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8 Cards in this Set
- Front
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Transcription and Translation: How do gene "code' for proteins? |
-There is a link between an individual's DNA and that individual's proteins that are synthesized in each cell. -DNA is ultimately converted into a sequence of amino acids that together are called a protein. How does the cell do this? What information would you need to know in order to take a sequence of DNA and figure out what sequence of amino acids it codes for? |
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What are the steps of Transcription? |
1.) In order for genes to make a product, they must first be transcribed into RNA. 2.) "RNA" stands for ribonucleic acid. It is also made up of a phosphate-sugar backbone and nitrogen bases. It is different from DNA in that -RNA is usually single stranded -It has four bases. They are adenine, cytosine, guanine, and uracil. Uracil is unique in that is found only in RNA. Uracil replaces thymine. - It has the sugar ribose instead of dexoyribose. 3.) In eukaryotic cells, transcription occurs in the nucleus. Later, the RNA is transported to the cytoplasm to make protein (translation). 4.) Transcription requires a protein called RNA polymerase to read the DNA and synthesize the new RNA strand 5.) For each gene, RNA is transcribed form only one of the two DNA strands. The strand that looks like the new RNA strand is called the coding strand. This is the sequence of the gene you would normally see written out. The RNA will have the same sequence, except with Us in place of Ts. The template strand is the other strand: it is the strand that is read by RNA polymerase to produce the new messenger RNA strand. |
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What is the modification of mRNA in preparation for translation? |
-Immediately after transcription, the mRNA is called a "pre mRNA", because it's not quite ready for translation. Before the mRNA can actually be read into protein, it undergoes some important modifications. The modifications prepare the RNA for being read... and also help with transporting the mRNA into the cytoplasm, the site of protein synthesis. - the mRNA contains sequences that do not code for protein. There regions have to be removed, or "spliced" out, away from the protein-encoding sequences. |
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How are introns removed from the mRNA. |
- introns are transcribed but are removed by a complex called the spliceosome. The spliceosome contain both proteins and small RNAs. -introns can be small or large (65 bases to 100,000) -introns make up much of the DNA present in the human genome -introns are important even though they do no make proteins, because they can contain important information (regulatory regions) that controls whether and where genes get expressed (transcribed). -once the introns are removed, the exons are hooked back together, and now the mRNA is ready to be transported out into the cyoplasm where it can be read into protein. In addition to this normal splicing, there is a process called " alternative splicing" in which an exon may be excluded from the final mRNA transcript in some cells, while in another cell a different exon is excluded, while in a third, all exons are included. This process allows variation a particular protein even though all variations were derived from the same original DNA gene sequence |
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What occurs during translation? |
Genetic information moves form the DNA to RNA by the process of transcription. The term transcription is used because DNA and RNA are complementary "languages". Both are nucleic acids. The information in RNA is translated into a polypeptide. The term translation is used because RNA and proteins are different "languages". RNA is composed of bases (A,U,C, and G) while a protein or polypeptide is composed of amino acids 1.) Polypeptides (proteins) are built from amino acids 2.) There are twenty different amino acids. 3.) For many genes, the protein is functional molecule originally encoded by the DNA (in rare cases RNA is the functional molecule) 4.) Changes in DNA sequence that block the production of a functional protein will often be observed as an altered phenotype. These changes in DNA sequence are what we have been discussing when we talked about alleles, and the changes in protein function cause the phenotypes we have been discussing. -to translate mRNA into a protein, you need to know the genetic code. It is the dictionary that tells you what bases (A,U,C, and G) correspond to what amino acids. |
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How do you translate a language with 4 letters into a language with 20 letters? |
1.) A one-to-one correspondence will not work sine it will produce only 4 letters 2.) A one-to-two( two bases code 1 amino acid) correspondence will not work since it will produce only 16 letters. 3.) A one-to-three (three bases code 1 amino acid) correspondence will work since it will produce 64 letters. This would work, but it would produce more combinations than there are amino acids. T his turns out to be the case: there are multiple units of three that correspond to the same amino acid. thus, the code is redundant. - a triplet of mRNA is called an codon and it is the unit that is translated into an amino acid. -AUG is the start codon |
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Why is the genetic code essentially universal. |
1.) the same dictionary (genetic code) can be used to translate almost all mRNAs in all species. 2.) The exceptions are rare. There is a slightly different code in some mitochondrial genomes and in a few protozoans. 3.) This universality means that a gene from humans can be put into bacteria and make a functional protein-- ie, bacterial cells use the same building blocks (DNA) and the same code to translate RNA into protein. |
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What codon is used for what amino acid? |
-Marshall Nirenburg received the Nobel Prize for experiments to decipher the genetic code. He artificially generated an mRNA that was a string of U (uracil). The protein that was produced was a string of the amino acid phenylalanine. He deduced that the codon UUU was translated to phe. Next he made a mRNA that was a string of C (cytosine). the protein that was produced was all proline (pro). He deduced that the codon CCC was translated to pro. After he and make strings of single bases A,U, G, and C, he began to mix bases. Eventually, all base combinations were made, and the amino acids determined for each codon. |
