DNA and Protein Synthesis Notes PDF

DNA AND ITS ROLE INSIDE THE CELL DNA is found in chromosomes. __________________________________________________________________________________________________. In eukaryotic cells, chromosomes always remain in the nucleus. James Watson and Francis Crick _________________________________________...

DNA AND ITS ROLE INSIDE THE CELL DNA is found in chromosomes. __________________________________________________________________________________________________. In eukaryotic cells, chromosomes always remain in the nucleus. James Watson and Francis Crick _______________________________________________________ are usually given credit for discovering that DNA has a double helix shape, like a spiral staircase. _______________________________ Rosalind Franklin who had used X rays to learn more about DNA’s structure. nucleotide monomers DNA, as a nucleic acid, is made from _____________________________________________. Each nucleotide consists of a sugar (deoxyribose), a phosphate group, and a nitrogen-containing base (A, C, G, or T). _______________________________________________________________________________________________________________________ ______________________________________________________________________________________________________________________. hydrogen bonds Scientists concluded that bonds __________________________________ between complementary bases hold together the two polynucleotide chains of DNA. These base pairs (A-T or G-C) stick into the middle of the double helix, forming, in essence, the steps of the spiral staircase. Hydrogen Bonds ________________________________________________________________________ are easily broken by certain enzymes, permitting the strands of a DNA molecule to separate. ______________________________________________________________________________________ RESPONSIBLE FOR THE FORMATION OF PROTEINS DNA= _____________________________________________________________________________________________ The DNA molecule is made up of two chains of nucleotides wound around each other. The handrails consist of alternating sugar and phosphate groups. ________________________________________________________________________________________________________________________ The rungs are made of nitrogenous bases. ________________________________________________________________________________________________________________________ ________________________________________________________________________________________________________________________ There are three components of a DNA strand __________________________________________________________________________________ : phosphate group, a 5-carbon sugar (deoxyribose), and a nitrogen base. ________________________________________________________________________________________________________________________ There are five types of nitrogen bases: Adenine (A), Guanine (G). ___________________________________________________ Thymine (T), Cytosine (C), and Uracil (U). ___________________________________________________ Three are pyrimidines thymine (T) cytosine (C) uracil (U) PURINE = DOUBLE RINGED PYRIMIDINE = SINGLE RINGED Uracil replaces thymine in a related nucleic acid, RNA. Uracil is found in RNA, and thymine is found only in DNA. ___________________________________________________________________________________ ________________________________________________________________________________________________________________________ Chargaff’s Rules Erwin Chargaff studied DNA from many different species. He studied the four different nitrogen bases of DNA: adenine (A), guanine (G), cytosine (C), and thymine (T). Chargaff Determined that the concentration of adenine was always about the same as the concentration of thymine and the concentrations of guanine and cytosine were about the same. Adenine only pairs with thymine (A–T or T–A pairing) Guanine only pairs with cytosine (G-C or C–G pairing) For example, if the sequence along part of one strand (or half of the ladder) was ACC-TGA using the A - T and G – C pairing, the corresponding part of the other strand (the other half of the ladder) would be TGG-ACT. ACC-TGA Strand 1 ___________________________________________________________ TGG-ACT Strand 2 ___________________________________________________________ Genes a certain segment of DNA that codes for a specific protein for a particular trait. ________________________________________________________________________________________________________________________ ________________________________________________________________________________________________________________________ DNA and Protein Synthesis protein synthesis DNA is responsible for ______________________________. There are 20 different amino acids that can be used to form polypeptide chains or proteins. Since the type of protein is dependent on the amino acids joined together, DNA can be thought of as a code that specifies how to join the amino acids in a certain order to form the desired protein. Since the DNA remains in the nucleus, while proteins are synthesized around the ribosomes in the cytoplasm ________________________________________________________________________________________________________________________ ________________________________________________________________________________________________________________________ there has to be some sort of messenger system between the DNA and the ribosomes. This messenger is another nucleic acid called ribonucleic acid or RNA. The process of the transfer of genetic information is sometimes termed gene expression. It can be summarized as follows. Transcription_________________________________________________________________________________________ the genetic information is transcribed from DNA to RNA. : the genetic information is translated from the RNA to the protein. Translation___________________________________________________________________________________________ TRANSCRIPTION Transcription is the term given to the formation, or synthesis of RNA. nucleus. The transcription process occurs in the ___________________________The goal of transcription is to make a copy of a small piece of the DNA. ___________________________________________________________________________________________________ Transcription takes place in three steps: initiation, elongation, and termination. RNA polymerase 1. Initiation: The enzyme __________________________________ binds to a region of a gene called the promoter. This signals the DNA to unwind so the enzyme can “read” the bases in one of the DNA strands. The enzyme is ready to make a strand of mRNA with a complementary sequence of bases. 2. Elongation is the addition of nucleotides to the mRNA strand. 3. Termination is the ending of transcription. The mRNA strand is complete, and it detaches from DNA. Processing mRNA In eukaryotes, the new mRNA is not yet ready for translation. It must go through more processing before it leaves the nucleus. This may include splicing, editing, and polyadenylation. These processes modify the mRNA. Splicing removes introns from mRNA. Introns are regions that do not code for proteins. _____________________________________________________________________________________________________The remaining mRNA consists only of regions that do code for proteins, which are called _____________________. exons. Polyadenylation adds a “tail” to the mRNA. The tail consists of a string of As (adenine bases). It signals the end of mRNA. It is also involved in exporting mRNA from the nucleus. In addition, the tail protects mRNA from enzymes that might break it down. As in DNA, the nucleotides in RNA are also grouped in series of three to serve as messengers in protein formation. codons. These are called ____________________________________________________________________ Transcription, of RNA stops at a certain point and the single strand ribonucleic acid separates from the DNA and leaves the nucleus through its membrane. The RNA is ready to transport the information for protein synthesis to the ribosomes. At this point it is termed ___________________________________________. messenger RNA (mRNA) Once outside the cell, the mRNA finds a ribosome and attaches to its outer surface.  TRANSLATION The process in which codons and anticodons form proteins is called translation. Once the mRNA reaches the ribosomes, the genetic information is ready to be deciphered, or translated. Transfer RNA (tRNA) Transfer RNA (tRNA) is another kind of RNA found in the cell's cytoplasm. The nucleotides in transfer RNA are not identical to those in the messenger RNA but complement them according to the A-T (A-U) and C-G pairings. For this reason, the term anticodon _________________________________ is sometimes applied to transfer RNA. The short strands of tRNA, or anticodons, form attachments with specific amino acids. Transfer RNA finds spots to line up along the messenger RNA so that the adenine-uracil, guanine-cytosine, pairings are consistent. As this happens, the amino acids join to (eventually) form a protein. After an amino acid is joined, a transfer RNA disconnects from both the amino acid and messenger RNA to return to the cytoplasm for another amino acid. In this manner, a protein is built up according to original directions from the DNA in the nucleus. Follow the process for a single codon through DNA codon – (messenger) RNA codon – (transfer) RNA anticodon for the example below. DNA codon: ACC mRNA codon: UGG tRNA codon: ACC (Recall that in messenger and transfer RNA, uracil takes the place of thymine. This is why messenger RNA in this sequence is UGG, rather than TGG.) Note that the transfer RNA anticodon is exactly the same as the DNA codon. THE GENETIC CODE It is now thought that the nitrogen bases arrange themselves in series of threes, called nitrogen base triplets or codons (or anticodons, in transfer RNA). Each codon identifies with a specific amino acid. The triplet arrangements or "codes" can give 64 different possible combinations with the four nitrogen bases. Some triplet codes do not identify specific amino acids; instead, some of these codons signal the beginnings of protein chains, others stand for the ends, and some do not seem to signify anything. Example: Given the DNA codon sequence: ACA – TGG – CGT -- determine the sequence for the mRNA, tRNA and name each of the 3 amino acids formed.