Bio. B.1.2: Explain how genetic information is inherited
Bio.B.1.2.1-Describe how the process of DNA replication results in
the transmission and/or conservation of genetic material.
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Before we get started What is genetics? What is the genetic
material?
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The Role of DNA: What is the role of DNA in heredity? DNA must
be capable of: 1. Storing information 2. Copying information 3.
Transmitting information
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DNA stores information
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DNA copies and transmits information
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DNA is made of nucleotides Nucleotides are the building blocks
of DNA Nucleotides composed of: 1. Phosphate 2. Sugar (deoxyribose)
3. Nitrogen Base Adenine (A) Guanine (G) Cytosine (C) Thymine
(T)
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Nucleotides link together
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STRUCTURE of DNA Chargaff: Chargaffs Rule: percentages of A
(adenine) and T(thymine) were equal in many sample of DNA
percentages of C (Cytosine) and G (Guanine) were also equal
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STRUCTURE of DNA Chargaffs Data If a species has 35% adenine in
its DNA, what is the percentage of the other three bases? Can you
figure it out?
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STRUCTURE of DNA Rosalind Franklin X-ray picture of DNA DNA had
two strands that twisted around each other like a coil
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STRUCTURE of DNA Watson and Crick James Watson and Francis
Crick built a three dimensional model of DNA Shape of the DNA =
double helix. Strands run in opposite direction (anti-parallel)
Base pairing rules (A pairs with T; C pairs with G) Strands held
together by hydrogen bonds Watson TED talk
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Antiparallel DNA Strands:
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What happens to the DNA structure during S phase? DNA
replicates (duplicates, is copied, etc.) Watson and Cricks 3D model
immediately proposed a replication mechanism animation
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DNA Replication: DNA gets copied during interphase Ensures that
each resulting cell has the same complete set of DNA Each strand
has all the information needed to construct the other strand
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Process of DNA Replication: 1. DNA is unzipped or separated
Enzyme = helicase Breaks hydrogen bonds that hold the two strands
of DNA together
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2.New strands are built Enzyme = DNA polymerase Joins
individual nucleotides together to produce a new strand of DNA that
is complementary to the other Proofreads each new strand Process of
DNA Replication:
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How is replication different in prokaryotes? In eukaryotes,
replication begins at many different locations and proceeds in both
directions until each chromosome is completely copied In
prokaryotes, replication begins at one point and proceeds in two
directions until the entire chromosome Is copied
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DNA Replication Prokaryotes Vs eukaryotes
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Quick Check 1. A nucleotide does not contain A.A 5-carbon sugar
B.An amino acid C.A nitrogen base D.A phosphate group
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Quick Check 2. According to Chargaffs rule of base pairing
which of the following is true about DNA? A.A=T and C=G B.A=C and
T=G C.A=G and T=C D.A=T=G=C
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Quick Check 3. The bonds that hold the two strands of DNA
together come from A.The attraction of phosphate groups for each
other B.Strong bonds between nitrogenous bases and the
sugar-phosphate backbone C.Weak hydrogen bonds between bases
D.Carbon-to-carbon bonds in the sugar portion of the
nucleotides
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Quick Check 4. In prokaryotes, DNA molecules are located in the
A.Nucleus B.Ribosomes C.Cytoplasm D.histones
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Quick Check 5. In eukaryotes, nearly all the DNA is found in
the A.Nucleus B.Ribosomes C.Cytoplasm D.histones
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Quick Check 6. The main enzyme involved in linking individual
nucleotides into DNA molecules is A.DNA protease B.Ribose
C.Carbohydrate D.DNA polymerase
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PREC-CLASS All of the parts of a cell are controlled by the
information in DNA, yet DNA does not leave the nucleus. How do you
think the information in DNA might get from the nucleus to the rest
of the cell?
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Central Dogma of Molecular Biology Describes flow of
information from DNA to protein RNADNAProtein
transcriptiontranslation RNA is the link between DNA and
proteins.
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Analogy for central dogma The master plan has all the
information needed to construct a building.
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Analogy for central dogma But builders never bring a valuable
master plan to the building site where is might be damaged or
lost.
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Analogy for central dogma Instead, builders work from
blueprints, inexpensive disposable copies of the master plan.
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Analogy for central dogma Master plan = DNA Building site =
ribosomes (in cytoplasm) Blueprint copies = RNA
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DNA vs RNA DNA Double stranded Made of nucleotides Sugar =
deoxyribose Bases = C,G, A, T RNA Single stranded Made of
nucleotides Sugar = ribose Bases = U instead of T
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Different types of RNA 1.Messenger RNA carries the instructions
from DNA to cytoplasm on how to make the protein 2.Ribosomal RNA
form ribosomes in cytoplasm to help build the protein 3.Transfer
RNA delivers the amino acids needed to build the protein
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Transcription (RNA synthesis) DNA RNA Occurs in the nucleus
Requires RNA polymerase Builds RNA strand Uses one strand of DNA as
template Involves single gene Produces MANY RNA copies
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RNAi Video RNAi Video
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Replication vs Transcription Replication copies the entire DNA
Transcription only copies one gene Replication only makes one copy
Transcription makes many copies BOTH involve complex enzymes BOTH
follow complementary base pairing BOTH occur in the nucleus
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If you were given the sequence of a DNA strand, could you
figure out the sequence of the mRNA strand? Remember, U instead of
T in RNA!!! For example: DNA T A C G C C C T A T T G A T mRNA ?? A
U G C G G G A UA AC U A
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Central Dogma of Molecular Biology Describes flow of
information from DNA to protein RNADNAProtein
transcriptiontranslation
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Translation (protein synthesis) RNA protein Occurs in the
cytoplasm Involves ribosome, mRNA, tRNA and amino acids RNA is
translated into amino acid sequence
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The language of protein synthesis Language of RNA = nucleotides
Language of protein = amino acids Triplet code: three mRNA bases
(codon) code for one amino acid
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Genetic Code: Codon = a group of three nucleotide bases in the
mRNA that codes for a particular amino acid
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Genetic Code: (mRNA codon to amino acid)
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Genetic Code START codon signals the start of translation AUG
also codes for methionine STOP codons signal stop of translation
UGA, UAA, UAG Do not code for any amino acid
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Genetic Code = common language UNIVERSAL shared by all
organisms REDUNDANT more than one codon may code for the same amino
acid Allows flexibility if mistakes are made
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Quick Check A certain gene has the following base sequence:
GACAAGTCCAATC Write the sequence of the mRNA molecule transcribed
from this gene Divide you mRNA sequence into codons How many
codons? What amino acid does each codon code for? How many amino
acids?
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QUICK CHECK Remember, U instead of T in RNA!!! For example: DNA
T A C G C C C T A T T G A T A mRNA ?? Amino acids
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The role of ribosomes in translation Ribosomes act as the
machinery Ribosomes use the sequence of codons in mRNA to assemble
amino acids into protein chains
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Each tRNA molecule carries one kind of amino acid Anticodon on
tRNA recognizes complementary codon on mRNA For example, tRNA for
methionine has the anticodon UAC which pairs with the methionine
codon (AUG) The role of tRNA in translation
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Process of Translation 1.Ribosome binds to mRNA 2.mRNA codons
attract complementary tRNA anticodons 3.peptide bond forms between
amino acids then breaks bond holding the amino acid to the tRNA
4.Empty tRNA leaves; the ribosome pulls the mRNA exposing the next
codon
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QUICK CHECK Remember, U instead of T in RNA!!! For example: DNA
T A C G C C C T A T T G A T A mRNA ?? Amino acids tRNA
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Central Dogma of Molecular Biology Describes flow of
information from DNA to protein RNADNAProtein
transcriptiontranslation
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Mutations are changes in the DNA 1.Gene mutations (single gene)
2.Chromosomal mutations (multiple genes involved) mutated base
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1. Gene Mutations Also known as point mutations because they
occur at a single point in the DNA sequence Occur during
replication Different types A.Substitutions B.Insertions and
deletions
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A. Substitutions One base is changed to a different base Only
affect one amino acid Sometimes have no effect (silent) EX:
changing mRNA codon from CCC to CCA Codon still specifies proline;
SILENT EX: changing mRNA codon from CCC to ACC Replaces proline
with threonine
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B. Insertions and Deletions Frameshift mutations shift the
reading frame Effects are dramatic Can change every amino acid
after the mutation
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Frameshift Mutations
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2. Chromosome mutations Changes in number or structure of
chromosomes Occur during meiosis Four types A.Deletion (loss of all
or part of a chromosome) B.Duplication (extra copy) C.Inversion
(reverse in the direction of a chromosome) D.Translocation (one
chromosome attaches to another)
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Mutagens Chemical or physical agents in the environment that
can cause mutations in DNA Include Pesticides, tobacco,
environmental pollutants, UV light, X-rays
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Harmful and Helpful Mutations Mutations can be harmful if They
cause drastic changes in the protein that is produced Defective
proteins can disrupt normal function Ex: sickle cell anemia, some
cancer
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Harmful and Helpful Mutations Beneficial effects Variation
produced by mutations can be highly advantageous to organisms in
different or changing environments Responsible for evolution EX:
pesticide resistance (bad news for humans but good news for
mosquitoes) EX: human resistance to HIV