Transcription and Translation How genes are expressed (a.k.a. How proteins are made) Biology

The “Central Dogma” of Genetics DNA  RNA  Protein

DNA vs. RNA DNA: Double stranded Deoxyribose is the sugar in the backbone Nucleotide base pairs: A with T, C with G RNA Single stranded Ribose is the sugar in the backbone There is NO Thymine in RNA Instead of Thymine, RNA has Uracil So… If there’s a A, there’s now a U in the RNA.

Types of RNA mRNA: Messenger RNA These molecules are made from DNA and sent to make protein rRNA: Ribosomal RNA These molecules make up the ribosome, an organelle responsible for reading the mRNA and making protein. tRNA: Transfer RNA These molecules transfer each amino acid to the ribosome as the RNA message is coded into a protein sequence.

Transcription DNA is read and “transcribed” into a similar nucleic language RNA is made DNA  RNA Steps: 1. The enzyme RNA polymerase binds to DNA and separates the DNA strands. 2. RNA polymerase uses one DNA strand as a template and nucleotide bases are added to form a new mRNA strand.

Transcription

Translation The RNA is used as a code to create a chain of amino acids A chain of amino acids = a polypeptide or protein Each 3-letter segment of the RNA is called a codon (like a “word”)and encodes for a certain amino acid.

Amino acids The building blocks (or monomers) of protein 20 amino acids

Amino Acid chart (continued) The Genetic Code: Each codon encodes for a different amino acid.

Amino Acid chart (continued) The Genetic Code: Each codon encodes for a certain amino acid. (Same chart but different way of looking at it…)

Translation (continued) mRNA is read as a code to make an amino acid chain (or protein) Steps: 1. mRNA attaches to a ribosome 2. the mRNA moves through the ribosome 3. When a “start codon” is reached, the ribosome starts reading the mRNA (AUG, amino acid: Methionine or Met). 3. As each codon is read by the ribosome, the matching amino acid is added to the polypeptide chain (according to the amino acid chart). 4. The polypeptide chain continues to grow until a stop codon is reached (UAA, UAG, UGA). 5. The ribosome releases the newly formed polypeptide chain and the mRNA.

Translation (continued)

Summary: DNA  RNA  Protein Transcription DNA is used as a template to form a mRNA strand Translation mRNA is read by a ribosome An amino acid is added for each codon in the mRNA A polypeptide chain is formed Sometimes 1 protein = 1 polypeptide chain Other times 1 protein = several polypeptide chains working together