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Protein Synthesis and Gene Expression Why does a cell need proteins to function properly? Time to make the proteins... SO…how does a cell make proteins anyway? There are two important nucleic acids involved in making proteins... 1. DNA 2. RNA Where are proteins made? B. Ribosomes Let’s Review DNA & RNA DNA: deoxyribonucleic acid DNA is double stranded. Contains sugar deoxyribose. DNA contains bases adenine, thymine, guanine, cytosine. DNA never leaves the nucleus. RNA: ribonucleic acid RNA is single stranded. Contains sugar ribose. RNA contains bases adenine, guanine, cytosine and URACIL. RNA can leave the nucleus. Remember there are three types of RNA mRNA: messenger RNA DNA mRNA tRNA: transfer RNA. Transcription tRNA towing rRNA: ribosomal RNA Translation Overall process of protein synthesis transcription DNA translation mRNA Protein Summary of Protein Synthesis DNA mRNA tRNA protein 1. The process of going from DNA to mRNA is transcription. 2. The process of going from mRNA to protein is translation. Let’s explore this in a little more detail... First, let’s see how the message in DNA gets to the ribosomes… 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. IV. Transcription a. The process of going DNA to mRNA IV. Transcription b. The steps of transcription: 1. First DNA unzips itself along the segment of code needed for a certain protein. 2. mRNA is made by forming complementary bases on the unzipped portion of DNA. IV. Transcription DNA→RNA DNA A-T T-A G-C C-G RNA A U G C IV. Transcription b. The steps of transcription: 3. DNA’s code is copied into groups of 3 bases at a time called a codon. 4. Each codon codes for 1 amino acid. 5. Once the mRNA strand is transcribed, it can leave the nucleus to find a ribosome to carry out the next step. 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 complementary fashion Some additional notes about making mRNA… DNA contains two kinds of sequences: Coding and Noncoding regions Some additional notes about making mRNA… One kind of noncoding is used to start transcription Another kind is call Introns and is old, unused sequences of bases The coding regions are called Exons Final Processed mRNA is made from Exons 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 Translation Translation mRNA meets the Ribosomes! (No, it’s not a new sitcom on FOX…) mRNA tries to talk to the ribosomes… I have a message mRNA leaves the for you! It’s nucleus and travels from DNA! 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. Why don’t they get it??? @%$!! Why can’t we tell what he’s saying? However, the ribosomes cannot understand the message mRNA is carrying. 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 1. Chemically, tRNA is clover-leaf shaped. 2. At one end, it carries an amino acid (like a tow truck). 3. 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 Other Codon Charts Reading a Codon Chart 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. Methionine 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. Methionine Animation of translation Click to automatically start animation. This is a ribosome. Single Messenger RNA Strand Met Single Messenger RNA Strand Met Ala Single Messenger RNA Strand Met Ala Single Messenger RNA Strand Met Ala Single Messenger RNA Strand Met Ala Single Messenger RNA Strand Met Ala Single Messenger RNA Strand Met Ala Single Messenger RNA Strand Met Ala Single Messenger RNA Strand Met Ala Single Messenger RNA Strand Met Ala Single Messenger RNA Strand Met Ala Single Messenger RNA Strand Met Ala Single Messenger RNA Strand Met Ala Single Messenger RNA Strand Met Ala Single Messenger RNA Strand Met Ala Single Messenger RNA Strand Met Ala Pro Single Messenger RNA Strand Met Ala Pro Single Messenger RNA Strand Met Ala Pro Single Messenger RNA Strand Met Arg Pro Single Messenger RNA Strand Met Pro Ala Single Messenger RNA Strand Met Pro Ala Single Messenger RNA Strand Met Pro Ala Single Messenger RNA Strand Met Pro Ala Single Messenger RNA Strand Met Pro Ala Single Messenger RNA Strand Met Pro Ala Single Messenger RNA Strand Met Pro Ala Single Messenger RNA Strand Met Pro Ala Single Messenger RNA Strand Met Pro Ala Single Messenger RNA Strand Met Pro Ala Single Messenger RNA Strand Met Pro Ala Single Messenger RNA Strand Met Pro Ala Single Messenger RNA Strand Met Pro Ala Single Messenger RNA Strand Met Pro Ala Single Messenger RNA Strand Met Pro Ala Phe Single Messenger RNA Strand Met Pro Ala Phe Single Messenger RNA Strand Met Pro Ala Phe Single Messenger RNA Strand Met Ala Pro Phe Single Messenger RNA Strand Met Ala Gly Phe Single Messenger RNA Strand Met PhePro Ala Single Messenger RNA Strand Met Phe Pro Ala Single Messenger RNA Strand Met Phe Pro Ala Single Messenger RNA Strand Met Phe Pro Ala Single Messenger RNA Strand Met Phe Pro Ala Single Messenger RNA Strand Met Phe Pro Ala Single Messenger RNA Strand Met Phe Pro Ala Single Messenger RNA Strand Met Phe Pro Ala Single Messenger RNA Strand Met Phe Pro Ala Single Messenger RNA Strand Met Phe Pro Ala Single Messenger RNA Strand Met Phe Pro Ala Met Phe Pro Ala Ala Met Pro Phe Stop Ala Met Pro Phe Stop Ala Met Pro Phe Stop Ala Met Pro Phe Stop Ala Met Pro Phe Stop Pro Phe Stop Phe Stop Stop Stop Stop Stop Stop Stop Stop Stop Stop Stop How Does it Know When to Quit? This process continues until a stop or a termination codon (found on mRNA) is reached. There are three stop codons: UGA, UAA and UAG. STOP Regulation of Transcription and Translation Think about your house, do you keep all the lights on ALL the time in every room?? Gene expression is a regulated process where genes can be turned on and off as needed due to environmental factors. In summary… DNA contains the information needed to make proteins. However, DNA is too large to leave the nucleus. RNA acts as a set of working instructions for ribosomes to make proteins. This process is also known as gene expression. Gene expression is a regulated process. The Central Dogma is Universal