Transcript Ch. 10 DNA, RNA, PROTEIN SYNTHESIS

Ch. 10 DNA, RNA,
PROTEIN SYNTHESIS
Discovery of DNA
• In 1928, Fredrick Griffith (a British medical officer)
was studying a bacterium called Streptococcus
pneumoniae.
– He was trying to develop a vaccine for the virulent strain
of the bacterium.
– The virulent strain is protected by a polysaccaharide
capsule which will protect it from the body’s defense
system.
– He grew 2 strains in petri dishes the virulent strain was
called the S strain; the non-virulent was called the R
strain and lacked a capsule.
© 2008 by Sinauer Associates, Inc.;
http://www.nature.com/scitable/topicpage/isolating-hereditary-material-frederick-
• Griffith concluded that some hereditary information
could be transferred from the virulent bacteria to the
non-virulent which would transform the non-virulent
into the virulent strain.
– Transformation- is the transfer of genetic material from
one cell/organism to another cell/organism.
• In 1940’s Oswald Avery, an American researcher, and his
colleagues wanted to determine what the transformation
agent in Griffith’s experiment was: Protein, DNA, or RNA.
– The scientists used separate enzymes in heat-killed S cells to
destroy the three molecules separately to determine agent.
• Used protease enzyme to destroy the protein
• Used RNase enzyme to destroy the RNA
• Used DNase enzyme to destroy the DNA
– They then mixed the individual heat-killed S cells batches
separately with live R cells then injected the mixture into mice.
• The researchers found the cells missing protein and RNA were able to
transform the R cells into virulent S cells.
• The cells absent of DNA did not transform R cells.
• Conclusion: DNA was responsible for the transformation in bacteria.
• In 1952, Martha Chase and Alfred Hershey, American
researchers, researched whether DNA or protein was the
hereditary material a virus transfers when the virus enters a
bacterium.
– Viruses which infect bacteria are known as bacteriophages.
• They utilized E. coli (Escherischia coli) and determined
DNA was the hereditary material utilized.
DNA Structure
• In the 1950’s, James Watson and Francis Crick teamed
together to determine the structure of DNA.
– By 1953 they had concluded DNA was made of 2 strands and was
shaped like a spiral staircase and they illustrated their findings in a
model which was correct and explained how DNA replicated.
– Watson and Crick utilized other scientists work and findings, to
direct their modeling research, such as X-Ray diffraction by
Maurice Wilkins and Rosalind Franklin.
• In 1962, Watson, Crick, Wilkins received the Nobel Peace
Prize in Medicine for their work Franklin was not included
as she had passed away in 1958 no one is honored with a
Nobel Award post-humously.
• DNA- Deoxyribonucleic Acid
– Nucleic Acid made of 2 strands in the form of a double
helix (spiral staircase)
• Consists of nucleotides which has 3 parts:
– A phosphate group
– A 5-carbon sugar (Deoxyribose)
– 1 of 4 different Nitrogenous bases
» Adenine- Purine (double ring) always binds w/ Thymine
» Thymine- Pyrimidine (single ring) always binds w/ Adenine
» Guanine- Purine; always binds w/ Cytosine
» Cytosine- Pyrimidine; always binds w/ Guanine
• The double helix is held together by hydrogen bonds between
the nitrogen bases attached to the 2 different strands.
– The nitrogenous bases make the steps of the spiral staircase structure.
– The rails (backbone) consists of phosphate groups bound to the 5carbon sugars; the 5-carbon sugars bond to the nitrogenous bases.
http://library.thinkquest.org/27819/ch6_3.shtml
X-ray diffraction image from:
http://www.emc.maricopa.edu/faculty/farabee/biobk/biobookdnamolgen.html
Watson and Crick and their tin-and-wire model of DNA, image from:
http://www.emc.maricopa.edu/faculty/farabee/biobk/biobookdnamolgen.html
• In 1949, the nitrogenous bases were found to be in
complimentary percentages by Erwin Chargaff.
– He discovered that adenine was always present in the same
percentages as thymine; he also found the remaining percentage of
bases consisted equally of guanine and cytosine.
– These pairs of bases are known as complimentary base pairs.
– The observations led to the development to base-pairing rules in
DNA.
• Adenine – Thymine (A – T)
Cytosine – Guanine (C – G)
• The order of nitrogenous bases on a DNA chain is known as base sequence.
• Ex: A C C T G T G A G A C
TGGACACTCTG
• DNA Replication
– Is the process by which DNA is copied within a cell before a cell
undergoes division.
– Step 1: Helicases (an enzyme) separate the DNA strands by
breaking the Hydrogen bonds which connect the nitrogenous
bases. Creating the replication fork (the Y-shaped region created
when the DNA strands separate.
– Step 2: DNA Polymerases (an enzyme) bring free floating
nitrogenous bases to the now exposed DNA strands creating new
hydrogen bonds between the original strands and the new bases
creating 2 new DNA molecules.
– Step 3: DNA Polymerase finish creating replicating the 2 exposed
strands and then falls off, resulting in 2 new DNA molecules.
• Replication occurs at the replication fork in two separate directions at
the same time; always in the 3’ to 5’ direction.
– Replication errors are rare about 1 in 1 billion paired nucleotides added (similar
to typing our Biology textbook 1000 times!)
• Protein Synthesis
– 1st begins with the synthesis of RNA (Ribonucleic Acid)
called Transcription.
– Transcription is the process of RNA polymerase (an enzyme)
copying certain sections of DNA.
– These sections are known as genes which control particular
enzymes or proteins.
• The polymerase will begin transcription at a promoter and end at a
termination signal. (this would be the length of a gene)
– RNA is a single strand of nucleotide bases.
• RNA nitrogenous bases:
Cytosine – Guanine
Adenine – Uracil
• There are 3 types of RNA:
– mRNA: MessengerRNA - carries the message to be translated.
– tRNA: TransferRNA - translates the message found w/in mRNA.
– rRNA: RibosomalRNA - structural component of ribosomes.
• The newly formed RNA molecule (mRNA
molecule) is encoded with valuable instructions
called the genetic code.
– The genetic code is the base sequence of an RNA
molecule as it relates to the 3 base sequences called
codons which represent amino acids.
• Each codon represents a start or stop signal, or an amino acid.
– AUG (start codon) – Methionine
– UAA, UAG, UGA (stop codons)
• There are 64 mRNA codons which code for 20 amino acids.
– Amino acids are the subunits of polypeptides (proteins).
• The # and sequence of amino acids will determine what protein
is created.
• Translation
– The synthesis of a protein from the message carried
within the mRNA molecule.
– mRNA molecule attaches
to ribosome where tRNA
molecules w/ an anticodon
subunit on one end which
is complementary to a
codon on the mRNA strand
carries the amino acid coded
for by the mRNA codon
http://www.wiley.com/college/boyer/0470003790/structure/tRNA/trna_intro.htm
• tRNA molecules bind to the mRNA molecule one at
a time, when the 2nd attaches the first transfers its
amino acid to the 2nd’s amino acid by forming a
peptide bond.
– After the 1st tRNA releases its amino acid it will release
from the mRNA molecule. Each subsequent tRNA
molecule connection will restart the events above.
– The synthesis of the protein will end when the ribosome
reaches a stop codon at which point the newly formed
protein is released.
• DNA  DNA = Replication
• DNA  RNA = Transcription
• RNA  Protein = Translation
DNA
5-Carbon Sugar:
RNA
Deoxyribose
Nitrogenous Base:
Adenine – Thymine
Guanine – Cytosine
Structure:
Function:
Double Helix
Genetic Information
(Heredity)
Ribose
Adenine – Uracil
Guanine – Cytosine
Single Strand
Protein Synthesis