1. DNA can’t do it alone so it
Bio NOTES: Protein Synthesis
Remember…
DNA contains the instructions for making proteins
the sequence of nucleotides in DNA codes for proteins
proteins are very important for all life’s functions
DNA makes proteins through a process called
protein synthesis, which occurs in the ribosome.
Protein Synthesis occurs in 2 parts:
part I - transcription
part II - translation
DNA can’t do it alone so it
gets help from another
nucleic acid - RNA.

2. What is RNA? Types of RNA mRNA – messenger RNA tRNA – transfer RNA
RNA stands for ribonucleic acid
It is made of ribose sugars, phosphates,
and nitrogen bases
RNA is single-stranded
There is NO thymine in RNA –
only adenine, cytosine, guanine and uracil
- uracil takes the place of thymine
A pairs with U
C pairs with G
Types of RNA
mRNA – messenger RNA
takes DNA information from nucleus to the ribosome
tRNA – transfer RNA
transfers or transports amino acids to the ribosome
rRNA – ribosomal RNA
used in making ribosomes

3. Part I: Transcription
transcription = process where DNA is copied into mRNA
occurs in the nucleus
DNA cannot leave the nucleus but the message of DNA needs
to get out of the nucleus
What is the message of DNA?? the order of nucleotides that
determine a specific protein
mRNA can take message of DNA out of the nucleus
Steps of Transcription:
DNA unzips
mRNA bases pair with
one of the DNA strands
3. a single-stranded mRNA
is made
4. mRNA leaves the nucleus
5. DNA zips back up

4. Part I: Transcription DNA mRNA A U triplet = 3 nucleotides
on a DNA molecule
triplet
codon T A G C
codon = 3 nucleotides
on an mRNA molecule G C C G
DNA (triplets)
ATT
CCT
GAG
TTC A U
mRNA (codons)
UAA
GGA
CUC
AAG
Each codon codes for a specific amino acid. The sequence of
amino acids determines the type of protein to be made.
Remember that amino acids are the monomers of proteins.
All organisms use the same genetic code for amino acids and
assembling proteins. That is why the genetic code is said to
be universal.
mRNA codon: UUG
*See Genetic Code*
amino acid: leucine

5. The Genetic Code 1. UUC Phenylalanine 2. CCC Proline 3. AGC Serine
4. UGA
Stop

6. Part II: Translation
translation = process where the cell uses information
from mRNA to produce proteins
occurs in the ribosomes of the cytoplasm
Steps of Translation:
1. The mRNA strand attaches
to a ribosome in the cytoplasm
2. tRNAs carry specific amino acids
to the ribosome
3. The tRNA anticodon pairs with the
correct mRNA codon
4. The ribosome slides along the
mRNA to the next codon while the
tRNAs bring more amino acids
5. The amino acids are joined together
by peptide bonds
6. Continues until a STOP codon is reached

7. Part II: Translation mRNA tRNA A U codon U A codon = 3 nucleotides
Start U A
codon = 3 nucleotides
on an mRNA molecule G C
anticodon = 3 nucleotides
on a tRNA molecule C
anticodon G U
tRNA is responsible for bringing amino acids to the
ribosome. tRNA has an anticodon, which is the opposite of
the mRNA codon.
It is important to remember that the mRNA codon determines
the amino acid, NOT the tRNA anticodon.
mRNA:
U U A C G A A G C U C G
tRNA:
A A U
G C U U C G A G C
amino
acid:
Leucine
- Arginine - Serine - Serine

8. Complete the Following Chart:
DNA:
TAC AAG CTT GGG ATA CGC TAA ATT
mRNA:
AUG
UUC GAA CCC UAU GCG AUU UAA
tRNA:
UAC
AAG CUU GGG AUA CGC UAA AUU
amino
acids:
Phenylalanine - Glutamic Acid - Proline -
Tyrosine - Alanine - Isoleucine - Stop
Start -
**Remember – use the mRNA codons to determine the
amino acids!!