dna and rna chapter 12 pptb.pdfnov 19, 2012 · dna - hershey-chase experiment • martha chase and...
TRANSCRIPT
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DNA and RNA
Chapter 12
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DNA
Section 12-1
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DNA – Griffith and Transformation
• Frederick Griffith –
bacteriologist studying how
certain types of bacteria
produce pneumonia
– Isolated 2 strains of
pneumonia from mice
• Smooth(S) disease causing
strain and Rough(R)
harmless strain
– Injected heated (heat-killed) Disease causing strain into mice
• didn’t cause pneumonia
– Combined harmless strain and heat-killed disease causing strain and injected into mice
• caused pneumonia
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DNA – Griffith and Transformation
• Transformation – the two types injected
together caused the mice to die! Some
transformation had to take place for the
harmless bacteria to change into the deadly
pneumonia-causing strain!
– The heat killed bacteria had passed their disease
causing ability to the harmless strain!
– Concluded that some factor had to be transferred
between the two strains of bacteria – something
that heat did not kill!
• And the offspring of the transformed bacteria also had
this factor so he suspected that the factor may be a
gene
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DNA – Avery and DNA
• Oswald Avery repeated the experiment but
isolated the factor that transmitted the
disease causing ability
– Treated bacteria with specific enzymes to destroy
only certain parts of the bacteria (proteins, RNA,
etc)
• Only bacteria whose DNA had been destroyed failed to
transmit the disease causing ability
• Showed that DNA was the source of this transformation
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DNA - Hershey-Chase Experiment
• Martha Chase and Alfred Hershey
discovered that DNA stores and transmits
genetic information
– Did so by studying bacteriophages (viruses that
attack bacteria)
– These viruses are
comprised of a
DNA center and a
protein coat
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DNA - Hershey-Chase Experiment
– How do bacteriophages work?
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DNA - Hershey-Chase Experiment
– Radioactive Marker Experiment
• Used radioactive substance as markers in
bacteriophages
– Protein coat – Sulfur-35 (35S)
– DNA core – Phosphorous-32 (32P)
• “Marked” bacteriophages and bacteria were mixed
together and they waited for the virus to inject their
genetic material
– Bacteria were then tested for radioactivity
– The type of radioactivity detected would tell Chase and
Hershey which part of the bacteriophage was transmitting
information
– Nearly all was from 32P marker in DNA not
protein coat
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DNA - Hershey-Chase Experiment
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DNA – Activity
• Genes are made of DNA, a large, complex molecule. DNA is composed of individual units called nucleotides. Three of these units form a code. The order, or sequence, of a code and the type of code determine the meaning of the message.
– 1. On a sheet of paper, write the word cats. List the letters or units that make up the word cats.
– 2. Try rearranging the units to form other words. Remember that each new word can have only three units. Write each word on your paper, and then add a definition for each word.
– 3. Did any of the codes you formed have the same meaning?
– 4. How do you think changing the order of the nucleotides in the DNA codon changes the codon’s message?
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DNA – Video on DNA and Genes
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DNA –The Components and
Structure of DNA • DNA – (Deoxyribonucleic acid) is made of units
called nucleotides
• Nucleotides – 3 basic components – Deoxyribose – 5-carbon sugar
– Phosphate group
– Nitrogen bases • Adenine (a purine)
• Guanine (a purine)
• Cytosine (a pyrimidine)
• Thymine (a pyrimidine)
– Complementary Pairing – Base Pairing rules:
• Adenine Thymine
• Cytosine Guanine
– Sequence of one strand determines sequence of other
Adenine Guanine Cytosine Thymine
Phosphate
group Deoxyribose
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DNA –The Components and
Structure of DNA • The “backbone” of DNA is the sugar and phosphate
groups (deoxyribose and the phosphate group) of each nucleotide.
• The nitrogenous bases stick out like a staircase tread (sideways) from this backbone
• Nucleotides can be joined in any sequence – Several nucleotides together make
a gene
– But scientists were still puzzled about how this string could carry genetic information (weren’t there other molecules that were strung together?) So there had to be more to DNA’s structure
Adenine Guanine Cytosine Thymine
Phosphate
group Deoxyribose
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DNA –The Components and
Structure of DNA • Chargaff’s Rules
– Erwin Chargaff noted that regardless of species, or even kingdom, DNA bases always appeared in the same proportions as each other
– Concluded that bases are paired: • [A = T]
• [G = C]
– But why?
• X-Ray evidence – Rosalind Franklin used x-rays to
study the structure of DNA
– Looked at how the x-rays scattered on the film
• From the X shaped pattern, she concluded that DNA was twisted in a coil-like shape (a helix), that there may be two strands, and that the nitrogenous bases were near the center
Adenine Guanine Cytosine Thymine
Phosphate
group Deoxyribose
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Nucleotide
Hydrogen
bonds
Sugar-
phosphate
backbone
DNA –The Components and
Structure of DNA
• The Double Helix
– Francis Crick and James Watson also working on DNA
structure
– Saw work of Rosalind Franklin
and used it to build a structural
model of DNA
• A double helix
• Hydrogen bonds hold
strands together at
nitrogenous bases
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CHROMOSOMES AND DNA
DUPLICATION
Section 12-2
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Chromosomes and DNA Replication
– Chromosome Structure
• Chromatin – Consists of DNA tightly coiled around proteins called Histones
– Histones – forms nucleosome (believed to help in separating chromosomes in mitosis)
• Coiled and super-coiled to form chromosomes
Chromosome
Supercoils
Coils
Nucleosome
Histones
DNA
double
helix
• 4 million base-pairs
per cell (in both
prokaryotic and
eukaryotic cells)
• More than a meter
long in humans
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DNA Replication
• DNA Replication – the process in which DNA strands and duplicate strands are produced – Results in two DNA Molecules each with one new
strand and one original strand
• The DNA strands separate at areas along the chromosome called replication forks – In most prokaryotes this is a single point
– In larger eukaryotic chromosomes, this may be hundreds of points
• DNA polymerase – an enzyme that joins DNA nucleotides to the opened parent strands
• Two complimentary strands are produced according to base-pairing rules
• A DNA strand that has the bases CTAGGT produces a strand with the bases? _ _ _ _ _ _
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DNA Replication
Replication
fork
DNA
polymerase
New strand
Original
strand DNA
polymerase
Nitrogenous
bases
Replication
fork
Original
strand
New strand
Growth
Growth
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DNA Replication
• Enzymes (DNA polymerase) “unzip” the DNA strand by
breaking the hydrogen bonds
• Also allows for “proofreading” what has been produced
so that DNA is replicated with near 100% accuracy
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DNA Replication
• Short videos on DNA Replication
– DNA replication animation by interact Medical –
YouTube
• http://www.youtube.com/watch?v=zdDkiRw1PdU&featur
e=related
– DNA replication (6 10) – YouTube
• http://www.youtube.com/watch?v=z685FFqmrpo&featur
e=channel
http://www.youtube.com/watch?v=zdDkiRw1PdU&feature=relatedhttp://www.youtube.com/watch?v=zdDkiRw1PdU&feature=relatedhttp://www.youtube.com/watch?v=zdDkiRw1PdU&feature=relatedhttp://www.youtube.com/watch?v=z685FFqmrpo&feature=channelhttp://www.youtube.com/watch?v=z685FFqmrpo&feature=channelhttp://www.youtube.com/watch?v=z685FFqmrpo&feature=channel
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DNA Replication relating to Cell
Reproduction
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RNA AND PROTEIN SYNTHESIS
Section 12-3
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RNA and Protein Synthesis
• Structure of RNA
– Similarities:
• Made up of a chain of nucleotides (like DNA)
• Has a phosphate group, a 5-carbon sugar and a
nitrogenous base
– Differences
• Sugar is ribose (not deoxyribose)
• RNA is single stranded (not a double helix)
• Contains uracil instead of thymine
– Often just a segment that corresponds to a
segment of DNA – often a single gene
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RNA and Protein Synthesis
• General Functions of RNA
– It can be varied but is generally protein synthesis
• Types and functions of RNA
– Messenger RNA (mRNA)
• Carries copies of the genetic instructions for assembling
amino acids into proteins
• Serve as messengers from DNA to the rest of the cell
– Ribosomal RNA (rRNA)
• Part of the structure of ribosomes (where proteins are
actually made)
– Transfer RNA (tRNA)
• Transfers each amino acid to the ribosomes as it is
specified in the instructions provided by mRNA
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RNA and Protein Synthesis
• Transcription
– The process of producing RNA from a sequence
of DNA molecule
– Requires an enzyme called RNA polymerase
(very similar to DNA polymerase)
• Separates the DNA strands then uses one strand of
DNA to assemble nucleotides to form the single
stranded RNA molecule which separates and then DNA
is rejoined.
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RNA and Protein Synthesis
• Transcription Process
– RNA polymerase only binds to
specific regions called promoters
(have specific base sequences) –
also provides signals for when to
stop
– RNA polymerase separates DNA
by breaking the hydrogen bonds
– RNA nucleotides are assembled
according to base pairing rules:
• (G – C) Guanine to Cytosine
• (A – U) Adenine to Uracil
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RNA and Protein Synthesis
• Transcription
Process
– Begins at a
promoter
region (a
section of
DNA with
a specific
sequence
– Similar
process to end
Adenine (DNA and RNA)
Cystosine (DNA and RNA)
Guanine(DNA and RNA)
Thymine (DNA only)
Uracil (RNA only)
RNA polymerase
RNA DNA
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RNA and Protein Synthesis
• RNA Editing
– Makes RNA molecule “functional”
– Most DNA are not involved in coding for proteins
but get transcribed anyway
• “Non-coding” segments of RNA must be removed
• Introns – non-coding regions
– Coding segments of RNA are spliced together
• Exons – coding regions; instructions to make proteins
– All this editing takes place inside the nucleus
before the mRNA heads out for the ribosomes
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RNA and Protein Synthesis
• The Genetic Code
– Translates mRNA
“language” into
proteins (amino acids)
– Codon – 3 nucleotide
sequence that
specifies for a single
amino acid
– Sample RNA
sequence: AUG UCG
CAC GGU UAG
• What amino acid
sequence will the
above RNA sequence
produce?
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RNA and Protein Synthesis
• The Genetic Code
– Sample RNA
sequence: AUG UCG
CAC GGU UAG
• What 5-protein
sequence will the above
RNA sequence
produce?
– ANSWER:
• Methionine-Serine-
Histidine-Glycine-Stop
– **NOTE – AUG can be
a “start” sequence or
Methionine; most
proteins begin with the
amino acid Methionine
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RNA and Protein Synthesis
• Translation
– The process of decoding an mRNA message into a
protein (a polypeptide chain)
– Takes place on the ribosomes
– Process
• Begins when mRNA attaches to a ribosome
• As each codon moves through the ribosome, the correct amino
acid is brought by tRNA
– tRNA only carries one amino acid (corresponding to one codon)
– tRNA also has 3 unpaired bases called an anticodon (corresponding
to the codon that the tRNA is supposed to attach to)
• Amino acids are joined together into long chains in the ribosome
• Continues until a “stop” codon is reached (there are several)
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RNA and Protein Synthesis -
Translation
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RNA and Protein Synthesis –
Translation (continued)
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RNA and Protein Synthesis
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from to to make up
RNA Concept Map
also called which functions to also called also called which functions to which functions to
can be
RNA
Messenger RNA Ribosomal RNA Transfer RNA
mRNA Carry instructions rRNA Combine
with proteins tRNA
Bring
amino acids to
ribosome
DNA Ribosome Ribosomes
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MUTATIONS
Section 12-4
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Mutations - Activity
1. Copy the following information about Protein X: Methionine—Phenylalanine—Tryptophan—Asparagine—Isoleucine—STOP.
2. Use Figure 12–17 on page 303 in your textbook to determine one possible sequence of RNA to code for this information. Write this code below the description of Protein X. Below this, write the DNA code that would produce this RNA sequence.
3. Now, cause a mutation in the gene sequence that you just determined by deleting the fourth base in the DNA sequence. Write this new sequence.
4. Write the new RNA sequence that would be produced. Below that, write the amino acid sequence that would result from this mutation in your gene. Call this Protein Y.
5. Did this single deletion cause much change in your protein?
Explain your answer.
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Mutations
• DNA contains the code of instructions for
cells. Sometimes, an error occurs when the
code is copied. Such errors are called
mutations.
• Two main types
– Gene mutations
• Changes in one or just a few nucleotides at a single
point in the DNA sequence
– Chromosomal mutations
• Changes in the number or structure of chromosomes
• May even change the location of genes on the
chromosomes or the number of copies of the genes
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Mutations
• Gene Mutations
– Caused by errors in replication
– Changes in DNA affect the amino acid sequence
– Point mutations – occur at a single point in the
DNA sequence
– Substitutions – one base is changed into another
• Usually affects one amino acid in the protein
– Insertions and Deletions – a base is inserted or
removed from the DNA sequence
• Causes frameshift mutations
• The “reading frame” of the genetic message is shifted and
chances every amino acid that follows the point of the
mutation
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Mutations
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Substitution Insertion Deletion
Section 12-4
Gene Mutations: Substitution,
Insertion, and Deletion
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Mutations
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Mutations
• Chromosomal Mutations – Changes the structure of chromosomes by changing
the location or the number of genes on a chromosome
– Deletions – the loss of all or part of a chromosome
– Duplications – produce extra copies of parts of a chromosome
– Inversions – Reverse the direction of parts of chromosomes
– Translocations – part of one chromosome breaks off and attaches to another
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Deletion
Duplication
Inversion
Translocation
Chromosomal Mutations Section 12-4
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Chromosomal Mutations
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Mutations
• Significance of Mutations
– Most mutations are neutral – have little or no
effect on the expression of genes or the coding of
proteins
– Dramatic changes can cause harmful results
• Genetic disorders (Chapter 14)
• Disruption of normal biological activities
• Cancer (many kinds)
• Some may even be incompatible with life!
– Also the source of genetic variability and
adaptation to new or changing environments
• Galapagos Island finches and beak size
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GENE REGULATION
Section 12-5
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Gene Regulation
• If a specific kind of protein is not continually used the gene for that protein can be turned “off” – Repressor Proteins – bind to the chromosome to block
transcription from occurring (common in prokaryotic cells)
• Operon – a group of genes that operate together
• Example: – Lac operon in E. coli – group of genes that code for proteins
that breakdown lactose (lactase)
– Lac repressor –
• Protein that bind to chromosome to block transcription of lac operon
• “turn off” the lac genes when lactose isn’t present
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Gene Regulation
• Eukaryotic Gene Regulation – Operons are not usually found in eukaryotic cells
• Most genes are controlled individually with more complex regulatory sequences than operons
– Many eukaryotic genes have a sequence of TATATA or TATAAA before the start of transcription
• Called a “TATA box”
• Promoters are usually found just before this spot
– Many different proteins can bind to these enhancer sequences resulting in very complex gene regulation for eukaryotes
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Gene Regulation
• Eukaryotic Gene Regulation (continued) – Allows for cell specialization
• All cells have a specific function for the body – Nerve cell genes are not expressed in liver cells
– Specialized cells: • regulate the expression of its genes
• only need to express genes it uses to function
– Areas of chromosome that help to regulate gene expression in Eukaryotes:
• Enhancer Sequence – Opening tightly packed chromatin
– Attract RNA polymerase
– Can act as a repressor to block transcription
• Promoter Sequence – a spot for RNA polymerase to bind to start transcription
• “TATA Box” - helps position RNA polymerase for transcription
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Gene Regulation
• Development and Differentiation – All cells in developing embryo undergo differentiation
• Cells become specialized in structure and function
– Hox Genes – • control the development and differentiation by “telling”
cells how they should differentiate as the body develops
• Determine an animal’s basic body plan
– Hox genes – expressed like cascade affect • Genes for head formation – toward one end of chromosome
• Genes for posterior body parts – at other end of chromosome
– Hox genes are turned on in precise order • Genes for anterior formation get turned on first and then
genes for development of posterior formations are turned on
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Gene Regulation
• Development and
Differentiation
– No mutations
normally occur on
Hox Genes
• Often lethal
– When mutations do
occur
• Change the organs
and body segments
during development
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Gene Regulation
• Development and
Differentiation
– No mutations normally
occur on Hox Genes
• Often lethal
– When mutations do occur
• Change the organs and
body segments during
development