Biology 1002B Lecture : CHAPTER 14.docx

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greenlocust120

21 Apr 2012

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14. 1 the connection between dna, rna, and proteins. Arg mutants they hypothesized had a deficiency in an ezyme needed for the synthesis of argenine. Scientists knew that there were 20 amino acids. If 1 base pair coded for 1 a. a. = 4 a. a. "s. If 2 base pairs coded for one a. a. = 4^2 = 16 amino acids. So smallest possible number is 3 (4^3 = 64) Nirenberg & leder (synthesising all possible codon"s and combining them in a mixture of trnas) and khorana (synthesising long and repeatative mrna"s and mixing with ribosomes) experiment"s helped plot the genetic code. Sense codons they specify a certain amino acid (61 of 64 codons are sense: aug codes for methionine, it is the start/ initiator codon. Nonsense/ termination codons have no corresponding amino acid: uaa, uag, uga. Genetic code is degenerate (more than one codon for more amino acids) It is also commaless must be read in the correct manner to make sense.

Related Questions

22. There are 20 amino acids and 64 possible codons. Which of the following is closer to the actual number of different tRNA molecules in a cell?

A. 4

B. 16

C. 20

D. 61

E. 64

23. There are 20 amino acids and 64 possible codons. How many different eukaryotic aminoacyltRNA synthetases are there? A. 1

B. 16

C. 20

D. 61

E. 64

24. Which way are the amino acid and tRNA attached in a charged tRNA?

A. Amino acid-5'tRNA3'-AMP B

. Amino acid-AMP-3'tRNA

C. AMP-amino acid-3'tRNA

D. Amino acid-3'tRNA5'-AMP

E. Amino acid-AMP-5'tRNA

25. The anticodon that recognizes the initiation codon in translation is

A. 5' AUG 3'

B. 3' AUG 5'

C. 5' ACU 3'

D. 5' UAC 3'

E. 3' UAC 5'

26. The first amino acid incorporated into a growing polypeptide

A. In bacteria is methionine and it is also methionine in eukaryotes

B. In bacteria is tryptophan, while it is methionine in eukaryotes

C. In bacteria is N-formyl methionine, while it is methionine in eukaryotes

D. In bacteria is N-formyl methionine and it is also N-formyl methionine in eukaryotes

E. In bacteria is methionine, while it is N-formyl methionine in eukaryotes

27. In E. coli the IF3 forces tRNAf Met to bind with

A. The A site of the ribosome

B. The P site of the ribosome

C. The E site of the ribosome

D. IF1

E. IF2

You perform a series of experiments on the synthesis of thepituitary hormone prolactin, which is a single polypeptide chain199 amino acids long. in the first experiment, the mRNA coding forprolactin is translated in a cell free protein synthesizing systemcontaining ribosomes, amino acids, tRNAs, aminoacyl-tRNAsynthetases, ATP, GTP and the appropraite initiation, elongationand termination factors. Under these conditions, a polypeptidechain 227 amino acids long is synthesized. In a second experiment,the mRNA is translated in the same cell-free system to which youhave added SRP. In this case, translation stops after a peptideabout 70 amino acids long has been produced. In a third experiment,you ise the same cell free translation system to which you haveadded both SRP and endoplasmic reticulum vesicles, and you fingthat the prolactin mRNA no prduces a polypeptide that is 199 aminoacids long. Explain these results. Where would you find thepolypeptide produced in experiment 3?

redcamel210

Several experiments were conducted to obtain information about how the eukaryotic ribosome recognizes the AUG start codon. In one experiment, the gene that encodes the methionine initiator tRNA (tRNAmet) was mutated so that its anticodon was changed from 5â-CAU-3â to 5â-CCA-3â. When this mutated gene was placed in a eukaryotic cell, protein synthesis took place but the proteins produced were abnormal. Some of the proteins contained extra amino acids, while others contained fewer amino acids than normal. Knowing what you do about how Eukaryotic ribosomes know where to start translating, explain why some proteins produced by this mutated tRNA have extra amino acids while other proteins have fewer amino acids.

Biology 1002B Lecture : CHAPTER 14.docx

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