DNA is used to make Protein: Transcription and Translation Click here for the Intro Videoclip Protein Synthesis DNA is used to make Protein: Transcription and Translation

What's in your genes? Genes are sequences of nucleotides along DNA strands. Genes (100s-1000s of nucleotides long) code for polypeptides. Each DNA strand could hold a couple thousand genes (humans).

Polypeptide (protein) Gene expression DNA RNA Polypeptide (protein)

What is Protein Synthesis? Each gene codes for one polypeptide Proteins determine our traits: Enzymes Hormones Structural parts of our cells and body Proteins have to be created by our cells. They are built (with amino acids) based on information stored in our DNA.

How does DNA direct protein synthesis? RNA! RNA = Ribonucleic acid RNA is very similar to DNA. There are three differences: The sugar part of RNA is ribose (DNA uses deoxyribose) RNA substitutes the nitrogenous base URACIL for thymine in DNA RNA is usually just a single strand, not a double helix.

DNA vs. RNA DNA RNA Similarities Nucleic acids Basic unit = nucleotide Use Bases A, C, G 3 differences RNA is a single strand DNA is a double strand RNA has ribose sugar DNA has deoxyribose sugar RNA has uracil DNA has thymine

Types of RNA Messenger Carries message of DNA to the cytoplasm mRNA rRNA tRNA Messenger Carries message of DNA to the cytoplasm Ribosomal Combines with proteins to make a ribosome Transfer Carries amino acids to the ribosome

Bring amino acids to ribosome/mRNA Concept Map from to to make up also called which functions to can be RNA Messenger RNA Ribosomal RNA Transfer RNA mRNA Carry instructions rRNA Combine with proteins tRNA Bring amino acids to ribosome/mRNA DNA Ribosome Ribosomes

Protein Synthesis 2 Steps: Transcription: DNA  mRNA Takes place in nucleus Translation: mRNA  protein Takes place in cytoplasm

Transcription Animation (DNA tube) Transcription Animation (DNALC)

Steps of Transcription DNA molecule ‘unzips’ Free RNA nucleotides form hydrogen bonds with complementary bases RNA polymerase bonds RNA nucleotides together. mRNA detaches from DNA.

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

Practice transcribing… If your DNA strand says this… TAC AGG TCA GAC TTC What will your complementary RNA strand say? AUG UCC AGU CUG AAG

After transcription comes translation (protein synthesis) Nuclear membrane Transcription Translation After transcription comes translation (protein synthesis)

The DNA Code The order of bases along a DNA strand (and therefore its mRNA transcript) is a code that specifies the order of amino acids in a protein. Three bases are read at a time. One triplet (ie AGA) codes for one of 20 amino acids. Translation is the process by which the nucleotide language of mRNA is translated into amino acid language.

DNA triplet mRNA codon tRNA anticodon Amino acid Translation animation - DNALC

Steps of Translation mRNA enters the cytoplasm and attaches to a ribosome. 1. Translation begins at AUG, the start codon. 2. Each tRNA has an anticodon whose bases are complementary to a codon on the mRNA strand. E.g. codon = AUG, anticodon=? UAC 3. Two tRNAs at a time bring the correct amino acids to the ribosome

tRNA: a closer look Each tRNAs anticodon is complementary to a specific mRNA codon.

Translation mRNA Nucleus Messenger RNA mRNA Lysine Phenylalanine tRNA Messenger RNA is transcribed in the nucleus. mRNA Lysine Phenylalanine tRNA Transfer RNA The mRNA then enters the cytoplasm and attaches to a ribosome. Translation begins at AUG, the start codon. Each transfer RNA has an anticodon whose bases are complementary to a codon on the mRNA strand. The ribosome positions the start codon to attract its anticodon, which is part of the tRNA that binds methionine. The ribosome also binds the next codon and its anticodon. Methionine Ribosome mRNA Start codon

Steps of Translation 4.The ribosome joins the two amino acids carried by the two tRNAs and breaks the bond between amino acid and its tRNA. 5. The tRNA floats away to pick up new amino acids 6. The ribosome moves along the mRNA, binding new tRNA molecules and amino acids. 7. Translation stops when a stop codon is reached.

Translation (continued) The Polypeptide “Assembly Line” The ribosome joins the two amino acids—methionine and phenylalanine—and breaks the bond between methionine and its tRNA. The tRNA floats away, allowing the ribosome to bind to another tRNA. The ribosome moves along the mRNA, binding new tRNA molecules and amino acids. Growing polypeptide chain Ribosome tRNA Lysine tRNA mRNA Completing the Polypeptide The process continues until the ribosome reaches one of the three stop codons. The result is a growing polypeptide chain. mRNA Translation direction Ribosome

Translation mRNA is "read" as codons, combinations of 3 nucleotides. One codon, AUG, always signals that start of a gene sequence. Three codons (UAA, UAG, and UGA) are stop signals, ending the formation of a polypeptide. Genetic code= set of rules giving the correspondence between codons in RNA and amino acids in proteins. There is redundancy in the code, but no ambiguity. Take a moment to look at your chart. What observations can you make about this code?

Practice: What is the Code? CCC ? CGA ? AGA ? UGA ? AAA ? GGG ? Proline Arginine STOP Lysine Glysine

Self-Quiz: The Genetic Code Translate: AUG CGC AAA UUC UGA CGG

Translating practice Try these with the wheel: CCC AGU UCA GUC Use the square table to tell what amino acid each of the following codons corresponds to? AAA GCA UGU CAG Lysine Try these with the wheel: CCC AGU UCA GUC Alanine Cysteine Proline Glutamine Serine Serine Valine

Summary Watch the Intro video again – you’ll catch more details! DNA – Secret of Life (Episode 1 of 5) PBS