DNA, RNA, and Protein Synthesis

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Transcript DNA, RNA, and Protein Synthesis

DNA, RNA, and Protein
Chapter 12
Section 1-4
DNA 12-1
To understand genetics, biologists had to learn
the chemical structure of genes.
 Frederick Griffith- 1928; He tried to figure out
how bacteria makes people sick like
pneumonia. He injected mice with a mixture
of heat-killed bacteria, disease-causing
bacteria, & live harmless bacteria. The result
was that the mice developed pneumonia.
Griffith Discovers
Transformation – disease causing bacteria
pass the disease causing ability on to
the harmless strain of bacteria.
One permanently changed another.
Other Scientists
Oswald Avery – 1944; He & his research group
repeated Griffith’s work and found that
bacteria are transformed by DNA.
That DNA stores and transmits the genetic
information from one generation of an
organism to the next.
Other Scientist
Alfred Hershey & Martha Chase – 1952; They
performed experiments with bacteriophages
& showed that genes are made of DNA.
Other Scientist
James Watson and Francis Crick created the first double
helix model. ( they eventually won the nobel prize for it in 1962
for their work)
Rosalind Franklin also played a major role in the ladder’s
discovery because Watson and Crick used her photos of the
DNA ladder to assemble the model. (Unfortunately she died 4
years before nobel prize was awarded)
Pictures of Watson and Crick, Rosalind
Franklin and her X-ray photos of DNA
Hershey & Chase
Bacteriophage – “bacteria eater”; a kind of virus that infects
bacteria. See pg. 289, Fig. 12-3
Radioactive Markers – used by Hershey & Chase to determine
which part of the virus (protein coat or the DNA coat) entered
the infected cell. As a result, they could learn whether genes
were made of protein or DNA.
32P & 35S – Phosphorous 32 is not often found in protein and
Sulfur 35 in not found in DNA.
 The presence of 35S in bacteria means that the viruses’
protein was in the bacteria.
 The presence of 32P in bacteria means the DNA was in the
 Conclusion – Genetic material of bacteriophage was DNA,
not protein.
What is DNA?
Deoxyribonucleic acid is the nucleic acid
stores the genetic code.
 Contains the blueprints for making proteins.
 Genetic codes: “program” of the cells; how
cells store information they pass from one
generation to the next.
 DNA is a polymer (large molecule)formed
from units called nucleotides.
Location & Structure of DNA
 in the nucleus of eukaryotic cells.
 In the cytoplasm of prokaryotic cells.
Double stranded (double helix)
Composed of 3 part nucleotides:
Deoxyribose (5 carbon sugar)
 Phosphate group (PO4)
Note: The two alternate S-P-S-P with the nitrogen bases
always lined up on the Sugars (deoxyribose)
Nitrogen base (1 of 4)
 Adenine (A) – purine
 Guanine (G) - purine
 Thymine (T) – pyrimidine
 Cytosine (C) - pyrimidine
See pg. 291, Fig. 12-5
Base Pairing Rule
Hydrogen Bonds
hold the nitrogen
bases together in
the middle
Adenine pairs with Thymine
Cytosine pairs with Guanine
Structure cont.
Purines – have 2 rings in their structure.
Pyrimidines – have 1 ring in their structure.
Double Helix – 2 strands wound around each
other; twisted ladder.
Base pairing – hydrogen bonds hold 2 strands
together & can form between certain base
pairs. A-T, T-A, G-C, C-G
Discovered by Watson & Crick and won a
nobel prize.
See pg. 294, Fig. 12-7
Chromosomes & DNA
Replication (synthesis) 12-2
DNA is very long & must fold up tightly to fit inside a cell. Ex.
Trying to pack a 300m length rope into a backpack.
Chromosome Structure:
DNA is wound around proteins.
DNA & proteins wind together to form nucleosomes.
Nucleosomes pack together to form thick fiber.
See pg. 297, Fig. 12-10
Chromosomes contain DNA & proteins called histones.
Most of the time nucleosomes are spread out & the chromosomes
are not visible but during mitosis, the nucleosomes become
more tightly packed & the chromosomes can be seen under a
DNA Replication
Each strand of DNA serves as a template for a new
strand of DNA
During cell reproduction an exact copy of the parent
cell DNA is made.
Enzymes unzip DNA (separates) breaking hydrogen
bonds between bases.
2 strands unwind.
2 new strands form using Base pairing.
DNA replicates itself exactly so that each new cell will
have an identical copy of the original DNA.
Example: template DNA: TACGTT
DNA Replication
Process of DNA Replication
See pg. 298, Fig. 12-11
2 strands separate.
Replication forks form.
New strands form.
New bases are added (base pairing).
It is semi-conservative- 1 original strand and 1 new
2 DNA molecules identical to each other & to the
original molecule.
DNA polymerase – enzyme that unzips DNA molecules when
hydrogen bonds b/w the base pairs are broken. 2 strands
unwind & join nucleotides.
Can you write the
corresponding Nitrogen Base?
Replication animation
Making Proteins
DNA contains the instructions for
building proteins
 Proteins are made at the ribosomes
 DNA cannot leave the nucleus
 How does DNA’s information get to the
RNA & Protein Synthesis 12-3
Genes – coded DNA which contain
instructions for assembling proteins.
The first step in decoding the genetic
messages is to copy part of the
nucleotide sequence from DNA into
What is RNA?
Ribonucleic acid
mRNA –nucleic acid that acts as a messenger b/w
DNA & ribosomes & carries the genetic code for
making proteins from the amino acids.
RNA is a disposable copy of a segment of DNA.
RNA has 1 job – (protein synthesis) controlling the
assembly of amino acids into proteins.
Contains coded information for making proteins.
Location & Structure of RNA
In the nucleus
Single Strand
Nucleotides composed of:
 Ribose (5-carbon sugar)
 Phosphate group
 Nitrogen bases:
Adenine (A)
 Guanine (G)
 Cytosine (C)
 Uracil (U)
RNA does not contain thymine
but has uracil
3 Types of RNA
All are involved in Protein Synthesis & are copied from
the DNA
Messenger RNA – (mRNA) carry copies from
DNA to rest of cell.
Ribosomal RNA – (rRNA) it is on the
ribosomes where proteins are assembled.
Transfer RNA – (tRNA) transfers each amino
acid to the ribosome according to the coded
messages in mRNA.
See pg. 300, Fig. 12-12
Why make proteins?
Needed for cell structure and
movement, makes enzymes and
The process in which a molecule of DNA is copied
into a complementary strand of RNA.
Occurs inside the nucleus b/c DNA is in the nucleus &
cant leave so a messenger RNA (mRNA) must bring
the genetic information from the nucleus to the
ribosomes in the cytoplasm.
RNA polymerase – enzyme that attaches to DNA & moves
along it unwinding the two strands
Promoters – signals in the DNA that indicate to the RNA
polymerase where to bind.
The instructions for making proteins are specified by genes & are found in the 4
nitrogenous bases.
Transcription animation
Imagine that you are a mechanic. The repair
manual that you use is the DNA ladder.
 If you wanted to copy the instructions to
install a radio in your car, would you copy the
entire repair manual?
 NO!!! You would only copy the portion
pertaining to installing the radio. That is what
transcription does.
Genetic Code
See pg. 303, Fig. 12-17
The genetic code is read 3 letters at a time, 3 bases long.
Proteins are determined by the order in which amino acids are
joined together
Codon – 3 letter word composed of 3 nucleotides on mRNA
Each codon codes for a particular amino acid while chains of
amino acids form proteins.
With 4 bases, there are 64 possible 3-base codons & there can
be more than 1 codon for each amino acid.
There are start and a stop codons.
Ex. This RNA sequence
Read 3 bases at a time UCG-CAC-GGU
Different amino acids UCG Serin - CAC Histidine – GGU Glycine
See pg. 304-5, Fig.12-18
The process of building a protein
molecule according to code in mRNA.
 During the process transfer RNA (tRNA)
carries amino acids to the ribosomes
where the amino acids are joined to
form the protein
 Ribosomes are where proteins are
Steps of translation:
tRNA binds to the mRNA
A “start” codon starts the protein chain
tRNA contain 3 complementary nucleotides to the
mRNA called the anticodon; once it matches it
leaves behind an amino acid and the next codon is
more tRNA molecules will come together to
create the next polypeptide
Once a “stop” codon is read, the new polypeptide
chain is released as a new protein.
Translation animation
What happens to mRNA at the
mRNA is transcribed from the DNA in the nucleus.
mRNA moves into the cytoplasm & attaches to a
tRNA will read mRNA in 3 part sections (codons).
tRNA carries amino acids to the ribosome.
A polypeptide assembly line forms.
Amino acids bond to form proteins.
Role of RNA & DNA
Compare RNA & DNA to Builders:
A master plan has all the information needed to
construct a building. But builders never bring the
valuable master plan to the site where it could get
damaged or lost. They prepare inexpensive,
disposable copies of the plan called blueprints.
The master plan is safe inside the office while the
blueprints are taken to the job site. Similarly, the
cell uses the vital DNA “master plan” to prepare
the RNA “blueprints”. The DNA is safe in the
nucleus, while the RNA goes to the proteinbuilding sites in the cytoplasm – the ribosomes.
Mutations 12-4
Mutations – are changes in the genetic
 2 Kinds:
Gene mutations
Chromosomal mutations
Gene Mutations
See pg. 307, Fig. 12-20
Produce changes in a single cell.
Point mutations – involves changes in one or a few
nucleotides and occur at a single point in the DNA sequence.
Substitutions – one base is changed to another; only affects a
single amino acid.
Insertions & Deletions– a base is inserted or removed from the
DNA sequence; much more dramatic because the genetic code
is read in 3-base codons.
Frameshift mutations – the shifting of codons & the “reading
frame” which may change every amino acid that follows the
point of the mutation. It can alter a protein so much that it
is unable to perform its normal functions.
Chromosomal Mutations
See pg. 308, Fig. 12-21
Produce changes in whole chromosomes.
Deletions – involve the loss of all or part of a
Duplications – produces extra copies of parts of a
Inversions – reverse the direction of parts of a
Translocation – when part of one chromosome
breaks off & attaches to another.