Name: __________________________________
Activity: Genetic Code Problem Set
Part 1: DNA Base Pairing
Watson and Crick discovered that hydrogen bonds could form between certain nitrogenous bases and provide just enough force to
hold the two strands together. Hydrogen bonds can only form between certain nitrogenous base pairs – adenine [A] and thymine
[T] and guanine [G] and cytosine [C]. Once they saw this, they also realized that this principle explained Chargaff’s rules. Now there
was a reason for the [A] = [T] and [G] = [C].
Write a sentence that summarizes the key points in the paragraph above:
Use the base-pairing rules to write the base sequence of the COMPLEMENTARY DNA strand.
1. Template Strand:
TTACGGGTCACCAAGCGTG
Complementary DNA Strand: _____________________________________________________
2. Template Strand:
CCAAGCGTGGGG CTACTA
Complementary DNA Strand: _____________________________________________________
3. Template Strand:
TTG GGGTCAAGCGTGTAC
Complementary DNA Strand: ______________________________________________________
Part 2: Transcription
During transcription, RNA polymerase binds to DNA and separates the DNA strands. RNA polymerase then uses one strand of DNA
as a template from which nucleotides are assembled into a strand of RNA. How does RNA polymerase know where to start and stop
making an RNA copy of dhe? The answer to this question begins with the observation that RNA polymerase doesn’t bind to DNA just
anywhere. The enzyme will only bind to regions of the DNA known as promoters, which have specific base sequences. In effect,
promoters are signals in DNA that indicate to the enzyme where to bind to make RNA.
Write a sentence that summarizes the key points in the paragraph above:
Use the base-pairing rules to TRANSCRIBE the following DNA sequence into mRNA.
4. Template DNA Strand:
TTACGGGTCACCAAGCGTG
RNA Strand: ______________________________________________________
5. Template DNA Strand:
CCAAGCGTGGGG CTACTA
RNA Strand: _____________________________________________________
6. Template DNA Strand:
TTG GGGTCAAGCGTGTAC
RNA Strand: ______________________________________________________
Part 3: The Genetic Code
Proteins are made by joining amino acids into long chains called polypeptides. Each polypeptide contains a
combination of any or all of the 20 different amino acids. The properties of proteins are determined by the
order in which different amino acids are joined together to produce polypeptides.
Write a sentence that summarizes the key points in the paragraph above:
The “language of mRNA instructions is called the genetic code. The code has only four “letters”: A, U, C, & G.
How can a code with just four letters carry instructions for 20 different amino acids? The genetic code is read
three letters at a time, so that each “word” of the coded message is three bases long. Each three letter
”word” in mRNA is known as a codon. A codon consists of three consecutive nucleotides that specify a single
amino acid that is to be added to the polypeptide.
Write a sentence that summarizes the key points in the paragraph above:
a.
b.
There is one codon, AUG, that codes for the amino acid methionine (met). This codon is the start codon for
protein synthesis. There are three “stop” codons that do not code for an amino acid. Stop codons act like the
period at the end of the sentence; they signify the end of a polypeptide.
Write a sentence that summarizes the key points in the paragraph above:
Part 4: Translation
The decoding of an mRNA message into a polypeptide chain is known as translation. Translation takes place
on ribosomes. During translation, the cell uses information from messenger RNA to produce proteins.
Write a sentence that summarizes the key points in the paragraph above:
Use the base-pairing rules to pair the mRNA codons to the tRNA anit-codons. Draw lines after every codon to
help you read the sequence. DON’T FORGET TO LOOK FOR THE START CODON!!
7. mRNA Strand:
tRNA anti-codon:
8. mRNA Strand:
tRNA anti-codon:
9. mRNA Strand:
tRNA anti-codon:
AUG CGG GUCACCAAGCGU
_____________________________________________________________
AUGG GUCCCAACUGCGUG
_________________________________________________________________
CUAUGCCAAGCGUGAUUUCG
_________________________________________________________________
Use the GENETIC CODE to TRANSLATE the following mRNA sequence into and amino acid sequence. Draw lines
after every codon to help you read the sequence. DON’T FORGET TO LOOK FOR THE START CODON!!
10. mRNA Strand:
AUG CGG GUCACCAAGCGU
Amino Acid Sequence:
_________________________________________________________________
11. mRNA Strand:
AUGG GUCCCAACUGCGUG
Amino Acid Sequence:
__________________________________________________________________
12. mRNA Strand:
CUAUGCCAAGCGUGAUUUCG
Amino Acid Sequence:
__________________________________________________________________
Part 5: Protein Synthesis
DRAW A Graphic Organizer (FLOW MAP) TO SHOW HOW A CELL BUILDS A PROTEIN FROM THE INFO
CONTAINED IN THE DNA IN THE SPACE BELOW.
Part 6: Problem Set
1. Explain to someone who has never seen the genetic code before how to interpret the above diagram.
2. As precise as they are, every now and then cells make mistakes in copying their own DNA, inserting an
incorrect base or sometimes even skipping a base as the new strand is put together. What would happen to
the resulting amino acid chain if a mistake was made?
3. The following nucleotide sequence occurs at the beginning of a mRNA.
5' UGGGGUUAAUGUUGAUGGUAUGCAUU 3'
In the gene encoding this, a stable mutation occurs changing the C to a T. What is the consequence? (Assume
that translation of this mRNA begins at the first AUG codon.)
2. Draw a schematic of tRNA molecule and use arrows to show the following:
a) loops
b) stems
c) amino acid attachment site
d) anticodon
e) 5’ end
3. What amino acid is delivered to the ribosome by the tRNAs with anti-codon sequence 5' UUC 3'? 5’-AAA-3’?