Download THE CENTRAL DOGMA

THE CENTRAL DOGMA
10-1 DNA
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Polymer of nucleotides
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Nucleotide – a 5 carbon sugar (deoxyribose), a phosphate group and a nitrogenous base (adenine,
guanine, thymine, cytosine)
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C + T = pyrimidines – 1 ring
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A + G = purines – 2 rings
DOUBLE HELIX
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DNA = 2 nucleotide chains wrapped in a double spiral (twisted ladder)
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Structure discovered by Watson and Crick and Wilkins = Nobel prize – Rosalind Franklin died
before
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Alternating sugar – phosphate – sugar – phosphate …covalently bonded – sides of the ladder (AKA
backbone)
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Bases are covalently bonded to the sugar; rungs of ladder are made up of bases hydrogen bonded
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Complementary base pairing – A + T and C + G
DNA REPLICATION
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Process by which DNA is copied
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2 nucleotide chains separate -> replication fork
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Helicase opens chain, breaking H bonds
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Topoisomerase – allows swiveling by nicking strand
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Primase ~ 10 nucleotides set down first
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DNA polymerase binds and adds complementary nucleotides to parent strands – can only add 5’ ->
3’
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Replication is discontinuous on lagging strand – forming Okazaki fragments – fragments are linked
together by ligase
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Other strand is leading strand; replication is continuous
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When replication is completed, 2 new exact copies of original DNA molecule are produced -> cell is
now ready to divide
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Replication is accurate
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Change in nucleotide sequence = mutation
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Repair enzymes fix mutations
10 -2 RNA
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Polymer (macromolecule) made up of nucleotides
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Sugar is ribose
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Uracil replaces thymine
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3 types:
o mRNA – copies protein recipe (message) from DNA in nucleus, carries it out to cytosol
o tRNA – cloverleaf shaped molecule that transports (tRNAsports) amino acids to ribosome
o rRNA – with protein, makes up ribosomes ( reads and rides down mRNA)
TRANSCRIPTION
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Describes process by which info from DNA is copied to RNA
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RNA polymerase – recognizes promoter region (beginning) and binds to it; DNA separates – only
one strand is transcribed – coding (sense) strand
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Nucleotides complementary to coding strand are added to RNA until termination signal is reached
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RNA moves through nuclear pores -> into cytosol where it directs synthesis of proteins
10-3 PROTEIN SYNTHESIS
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Proteins are polymers of one or more polypeptides, each consisting of
a specific sequence of amino acids
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Sequence determines the 3-d shape of the finished protein
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Function depends on structure
THE GENETIC CODE
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Genetic code used to translate mRNA into proteins
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A codon (sequence of three mRNA nucleotides) codes for a specific amino acid (codon =AKA =
triplet)
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Each amino acid may be specified by more than one triplet
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Code is non-overlapping – read in groups of three
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Code is non-random – similar types of amino acids have similar codons
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Code is nearly universal
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Start codon = AUG; methionine
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Stop codons DO NOT code for amino acids (UAA, UGA, UAG)
TRANSLATION
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mRNA leaves nucleus through nuclear pores, migrates to a ribosome, where proteins are synthesized
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Free floating amino acids are transported to the ribosomes by tRNA
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The loop on the tRNA opposite the amino acid attachment contains the anticodon (complementary to
and paired with the corresponding mRNA codon
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Ribosomes = rRNA and protein, found free floating in cytosol and attached to the rough ER
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Ribosomes floating freely make proteins for use in the cell itself; those attached to the ER make
proteins for export
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Binding sites on ribosomes = P site holds the growing polypeptide chain and the A site is empty for
incoming tRNA with its attached amino acid
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AUG is start codon – ribosome subunits assemble, methionine is first amino acid in poypeptide
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As each amino acid is added to the polypeptide chain, ribosome moves down one codon (three
mRNA nucleotides) and next codon is translated
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Eventually, stop codon is reached and ribosome subunits disassemble, and polypeptide is complete
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Several ribosomes translate an mRNA sequence
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Polypeptide chain is the protein primary structure; this folds and coils and assumes its completed
protein structure