Button onclick problem.

So, I am making a doodle jump game. I have added left and right movement with left and right arrow keys on the keyboard, but now I created 2 buttons that are taking the whole screen, one is on the left half, and one is on the right half. When I click the left one, I want the player to move left and when I click the right one the player moves to the right. I have copied the code that moves the player and have pasted it inside a public void and assigned it for onclick function in unity. Here is the moving script for arrows:

 void FixedUpdate () 
     {
             if (Input.GetKey (KeyCode.LeftArrow) || Input.GetKey (KeyCode.A)) 
             {
                 this.gameObject.transform.Translate (Vector3.left * Time.deltaTime * speed);                                                
             } 
             else if (Input.GetKey (KeyCode.RightArrow) || Input.GetKey (KeyCode.D)) 
             {
                 this.gameObject.transform.Translate (Vector3.right * Time.deltaTime * speed);
             }
     }

But when I copy it in my script for buttons it doesn't work!

 using UnityEngine;
 using System.Collections;
 
 public class LeftButton : MonoBehaviour {
     float speed = 4f;
     public GameObject player;
 
 
     public void LeftMovement()
     {
         this.gameObject.transform.Translate (Vector3.left * Time.deltaTime * speed);    
         Debug.Log ("Touched!");
     }
     public void RightMovement()
     {
         this.gameObject.transform.Translate (Vector3.right * Time.deltaTime * speed);    
         Debug.Log ("Touched243!");
     }
 
 
 }

I have assigned everything correctly, that is for sure. Please help me repair the problem. Here is a screenshot with buttons! Please help me!