• Proteins
• Transcription (DNA to mRNA)
• Translation (mRNA to tRNA to proteins)
• Gene expression/regulation (turning genes on and off)
• Viruses
1

1) Fill in the blanks.
2) What is the amino acid sequence corresponding to the
DNA and RNA sequences below?
Met-Leu-Arg-Asn
Template DNA 3 ’ T A C A A T G C A T T G __’
Non-Template 5 ’ A T G T T A C G T A A C __’ mRNA 5’ A U G U U A C G U A A C 3’

• What is gene regulation? Why do cells do it?
• How genes are regulated
– Bacteria
– Eukaryotes
• Mechanisms of Development
3

Is the DNA in this cell
Different From this one?
Or this one?
4

What is gene regulation?
• Turning genes on and off in the right time and place
• Controlling the quantity of proteins produced
5

Why do genes need to be regulated?
• Every cell in our body has the same set of genes
• Our body consists of trillions of cells and millions of distinct cell types .
 What makes a skin cell different from a liver cell?
6

Why do genes need to be regulated?
1. Differentiated structures/organs
2. Not all of a single cell’s functions are needed all the time (e.g. we shouldn’t make insulin constantly)
7

Why do genes need to be regulated?
1.
Differentiated structures/organs
2.
Not all of a single cell’s functions are needed all the time (e.g. we shouldn’t make insulin constantly)
3.
Waste of energy/molecules to express genes whose products are not needed
8

Why do genes need to be regulated?
1.
Differentiated structures/organs
2.
Not all of a single cell’s functions are needed all the time (e.g. we shouldn’t make insulin constantly)
3.
Waste of energy/molecules to express genes whose products are not needed
4.
Some functions are mutually exclusive; two enzymes may have opposite functions
9

Examples: different cell types within a human
• Muscle cells express muscle actin and myosin
• Hair and nail cells express keratin
• Blood cells express hemoglobin
10

• What is gene regulation? Why do cells do it?
• How genes are regulated
– Bacteria
– Eukaryotes
• Mechanisms of Development
11

“…Consider, for instance, an individual E. coli cell living in the...human colon, dependent for its nutrients on the whimsical eating habits of its host” textbook, p. 352 express genes for tryptophan synthesis tryptophan present?
NO
HOW?
need to synthesize tryptophan
YE
S no need to synthesiz e tryptoph an 12

 Molecules can act as signals by directly influencing transcription
13

How does this really work?
Example: E. coli regulation of tryptophan
14

If something is present, don’t make more of it!
-
Negative Feedback
15
Sweatblock.com; netropolus.com

Gene regulation in bacteria
Operator: the “on-off switch” that controls the access of RNA polymerase to the genes
Operon: promoter, operator, and genes
16

(2) expressing the genes of the operon at the right time
For the trp operon, RNA polymerase can bind when nothing is bound to the operator
17

(2) expressing the genes of the operon at the right time
18

(2) expressing the genes of the operon at the right time
A system of negative feedback
19

(2) expressing the genes of the operon at the right time
How do we stop repression?
• Binding of tryptophan to repressor is reversible
• Repressor activation/deactivation depends upon relative concentrations of tryptophan and repressor protein
20

• What is gene regulation? Why do cells do it?
• How genes are regulated
– Bacteria
– Eukaryotes
• Mechanisms of Development
21

Differential Gene Expression
• Differences between cell types result from differential gene expression
(a) Fertilized eggs of a frog
(b) Newly hatched tadpole
22

Fig. 18-6
Signal
NUCLEUS
Chromatin
Chromatin modification
DNA
Cap
RNA
Gene available for transcription
Gene
Transcription
Exon
Primary transcript
Intron
RNA processing
Tail mRNA in nucleus
Transport to cytoplasm
CYTOPLASM mRNA in cytoplasm
Translation
Degradation of mRNA
Polypeptide
Protein processing
Degradation of protein
Active protein
Transport to cellular destination
Cellular function
In eukaryotes, gene expression can be regulated at many different stages.
23

Fig. 18-6a
Signal
NUCLEUS
Chromatin
Chromatin modification
DNA
Cap
RNA
Gene available for transcription
Gene
Transcription
Exon
Primary transcript
Intron
RNA processing
Tail mRNA in nucleus
Transport to cytoplasm
CYTOPLASM
24

Fig. 18-6b
Degradation of mRNA
Degradation of protein
CYTOPLASM mRNA in cytoplasm
Translation
Polypeptide
Protein processing
Active protein
Transport to cellular destination
Cellular function
25

How is transcription regulated in eukaryotes?
Promoters and introns aren’t the only non-coding regions of DNA!
Meet the Enhancers :
26 http://bja.oxfordjournals.org

How is transcription regulated in eukaryotes?
Meet the Enhancers :
• DNA control regions corresponding to a specific gene
• Can be upstream, downstream, or in an intron
• Comprised of control elements
Lens enhancer
Control Elements
Promoter
Liver enhancer
Lens gene (crystallin)
Liver gene (enzyme)
27

How is transcription regulated in eukaryotes?
How does a DNA region control a gene?
• Through activators specific to each control element
• Activators are specialized transcription factors (proteins)
Lens enhancer
Control Elements
Promoter
Liver enhancer
Lens gene (crystallin)
Liver gene (enzyme)
28

Would you go down this: sfomom.blogspot.com; sabotagetimes.com
Without this?
29

30

Liver activators
Lens enhancer
Liver enhancer
Liver cell
Pro.
Pro.
Lens gene (crystallin)
Liver gene (enzyme)
Lens cell
Lens activators
Liver gene ON
Lens gene OFF
Liver gene OFF
Lens gene ON
Animation
31

• What is gene regulation? Why do cells do it?
• How genes are regulated
– Bacteria
– Eukaryotes
• Mechanisms of Development
– Example of malformed frogs
32

1. Determination and Differentiation
2. Getting the right parts in the right places:
Pattern formation
33

Zygote embryonic development
34

1. Differentiation and determination
(a) Fertilized eggs of a frog one zygote
(b) Newly hatched tadpole
   many cell types, tissues, organs cell division (mitosis), differentiation, morphogenesis
The key is differential gene regulation
35

1. Differentiation and determination
The process of development: some useful terms
When I grow up I will be a heart cell!
Hello, my name is
Celly
Better start making actin and myosin!
Hello, my name is
Celly
Hello, my name is
Celly
You’re a heart cell too! Yay!
Hello,
Cella

37

1. Differentiation and determination
TWO COMPLEMENTARY MECHANISMS of
DIFFERENTIATION
• Cytoplasmic Determinants
 before fertilization, when eggs are made
 maternally derived
• Inductive Signals
 once there are multiple cells
 substance from outside a cell (e.g., signal from nearby cell) influences cell’s gene expression
38

Unfertilized egg
Sperm
Nucleus
Fertilization
Two different cytoplasmic determinants
Zygote
Mitotic cell division
Two-celled embryo
(a) Cytoplasmic determinants
39

1. Differentiation and determination
Early embryo NUCLEUS
Chain reaction
Signal receptor
Signal molecule
(inducer)
(b) Induction by nearby cells
40

Nucleus master regulatory gene myoD
Embryonic precursor cell
DNA
OFF
Other muscle-specific genes
OFF has potential to develop into a variety of different cell types
41

Embryonic precursor cell
Nucleus master regulatory gene myoD
DNA
OFF
Other muscle-specific genes
OFF
Muscle cell precursor
(determined) mRNA
MyoD protein
(transcription factor)
OFF
42

Nucleus
Embryonic precursor cell master regulatory gene myoD
DNA
OFF
Other muscle-specific genes
OFF
Muscle cell precursor
(determined) mRNA
MyoD protein
(transcription factor)
OFF mRNA mRNA
Part of a muscle fiber
(fully differentiated cell)
MyoD Another transcription factor mRNA mRNA muscle proteins
43

1. Determination and Differentiation
2. Getting the right parts in the right places:
Pattern formation
44

How do you get the right tissues/organs in the right places???
Eye
Antenna
Wild type
Leg
Mutant
45

Pattern Formation: Setting Up the Body Plan
• Pattern formation = development of spatial organization of tissues and organs
 establishment of major body axes
• Positional information = molecular cues that tell a cell its location
46

Cytoplasmic determinants in eggs are products of maternal effect genes (a.k.a. egg polarity genes ) unevenly distributed RNA, proteins (from mother)
Unfertilized egg
47

A closer look at the formation of the anterior-posterior (head-tail) axis: the bicoid gene
Presence of bicoid protein = “put head here”
OR
Lack of bicoid protein = “head does not go here”
48

Cytoplasmic determinants in eggs are products of maternal effect genes (a.k.a. egg polarity genes ) mutation in maternal effect gene unevenly distributed RNA, proteins (from mother)
Unfertilized egg
49


Gradient of bicoid protein determines anteriorposterior axis
50

• Gene expression can be regulated at many stages
• Transcription regulation is a common mechanism
• Eukaryotes use enhancers and activators for differential gene expression
• Protein concentrations from mom’s egg play a key role in development
51

Describe, in your own words, the role of enhancers and activators in eukaryotic gene regulation.
52