Transcript CHAPTER 11: Gene Expression

CHAPTER 11: Gene Expression
Recall that gene information
codes for the proteins a cell
needs for structure &
function.
**But not all proteins are
needed all the time.
**How does a cell control
when & which proteins
are made???
http://upload.wikimedia.org
I. Control of Gene Expression
A. Gene Expression-Is the activation,
or “turning on” of a gene that results in
transcription & the production of mRNA.
• Most of the mRNA is then
translated into proteins.
• Genome- is the complete
genetic material contained in
an individual.
B.
Prokaryotic Gene Expression
• Since prokaryotes are simpler cells (single
ring of DNA- no nucleus)- they are easier to
study.
• Scientists-Francois Jacob & Jacques Monod
– in the 1960’s studied E. coli.
– discovered how E. coli genes
– control the metabolism of
sugar (lactose).
– Won noble prize 1965.
http://zebu.uoregon.edu/~imamura/121/images/e_coli.gif
• Operon- a series of genes that code for
specific products plus the regulatory
elements that control these genes.
• Lac operon – is the operon in E. coli that
codes for enzymes that regulate lactose
metabolism.
Parts of the lac operon & their purpose:
1. Structural genes: genes that code for
polypeptides.
–
In E. coli, there are 3
structural genes right
next to each other- these code for the 3 enzymes
that are needed to break up lactose (a disaccharide)
into 2 monsaccharides ( glucose & galactose)
http://dspace.dial.pipex.com/town/park/gfm11/nomilkgif/LACTOSE.JPG
2. Promoter- a nucleotide sequence on a
DNA molecule that is recognized by the
enzyme RNA polymerase (& is where it
binds), that initiates the transcription of a
specific gene.
3. Operator – a short sequence of
bacterial (or viral) DNA to which a repressor
binds to prevent transcription (mRNA
synthesis) of the adjacent gene in an operon.
Lactose Metabolism
http://www.phschool.com/science/biology_place/biocoach/images/lacoperon/pluslac2.gif
Turing Operons on & off
depends on presence of lactose.
• Inducer- molecule that (if lactose is present)
– turns on the gene with its 3 structural proteins
– to start translating which makes 3 enzymes
needed to break up lactose
• Repressor protein turns gene off
– If no lactose is present- inhibits genes from
being expressed.
– The repressor protein is coded for by a
regulator gene.
C. Eukaryotic Gene Expression
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Very Different than prokaryotes.
Eukaryotes MUCH more complex.
Operons rarely used.
Multicellular,
Specialized cells
– Some cells use different proteins
– not all genes expressed at times
1. Eukaryotic Gene Structure
• Chormosomes- tightly coiled DNA for
cell division.
– Some DNA remains tightly coiled & is not
transcribed.
– Some DNA uncoils- allows
transcription
• Euchromatin- uncoiled
DNA molecule– Site of active transcription
http://www.llnl.gov/str/June03/gifs/Stubbs1.gif
Turning “on” Different than Prokaryotes
• Beyond promotor = 2 sections of DNA
• Introns- DNA section that is transcribed but not
translated.
• Exons –DNA section that is transcribed AND translated.
Control After Transcription
• In eukaryotic nucleus:
-Pre-mRNA is large molecule of both
introns & exons.
-Splicing of introns results in mRNA
• mRNA leaves nucleus & goes into cytoplasm
where transcription takes place.
• Transcription factors – regulatory proteins
• Enhancers- located far from promoter, helps
activate promoter.
Section 1 Review Questions p. 222
http://gremlin1.zool.iastate.edu/~volker/img/ps-fig.jpg
II. Gene Expression in
Development & Cell Division
• All multicellular, sexually reproducing
organisms begin life as a zygote (fertilized egg).
• Cell Differentiation- the
development of cells that have specialized
functions.
• Morphogenesis- the development of
form in an organism.
Homeotic Genes
• Regulatory genes that determine where
certain anatomical structures, such as
appendages, will develop in an organism
during morphogenesis.
• Considered “master genes” of development.
• How they work:
– Make regulatory proteins– switch on certain genes– controls growth rate in specific areas
– Produces structural development.
Homebox Sequences
• A DNA sequence within a
homeotic gene that
regulates development in
animals.
• Example –Fruit Fly (Drosphilia sp.)
– Specific homeoboxes control
regional morphogenesis.
– Can manipulate in lab – or if natural
mutation- abnormality results.
*Throughout an organism’s life:
– Genes are switched on & off
– Only a fraction of genes are expressed in any 1
cell.
*DNA chip- tool used to track gene
expression.
-DNA fragments are “tagged” with a florescent
compound & when mRNA is studied- look for
“light-up” segments.
-useful especially in medicine, cancer study.
III. Cancers
• Tumor- abnormal proliferation of cells.
• Benign Tumor- growth of cells that
remains within a mass. (doesn’t spread)
• Cancer- uncontrolled growth of cells that can
invade other parts of the body.( spreads- more
dangerous, deadly)
2 ways to suppress uncontrolled
cell growth.
• Tumor suppressor genes – code for
proteins that prevent uncontrolled cell division.
• Proto-oncogenes- code for proteins that
help regulate cell division.
– are genes which regulate cell growth.
– Ensure events occur properly.
A mutation can causes changes in proto-oncogenes or
tumor suppressor genes - turns them into Oncogenes.
Onogene- gene can cause uncontrolled cell growth.
• Metastasis- spread of cancer cells beyond original
site.
• Carcinogen- any substance that can induce or
promote cancer.
• Mutagen- agents that cause changes in the cell.
Types of cancers
• Carcinoma- growth in the skin, tissues
that line the organs of the body.
• Sarcomas- grow in bone, muscle tissue.
• Lymphomas- solid tumors in lymphatic
system tissue.
• Leukemia- uncontrolled production of
white blood cells.
http://www.cancer-info.com/cancer.gif