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DNA, RNA, Protein
Synthesis
DNA Goals
• The Human Genome
• List the contributions of various scientists
to the idea that DNA carries the genetic
code.
• Describe the structure and function of
DNA.
• Summarize the process of DNA replication.
DNA History
• The genetic code: the way in which cells
store the program that they seem to
pass from one generation of an organism
to the next generation.
• Who discovered the molecule that
carries the genetic code?
• How did they do it?
DNA History
• Frederick Griffith – experimented with
mice and a disease-causing strain of
bacteria in which mice got pneumonia
and died.
• Found that one strain of bacteria had
been transformed into another
• He called it Transformation
DNA History
•Frederick Griffith
DNA History
• Oswald Avery – wanted to test this
experiment to see which molecules of
the cell were the transforming factors.
• Found that DNA is the transforming
factor
• DNA is the nucleic acid that stores and
transmits the genetic information from
one generation of an organism to the
next.
DNA History
•Alfred Hershey and Martha Chase –
experimented to find the kinds of viruses
that infect bacteria.
•Known as bacteriophages (composed of a
DNA core and a protein coat, they attach
themselves to the surface of a bacterium
and then inject a material into the
bacterium which allows them to replicate
themselves)
DNA History
Alfred Hershey and Martha Chase –
•Discovered that only the DNA entered
the bacterium and that the protein coat
remained outside the bacterium
•Convincing evidence that DNA contains
the genetic information.
DNA History
Alfred Hershey and Martha Chase –
DNA - Unseeable Biology
DNA Goals
• List the contributions of various scientists
to the idea that DNA carries the genetic
code.
• Describe the structure and function of
DNA.
• Summarize the process of DNA replication.
DNA STRUCTURE
• Chromatin is the long
uncoiled strand of
DNA that makes up
chromosomes
• Chromosomes are
coiled DNA
DNA STRUCTURE
• DNA is coiled around 2 structures:
– Histones
• class of proteins that bind to DNA
• form tiny particles called nucleosomes
– Nucleosomes
• structure that helps to fold and package DNA
• plays a role in regulating the way genes are
transcribed.
DNA STRUCTURE
DNA is a polymer formed from units
called Nucleotides
Made of 3 basic parts:
–A 5-carbon sugar called deoxyribose
–A phosphate group
–Nitrogenous base
DNA STRUCTURE
Nitrogenous bases have two classes:
–Purines (larger of the two) – Pyrimidines
• Cytosine (C)
•Adenine (A)
• Thymine (T)
•Guanine (G)
DNA STRUCTURE
• Individual nucleotides are joined
together to form a long chain.
• Sugars and phosphate groups form the
backbone and the nitrogenous bases stick
out to form the rungs of the ladder.
DNA STRUCTURE
DNA STRUCTURE
How do we know?
Rosalind Franklin: used
x-rays to look at a
pattern of DNA.
-3-D look.
Gave important clues
on the structure of
DNA.
DNA STRUCTURE
Chargaff’s Rule: pyrimidines can only pair with
purines and visa versa.
A-T, T-A : G-C, C-G
•This base pairing (hydrogen bonding) is the
force that holds the two strands of the
double helix together.
DNA STRUCTURE
James Watson & Francis Crick: Were trying to
figure out the three-dimensional model of DNA
when they saw Franklins x-ray.
•Developed the double helix shape
•The nitrogenous bases on each of the strands
are positioned exactly opposite each other
•Watson and Crick won the Nobel Prize in 1962
DNA STRUCTURE
DNA Molecule
DNA Replication
•Takes place in the nucleus
•Each half, each strand, is said to be complementary
•Before the cell divides, it must duplicate its DNA.
– Semi-conservative process
• The duplicated DNA contains part of the old
DNA.
•This is known as REPLICATION
DNA REPLICATION
• It is carried out by enzymes:
– DNA Helicases
• unzip or separate the 2 strands of the
double helix
• hydrogen bonds are broken
– DNA Polymerases
• insert the appropriate bases
• complementary to each new strand
• “proofread” the bases that have been
inserted to ensure that they are paired
correctly
– DNA Ligases
• produce sugar-phosphate links to extend
the growing DNA chains
DNA Replication
DNA Replication
• 4 steps to DNA Replication
– DNA molecule unwinds
– Hydrogen bonds break between the nitrogen
bases
– new nucleotides are inserted that are
complementary to the original (parent) strand
– End up with 2 identical strands of DNA
Enzymes in Replication
RNA Goals
• State the function of the different types of RNA.
• Compare the structures of RNA and DNA.
• Describe the process of transcription.
RNA Structure
•acts a messenger for DNA
•carries out the process by which proteins are made from amino
acids
•RNA is a polymer formed from units called Nucleotides
RNA Structure
Made of 3 basic parts:
•A 5-carbon sugar called ribose*
•A phosphate group
•Nitrogenous base
–Purines (larger of the two)
•Adenine
•Guanine
–Pyrimidines
• Cytosine
• Uracil *(RNA only)
•Is single stranded*
•RNA can leave the nucleus*
*differences from DNA
RNA Structure
•RNA molecule is a disposable copy of a segment of DNA
•There are 3 types of RNA
–mRNA – messenger
• carries protein-building instruction
–tRNA – transfer
• delivers amino acids to ribosomes
–rRNA – ribosomal
• major component of ribosomes
RNA Structure
RNA Transcription
process by which a molecule of DNA is copied into a complementary strand
of RNA
* mRNA
Why necessary?
•DNA is only found in the nucleus
•Ribosomes found in the cytoplasm
•A carrier is needed to bring the genetic information from the DNA in the
nucleus to the ribosomes in the cytoplasm
RNA Transcription
Steps of transcription:
1.
RNA polymerase attaches to a special place on the DNA molecule called
the Promoter *(“initiator”) – TATA box.
2.
RNA polymerase separates the two strands of the double helix
a.) Breaks the hydrogen bonds between the nitrogen bases
RNA Transcription
Steps of transcription:
3. RNA nucleotides come in and pair up to the
DNA template
a.) mRNA: the messenger, or carrier, that brings
the genetic info from the DNA to the ribosome
4. RNA polymerase releases the newly
synthesized mRNA molecules *(“stop”)
a.) leaves the nucleus to go to the
ribosome in the cytoplasm
RNA Transcription
Protein Synthesis Goals
• Explain the terms codon, anticodon.
• Describe the 3 stages of translation.
Protein Synthesis
•Proteins are made by stringing together long chains of amino acids.
•There are 20 amino acids
•DNA contains only 4 different nitrogenous bases
•The genetic code must have a four-letter “alphabet”
•The smallest size for a code word in DNA is three nucleotides (to
make 20 amino acids)
Protein Synthesis
Codon:
each combination of three nucleotides of the mRNA
•Each codon specifies a particular amino acid that is to be placed
in the polypeptide chain.
•AUG is called the “initiator” codon (*refer to RNA polymerase
notes)
•UAA, UAG, & UGA are called the “stop” codons; they signify the
end of a polypeptide sequence.
Protein Synthesis
Translation
decoding of a mRNA message into a polypeptide chain (protein) using
tRNA, rRNA, and the ribosome.
–tRNA: there are three exposed bases on each tRNA molecule, these
will base pair with a codon on mRNA
•These nucleotides on the tRNA are called the anticodon
• Referred to as the taxi service
Protein Synthesis
Protein Synthesis
–Attached to each tRNA is the amino acid specified by the
codon to which it base pairs
–By matching the tRNA anticodon to the mRNA codon, the
correct amino acid is put into place.
Protein Synthesis
• Ribosome:
– made up of two subunits a large one and a small one. Each
subunit consists of rRNA and proteins
– site where mRNA and tRNA come together
Binding Sites
binding site for mRNA
P (first
binding site
for tRNA)
A (second
binding site
for tRNA)
Initiation
• Initiator tRNA binds to small ribosomal
subunit
• Small subunit/tRNA complex attaches to
mRNA and moves along it to an AUG
“start” codon
• Large ribosomal subunit joins complex
Elongation
• mRNA passes through ribosomal subunits
• tRNAs deliver amino acids to the ribosomal binding site in the
order specified by the mRNA
• Peptide bonds form between the amino acids and the growing
polypeptide chain
Termination
•
•
•
•
Stop codon into place
No tRNA with anticodon
Release factors bind to the ribosome
mRNA and polypeptide (protein) are
released
mRNA
new
polypeptide
chain
Protein Synthesis
DNA – RNA - Protein
Putting it all together
DNA:
ATG CCT AAG GCA CGG TAA AAG
cDNA
Protein Synthesis