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Gene Expression Dr. Kevin Ahern Gene Expression Dr. Kevin Ahern

Gene Expression Dr. Kevin Ahern - PowerPoint Presentation

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Gene Expression Dr. Kevin Ahern - PPT Presentation

Gene Expression Gene Expression Transcription Splicing Polyadenylation mRNA Stability Translation Protein Stability Controls on Protein Levels Transcription Control Prokaryotic Promoter Transcription Control Prokaryotic Promoter ID: 811095

transcription rna expression gene rna transcription gene expression control eukaryotic mrna chromatin prokaryotic dna iron translation interference risc histone

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Presentation Transcript

Slide1

Gene Expression

Dr. Kevin Ahern

Slide2

Gene Expression

Slide3

Gene Expression

Transcription

Splicing

Polyadenylation

mRNA Stability

Translation

Protein Stability

Controls on Protein Levels

Slide4

Transcription Control - Prokaryotic Promoter

Slide5

Transcription Control - Prokaryotic Promoter

Polycistronic Message in Prokaryotes

Slide6

Transcription Control - Prokaryotic Promoter

Allo-Lactose

Lactose

Slide7

Transcription Control - Prokaryotic Promoter

Slide8

Transcription Control - Prokaryotic Promoter

Slide9

Transcription Control - Prokaryotic Promoter

CAP

CAP Site of DNA

cAMP

Slide10

From Wikimedia Commons

Transcription Control - Prokaryotic Promoter

Slide11

From Wikimedia Commons

Prokaryotic Transcription Control - Termination/Attenuation

Slide12

Prokaryotic Transcription Control - Termination/Attenuation

Slide13

Transcription/Translation Control - Riboswitches

Anti-terminator

Terminator

Cis-acting sequences

Slide14

Transcription/Translation Control - Riboswitches

Lysine Bound to Riboswitch

Slide15

Eukaryotic Gene Expression

Much More Complexity

Chromatin

Many Transcription Factors

Enhancers

Slide16

Transcriptional Control - Eukaryotes

Slide17

Increasing Magnification

RNA

Eukaryotic Gene Expression - Chromatin

Chromatin is the Complex of DNA, Protein, and RNA Comprising Eukaryotic Chromosomes

For RNA Polymerase to Perform Transcription, Access Must Be Gained to the DNA

Slide18

RNA

Eukaryotic Gene Expression - Epigenetics

Slide19

RNA

Eukaryotic Gene Expression - Chromatin

A Nucleosome is a Fundamental Unit of Chromatin Structure

Contains Two Copies Each of Four Histone Proteins - H2a, H2B, H3, and H4

DNA is Wrapped Around this Octet Core and Histone H1 is on the Outside

Slide20

RNA

Eukaryotic Gene Expression - Chromatin

Histone Proteins Are Rich in Basic Amino Acids, Making Them Positively Charged

The Positively Charged Proteins Are Attracted Strongly

to the Negatively Charged Phosphates of the DNA

Chemical Modifications That Affect These Charges Influence Transcription

Slide21

RNA

Eukaryotic Gene Expression - Chromatin

Slide22

RNA

Eukaryotic Gene Expression - Chromatin

Histone Acetyl Transferases (HATs) Use Acetyl-CoA to Put Acetyl Groups on Lysines in Histones

This Neutralizes Their Positive Charge and Loosens Interactions With the Histones, Facilitating “Remodeling” or Restructuring of Chromatin to Allow Transcription to Occur

Acetylated Lysines Can Also be Binding Targets for Proteins Affecting Transcription

Chemical Modification

Unwinding of Complex

Slide23

RNA

Eukaryotic Gene Expression - Epigenetics

Slide24

RNA

Eukaryotic Gene Expression - Chromatin

Histone Acetylation Favors Euchromatin and Stimulates Transcription

Histone De-Acetylases Reverse These Effects, Favoring Heterochromatin and Gene Silencing

The Sirtuin 1 deacetylase in humans down-regulated with insulin resistance

Numerous Chemical Modifications are Made to Histone Proteins

Acetylation / Deacetylation

Methylation / Demethylation

Phosphorylation / Dephosphorylation

Ubiquitination

Chemical Modification to Bases in DNA

Can Also Affect Transcription

Open and Accessible to

Transcription Complex

Condensed and

Not Accessible

Slide25

RNA

Eukaryotic Gene Expression - Epigenetics

Slide26

Epigenetics

Chemical Modifications in Histones and DNA Can Cross Generational Barriers

Transcriptional Effects Can Thus Be Transmitted From Parent to Progeny

Independent of the Sequence of the DNA.

Such Influences are Called Epigenetic

Slide27

Slide28

Transcriptional Control - Eukaryotes

Methylation of CpG sequences in

eukaryotes inhibits transcription

Slide29

Transcriptional Control - Eukaryotes

Slide30

Slide31

Transcriptional Control - Eukaryotes

Slide32

RNA

Eukaryotic Gene Expression - Transcription

Insulators Can Block Enhancer’s Activation of Transcription

Blocking Insulators Allows Enhancer to Activate Transcription

Slide33

Iron Transfer & Storage

Ferritin - Cellular Protein to Bind Iron

Transferrin Receptor - Membrane Protein to Transfer Iron

Slide34

Iron Transfer & Storage

Iron Response Element (IRE)

Iron Response Element

Binding Protein (IRE-BP)

Slide35

Iron Transfer & Storage - Translation Regulation

Slide36

Iron Transfer & Storage - mRNA Stability

Slide37

RNA

RNA Interference

RNA Interference is a Powerful Means of Controlling Gene Expression

Viral and Endogenous Cellular Genes Are Targets

A Similar System Called piRNA (piwi RNA) Protects Against Transposon

Genes

Considerable Interest in Using Technique to Genetically Transform

Organisms for Protect Against Pathogens

Slide38

RNA

RNA Interference

Cellular Source

Cellular Pre-Processing

Double-Stranded RNA is Stimulus

Target Complementary Sequences in mRNAs

Viral Infection

Transcription

Processing

RISC

RISC

20 bp pieces

Slide39

RNA

RNA Interference

RISC

+

mRNA

Complementary Sequences Align

RISC

Argonaute Activity

in RISC Breaks

mRNA, Stops

Translation

RISC

+

Translation of mRNA Stopped

Slide40

RNA

RNA Interference

Protection Against Invading Viruses

Stimulated by dsRNA

miRNA (cellular) & siRNA (foreign)

Cellular piwi RNAs (piRNA) have similar functions in silencing transposons

Widespread in Eukaryotes

Actions referred to as RNA Interference (RNAi)

RNA Interference Operates Through the Silencing of Gene Expression

DS RNA induces Dicer to chop it into 20 BP Pieces

These siRNAs/miRNAs bind to the RNA Induced Silencing Complex (RISC)

One Strand is Destroyed and One Retained to Bind to Complementary

mRNA sequences

RISC Nuclease Activity (Argonaute)

1. Destroys mRNA Where Strand Binds or

2. siRNA/miRNA strand on mRNA blocks translation or

3. si/RNA/miRNA strand destabilizes mRNA and Targets for Destruction

Slide41

RNA

RNA Interference

Bonding to mRNA

Premature

Stopping of

Translation

Degradation of

mRNA