I got my program working correctly but I want to streamline the code and the GUI for better performance. right now i can press a button, select either a text file with a DNA sequence and it will automatically convert into RNA and display it onto a second screen then translate the RNA sequence into protein and display that into a 3rd text box. the problem I'm having is i have to use the extra text box to print the converted DNA to RNA sequence and then extract the sequence from that text box just to input the text into a variable in order to convert the RNA string of text into protein. what I want to do is convert the DNA to RNA internally and input that RNA string sequence into a list or array dynamically and just print out the protein sequence from there to the final text box instead of having to use the extra text box in between. everything in my code that's commented out is basically what I'm trying to do but instead of it printing out the converted DNA to RNA it prints out the number of codons which is wrong ("only 16 should be over 200") and no characters from the sequence. How can I do this without using the extra text box?

i posted the whole code to give an Idea of what the program does.
I have a snippet below.
Thanks for taking a peek at this.

Code:
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Data.SqlClient;


namespace bioinformaticsCal
{

    public partial class Form1 : Form
    {
        int numberOfCodons;
        int rnaLength;
        int beginIndex;
        int endIndex;
        int i;
        int j;
        int k;
        string[] codons = { "UUU", "UUC", "UUA", "UUG", "UCU", "UCC", "UCA", "UCG", "UAU", "UAC", "UAA", "UAG", "UGU", "UGC", "UGA", "UGG", "CUU", "CUC", "CUA", "CUG", "CCU", "CCC", "CCA", "CCG", "CAU", "CAC", "CAA", "CAG", "CGU", "CGC", 
                              "CGA", "CGG", "AUU", "AUC", "AUA", "AUG", "ACU", "ACC", "ACA", "ACG", "AAU", "AAC", "AAA", "AAG", "AGU", "AGC", "AGA", "AGG", "GUU", "GUC", "GUA", "GUG", "GCU", "GCC", "GCA", "GCG", "GAU", "GAC", "GAA", "GAG", "GGU", "GGC", "GGA", "GGG" };
        string[] aminoAcids = { "Phenylalanine", "Phenylalanine", "Leucine", "Leucine", "Serine", "Serine", "Serine", "Serine", "Tyrosine", "Tyrosine", "Stop", "Stop", "Cysteine", "Cysteine", "Stop", "Tryptophan", "Leucine", "Leucine", "Leucine", "Leucine", "Proline", "Proline", "Proline", "Proline", "Histidine", "Histidine", "Glutamine", "Glutamine", "Arginine", "Arginine", "Arginine", "Arginine", 
                                  "Isoleucine", "Isoleucine", "Isoleucine", "Methionine", "Threonine", "Threonine", "Threonine", "Threonine", "Asparagine", "Asparagine", "Lysine", "Lysine", "Serineine", "Serineine", "Arginine", "Arginine", "Valine", "Valine", "Valine", "Valine", "Alanine", "Alanine", "Alanine", "Alanine", "Aspartate", "Aspartate", "Glutamate", "Glutamate", "Glycine", "Glycine", "Glycine", "Glycine" };
        string codon = "";
        string protein = "";
        string SEQ;
        int len;
        string Str_len;
       
 //List<string> RNA = new List<string>(); //Trying to make this work ****************************************************
        
        public Form1()
        {
            InitializeComponent();
        }


        private void Form1_Load(object sender, EventArgs e)
        {
           

        }



        public void button1_Click(object sender, EventArgs e)
        {
            OpenFileDialog Fd = new OpenFileDialog();
            if (Fd.ShowDialog() == System.Windows.Forms.DialogResult.OK)
            {
                StreamReader Sr = new StreamReader(File.OpenRead(Fd.FileName));

                SEQ = Sr.ReadToEnd();
            }

            string strCompare = SEQ;
            string strStringContains = "T";

            var matchingString = strCompare.IndexOfAny(strStringContains.ToCharArray()) != -1;
            if (matchingString)
            {

                richTextBox3.AppendText("You Have entered a DNA sequence");
                richTextBox3.AppendText("\n\r");
                richTextBox3.AppendText("Click the Translate button to begin Translation");
                richTextBox3.AppendText("\n\r");
                richTextBox3.AppendText(SEQ);
                richTextBox3.AppendText("\n\r");

                for (int i = 0; i < SEQ.Length; i++)
                {

                    if (SEQ[i] == 'A')
                    {
                        richTextBox1.AppendText("U");
                        //RNA.Add("U");  //Trying to make this work like the above statement****************************************************
                    }
                    if (SEQ[i] == 'G')
                    {
                        richTextBox1.AppendText("C");
                        //RNA.Add("C"); //Trying to make this work like the above statement****************************************************

                    }
                     if (SEQ[i] == 'C')
                    {
                        richTextBox1.AppendText("G");
                        //RNA.Add("G");   //Trying to make this work like the above statement****************************************************

                    }

                    if (SEQ[i] == 'T')
                    {
                        richTextBox1.AppendText("A");
                        //RNA.Add("A"); //Trying to make this work like the above statement****************************************************
                        
                    }
                    len++;

                }

                richTextBox3.AppendText("\n\r");
                Str_len = len.ToString();
                richTextBox3.AppendText("Number of Bases: ");
                richTextBox3.AppendText(Str_len);
                richTextBox3.AppendText("\n\r");


            }
            else
            {
                richTextBox3.AppendText("You have entered an  RNA sequence");
                richTextBox3.AppendText("\n\r");
                richTextBox1.AppendText(SEQ);
                for (int i = 0; i < SEQ.Length; i += 3)
                {
                    richTextBox3.AppendText(SEQ[i].ToString());
                    if (i + 1 < SEQ.Length)
                    {
                        richTextBox3.AppendText(SEQ[i + 1].ToString());
                    }
                    if (i + 2 < SEQ.Length)
                    {
                        richTextBox3.AppendText(SEQ[i + 2].ToString());
                    }
                    richTextBox3.AppendText(" ");


                }
                richTextBox3.AppendText("Click the Translate button to begin Translation");
                richTextBox3.AppendText("\n\r");
            }
        }


    private void Tranlate_Click(object sender, EventArgs e)
        {
            SEQ = richTextBox1.Text.ToString();  
            
            //SEQ = RNA.ToString();    //Trying to make this work like the above statement****************************************************
            
            rnaLength = SEQ.Length;
            numberOfCodons = rnaLength / 3;
            beginIndex = 0;
            richTextBox2.AppendText("Sequence has been Translated to Protein");
            richTextBox2.AppendText("\n\r");
            richTextBox2.AppendText("Total Number Of codons are: ");
            richTextBox2.AppendText(numberOfCodons.ToString());
            richTextBox2.AppendText("\n\r");
            
            for (i = 0; i < numberOfCodons; i++)
            {
                
                endIndex = beginIndex + 3;
                codon = "";
                {
                    codon += (SEQ.Substring(beginIndex, endIndex - beginIndex)) ;
                }
                for (k = 0; k < 64; k++)
                {
                    if (codon == codons[k])
                    {
                        protein += (codon + "_" + aminoAcids[k]) + "  ";
                    }

                }
                beginIndex += 3;
            }

            richTextBox2.AppendText(protein);
      }

       
        private void button2_Click(object sender, EventArgs e)
        {

            SaveFileDialog sfd = new SaveFileDialog();
            sfd.Filter = "Text File |*.txt";
            sfd.FileName = "Save File As";
            sfd.Title = "Save Bioinformatic Text File";
            if (sfd.ShowDialog() == System.Windows.Forms.DialogResult.OK)
            {
                string path = sfd.FileName;
                BinaryWriter bw = new BinaryWriter(File.Create(path));

                bw.Write(textBox2.Text);
                bw.Write(richTextBox3.Text);
                bw.Write(richTextBox1.Text);
               
                bw.Write(richTextBox2.Text);
                bw.Dispose();

            }
        }

       
        private void Reset(object sender, EventArgs e)
        {

            richTextBox1.Clear();
            richTextBox2.Clear();
            richTextBox3.Clear();
            richTextBox3.AppendText("Enter Another Sequence");
            richTextBox3.AppendText("\n\r");
        }

        private void richTextBox3_Load(object sender, EventArgs e)
        {



        }
        private void textBox2_TextChanged(object sender, EventArgs e)
        {

        }


        class sampleInfo
        {
            public string sampleSource
            {
                get;
                set;
            }
            public string sampleReference
            {
                get;
                set;
            }
            public string sampleType
            {
                get;
                set;
            }
            public string fileName
            {
                get;
                set;

            }
            public string fileContent
            {
                get;
                set;
            }
            public string conversionResults
            {
                get;
                set;
            }
            public string richTextBox3
            {
                get;
                set;
            }
        }

       
       
    }
}
Basically this part of the code is where I want to improve
the commented parts are what I'm trying to make work

Code:
//List<string> RNA = new List<string>(); //Trying to make this work****************************************************
        
        public Form1()
        {
            InitializeComponent();
        }


        private void Form1_Load(object sender, EventArgs e)
        {
           

        }



        public void button1_Click(object sender, EventArgs e)
        {
            OpenFileDialog Fd = new OpenFileDialog();
            if (Fd.ShowDialog() == System.Windows.Forms.DialogResult.OK)
            {
                StreamReader Sr = new StreamReader(File.OpenRead(Fd.FileName));

                SEQ = Sr.ReadToEnd();
            }

            string strCompare = SEQ;
            string strStringContains = "T";

            var matchingString = strCompare.IndexOfAny(strStringContains.ToCharArray()) != -1;
            if (matchingString)
            {

                richTextBox3.AppendText("You Have entered a DNA sequence");
                richTextBox3.AppendText("\n\r");
                richTextBox3.AppendText("Click the Translate button to begin Translation");
                richTextBox3.AppendText("\n\r");
                richTextBox3.AppendText(SEQ);
                richTextBox3.AppendText("\n\r");

                for (int i = 0; i < SEQ.Length; i++)
                {

                    if (SEQ[i] == 'A')
                    {
                        richTextBox1.AppendText("U");
                        //RNA.Add("U");  //Trying to make this work like the above statement****************************************************

                    }
                    if (SEQ[i] == 'G')
                    {
                        richTextBox1.AppendText("C");
                        //RNA.Add("C");  //Trying to make this work like the above statement****************************************************

                    }
                     if (SEQ[i] == 'C')
                    {
                        richTextBox1.AppendText("G");
                        //RNA.Add("G");   //Trying to make this work like the above statement****************************************************

                    }

                    if (SEQ[i] == 'T')
                    {
                        richTextBox1.AppendText("A");
                        //RNA.Add("A");  //Trying to make this work like the above statement****************************************************
                        
                    }
                    len++;

                }

                richTextBox3.AppendText("\n\r");
                Str_len = len.ToString();
                richTextBox3.AppendText("Number of Bases: ");
                richTextBox3.AppendText(Str_len);
                richTextBox3.AppendText("\n\r");


            }
            else
            {
                richTextBox3.AppendText("You have entered an  RNA sequence");
                richTextBox3.AppendText("\n\r");
                richTextBox1.AppendText(SEQ);
                for (int i = 0; i < SEQ.Length; i += 3)
                {
                    richTextBox3.AppendText(SEQ[i].ToString());
                    if (i + 1 < SEQ.Length)
                    {
                        richTextBox3.AppendText(SEQ[i + 1].ToString());
                    }
                    if (i + 2 < SEQ.Length)
                    {
                        richTextBox3.AppendText(SEQ[i + 2].ToString());
                    }
                    richTextBox3.AppendText(" ");


                }
                richTextBox3.AppendText("Click the Translate button to begin Translation");
                richTextBox3.AppendText("\n\r");
            }
        }


    private void Tranlate_Click(object sender, EventArgs e)
        {
            SEQ = richTextBox1.Text.ToString();  
            
            //SEQ = RNA.ToString();   //Trying to make this work like the above statement****************************************************
            
            rnaLength = SEQ.Length;
            numberOfCodons = rnaLength / 3;
            beginIndex = 0;
            richTextBox2.AppendText("Sequence has been Translated to Protein");
            richTextBox2.AppendText("\n\r");
            richTextBox2.AppendText("Total Number Of codons are: ");
            richTextBox2.AppendText(numberOfCodons.ToString());
            richTextBox2.AppendText("\n\r");
            
            for (i = 0; i < numberOfCodons; i++)
            {
                
                endIndex = beginIndex + 3;
                codon = "";
                {
                    codon += (SEQ.Substring(beginIndex, endIndex - beginIndex)) ;
                }
                for (k = 0; k < 64; k++)
                {
                    if (codon == codons[k])
                    {
                        protein += (codon + "_" + aminoAcids[k]) + "  ";
                    }

                }
                beginIndex += 3;
            }

            richTextBox2.AppendText(protein);
      }