Download 3-4 DNA F11 - De Anza College

DNA Functions
Ch 21:
DNA Biology and Technology
 
DNA
 
 
 
Stores genetic information
Can be copied and passed from
generation to generation
Directs the synthesis of proteins
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
DNA and RNA Structure
What are genes?
 
The information in DNA is
stored in blocks called
genes
 
 
Genes code for proteins;
they’re “recipes” for proteins
DNA stores the genetic
information safely in the
nucleus
 
DNA and RNA are nucleic acids.
 
 
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
Watson and Crick’s Discovery
of the Double Helix
RNA and DNA structure
 
 
 
Both are polymers of
nucleotides
Different number of
strands
1 base is different
 
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
They are polymers of nucleotides.
The nucleotides are joined by a sugar-phosphate
backbone.
 
James Watson and
Francis Crick
determined that
DNA is a double
helix in 1950.
In RNA, U
substitutes for T
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
1
DNA structure – a helix
 
DNA structure–a double helix
Watson and Crick
used X-ray
crystallography data
to reveal the basic
shape of DNA.
 
Rosalind Franklin
collected the X-ray
crystallography data.
The model of a double helix – a rope ladder twisted
into a spiral.
Each rung stands for a pair of bases connected by
hydrogen bonds
 
 
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
DNA Replication
 
 
DNA replication
When a cell divides, it
ensures that daughter cells
carry the same genetic
information
DNA replicates by a template
mechanism.
 
 
The DNA molecule ‘unzips’
The parent DNA (blue) serves
as a template for making
daughter strands (orange)
 
DNA polymerase binds to specific sites on the double helix.
 
Proceeds in both directions
 
shortens the time needed for DNA replication.
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
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
The flow of genetic information
The flow of genetic information
DNA → RNA → Protein
DNA → RNA → Protein
 
 
Recipe (RNA)
DNA carries the directions
for an organism.
How are these directions
carried out?
 
Dish
Cook book (DNA)
Protein
A block of DNA is copied into
RNA in the nucleus
 
 
Transcription
The RNA travels to the
cytoplasm where it directs
the assembly of proteins
 
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
http://www.youtube.com/watch?v=4jtmOZaIvS0
Translation
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
2
From Nucleotides to Amino
Acids: An Overview
 
 
Genetic information
in DNA is
transcribed into RNA
and then translated
into polypeptides.
What is the
language of DNA
and RNA?
Transcription and translation
 
 
RNA is then translated
into a sequence of
amino acids
RNA is divided into
codons (3 RNA bases)
 
Each codon specifies an
amino acid
the sequence of bases
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
How do genes code for
proteins?
 
The genetic code
 
 
the rules for translating
the order of bases in
DNA into the order of
amino acids in a
protein
The genetic code
The RNA codons
for each amino
acid
Codon: 3 bases that
code for an amino
acid
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Transcription and translation
Transcription:
From DNA to RNA
Transcription
 
 
mRNA is transcribed in the
nucleus.
And translated into a chain of
amino acids in the cytoplasm.
Translation
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
3
Transcription
Transcription of a gene
DNA → RNA.
An RNA molecule is copied
from a DNA template.
 
 
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
The RNA nucleotides follow
the same base-pairing rules
that govern DNA replication,
except that U pairs with A
 
The RNA nucleotides are
linked by the enzyme RNA
polymerase (orange blob)
 
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
An additional twist:
not all DNA = protein recipe
 
RNA splicing:
 
e
Removing introns
 
 
e = exons
Parts of DNA that do
not code for the
protein
i = introns
i
e
i
poly-A
tail
cap
e
i
e
(cut-out)
Splicing exons
together
e
Translation:
RNA → protein
DNA
e
transcription
i
e
AAAAA
(cut-out)
e
e
mature
mRNA
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
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Translation: 3 main players
Messenger RNA (mRNA)
 
mRNA
mRNA – the copy of the DNA that codes
for a protein
tRNA
Ribosome
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
4
Transfer RNA (tRNA)
 
 
 
Carries amino acids
to the ribosome
The anticodon
matches with the
codons in mRNA
Inserts the correct
amino acid
Ribosomes
 
Are organelles that
actually make the
proteins.
 
aa
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fully assembled ribosome
 
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2 subunits
Binding sites for mRNA
and tRNA
 
Miniature factory for
making protein
Holds 2 tRNA
molecules and
mRNA.
The growing
polypeptide is
attached to one of
the tRNAs.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Translation: The Process
 
What happens?
 
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Translation is divided into 3 phases:
 
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The process of Elongation
1. 
Codon recognition
1. 
2. 
3. 
Initiation
Elongation
Termination
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
The initiation of translation
1. 
The genetic code of mRNA is translated
into a sequence of amino acids.
An incoming tRNA,
carrying its amino
acid, pairs with the
mRNA codon in the
A site.
An mRNA binds to the small ribosomal subunit.
A special initiator tRNA binds to the start codon, AUG
The large ribosomal subunit binds, creating a functional
ribosome.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
5
Elongation
Elongation
2. Peptide bond
formation
 
3. translocation
 
The ribosome
catalyzes bond
formation between
amino acids.
 
 
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
A summary of transcription
and translation
Termination
 
 
A tRNA leaves the P
site of the ribosome.
The ribosome moves
the remaining tRNA
to the P site. The
tRNA and mRNA
move as a unit.
The process begins
again with step 1.
 
Transcription
Elongation continues
until the ribosome
reaches a stop codon.
The completed
polypeptide is freed
and the ribosome splits
into its subunits.
 
Transcription – in the
nucleus.
Translation – in the
cytoplasm.
Translation
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Recap: The flow of genetic
information in a cell
 
 
 
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
The order of DNA
bases
the order of mRNA
bases
the order of the
amino acids in the
protein
Shorthand:
The flow of genetic information
DNA→ RNA→ Protein
 
The central dogma of modern biology
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
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