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The Central Dogma of DNA
DNA codes for RNA, which codes for protein synthesis
1. Why are proteins important?
Part one – Structure of DNA and Replication
Choose six cut out nucleotides at random, making sure you have at least one A (adenine), T (thymine),
G (guanine) and C (cytosine). Place the nucleotides face down on your desk and mix them up. Randomly turn over each
nucleotide one by one, and link each one together by taping them along the sugar-phosphate “backbone”. You have just
made one strand of DNA.
The letter code of your six nucleotides is written in order of their placement on the chain, in groups of three.
2. Write the 6 letter code of your DNA strand here:
3. Explain why each written chain is probably unique.
Complementary base pair six free nucleotides to your strand of DNA and tape the new sugar-phosphate backbone
together. Leave the bases untapped.
4. What purine-pyrimidine pairs can be formed?
5. What type of bond holds the nitrogen base pairs together?
6. Describe what your DNA molecule looks like.
7. Why are paired bases said to be complimentary?
DNA replication
DNA copies itself during replication. The parental strands of DNA separate, serve as templates, and make two new
molecules of DNA. Because each new DNA molecules has one strand of parental DNA and one strand of new DNA is
described as being semiconservative replication.
“Unzip” your DNA molecule by breaking apart the hydrogen bonds holding the base pairs together (The ladder comes
apart at the middle of each rung). The sugar-phosphate backbones remain taped together but you now have exposed
nitrogen bases.
8. What type of protein “unzips” or breaks the hydrogen bonds of your DNA molecule (hint: they help speed up chemical reactions)?
Use the base-pairing rule to match unused nucleotides to each side of your DNA ladder. Continue adding nucleotides
until all the bases are connected. Tape together the sugar-phosphate backbones of the nucleotides you added but do not
tape the bases. You should now have two copies of your original molecule of DNA.
9. How does each new nucleotide chain compare to the one on which it was formed?
10. Why is DNA replication described as being semiconservative?
11. Why is it important that DNA is semiconservative?
12. Write in your own words the end result of DNA replication.
Part 2 – DNA transcription
In order for a cell to make proteins, the code that DNA contains must leave the nucleus and travel into the cytoplasm for
protein synthesis.
The DNA code for making proteins is re-written into a different form called mRNA. This process is called transcription.
RNA differs from DNA in three ways. RNA has a different sugar, a different nitrogen base and is made up of a different
number of strands.
13. What is the name of the sugar found in RNA?
14. The nitrogen base ____________________________________ found in RNA replaces thymine in DNA.
15. RNA is _____________________________ stranded, while DNA is double stranded.
The process of transcribing DNA into mRNA is very similar to replication. “Unzip” your DNA molecule by breaking
apart the hydrogen bonds holding the base pairs together. The sugar-phosphate backbones remain taped together but
you now have exposed nitrogen bases. Attach six mRNA nucleotides to your original DNA strand. Remember T (thymine)
is replaced by U (uracil) when making RNA. Because mRNA is single stranded, it is only formed on one half of your
DNA.
Remove your mRNA strand from the DNA strand and put your DNA strands back together. You have now transcribed the
DNA code into an mRNA code that can travel outside the nucleus to make proteins.
16. Which mRNA bases attach to which DNA bases?
17. Write the 6 letter code for your newly created mRNA strand here:
18. What is the purpose of mRNA?
19. Write in your own words what it means to transcribe DNA
There are two other types of RNA, besides mRNA.
20. Give the name and explain the purpose of each of the two other types of RNA
Name of rRNA:
Purpose of rRNA:
Name of tRNA:
Purpose of tRNA:
Part 3 - mRNA Translation
The code carried by the mRNA contains the information to make proteins in the process of translation.
21. What are the subunits that make up proteins called?
Therefore, the code carried by the mRNA contains the order of amino acids to make specific proteins. These amino acid
subunits are determined by a three-base code sequence called a codon.
22. What is the name of each three-nucleotide sequence?
23. How many mRNA codons have you formed?
24. List your mRNA codons here:
There is a universal chart or “dictionary” of the mRNA genetic code which tells us the order of amino acids the DNA
code contains.
25. What organelle is in charge of making proteins?
26. Look at an mRNA chart and write down the name of the two amino acids your mRNA codons code for.
27. Write in your own words what is means to translate mRNA
Summarize in your own words what the Central Dogma of DNA means.