DNA & RNA
Griffith and Transformation
• 1928- Frederick Griffith was trying to figure
out how bacteria made people sick
• Pneumonia
• Cause of pneumonia was not a chemical
poison released by disease causing bacteria
• The heat killed bacteria had passed their
disease-causing ability to the harmless strain
Griffith Experiment
Transformation
• Transformationprocess in which one strain of bacteria is
changed by a gene or genes from another
strain of bacteria
• Which molecule was responsible?
Avery and DNA
• 1944- Avery, Macleod, and McCarty wanted to
determine what molecule in the heat killed
bacteria was most important for transformation.
• *** Avery and other scientists discovered that
the nucleic acid DNA stores and transmits the
genetic information from one generation of an
organism to the next.
• Genes are made of DNA ***Deoxyribonucleic
acid
The Hershey-Chase Experiment
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1952- Alfred Hershey and Martha Chase
Collaborated in studying viruses
Bacteriophage
“Bacteria eater”
Composed of DNA or RNA core and a protein
coat.
• Bacteriophage enters a bacterium, the virus
attaches to the surface of the cell and injects its
genetic info into it
The Hershey-Chase Experiment
• The viral genes act to produce many new
bacteriophages and they gradually destroy the
bacterium.
• When the cell splits open, hundreds of new
viruses burst out.
• Need to determine which part of the virus ( the
protein coat or the DNA core) entered the
infected cell
• They would determine whether genes were made
of protein or DNA
The Hershey-Chase Experiment
• Concluded- The genetic material of the
bacteriophage was DNA, not protein.
• NEED radioactive stuff
• http://www.youtube.com/watch?v=9hzUjx_oD8E
• http://www.youtube.com/watch?v=eTvmpn467q
0
• http://www.youtube.com/watch?v=zGSSDJhHgp0
The components and structure of DNA
• Three critical things genes were known to do
– Carry info from 1 generation to the next
– Put that info to work by determining the heritable
characteristics of organisms
– Had to be easily copied, because all of a cell’s
genetic info is replicated every time a cell divides
The components and structure of DNA
• DNA is a long molecule made up of units called
nucleotides
• Two strands form a double helix
The components and structure of DNA
• Nucleotides
• 3 components:
– Phosphate grp
– Pentose ( 5 carbon sugar)
- deoxyribose
– Nitrogenous base
(contain nitrogen)
Four kinds of nitrogenous bases
PURINES
Guanine
Adenine
Two ring structure
PYRIMIDINES
Cytosine
Thymine
One ring structure
The components and structure of DNA
• Backbone of a DNA
formed by
– Sugar and phosphate
• Nitrogenous bases stick
out sideways from chain
The components and structure of DNA
Replication
Prokaryote
• Lack nuclei and other
organelles
• Single circular DNA
• DNA molecules found in
cytoplasm
Eukaryote
• 1000 x amt of DNA than
Prokaryote
• Found in nucleus form of a
# of chromosomes
• Humans- 46 chromosomes
• Drosophilia fly-8
• Giant Sequoia tree- 22
DNA Replication
• Needs to be folded “nicely” inside of cell to be able to be
unraveled easily.
• DNA and protein packed together to form- chromatin.
• Chromatin – DNA that is tightly coiled around proteins
called histones.
• DNA and histones form a beadlike structure- nucleosome.
• Nucleosome- - tightly coiled and super coiled to form
chromosomes
• http://www.youtube.com/watch?v=gbSIBhFwQ4s&NR=1
DNA Replication
DNA Replication
• Two parental strands serve as template
strands
• New nucleotides must obey the AT/GC rule
• End result 2 new double helixes with same
base sequence as original
DNA Replication
• During DNA replication,
the DNA molecule
separates into two
strands, then produces
two new complementary
strands following the
rules of base pairing. Each
strand of the double helix
of DNA serves as a
template, or model, for
the new strand.
•
http://www.youtube.com/watch?v=hfZ8o9D1tus&feature=re
lated
DNA Replication
• Origin of replication– Prokaryote- single origin
– Eukaryote- multiple origins
• Starts at replication forks
• Replication proceeds
outwards in opposite
directions
• Enzymes – “unzip”
(helicase) a molecule of
DNA
– Breaks the hydrogen bonds
DNA Replication
• As new strand forms follows base pairing
• DNA Polymerase- joins individual nucleotides
to produce a DNA molecule.
• DNA Polymerase also “proofreads” to make
sure each new strand is a perfect copy.
•
http://www.youtube.com/watch?v=hfZ8o9D1tus&feature=related
DNA Replication
• Replication is very accurate
– Hydrogen bonding between base pairs more
stable
– Polymerase unlikely to form bonds if pairs are
mismatched
– Polymerase removes mismatched pairs
– Proofreading results in DNA polymerase backing
up and digesting linkages
– Other DNA repair enzymes are involved
DNA and RNA
differences
• Sugar in RNA is ribose
• RNA is single stranded
• RNA contains uracil in
place of thymine
TRANSCRIPTION
DNA language
RNA language
TRANSCRIPTION
DNA language
RNA language
• Definition- RNA polymerase binds to DNA and
separates the DNA strands. RNA polymerase
then uses one strand of DNA as a template
from which nucleotides are assembled into a
strand of mRNA
TRANSCRIPTION
DNA language
RNA language
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3 steps
Initiation
Elongation
Termination
TRANSCRIPTION
DNA language
RNA language
• INITIATION
– RNA polymerase bind only to regions of DNApromoters
• Have specific base sequences
• signals to start transcribing
• TERMINATION
– RNA polymerase reaches the
termination sequence on
the strand
– This causes the newly made
mRNA dissociate from the
DNA
– Hairpin loop forms in mRNA
– causing it to come off
– http://www.youtube.com/w
atch?v=ztPkv7wc3yU&featur
e=related
TRANSCRIPTION
DNA language
RNA language
• New mRNA need to be
“edited” before Translation.
• DNA has sequences that
aren’t involved in protein
synthesis – introns
• DNA sequences that code
for proteins – exons
• Still in the nucleus- introns
are cut out of mRNA
sequence
• Exons are spliced together
• Cap and tail are added to
form final mRNA molecule
Translation
RNA
Protein
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Antibodies
Contractile proteins- movement
Enzymes
Hormones- messengers for body functions
Structural- Keratin, collagen,
Transport proteins
Translation
RNA
Protein
Translation
RNA
Protein
• Proteins are made by joining long chain of
amino acids
• Codon- three consecutive nucleotides that
specify a single amino acid
Translation
RNA
Protein
Translation
RNA
Protein
• The cell uses information from messenger
RNA to produce proteins
• 3 steps
– Initiation
– Elongation
– Termination
• But first……
– mRNA is transcribed from DNA in the nucleus and
released into the cytoplasm
Translation
RNA
Protein
Initiation
• rRNA provides the site for translation
• AUG is the start codon
• mRNA attaches to a ribosome
• tRNA brings the proper amino acid to the
ribosome
Translation
RNA
Protein
Initiation
• rRNA provides the site for translation
• AUG is the start codon
• mRNA attaches to a ribosome
• tRNA brings the proper amino acid to the
ribosome
Translation
RNA
Protein
• TERMINATION
• Stop codon is encountered the ribosome and
mRNA detach and the amino acid is released
•
http://www.youtube.com/watch?v=B6O6uRb1D38&feature=related
Mutations
Mutations are changes in
the genetic material
• Point mutation –
changes in one or a few
nucleotides. They occur
at a single point in the
DNA sequence.
– Substitutions, insertions
and deletions
Sickle cell anemia
• Missense mutation – base
substitution that changes a
single amino acid on a
polypeptide sequence.
• Involves a mutation in the
gene that code for the
proteins that makeup
hemoglobin.
DNA Replication
• DNA to Chromosomes
• http://www.allthingsscience.com/video/715/
Human-Chromosomes
• http://www.youtube.com/watch?v=OStI5pniH
PA&feature=related
RNA editing