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DNA - Transcription, Translation, and Mutations
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DNADNA Two strands coiled called
a double helix Sides made of a pentose
sugar Deoxyribose bonded to phosphate (PO4) groups by phosphodiester bonds
Center made of nitrogen bases bonded together by weak hydrogen bonds
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DNA Double HelixDNA Double Helix
NitrogenousNitrogenousBase (A,T,G or C)Base (A,T,G or C)
““Rungs of ladder”Rungs of ladder”
““Legs of ladder”Legs of ladder”
Phosphate &Phosphate &Sugar BackboneSugar Backbone
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Antiparallel StrandsAntiparallel Strands
One strand of DNA goes from 5’ to 3’ (sugars)
The other strand is opposite in direction going 3’ to 5’ (sugars)
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DNADNA
P
P
P
O
O
O
1
23
4
5
5
3
3
5
P
P
PO
O
O
1
2 3
4
5
5
3
5
3
G C
T A
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Synthesis Phase (S Synthesis Phase (S phase)phase) S phase during interphase of
the cell cycle Nucleus of eukaryotes
Mitosis-prophase-metaphase-anaphase-telophase
G1 G2
Sphase
interphase
DNA replication takesDNA replication takesplace in the S phase.place in the S phase.
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DNA ReplicationDNA Replication
Begins atBegins at Origins of ReplicationOrigins of Replication Two strands open forming Two strands open forming
Replication Forks (Y-shaped Replication Forks (Y-shaped region)region)
New strands grow at the forksNew strands grow at the forks
ReplicationReplicationForkFork
Parental DNA MoleculeParental DNA Molecule
3’
5’
3’
5’
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Proofreading New DNAProofreading New DNA
DNA polymerase initially makes DNA polymerase initially makes about about 1 in 10,0001 in 10,000 base pairing base pairing errorserrors
EnzymesEnzymes proofread and correct proofread and correct these mistakesthese mistakes
The new error rate for DNA that The new error rate for DNA that has been proofread is has been proofread is 1 in 1 1 in 1 billionbillion base pairing errors base pairing errors
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DNA Damage & DNA Damage & RepairRepair Chemicals & ultraviolet radiation
damage the DNA in our body cells Cells must continuously repair
DAMAGED DNA Excision repair occurs when any of
over 50 repair enzymes remove damaged parts of DNA
DNA polymerase and DNA ligase replace and bond the new nucleotides together
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The Code
Experiments during the 1960s demonstrated that the DNA code was a three-base code.
The three-base code in DNA or mRNA is called a codon.
DNA, RNA, and Protein
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Central Dogma
DNA is copied as RNA – Transcription RNA uses U
instead of T RNA is read to
make proteins – Translation Read by using
the reverse of RNA, similar to DNA’s 2nd strand
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Translation In translation, tRNA
molecules act as the interpreters of the mRNA codon sequence.
At the middle of the folded strand, there is a three-base coding sequence called the anticodon. Each anticodon is complementary to a codon on the mRNA.
DNA, RNA, and Protein
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Activity The first number tells you where the mutation starts,
followed by the number or what is deleted Ex: 487del7 means starting at base 487 7 bases
are deleted.
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What Are Mutations?What Are Mutations? Changes in the nucleotide
sequence of DNA May occur in somatic cells
(aren’t passed to offspring) May occur in gametes (eggs &
sperm) and be passed to offspring
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Chromosome Mutations
Five types exist:DeletionInversionTranslocation (don’t worry)Nondisjunction (don’t worry)Duplication
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DeletionDue to breakageA piece of a chromosome is lost
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InversionChromosome segment breaks off
Segment flips around backwards
Segment reattaches
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DuplicationOccurs when a gene sequence is repeated