Chapter 14 Protein Synthesis

Transcription

1 1 Chapter 14 Protein Synthesis Go to: Go through the various sites and review DNA synthesis Go to: Know the genetic code for the synthesis of polypeptides. Go to: Be able to decode table for the synthesis of polypeptides. Be able to do these questions without looking up the answers. Go to: The University of Washington provide information on various chromosomal abnormalities. Check it out. Rather technical but if you are going into bio-chemistry you may try following this site through This last web site is the genetic code which you can also find in text book.

2 2 I. What is the role of proteins in a cellular system Chapter 14 Protein Synthesis A. Proteins are used for maintenance, growth and development II. How are proteins made : TRANSCRIPTION and TRANSLATION A. DNA 1. Instructions are coded in nucleotides consisting of : A - adenine T - thymine G - guanine C - cytosine 2. Twisted double stranded DNA bases pair in : A - T ; C - G 3. In DNA replication base pairs unwind to serve as templates assembly of new complementary strand 4. Gene - a linear stretch of DNA nucleotide sequence a. Coding for an assembly of amino acids that forms a polypeptide chain 5. The path for gene expression has two steps : a. Transcription - mrna strand coded from DNA strand in a 5-3 direction b. Translation - mrna moved from nucleus to cytoplasm proteins are synthesized in the ribosome B. Three kinds of RNA play a part in protein synthesis 1. mrna : Single strand of information coded from DNA 2. rrna : Ribosome RNA functions as a catalytic site for acid assembly into a protein 3. trna : Transfer RNA which bring the correct amino acid to the ribosome

3 3 III. TRANSCRIPTION OF DNA TO RNA A. RNA assembly 1. Three ways RNA differs from DNA (a comparison and contrast) a. RNA is single strand DNA is double strand b. RNA uses Uracil DNA uses Thymine c. RNA uses ribose sugar DNA uses deoxyribose sugar B. RNA transcription differs from DNA replication a. A single strand of RNA is synthesized from DNA b. RNA polymerase catalyzes the synthesis of mrna 1. DNA replication uses DNA polymerase c. mrna uses single region of a single strand of DNA is as a template C. Final modification to mrna 1. New mrna not ready to use 2. mrna is modified prior to export from nucleus IV. mrna to PROTEINS A. Genetic code a. The 5 end of mrna is capped with a start signal for translation b. A poly-a tail is added to the 3 end of the mrna c. Non-coding portions (introns) are snipped out of mrna Coding regions (exxons) are spliced together. 1. Every three base pairs (triplets) of mrna specifies an amino acid to be included in a growing polypeptide chain a. mrna bases pairs are referred to as CODONS b. 61 base pairs code for 20 amino acids and 3 base pairs serve to stop protein synthesis : (UAA, UAG, UGA) c. AUG (specifies methionine) is the start codon

4 4 B. The roles of trna & mrna in protein synthesis 1. Each of the 20 amino acids must attach to a specific trna a. Each trna has specific triplet base pair (ANTI-CODON) specific for the mrna triplet base pair 2. After mrna arrives in cytoplasm an anticodon of trna binds to the correct codon sequence of the mrna a. The first two base pairs of anticodon must pair with the codon by the rules of A with U & G with C b. The third base pair has some latitude in pairing resulting in condition of WOBBLE effect c. Transcription takes place within a ribosome structure 1) The ribosome is composed of rrna and proteins which work together during protein synthesis C. STAGES OF TRANSLATION 1. (1) Initiation; (2) Elongation; (3) Termination 2. Initiation a. A complex is formed between trna the small ribosomal subunit, mrna and the large ribosomal subunit 1) Initiation step begins with initiator trna (a trna containing methionine amino acid) 2) Initiator trna binds to P site of small ribosomal subunit 3) Scanning of mrna allows recognition of codon AUG 4) Large ribosomal subunit binds to small ribosomal subunit 5) Specific trna for mrna (anticodon to codon) binds to A site of small ribosomal subunit 6) Reaction catalyzed between amino and carboxyl group resulting in peptide bond

5 5 3. Elongation a. A series of trnas delivers amino acids in sequence by codon anti-codon matching forming peptide bonds 4. Termination a. Stop codon reached b. Polypeptide chain is released into cytoplasm 5. Several ribosomes (POLYSOME) may be moving along the same mrna simultaneously V. MUTATION AND PROTEIN SYNTHESIS A. Changes in the genetic struction of DNA 1. Changes in the protein structure should result B. Gene mutation results from: 1. Bases being added, deleted, or replaced 2. Mutations are rare and may result from mutagens such as: a. Viruses, ultraviolet light (UV), & chemicals 3. Spontaneous mutations a. Sickle-cell anemia (single base-pair substituition) b. DNA template frameshift c. Transposable elements of DNA jumping to a new location on the DNA

6 Biology 101 Chapter 14 Name: Fill-in-the-Blanks Which base follows the next in a strand of DNA is referred to. as the base (1). The region of DNA that calls for the assembly of specific amino acids into a polypeptide chain is a (2). The two steps from genes to proteins are called (3) and (4).. In eukaryotes, during (5), single-stranded molecules of RNA are assembled on DNA templates in the nucleus. During (6), the RNA molecules are shipped from the nucleus into the cytoplasm, where they are used as templates for assembling (7) chains. Following translation, one or more chains become (8) into the three-dimensional shape of protein molecules. Proteins have (9) and (10) roles in cells, including control of DNA. Complete the Table Three types of RNA are transcribed from DNA in the nucleus (from genes that code only for RNA). Complete the following table, which summarizes information about these molecules. RNA Molecule Abbreviation Description/Function a. Ribosomal RNA b. Messenger RNA c. Transfer RNA

7 Sequence Arrange the steps of transcription in correct chronological sequence. Write the letter of the first step next to 15, the letter of the second step next to 16, and so on. 15. A. The RNA strand grows along exposed bases until RNA polymerase meets a DNA base sequence that signals "stop." 16. B. RNA polymerase binds with the DNA promoter region to open up a local region of the DNA double helix. 7. C. An RNA polymerase enzyme locates the DNA bases of the promoter region of one DNA strand by recognizing DNA-associated proteins near a promoter. 18. D. RNA is released from the DNA template as a free, single-stranded transcript. 19. E. RNA polymerase moves stepwise along exposed nucleotides of one DNA strand; as it moves. the DNA double helix keeps unwinding. Completion 20. Suppose the line below represents the DNA strand that will act as a template for the production of mrna through the process of transcription. Fill in the blanks below the DNA strand with the sequence of complementary bases that will represent the message carried from DNA to the ribosome in the cytoplasm. (Transcribe single-strand of mrna) Matching 1. codon 2. three at a time 3. sixty-one 4. the genetic code 5. release factors 6. ribosome 7. anticodon 8. the "stop" codons A. Composed of two subunits, the small subunit with P and A amino acid binding sites as well as a binding site for mrna B. Reading frame of the nucleotide bases in mrna C. Detach protein and mrna from the ribosome D. UAA, UAG, UGA E. A sequence of three nucleotide bases that can pair with a specific mrna codon F. Name for each base triplet in mrna G. The number of codons that actually specify amino acids H. Term for how the nucleotide sequences of DNA and then mrna correspond to the amino acid sequence of a polypeptide chain

8 Complete the Table 9. Complete the following table, which distinguishes the stages of translation. Translation Stage a. b. Description Special initiator trna loads onto small ribosomal subunit and recognizes AUG; small subunit binds with mrna, and large ribosomal subunit joins small one. Amino acids are strung together in sequence dictated by mrna codons as the RNA strand passes through the two ribosomal subunits; two trnas interact at P and A sites c. mrna "stop" codon signals the end of the polypeptide chain; release factors detach the ribosome and polypeptide chain from the mrna. Completion 10. Given the following DNA sequence, deduce the composition of the mrna transcript: TAC AAG ATA ACA TTA TTT CCT ACC GTC ATC (mrna transcript) 11. Deduce the composition of the trna anticodons that would pair with the above specific mrna codons as these trnas deliver the amino acids (identified below) to the P and A binding sites of the small ribosomal subunit. (trna anticondons) From the mrna transcript, use the text to deduce the composition of the amino acids of the polypeptide sequence. (amino acids)

9 Fill-in-the-Blanks The order of (13) in a protein is specified by a sequence of nucleotide bases. The genetic code is read in units of (14) nucleotides; each unit of three codes for (15) amino acids). In the table that showed which triplet specified a particular amino acid, the triplet code was incorporated in (16) molecules. Each of these triplets is referred to as a(n) (17) (18) alone carries the instructions for assembling a particular sequence of amino acids from the DNA to the ribosomes in the cytoplasm, where (19) of the polypeptide occurs. (20) RNA acts as a shuttle molecule as each type brings its particular (21) to the ribosome where it is to be incorporated into the growing (22). A(n) (23) is a triplet on mrna that forms hydrogen bonds with a(n) (24), which is a triplet on trna. Fill-in-the-Blanks In addition to changes in chromosomes (crossing over, recombination, deletion, addition. translocation. and inversion), changes can also occur in the structure of DNA; these modifications are referred to as gene mutations. Complete the following exercise on types of spontaneous gene mutations. Viruses, ultraviolet radiation, and certain chemicals are examples of environmental agents called (2) that may enter cells and damage strands of DNA. If A becomes paired with C instead of T during DNA replication. this spontaneous mutation is a base-pair (3). Sickle-cell anemia is a genetic disease whose cause has been traced to a single DNA base pair; the result is that one (4) is substituted for another in the beta chain of (5). A(n) (6) mutation is defined as the insertion or deletion of one to several DNA base pairs; this puts the nucleotide sequence out of phase. and abnormal proteins are produced. Some DNA regions "jump" to new DNA locations and often inactivate the genes in their new environment; such (7) elements may give rise to observable changes in the phenotype of an organism. (8) is the source of the unity of life; (9) are the original source of life's diversity; they are heritable, small-scale alterations in the (10) sequence of DNA. Each gene has a characteristic (11), which is the probability it will mutate spontaneously during a given interval of time. But not all mutations are spontaneous. (12) radiation causes base substitutions or breaks in. one or both strands.

10 Self Quiz 1. Transcription a. occurs on the surface of the ribosome b. is the final process in the assembly of a protein c. occurs during the synthesis of any type of RNA by use of a DNA template d. is catalyzed by DNA polymerase 2. carry(ies) amino acids to ribosomes, where amino adds are linked into the primary structure of a polypeptide. a. mrna b. trna c. Introns d. rrna 3. Transfer RNA differs from other types of RNA because it a. transfers genetic instructions from cell nucleus to cytoplasm b. specifies the amino acid sequence of a particular protein c. carries an amino add at one end d. contains codons 9. The cause of sickle-cell anemia has been traced a. to mosquito-transmitted virus b. two DNA mutations that result in two incorrect amino acids in a hemoglobin chain c. three DNA mutations that result in three incorrect amino acids in a hemoglobin chain d. one DNA mutation that results in one incorrect amino acid in a hemoglobin chain 10. An example of a mutagen is a. virus b. ultraviolet radiation c. certain chemicals d. all of the above 4.dominates the process of transcription. a. RNA polymerase b. DNA polymerase c. Phenylketonuria d. Transfer RNA 5. and, are found in RNA but not in DNA. a. Deoxyribose; thymine b. Deoxyribose; uracil c. Uracil; ribose d. Thymine; ribose 6. If each kind of nucleotide is coded to select only one amino acid, how many different types of amino acids could be selected? a. four b. sixteen c. twenty d. Sixty-four 7. Each "word" in the mrna language consists of letters. a. three b. four c. five d. more than five 8. The genetic code is composed of codons. a. three b. twenty c. sixteen d. sixty-four