Download 1-6 DNA Sp12

The molecule of heredity
Ch 20:
Genes and Protein Synthesis
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DNA
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Stores the genetic
information safely in the
nucleus
Can be copied and
passed from generation
to generation
Directs the synthesis of
proteins
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Watson and Crick’s Discovery
of the Double Helix
DNA bases pair according to
special rules
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Discovered in 1950
Important because it
revealed how DNA
can be duplicated
from cell to cell
And led to the birth
of molecular biology
There are only 4 kinds of bases (A, T, C, G):
A always pairs with T, and C with G
Figure 10.5
Close chemical cousins –
DNA and RNA
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Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
What are genes?
Both are
macromolecules
made up of
nucleotides
Different number of
strands
1 base is different
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In RNA, U
substitutes for T
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Genes
The information in DNA
is stored in blocks called
genes
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Genes code for proteins;
they’re “recipes” for
proteins
chromosome
genetics 101 part 1 What are genes?
http://www.youtube.com/watch?v=eOvMNOMRRm8
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
What happens to chromosomes
when a cell divides?
DNA Replication
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DNA replicates by a
template mechanism.
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A copy is made of each chromosome before cell
division begins
Each daughter cell ends up with a complete set of
chromosomes
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Overview of DNA replication 0:48
http://www.youtube.com/watch?v=hfZ8o9D1tus&feature=related
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Copying DNA is a complex
process
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DNA → RNA → Protein
Recipe (RNA)
“Unzips” the DNA
Breaks hydrogen bonds
between DNA strands
Dish
DNA polymerase
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DNA directs protein synthesis
Enzymes needed for DNA
replication
DNA helicase
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The DNA molecule
‘unzips’
The parent DNA (blue)
serves as a template
for making daughter
strands (orange)
Cook book (DNA)
Joins free nucleotides into a
new strand of DNA
Protein
Real-time animation 1:10
http://www.youtube.com/watch?v=4jtmOZaIvS0
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
The flow of genetic information
What is the language of DNA?
DNA → RNA → Protein
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DNA carries the directions
for an organism.
How are these directions
carried out?
A block of DNA is copied
into RNA in the nucleus
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Transcription
The RNA travels to the
cytoplasm where it directs
the assembly of proteins
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Just 4 “letters,” A, C, G & T,
encode our entire genetic
makeup
DNA sequence is read in 3letter words or codons
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Each “word” codes for an
amino acid
The words are put together
into sentences (chains of
amino acids or proteins)
Translation
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Transcription and translation
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Information in DNA is
transcribed into RNA
and then translated
into a chain of amino
acids.
What is the language
of DNA and RNA?
How do genes code for
proteins?
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The genetic code
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the order of bases in
DNA → the order of
amino acids in a
protein
the sequence of bases
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
The genetic code:
RNA codons for each amino acid
The genetic language is the
same in all living things
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61 “words” code
for amino acids; 3
are stop codons
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Note: RNA uses
the letter “U”
instead of “T”
Jellyfish make a
green fluorescent
protein (GFP)
Researchers
incorporated the
gene for GFP into
the DNA of a mouse
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Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Here a mouse
expresses a jellyfish
gene
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Recap: The flow of genetic
information in a cell
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Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
The order of DNA
bases
the order of mRNA
bases
How a cell makes protein
An Overview
the order of the
amino acids in the
protein
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Copying and delivering the
recipe
Copying and delivering the
recipe
The 1st step is to make
a copy of the gene
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Transcription
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Called mRNA
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The mRNA moves into
the cytoplasm
Delivers the recipe to a
ribosome (the chef)
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Making the protein
The ribosome “reads”
the sequence of bases
Each amino acid called
for is connected to the
growing chain of amino
acids
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Summary: copying the recipe
and making a protein
Transcription
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The mRNA is transcribed
in the nucleus.
And translated into a
chain of amino acids in the
cytoplasm.
Translation
Translation
http://www.youtube.com/watch?v=41_Ne5mS2ls&feature=related
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Transcription
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Copying the gene (transcription)
DNA → RNA
The gene (DNA) is copied
into RNA
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Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
The RNA bases follow the
same base-pairing rules that
govern DNA replication,
except that U pairs with A
The RNA bases are linked
by the enzyme RNA
polymerase (orange blob)
Three phases:
 RNA polymerase
attaches to the
promoter DNA and
starts synthesizing RNA
 The RNA grows longer
 RNA polymerase
reaches the terminator
DNA (stop signal) and
detaches
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
An additional twist:
not all DNA = protein recipe
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Parts of DNA do not
code for protein
RNA splicing:
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e = exons
e
i = introns
i
e
i
poly-A
tail
cap
e
i
e
(cut-out)
e
DNA
e
transcription
Removing noncoding regions or
introns
Splicing exons
together
Translation: 3 main players
i
e
mRNA
AAAAA
e
e
mature
mRNA
Ribosome
mRNA splicing - editing the message 0:39
http://www.youtube.com/watch?v=hV6NSHjTR1s&feature=related
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fully assembled ribosome
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Miniature factory for
making protein
Holds mRNA and 2
tRNA molecules.
The growing
polypeptide is
attached to one of
the tRNAs.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Translation: making the chain
of amino acids
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Elongation
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An incoming tRNA,
carrying its amino acid,
pairs with the mRNA
codon
The ribosome catalyzes
bond formation
between amino acids.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
tRNA
(cut-out)
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Translation: getting started
1.
2.
3.
An mRNA binds to the small ribosomal subunit.
A special initiator tRNA binds to the start codon
The large ribosomal subunit binds, creating a
functional ribosome.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Translation: signing off
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Termination
Elongation continues
until the ribosome
reaches a stop codon.
The completed protein
is freed and the
ribosome splits into its
subunits.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
The chain of amino acids folds
into an active protein
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The chain of amino
acids folds into the
elaborate structure
that is characteristic
of that protein
Once it folds, the
protein can function
Shorthand:
The flow of genetic information
replication
transcription
translation
DNA → RNA → Protein
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The central dogma of modern biology
For a good review watch
Animation of transcription and translation (4:06)
http://www.youtube.com/watch?v=41_Ne5mS2ls&feature=related
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Mutations
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
What is a mutation?
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Any change in the nucleotide sequence of
DNA
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Here a single base is changed:
Misspelling
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Mutations:
2 general ways to alter DNA
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Change a single DNA base
Or entire sections of DNA can move from one
place to another
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Changes in a single DNA base
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Caused by errors in DNA replication, UV
radiation, or chemical carcinogens
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Changes in a single DNA base
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Insertions and
deletions
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Can have disastrous
effects.
Change the reading
frame of the gene.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Mutations are rare
Mistakes happen – DNA repair
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Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Mutations–key features
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Mutations are rare changes in DNA
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can affect genes and the proteins they
encode
Mutations are inherited only if they
occur in germ-line cells
Mutations are important for genetic
variation and evolutionary change
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
DNA proofreading
mechanisms to correct these mistakes
The cell uses
The daughter strand is compared to the
parent DNA to check for mistakes
Proofreading is not perfect – mutations
are still possible, although rare
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings