Making Proteins
 Cell Structure
 (80% of cell membrane is proteins)
 Transport Channels
 Cell Processing
 Hormones (signals)
 Enzymes
 What else?
DNA
1.
•
Is the template for making mRNA during
transcription
RNA
2.
mRNA =messenger RNA


Makes and takes copy DNA to cytoplasm
tRNA = transfer RNA



Matches with mRNA on ribosomes
Carries Amino Acids
rRNA = ribosomal RNA




Part of ribosome
Reads mRNA
Directs tRNA
 3. Ribosome
 Reads mRNA
 Directs tRNA
 Creates peptide bonds between AA’s
4. Amino Acids (AA’s)
 Building blocks of proteins
 (20 AAs essential)
 Protein = AA chain = polypeptide chain
 ORDER MATTERS!
 AA order determines f(x) of protein
http://www.columbia.edu/
cu/biology/courses/c2005/i
mages/animtransln.gif
TRANSCRIPTION: writing the message
 DNAmRNA
STEPS:
1. unwind DNA in nucleus with help of
enzyme
2. DNA polymerase pairs RNA nucleotides
with DNA nucleotides =mRNA
 * U replaces T in RNA *
 3 DNA nucleotides (triplet)
 m RNA CODON
Start
Codon
Codons
TRANSLATION:
 mRNA tRNA Protein (AA chain)
Steps:
1. mRNA leaves nucleus and binds to
ribosome
2. tRNA (anticodon) brings the amino acid
to the mRNA (codon) on ribosomes
3. Ribosomes move down mRNA to next
codon
4. tRNA anticodon brings and attaches
next AA with peptide bond
5. tRNA leaves ribosome once AA
attached
6. Repeat above steps to add AA until
STOP CODON to signal end of
protein

UAG, UAA, or UGA
7. Polypeptide chain releases from
ribosomes
This is a molecule of messenger RNA.
It was made in the nucleus by
transcription from a DNA molecule.
codon
AUGGGCUUAAAG CAGUGCACGUU
mRNA molecule
A ribosome on the rough
endoplasmic reticulum attaches to
the mRNA molecule.
ribosome
AUGGGCUUAAAG CAGUGCACGUU
Amino acid
tRNA molecule
A transfer RNA molecule arrives.
It brings an amino acid to the first three bases
(codon) on the mRNA.
anticodon
The three unpaired bases (anticodon) on the
tRNA link up with the codon.
UAC
AUGGGCUUAAAG CAGUGCACGUU
Another tRNA molecule comes into place,
bringing a second amino acid.
Its anticodon links up with the second codon on
the mRNA.
UAC
AUGGGCUUAAAG CAGUGCACGUU
Peptide bond
A peptide bond forms between the two amino
acids.
AUGGGCUUAAAG CAGUGCACGUU
The first tRNA molecule releases its amino acid and
moves off into the cytoplasm.
AUGGGCUUAAAG CAGUGCACGUU
The ribosome moves along the mRNA to the next
codon.
AUGGGCUUAAAG CAGUGCACGUU
Another tRNA molecule brings the
next amino acid into place.
AUGGGCUUAAAG CAGUGCACGUU
A peptide bond joins the second and third
amino acids to form a polypeptide chain.
AUGGGCUUAAAG CAGUGCACGUU
The process continues.
The polypeptide chain gets longer.
This continues until a termination (stop)
codon is reached.
The polypeptide is then complete.
AUGGGCUUAAAG CAGUGCACGUU
 DNA : A=T and C=G
 RNA: A=U and C=G *So, when transcribing DNA into RNA “T” is
replaced with “U”
 Example:
 Original DNA:
 Complementary DNA:
ATCG
TACG
 Transcription example:
 Original DNA:
 Messenger RNA:
 (CODON)
ATCG
UACG
 Translation Example:
 Messenger RNA:
 (CODON)
UACG
 Transfer RNA:
 (ANTICODON)
AUGC
 tRNA brings the AA so they can bond to make protein
DNA
(triplet)
TAC
GGA
CCT
TAT
ACT
mRNA
(codon)
tRNA
(anti-codon)
AUG (start)
UAC
CCU
GGA
GGA
CCU
AUA
UAU
UGA (stop)
ACU
 Use mRNA codon and use the Universal Genetic Code
Chart.
 AUG (codon)
 A = 1st base
 U = 2nd base
 G = 3rd base