GENE REGULATION RESULTS IN DIFFERENTIAL GENE EXPRESSION, LEADING TO CELL SPECIALIZATION

Eukaryotic DNA

Epigenetics – Ghost in Your Genes Watch to see how your environment and

your choices influence inheritance… http://www.youtube.com/watch?v=CiAyL

PeCTMU&feature=share&list=PLA2E1F3FFBFAE1CB6

Differential Gene Expression Nucleosome Packing: DNA

wraps around histone proteins to form a structure called a nucleosome. Nucleosomes help pack DNA into eukaryotic chromosomes. When acetyl groups attach to

the histone proteins the DNA in chromosomes loosens to allow for transcription.

The addition of methyl groups to histone proteins can cause DNA to condense thus preventing transcription.

In Genomic Imprinting, methylation regulates expression of either the maternal or paternal alleles of certain genes at the start of development.

Fig. 18-8-3

Enhancer(distal control

elements)

Proximalcontrol

elements

Poly-A signal

sequenceTermination

region

DownstreamPromote

r

Upstream

DNAExonExon ExonIntro

nIntro

n

Exon Exon ExonIntron

Intron Cleaved 3

endof primarytranscript

Primary RNA

transcript

Poly-A

signal

Transcription

5 RNA

processingIntron

RNA

Coding segmentmRN

A5

Cap

5 UTR

Startcodon

Stopcodon 3

UTR

Poly-A

tail

3

Organization of Typical Eukaryotic Genes

The Roles of Transcription Factors Regulatory Proteins, repressors and

activators, operate similarly to those in prokaryotes, influencing how readily RNA polymerase will attach to a promoter region. In many cases, numerous activators are acting in concert to influence transcription.

Fig. 18-9-3

Enhancer

TATA

box

Promoter

ActivatorsDN

A

Gene

Distal control

element

Group ofmediator

proteins

DNA-bending

protein

Generaltranscripti

onfactors

RNApolymerase

II

RNApolymerase

II

Transcriptioninitiation

complexRNA

synthesis

Coordinately controlled eukaryotic genes

A particular combination of control elements can activate transcription only when the appropriate activator proteins are present.

All cells of an organism have all chromosomes/genes but certain genes are only active in certain cells. The transcription factors present in the cell determine which genes will be active and which won’t (but they are both still present)

Fig. 18-10

Controlelemen

ts

Enhancer

Available

activators

Albumin gene

(b) Lens cell

Crystallin gene

expressed

Available

activators

LENS CELLNUCLEUS

LIVER CELL

NUCLEUS

Crystallin gene

Promoter

(a) Liver cell

Crystallin gene

not expressed

Albumin gene

expressed

Albumin gene

not expressed

Post Transcriptional Regulation Alternate Gene Splicing - different

mRNA molecules are produced from the same primary transcript, depending on which RNA segments are treated as exons and which as introns

Fig. 18-11

or

RNA splicing

mRNA

PrimaryRNAtranscri

pt

Troponin T gene

Exons

DNA

Noncoding RNAs role in gene expression

RNA Interference, noncoding RNAs play multiple roles in controlling gene expression. MicroRNAs (miRNAs) and Small inserting RNAs (siRNAs) are small single-stranded RNA molecules that can bind to mRNA. These can degrade mRNA or block its translation. The difference between the two is that they form from different RNA precursors.

Fig. 18-13

miRNA-proteincomple

x(a) Primary miRNA

transcript

Translation blocked

Hydrogen

bond

(b) Generation and function of miRNAs

Hairpin

miRNA

miRNA

Dicer

3

mRNA degraded

5