Chapter 15.3, Problem 34AQP

(a)

Summary Introduction

To determine:

The effect on translation process if Initiation factor-3 was removed from the cell-free protein-synthesizing system

Introduction:

Protein synthesis involves translation of mRNA into a protein that requires three complex stages: initiation, elongation, and termination. For the translation process to be completed, it requires several elements, such as ribosomes, tRNA, initiation factor, elongation factor, start codon, stop codon, release factor and so on. The translation process is completed when the ribosome translocates to a stop codon. If any of thesecomponents of translational machinery were omitted then the process of protein synthesis will be affected.

Explanation of Solution

(a) Initiation factor-3

The process of translation begins with the initiation stage, which requires initiation factors. Initiation factor 3 (IF-3) first come into the role in the translational process, it binds to the small subunit of the ribosome and restricts the association of large ribosomal subunit during initiation. The 30S initiation complex is formed by the binding of mRNA to the 30S ribosomal subunit. Initiation factor 3 attaches to the 30S subunit before the synthesis of the 30S initiation complex. During the last stage of the initiation process, IF-3 detaches from the 30S ribosomal subunit and facilitates the binding of the large ribosomal subunit to form a 70S initiation complex.

Therefore, elimination of IF-3 from cell-free protein synthesizing system would result in the decreased amount of protein synthesis and it also lowers the pace of initiation because more of 30S ribosomal subunit remains bound to the 50S subunit.

(b)

Summary Introduction

To determine:

The effect on translation process if Initiation factor-2 was removed from the cell-free protein-synthesizing system.

Introduction:

Protein synthesis involves translation of mRNA into a protein that requires three complex stages: initiation, elongation, and termination. For the translation process to be completed, it requires several elements, such as ribosomes, tRNA, initiation factor, elongation factor, start codon, stop codon, release factor and so on. The translation process is completed when the ribosome translocates to a stop codon. If any of thesecomponents of translational machinery were omitted then the process of protein synthesis will be affected.

Explanation of Solution

(b) Initiation factor-2

The process of translation begins with the initiation stage which requires initiation factors. Initiation factor 2 (IF-2) is a very essential component of translation as the binding of fMet-tRNA with the initiation codon is done through IF-2. If initiation factor 2 is removed from the translational machinery then the process of protein synthesis would terminate. fMet-tRNA would not be transferred to the 30S ribosomal subunit, which prevents the synthesis of the 30S initiation complex, in the absence of IF-2. The translation process will be ceased due to the absence of IF-2.

(c)

Summary Introduction

To determine:

The effect on translation process if Elongation Factor-Tu was removed from the cell-free protein-synthesizing system.

Introduction:

Protein synthesis involves translation of mRNA into a protein that requires three complex stages: initiation, elongation, and termination. For the translation process to be completed, it requires several elements, such as ribosomes, tRNA, initiation factor, elongation factor, start codon, stop codon, release factor and so on. The translation process is completed when the ribosome translocates to a stop codon. If any of thesecomponents of translational machinery were omitted then the process of protein synthesis will be affected.

Explanation of Solution

(c) Elongation Factor Tu (EF-Tu)

Elongation is one of the major stages in the synthesis of proteins. Elongation involves the joining of amino acids to produce a polypeptide chain. Elongation process requires several elongation factors. Elongation factor Tu comes into role first, it allows the binding of tRNA to the A site of the ribosome. This elongation factor joins with GTP and further with a charged tRNA to produce a three-part complex.

EF-Tu helps in the elongation of the polypeptide by forming three-part complex, this complex enters into A site of the ribosome where it delivers the charged tRNA. If EF-Tu were omitted from translation machinery then the charged tRNA would not be transferred to the A site of the ribosome and thus the process of translation will stop.

(d)

Summary Introduction

To determine:

The effect on translation process if Elongation Factor-G was removed from the cell-free protein-synthesizing system.

Introduction:

Protein synthesis involves translation of mRNA into a protein that requires three complex stages: initiation, elongation, and termination. For the translation process to be completed, it requires several elements, such as ribosomes, tRNA, initiation factor, elongation factor, start codon, stop codon, release factor and so on. The translation process is completed when the ribosome translocates to a stop codon. If any of thesecomponents of translational machinery were omitted then the process of protein synthesis will be affected.

Explanation of Solution

(d) Elongation Factor G (EF-G)

Elongation is one of the major stages in the synthesis of proteins. Elongation involves the joining of amino acids to produce a polypeptide chain. Elongation process requires several elongation factors. Elongation factor-G is required during the translocation of ribosome down the mRNA in $5^{\text{'}}\to 3^{\text{'}}$ direction. EF-G and hydrolysis of GTP to GDP facilitate the movement of ribosome down the mRNA.

If EF-G component were omitted from translation machinery then the movement of the ribosome along the mRNA will not occur and thus it will prevent the reading of new codons. The elongation of the polypeptide chain will stop and it will hamper the protein synthesis.

(e)

Summary Introduction

To determine:

The effect on translation process if Release factors was removed from the cell-free protein-synthesizing system.

Introduction:

Protein synthesis involves translation of mRNA into a protein that requires three complex stages: initiation, elongation, and termination. For the translation process to be completed, it requires several elements, such as ribosomes, tRNA, initiation factor, elongation factor, start codon, stop codon, release factor and so on. The translation process is completed when the ribosome translocates to a stop codon. If any of thesecomponents of translational machinery were omitted then the process of protein synthesis will be affected.

Explanation of Solution

(e) Release factors RF-1, RF-1, and RF-3

Release factors play important role in recognition of termination codon which aids in the ending of the translation process. RF-1 is used to recognize the termination codon UAA and UAG while RF-2 identifies UGA and UAA. RF-1 and RF-1 bind with each other at the A site of the ribosome and promotes the freeing of a polypeptide chain and the cleavage of tRNA at P site of the ribosome. RF-3 binds with GTP and forms RF-3-GTP complex, which binds to the ribosome and results in a conformational change in it. The complex releases the RF-1 or RF-2 from A site of the ribosome, and the tRNA moves to the E site from P site. Finally, the GTP complex is being hydrolyzed and the tRNA is released from the P site. The mRNA is cleaved fromthe ribosome and this marks the termination of the translation process.

(f)

Summary Introduction

To determine:

The effect on translation process if ATP was removed from the cell-free protein-synthesizing system.

Introduction:

Protein synthesis involves translation of mRNA into a protein that requires three complex stages: initiation, elongation, and termination. For the translation process to be completed, it requires several elements, such as ribosomes, tRNA, initiation factor, elongation factor, start codon, stop codon, release factor and so on. The translation process is completed when the ribosome translocates to a stop codon. If any of thesecomponents of translational machinery were omitted then the process of protein synthesis will be affected.

Explanation of Solution

(f) ATP

ATP is required for the charging of tRNA with aminoacyl-tRNA synthetase. The coupling of tRNA to its suitable amino acid is termed as tRNA charging which requires ATP. If ATP were omitted from translational machinery, the charging of tRNAs will not occur. If tRNA will not charge then no amino acids will be available for translation and thus protein synthesis will not occur.

(g)

Summary Introduction

To determine:

The effect on translation process if GTP was removed from the cell-free protein-synthesizing system.

Introduction:

Protein synthesis involves translation of mRNA into a protein that requires three complex stages: initiation, elongation, and termination. For the translation process to be completed, it requires several elements, such as ribosomes, tRNA, initiation factor, elongation factor, start codon, stop codon, release factor and so on. The translation process is completed when the ribosome translocates to a stop codon. If any of thesecomponents of translational machinery were omitted then the process of protein synthesis will be affected.

Explanation of Solution

(g) GTP

GTP plays a significant role in the process of initiation, elongation, and termination during protein synthesis. If GTP were omitted then the process of protein synthesis will not occur. GTP forms an importantcomplex with the components involves in translation and support the protein synthesis.