understanding dna
TRANSCRIPT
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Understanding DNA
Presented by:
Mrs. Nelson
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OVERVIEW Name the four organic compounds
found in all living things. The focus of this chapter will be: What are the elements found in nucleic
acids? What is the subunit? What are the two types of nucleic acids? What is the function of DNA?
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Discovering DNA Frederick Griffith
studied bacteria cause pneumonia.
Smooth strain -disease
Rough strain - harmless
What caused the difference?
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Griffith’s Experiment
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Griffith’s Conclusion
The harmless bacteria could “acquire” the ability to cause disease. How?
Transformation Bacteria can take “something” from
each other By doing so, they can take on different
traits.
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Transformation
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Discovery of DNA
Griffith didn’t know what it was that bacteria were taking from each other.
He did know that this “something” gave organisms their traits.
Later, it was discovered that this was DNA.
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DNA (Deoxyribonucleic acid). All living things contain DNA. Source of genetic traits because it is the
the directions cells use to build proteins.
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Where is DNA?Cell Nucleus Chromosome Gene DNA
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Chromosomes a closer look …
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What does DNA look like? DNA made subunits: nucleotides Nucleotide: sugar (deoxyribose),
phosphate group, nitrogen base DNA 4 nitrogen bases: adenine,
guanine, thymine and cytosine ***Scientists knew DNA was made of
these parts- they did NOT know how all the pieces fit together!
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“The race to build the 1st DNA model”
Rosalind Franklin
1) 2 strands like a twisted rope
2) Molecules were evenly spaced out…
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2 Categories of Bases: Purines-
“larger bases”
adenine (A)
guanine (G) Pyrimidines-
“smaller bases”
cytosine (C)
thymine (T)
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Chargaff’s Rule
Measured amounts of each base in various organisms and found:
amount of adenine (A) = thymine (T) amount of cytosine (C) = guanine (G)
This meant A only bonds T and C only bonds G
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Structure of DNA Double helix- “spiral staircase”, 2 strands of
nucleotides “siderails” sugar and phosphate “rungs” bases (base pairs connected by hydrogen
bonds) bases attach sugar molecules, phosphate molecules
between sugars complementary- sequence of bases on one strand
determines the sequence of bases on other strand antiparrallel- strands are oriented opposite to each
other with respect to the carbon atoms in the sugar molecules
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Watson and Crick “Double Helix”
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Antiparallel- 5’ and 3’ ends
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What is the job of all cells??? Process called Protein Synthesis: DNARNA Protein 2 stages: Transcription and Translation
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RNA (Ribonucleic acid)
Nucleic acid… helps DNA make proteins _____RNA____vs._____DNA___
single strand double strand
sugar= ribose sugar= deoxyribose
A, C, G, U (uracil) A, T, C, G
mRNA, rRNA, tRNA “DNA is DNA”
all over nucleus only
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Structure RNA
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Transcription: Part 1 :Protein Synthesis Problem:
DNA (directions build protein) can not leave nucleus go to ribsome
Information DNA copied RNA (messenger)
DNA complementary mRNA occurs nucleus
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Steps in Transcription 1st- DNA untwists 2nd- enzyme RNA polymerase
moves along DNA strand creating “complementary mRNA”
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Genetic Code
Goal make protein protein - bunch amino acids every 3 bases (nucleotides) mRNA
code amino acid - called codon DNA: ATA CGG AAT (3
triplets) mRNA: UAU GCC UUA (3
codons)
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What amino acids are needed to build the protein?
mRNA - UAU GCC UUA
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Translation: Part 2:Protein Synthesis
Protein builtHappens ribosomerequires tRNA (transfer RNA) tRNA carries amino acids ribosomemRNA complementary tRNA
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tRNA One end amino
acid Other end 3
bases called anticodon
anticodon complementary codon (mRNA/tRNA)
“safety check”
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Steps Translation mRNA leaves nucleus goes ribosome (made
of rRNA) 1st- “start” codon 2nd- tRNA brings amino acids ribosome
(codons-anticodons pair) 3rd- bonds join amino acids 4th- stop codon ribosome releases protein cytoplasm
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What is DNA Replication?
Process of “copying” DNA exactly Process must be completed before
cells can divide (reproduce) Multicellular organisms- cell division =
growth and repair/replacement Unicellular organisms- cell division =
reproduction
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DNA Replication
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DNA Replication (process) 1st- enzyme helicase
attaches to DNA and causes it to unzip at the replication fork (must break hydrogen bonds-bases)
2nd- enzyme DNA polymerase moves along leading strand adding complementary bases (continuously in 5’3’ direction toward replication fork)
3rd- lagging strand completed next but Okazaki fragments result (discontinuous away from replication fork)
4th- enzyme ligase joins the fragments on lagging strand Summary: 1 DNA molecule 2 DNA molecules
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Mutations
If DNA does not get copied correctly, a mutation can arise.
Mutation- change in DNA sequence “Mutagens” are things found in the
environment that can get into your cells and “scramble” your DNA.
Three known mutagens:
1.) chemicals 2.) viruses 3.) UV radiation
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Mutations – change in DNA
Substitution
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Effects of Mutations… DNA carries instructions to build proteins. If the DNA is changed, proteins will be built
incorrectly. Two general types of mutations:
1. Gene mutation (effects one gene on chromosome)
2. Chromosome mutation Three different types of gene mutations
1. subsitution
2. Insertion
3. Deletion
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Substitution
THE FAT CAT SAT
THE FAT RAT SAT
Changing one letter, changes one word, which changes the meaning of the sentence.
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SubstitutionDNA: TAC GCA TGG AATMRNA: AUG CGU ACC UUAA.ACID: Met - Arg - Thr - Leu
DNA: TAC GTA TGG AATMRNA: AUG CAU ACC UUAA. ACID: Met - His - Thr - Leu
Results in one amino acid being altered
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Insertion
THE FAT CAT SAT
THE SFA TCA TSA T
Inserting one letter, shifts all other letters over, creating several words to be incorrect. This is also known as a “frame-shift” mutation.
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InsertionsDNA: TAC GCA TGG AATMRNA: AUG CGU ACC UUAA.ACID: Met - Arg - Thr - Leu
DNA: TAT CGC ATG GAA TMRNA: AUA GCG UAC CUU AA.ACID: Iso - Ala - Tyr - Leu
Results in several amino acids being altered
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Deletion
THE FAT CAT SAT
THE ATC ATS AT
Similar to Insertion (frame-shift).
REMOVE
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Deletion
DNA: TAC GCA TGG AATMRNA: AUC CGU ACC UUAA.ACID: Met - Arg - Thr - Leu
DNA: TAG CAT GGA ATMRNA: AUC GUA CCU UAA. ACID: Iso - Val - Pro - None
Results in several amino acids being altered
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Significance of Mutations Some mutations may be “neutral,” they
won’t have an effect on the protein being built.
Some mutations can be very harmful and cause genetic disorders.
Some mutations lead to genetic variation in a species.
(Ex. Tongue rolling)
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