Regulation of Gene Expression

Page
4

transcribes

Inactive lac

repressor

lacZ

Operator

Promoter

DNA

CAP-binding site

lacI

RNA

polymerase less

likely to bind

Inactive

CAP

(a) Lactose present, glucose scarce (cAMP level

high): abundant lac mRNA synthesized

Slide 22

Concept 18.2: Eukaryotic gene expression can be regulated at any stage

All organisms must regulate which genes are expressed at any given time

In multicellular organisms gene expression is essential for cell specialization

Slide 23

Differential Gene Expression

Almost all the cells in an organism are genetically identical

Differences between cell types result from differential gene expression, the expression of different genes by cells with the same genome

Errors in gene expression can lead to diseases including cancer

Gene expression is regulated at many stages

Slide 24

Fig. 18-6

DNA

Signal

Gene

NUCLEUS

Chromatin modification

Chromatin

Gene available

for transcription

Exon

Intron

Tail

RNA

Cap

RNA processing

Primary transcript

mRNA in nucleus

Transport to cytoplasm

mRNA in cytoplasm

Translation

CYTOPLASM

Degradation

of mRNA

Protein processing

Polypeptide

Active protein

Cellular function

Transport to cellular

destination

Degradation

of protein

Transcription

Slide 25

Fig. 18-6a

DNA

Signal

Gene

NUCLEUS

Chromatin modification

Chromatin

Gene available

for transcription

Exon

Intron

Tail

RNA

Cap

RNA processing

Primary transcript

mRNA in nucleus

Transport to cytoplasm

CYTOPLASM

Transcription

Slide 26

Fig. 18-6b

mRNA in cytoplasm

Translation

CYTOPLASM

Degradation

of mRNA

Protein processing

Polypeptide

Active protein

Cellular function

Transport to cellular

destination

Degradation

of protein

Slide 27

Regulation of Chromatin Structure

Genes within highly packed heterochromatin are usually not expressed

Chemical modifications to histones and DNA of chromatin influence both chromatin structure and gene expression

Slide 28

Histone Modifications

In histone acetylation, acetyl groups are attached to positively charged lysines in histone tails