Protein Synthesis
Essential Question
How does DNA code for making proteins (protein synthesis) and
how is this process essential to life?
Protein synthesis is important because your cells need to rely on
RNA to transfer the information. DNA codes for making proteins
by providing instructions to make each protein.
Activating
Strategy
DNA complementary base pairs: ATGC
RNA complementary base pairs: AUGC
Transcribe the following DNA strand to RNA: ATGGCTATCTAA
UACCGAUAGAUU
Transcription- the process of making mRNA from DNA’s
instructions
1. Enzymes unzip the molecule of DNA by breaking a specific
bond. Hydrogen
2. Free RNA nucleotides attach to one exposed strand of DNA
3. The sugar-phosphate backbone bonds. This time is uses U
instead of deoxy-ribose.
4. The mRNA breaks away as the DNA strands rejoin. The
DNA returns to its original state
5. mRNA leaves the nucleus and enters the cytoplasm. It is
headed to ribosomes.
- mRNA carries a genetic message (a sequence of nucleotides
that instruct how to build proteins)
- amino acids make up proteins
- there are only 20 common amino acids in the world
Codon = a sequence of 3 nitrogenous bases that match with a
specific amino acid
Example: The RNA strand AUGUAAAUU is actually the
following three codons: AUG UAA AUU
The order of the nitrogenous bases in the mRNA determines the
type and order of the amino acids in a protein.
There are 64 possible codons but only 20 Possible Amino Acids
Stop codons = UAA UAG UGA
Start codon = AUG (Methionine or Met)
More than one codon can code for the same amino acid BUT for
any one codon, there can only by one amino acid!!!
The genetic code is Universal. (i.e. all organisms use this code and
follow it to make proteins)
Translation = The process of making proteins from amino acids
using the instructions written on mRNA
Translation happens in the cytoplasm at the ribosome.
1. The strand of mRNA attaches to the ribosome.
2. A tRNA molecule brings the first amino acid to the mRNA
strand that is attached to the ribosome.
3. A tRNA anticodon pairs with the first mRNA codon
temporarily. What is the first mRNA codon? AUG
Anticodon = Region of tRNA that is complimentary (or
reverse) to the codon of the mRNA. This is where it attaches
4. AUG signals the start of protein production.
5. The ribosome slides along the mRNA to the next codon.
6. A new tRNA carrying an amino acid pairs with the second
mRNA codon.
7. The first and second amino acids bond together in a peptide
bond.
8. This process continues joining amino acids until the
ribosome reaches a stop codon on the mRNA strand.
9. The amino acid strand (now an amino acid chain) is released
from the ribosome.
10. Once released the Amino Acid Chain folds into a protein
(tertiary structure!)
Comparison of Replication and Transcription
DNA Replication
DNA Transcription
1. DNA to DNA
2. DNA is permanently split and now has a
parent and daughter strand
3. Final product prepares for cell division
but remains in the nucleus (because DNA
never leaves)
1. DNA to RNA
2. DNA returns to original state
3. Final product shoots out of the nucleus
into the cytoplasm to make proteins at the
ribosome
Assessment Prompt:
Using the Codon Chart determine the amino acid that matches the given codons below.
ACU- Thr
AUG- Met
CCC- Pro
TAT- lle
GCA- Ala
UGA- Stop
GGU- Gly
CAT- Val