Transcript Ch 18 -19 Review Lecture

Ch. 18-19 Review Lecture
1. Name the two types of operons
that we have studied and by what
mechanism do they work?
Fig. 18-2
Precursor
Feedback
inhibition
trpE gene
Enzyme 1
trpD gene
Regulation
of gene
expression
Enzyme 2
trpC gene
trpB gene
Enzyme 3
trpA gene
Tryptophan
(a) Regulation of enzyme
activity
(b) Regulation of enzyme
production
2. What are the major parts of an
operon?
Fig. 18-3
trp operon
Promoter
Promoter
Genes of operon
DNA
trpR
Regulatory
gene
mRNA
5
Protein
trpE
3
Operator
Start codon
mRNA 5
RNA
polymerase
Inactive
repressor
E
trpD
trpB
trpA
B
A
Stop codon
D
C
Polypeptide subunits that make up
enzymes for tryptophan synthesis
(a) Tryptophan absent, repressor inactive, operon on
DNA
No RNA made
mRNA
Active
repressor
Protein
trpC
Tryptophan
(corepressor)
(b) Tryptophan present, repressor active, operon off
3. What are the categories for each
type of operon? Define what they
mean.
Repressible and Inducible Operons: Two Types of
Negative Gene Regulation
• A repressible operon is one that is usually
“on”; binding of a repressor to the operator
shuts off transcription
• The trp operon is a repressible operon
• An inducible operon is one that is usually
“off”; a molecule called an inducer
inactivates the repressor and turns on
transcription
Fig. 18-4
Regulatory
gene
Promoter
Operator
lacZ
lacI
DNA
No
RNA
made
3
mRNA
RNA
polymerase
5
Active
repressor
Protein
(a) Lactose absent, repressor active, operon off
lac operon
DNA
lacZ
lacY
-Galactosidase
Permease
lacI
3
mRNA
5
RNA
polymerase
mRNA 5
Protein
Allolactose
(inducer)
lacA
Inactive
repressor
(b) Lactose present, repressor inactive, operon on
Transacetylase
4. Which metabolic pathway does
each operon operate. Explain how?
• Inducible enzymes usually function in catabolic
pathways; their synthesis is induced by a
chemical signal
• Repressible enzymes usually function in
anabolic pathways; their synthesis is repressed
by high levels of the end product
• Regulation of the trp and lac operons involves
negative control of genes because operons are
switched off by the active form of the repressor
5. Name two secondary messengers.
Explain what occurs if lactose is
present but glucose is scarce.
Fig. 18-5
Promoter
Operator
DNA
lacI
lacZ
RNA
polymerase
binds and
transcribes
CAP-binding site
Active
CAP
cAMP
Inactive lac
repressor
Inactive
CAP
Allolactose
(a) Lactose present, glucose scarce (cAMP level
high): abundant lac mRNA synthesized
Promoter
DNA
lacI
CAP-binding site
Inactive
CAP
Operator
lacZ
RNA
polymerase less
likely to bind
Inactive lac
repressor
(b) Lactose present, glucose present (cAMP level
low): little lac mRNA synthesized
6. How many ways can gene
regulation be controlled in the
nucleus? How is DNA controlled?
1. Chromatin Modification
• Histone acetylation occurs
on histones and
increases gene
expression
• DNA methylation occurs
primarily on the DNA and
reduces gene expression.
7. What is important further up
the DNA for transcription?
2. Regulation of Transcription Initiation
• Associated with most eukaryotic genes are
control elements, segments of noncoding
DNA that help regulate transcription by binding
certain proteins
• Control elements and the proteins they bind
are critical to the precise regulation of gene
expression in different cell types
http://vcell.ndsu.edu/animations/transcription/index.htm
Fig. 18-9-3
Promoter
Activators
DNA
Enhancer
Distal control
element
Gene
TATA
box
General
transcription
factors
DNA-bending
protein
Group of
mediator proteins
RNA
polymerase II
RNA
polymerase II
Transcription
initiation complex
RNA synthesis
Fig. 18-8-3
Enhancer
(distal control elements)
Poly-A signal
sequence
Termination
region
Proximal
control elements
Exon
Intron
Exon
Intron Exon
DNA
Upstream
Downstream
Promoter
Primary RNA
5
transcript
Transcription
Exon
Intron
Exon
Intron Exon
RNA processing
Cleaved 3 end
of primary
transcript
Poly-A
signal
Intron RNA
Coding segment
mRNA
3
5 Cap
5 UTR
Start
codon
Stop
codon
3 UTR Poly-A
tail
8. What occurs before the RNA
can leave the nucleus?
3. Mechanisms of Post-Transcriptional Regulation
http://highered.mcgrawhill.com/olc/dl/120080/bio31.swf
9. Explain what function miRNA
serves.
Fig. 18-13
Hydrogen
bond
Dicer
miRNA
mRNA degraded
miRNAprotein
complex
Translation blocked
(b) Generation and function of miRNAs
10. What is the name of the
enzyme that degrades proteins?
Non-Coding RNA and gene expression regulation
11. Give three things that must
occur for a zygote to become an
embryo.
A Genetic Program for Embryonic Development
• The transformation from zygote to adult results
from :
1. Cell division-is the series of mitotic
divisions that increases the number of cells
2. Cell differentiation
3. Morphogenesis
What controls cell differentiation and
morphogenesis?
11. What are the two things that
control morphogenesis?
Fig. 18-15a
Unfertilized egg cell
Sperm
Fertilization
Nucleus
Two different
cytoplasmic
determinants
Zygote
Mitotic
cell division
Two-celled
embryo
(a) Cytoplasmic determinants in the egg
12. How do cells communicate?
Name the four ways.
13. Differentiate between plant and
animal cell communication.
Fig. 18-15b
Early embryo
(32 cells)
Signal
transduction
pathway
Signal
receptor
Signal
molecule
(inducer)
(b) Induction by nearby cells
NUCLEUS
Sequential Regulation of Gene Expression During
Cellular Differentiation
• Determination commits a cell to its final fate
and is irreversible
• Cell differentiation is marked by the production
of tissue-specific proteins (found only in a
specific cell type and give the cell its
characteristic structure and function.
Fig. 18-16-3
Nucleus
Master regulatory gene myoD
Embryonic
precursor cell
Other muscle-specific genes
DNA
Myoblast
(determined)
OFF
OFF
mRNA
OFF
MyoD protein
(transcription
factor)
mRNA
MyoD
Part of a muscle fiber
(fully differentiated cell)
mRNA
Another
transcription
factor
mRNA
mRNA
Myosin, other
muscle proteins,
and cell cycle–
blocking proteins
14. Define pattern formation and
positional formation. Give an
example of a gene involved in this
process.
Pattern Formation: Setting Up the Body Plan
• Pattern formation is the development of a
spatial organization of tissues and organs
• In animals, pattern formation begins with the
establishment of the major axes
• Positional information, the molecular cues
that control pattern formation, tells a cell its
location relative to the body axes and to
neighboring cells
Bicoid: A Morphogen Determining Head
Structures
• One maternal effect gene, the bicoid gene,
affects the front half of the body
• An embryo whose mother has a mutant bicoid
gene lacks the front half of its body and has
duplicate posterior structures at both ends
• An identical or very similar nucleotide sequence has been
discovered in the homeotic genes of both vertebrates and
invertebrates
• Homeotic genes in animals are called Hox genes
– Sometimes small changes in regulatory sequences of certain genes lead to major
changes in body form
– For example, variation in Hox gene expression controls variation in leg-bearing
segments of crustaceans and insects
15. What is cell death? How it is
used in our bodies? Describe.
Apoptosis- programmed cell death
• suicide genes code for products that
activate proteins present in the cell and
cause the self-destruction of the cell
• very common in vertebrate development of
nervous system
-failure of apoptosis in human development -> webbed hands and feet!
16. Are viruses alive? Why?
17. Give the three major parts of a
virus.
Structure of Viruses
• Viruses are not cells
• Viruses are very small infectious particles
consisting of:
1. nucleic acid
2. enclosed in a protein coat
3. in some cases, a membranous envelope
18. Give two examples and describe
the structure of common viruses.
Fig. 19-3
RNA
DNA
Capsomere
Membranous
envelope
RNA
Head
DNA
Capsid
Tail
sheath
Capsomere
of capsid
Glycoproteins
Glycoprotein
18  250 nm
70–90 nm (diameter) 80–200 nm (diameter)
20 nm
50 nm
(a) Tobacco mosaic (b) Adenoviruses
virus
50 nm
Tail
fiber
80  225 nm
50 nm
(c) Influenza viruses (d) Bacteriophage T4
19. Explain why viruses cannot
reproduce forever.
Concept 19.2: Viruses reproduce only in host cells
• Viruses are obligate intracellular parasites,
which means they can reproduce only within a
host cell
• Each virus has a host range, a limited variety
of host cells that it can infect
20. Explain the four step process
of the virus reproductive cycle.
Fig. 19-4
VIRUS
1 Entry and
DNA
uncoating
Capsid
3 Transcription
and manufacture
of capsid proteins
2 Replication
HOST CELL
Viral DNA
mRNA
Viral DNA
http://www.npr.org
/templates/story/st
ory.php?storyId=11
4075029&sc=emaf
Capsid
proteins
4 Self-assembly of
new virus particles
and their exit from
the cell
21. Explain the two phage
reproductive cycles.
Fig. 19-6
Phage
DNA
Daughter cell
with prophage
The phage injects its DNA.
Cell divisions
produce
population of
bacteria infected
with the prophage.
Phage DNA
circularizes.
Phage
Bacterial
chromosome
Occasionally, a prophage
exits the bacterial
chromosome,
initiating a lytic cycle.
Lytic cycle
Lysogenic cycle
The bacterium reproduces,
copying the prophage and
transmitting it to daughter cells.
The cell lyses, releasing phages.
Lytic cycle
is induced
or
New phage DNA and proteins
are synthesized and
assembled into phages.
Lysogenic cycle
is entered
Prophage
Phage DNA integrates into
the bacterial chromosome,
becoming a prophage.
22. Explain the HIV reproductive
cycle.
Fig. 19-8a
Glycoprotein
Viral envelope
Capsid
Reverse
transcriptase
RNA (two
identical
strands)
HOST CELL
HIV
Reverse
transcriptase
• The viral DNA that is
integrated into the host
genome is called a
provirus
Viral RNA
RNA-DNA
hybrid
DNA
•Unlike a prophage, a
provirus remains a
permanent resident of
the host cell
NUCLEUS
Provirus
Chromosomal
DNA
RNA genome
for the
next viral
generation
New virus
mRNA