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Unit 1: Central Code and
Genetic Material
Paz Etcheverry
NS 315
Topics to cover
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Cell structure
DNA structure
DNA replication
RNA structure
The Central Dogma of Biochemistry
Transcription: DNA to mRNA
Translation: mRNA to protein
Codons and anticodons
Cell structure
Cytosol or cytoplasm
The nucleus: contains
23 pairs of chromosomes.
DNA is arranged in these
chromosomes.
Where replication and
transcription occurs.
The ribosome: where
protein is synthesized
(i.e. translation occurs)
DNA structure
The nucleus: contains
23 pairs of chromosomes.
DNA is arranged in these
chromosomes
23 pairs of chromosomes:
http://ghr.nlm.nih.gov/handbook/basics/howmanychromosomes
How many chromosomes
does each human cell have?
Each human cell contains 46
chromosomes:
– 22 pairs of somatic (non sex) chromosomes
– 2 sex chromosomes:
Female sex chromosomes: 2 X
 Male sex chromosomes: 1 X and 1 Y
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A chromosome pair
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Centromere
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DNA
Inside each of the 23
pairs of chromosome,
there is DNA.
DNA is tightly packed
inside each of the
chromosomes.
Each chromosome is
composed of two
chromatids joined by a
centromere.
DNA (deoxyribonucleic
acid)
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Double helix
Double= 2
polynucleotide chains
Helix= helical structure
(like a spring)
Each chain contains
nucleotides (joined to
each other) and a
sugar/phosphate
backbone
http://instruct.westvalley.edu/svensson/CellsandGenes/dna-structure%5b1%5d.gif
Nucleotides in DNA
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The nucleotides are
–
–
–
–
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Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
A binds to T
C binds to G
A and G= purine bases
T and C= pyrimidine
bases
http://instruct.westvalley.edu/svensson/CellsandGenes/dna-structure%5b1%5d.gif
Sugar backbone
Sugar backbone
Notice how the two
sugar chains run
opposite each other:
The 5’ end (which has
a phosphate group),
faces the 3’ end
(which has a
hydroxyl (OH) group)
and vice versa.
Who discovered the
structure of DNA?
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James Watson, a young American scientist and Francis Crick,
a young English researcher.
In 1953, Watson and Crick published a paper in which they
proposed and described the structure of DNA.
Rosalind Franklin (an English researcher) was within a couple
days of coming to the same conclusion when their paper was
published.
Watson and Crick received the Nobel prize in 1962.
Rosalind Franklin died in 1958 of ovarian cancer, probably due
in large part to her work with x-rays.
Since the Nobel prize is not awarded posthumously, people
have often wondered if the Nobel committee would have
included Franklin if she had still been alive.
http://biology.clc.uc.edu/courses/bio104/dna.htm
DNA replication
What is DNA replication?
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DNA replication is a
fundamental process
occurring in all living
organisms to copy their
DNA.
The point of DNA
replication is to ensure
that each of our cells
contain the same copy
of DNA when the cells
divide.
http://www.le.ac.uk/ge/genie/vgec/images/mitosis_meiosis.png
Replication-Steps
1) The DNA unzips (helix opens up)
2) DNA polymerase (enzyme) starts
bringing new nucleotides and
building two DNA molecules
3) At the end of the replication
procedure, there will be 2 DNA
molecules each with a parent chain
and a daughter (new) chain
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DNA replication is
very important
Replication ensures
that when our cells
divide, so does our
genetic information
(DNA)
http://courses.cm.utexas.edu/jrobertus/ch339k/overheads-2/ch10_DNA-rep.jpg
RNA structure
RNA (ribonucleic acid)
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The structure is like the DNA except that it
is single stranded (1 strand as opposed to 2
strands/chains)
It contains 1 polynucleotide chain and the
nucleotides are:
–
–
–
–
Adenine (A)
Uracil (U) –no Thymine in RNA
Guanine
Cytosine
http://en.wikivisual.com/images/0/04/NA-comparedto-DNA_thymineAndUracilCorrected.png
Types of RNA
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Messenger RNA (mRNA)
Transfer RNA (tRNA)
Ribosomal RNA (rRNA)
The Central Dogma of
Biochemistry
The Central Dogma of
Biochemistry
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•
Life depends upon the ability to
change genetic information into
functional proteins.
This is referred to as the central
dogma of biochemistry and consists of
two processes:
• transcription
• translation
The Central Dogma of
Biochemistry
transcription
DNA
in the nucleus
translation
RNA
in the cytosol
Protein
The Central Dogma of
Biochemistry
transcription
DNA
in the nucleus
translation
RNA
in the cytosol
Protein
Transcription:
The synthesis of mRNA
Transcription
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Occurs in the nucleus (in eukaryotes)
It is the process whereby a copy of DNA (called
mRNA) is made, via action of RNA polymerase
RNA polymerase reads DNA from 5’ to 3’ end
The residues are paired
DNA
RNA
A
U (remember no T in RNA)
T
A
G
C
C
G
RNA polymerase
5’
3’
http://www.brooklyn.cuny.edu/bc/ahp/BioInfo/TT/TscriptD.html
RNA polymerase
3’
5’
DNA
http://www.brooklyn.cuny.edu/bc/ahp/BioInfo/TT/TscriptD.html
Transcription
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Occurs in the nucleus (in eukaryotes)
It is the process whereby a copy of DNA (called
mRNA) is made, via action of RNA polymerase
RNA polymerase reads DNA from 5’ to 3’ end
The residues are paired
DNA
RNA
A
U (remember no T in RNA)
T
A
G
C
C
G
Transcription (contd)
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When RNA polymerase binds to DNA
to transcribe the DNA into mRNA, it
binds to a part of DNA called the
promoter region.
Promoter region
(where RNA polymerase binds)
5’
Response element
DNA
3’
Area that will be ‘read’ by RNA
polymerase to create mRNA
Promoter region
DNA
5’
3’
RNA polymerase
mRNA
DNA
5’
3’
RNA polymerase
Notice how RNA polymerase reads DNA from the
5’ end to the 3’ end strand.
mRNA
DNA
5’
3’
RNA polymerase
RNA polymerase
mRNA
5’
3’
RNA polymerase dislodges from the DNA when
it reads an unusual sequence of DNA
Translation:
The synthesis of proteins from
mRNA
The Central Dogma of
Biochemistry
transcription
DNA
in the nucleus
translation
RNA
in the cytosol
Protein
Translation
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Once mRNA was synthesized (via
transcription), it leaves the nucleus of
the cell and goes to the cytoplasm
(aka cytosol)
In the cytoplasm, there is an organelle
called the endoplasmic reticulum (ER)
which contains ribosomes
Ribosomes facilitate protein synthesis
protein
amino acid
tRNA
mRNA
rRNA
http://www.biologycorner.com/resources/translation_lettered.jpg
Translation (contd)
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During translation, mRNA binds to rRNA
(ribosomal RNA).
tRNA (transfer RNA) holds one amino acid in
the form of amino acyl-tRNA complex
The mRNA guides the order (sequence) of
amino acids forming the protein
rRNA serves as an anvil, aligning both
mRNA and tRNA so that a peptide or protein
is formed
Step 1 of Translation
mRNA
AUG CCA ACG AUA UCC AGG GAG UAG
mRNA, produced in the nucleus through
the process of transcription, is now in the
cytoplasm of the cell.
Step 2 of Translation
mRNA
AUG CCA ACG AUA UCC AGG GAG UAG
rRNA
(ribosomal RNA)
rRNA binds to the mRNA strand. It serves
to hold the mRNA in place.
Step 3 of Translation
met
tRNA
mRNA
UAC
AUG CCA ACG AUA UCC AGG GAG UAG
rRNA
(ribosomal RNA)
A tRNA (transfer RNA) that matches the
sequence in mRNA (AUG) arrives, carrying an
amino acid. AUG codes (codon) for methionine
(met)
Step 4 of Translation
pro
mRNA
met GGU
AUG CCA ACG AUA UCC AGG GAG UAG
rRNA
(ribosomal RNA)
The first tRNA leaves the scene.
Another tRNA that matches the
sequence CCA in mRNA arrives, carrying the
amino acid proline (pro).
Step 5 of Translation
thr
met pro
mRNA
UGC
AUG CCA ACG AUA UCC AGG GAG UAG
rRNA
(ribosomal RNA)
The second tRNA leaves the scene.
Met and pro form a bond (peptide bond)
Another tRNA that matches the
sequence ACG arrives, carrying the amino
acid threonine (thr).
Step 6 of Translation
tyr
met pro thr
mRNA
UAU
AUG CCA ACG AUA UCC AGG GAG UAG
rRNA
(ribosomal RNA)
The last tRNA leaves the scene.
Pro and thr form a bond (peptide bond)
Another tRNA that matches the
sequence AUA arrives, carrying the amino
acid tyrosine (tyr).
Final Step of Translation
Stop codon
met
pro thr
tyr
mRNA
ser arg glu
AUG CCA ACG AUA UCC AGG GAG UAG
rRNA
(ribosomal RNA)
UAG is a stop codon, which tells the tRNA that
no more amino acids should be incorporated.
When a stop codon is reached, rRNA
dissociates from mRNA and a protein is formed.
The protein that is
synthesized via translation
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Can become enzymes (compounds that
speed up a reaction):
– Enzymes involved in digestion
– Enzymes involved in metabolism
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Can become muscle proteins
Can become transport proteins that allow
entry of certain molecules inside the cell
Can become hormones (insulin, cortisol,
adrenaline, etc)
Etc…
Amino acids and protein
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Amino acids (there are 20 of them in
nature) are the building units of
protein.
Amino acids include: Alanine, Arginine,
Asparagine, Aspartic acid, Cysteine,
Glutamic acid, Glutamine, Glycine, Histidine,
Isoleucine, Leucine, Lysine, Methionine,
Phenylalanine, Proline, Serine, Threonine,
Tryptophan, Tyrosine, Valine
Codons and anticodons
Translation
tyr
met pro thr
UAU
AUG CCA ACG AUA UCC AGG GAG UAG
rRNA
(ribosomal RNA)
mRNA
More about translation…
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Three nucleotides (in a specific order)
code for a specific amino acid
The nucleotide sequence in the mRNA
is called codon
The corresponding nucleotide
sequence in the tRNA is called the
anticodon
Translation
tyr
anticodon
met pro thr
UAU
AUG CCA ACG AUA UCC AGG GAG UAG
rRNA
(ribosomal RNA)
codon
mRNA
protein
amino acid
tRNA
anticodon
codon
mRNA
rRNA
http://www.biologycorner.com/resources/translation_lettered.jpg
Amino Acid
DNA Base Triplets
mRNA Codons
tRNA Anticodons
alanine
CGA, CGG, CGT, CGC
GCU, GCC, GCA, GCG
CGA, CGG, CGU, CGC
arginine
GCA, GCG, GCT, GCC
TCT, TCC
CGU, CGC, CGA, CGG
AGA, AGG
GCA, GCG, GCU, GCC
UCU, UCC
asparagine
TTA, TTG
AAU, AAC
UUA, UUG
aspartate
CTA, CTG
GAU, GAC
CUA, CUG
cysteine
ACA, ACG
UGA, UGC
ACA, ACG
glutamate
CTT, CTC
GAA, GAG
CUU, CUC
glutamine
GTT, GTC
CAA, CAG
GUU, GUC
isoleucine
TAA, TAG, TAT
AUU, AUC, AUA
UAA, UAG, UAU
leucine
AAT, AAC, GAA, GAG
GAT, GAC
UUA, UUG, CUU, CUC
CUA, CUG
AAU, AAC, GAA, GAG
GAU, GAC
lysine
TTT, TTC
AAA, AAG
UUU, UUC
methionine
TAC
AUG
UAC
phenylalanine
AAA, AAG
UUU, UUC
AAA, AAG
proline
GGA, GGG, GGT, GGC
CCU, CCC, CCA, CCG
GGA, GGG, GGU, GGC
serine
AGA, AGG, AGT, AGC
TCA, TCG
UCU, UCC, UCA, UCG
AGU, AGC
AGA, AGG, AGU, AGC
UCA, UCG
stop
ATG, ATT, ACT
UAA, UAG, UGA
AUG, AUU, ACU
http://waynesword.palomar.edu/codons.htm
The start and end codon
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The start codon is the one that makes the
tRNA insert its first amino acid
The start codon is usually AUG and codes
for methionine
So almost all proteins begin with methionine
as its first amino acid
The stop codon is the one that makes the
tRNA stop inserting amino acids
UAA, UAG, UGA are all stop codons
Summary…
Cytosol or cytoplasm
The nucleus: contains
23 pairs of chromosomes.
DNA is arranged in these
chromosomes.
Where DNA replication and
transcription occurs.
DNA replication: DNA copies
itself, every time the cell
divides.
Transcription: A copy of
DNA is made. This copy is
called mRNA.
The ribosome: where
protein is synthesized
(ie translation occurs).
In translation, mRNA is
converted into protein.
replication
transcription
DNA
in the nucleus
translation
RNA
in the cytosol
Protein
Replication of DNA is important, since it ensures that every cell will have a
Copy of DNA each time the cell undergoes division.
Central Dogma of Biochemistry:
Life depends upon the ability to change genetic information into functional
proteins, via the processes known as transcription and translation.