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Protein Synthesis and Gene Expression Let’s Review DNA & RNA DNA: deoxyribonucleic acid--contains sugar deoxyribose. DNA is double stranded. DNA contains bases adenine, thymine, guanine, cytosine. DNA never leaves the nucleus. RNA: ribonucleic acid-contains sugar ribose. RNA is SINGLE stranded. RNA contains bases adenine, guanine, cytosine and URACIL. RNA can leave the nucleus. Remember there are three types of RNA mRNA: messenger RNA mRNA tRNA: transfer RNA. rRNA: ribosomal RNA tRNA towing Overall process of protein synthesis transcription DNA translation RNA Protein TRANSCRIPTION translation Takes place in the nucleus Moves out of nucleus into the cytoplasm & attach to ribosome DNA’s tragedy If I could only get out there… I’d show them a thing or two! DNA contains volumes of information about making protein. Unfortunately, DNA is too huge to leave the ribosomes nucleus. nucleus How does the cell solve this problem….transcription That’s where mRNA comes in. mRNA helps get DNA’s message out to the ribosomes... How do I tell those guys what I want them to do? I can help! First, DNA unzips itself... DNA unzips itself, exposing free nitrogen bases. First, DNA unzips itself... DNA unzips itself, exposing free nitrogen bases. First, DNA unzips itself... DNA unzips itself, exposing free nitrogen bases. First, DNA unzips itself... DNA unzips itself, exposing free nitrogen bases. First, DNA unzips itself... DNA unzips itself, exposing free nitrogen bases. Next, mRNA is made... mRNA is made from the DNA template mRNA matches with free DNA nitrogen bases in a complimentary fashion Next, mRNA is made... mRNA is made from the DNA template mRNA matches with free DNA nitrogen bases in a complimentary fashion Next, mRNA is made... mRNA is made from the DNA template mRNA matches with free DNA nitrogen bases in a complimentary fashion Next, mRNA is made... mRNA is made from the DNA template mRNA matches with free DNA nitrogen bases in a complimentary fashion Next, mRNA is made... mRNA is made from the DNA template mRNA matches with free DNA nitrogen bases in a complimentary fashion Next, mRNA is made... mRNA is made from the DNA template mRNA matches with free DNA nitrogen bases in a complimentary fashion Next, mRNA is made... mRNA is made from the DNA template mRNA matches with free DNA nitrogen bases in a complimentary fashion Next, mRNA is made... mRNA is made from the DNA template mRNA matches with free DNA nitrogen bases in a complimentary fashion Next, mRNA is made... mRNA is made from the DNA template mRNA matches with free DNA nitrogen bases in a complimentary fashion Next, mRNA is made... mRNA is made from the DNA template mRNA matches with free DNA nitrogen bases in a complimentary fashion Next, mRNA is made... mRNA is made from the DNA template mRNA matches with free DNA nitrogen bases in a complimentary fashion Next, mRNA is made... mRNA is made from the DNA template mRNA matches with free DNA nitrogen bases in a complimentary fashion Next, mRNA is made... mRNA is made from the DNA template mRNA matches with free DNA nitrogen bases in a complimentary fashion Next, mRNA is made... mRNA is made from the DNA template mRNA matches with free DNA nitrogen bases in a complimentary fashion Next, mRNA is made... mRNA is made from the DNA template mRNA matches with free DNA nitrogen bases in a complimentary fashion Next, mRNA is made... mRNA is made from the DNA template mRNA matches with free DNA nitrogen bases in a complimentary fashion Next, mRNA is made... mRNA is made from the DNA template mRNA matches with free DNA nitrogen bases in a complimentary fashion Next, mRNA is made... mRNA is made from the DNA template mRNA matches with free DNA nitrogen bases in a complimentary fashion mRNA leaves the nucleus... I hope he can tell them what to do! DNA’s code is copied to mRNA in three letter groups called codons. After mRNA is made from the DNA template, it is ready to leave the nucleus. The next step...Translation mRNA meets the Ribosomes! (No, it’s not a new sitcom on Fox…) mRNA tries to talk to the ribosomes… mRNA leaves the I have a message for you! It’s nucleus and from DNA! travels to the cytoplasm, where the ribosomes are located. Once there, mRNA meets up with the ribosomes What does he want now? It’s always something! mRNA tries to talk to the ribosomes…but is unsuccessful. However, the ribosomes cannot understand the message mRNA is carrying. Why don’t they get it??? @%$!! Why can’t we tell what he’s saying? We need a translator! tRNA Saves the Day! Tyrosine The boss will NOT be happy about this... We won’t work until we know what to do! Where is that translator? Looks like trouble for this cell… I’d better help! Now the cell can make a protein! tRNA: Transfer RNA Tyrosine Chemically, tRNA is clover-leaf shaped. At one end, it carries an amino acid. At the other end, it has a three letter code known as an anticodon. Anticodon? What’s that? This anticodon is the complement to the codons contained within mRNA. Can you find the mRNA complement to the anticodon on tRNA? Tyrosine Some notes about Amino Acids There are 20 known amino acids present in living things. How is it possible to get a group of four letters to code for 20 things? Put them into groups of three… 43 = 64 codes Number of members in a group of nitrogen bases Number of nitrogen bases What’s a codon, anyway? Here is what a codon looks like. It is a sequence of 3 bases. How we determine what amino acid each codon codes for must be read off of a codon chart. This is also known as the genetic code. Codon chart Second Base U A G Phenylalanine Phenylalanine Leucine Leucine Serine Serine Serine Serine Tyrosine Tyrosine Stop Stop Cysteine Cysteine Stop Tryptophan U C A G C Leucine Leucine Leucine Leucine Proline Proline Proline Proline Histidine Histidine Glutamine Glutamine Arginine Arginine Arginine Arginine U C A G A Isoleucine Isoleucine Isoleucine Methionine Threonine Threonine Threonine Threonine Asparagine Asparagine Lysine Lysine Serine Serine Arginine Arginine U C A G Valine Valine Valine Valine Alanine Alanine Alanine Alanine Aspartic Acid Aspartic Acid Glutamic Acid Glutamic Acid Glycine Glycine Glycine Glycine U C A G U First Base C G Third Base The Wonderful World of Amino Acids It is possible for some amino acids to have more than one codon. There are three stop codons…they are UAA, UGA and UAG. There is also one START codon…AUG. How a Translator works… First, the anticodons on tRNA meet up with the mRNA start codon (AUG) at the ribosome Next, another tRNA meets up with it’s corresponding mRNA. Each tRNA carries an amino acid. Tyrosine How a Translator works… Once two amino acids are made, a bond forms between them This process continues until a stop codon on mRNA is reached. Tyrosine