DNA in the Cell

• Stored in Number of Chromosomes (24 in Human Genome)

• Tightly coiled threads of DNA and Associated Proteins: Chromatin

• 3 billion bp in Human Genome: Total genetic content of cell

• DNA can be replicated

• Genes: Specific sequence of bases (one polypeptide

Central Dogma

Flow of Information

• DNA store a lot of information

• A little bit used at a time

• Small bits copied into temporary molecules

• messenger RNA (mRNA)

• Transcription

• RNA - Single Stranded– U for T– Ribose is sugar

Coding

• Sets of three letter from (A,G,C,T) codes for amino acid (codon)

• Stop codons (3)

• Universal language for Amino Acids

Transcription

• Transcription to preserve the DNA (sense)

• RNA (antisense) made by RNA Polymerase

• Polymerase binds at DNA promoter sequence just before the gene

• Nucleotides from environment added to RNA chain based on DNA Template

• Continues until terminator sequence

Genes

• 10% of DNA encodes for Genes

• Exons: Coding Sequences for Proteins

• Introns: Non-Coding Sequences

• Human Genome: 100,000 Genes

• 100,000 Proteins synthesized from genes

• Genes encode for Amino Acids(Codons)

• Building blocks for proteins (workers)

• DNA to messenger RNA (mRNA)

• Direct for prokaryotes

• From Nucleus to Cytoplasm for eukaryotes

• Introns removed from mRNA

• Template for Protein Synthesis by Ribosome

Translation

• mRNA copy to Protein

• Translation: Process of Protein Synthesis

• Occurs on Ribosomes: Large structures consisting of proteins and RNA

• Many of them in the cell

• transfer RNA (tRNA) which accomplish actual translation

tRNA

• At one anticodon (three base sequence)• Complementary to one of codons on mRNA• At other end is a chemical group to attach an

amino acid• Read codons, Bind to them, Bring amino acid

to ribosome• Shape dependent -- Energy Consuming (50%

in bacteria)

Signals for Protein Synthesis

• Stop Codons• Start Codon

– Beginning of mRNA sequence– Reading Frame (way message divided into

codons)

• AUGCCUGUCAAA• AUG CCU GUC AAA• A UGC CUG UCA AA

DNA Replication

• Copy DNA for new cells

• DNA Polymerases

• Mistakes corrected by enzyme itself

• Proofreading

• Mistake 1 in 10^9