Worksheet: DNA, RNA, and Protein Synthesis | Exercises Genetics ... - Free Printable

Let’s go step by step to solve each question on the worksheet.

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1. Define the following terms:

a. Replication – This is when DNA makes a copy of itself before a cell divides. It happens in the nucleus and results in two identical DNA molecules.

b. Transcription – This is when a section of DNA is copied into mRNA (messenger RNA). The mRNA carries the code from the DNA out of the nucleus to make proteins.

c. Translation – This is when the mRNA is read by ribosomes to build a protein. tRNA brings amino acids to match the mRNA codons, and they link together to form a protein chain.

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2. Break the following DNA sequence into triplets.

Original sequence:
CCGATACGCGGTATCCCAGGGCTAATTUAA

Wait — there’s a problem here. DNA uses bases A, T, C, G — but this sequence has a “U” at the end. U (uracil) is found in RNA, not DNA. So likely, this is a typo or mistake in the worksheet. But since the question says “DNA sequence,” we’ll assume it should be all DNA bases — so maybe that last “U” was meant to be “T”. Let’s fix that for accuracy:

Assume correct DNA sequence:
CCGATACGCGGTATCCCAGGGCTAATTAAA

Now break into groups of 3 letters (triplets):

CCG | ATA | CGC | GGT | ATC | CCA | GGG | CTA | ATT | AAA

✔ That’s 10 triplets.

*(Note: If you must use the original with “U”, then it would be: ...ATT|UAA — but U doesn’t belong in DNA. We’ll proceed assuming it’s a typo and use T instead.)*

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3. Complementary strand of DNA

Remember base pairing rules for DNA:
- A pairs with T
- T pairs with A
- C pairs with G
- G pairs with C

Original strand (corrected):
CCG ATA CGC GGT ATC CCA GGG CTA ATT AAA

Complementary strand (write opposite bases):

GGC | TAT | GCG | CCA | TAG | GGT | CCC | GAT | TAA | TTT

So full complementary strand:
GGCTATGCGCCATAGGGTCCCGATTAATTT

*(Again, if you used the original with “U”, you’d have to treat it as RNA — but question says “complementary strand of DNA”, so we stick with DNA rules.)*

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4. What would the code in problem #2 be transcribed into? (mRNA sequence)

Transcription means making mRNA from DNA template strand.

But note: In transcription, the mRNA is made complementary to the *template* DNA strand — and it uses U instead of T.

However, often in worksheets like this, they give you the “coding strand” (which looks like the mRNA except T→U), and ask you to transcribe it — meaning just replace T with U.

Looking back at problem #2: They gave us a DNA sequence and asked to break into triplets — probably treating it as the coding strand.

So to get mRNA: take the DNA sequence and swap T → U.

Original DNA (from #2, corrected):
CCGATACGCGGTATCCCAGGGCTAATTAAA

Replace T with U:
CCGAUACGCGGUAUCCCAGGGCUAAUUAAA

Break into codons (same grouping as before):
CCG | AUA | CGC | GGU | AUC | CCA | GGG | CUA | AUU | AAA

✔ So mRNA sequence: CCGAUACGCGGUAUCCCAGGGCUAAUUAAA

*(If you kept the original “U” in DNA, it wouldn’t make sense — because DNA doesn’t have U. So again, we assume typo and fixed it.)*

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5. How many codons are there in the above problem?

We broke the mRNA into 10 groups of 3 bases → that’s 10 codons.

✔ Answer: 10

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6. What is the three letter sequence on a tRNA molecule called?

It’s called an anticodon. It matches up with the codon on mRNA during translation.

✔ Answer: Anticodon

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7. How many different amino acids are there that make up all of the proteins in our body?

There are 20 standard amino acids that build all human proteins.

✔ Answer: 20

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8. How many different codons are there?

Each codon is 3 bases long. There are 4 bases (A, U, C, G in mRNA).

Total possible combinations: 4 × 4 × 4 = 64

Some code for same amino acid, some are stop signals — but total different codons = 64.

✔ Answer: 64

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Final Answer:

1.
a. Replication – DNA copying itself before cell division.
b. Transcription – Making mRNA from DNA.
c. Translation – Using mRNA to build a protein.

2. Triplets: CCG | ATA | CGC | GGT | ATC | CCA | GGG | CTA | ATT | AAA
*(Assuming "U" was typo and should be "T")*

3. Complementary DNA strand: GGCTATGCGCCATAGGGTCCCGATTAATTT

4. mRNA sequence: CCGAUACGCGGUAUCCCAGGGCUAAUUAAA

5. Number of codons: 10

6. Three-letter sequence on tRNA: Anticodon

7. Different amino acids: 20

8. Different codons: 64