Transcript DNA and Gene Expression

DNA and Gene
Expression
DNA
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Deoxyribonucleic Acid
Double helix
Carries genetic information
Located in the nucleus
The monomer is a nucleotide
– A phosphate
– A ribose sugar
– A nitrogenous base
What are the bases in DNA
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A – adenine
T – thymine
C – cytosine
G – guanine
Base pair rules
Where is DNA located in the Cell?
Where are the genes located?
Genes are located on
the chromosomes.
 Every species has a
different number of
chromosomes.
 There are two types
of chromosomes:
autosomes and sex
chromosomes
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Genes are located on the chromosomes
which are found in the nucleus of a cell.
 When a cell is undergoing cell
reproduction, the chromosomes are
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visible. Chromosomes appear when the
chromatin condenses and become visible.
What is gene expression?
Gene expression is the
activation of a gene
that results in a
protein.
Gene expression takes place differently
in prokaryotes and eukaryotes.
What is a prokaryotes? Eukaryotes?
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Prokaryotes
– No membrane bound
organelles (nucleus)
– More primitive
organisms
– Only one circular
chromosome
– Bacteria are the only
organisms that are
prokaryotes.
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Eukaryotes
– Membrane bound
organelles ( specialize in
function –nucleus,
mitochondria, chloroplast)
– Chromosomes are in pairs
and not circular
– All organisms that are not
bacteria: protist, fungi,
plants and animals
In Eukaryotes, following mitosis or meiosis, DNA
recoils but certain regions remain relaxed for
transcription. The areas of relaxed DNA are
called euchromatin.
 Transcription is the
Reading of the DNA and
Changing the code to
mRNA.
 Translation is changing
The mRNA into a trait by
Using tRNA to interpret the
mRNA.
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DNA in eukaryotes has regions of coding and
noncoding DNA. The regions of DNA that code
for proteins or traits are called EXONS, while
the regions that do not code for proteins are
called INTRONS.
cytoplasm
cytoplasm
In prokayotes, transcription and
translation occur in the cytoplasm.
 In eukaryotes, transcription occurs inside
the nucleus in a two step sequence of
events.
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– Pre-mRNA includes both introns and exons for
the gene.
– mRNA is only the coding portion (exons).
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Translation occurs in the cytoplasm at the
ribosomes.
– Reminder: The are three (3) types of RNA
 Messenager (mRNA)
 Transfer (tRNA)
 Ribsomal (rRNA)
Translation
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RNA
– Single stranded
– Does not contain thymine
but has uracil instead.
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tRNA carries 3 base pair
code for specific amino
acid.
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One or more polypeptide
chains compose a
protein
proteins provide the
“blueprints” for our
characteristics and
functions.
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In Prokaryotes there are three (3)
regulatory elements that control gene
expression.
1. Structural genes – genes that code for a
specific polypeptide (protein).
2. Promoter – DNA segment that recognizes
RNA polymerase.
3. Operator – element that serves as a binding
site for an inhibitor protein that blocks
transcription.
Enhancer Control
Eukaryote genes on a
DNA strand also have
noncoding control
sequences that
facilitate transcription.
 These are called
enhancers.
 Transcription factors
are additional proteins
that bind to RNA
polymerase and
enhancers to help with
transcription.
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Cell Differentiation
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Cell differentiation is the development
of cells into cells with specialized
functions.
– Examples: muscle cells, liver cell, red blood
cells
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As organisms grow and develop, organs
and tissues develop to produce a
characteristic form. The process is call
morphogenesis.
Homeotic Genes
Homeotic genes are regulatory
genes that determine where
certain anatomical structures,
such as appendages, will
develop in an organism during
morphogenesis.
 These seem to be the master
genes of development
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Normal
Mutant with legs
growing out of head
Homeobox
In Drosophila (fruit flies)
the specific DNA sequence
within a homeotic gene
that regulates patterns of
development is the
homeobox.
 The same or very similar
homeobox sequences have
been found in many other
eukaryotic organisms
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Cancer
Leading cause of death in the United
States
 A genetic disease caused by a mutation in
the genes that control cell division
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Tumor – abnormal proliferation of cells
that results from uncontrolled, abnormal
cell division
 Benign – a tumor that remains within a mass
 Malignant tumor- uncontrolled dividing cells
that invade and destroy healthy tissue
elsewhere in the body
 Metastasis – spread of cancer cells beyond
their original site
Kinds of Cancer
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Carcinomas – grow in skin and tissues that
line the organs of the body
– Example: lung and breast
Sarcomas – grow in bone and muscle
tissue
 Lymphomas – solid tumors that grow in
tissues that form blood cells
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– Example: leukemia
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In normal cells, that frequency of cell
division is governed by several
factors:
Adequate nutrition
Attachment to other cells,
membranes or fibers
Division stops if cell become crowded
(usually after 20 – 50) divisions
Cancer cell continue dividing and
ignore the normal messages to stop
dividing.
What Causes Cancer?
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Mutations that alter the genes coding
for growth factors.
May occur spontaneously
Result from exposure to an carcinogen
( any substance that increases the risk of
cancer.)
Usually there is more than one
mutation.
 There are two types of genes that
control cell division
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Proto-oncogens
Tumor suppressing genes (p53 gene)