DNA/RNA/PROTEIN SYNTHESIS NOTES
1. The Chemical makeup of DNA and RNA a. DNA – is made up of many DNA nucleotides (nucleotides are the building blocks of
nucleic acids). Each DNA nucleotide is composed of deoxyribose (a pentose, or five
carbon sugar), a phosphate molecule and one of four nitrogenous bases: Adenine,
Thymine, Cytosine and Guanine. (A, T, C, G). The picture below shows the double
stranded DNA structure and complementary bases of the DNA bases.
b. RNA – is made up of many RNA nucleotides (nucleotides are the building blocks of
Nucleic acids). Each RNA nucleotide is composed of ribose (a pentose, or five carbon
sugar), a phosphate molecule and one of four nitrogenous bases Adenine, Uracil,
Cytosine and Guanine. (A, U, C, G).
c DNA and RNA Nucleotide Diagrams
The diagrams below show different diagrams of nucleotides, both RNA and DNA. Be
able to recognize the sugar, the five sided figure in the first two diagrams and the five
sided figure labeled Y in the third diagram, the phosphate (the circle with the P or Z
inside) and the base (the six sided figure with the N in its structure, labeled W or X in the
third diagram) The last diagram shows 4 nucleotides, showing bases, sugars and
phosphates
2. DNA Replication - DNA is copied exactly to produce DNA. The diagram below
shows the process
Steps in DNA Replication
a. Unzipping - the molecule of DNA is unzipped. The hydrogen bonds between the
complementary base pairs are broken. Helicase is the enzyme which causes the DNA
molecule to unzip. The DNA bases are exposed so complementary base pairing can
occur. See the diagram of unzipping below.
b. Complementary base pairing - The nucleotide bases that make up the 2 strands of the
DNA molecule are exposed and nucleotides located in the nucleus move into place by
complementary base pairing. eg. Adenine is complementary to Thymine and vice versa,
so A only bonds with T and T only bonds with A. Cytosine is complementary to
Guanine and vice versa so C only bonds with G and G only bonds with C. The pairs of
complementary nucleotides form the cross bridges of the DNA molecule (W and X in the
diagram below). (the ladder steps)
In Transcription it is the same process only RNA is produced. (Uracil instead of
Thymine).
See the diagrams of complementary base pairing below.
c. Joining of adjacent nucleotides - Using the diagram above, the vertical part (up and
down) of the DNA molecule is formed when the sugar part (labeled Y) of one nucleotide
bonds with the phosphate part (labeled Z) of an adjacent nucleotide. These bonds produce
the sides of the ladder. The joining of the sugar/phosphate parts of adjacent nucleotide
molecules causes the length of the new DNA molecule to increase. Two complete
molecules of DNA are formed, identical to the original one. The diagram below shows
how the sugar and the phosphate join.
3. Protein Synthesis – transcription then translation
A) Transcription - is the copying of the DNA molecule by mRNA
The 3 steps in Transcription: unzipping, Complementary base pairing and Joining of
adjacent nucleotides
i. Unzipping
-A segment of DNA unzips. An enzyme (helicase) breaks the hydrogen bonds between
the nitrogenous bases.
ii. Complementary Base Pairing
-RNA nucleotides bind with DNA nucleotides by complementary base pairing on one of
the two DNA strands that are exposed after unzipping.
iii. Joining of Adjacent Nucleotides
An enzyme catalyzes the reaction that joins the sugar/phosphate molecules of adjacent
nucleotides together.
-The newly produced mRNA strand passes from the nucleus into the cytoplasm to join
with a ribosome.
B) Translation - mRNA codons are read, amino acids are brought to the mRNA strand
and polypeptides (proteins) are produced at the ribosomes. Translation ends with the
production of a protein.
The three specific parts of translation are:
i. Initiation - the ribosomal RNA (ribosome) and the mRNA strand become attached.
ii. Elongation - the polypeptide lengthens one amino acid at a time
-the tRNA anti-codons (3 letter code of the tRNA) bond to the mRNA codons (3 letter
code of the mRNA) by complementary base pairing at the ribosome. The codons
determine the type of amino acid brought to the polypeptide chain.
-The ribosome is large enough to accommodate two tRNA molecules at a time, one
incoming and one outgoing The amino acid on the incoming tRNA forms a peptide bond
with the amino acid on the outgoing tRNA.
-The ribosome then moves laterally, allowing the outgoing tRNA to leave and making
space for a new incoming tRNA.
iii. Termination - occurs at the stop codon on the mRNA. The completed polypeptide
dissociates from the ribosome
-Translation is shown in the diagram below. Be able to label the ribosomes (they look
like snowmen, the mRNA strand (labeled X) and the polypeptide strand.
4. Determine the amino acids coded for by a strand of DNA
1. Determining codons from a strand of DNA
Consider the following strand of DNA read from left to right:
TTATGCTCCTAA
When complementary base pairing occurs the following strand of mRNA is obtained.
AAUACGAGGAUU
The codons are read three letters at a time from the transcribed mRNA. The codons are:
AAU
ACG
AGG
AUU
2. Determining amino acids from mRNA codons
Find the codons in the table of mRNA codons below and the amino acids they code for.
AAU -Asparagine ACG - Threonine AGG - Arginine AUU -Isoleucine
5 steps in protein synthesis
-DNA serves as a code for proteins
-Transcription occurs. One strand of DNA serves as a template (blueprint) for the
formation of mRNA.
-after transcription, the newly formed mRNA goes into the cytoplasm and attaches to a
ribosomes.
-tRNA which carry specific amino acids, have anticodons which bind complementarily
with the mRNA codons
-The ribosome moves along the mRNA strand reading each codon. The tRNA anticodon
bonds to it complementary codon. The amino acid carried by the tRNA is bonded to the
polypeptide. The ribosome moves down the mRNA strand one codon at a time releasing
a tRNA as it does and making room for another tRNA carrying an amino acid to join the
mRNA.
a. DNA - carries the blueprint for the order of amino acids to be produced during protein
synthesis.
b. Messenger RNA (mRNA) - copies the DNA molecule in the nucleus during
transcription and goes into the cytoplasm and attaches itself to a ribosome. One 3 letter
unit in an mRNA chain is called a codon.
c. Transfer RNA (tRNA) - drops off amino acids it is coded to carry at the ribosome. The
3 letter code is complementary to mRNA and this 3 letter code is called the anti-codon
d. Ribosome (rRNA) - this is where protein synthesis occurs. (Where the protein is
assembled)
Recombinant DNA - contains DNA from 2 different sources. Organisms that have
had a foreign gene inserted into them are called transgenic organisms
Use of Recombinant DNA research
a. in Bacteria - used to produce large amounts of protein, eg insulin, human growth
hormone, and hepatitis vaccine.
b. in plants - genes transferred to cotton, corn, and potato strains have made these plants
resistant to pests, because these cells produce an insect toxin.
-Plants have also been engineered to produce, hormones, clotting factors and antibodies
c. in animals. - genepharming using transgenic organisms to produce pharmaceuticals eg
genes that code for therapeutic and diagnostic proteins are incorporated in and animal's
DNA and appear in milk. There are plans to produce drugs for the treatment of cystic
fibrosis, cancer, blood diseases, and other disorders. Antithroujmbi III is used for
preventing blood clots in surgery is being produced by a herd of goats
DNA QUIZ QUESTIONS
1. What is the general name for chemicals like DNA and RNA
2. What general shape does the DNA molecule have?
3. List 4 differences between RNA and DNA
4. Describe the function of the mRNA in Protein Synthesis
5. What is the definition of a codon
6. What is the definition of an anti-codon
7. How many amino acids will result from the following strand of DNA?
ACGCCCAAATAC
8. Name the two stages that make up protein synthesis
9. Where in the cell does replication take place?
10. Describe the function of the tRNA in Protein Synthesis?
11. Describe briefly the events that occur during transcription?
12. Name 2 common environmental mutagens
13. Describe briefly the events that occur during translation?
14. What is the definition of a) translation
b) transcription
16. Define complementary base pairing and give an example?
17. Describe the function of the ribosome during protein synthesis
18. From a given strand of DNA. Show the results of Transcription or Replication
19. Make a drawing of DNA or RNA nucleotide and label the parts
20. Give 2 examples of a) purines
b) pyrimidines
21. Name the 4 bases that make up DNA or RNA molecules
22. Describe how an environmental mutagen could cause a mutation
23. Describe briefly the events that occur during replication?
24. List 3 functions of DNA
25. Describe the function of the DNA in Protein Synthesis
26. What is the definition of a chromosomal mutation
27. What is the definition of a gene mutation
28. If the Nucleic acids are like ladders: What chemicals form the backbone of DNA or
RNA molecules?
29. If the Nucleic acids are like ladders: What chemicals form the rungs of DNA or RNA
molecule?
30. Briefly describe what occurs during Protein synthesis
31. What is recombinanant DNA. Give two uses of recombinant DNA