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AP Biology Chapter 17 Review
Transcript of AP Biology Chapter 17 Review
DNA to RNA to Protein Transcription, the making of mRNA from DNA in the nucleus goes as follows:
1. Initiation: In initiation, RNA polymerase II attaches to the promoter, a region where transcription can begin. For eukaryotes, transcription factors (i.e. a TATA box) mediate the binding and the transcription factors paired with the promoter is called a transcription initiation complex.
2. As RNA polymerase II moves along DNA, it unwinds the DNA and separates the two strands. One strand, the coding strand, is not a part of transcription. The other strand, the template strand, is what RNA polymerase II uses to code. As RNA polymerase II moves downstream, it makes a complementary RNA strand to the template strand.
3. At a certain point, the RNA transcript will be released and RNA polymerase II will detach. At this time, however, the RNA transcript is known as pre-mRNA, not mRNA because three things must happen for it to become mRNA.
4. First, the 5' end of the pre-mRNA must receive a methyl-guanine cap and the 3' end of the pre-mRNA must receive a poly-A tail consisting of 50-250 adenine nucleotides. These modifications do three things: they protect the mRNA from hydrolytic enzymes, they allow the mRNA to leave the nucleus, and they help ribosomes attach to the 5' end of the mRNA.
5. Lastly, snRNP's collectively called a spliceosome must cleave out introns (noncoding segments of nucleic acid) and fuse together exons (coding segments). Translation Codon: a series of three nucleotides that codes for an amino acid Translation, the making of proteins from mRNA goes as follows:
1. The 5' end of mRNA attaches to the ribosome, which consists of a large subunit and a small subunit. The large subunit consists of three parts: the A site (aminoacyl tRNA synthetase site), the P site (peptidyl-tRNA site) and the E site (exit site).
2. Once attached tRNA (transfer RNA) must be correctly matched to its amino acid. In order for this to occur, ATP and an amino acid will bind to the A site. Then, ATP will give two phosphate groups to the amino acid. After that, complementary tRNA will covalently bond to the amino acid. Finally, the activated amino acid will be released.
3. Initiation can now occur: the small subunit moves mRNA downstream until it reaches a start codon, AUG, which signals for the start of translation. TRNA will then hydrogen bond with the start codon.
4. Elongation: The anticodon of tRNA basepairs with the complementary mRNA codon at the A site (hydrolysis of 2 GTP speeds up this process), allowing for the addition of an amino acid to the polypeptide chain. An rRNA molecule catalyzes the formation of a peptide bond between the new amino acid and the growing polypeptide chain. TRNA is translocated from the A site to the P site. When it is empty, it is moved to the E site where it is released.
5. Termination: Termination occurs when the ribosome reaches a stop codon on the mRNA (UAG, UAA, or UGA). The A site then accepts a release factor which hydrolyzes the bond between tRNA in the P site and the last amino acid in the polypeptide chain.
6. The polypeptide chain will be released from the ribosome and will receive and SRP signal from the golgi apparatus. This signal will tell the polypeptide chain where to go after it folds into its final conformation. It can go to one of six places: the nucleus, mitochondria, transport, chloroplast, cell membrane, or golgi. Mutations Mutations: changes in the genetic material of a cell Point mutations: chemical changes in just one base pair of a gene, can be divided into two general categories~base-pair substitutions and base-pair insertions or deletions
base pair substitution-the replacement of one nucleotide and its partner with another pair of nucleotides
missense mutations- the altered codon still codes for an amino acid and thus makes sense but not necessarily the right sense
nonsense mutations-a mutation that causes translation to be terminated prematurely
insertion and deletions- additions or losses of nucleotide pairs in a gene, have a disastrous efffect on the resulting protein
frameshift mutation-occurs whenever the number of nucleotides inserted or deleted is not a multiple of three, all the nucleotides downstream of that mutation will be improperly grouped into codons Works Cited (16 and 17) **All images solely have URL due to lack of an APA citation generator for images
Campbell, N., & Reece, J. (2005). From Gene to Protein. Biology (pp. 309-331). Menlo Park : Benjamin Cummings Publishing.