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Who introduced the double-helical model for the structure of DNA?
James Watson and Francis Crick
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What is encoded in DNA and reproduced in all cells if the body?
Hereditary information
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Where are genes located?
on chromosomes
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What are the two components of chromosomes?
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who began the discovery of the genetic role of DNA? How did he experiment this?
- Fredrick Griffith
- he worked with two strains of bacterium, one pathogenic and one harmless.
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What is transformation?
a change in genotype and phenotype due to assimilation of foreign DNA.
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Why might some biologists have thought that proteins would be a better candidate than DNA to carry genetic material?
number of amino acids in protein is more than number of nucleotides in DNA
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What elements are found in nucleic acid?
carbon, hydrogen, oxygen, nitrogen, phosphate
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What elements are found in proteins?
carbon, hydrogen, oxygen, nitrogen, and sulphur
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What did Alfred Hershey and Martha Chase concluded after their experiment with phages?
they concluded that the injected DNA of the phage provides the genetic information
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What do nucleotides consist of?
- nitrogenous base
- sugar
- phosphate group
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What does Chargaff's rules state?
that in any species there is an equal number of A and T bases and an equal number of G and C bases
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What did Rosalind Franklin discover?
They discovered the that phosphate group and sugar were in the backbones of DNA with the nitrogenous base pairs in the interior.
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How is the nitrogenous bases paired generally?
a purine is paired with pyrimidine and this resulted in a uniform width
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What do you know about the structure of DNA that suggests a mechanism for replication?
each strand can act as a template
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Why is possible for each strand of DNA to act as a template for building a new stand in replication?
because the two strands of DNA are complementary
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What was the semi-conservative model?
predicts that when a double helix replicates, each daughter molecule will have one old strand and one newly made strand
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What was the conservative model?
the two parent strands rejoin
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What was the dispersive model?
each strand is a mix of old and new
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Where does DNA replication begin?
at sites called Origins of replication
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What happens in DNA replication?
The two DNA strands are separated, opening up a replication bubble.
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In which direction does replication proceed?
in both directions from each origin, until the entire molecule is copied
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Which direction does DNA replication synthesize? Nucleotide's can only be added to which end?
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what is at the end of each replication bubble?
replication fork
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What is a replication fork?
a y-shaped region where the new DNA strands are elongating.(extending)
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What are helicases?
enzymes that untwist the double helix at the replication forks.
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What is a single-strand binding protein?
binds to and stabilizes single-stranded DNA until it can until it can be used as a template.
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What is topoisomerase? (2)
- corrects "over winding" ahead of replication forks, by breaking, swiveling, and rejoining DNA strands
- reduces tension
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What is DNA polymerase?
enzyme that catalyzes the elongation of new DNA at a replication fork
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Most DNA polymerases require what two things?
- primer
- DNA template strand
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What are the two main DNA polymerases in E. coli?
- DNA polymerase 3
- DNA polymerase 1
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What can DNA polymerase do and not do?
- DNA polymerase cannot initiate synthesis of a polynucleotide
- they can only add nucleotides to the 3' end
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what is the initial nucleotide strand in DNA replication?
RNA primer
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What is the function of primase?
an enzyme that can start an RNA chain from scratch and adds RNA nucleotides one at a time using the parental DNA as a template
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What end serves as the starting point for the new DNA strand?
3' end
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Each nucleotide that is added to a growing DNA strand is a _____________. What is an example?
- nucleoside triphosphate
- ATP
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As each monomer of dATP joins the DNA strand, what happens?
it loses two phosphate groups as a molecule of pyrophosphate
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A DNA strand can only elongate in which direction?
5' to 3' direction
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What is the function of DNA polymerase 3?
synthesizes new DNA strand by covalently adding nucleotides to the 3' end of pre-existing DNA or RNA primer
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which way does polymerase 3 synthesize when synthesizing a leading strand?
moving towards the replication fork
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which way does polymerase 3 synthesize when synthesizing a lagging strand?
away from the replication fork
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How is the lagging strand synthesized?
synthesized as a series of segments called Okazaki fragments, which are joined together by DNA ligase
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What is the function of polymerase 1?
removes RNA nucleotides of primer from 5' end and replaces them with DNA nucleotides
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What are the two functions of DNA ligase?
- joins 3' end of DNA that replaces primer to rest of leading strand
- joins Okazaki fragments of lagging strands
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__________ proofread newly made DNA, replacing any incorrect nucleotides
DNA polyermase
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What happens in mismatch repair of DNA?
repair enzymes correct errors in base pairing
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What are some things DNA can be damaged by? (5)
- chemicals
- radioactive emissions
- X-rays
- UV light
- certain molecules
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What is the function of nuclease in nucleotide excision repair?
cuts out and replaces damaged stretches of DNA
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What are telomeres and what are their function?
- TTAGGG repeated 100 to 1000 times
- they postpone the erosion of genes near the ends of DNA molecules
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What is telomerase?
an enzyme that catalyzes the lengthening of telomeres in germ cells
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How can telomerase protect cells from cancerous growth?
by limiting the number of cell divisions
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Define chromatin. (2)
- only found in eukaryotic cells
- is a complex of DNA and protein and is found in nucleus
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Eukaryotic chromosomal DNA molecules have at their ends nucleotide sequence called __________.
telomeres
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What is euchromatin?
loosely packed chromatin
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What is heterochromatin?
highly condensed chromatin
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What difficulty does the dense packing of heterochromatin cause?
make it difficult for the cell to express genetic information coded in these regions
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