From DNA to Protein

Bellringer 11/4/10 Based on the picture on the board, where does transcription occur? Where does translation occur?

Section 2: Genes and Proteins The sequence of nucleotides in DNA contain information. This information is used to make proteins Proteins make cells and regulate their functions. Proteins are made of subunits/monomers called amino acids The sequence of DNA nucleotides determine the amino acids used to build proteins

RNA-Ribonucleic Acid Full name: Ribonucleic Acid In base pairing, thymine (T) is replaced by uracil Function: plays a role in making proteins RNA Nucleotide Structure: Ribose (sugar) Phosphate Nitrogen bases A pairs with U C pairs with G

Types of RNA mRNA: messenger RNA; made from DNA & it carries DNA information from the nucleus to the cytoplasm rRNA: ribosomal RNA; combines with ribosomes to make proteins tRNA: transfer RNA; carries amino acids to the ribosomes

Types of Bases/Base Pairs Comparing DNA and RNA DNA RNA Strands 2 1 Sugar Deoxyribose Ribose Types of Bases/Base Pairs A-T C-G DNA – RNA RNA-RNA A-U U-A C-G C-G So why is RNA important? Because DNA is too big to leave the nucleus and it uses RNA to take its message out into the cytoplasm.

Transcription Location: Nucleus Purpose: DNA information is copied into mRNA. Caused by RNA Polymerase (an enzyme) DNA is safe in the nucleus Uses mRNA To send a message to the cytoplasm

FYI: How does this happen? Unzip one gene in DNA Match up bases to one side of gene in DNA A binds with U, C binds with G. mRNA detaches from the DNA mRNA moves out of the nucleus and into the cytoplasm DNA: GAG AAC TAG TAC RNA: CUC UUG AUC AUG

Translation Location: Cytoplasm at the Ribosomes Purpose: tRNA matches to the mRNA to make a specific amino acid chain which is a protein.

How are the Nucleotides of Messenger RNA Translated into a Protein? Events of translation: The first three bases of mRNA (codon) join the ribosome. Its usually AUG – considered the start codon). tRNA brings the “amino acid” down to the ribosome. The three bases on tRNA (anticodon) match the complementary bases on mRNA. Each tRNA has an amino acid, which is determined by its anticodon. Ex: codon (AUG) is for the amino acid - methionine The amino acids are joined by polypeptide bonds. The resulting chain of amino acids are called a PROTEIN.

Codons & Anticodons CODON: mRNA bases needed to call an amino acid to the ribosome Start codon: AUG and it codes for the amino acid methionine Stop codon: mRNA that means the end of the AA chain has been reached ANTICODON - segment of three bases on tRNA that is complementary to the mRNA codon.

Practice with Protein Synthesis

DNA DNA with DNA mRNA DNA with RNA mRNA with tRNA Process Information for process Product Type of Base Pairing Required Replication (synthesis of DNA) Entire length of double helix DNA DNA with DNA Transcription (synthesis of RNA) Small part of a DNA strand mRNA DNA with RNA Translation (synthesis of protein) Protein mRNA with tRNA

But What Happens When Any of These Processes Goes Wrong…

Mutations… What is a mutation? Any change in the DNA sequence What is a mutagen? Any agent that can cause a change in DNA How can mutations happen? Spontaneous mistakes in base pairings radiation chemicals high temperatures

Types of Mutations Point Mutation: a change in a single base (like a substitution) GAG CTC CUC Leucine Correct DNA Correct mRNA Correct AA GCG CTC CGC Arginine A should pair with T, but instead C is mismatched to T Point mutation mutated mRNA Wrong AA

Mutations Example: Sickle Cell Anemia

Frameshift mutation: when one or more bases are added or deleted from DNA. Correct DNA: ATA CCG TGA TAT GGC ACT Correct mRNA: UAU GGC ACU Correct amino acids: Tyrosine Glycine Threonine Extra inserted base SHIFTS how we read the codons (3 bases), which changes the amino acids Frameshift mutation ATG ACC GTG A in DNA: TAC TGG CAC T Mutated mRNA: UAC UGG CAC U Wrong amino acids: Tyrosine Tryptophan Histadine

Frameshift Mutations: Insertions

Frameshift Mutations: Deletions

Chromosomal Mutations Structural changes in chromosomes Caused by four types of mistakes

Insertion- When a part of a chromatid breaks off and is added to its sister chromatid so that the gene is duplicated

Deletion- When a part of a chromosome is left out

Translocation & Inversion Translocation: When a part of the chromosome breaks off and is added to a different chromosome Inversion: When a part of the chromosome breaks off and is reattached backwards

Mutations Frameshift mutations can have catastrophic effects on genes because ALL the codons that follow the shift will be altered, not just one. Proofreading enzymes are able to repair some damages to DNA