regulation of gene expression in eukaryotes

1. Chapter 19:Chapter 19:
EukaryoticEukaryotic Genomes-Genomes-
Organization,Organization,
Regulation, & EvolutionRegulation, & Evolution

2. Objectives for this lecture
1. Understand how DNA is organized, and how that
organization helps us control gene expression
2. Understand how regulation of transcription helps
us control gene expression
3. Understand how regulation of translation helps us
control gene expression

3. Terms Definitions
1. Gene expression
2. Regulation
3. Transcription
4. Translation
5. mRNA
6. Protein
A. Controls, rules
B. Produced during
transcription
C. DNA  RNA  protein
 cell product
D. The product of
translation
E. DNA  mRNA
F. mRNA  protein
Warm up, matching

4. for your notes…
Underlined and
colored text most
critical

5. HOW DNA IS
ORGANIZED
Section 1

6. •Eukaryotic genomes have much more DNA than
prokaryotes genomes
•Eukaryotic DNA must be specially organized to
maintain efficiency
Chromatin:
DNA
wrapped
around
protein

7. Chromatin Structure is Based on
Successive Levels of DNA Packing
DNA in a eukaryotic chromosome
White center =
main axis of the
chromosome
Red loops = DNA
that is being
actively
transcribed

8. •A special problem: All prokaryotic & eukaryotic
cells must be able to express certain genes as needed
•All cells contain the same, complete set of DNA
•Cells are different because they EXPRESS different
genes

9. DNA organization changes throughout the cell cycle:

10. •Histones are proteins that are like spools that DNA
wraps around
•A
nucleosome
is a section
of DNA
wrapped
around 2
histones.

12. Higher Levels of DNA Packing
•The 10nm fiber continues to coil to 30nm as linker
DNA attracts to histone tails and the H1 histone

13. Higher Levels of DNA Packing
•The 30nm fiber then
forms looped domains
•Protein scaffolds are
made of non-histone
proteins
•Looped domains
compact further to form
the characteristic
metaphase chromosome

14. Regulation of Chromatin StructureRegulation of Chromatin Structure
•Genes in highly condensed heterochromatin are
usually not expressed
•Genes in the looser packing of euchromatin usually
are expressed

15. DNA MethylationDNA Methylation
•Genes that are not expressed are usually heavily
methylated

16. Acetyl groups bind to
histone tails, keep the
DNA loose so
transcription can
happen
Histone AcetylationHistone Acetylation

17. QUICK THINKQUICK THINK
Draw the levels of
organization of
DNA, putting methyl
and acetyl groups on
the DNA to show
hetero and
euchromatin

18. Now you explain it

19. REGULATION OF GENE EXPRESSION BY CONTROL OF
TRANSCRIPTION
Section 2

20. First, a review of genes & their transcripts:
promoter
1. Transcription begins when a cluster of proteins called
a transcription initiation complex binds to the of the gene
RNA pol II2. The enzyme transcribes the gene into a molecule of
pre-mRNA
a 5’ cap & poly-A tail3. RNA processing includes the addition of
as well as cutting out the introns

21. Control elements : sequences of non-coding DNA that
regulate transcription by binding to certain proteins.
*They are often found upstream of eukaryotic genes

22. Proximal control elements• _________________________ are close to the promoter
•__________________________ , AKA enhancers, are farther away
and can even be within introns
Distal control elements

23. LE 19-6
Distal control
element Activators
Enhancer
DNA
DNA-bending
protein
TATA
box
Promoter
Gene
General
transcription
factors
Group of
mediator proteins
RNA
polymerase II
RNA
polymerase II
RNA synthesis
Transcription
Initiation complex

24. RNA Processing
The original RNA transcript can
produce various mRNAs depending
on which part of the pre-mRNA is
treated as introns & which are treated
as exons

25. mRNA DegradationmRNA Degradation
Enzymes may
remove the 5’ cap
& the poly-A tail.
This exposes the
mRNA to
nucleases that
break it down.

26. microRNAs (miRNAs)
miRNAs are single-stranded RNA molecules that bind to mRNA
to either degrade the mRNA or block translation
miRNA starts off as a segment of RNA
that is H-bonded to itself, then it gets
chopped into smaller pieces by an
enzyme called dicer

27. REGULATION AFTER TRANSCRIPTION HAS OCCURRED
Section 3

28. Post-Transcriptional RegulationPost-Transcriptional Regulation
Protein production
can be controlled
at other points
before the protein
becomes fully
functional

29. Regulation of Translation
Regulatory proteins may bind to the 5’ end of mRNA,
which makes the ribosome unable to attach

30. Protein Processing & Degradation
•Proteins that are to be degraded are tagged with a ubiquitin
marker protein
•Giant protein complexes called proteasomes recognize and
break down the tagged proteins

32. LE 19-3
Signal
NUCLEUS
DNA
RNA
Chromatin
Gene available
for transcription
Gene
Exon
Intro
Transcription
Primary transcript
RNA processing
Cap
Tail
mRNA in nucleus
Transport to cytoplasm
CYTOPLASM
mRNA in cytoplasm
Translation
Degradation
of mRNA
Polypeptide
Cleavage
Chemical modification
Transport to cellular
destination
Degradation of protein
Active protein
Degraded protein
Eukaryotic gene
expression can
be controlled at
multiple steps
1.
2.
3.
4.
5.
6.

33. QUICK THINK
Once mRNA is in the cytoplasm, describe some ways that
regulate the amount of active protein in the cell