Transcript Gene Expression

Gene Expression
via Modern Biology
The activation of a gene that results
in the formation of a protein
Gene expression
• Proteins have different functions
• Some proteins form a structural role
• Others proteins are enzymes that act as
catalysts to speed up chemical reactions
• Proteins are produced when needed
Genome
• The complete genetic material in an individual
• Gene expression occurs through transcription and
translation
• Gene expression begins when the enzyme RNA
polymerase transcribes the DNA nucleotide
sequence of a gene into a specific mRNA
• During translation, this mRNA migrates to a
ribosome to be translated into a specific protein.
Gene Expression in Prokaryotes
(simple, single celled organisms)
• Structural genes are genes that code for particular
polypeptides
• Promoter recognizes the enzyme RNA polymerase and
promotes transcription
• Operator is a DNA segment that is a binding site for an
inhibitory protein that blocks transcription and
prevents the synthesis of protein.
• Promoter + Operator = Operon: series of genes that
code for specific products and the elements that
regulate or control these genes. Ex: lac operon are
structural genes coded for the enzymes that regulate
lactose metabolism.
Prokaryote Gene Expression con’t.
• Repressor protein: inhibits a specific gene
from being expressed, the blocking of
transcription by the action of this protein is
repression
• Transcription is controlled by a regulator gene
• Inducer: initiates gene expression
• Activation is the initiation of transcription by
the removal of a repressor protein
Gene expression in Eukaryotes
( multicellular organisms)
• Genomes are much larger than Prokaryotes
• DNA is located in several individual
chromosomes
• Cells are specialized and differentiated
Eukaryotic Gene Structure
• Euchromatin: the uncoiled part of a
chromosome where active transcription of
DNA and RNA take place
• Introns: The sections of a structural gene that
do not code for amino acids
• Exons: The sections of a structural gene that
are translated into proteins when expressed
Control after Transcription
• Introns and exons are transcribed to form PremRNA. Enzymes cut out the introns and join
remaining exons together forming mRNA. This
leaves the nucleus and travels through the
nuclear pore to the cytoplasm where
translation occurs.
Enhancer control
• Enhancer are noncoding control sequences that
produce transcription, this must be activated for
its associated gene to be expressed.
• Transcription factors bind to enhancers and RNA
polymerase to regulate transcription
• Many enhancers are located far away from their
genes they need to activate.
• Transcription factors bend the DNA strand to
bring the enhancer close to the RNA polymerase
so transcription can begin.
Cell Differentiation
• The development of cells having specialized
function
• Morphogenesis is the growth and development
of these organs and tissue into an organism
• Homeotic genes are regulatory genes that
determine where certain anatomical structures
like appendages will develop in an organism
• Homeobox is the specific DNA sequence that
regulates patterns of development.
Cancer
• A tumor is uncontrolled, abnormal cell
division
• Benign tumors remain within a mass and are
usually not life threatening
• Malignant tumors are uncontrolled dividing
cells that invade and destroy healthy tissues
all over the body.
• Metastasis is the spread of the cancer beyond
their original site
Kinds of Cancer
• Carcinomas grow in the skin and tissues that
line the organs
• Sarcoma grow in bone and muscle tissue
• Lymphomas are solid tumors that grow in the
tissue that form blood cells
• Leukemia are tumors in blood forming tissues
that produce an uncontrolled amount of white
blood cells
Causes of Cancer
• Normal cells will stop dividing when crowded,
cancer cells keep dividing ignoring the cellular
message
• Growth factors are not controlled in a proper
sequence at a proper rate which are mutations in
gene expression.
• Carcinogens increase the risk of cancer
• Mutagens are carcinogens that cause mutations
to occur.
• Usually more than one mutation is needed to
produce cancer
Oncogenes
• They are a gene that causes cancer or other
uncontrolled cell growth
• Proto-oncogenes are normal genes that
control a cells growth and differentiation
• Tumor-suppressor genes code for proteins
that prevent uncontrolled rate of cell division.
• Viruses can cause cancer and stimulate
uncontrolled cell growth and mutations.