DNA to Protein Molecule

DNA to Protein Molecule DNA makes messenger RNA (mRNA), which makes proteins. This shows the three processes that convert DNA’s information (code) into protein molecules: replication, transcription and translation. This is called the Central Dogma of Genetics. Cell Cell Nucleus REPLICATION mRNA Outside Nucleus in Cytoplasm TRANSCRIPTION Inside Nucleus Ribosome Protein TRANSLATION DNA Replication Replication is really just gene-copying. Organisms must be able to exactly copy and distribute all their DNA during every cell division. When DNA is ready to multiply, the double helix unwinds and unzips. A new strand will form and bond with the complementary base pairs for each side. Here are the steps: 1. There are free nucleotides floating in the cell’s cytoplasm. 2. Each one contains one of the four bases, a sugar and three phosphates. The base attaches along the strand to its complementary matching base. 3. Non-matching bases are pushed away. 4. As all the matching bases are lined up, an enzyme binds the two sides together. 5. This results in two DNA double helixes that are identical to the first. 6. A new strand of DNA has been made – replicated. T A C T Original DNA strand C C G A C G G T C G A T A A C T phosphate G sugar C T G A A T T T A A daughter strands C G T A CG C GG A T guanine cytocine sugar Transcription Transcription is copying a gene’s DNA sequence to make an RNA molecule. This is the first step in gene expression. 1. Transcription begins with the DNA double-helix unwinding and unzipping (as in replication). 2. A strand of messenger RNA comes in, reads, and copies the section of base pairs. 3. The order of the base pairs is like a code that names amino acids for building proteins. 4. mRNA carries the code out of the nucleus into the cell cytoplasm. 5. Transcription is complete. a g Anti-sense Strand c g t g g u c t t c g t g c t a a g t c t g a a g a c t a g c g u c t g a DNA g c u t c g c g a RNA polymerase Sense Strand is coding DNA 1. Messenger RNA is similar to DNA except that the sugar in RNA is a ribose (DNA’s sugar is a deoxyribose). u u g g mRNA Facts: g c c mRNA 2. RNA is shorter in length than DNA with only 50-1000 nucleotides (DNA can have a million). 3. Instead of the base Thyamine (T) - RNA has Uracil (U), which is complementary to Adenine (A). Translation 1. When the messenger RNA (mRNA) copy of the code is finally carried out of the nucleus, it leaves through small openings called nuclear pores and enters in the cell’s cytoplasm. 2. Here the mRNA runs the code through a ribosome (an organelle in the cytoplasm). The ribosome will do the translation. Each set of three bases that will be read is called a codon. 3. At the ribosome, another molecule, called transfer RNA (tRNA), goes to work. 4. Transfer RNA carries a three base “anticodon” at one end and an amino acid at the other end. The anticodon binds with the matching codon on the mRNA. 5. In this way tRNA delivers the correct amino acid for the protein being built. 6. Protein synthesis is complete. amino acid tRNA outside cell inside cell nucleus polypeptide chain of amino acids anticodon nuclear pores codon mRNA ribosome cell cytoplasm mRNA strand ribosomes Tr anslation Translation to tRNA Tr anscription Transcription to mRNA Transcription to Protein Synthesis Amino Acids Chain Protein Synthesis