Thymine = orange Adenine = dark green Guanine = purple Cytosine = yellow Uracil = brown

Transcription

1 1 DNA Coloring - Transcription & Translation Transcription RNA, Ribonucleic Acid is very similar to DNA. RNA normally exists as a single strand (and not the double stranded double helix of DNA). It contains the same bases, adenine, guanine and cytosine. However, there is no thymine found in RNA, instead there is a similar compound called uracil. Transcription is the process by which RNA is made from DNA. It occurs in the nucleus. Label the box with the x in it near the nucleus with the word TRANSCRIPTION and proceed to color the bases according to the key below Thymine = orange Adenine = dark green Guanine = purple Cytosine = yellow Uracil = brown Color the strand of DNA dark blue (D) and the strand of RNA light blue (R). Color the nuclear membrane (E) gray. Translation 1 Taken from and

2 Translation occurs in the cytoplasm, specifically on the ribosomes. The mrna made in the nucleus travels out to the ribosome to carry the "message" of the DNA. Here at the ribosome, that massage will be translated into an amino acid sequence. Color the ribosome light green (Y) and note how the RNA strand threads through the ribsosome like a tape measure and the amino acids are assembled. The RNA strand in the translation area should also be colored light blue, as it was colored in the nucleus. Label the box with the X in the stranslation area with the word TRANSLATION. Important to the process of translation is another type of RNA called Transfer RNA (F) which function to carry the amino acids to the site of protein synthesis on the ribosome. Color the trna red. A trna has two important areas. The anticodon, which matches the codon on the RNA strand. Remember that codons are sets of three bases that code for a single amino acid. Make sure you color the bases of the anticodon the same color as the bases on your DNA and RNA strand - they are the same molecules! At the top of the trna is the amino acids. There are twenty amino acids that can combine together to form proteins of all kinds, these are the proteins that are used in life processes. When you digest your food for instance, you are using enzymes that were originally proteins that were assembled from amino acids. Each trna has a different amino acid which link together like box cars on a train. Color all the amino acids (M) pink. Questions: 1. How many different kinds of bases can be found on DNA 2. What base is found on RNA but not on DNA? 3. How many bases are in a codon? In an anticodon? 4. How many amino acids are attached to a single transfer RNA? 5. Transcription occurs in the ; translation occurs in the. 6. The process of making RNA from DNA is called and it occurs in the 7. The process of assembling a protein from RNA is called and it occurs in the

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4 The Central Dogma: From DNA to Proteins I. How in the information in DNA turned into Protein? The Central Dogma. DNA is a huge information database that carries the complete set of instructions for making all the proteins a cell will ever need! Although there are only four different bases in DNA (A, C, G and T), the order in which the bases occur determines the information to make a protein, just like the 26 letters of the alphabet combine to form words and sentences: Compare: RAT - TAR - ART - same 3 letters; completely different meanings. And with DNA: GAC - AGC - CGA - same 3 'letters'; completely different meanings to the cell (specifies the amino acids Aspartic Acid, Serine, and Arginine) Q: Review: What are genes? A: We know from the results of the Human Genome project, that most of the cell's DNA (~97%) does NOT code for proteins, but has structural or regulatory functions. The DNA in each chromosome that DOES provide the instructions for a protein is called a gene. In the 1940s, scientists proposed, fairly correctly, that each gene "codes for" (contains the instructions for) one protein. This is referred to as the "one-gene, one-protein" hypothesis. As we have learned more about the human genome in the last 10 years or so, however, we are now finding that more often than not, one gene will code for perhaps two or more related proteins. This was a Big Surprise of the Human Genome Project in scientists realized that we had

5 only about 30,000 genes, coding for 100,000 different proteins - rather than the 100,000 genes that had been estimated for the human genome The basic hypothesis is still the same, but we know a lot more details now! Q: If DNA is in the nucleus and proteins are synthesized in the cytoplasm, on ribosomes and in the rer, how to they "get together"?a: The answer: use a "messenger" to carry the instructions from DNA out into the cytoplasm. A nucleic acid very similar to DNA, called mrna or messenger RNA, is a copy of a gene, and serves this function the "bridge" between DNA and protein: The Central Dogma: DNA encodes the information to make RNA...and RNA molecules function together to make protein II. What is RNA and how is it different from DNA? Two big differences between DNA and RNA: 1. The sugar in DNA is deoxyribose; in RNA it is ribose 2. The nitrogenous base uracil (U) is used in RNA in place of T (they are very similar bases; in

6 RNA U= A just like T = A.) III. Transcription = Re-writing DNA into RNA

7 DNA is "transcribed" or re-written into RNA in a very complicated process called transcrption. (Think of a transcriptionist that takes spoken words from one source, like a court judge, and makes a copy of those words on paper. If that helps...). Simply stated, during transcription, one gene (DNA) is 're-written' into an RNA in the nucleus: A team of enzymes and proteins binds to the promoter, or starting region, of a gene. These enzymes and proteins unzip the DNA double helix just at the region of the gene. The enzyme RNA polymerase uses one of the DNA strands to make an RNA copy of that one gene.

8 This copy, which contains the instructions to make 1 protein, is called an mrna or messenger RNA. After the mrna is made, it is trimmed down to a final size, and shipped out of the nucleus! When the mrna gets into the cytoplasm, it is made into protein. IV. What's the connection between mrna and protein? The order of the bases in the DNA specifies the order of bases in the mrna, and The order of bases in the mrna specifies the order of amino acids in a protein. The genetic code is a triplet code (handout) 1. Nucleotides on mrna are read "three at a time" by the ribosome. Every three nucleotides in an mrna (a 'codon') specifies the addition of one amino acid in a protein. For example, a 600 nucleotide mrna will code for a 200 amino acid protein. 2. The amino acids corresponding to all 64 codons have been determined - this was all worked out in the 1960s by Marshall Nirenberg, Robert Holley, and Har Khorana (Nobel Prize!) All proteins start with the initiation codon AUG (Met) All proteins end with stop codons -either UAA, UGA, or UAG Some codons that differ in the third nucleotide can still code for the same amino acid - this is called "wobble".

9 The genetic code chart represents the sequence on the mrna codon. All living organisms and viruses use this triplet genetic code - its that "biological unity" idea again!!! Worksheet

10 V. Translation = De-coding RNA into protein During translation, the mrna transported to the cytoplasm is "de-coded" or "translated" to produce the correct order of amino acids in a protein.. Translation requires numerous enzymes. To know the full story, we need to look at two other RNA "Key Players" - rrna and trna rrna = ribosomal RNA; these RNA molecules associate with other proteins to form the ribosomes. Each ribosome can accept two trnas at a time (carrying amino acids) and one mrna. trna = transfer RNA; small RNA molecules that carry a specific amino acid at one end and an anticodon region that recognizes and binds mrna at the other end. The trna that binds to that mrna codon determines what amino acid is added to a protein chain. The Three RNAs (mrna, trna, and rrna) all work together to turn the information in DNA into a beautiful, 3-dimestional protein!!!

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12 The steps of translation: 1. Initiation: mrna enters the cytoplasm and becomes associated with ribosomes (rrna + proteins). trnas, each carrying a specific amino acid, pair up with the mrna codons inside the ribosomes. Base pairing (A-U, G-C) between mrna codons and trna anticodons determines the order of amino acids in a protein. 2. Elongation: addition of amino acids one-by-one: As the ribosome moves along the mrna, the trna transfers its amino acid to the growing protein chain, producing the protein - codon by codon! 3. Termination: when the ribosomes hits a stop codon - UAA, UGA, or UAG - the ribosome falls apart! The same mrna may be used hundreds of times during translation by many ribosomes before it is degraded (broken down) by the cell. How does translation relate to YOUR life? (Why do you need to know this, anyway?) All the proteins that make up YOU, your cells, your body, the foods you eat, all the living cells in the world, etc - are made this way! Every time your body needs more of a protein -

13 muscle protein, hair protein, enzymes, hormones, hemoglobin molecules, a gene carrying the information for that protein is transcribed into mrna, and the mrna is made into protein! Better living through transcription and translation! We will talk about how this related to GENETICS and INHERITANCE very soon! Objectives : 1. Name the two differences between DNA and RNA 2. Use the triplet code to determine the order of amino acids in a protein (worksheet) 3. Describe the "bottom line" of transcription 4. Describe the "bottom line" of translation 5. Define the words: gene, codon, amino acid, mutation, mrna, trna, rrna

14 14 1. What is the mrna strand that would be copied from this DNA strand? G G C T A T A T C C T G C G C T A T A C G C T A 2. The m in mrna stands for. 3. What is the function of mrna? 4. Draw a picture of the monomer of RNA, called a. 5. In your picture label the following parts ribose sugar, base, and phosphate group. 6. What are three differences between RNA and DNA? 7. What are the three types of RNA?

15 15 8. If the following strand is a trna, what is the sequence of the DNA strand it copied itself from? U U A G C G C G G G A U U A A G C U C G A A U A 9. What is the function of trna? 10. Proteins are made up of, which our bodies either make or come from our food. 11. What does rrna do? 12. Name the two places in the cell where you can find RNA. 13. Name the place in the cell where you can find DNA. 14. Draw an mrna strand that would complement the DNA strand CCAAT. 15. In your picture above, circle an RNA nucleotide. 16. What are the four steps of transcription?