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33 Cards in this Set
- Front
- Back
Molecule of heredity
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Deoxyribonucleic acid (DNA)
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Gene
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sequence of nucleotides in DNA that codes for a single polypeptide
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Three (3) Key Processes of Macromolecular Synthesis
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(1) DNA replication
(2) transcription (3) translation |
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Two (2) Major Differences between Prokaryotic and Eukaryotic genomes
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(1) Eukaryotes have non-coding regions called introns
(2) Single prokaryotic mRNA often contains more than one coding region |
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DNA base pairing
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Adenine = thymine (A=T)
Guanine =- cytosine (G=-C) > hydrogen bonds hold the two strands together |
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Deoxyribonucleotide
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sugar deoxyribose +
nitrogenous base + phosphate |
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Bonds linking deoxyribonucleotides
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covalent phosphodiester bonds
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Purines
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Adenine (A) and Guanine (G)
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Pyrimidines
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cytosine (C) and thymine (T)
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Size of DNA (bacterial nucleoid) compared to cell
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E. coli circular dsDNA is
1500x the size of the cell > prokaryotic circular DNA is supercoiled |
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Supercoiling
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methods of compacting DNA by breaking and resealing DNA
> DNA gyrase/topoisomerase |
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Genetic elements in cells
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(1) DNA
(2) plasmids (3) mitochondria/chloroplasts (4) transposable elements |
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Effect of Temp on DNA Structure
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> hydrogen bonds weak
> covalent phosphodiester bonds strong Apply heat = H bonds break, not covalent = denaturing of DNA |
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DNA replication is ________.
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Semi-conservative
> both DNA strands serve as templates for new strands |
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DNA replication in Prokaryotes
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begins at origin of replication (oriC)
ends at terminus (ter site) > Prokaryotes have single oriC (Eukaryotes many) > bidirectional replication (in both directions) = starts at oriC, ends at ter site halfway around |
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Major Enzymes in DNA replication
(in order) |
(1) Helicase (unwinds)
(2) Primase (primes) (3) DNA polymerase III (4) DNA polymerase I (excises primer) (5) Ligase (seals nicks) |
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Helicase
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unwinds helix at replication fork
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Primase
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primes strands of DNA with RNA primer
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DNA polymerase III
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adds deoxyribonucleotides to the 3' OH end
> 5' -> 3' (only add on to 3') > cannot begin new DNA strand (must have primer) |
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DNA polymerase I
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excises RNA primer and fills gap
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Ligase
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seals nicks (absence of phosphodiester bond) in DNA
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Leading strand
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in DNA replication, the strand made toward the replication fork
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Lagging strand
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in DNA replication, the strand made away from the replication fork
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What bonds are formed when DNA is synthesized?
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(1) covalent phosphodiester bonds between the sugar of one nucleotide and the phosphate of the next (DNA polymerases)
(2) hydrogen bonds |
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Okazaki fragments
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lagging strand fragments that contain both DNA and RNA primer
> DNA polymerase III builds DNA up to the fragment, then DNA polymerase I removes RNA primer and fills in with DNA |
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Accuracy of DNA replication
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Error: 1 per 10^9 nucleotides
(1) proofreading by DNA polymerase III (exonuclease removes and replaces) (2) complementary base-pairing |
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Plasmids
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extrachromosomal pieces of DNA
low-copy-number plasmids (1 or 2 per cell) high-copy-number plasmids (up to 50 per cell, divide continuously) |
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Plasmid Replication
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(1) bidirectional replication
(2) unidirectional ("rolling circle") replication - used by many bacteriophages (may produce concatemers) |
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Concatemer
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long continuous DNA molecule that contains multiple copies of the same DNA sequences linked in series by cos sites
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Cos sites
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a protein binding nucleotide sequence that occurs once in each copy of the genome (linking DNA sequences in a concatemer)
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Determining DNA Base Sequences
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(1) Restriction enzymes cut DNA; reveal locations of specific sequences
(2) PCR [primers bind to complementary DNA sequences, Taq polymerase (archaeal) synthesizes DNA, rapidly amplifies segment] (3) Sanger method (determines up to 1000 bases) |
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What prevents the DNA strands from annealing during replication?
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single-strand binding protein (ssb)
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Benefit of Plasmids
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Genes for...
> antibiotic-resistance > resistance to toxic metals > proteins to metabolize rare food sources > allow pathogenesis (virulence genes) > allow symbiosis |