DNA, RNA, and Protein
Replication
Transcription
Translation
Replication
• Occurs during S phase of cell cycle
• DNA unwinds, in increments, via helicase
• DNA polymerase makes 2 copies of DNA
– Complementary base pairing: G=C; T=A
– Leading strand has continuous replication
– Lagging strand done in Okazaki fragments
• Ligase joins segments on lagging strand
Making copies of DNA
• 5’TACCGACTTGATCATTTAGGTAGACATATT …3’
3’ATGGCTGAACTAGTAAATCCATCTGTATAA …5’
DNA splits into leading (5’) & lagging (3’) strands
Each strand does complementary base pairing.
• 5’TACCGACTTGATCATTTAGGTAGACATATT …3’
3’ATGGCTGAACTAGTAAATCCATCTGTATAA …5’
and
• 3’ATGGCTGAACTAGTAAATCCATCTGTATAA…5’
5’TACCGACTTGATCATTTAGGTAGACATATT …3’
Transcription
• Makes RNA copy of DNA via RNA polymerase
• Makes mRNA, tRNA, or rRNA
• RNA polymerase binds to DNA promoter
• DNA strands unwind & separate
• RNA polymerase adds free RNA nucleotides to
complement 1 strand of DNA bases.
• G =C; C=G; T=A; A=U
• RNA polymerase releases DNA & new RNA
when reaches a termination signal.
Transcription & Translation
DNA:5’TACCGACTTGATCATTTAGGTAGACAT…3’
mRNA:AUGGCUGAACUAGUAAAUCCAUCUGUA…
• mRNA exits nucleus after processing cap & tail
• mRNA on ribosome is translated via tRNAs.
• tRNA anticodons pair with mRNA codons (UAA, UAG, UGA).
• Each tRNA carries a specific amino acid or a stop signal.
• Genetic code is maintained universally.
mRNA: AUGGCUGAACUAGUAAAUCCAUCUGUA
polypeptide: met-ala-glt-leu-val-ast-pro-ser-val-
Translation
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Involves all 3 types of RNA: mRNA, tRNA, rRNA
Produces polypeptides which form proteins
Peptide bonds link amino acids together
There are 20 essential amino acids found in all
living things. Some have modifications.
o o
o
• Amino acids form 1 , 2 & 3 protein structures
– Structures are essential to protein function
Steps of Translation
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mRNA docks on ribosome. Its 1st codon is AUG
tRNA with met binds via its anticodon UAC.
tRNA with its amino binds to 2nd codon.
Ribosome detaches met from 1st tRNA.
Peptide bond forms between met & 2nd amino acid.
First tRNA exits the ribosome & 3rd tRNA enters.
Elongation continues until reaches stop codon
Ribosome separates from mRNA with last tRNA
Translation machinery then translates same or new
mRNA
Human Genome
• The entire gene sequence of human DNA
• 3.2 billion base pairs in our 23 chromosomes
• Use computers to analyze DNA sequences
– Bioinformatics , a new field, compares these.
• Help predict loci of genes
• Don’t know yet what all 30,000 genes encode
• Field of proteomics links gene to protein made