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DNA STRUCTURE AND REPLICATION BUILDING BLOCKS OF DNA: Nucleotides:
1. 5 carbon sugar (deoxyribose) 2. Nitrogenous base (A, T, C, or G) 3. Phosphate group
NITROGENOUS BASESPYRIMIDINES PURINESSingle ring structure C and T Double ring structure G and A
Cytosine Guanine
Thymine Adenine
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DNA STRUCTURE
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Hydrogen bonds
C and G H bonds between 3 −
A and T H bonds between 2 −
hold bases togetherHydrogen bonds −C – G −A – T −Purine – pyrimidine − bases 2 −
Rungs of ladder phosphate groups of alternating sugar & Sides of ladder consist Twisted ladder Double stranded Double helix
One strand 5’ at top & 3’ at bottom ANTIPARALLEL STRANDS Other strand: 5’ at bottom & 3’ at top
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Nucleotide
deoxyribose carbon in rd3
’ end 3
deoxyribose carbon in th5
’ end 5
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codonAnti-
specific • with codon on mRNA Anti-codon base pairs • ribosomes carries amino acid to • transfer RNA •
tRNA
acid Amino
Site of protein synthesis % protein 40
(rRNA)RNAibosomal 60% rlarge small
subunits2
Ribosomes
cytoplasm to ribosomes in DNA in nucleus proteins from making carries code for
bases = AUCGsugar = ribose
single stranded
messenger RNA mRNA
Transcription
Transcription
Transcription
Bases = ATCG • deoxyribose Sugar = •
Double stranded• DNA
YNTHESISSROTEIN P
GENETIC CODE 1 codon = 3 consecutive bases 1 codon codes for 1 amino acid (A.A.) There are 4 bases (A, T, C, G) Thus 43 (64) possible combinations of codons There are 20 amino acids Code is redundant (2 or more codons code for same amino acid) but not ambiguous (no codon codes for more than 1 amino acid)
PROTEIN SYNTHESIS – OVERVIEWCentral Dogma of Biology
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Protein
build protein) uses codons in mRNA to (
Translation
Transcription
mRNA
DNA (Coding strand)
• base-pairs RNA nucleotides with exposed DNA bases
• stops when reaches terminator
RNA Processing
occurs in eukaryotic cells
• Introns removed • Exons linked • 5’ cap added • Poly-A tail added
Spliceosome • Cut out introns
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separates DNA strands • binds to promoter (TATA box) •
RNA polymerase
grows in 5’ to 3’ direction
mRNA
DNA
RANSCRIPTION– TYNTHESIS SROTEIN P
’ cap 5
Poly-A tail
• Slice exons together • consist of protein and snRNPs
PROTEIN SYNTHESIS – TRANSLATION
Initiation
mRNA binds to
small
l
ribosomal subunit
Initiator tRNA base pairs with 1st codon (start codon) on mRNA 1st amino acid - methionine
Large ribosomal subunit binds to complex Initiator tRNA located at P site P site – peptidyl-tRNA binding site A site = Aminoacyl-tRNA binding site
Elongation
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2nd tRNA base pairs with 2nd
codon on mRNA at A site
• Peptidyl transferase forms peptide bond between 1st and 2nd amino acids
• 1st tRNA exits • mRNA shifts position by 1
codon • 2nd tRNA now at P site • 3rd tRNA base pairs with 3rd
codon at A site • process continues until stop
codon reaches A site
Termination
• Stop codon (UGA, UAA, UAG) reaches A site
• Release factor binds to stop codon
• Polypeptide hydrolyzed from tRNA at P site
• Complex disassembles • mRNA can be used again
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• Polypeptide released
GENETIC ENGINEERING
RECOMBINANT DNA
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