How does DNA instruct cells to make PROTEINS?

Part I DNA, Genes, and Proteins

DNA and genes Some stretches of DNA are called genes. Genes are stretches of nucleotide bases (DNA) that code for proteins. Proteins are used to build cells and do much of the work inside cells.

Genes and Proteins Each gene code is copied in the nucleus and taken to the cytoplasm. Here the code is deciphered and converted into a string of amino acids (a protein) Each different protein has its own gene, somewhere on the chromosome, that codes for it.

Part II COPYING THE GENE

DNA cannot leave the nucleus of eukaryotic cells DNA cannot leave the nucleus of eukaryotic cells... but proteins are made outside of the nucleus by organelles called ribosomes human cheek cell Elodea leaf cell mitochondria chloroplasts vacuole nucleus (DNA here) (DNA here)

Think of ribosomes as factories that make proteins (proteins made here) (proteins made here) nucleus (DNA here) (DNA here)

DNA and ribosomes are at different locations in a prokaryotic cell. (proteins made here) ribosomes Q. Ribosomes make protein but are not in the same location as DNA in a cell. How can proteins be made according to the DNA information when they are in different places?

A. Take a copy of the Gene to the ribosome. mRNA transfers a copy of the gene on the DNA in the nucleus to the ribosomes. Ribosomes build proteins according to the mRNA information received.

mRNA: the messenger RNA is how the body gets information from the nucleus (DNA) to the place where protein gets made (ribosomes)

Information flow from DNA to trait Observed trait DNA protein Made by ribosomes outside of nucleus Stored in nucleus

Information flow from DNA to trait messenger RNA Observed trait DNA protein Made by ribosomes outside of nucleus Stored in nucleus

DNA information  mRNA information messenger RNA DNA Transcription is the process used to convert DNA information into mRNA information. Note: DNA does not become RNA; the information in DNA is copied as RNA

Part III RNA (Ribonucleic acid) and Transcription

What is RNA, anyways? How is it different than DNA?

Differences between DNA and RNA Double strand Deoxyribose sugar Contains thymine (and A, G, & C) Very large molecule RNA Single strand Ribose sugar Contains uracil (and A, G, & C) Small molecule

Different Sugars DNA RNA Can you spot the difference? http://www.layevangelism.com/bastxbk/images/deoxyribose.jpg RNA Can you spot the difference?

Different Bases Can you spot the difference? http://images.google.com/imgres?imgurl=http://www.starsandseas.com/SAS_Images/SAS_chem_images/thymine.jpg&imgrefurl=http://www.starsandseas.com/SAS%2520OrgChem/SASNucleic.htm&h=202&w=180&sz=5&hl=en&start=5&tbnid=t1HbUPbbgV4YhM:&tbnh=105&tbnw=94&prev=/images%3Fq%3Dthymine%26svnum%3D10%26hl%3Den%26rlz%3D1T4GFRC_enUS204US204 Can you spot the difference?

(double stranded, kept “safe” in nucleus) (single stranded - mobile) RNA IS COPIED FROM DNA DNA (double stranded, kept “safe” in nucleus) Genes are Copied RNA (single stranded - mobile)

The Transcription process Promoters are a specific set of bases on DNA that show where a gene begins. For transcription to occur, the enzyme RNA polymerase binds to DNA at the promoter and separates the DNA strands RNA Polymerase then uses one strand of DNA as a template to assemble nucleotides into a copy of the gene (mRNA)

The Transcription Process Terminators! Are a specific set of bases to show where the gene ends. RNA polymerase stops copying the gene here, moves off to find another gene, the transcript is released and the DNA “zips” back up.

Transcription of RNA from a template strand of DNA

Transcription DNA zips back together DNA unzips DNA ACTTTACGGCAT ACTTTACGGCAT TGAAATGCCGTA ACTTTACGGCAT TGAAATGCCGTA RNA copy made ACUUUACGGCAU TGAAATGCCGTA RNA ACUUUACGGCAU

If the DNA sequence is this: TACGAGTTACATAAA ATGCTCAATGTATTT What is the sequence of the mRNA? (Use the bottom strand as the template for mRNA) UACGAGUUACAUAAA

Animation of Transcription http://www.fed.cuhk.edu.hk/~johnson/teaching/genetics/animations/transcription.htm

Part IV Decoding the mRNA: What is the code?

The Genetic Code “The Problem” Somehow we need to read the order of nucleotides on mRNA and have that tell us the order of amino acids within each protein As there are 20 amino acids and only 4 different bases each nucleotide on its own cant specify the position of a different amino acid

The genetic code “The solution” If a word can only be a single letter long how many words can there be in the English language? If we can have two letters form a word how many words can we make now? (aa, ab, ac, ba, bb, bc, etc.) If two nucleotides can code for an amino acid how many amino acids can we code for? There are 64 possible ways to combine three nucleotides (43). More than enough to code for 20 amino acids.

The Codon A codon is a set of three nucleotides on mRNA and designates an amino acid There are 20 amino acids, but 64 possible codons So each amino acid may have more than one codon that codes for it.

A Codon Chart Decode by reading the first then second then third base. Example: AUG codes for Methionine

Part IV Turning mRNA into protein: Translation

Introducing…. Another RNA molecule; the final player in our story… tRNA

Transfer RNA (tRNA) An RNA molecule with attachment site at one end for an amino acid. The opposite end has three nucleotide bases called the anticodon. If there are 64 possible codons how many different tRNA molecules do you think there are?

Transfer RNA Amino acid amino acid attachment site U A C anticodon

Codons and Anticodons Amino Acid The 3 bases of an anticodon are complementary to the 3 bases of a codon tRNA anticodon UGA GCAAUCACUACGGCA codon

Translation Translation is the process of of decoding the mRNA into a protein. Ribosomes read mRNA three bases or 1 codon at a time and construct the proteins

1. A Ribosome binds to mRNA U G C

2. The Ribosome helps the correct tRNA bind to mRNA G aa2 A U 1-tRNA U A C aa1 anticodon A U G C U A C U U C G A hydrogen bonds codon mRNA

The Ribosome then helps the next correct tRNA bind to mRNA and a peptide bond forms G A aa3 aa1 aa2 peptide bond 1-tRNA 2-tRNA U A C G A U A U G C U A C U U C G A mRNA

Ribosomes move over one codon aa1 4. All Change !! 3-tRNA G A aa3 aa2 1-tRNA U A C (leaves) 2-tRNA G A U A U G C U A C U U C G A mRNA Ribosomes move over one codon

G C U aa4 aa1 5. Etc. Etc. !! aa2 aa3 G A U G A A A U G C U A C U U C 4-tRNA G C U aa4 aa1 5. Etc. Etc. !! aa2 aa3 2-tRNA 3-tRNA G A U G A A A U G C U A C U U C G A A C U mRNA

Ribosomes move over one codon peptide bonds 4-tRNA G C U aa4 aa1 aa2 aa3 2-tRNA G A U (leaves) 3-tRNA G A A A U G C U A C U U C G A A C U mRNA Ribosomes move over one codon

peptide bonds aa1 aa2 aa4 aa3 G A A G C U G C U A C U U C G A A C U 3-tRNA 4-tRNA G A A G C U G C U A C U U C G A A C U mRNA

Ribosomes move over one codon U G A 5-tRNA aa5 aa1 aa2 aa3 aa4 3-tRNA G A A 4-tRNA G C U G C U A C U U C G A A C U mRNA Ribosomes move over one codon

aa5 aa4 aa3 primary structure of a protein aa2 aa1 A C U C A U G U U U terminator or stop codon 200-tRNA A C U C A U G U U U A G mRNA

End Product –The Protein! The end products of protein synthesis is a primary structure of a protein A sequence of amino acid bonded together by peptide bonds aa1 aa2 aa3 aa4 aa5 aa200 aa199

A Gene (DNA) A Protein A U G C aa1 aa2 aa3 aa4 aa5 aa6 peptide bonds mRNA start codon codon 2 codon 3 codon 4 codon 5 codon 6 codon 7 codon 1 methionine glycine serine isoleucine alanine stop codon protein A Protein aa1 aa2 aa3 aa4 aa5 aa6 peptide bonds

THE END!!!