DNA is the hereditary material that transfers info btwn bacterial cells

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Transcript DNA is the hereditary material that transfers info btwn bacterial cells

DNA, RNA and Protein
Synthesis= CH 10
Griffith’s Experiments
• Showed that hereditary material can pass from
one bacterial cell to another
• The transfer of genetic material from one cell to
another or organism to organism is called
transformation
• Heat killed virulent bacteria can transfer their
disease causing ability to harmless bacteria
Griffith’s Experiments
Avery’s Experiments
• Showed that: DNA is the hereditary
material that transfers info btwn
bacterial cells
• Cells missing RNA and Protein could
transform R into S cells
• Cells missing DNA could not transform
cells
Hershey-Chase Experiment
• DNA not protein is the
genetic material
• DNA of viruses enters
bacterial cells and this
causes the bacterial
cell to produce more
viruses containing DNA
• Protein doesn’t enter
cells
Discovery Of Structure
• 1953: Watson and Crick
put together a model
of DNA
using Franklin’s and Wilkins’s
DNA diffraction X-rays
Molecular Structure of DNA
• DNA is composed of 2 strands made of 4
kinds of nucleotides
• Each nucleotide consists of 3 parts:
– one 5-carbon sugar (deoxyribose)
– one phosphate group, and
– one of 4 bases
• adenine (A), guanine (G), thymine (T),
cytosine (C).
Structure of a nucleotide
• Sugar & Phosphate
are “sides” of ladder
and Bases are the
“rungs” & attach to
sugars
2 categories of DNA bases:
Purines vs Pyrimidines
PURINES = A, G
= SMALL WORD, BIG BASES = 2 RINGS
= PuAG
PYRIMIDINES = T, C
= BIG WORD, SMALL BASES= 1 RING
= PyTC
Purines vs Pyrimidines
• Chargaff showed that
– % of A always =
% of T
– % of G always =
% of C
• Purines always with pyrimidines
– BIG BASE ALWAYS WITH SMALL
DNA
Structure
Complementary base
pairing rules
• Base pairs
are formed
by
hydrogen
bonding
of
A with T (2 H
bonds),
and
G with C (3 H
bonds)
DNA Replication
DNA Replication =
in
S phase of cell
cycle
• An enzyme
(helicase) breaks
the H bonds
between base pairs
and unZIPS the
strands =
replication fork
DNA
Replication
• Another enzyme
(DNA polymerase)
attaches the
complementary
base to the original
DNA strand
DNA
Replication
• Results in DNA
molecules that consist
of one "old" strand
and one "new" strand
• Known as semiconservative
replication b/c it
conserves the original
strand).
DNA Errors in Replication
• Changes = mutation
• Proofreading & repair prevent
many errors
• Unrepaired mutation can cause
cancer
Flow of
Genetic
Material:
DNA → RNA → Proteins
RNA Structure
• RNA differs from DNA
– RNA uses ribose as the sugar
not deoxyribose.
– RNA bases are
A, G, C, and uracil (U).
• G-C
• A-U
– Single Stranded
– Shorter than DNA
– Can Leave the nucleus
3 Types of RNA
• rRNA - ribosomal
• mRNA - messenger
• tRNA - transfer
Messenger RNA (mRNA)
• Made from DNA in nucleus
using RNA Polymerase
• Is the “Blueprint" for a
protein
– Carried to ribosomes in
cytoplasm after “stop” is
reached
• Carries message from
nucleus to cytosol
Ribosomal RNA (rRNA)
• rRNA + protein makes a ribosome
• Site where proteins are assembled
in cytoplasm
Transfer RNA (tRNA)
• Carries
correct
AA to
ribosome/
mRNA
complex
Transcription
• DNA → RNA
– uses RNA Polymerase (binds at
“promoter” region)
– Process similar to DNA replication
– Begins with a START codon and ends
with a STOP codon
• Makes rRNA, tRNA or mRNA
•
Message is “transcribed” from DNA code to RNA code
Transcription
Protein Synthesis: Translation
• Making of protein at the rRNA
using mRNA and tRNA
• Each base triplet in mRNA is called
a codon
-specifies an amino acid to be
included into a polypeptide chain
–Uses genetic code to determine
amino acid
Genetic Code
• Universal for all forms of life
– 61 triplets specifying amino acids
– 3 “stop” codes
• Stop codes = UAA, UAG, UGA
• Start Codon = AUG = methionine
From
DNA
to Proteins
CODON CHART..from mRNA
Translation
• RNA → PROTEIN
• mRNA leaves nucleus goes to ribosome
• Begins when ribosome attaches to start
codon
• tRNA gets specific amino acid (floating free
in cytosol), anticodon matches codon of
mRNA and A.A.
• tRNA brings its AA to ribosome and
attaches it to growing chain of AA (protein)
• stops at “stop” codon
Chapter 11
Gene Expression
TURN “ON” GENES to
REGULATE PROTEIN AND
GENE EXPRESSION
Role of Gene Expression
• Activation of a gene that results in
transcription and production of
mRNA
• Only a fraction of a cell’s genes are
expressed at any one time
–You only express genes or make
proteins when NEEDED!
Gene Expression in Prokaryotes
-Studies in 1960’s by French
scientists
-Started with simple intestinal
prokaryotic cell= Escherichia coli
= E. coli
• Bacteria adapt to changes in their
surroundings by using proteins to turn
groups of genes on and off in response to
various environmental signals
• The DNA of Escherichia coli is sufficient to
encode about 4000 proteins, but only a
fraction of these are made at any one time.
E. coli regulates the expression of many of
its genes according to the food sources that
are available to it
• - Scientists discovered how genes
in this bacteria metabolize lactose
when present
• -lactose = disaccharide…needs
to be broken down into galactose
and glucose
Gene Expression in Prokaryotes
• When lactose is absent, E. coli will
not produce the protein…is
repressed
• When lactose is present, E. coli will
produces the 3 structural enzymes
–Meaning this will make the “protein”
or go through induction…..so it can
break down lactose!
Gene Expression in Prokaryotes
•
http://www.phschool.com/science/biology_place/biocoach/lacoperon/genereg.html
•
GREAT ANIMATION TO REVIEW AT HOME!
Gene Expression in Prokaryotes
• Operon: series of genes coding for
specific products = “lac” operon
• Operon = structural genes +
promoter + operator
Gene Expression in Prokaryotes
• Promoter: segment of DNA
recognized by RNA polymerase
which then starts transcription
• Operator: segment of DNA that
acts as “switch” by controlling the
access of RNA polymerase to
promoter
Prokaryotic On & Off switches
• Transcription can be turned “on or off”
depending on what the cell needs
• When turned “off” a repressor protein
is bound to DNA in front of the gene
• To turn a gene “on” an inducer
(lactose) binds to the repressor,
causing it to fall off….then gene is
expressed
Repression
Activation
Gene Expression in Eukaryotes
• Have not found “operons” in
eukaryotes
• Genomes are larger & more complex
• Organized into introns and exons
– Through removal of introns from premRNA
Controlling Transcription in
Eukaryotes
Removal of Introns After
Transcription
Eukaryotic Genes are made of
introns and exons
• Introns noncoding
portions of the gene,
removed by enzymes
before mRNA leaves the
nucleus (pre-mRNA)
• Exons portions that will
eventually be translated
remain in the finished
mRNA that leaves the
nucleus.
Gene Expression in Development
• Expressed Genes: have been
transcribed & translated
• Cell Differentiation: Development of cells
w/ different functions
• Morphogenesis: development of form in
an organism
• Homeotic genes (hox): determine where
anatomical structures
(appendages) will develop
& controls differentiation
in early development
Gene Expression in Development
• Homeobox Sequence:
– w/in homeotic genes
– Sequence of DNA that regulates
patterns of development
– Homeoboxes of
many diff eukaryotic
organisms appear
to be very similar
Gene Expression & Cancer
• Oncogene: Gene that causes cancer
• Proto-oncogene = normal gene,
regulates cell growth. May mutate into
oncogene that may lead to cancer
• Tumor-supressor gene (3 types): for
protein that prevents uncontrolled cell
division, mutation may stop this protein
production
• Viruses may have oncogenes or trigger
them in another cell
Cancer
• Continue to divide indefinitely, even if too
tightly packed or detach from other cells
• Tumor: uncontrolled, abnormal cell division
• benign tumor: does not migrate to other areas,
usually harmless
• malignant tumor: invade other healthy tissues
= cancer
• metastasis: breaking away and spreading to
other body parts to form new tumors
Causes of Cancer
• Carcinogen
– Chemicals in tobacco smoke, asbestos, UV
light from the sun
– Mutagen: causes a mutation
Kinds of Malignant Tumors
• Carcinoma: in skin & tissue lining
organs
• Sarcoma: in bone & muscle tissue
• Lymphoma: in tissues that form
blood
• Leukemia: uncontrolled production
of white blood cells
Causes of Cancer
• Mutations that change expression of genes
coding for growth factor proteins
• Usually comes after exposure to carcinogen
(tobacco, UV light etc.)
• usually need more than 1 mutation to get cancer
Genetic Engineering
and Biotechnology =
Ch 13
DNA Identification/fingerprinting
• Gene = segment of DNA bases that
code for traits and proteins
• Genetic engineering= use of genes
to create or modify the genome
• DNA fingerprinting = The repeating
sequences in noncoding DNA
(introns) vary between individuals &
thus be used to identify an
individual
Steps in DNA identification
(fingerprinting)
• Gel electrophoresis: pieces are separated
by size on a gel creating “bands” =
fingerprint
• Everybody has different number and size of
pieces because their DNA sequences are
different
• PCR = polymerase chain reaction =
duplicate DNA
– cut “digest” DNA with restriction enzyme to get
a bunch of pieces
Gel Electrophoresis
• DNA fragments placed into “wells” in
gel agarose
• Electricity pulls on DNA fragments,
DNA is “-” and thus goes toward “+”
side
• Fragments travel at
different rates based
on size and ability to
squeeze through
swiss-cheese-like
agarose
DNA Fingerprinting
DNA Fingerprinting
Polymerase Chain Reaction (PCR)
• Useful if you only have a little bit of DNA
and need to make copies of it
• Crime scenes, genetic disorders in
embryonic cells, study ancient DNA
fragments
Restriction
Enzymes
• Cuts DNA at
specific base
sequence
• Produces sticky
ends
• Recombinant DNA
= Complementary
sticky ends can be
fused together…is
recombined
Restriction Enzymes
Producing Restriction Fragments
• DNA ligase enzyme used to splice
together cut plasmids and
chromosome fragments
Producing & combining restriction
fragments
Cloning
• Making identical copies of cells
• Can clone genes or organisms
• Cloning a Gene= making large quantities of a
desired DNA piece …usually insert into a vector
(bacteria)
• Transfers gene between organisms
• Plasmids: circle of DNA in bacterium replicates
independently of the single main chromosome
Transplanting Genes
• Gene may be used to make bacteria
produce specific protein - insulin
production
Stem Cells
• Stem cells have the ability to
1. divide and renew themselves
2. remain undifferentiated in form
3. develop into a variety of specialized cell types
Genomic Library
• Includes all pieces of genome that
come from cutting with a particular
restriction enzyme
• Can have multiple libraries for the
same organism - all cut with different
R.E.’s
Transgenic Organism
• The host that has received the
recombinant DNA
• Organism produces the new protein
unless the gene gets “turned off”
• Keep gene “turned on” by splicing it in
near a gene that is frequently
expressed
Human Genome Project
• Sequence entire human genome
• Began in 1990 - expected completion
was 2005, but it was completed in
2000
• Thought humans had 100,000 genes,
but its fewer than 30,000
• We have the sequence of genes, but
don’t know what they all do yet
• Use info for diagnosis, treatment,
prevention of genetic disorders
Future of Genomics
• Bioinformatics: Uses computers to
catalog & analyze genomes
• Proteomics: studies the identities,
interactions, and abundances of an
organisms proteins
• Microarrays: two-dimensional
arrangement of cloned genes, useful to
compare specific proteins such as those
that cause cancer
Medical Applications
• Gene Therapy: Used on individuals
to insert normal genes (or repair
damaged DNA) into body cells to
cure disease
– Abnormal gene can
still be inherited
• Used on fertilized zygotes or
embryos to insert normal genes for
both developing body AND sex cells
– Genome changed permanently
Uses of DNA Technology
• Cloning
• Stem Cell Research
• Pharmaceutical Products
– insulin
• Vaccines
– work because body recognizes proteins, can
produce protein without introducing
pathogen
Uses of DNA Technology
• Agricultural Crops
– disease resistance
– herbicide
resistance
– Improve nutrition
– require less
fertilizer
(incorporate
nitrogen fixing
gene)
Concerns of DNA Technology
• Plants might produce toxins that
could cause allergies in people who
consume them
Concerns of DNA
Technology
• What if the plants
get into the “wild” forming
“superweeds”
• Do we really know
what we are doing
when we mix genes?