diff --git a/module/gff_file.py b/module/gff_file.py
index bdd32af..98b4345 100644
--- a/module/gff_file.py
+++ b/module/gff_file.py
@@ -183,9 +183,9 @@ def scan_mrna_sequence(self, base_url=None, fasta_file=None):
             else:
                 return False
 
-            mrna.coding_sequence_has_start_codon()
-            mrna.coding_sequence_has_stop_codon()
-            mrna.coding_sequence_no_internal_stop_codon()
+            mrna.has_start_codon()
+            mrna.has_stop_codon()
+            mrna.no_internal_stop_codon()
 
             if mrna.errors != {}:
                 gene_id = self.get_gene_id(mrna_id)
diff --git a/module/transcript.py b/module/transcript.py
index d57f04d..73c8cbe 100644
--- a/module/transcript.py
+++ b/module/transcript.py
@@ -16,6 +16,9 @@
 
 class CodingSequence:
     sequence_type = 'cds'
+    
+    start_codons = ('ATG')
+    stop_codons = ('TAA', 'TAG', 'TGA')
 
     def __init__(self, feature_name, organism_name, sequence_name):
         self.feature_name = feature_name
@@ -37,33 +40,34 @@ def get_sequence(self, base_url=None, fasta_file=None):
             else:
                 return False
         elif fasta_file:
-            file_handle = open(fasta_file, 'r')
-            for seq in file_handle:
-                if seq[0] != '>':
-                    self.sequence += seq.rstrip()
+            with open(fasta_file, 'r') as file_handle:
+                for seq in file_handle:
+                    if seq[0] != '>':
+                        self.sequence += seq.rstrip()
         else:
             return False
 
-    def coding_sequence_has_start_codon(self):
-        if self.sequence[0:3] == 'ATG':
+    def has_start_codon(self):
+        first_codon = self.sequence[0:3]
+        if first_codon in self.start_codons:
             return True
         else:
             self.errors['start_codon'] = 'no start codon'
             return False
 
-    def coding_sequence_has_stop_codon(self):
+    def has_stop_codon(self):
         last_codon = self.sequence[-3:]
-        if last_codon == 'TAA' or last_codon == 'TAG' or last_codon == 'TGA':
+        if last_codon in self.stop_codons:
             return True
         else:
             self.errors['stop_codon'] = 'no stop codon'
             return False
 
-    def coding_sequence_no_internal_stop_codon(self):
+    def no_internal_stop_codon(self):
         internal_stop_codon_count = 0
         for i in range(0, len(self.sequence) - 3, 3):
             codon = self.sequence[i:i + 3]
-            if codon == 'TAA' or codon == 'TAG' or codon == 'TGA':
+            if codon in self.stop_codons:
                 internal_stop_codon_count += 1
                 self.errors['no_internal_stop_codon'] = str(internal_stop_codon_count) + ' internal stop codon'
         if internal_stop_codon_count:
diff --git a/test/test_transcript.py b/test/test_transcript.py
index 4026c90..94a1a6b 100644
--- a/test/test_transcript.py
+++ b/test/test_transcript.py
@@ -12,46 +12,46 @@ def test_has_sequence(self):
     def test_has_start_codon(self):
         mrna = transcript.CodingSequence('b0b85443-0ff0-4fec-b919-f7bbeb626072', 'sandbox_arabiensis', 'SDBKB704125')
         mrna.sequence = "ATGCACTGA"
-        mrna.coding_sequence_has_start_codon()
-        self.assertEqual(True, mrna.coding_sequence_has_start_codon())
+        mrna.has_start_codon()
+        self.assertEqual(True, mrna.has_start_codon())
 
         mrna.sequence = "ATCCACTGA"
-        mrna.coding_sequence_has_start_codon()
+        mrna.has_start_codon()
         self.assertEqual('no start codon', mrna.errors['start_codon'])
 
     def test_has_stop_codon(self):
         mrna = transcript.CodingSequence('b0b85443-0ff0-4fec-b919-f7bbeb626072', 'sandbox_arabiensis', 'SDBKB704125')
 
         mrna.sequence = "ATGCACTGA"  # TGA amber stop codon
-        self.assertEqual(True, mrna.coding_sequence_has_stop_codon())
+        self.assertEqual(True, mrna.has_stop_codon())
 
         mrna.sequence = "ATGCAGTAA"  # TAA ochre stop codon
-        self.assertEqual(mrna.coding_sequence_has_stop_codon(), True)
+        self.assertEqual(mrna.has_stop_codon(), True)
 
         mrna.sequence = "ATGCAGTAG"  # TAG opal stop codon
-        self.assertEqual(mrna.coding_sequence_has_stop_codon(), True)
+        self.assertEqual(mrna.has_stop_codon(), True)
 
         mrna.sequence = "ATGCAGCAG"  # NO stop codon
-        self.assertEqual(mrna.coding_sequence_has_stop_codon(), False)
+        self.assertEqual(mrna.has_stop_codon(), False)
         self.assertEqual('no stop codon', mrna.errors['stop_codon'])
 
     def test_no_internal_stop_codon(self):
         mrna = transcript.CodingSequence('b0b85443-0ff0-4fec-b919-f7bbeb626072', 'sandbox_arabiensis', 'SDBKB704125')
 
         mrna.sequence = "ATGCACCTCGAGTAA"
-        mrna.coding_sequence_no_internal_stop_codon()
-        self.assertEqual(mrna.coding_sequence_no_internal_stop_codon(), True)
+        mrna.no_internal_stop_codon()
+        self.assertEqual(mrna.no_internal_stop_codon(), True)
 
         mrna.sequence = "ATGCACTAACTCGAGTAA"  # TAA
-        mrna.coding_sequence_no_internal_stop_codon()
+        mrna.no_internal_stop_codon()
         self.assertEqual(mrna.errors['no_internal_stop_codon'], '1 internal stop codon')
 
         mrna.sequence = "ATGCACCTCGAGTAGTAA"  # TAG
-        mrna.coding_sequence_no_internal_stop_codon()
+        mrna.no_internal_stop_codon()
         self.assertEqual(mrna.errors['no_internal_stop_codon'], '1 internal stop codon')
 
         mrna.sequence = "ATGTGACACCTCTAATAA"  # TGA,TAA
-        mrna.coding_sequence_no_internal_stop_codon()
+        mrna.no_internal_stop_codon()
         self.assertEqual(mrna.errors['no_internal_stop_codon'], '2 internal stop codon')