Cells Lecture IV DNA and Protein Synthesis

Biology Standards Covered 1d ~ students know the central dogma of molecular biology outlines the flow of information from transcription of ribonucleic acid (RNA) in the nucleus to translation of proteins on ribosomes in the cytoplasm

The Structure of DNA DNA is a long molecule made up of nucleotides Each nucleotide is made up of three parts: –5-carbon sugar called deoxyribose –Phosphate group –Nitrogen Base

AdenineGuanine Phosphate group CytosineThymine (Deoxyribose) 5-Carbon Sugar The Nucleotides Nitrogen Bases A- adenine G- guanine C- cytosine T- thymine

Chargaff’s Rules According to Erwin Chargaff: –AdenineThymine –Adenine always pairs with Thymine –Cytosine Guanine –Cytosine always pairs with Guanine

The Double Helix base pairing- hydrogen bonds forming only between certain “base pairs” Sugar- phosphate backbone Hydrogen bonds Nucleotide Key Adenine (A) Thymine (T) Cytosine(C) Guanine (G)

DNA Arranged in a Chromosome

Central Dogma The term central dogma is used in science to describe the “making of proteins” from instructions coded in the DNA An equation to remember for Central Dogma would be: DNA mRNA Amino Acid Chain Transcription Translation

Transcription inside the Nucleus Adenine (DNA and RNA) Cystosine (DNA and RNA) Guanine(DNA and RNA) Thymine (DNA only) Uracil (RNA only) RNA DNA RNA polymerase

Transcription Promoters RNA Polymerase transcriptionPromoters – specific sites where the enzyme-protein RNA Polymerase binds to the strand of DNA to begin transcription

Central Dogma polypeptidesProteins are assembled into polypeptides amino acids –These are long chains of amino acids amino acids –There are 20 different types of amino acids –The properties of proteins are determined by which order these amino acids are joined

Central Dogma three base pair sequenceEach of these amino acids that mRNA “codes” for recognizes the three base pair sequence codonA codon consists of “three nucleotides in a row” that code for a single amino acid –AUG codes for the amino acid Methionine

The (20) Amino Acids Methionine is the universal “start codon” for all proteins

Central Dogma twenty amino acids start stopAlong with the twenty amino acids there are “special” base pair sequences that “code for” start and stop codons Stop codons are like the “period at the end of a sentence”. –They signify the end of a polypeptide (amino acid chain)

The (20) Amino Acids

Translation The term central dogma is used in science to describe the “making of proteins” from instructions coded in the DNA An equation to remember for Central Dogma would be: DNA mRNA Amino Acid Chain Transcription Translation

Transfer RNA mRNA Start codon Ribosome Methionine Phenylalanine tRNA Lysine Nucleus Translation mRNA

Translation Each strand of mRNA is separated into three base pairs called codons AUG —- UUC --- AAA (mRNA)AUG —- UUC --- AAA (mRNA) This is where transfer RNA comes in (tRNA)This is where transfer RNA comes in (tRNA)

Translation tRNA is responsible for getting the right anticodon with each of the mRNA codons An amino acid is attached to each anticodon tRNA mRNA Ribosome Lysine (Amino Acid)

The Polypeptide “Assembly Line” The ribosome joins the two amino acids & breaks the bond between the tRNA & it’s amino acid mRNA Ribosome Translation direction Lysine tRNA Ribosome Growing polypeptide chain mRNA Completing the Polypeptide The process continues until the ribosome reaches one of the three stop codons. The result is a growing polypeptide chain.Translation