Central Dogma of Molecular Biology

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Central Dogma of Molecular Biology
DNA is copied into genetic messages, which are
then translated into proteins that go on to
perform the underlying biochemistry of an
organism This is the genetic Flow of
Information
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Why do we study DNA?

• We study DNA for many reasons
• its central importance to all life on Earth,
• medical benefits such as cures for diseases,
• better food crops.

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DNAs JOBS

• DNA makes copies of itself (DNA replication)
• DNA encodes information (protein synthesis)
• 3. DNA controls cells and tells them what to do
  (gene expression)
• 4. DNA changes by mutation

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DNA

• DNA is often called the blueprint of life
• DNA is the instructions for making proteins

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What happens when need to use genes in the code?

• Ex. Paper cut to repair only need info for skin
  cell production
• Copy only the portion of the master code that is
  needed (Transcription) into mRNA (messenger of
  DNA code)
• Occurs in the nucleus

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3 Important Gene Functions

• Carry information from one generation to
  the next.
• Put that information to work by determining
  the heritable characteristics of organisms by
  coding for proteins.
• 3. Have to be easily copied each time a cell
  divides.

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A 2-Step Process

• Transcription
• Writing the code
• Translation
• Reading the code

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Figure 5.28 DNA? RNA ? protein a diagrammatic
overview of information flow in a cell
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Figure 17.3 The triplet code
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RNAa different kind of nucleic acid

• Ribonucleic acid
• DIFFERENCES
• (from DNA)
• Sugar
• Strands
• Bases
• There are 3 types
• mRNA
• tRNA
• rRNA

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RNA and Protein Synthesis

• Types of RNA
• Messenger RNA (mRNA) carries information from
  DNA in the nucleus to the ribosomes where the
  proteins are assembled. It is a partial copy of
  ONLY the information needed for that specific
  job.
• It is read 3 bases at a time codon.
• 2. Ribosomal RNA (rRNA) found in ribosomes and
  helps in the attachment of mRNA and in the
  assembly of proteins.
• 3. Transfer RNA (tRNA) transfers the needed
  amino acids from the cytoplasm to the ribosome so
  the proteins dictated by the mRNA can be
  assembled. (The three exposed bases are
  complementary to the mRNA and are called the
  anticodon)

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TRANSCRIPTION(Making the Message)

• DNA is in the nucleus
• Proteins are made in the cytoplasm
• Where?

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Transcription(Make the message)

• Getting the genetic message from the _______ to
  the _________ in the _________order to make
  __________
• DNA makes a messenger to do this _______

ribosomes
nucleus
cytoplasm
proteins
mRNA
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transcription
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Translation(decoding the message)

• Reading the genetic code
• Happens on ribosomes
• Transfer RNA (tRNA) reads mRNA and brings in the
  correct amino acid

BOTTOM LINE Read the message sent from DNA
(mRNA) Decode it and make the proper Amino Acid
sequence protein
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Figure 17.13a The structure of transfer RNA
(tRNA)
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Transcription
Section 12-3
Adenine (DNA and RNA) Cystosine (DNA and
RNA) Guanine(DNA and RNA) Thymine (DNA
only) Uracil (RNA only)
Step 1 Area of DNA need to copy opens up
(helicase) Step 2 RNA nucleotides floating
in the nucleoplasm float in and pair up with the
complementary base on the DNA strand to make a
single-stranded mRNA (RNA polymerase) Step 3
The newly made mRNA strand leave the nucleus
through a pore and enters the cytoplasm
RNApolymerase
DNA
RNA
Note after the mRNA is made, the DNA molecule
will reform and retwist (DNA polymerase and
gyrase)
Go to Section
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Translation

• Step 1
• The mRNA strand travels to a ribosome rRNA
  anchors the mRNA strand in position on the small
  part of the ribosome a ribosome cap locks the
  strand in place
• Step 2
• The mRNA strand begins to feed through the
  ribosome as codons reach the decoding sites,
  anticodons on tRNA molecules pair up with the
  mRNA strand and deliver the appropriate amino
  acid
• Step 3
• When 2 codons are occupying the decoding sites, a
  covalent bond called a PEPTIDE BOND is formed
  between the amino acids being delivered
• Step 4
• After the amino acids are bonded, the ribosome
  moves down one decoding site to allow the next
  codon to be read again, the complementary tRNA
  delivers the amino acid, a bond forms, and the
  process repeats

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Figure 17.15 The anatomy of a functioning
ribosome
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Translation
Section 12-3
Nucleus
Messenger RNA Messenger RNA is transcribed in
the nucleus.
mRNA
Lysine
Phenylalanine
tRNA
Transfer RNA The mRNA then enters the cytoplasm
and attaches to a ribosome. Translation begins at
AUG, the start codon. Each transfer RNA has an
anticodon whose bases are complementary to a
codon on the mRNA strand. The ribosome positions
the start codon to attract its anticodon, which
is part of the tRNA that binds methionine. The
ribosome also binds the next codon and its
anticodon.
Methionine
Ribosome
Start codon
mRNA
Go to Section
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Translation (continued)
Section 12-3
Growing polypeptide chain
Ribosome
tRNA
Lysine
tRNA
mRNA
mRNA
Translation direction
Ribosome
Go to Section
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• NOTE
• A start amino acid is found at the beginning of
  most proteins methionine. The codon for this
  is AUG.
• A stop codon DOES NOT CODE FOR ANY AMINO ACID
  it is the signal that the protein is complete and
  can be released

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Figure 17.4 The dictionary of the genetic code
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The Genetic Code
Section 12-3
Go to Section
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Working with the Code use the box from your
notes

• Given TACGGGCCCCAAACT
• a. what is the mRNA made?
• b. what is the tRNA needed for translation?
• c. what is the protein made?
• (amino acid chain)
• 2. Given TACGCACATAATACT
• do a, b, and c as above