A C G C C T T G A T C T G T C G C A T T T A G C

Polypeptide: multiple dipeptides bonded together Proteins: multiple polypeptides bonded together smallest protein = 50 amino acids Largest protein = 100 000 amino acids Each different sequence of amino acids codes for a different protein Sections of folded chain will bond together to form cross-links Different shapes can therefore code for different proteins

Proteins A-A-A-C-G-C-G-A…. Dipeptide Polypeptide (1 or more) Amino acid + Amino acid + Amino acid… Dipeptide Polypeptide (1 or more) Proteins

The DNA code: The order of the nitrogenous bases in the DNA molecule is actually a “code” for the order of amino acids. Each string of 3 nitrogenous bases codes for an amino acid.

If there are 4 nitrogenous bases (Adenine, Thymine, Cytosine, and Guanine) then there are 64 different 3 base sequences. However, there are only 20 different amino acids in proteins. Therefore some amino acids have more than one code. Today scientists know that genes are made of many nucleotides. The order of the bases codes for the amino acids that will be added to the polypeptide chain.

A-A-A-C-G-A-T-A-T-T-G-C-C-G-A A A U U U G C U A U C G G C U Protein synthesis: 1) TRANSCRIPTION: takes place in the nucleus. The nucleus will copy the DNA code for a polypeptide into a molecule of RNA. The DNA strand separates for a short time to serve as a template (or pattern) for RNA. Complimentary RNA nucleotides take their place on the DNA strand (just like when DNA replicates, with one difference) A-A-A-C-G-A-T-A-T-T-G-C-C-G-A A A U U U G C U A U C G G C U

When the RNA reaches a specific “STOP” code (a code of Nucleic acids e When the RNA reaches a specific “STOP” code (a code of Nucleic acids e.g. UAC) it leaves the DNA strand. The RNA strand is now a separate molecule that carries the complete code for one Polypeptide The involved RNA in this step is known as messenger RNA or mRNA Codon: group of 3 bases on RNA that codes for an amino acid

TRANSLATION: code amino acids Once mRNA has copied the code, the next step is to actually create the polypeptides. Transfer RNA ---- tRNA There are 20 different kinds of tRNA, one for each amino acid The have a short tail on one end that can “pick up an amino acid” Each tRNA can carry only one specific amino acid

tRNA At the base is an Anticodon. that complements the mRNA code This is how the tRNA knows where to put its amino acid.

Ribosomal RNA -- rRNA Formed in the nuclei of the cell. A protein from the cytoplasm migrates in to the nucleus rRNA joins with a protein to create a ribosome rRNA + Protein = ribosome The ribosome is where a polypeptide is assembled during protein synthesis

Nucleus DNA strand mRNA tRNA rRNA Ribosome tRNA tRNA rRNA Protein Amino Acid Amino Acid Amino Acid Cytoplasm

Amino acids: the building blocks of proteins simple atomic structure: Central carbon atom bound to: 1 carboxyl group (COOH) 1 amino group (NH2) 1 hydrogen atom 1 side chain represented by “R” (meaning it is different in every amino acid)

Amino acids: the building blocks of proteins The sequence of nitrogenous bases in DNA is the “code” that tells cells what amino acids to produce There are 20 different amino acids that are commonly found in proteins Every 3 nitrogenous bases code for an amino acid

Example: CAC is a nitrogenous base sequence that codes for the amino acid histidine

Amino acids bond together by dehydration synthesis. Peptide bond forms between the amino group of one molecule and the carboxyl group of another. Resulting molecule is called a dipeptide