Ch. 12 – DNA
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Transcript of Ch. 12 – DNA
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Ch. 12 – DNA• Introduction to DNA (Sec. 12.1)
• History, important discoveries, who’s who in genetics
• Structure of DNA (Sec. 12.1)• Genes and the Double Helix
• Chromosomes and DNA replication (Sec. 12-2)
• Chromosome structure and function
• RNA and Protein synthesis (Sec. 12.3)• Structure and types of RNA• Transcription, Translation
• Mutations (Sec. 12.4)• Types of mutations and their significance
• Gene Regulation (Sec. 12.5)• Eukaryotes and Prokaryotes• Differentiation
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Where is DNA?
Chromatin
Nucleus
Chromatin = DNA bound to protein, arranged in units called chromosomes
DNA is located in the Nucleus of Eukaryote cells. Prokaryotes don’t have a nucleus so their DNA is floating in the cytoplasm.
Humans have 46 chromosomes
The Double HelixChromosomes are composed of two strands of DNA wrapped around each other, as shown to the left.
Sec. 12.1
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History of DNA• Fredrick Griffith (1928) wanted to find
out how bacteria caused pneumonia, his experiment:Disease-causing bacteria (smooth colonies)
Harmless bacteria (rough
colonies)
Heat-killed, disease-causing
bacteria (smooth colonies)
Control(no growth)
Heat-killed, disease-causing bacteria (smooth colonies)
Harmless bacteria (rough colonies)
Dies of pneumonia
Lives
Live, disease-causing
bacteria (smooth colonies)
Dies of pneumonia
Fred killed Kenny!
Griffith found that bacteria can “transform” each other, or share information, like how to kill a mouse
Lives
I didn’t die?
But how? What did they pass
to each other?
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History of DNA• Oswald Avery (1944) repeated Griffith’s work
and discovered that nucleic acid DNA stores and transmits the genetic information from one generation of an organism to the next
He aint bout that life doe.
Alfred and Martha
Aye, what yo name
is?
•Alfred Hershey and Martha Chase and the Hershey-Chase Experiment (1952):
-Studied viruses that infect bacteria = bacteriophage-Bacteriophages = “bacteria eaters” inject their own DNA into cell and use the cell to produce many copies of themselves, killing the bacteria because it splits open, releasing hundreds of new viruses! Eeek! -What Hershey and Chase found:
-Used “markers” or radioactive isotopes-Discovered that the genetic material of bacteriophage was DNA, not protein
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What is DNA? DeoxyriboNucleic Acid
• DNA is a molecule made up of Nucleotides• Nucleotides are made up of 3 things:
1. 5- carbon sugar called Deoxyribose
2. A nitrogenous base (contains nitrogen)3. A phosphate group (P= phosphate)
PP
sugar
aden
ine
guanin
e
sugarsugar
PP
cyto
sine
thym
ine These bases, A G
C T, are arranged into a sequence, or a gene, like letters of our alphabet are arranged into words.
1. Purines= 2 kinds
A = Adenine (AD-uh-neen) G = Guanine (GWAH-neen)
2. Pyrimidines = 2 kindsC = Cytosine (SY-tuh-zeen)
T = Thymine (THY-meen)
sugar
P
•There are 2 types of Nitrogenous bases in DNA
Adenine goes with Guanine A-G
Cytosine goes with Thymine C-TThymine (DNA only)Uracil (RNA only)
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Watson and Crick
• Francis Crick and James Watson (~1953)
Watson and Crick identified and linked together key pieces of research, and along with their own discoveries, described the basic structure of DNA
The “twisted ladder” shape of DNA became known as the double helix. The 2 DNA strands wind around each other, like a winding staircase
James Watson
Francis Crick
Hee hee, my dear Watson we’ve discovered the secret to life!
Yes, you bloody fool, we discovered
the double helix!
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Double Helix Structure
Key
Adenine (A)
Thymine (T)
Cytosine(C)
Guanine (G)
Each strand is made up of a chain of nucleotides. Nucleotide
Ribose and Phosphates join together forming the backbone of the DNA molecule
The 2 strands are held together by hydrogen bonds between the bases Adenine and Thymine and between Guanine and Cytosine.
Hydrogen
bonds
Sugar-phosphate backbone
DNA is a double helix in which two strands are wound around each other (like a twisted
ladder).
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Hydrogen Bonds• Hydrogen bonds (sharing of one electron
between 2 Hydrogens) between the nucleotides (AGCT) holds the 2 strands of DNA together with a fairly strong force
H H
DNA strand: A G C T G G C T A A T C GComplementa
ry DNA Strand:
T C TA A
A + T
=
love
G + C =
Love Forever!
A=T G=C
Sugar-phosphate backbone
Nucleotide
Hydrogen
bonds
The binding together of the nucleotides with Hydrogen bonds is called Base Pairing
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Horses = 64 chromosome
s
Cows = 60
Cats and Dogs = 38
Chickens = 78
Who has DNA? All living things do!• Prokaryotes (bacteria) don’t have a nucleus,
and their DNA is found floating in the cytoplasm; usually they have a single strand of DNA, or chromosome
• Of course, Eukaryotes are more complicated!– Eukaryote = YOU! And, any organism with
their DNA inside the nucleus. Eukaryotes generally have 1000X more DNA than bacteria
– Eukaryote DNA is organized into Chromosomes
Having MORE chromosomes doesn’t mean an organism is bigger or smarter!Cows are smarter than humans?NO!Chickens are bigger and smarter than dogs? Hmm…..
Humans = 46 chromosomes
Fly = 8
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DNA double helix
How DNA fits into a cell1. Eukaryotic chromosomes contain DNA wrapped around proteins called histones.
2. DNA and histone together = chromatin
3. Wound strands of chromatin are called nucleosomes, and these are tightly coiled and supercoiled to form chromosomes
Histones
Chromosome
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DNA Replication
DNA strand: A G C T C C G T C A A T T G
Opposite strand: T T TC C CG G G GA A A A
Complementary DNA strands
Complementary Strand of DNA
Complementary Strand of DNA
Replication = the process where DNA makes a copy of itself, base by base, producing 2 new complementary strands , and each strand serves as a template for the new strand.
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Original strand = blue
DNA Replication
New strand = orange
Growth
Growth
During Replication, the new strand is made from the original strand, which serves as a template.
The new strand (orange) is “complementary” to the new strand (blue).
Replication Fork
Nucleotides
DNA polymerase
DNA polymerase = an enzyme that joins two nucleotide bases to produce a DNA molecule and “proofreads” each copy to make sure it’s correct
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What does DNA have to do 1st, before it can replicate?
Answer: It has to unwind! Open up!! Unzip!!!!
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How does it…..?• Problem:
– DNA is in the nucleus and never leaves– Proteins are made in the cytoplasm– How does the instructions for the
protein, the DNA, get out to the ribosomes?
• Solution:– DNA doesn’t leave the nucleus, but the
information from DNA does– Send a copy of the instructions!
Section 12-3
Introducing the messenger service……. RNA
RNA = Ribonucleic Acid
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DNA to RNA, the 1st step• “I can’t help it, it’s in my genes!” or
“It’s genetic.”
•Genes = coded DNA instructions that control the production of proteins within the cell
•The double helix DNA structure doesn’t explain how a gene works, so to understand that, we have to decode the information within a gene
1st step in decoding genes = copy part of the nucleotide sequence from DNA to RNA
RNA (ribonucleic acid) = contains coded information for making proteins
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RNA Structure• RNA is like DNA, but with 3 main differences:
– 1. Sugar in RNA is ribose instead of deoxyribose– 2. RNA is generally single-stranded, not double
stranded– 3. RNA contains Uracil instead of Thymine
Think of RNA this way: Would you give your friend your original CD, or would you give
them a copy of it?
(YER-a-sil)
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Types of RNA
• 3 main types of RNA:1. Messenger RNA (mRNA)2. Ribosomal RNA (rRNA)3. Transfer RNA (tRNA)
Each type of RNA may have a different function, but all RNA has a single goal – to make proteins
It’s all they care about, all they want to do, they are obsessed with making proteins!
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Different Functions of RNA
•rRNA (ribosomal RNA) = what makes up a ribosome (the organelles that make proteins) thus it’s called “ribosomal” RNA
•tRNA (transfer RNA) = a molecule that “transfers” amino acids to the ribosome as directed by the coded mRNA, to form proteins
•mRNA (messenger RNA) = a messenger service, they carry messages (copies of a gene) from DNA, in the form of RNA, to the rest of the cell
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Transcription
Adenine (DNA and RNA)Cystosine (DNA and RNA)Guanine(DNA and RNA)Thymine (DNA only)Uracil (RNA only)
1. RNA polymerase binds to DNA and separates the 2 DNA strands (unzips them)
2. RNA polymerase only binds to regions of DNA called “promotors” that have specific base sequences that say, “Hey, start here!”
3. RNA polymerase then uses 1 strand of DNA as a “template” to assemble the strand of RNA
RNA polymerase
•Transcription = production of RNA molecules by copying part of the DNA nucleotide sequence into a complementary sequence of RNA
–Requires an enzyme called RNA polymeraseTranscription Process (How it
happens):
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RNA Editing
removedremoved
Exon Exon Exon
Exon Intron Exon Intron ExonRNA
“edited” mRNA
RNA editing is cutting out the introns, and splicing the exons together
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20 amino acids and only 4 nucleotide bases to code for them, AGCT, sounds impossible, but it’s not.
The Genetic Code• Proteins – made by joining amino acids into
long chains called polypeptides• Any combination of the 20 different amino
acids make up a protein• The arrangement of amino acids determines
what a protein is and what it does• So, we have the instructions (DNA) for
making a protein, but how do we translate that into a protein?
• We use the Genetic Code!
Poly = many!
Peptide = protein
The Genetic Code = the language of mRNA instructions for making proteins
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How it works…• The genetic code is read 3 letters, or bases,
at a time, and this forms a sort of “word”
• Each 3 letter “word” is in mRNA is known as a codon
• Codon = 3 consecutive (in a row) nucleotide bases that specify 1 amino acid to be added to the polypeptide chainmRNA sequence = UCGCACGGU
Now, read it 3 bases at a
time…
UCG CAC GGU
Each codon represents a different amino acid!
GlycineSerine –Histidine –
Box 64
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How It’s Done4 different bases (AGCT) = 64 possible 3-base codons
4 x 4 x 4 = 64
stop
stop1
23
Some amino acids, like Valine, Serine, Alanine, Arginine, etc. can be specified by more than one codon.
Box 65
Some codons, like AUG, specify only 1 amino acid. Ex. AUG can either be a “start” codon, or a Methionine.
Box 65
There are 3 “stop” codons that don’t code for any amino acid. Stop codons act like the period at the end of a sentence- they signal the end of the polypeptide sequence.
Box 65
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Can You Break the Code?
DNA: AAC GTA TGC GAT
mRNA: UUG CAU ACG CUA
Amino Acid Sequence:
Leu His Thr Leu
1
2
3
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Translation• You have the instructions (sequence of
nucleotide bases), but who “reads” them?
• The Ribosome “reads” the sequences in a process called Translation
You, go there, and you, go here, and stop pushing each other! Get in line,
you AA idiots!
Translation = occurs in the ribosomes, and is when the cell uses information from mRNA to produce, or assemble, proteins
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Translation
nucleus
mRNALysine
tRNA
Methionine
Phenylalanine
mRNA Start codon
ribosome
cytoplasm
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ribosome
ribosome
tRNA
tRNA
mRNA
mRNA
Growing polypeptide chain
Lysine
Peptide Bond
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Roles of RNA and DNA• DNA is the “Master Plan” for a
building (your body).• RNA=“Blueprints”• DNA is safely stored in the nucleus,
and the copies of DNA, or the RNA, go out into the cytoplasm where the proteins are built.
• What else can we compare this process to?
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•Genes code for enzymes and proteins that do everything from controlling the color of a flower petal to ones that determine your blood type.
Genes and Proteins• Most Genes contain instructions for assembling
proteins.•Many proteins are enzymes, and all enzymes are proteins that catalyze and regulate chemical reactions
•Proteins are the tools specifically designed to build or operate a part of a living cell.
Genes contain instructions for proteins and enzymes, the molecules that make
all life possible.
An important genetics concept!
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Mutations• Everyone makes mistakes, it’s a part of life.• Genetic mistakes are called Mutations• Mutation = any change in the genetic
material• All mistakes aren’t bad, and all Mutations
ain’t all bad either! • Types of mutations:
1. Point mutations = changes in 1 point, or
1 nucleotideThese can be either:Substitutions = 1 base is substituted for
anotherInsertions = 1 base is inserted into the DNA
sequenceDeletions = 1 base is deleted from the DNA
sequence
Section 12-4
The key to remember is a Point Mutation occurs at 1 point in the DNA sequence
Box 73
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Point Mutations• Changes at a single point, or a single
base, can either have NO effect (not change the amino acid specified), or have a HUGE effect
• Substitutions do NOT have as big of an effect as….– Insertions and Deletions usually have a
BIG effect on the amino acid sequence
• Try adding another letter to the word “CAT”
If you add an extra letter to CAT, it either becomes nonsense, or it has a different meaning!
CAT CYATCATS
Substitutions do NOT cause Frameshift mutations!!! Insertions and Deletions DO cause Frameshift
mutations!!!
Changes like this are called Frameshift Mutations because they are mutations that shift the “reading frame” by one letter
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Amino: Met Arg Thr Leu Acids
Frameshifts
DNA: TAC GCA TGG AATmRNA: AUG CGU ACC UUA
Amino: Met Arg Thr Leu Acids
Substitution
DNA: TAC GTA TGG AAT
mRNA: AUG CAU ACC UUA
DNA: TAC GCA TGG AAT
mRNA: AUG CGU ACC UUA
Amino: Met Arg Thr Leu Acids
Insertion
DNA: TAT CGC ATG GAA T
mRNA: AUA GCG UAC CUU A
Amino: Ile Ala Try Leu Acids
Big change, mRNA codes for different
amino acids!
No change, mRNA still codes for the amino acid Arg
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What about deletions?
THE FAT DOG ATE THE PIE
Deletion
THE FAT DOG ATE THE PIE
TEF ATD OGA TET HEP IE
Utter nonsense. The reading frame shift made the sentence change just as a deletion or insertion would change the amino acid sequence of a protein
If you delete the “H” in the, it moves the whole “reading” frame over one letter!
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Types of Mutations • 2. Chromosomal Mutations = involve
much larger changes because: – They involve the # or structure of
chromosomes themselves– And chromosomes contain 1000’s of
genes!!!!• What would happen if you lost a whole
chromosome? Added a whole chromosome?
You’d either be dead, or you’d have a bad disease!
Box 76
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Chromosomal Mutations
Deletion
Duplication
Inversion
Translocation
4 Types of Chromosomal Mutations:1. Deletions = lose part of a chromosome (many genes!)
Box 77
2. Duplications = gain extra parts of a chromosome, or an extra whole chromosome3. Inversions = reverse the direction of parts of a chromosome- mixes it up!4. Translocations = part of a chromosome breaks off and attaches to another chromosome
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Effects of Mutations• Many mutations are neutral, meaning they have little
effect on the expression of genes or the function of proteins coded by the genes
•Harmful mutations are the cause of many human genetic disorders, like cancer•Mutations that result in a BIG change in the DNA or amino acid sequences are usually harmful- they produce defective proteins or no protein at all!
•Beneficial mutations (yes there are some!) can give an organism a survival advantage (evolution
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Gene Regulation• Not all genes are expressed all the time• Expressed genes = a gene that is transcribed
into mRNA, which leads to creating a protein• Humans have ~30-40,000 genes and our
bodies can’t be making all those proteins all at once!
• In the jumble of DNA, there are patterns, and biologists have identified patterns that represent how gene expression is controlled
Section 12-5
–3 Examples are:–Promotors = binding sites for RNA polymerase–Start and Stop signals = starts and stops transcription–Operons = group of genes that operate together
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Eukaryote Gene Regulation• Prokaryote = organisms without a nucleus,
most are bacteria• Eukaryotes = (YOU!) organisms with their
DNA contained in a nucleus (humans, plants, animals, fungi, etc.)
• Eukaryote genes are mostly controlled individually and have complex regulatory sequences
1. TATAA = the “TATA” box, a sequence that occurs before the start codon, a place where RNA polymerase binds2. Promotors = sequences that are signals for RNA polymerase found just before the TATA box
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Typical Gene Structure
Promoter(RNA polymerase binding site)
Regulatory sites DNA
strand
Start transcription
Stop transcription
Direction of Transcription
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Development and Differentiation• Differentiation = when cells become specialized
in structure and functionEarly development, in the beginning, all of an embryo’s cells have the ability to become anything- heart, eye, leg, toe, wing, etc. Later development, cells specialize and become the toe, heart, leg or wing cell, and once they have specialized, they lose the ability to be anything else
Normal fruit fly
Legs instead of antennae! Caused by Human Hox-13 mutation
Hox genes = series of genes that control the differentiation of cells and tissues in the embryo, the BODY PLAN. A mutation in the Hox Genes can completely change the organs that develop in specific parts of the body.