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
6. •Eukaryotic genomes have much more DNA
than prokaryotes do
•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
10. •Histones are proteins that are like spools that DNA
wraps around
•A
nucleosome
is a section
of DNA
wrapped
around 2
histones.
11.
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
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
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
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
31.
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