operator (expression is normally “on”)

RNA polymerase binds to the promoter

Enzymes for synthesis of tryptophan are produced

If tryptophan is present:

Combines with repressor as corepressor

Repressor becomes functional

Blocks synthesis of enzymes and tryptophan

Animation


8

The trp Operon


When the repressorbinds to the operator,

transcription is prevented.

activerepressor

structural genes

regulator gene

promoter operator

9

The trp Operon



DNA

RNA polymerase


mRNA



DNA

inactive repressor


tryptophan

active repressor

5 3

10

Inducible Operons: The lac Operon

The regulator codes for a repressor

If lactose (a sugar that can be used for food) is absent: Repressor attaches to the operator

Expression is normally “off”

If lactose is present: It combines with repressor and renders it unable to bind to

operator

RNA polymerase binds to the promoter

The three enzymes necessary for lactose catabolism are produced

Animation


12

The lac Operon



DNA


RNA polymerase can bind to promoter.

active repressor

active repressor

mRNA

enzymes

active repressor

inactive repressor

b. Lactose present. Enzymes needed to take up and use lactose are produced only when lactose is present.

a. Lactose absent. Enzymes needed to take up and use lactose are not produced.

lactose

DNA

5 3

Animation


14

Action of CAP


DNA

inactive CAP

inactive CAP

active CAP

a. Lactose present, glucose absent (cAMP level high)

b. Lactose present, glucose present (cAMP level low)

DNA

cAMP

promoterCAP binding site

RNA polymerase bindsfully with promoter.

RNA polymerase doesnot bind fully with promoter.

promoter operator

operator

CAP binding site

Animation


16

Eukaryotic Regulation

A variety of mechanismsFive primary levels of control:

Nuclear levels Chromatin PackingTranscriptional ControlPosttranscriptional Control

Cytoplasmic levels Translational ControlPosttranslational Control

Animation

17


18

Regulation of Gene Expression:Levels of Control in Eukaryotes

functional protein

plasmamembrane

polypeptide chain

Posttranslationalcontrol

Posttranscriptional control

Transcriptional control

Translationalcontrol

nuclear pore

mRNA

pre-mRNA

intron exon

histones

nuclear envelope

Chromatinstructure


3

5

3

5

19

Chromatin Structure

Eukaryotic DNA associated with histone proteins Together make up chromatin As seen in the interphase nucleus

Nucleosomes: DNA wound around balls of eight molecules of histone

proteins Looks like beads on a string Each bead a nucleosome

The levels of chromatin packing determined by degree of nucleosome coiling

20

Chromatin Structure Regulates Gene Expression


DNA

histone protein

a. Darkly stained heterochromatin and lightly stained euchromatin

b. A nucleosomec. DNA unpacking

H2A

H2B

H3

H1

H4 histonetail

nucleosome

accessiblepromoter

DNA to be transcribed

inaccessiblepromoter

a: Courtesy Stephen Wolfe

euchromatinheterochromatin nucleolus

1 m

chromatin remodeling complex

21

Chromatin Packing

Euchromatin Loosely coiled DNA Transcriptionally active

Heterochromatin Tightly packed DNA Transcriptionally inactive

Barr Bodies Females have two X chromosomes, but only one is

active Other is tightly packed along its entire length Inactive X chromosome is Barr body

22

X-Inactivation in Mammalian Females

Coats of tortoiseshellcats have patchesof orange and black.

One X chromosome is inactivated ineach cell. Which one is by chance.

Females have twoX chromosomes.

active X chromosome

inactive X

inactive X

active X chromosome

allele fororange color

allele forblack color

cell division Barr bodies

© Chanan Photo 2004


23

Transcriptional Control

Transcription controlled by proteins called transcription factors

Bind to enhancer DNA

Regions of DNA where factors that regulate transcription can also bind

Always present in cell, but most likely have to be activated before they will bind to DNA

Animation


Animation


Animation


27

Eukaryotic Transcription Factors


promoter

DNA

enhancer

transcriptionactivator

mediator proteins

mRNA transcription

RNA polymerase

transcriptionfactor complex

gene

28

Posttranscriptional Control

Posttranscriptional control operates on primary mRNA transcript

Given a specific primary transcript: Excision of introns can vary Splicing of exons can vary Determines the type of mature transcript that leaves

the nucleus May also control speed of mRNA transport from

nucleus to cytoplasm Will affect the number of transcripts arriving at rough

ER And therefore the amount of gene product realized per

unit time

29

Processing of mRNA Transcripts


intronintron

intron

cap

protein product 1

mRNA

RNA splicing

poly-Atail

exon intron

protein product 2

RNA splicing

exon

a. b.

cap

A B C D E

A B C D E

A B C

C

D E

A D EB

pre-mRNA

mRNA

pre-mRNA poly-Atail

5 3 5 3

30

Function of microRNAs


pre-mRNA

MicroRNA is cut froma pre-mRNA and binds withproteins to form RISC.

Complementary base pairingbetween RNAs allows RISCto bind to mRNA.

Translationis inhibited.

The mRNAis degraded.

mRNA

RISC(RNA-inducedsilencing complex)

microRNA(miRNA)

proteins

or

RISC

5

3

3 5

5

3

31

Translational Control

Translational Control - Determines degree to which mRNA is translated into a protein product

Presence of 5′ cap

Length of poly-A tail on 3′ end

Posttranslational Control - Affects the activity of a protein product

Activation

Degradation rate

32

Regulation Through Gene Mutation

Mutation is a permanent change in the sequence of bases in DNA. No effect on protein activity Protein is completely inactivated

Germ-line mutations occur in sex cells Somatic mutations occur in body cells

33

Causes of Mutations

Spontaneous mutation DNA can undergo a chemical change Movement of transposons from one chromosomal location to

another Replication Errors

1 in 1,000,000,000 replications DNA polymerase

Proofreads new strands Generally corrects errors

Induced mutation: Mutagens such as radiation, organic chemicals Many mutagens are also carcinogens (cancer causing) Environmental Mutagens

Ultraviolet Radiation Tobacco Smoke

Animation


35

The Ames Test For Mutagenicity

bacterialstrain(requireshistidine)

Control

Mutation did not occurMutation occurred

Suspectedchemicalmutagen

bacterialstrain(requireshistidine)

Plate onto petri platesthat lack histidine.

Incubate overnightbacterialgrowth


36

Causes of Mutations

Ultraviolet (UV) radiation is easily absorbed by the pyrimidines in DNA.

Cause neighboring thymine molecules next to one another to bond togetherThymine dimers.

C G

C

A

A

G

kink

thyminedimer


T

T

37

Causes of Mutations

Usually, these dimers are removed by DNA repair enzymesDeficient DNA repair enzymes leave the skin

cells vulnerable to the mutagenic effects of ultraviolet light

Accumulation of mutationHigh incidence of cancer

Animation


39

XerodermaPigmentosome


© Ken Greer/Visuals Unlimited

40

Effect of Mutations on Protein Activity

Point Mutations Involve change in a single DNA nucleotide Changes one codon to a different codon Affects on protein vary:

Nonfunctional Reduced functionality Unaffected

Frameshift Mutations One or two nucleotides are either inserted or deleted

from DNA Protein always rendered nonfunctional

Normal : THE CAT ATE THE RAT After deletion: THE ATA TET HER AT After insertion: THE CCA TAT ETH ERA T

41

Point Mutations in Hemoglobin


b. Normal red blood cell

a.

c. Sickled red blood cell

No mutation

Val His Leu Thr Pro Glu Glu

(normal protein)

His His

(abnormal protein)

Glu Val

(incomplete protein)

Glu Stop

CTCCTCTGGAGTC A C G T G G A G

CTCCTCTGGAGTC A C G T G A G

Val His Leu Thr Pro Glu Glu

CTCCACTGGAGTC A C G T G G A G

Val His Leu Thr Pro Glu

CTCCATGGAGTC A C G T G G A G T

Val His Leu Thr Pro Stop

A

b, c: © Stan Flegler/Visuals Unlimited.

Val

3 5

42

Carcinogenesis

Development of cancer involves a series of mutations

Proto-oncogenes – Stimulate cell cycle

Tumor suppressor genes – inhibit cell cycle

Mutation in oncogene and tumor suppressor gene:

Stimulates cell cycle uncontrollably

Leads to tumor formation

43

Cell Signaling Pathway

Cell signaling pathway that stimulates a mutated tumor suppressor gene


receptor

inhibiting growth factor

cytoplasm

plasmamembrane

signaltransducers

transcription factor

nucleus

protein that isunable to inhibitthe cell cycleor promoteapoptosis

mutated tumor suppressor gene

44

Cell Signaling Pathway

Cell signaling pathway that stimulates a proto-oncogene


receptor

stimulating growth factor

cytoplasm

plasmamembrane

signaltransducers

transcription factor

nucleus

protein thatoverstimulatesthe cell cycle

oncogene

45

Review

Prokaryotic Regulation trp Operon lac Operon

Eukaryotic Regulation Transcriptional Control Posttranscriptional Control Translational Control Posttranslational Control

Genetic Mutations Cancer

Sylvia S

. Mad

er

Copyright © The McGraw Hill Companies Inc. Permission required for reproduction or display

PowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor

BIOLOGY10th Edition

Regulation of Gene Activity

Chapter 13: pp. 233 - 248

46



DNARNA polymerase


mRNA



DNA

inactive repressor


tryptophan

active repressor

5 3

Technology

13 Lecture Animation Ppt