Download xCh21 DNA W11

Bio11 – Announcements
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TODAY –
 Genetics (review) and quiz (CP #4)
 Structure and function of DNA
Extra credit – due today
Next week in lab: Case study presentations
Following week: Lab Quiz 2
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Ch 21:
DNA Biology and Technology
DNA Functions
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DNA
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Stores genetic information
Can be copied and passed from
generation to generation
Directs the synthesis of proteins
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What are genes?
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The information in DNA is
stored in blocks called
genes
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Genes code for proteins;
they’re “recipes” for proteins
DNA stores the genetic
information safely in the
nucleus
genetics 101 part 1 What are genes?
http://www.youtube.com/watch?v=eOvMNOMRRm8
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
DNA and RNA Structure
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DNA and RNA are nucleic acids.
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They are polymers of nucleotides.
The nucleotides are joined by a sugar-phosphate
backbone.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
How do DNA and RNA differ?
Nitrogenous bases
Sugar
DNA
RNA
C
G
A
T
Deoxyribose
C
G
A
U
Ribose
2
1
Number of strands
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Watson and Crick’s Discovery
of the Double Helix
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James Watson and
Francis Crick
determined that
DNA is a double
helix in 1950.
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DNA structure – a helix
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Watson and Crick
used X-ray
crystallography data
to reveal the basic
shape of DNA.
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Rosalind Franklin
collected the X-ray
crystallography data.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
DNA structure–a double helix
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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
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Replication:
copying DNA strands
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DNA Replication
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When a cell divides, it
ensures that daughter cells
carry the same genetic
information
DNA replicates by a template
mechanism.
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Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
The DNA molecule ‘unzips’
The parent DNA (blue) serves
as a template for making
daughter strands (orange)
DNA replication
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DNA polymerase binds to specific sites on the double helix.
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Proceeds in both directions
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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
http://www.youtube.com/watch?v=4jtmOZaIvS0
The flow of genetic information
DNA  RNA  Protein
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DNA carries the directions
for an organism.
How are these directions
carried out?
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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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Translation
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
From Nucleotides to Amino
Acids: An Overview
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Genetic information
in DNA is
transcribed into
RNA and then
translated into
polypeptides.
What is the
language of DNA
andsequence
RNA? of bases
the
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Transcription and translation
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RNA is then translated
into a sequence of
amino acids
RNA is divided into
codons (3 RNA bases)
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Each codon specifies
an amino acid
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
How do genes code for
proteins?
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The genetic code
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Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
the rules for translating
the order of bases in
DNA into the order of
amino acids in a
protein
Codon: 3 bases that
code for an amino
acid
The genetic code
The RNA codons
for each amino
acid
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
The genetic code is shared by
all organisms
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Here a mouse
expresses a jellyfish
gene
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Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Researchers
incorporated the
gene for GFP from a
jellyfish into the DNA
of a mouse
Transcription:
From DNA to RNA
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Transcription
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DNA  RNA.
An RNA molecule is copied
from a DNA template.
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Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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)
Transcription of a gene
Three phases:
 Initiation
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Elongation
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RNA polymerase
attaches to the promoter
and starts synthesizing
RNA
The RNA grows longer
Termination
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RNA polymerase
reaches the terminator
DNA (stop signal) and
detaches
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
RNA is processed in eukaryotes
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RNA processing
includes:
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Adding a cap and tail
Removing introns
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Internal noncoding
regions
Splicing exons together
The messenger RNA
(mRNA) travels to the
cytoplasm
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Translation:
RNA  protein
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Translation: The Players
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Three main players:
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Messenger RNA (mRNA)
Transfer RNA (tRNA)
Ribosomes
What do they do?
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Tranlate the genetic code from the nucleic
acid language to the protein language.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Messenger RNA (mRNA)
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mRNA – the copy of the DNA that codes
for a protein
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Is the first ingredient for translation.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Transfer RNA (tRNA)
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tRNA
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Acts as a “interpreter”
Carries amino acids.
Matches amino acids
with codons in mRNA
using anticodons.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Ribosomes
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Ribosomes
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Are organelles that
actually make the
proteins.
Made of ribosomal RNA
(rRNA) and protein
2 subunits
Binding sites for tRNA
and mRNA
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fully assembled ribosome
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A fully assembled
ribosome 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
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Translation is divided into three phases:
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Initiation
Elongation
Termination
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Initiation
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The first phase brings the players together:
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The mRNA
The first amino acid with its attached tRNA
The two subunits of the ribosome
An mRNA molecule has a cap and tail that help it
bind to the ribosome.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
The initiation of translation
1.
2.
3.
An mRNA binds to the small ribosomal subunit.
Then a special initiator tRNA binds to the start codon, AUG
The large ribosomal subunit binds, creating a functional
ribosome. The initiator tRNA fits into the P site on the
ribosome.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
The process of Elongation
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Step 1, codon
recognition
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The anticodon of an
incoming tRNA,
carrying its amino
acid, pairs with the
mRNA codon in the
A site.
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Elongation
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Step 2, peptide
bond formation
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The ribosome
catalyzes bond
formation between
amino acids.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Elongation
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Step 3, translocation
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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.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Termination
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Elongation continues
until the ribosome
reaches a stop codon.
The completed
polypeptide is freed
and the ribosome splits
into its subunits.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
A summary of transcription
and translation
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In eukaryotic cells,
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Transcription occurs in the
nucleus.
Translation occurs in the
cytoplasm.
Recap: The flow of genetic
information in a cell
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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The order of DNA
bases
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the order of mRNA
bases
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the order of the
amino acids in the
protein
Mutations
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Mutations
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A mutation is any change in the nucleotide
sequence of DNA.
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A small change can make a
BIG difference
Normal Hb
Mutant Hb
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A change in a single nucleotide in the gene for
hemoglobin
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A change in a single amino acid
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A change in the shape of the protein and RBC and
causes DISEASE
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Mutations–
2 general ways to alter DNA
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A change in a single DNA base
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Result from errors in DNA replication, UV
radiation, or chemical mutagens
Or entire sections of DNA can move
from one place to another
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Recombination
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Mutations in a single DNA base
Two categories:
1.
Base substitutions
2.
Base insertions or deletions
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Mutations
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Mistakes happen–DNA repair
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Because so much DNA is being replicated in
the many cells of the body, mistakes occur
The cell has many mechanisms to correct
these mistakes – called DNA repair or
proofreading mechanisms
The proofreading process involves comparing
the daughter strand to the parent DNA to
check for mistakes
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the proofreading is not perfect – mutations are still
possible, although rare
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Mutations in DNA repair genes
cause cancer
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Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
DNA repair or proofreading
genes help the cell to fix
mutations in its DNA.
When a DNA repair gene is
mutated, the cell can’t
repair mistakes in its DNA.
These mistakes build up
until an oncogene is hit.
Then the cell becomes
cancerous.
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