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Chapter 11: How Genes Are Controlled

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Jay Jolito

on 11 February 2016

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Transcript of Chapter 11: How Genes Are Controlled

Chapter 11: How Genes Are Controlled
Control of Gene Expression
Animal and Plant Cloning
Genetic Basis of Cancer

Control of Gene Expression
gene regulation
- turning genes on and off
gene expression
- overall process of flow of genetic information from DNA to proteins
operon
- a functional unit containing a cluster of genes controlled by a single promoter
- TYPES: inducible and repressible
promoter
- control sequence where RNA polymerase attaches and starts transcription
operator
- control sequence between the promoter and the genes; acts as an "on and off" switch
repressor
- a protein that binds to the operator to prevent RNA polymerase from working on the promoter; produced by regulatory genes
trp operon - an example of a repressible operon
In eukaryotes, gene expression is a little more complex.
chromosomal DNA need to be unpacked
like prokaryotes, they use repressor and promoter proteins
genes are not generally clustered as operons
requires a complex interaction of regulatory proteins to turn genes on and off
transcription factors
- proteins that control which genes are switched on or off
enhancer
- control sequences in DNA
promoter region
- segment of DNA that initiates transcription
DNA-bending proteins
- bring activators closer to the promoter region of DNA

RNA Splicing
- once transcribed, an RNA molecule has to be processed
RNA PROCESSING INCLUDES:
adding a cap and tail to prevent cleavage, facilitate transport and initiate translation
removal of introns
splicing together remaining exons
detachment from splicing machinery
ALTERNATIVE SPLICING
- when an mRNA can be spliced in different ways to form different proteins
OTHER RNA ARE TRANSCRIBED TO FORM tRNA AND rRNA.
microNRNA
miRNA
- small RNA sequences that binds to complementary sequences on mRNA molecules
HOW IT WORKS:
Form a complex with one or more proteins.
Bind to an mRNA molecule with 7-8 complementary bases.
Complex either degrades the mRNA or blocks its translation
RNAi - RNA interference
used as a molecular biology technique where designed miRNA is injected into the cell to inhibit the expression of certain genes
may have evolved naturally as a defense against RNA viruses
REGULATION IN LATER STAGES OF GENE EXPRESSION
mRNA Breakdown
- occurs a few minutes in bacteria; occurs in a few hours to a few weeks in eukaryotes;mammalian hemoglobin lasts for about 4 months
Initiation of Translation
- carried out by regulatory and/or promoter proteins
Post-translational Regulation
Protein activation
- cleavage of polypeptide
Protein Breakdown
- occurs to prevent an excess of proteins
cell differentiation
- the process by which less specialized (generic stem cell) becomes more specialized
In the head of the
Drosophila melanogaster
(fruit fly):
occur in the parent's ovaries
mRNA synthesis at one end of the unfertilized egg
Post-fertilization, cell signaling triggers development
Subdivision of the embryo into segments
Homeotic genes, which are master control genes, organize development.
Homeotic genes instructs cells in the head to form antennae and cells in the thorax to form legs.
error in gene expression
DNA microarray
genome-wide gene expression studies
used to determine:
which genes are transcribed in a particular situation
coordination in gene expression
SOME USES:
classifying leukemia into its subtypes
comparing patterns of gene expression in breast cancer tumors and noncancerous breast tissue
MAY result in the development of personalized medical treatment
can reveal general profiles of gene expression
SIGNAL TRANSDUCTION PATHWAY
A series of molecular changes that converts a signal on a target cell's surface to specific responses inside the cell
lac operon

lactose operon
inducible operon
required for the transport and metabolism of lactose in Escherichia coli and some other enteric bacteria
has three adjacent structural genes:
lacZ
lacY
lacA.

STEPS (simplified):
The cell sending a signal secretes the signaling molecule.
Molecule binds to a receptor on the target cell.
Molecule binding triggers a series of relay proteins that triggers expression of a particular gene.
Protein synthesis produces a protein that will carry out the function originally called for by the signal.
CLONING
- the process of producing organisms that are GENETICALLY IDENTICAL to the original
cloning of a carrot
QUESTION:
Based on the image of the carrot, would you say that:
a. unexpressed genes get permanently disabled.
b. unexpressed genes retain the potential to be
expressed
WHY???
Plant cloning is used extensively in agriculture.
seedless grapes, bananas and watermelon
increases fruit yield
ensures quality
promotes pest resistance
CLONING IS MORE COMPLICATED IN ANIMALS!
REGENERATION - the regrowth of lost body parts
REPRODUCTIVE CLONING
- cloning of a whole organism
- in animals, carried out by nuclear transfer
Therapeutic Cloning
- production of embryonic stem cells that can give rise to different types of specialized cells
CANCER
- 2nd leading cause of death in industrialized nations
- overall rate increases at about 1%/decade
MAY RESULT FROM:
oncogene
- cancer gene
mutated tumor-suppressor gene
chance
carcinogen
- cancer-causing mutagens
- may cause mutations and/or promote rapid cell
division
mutagen
- agent that alters DNA
X-ray
UV
TOBACCO
- causes more cases and types of cancer than any other carcinogen
TYPES OF CANCER THAT CAN EASILY BE DETECTED:
skin and oral cancer
-
by physical exam
breast cancer
-
by self examinations and mammograms
prostate
-
by rectal exam
cervix
-
by Pap smear
testicular
-
by self-exam
colon
-
by colonoscopy
(small nuclear
ribonucleoproteins)
Full transcript