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Criteria for DNA to be accepted as genetic material
Present in nuc and chromosomes, doubles in cell cycle, twice abundance in diploid, same pattern of transmission as its genetic information
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DNA was found by
Miescher
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What did Miescher do with cells
Isolated nuclei, fibrous substance nuclein was extracted. DNA was found in chromosomes using dyes.
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To help support Mieschers theory, what did they do with stained cells
They put them through a flow cytometer
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What did putting cells through flow cytometer do for miescher
Helped prove that nondividing cells have some amount of nuclear DNA and after meiosis, gametes have half
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What happens when a virus affects a bacterium
It injects only its DNA to change the genetic program of the bacterium.
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A type of experiment that showed that DNA from one strain could genetically transform to another
Transformation experiment.
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Two questions that scientists wanted to answer about DNA
How is it replicated and how does it direct protein synthesis.
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Who discovered shape of DNA
Rosalind Franklin. She saw it was spiral through crystallographs.
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Who found that A=T and C=G
Erwin Chargraff; chargraffs rule.
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Who built a model of dna and saw it was antiparallel and helical
Crick and Watson
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What did Watson and crick suggest about shape of DNA
Phosphate backbone, nucleotides on inside, base pairs have same width down helix
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4 key features of DNA structure:
Double-stranded helix, right handed, antiparallel, outer edges of bases are exposed in major and minor grooves
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Why do dna grooves exist
Because the backbone of dna strands not evenly spaced
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What are the outer edges of the base pairs on DNA exposed to?
Hydrogen bondng.
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Surfaces of AT and GC base pairs are
Chemically distinct
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4 important functions of DNA
Storage of info, replication, susceptibility to mutation, expression of coded info as phenotype
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What does semiconservative replication mean
That each parental strand serves as a template for a new strand.
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What are 2 steps of DNA replication
Unwind double helix so two templates are available, and two nucleotides form the base pairs with template strands that are linked together by phosphodiester bonds
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The template DNA is read in this direction
3-to-5
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During DNA synthesis, where are nucleotides added and why
To 3 end of strand because of free hydroxyl group (OH-)
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dNTPs stands for
deoxyribonucleoside triphosphates aka deoxyrybonucleotides
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these are the building blocks of DNA, where two phosphate groups are released and 3rd is bound to 3 end
dNTPs
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what does DNA replication begin with?
The binding of a large protein complex to a specific site on the DNA molecule
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What does the large protein complex contain? What does it do?
It contains DNA polymerase which catalyzes addition of nucleotides.
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Where does the large protein complex bind to
The ori
origin of replication
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Where does the DNA unwind
Replication fork
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How would replication be sped up
If a chromosome was linear and had multiple origins of replication
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What do you first need to begin DNA replication
A primer- a starter strand; it is complementary to the dna Template. You then need a primase (enzyme) to synthesize dna one nucleotide at a time.
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Where does DNA polymerase add nucleotides
To the 3 end
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DNA polymerases are larger than
Their substrates, dNTPs, and the template DNA
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In the hand shape enzyme, what does the palm and fingers do
Palm bring the active site and substrate together, fingers recognize nucleotide bases
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What direction does DNA replicate
5-to-3
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How is the leading strand oriented to grow
It grows its 3 end as the fork opens
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How is the lagging strand oriented
So that its 3 end is exposed and gets farther from the fork.
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What are okazaki fragments
Synthesized lagging strands that occur in small discontinuous stretches
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What does each okazaki fragment require?
It requires its own primer, synthesized by primase
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How does fragmentation happen in Okazaki fragments
DNA polymerase adds nucleotides to 3 until it reaches the primer of the previous fragment, a different DNA polymer replaces primer with DNA. The final phosphodiester linkage is catalyzed by DNA LIGASE
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DNA polymerase is very fast and it is processive. What does this mean?
It means it catalyzes many sequential polymerization reactions each time it binds to DNA.
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Okazaki fragment are added to RNA primers for what purpose
To replicate lagging strand
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When does fragmentation end in okazaki fragments
When the last primer is removed because there is no more 3 to extend.
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What happens to the ends of okazaki fragments
The ends are cut after replication and chromosome is slightly shortened after each division
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What are telomeres
Repetitive sequences at the ends of eukaryotic chromosomes.
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What do telomeres do
They prevent the chromosome ends from being joined by DNA repair system
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What is telomerase and what does it do
It contains RNA sequence; acts as template for telomeric DNA sequences. Lost over time in most cells but not in cells that continuously divide, like bone marrow and gametes
- How can errors in DNA replication be fixed
- Proofreading, mismatch repair
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How does proofreading work in repair mechanisms
If bases are paired incorrectly, the nucleotide is removed
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How does mismatch repair work in repair mechanisms
Other proteins scan for mismatched bases missed during the proofreading. They them replace them with the correct ones
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That are the 5 things that PCR technique requires
Double stranded DNA sample, two short primers complementary to ends of sequences to be amplified. Four dNTPs, a DNA polymerase that works at high temps, Salts and buffer
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Changes in the nucleotide sequence of DNA that are passed on from one cell to another
Mutation
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Two ways errors that are not corrected can be passed on to daughter cells
Somatic mutations & germ line mutations
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What are somatic mutations
They occur in somatic cells; passed on by mitosis bu not to sexually produced offspring
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What are germ line mutations
Give rise to gametes; passes mutation at fertilization.
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Which type of mutations do not affect protein function
Silent mutations
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What happens in a loss of function mutation?
Proteins are affected and may lead to structural proteins or enzymes that dont work anymore; they are almost always recessive
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What happens in a gain of function mutation
It leads to a protein with an altered function
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What is a conditional mutation
It means the phenotype will work under restrictive conditions, maybe temperature, but may not be detectable under permissive conditions
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What are the two categories of mutations
Point and chromosomal
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What is a point mutation
It results from the gain, loss or substitution of a single nucleotide
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What is a chromosomal mutation
It is more extensive than a point mutation; it may change the position of cause a DNA segment to double or disappear
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What are two types of chromosomal mutations
Deletions, inversions, translocations, duplications
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What is a deletion mutation?
The part of genetic material is removed; can be fatal
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What is a duplication mutation?
Homologous chromosomes break and recombine incorrectly; it may have two copies of segment while the other has none
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What is an inversion mutation
It results from breaking and rejoining.. only the segment is flipped
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What is a translocation mutation
Segment of DNA breaks off and is inserted to another chromosome; can lead to duplications and deletions
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How are mutations caused
Spontaneously and inducedly
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What are some types of spontaneous mutations?
Errors in replication by polymerase; bases have different structures (tautomers); chemical rxns change bases; imperfect meiosis; gene sequences disrupted
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What are some types of induced mutations?
Chemicals alter nucleotide bases; chemicals can add bases
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What types of radiation damage DNA
Ionizing radiation and UV radiation
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What happens in ionizing radiation
Free-radicals are ccreated and are highly reactive. Can change bases and break sugar phosphate bonds
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What happens in UV radiation.
The radiation is absorbed by thymine and it forms covalent bonds with nearby nucleotides, disrupting DNA replication
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Where do mutations occur most often
At base pairs
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What are some benefits of mutations
Raw material for evolution (genetic diversity); the diversity may benefit the organism somatically; may have advantageous changes in future offspring
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What can we learn from ancient DNA?
If some is left, we can PCR it. We learn that Neanderthals have 99%% identical DNA to humans. Had fair skin & red hair, were probably capable of speech and interbred with humans
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