Chapter 12: DNA, RNA,
AND PROTEIN
SYNTHESIS
Proteins Are Made by Decoding
Information in DNA
• Proteins have many different functions in
the body
– Hemoglobin (transports oxygen)
– Keratin (part of hair)
– Enzymes
• Proteins are not made directly from DNA
because it can not leave the nucleus
• Another molecule is involved…
Ribonucleic Acid (RNA)
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•
•
•
RNA is a nucleic acid like DNA, BUT…
It’s a single strand of nucleotides
It contains ribose instead of deoxyribose
It contains the base Uracil (U) instead of
Thymine (T)
Read page 336 in your book and
create a Venn Diagram comparing
and contrasting DNA and RNA…
Protein Synthesis Steps:
1. Transcription
2. Translation
Transcription
• DNA can not leave the nucleus so a
messenger is needed to get the
information to the rest of the cell
• Transcription is the process of making
a molecule of RNA (messenger) from
a molecule of DNA
• Like writing notes on another piece of
paper from information on this
powerpoint
Transcription
1. The enzyme RNA polymerase binds
to a segment of DNA and “unzips”
DNA similar to replication
2. RNA nucleotides assemble
themselves to match up with the
bases on DNA
3. This continues until a “stop” signal
is reached
Transcription
4. When transcription is complete, the
DNA “zips” back up and the new
mRNA (m = messenger) is
released.
5. The new mRNA travels out of the
nucleus to the cytoplasm and
attaches to a ribosome
Practice
Write the complementary base
sequence of the RNA molecule using
DNA as a template.
DNA =TAC ACC TTG AAG GGA
CCC AGC CGC TTC ACT
Answer:
AUG UGG AAC UUC CCU
GGG UCG GCG AAG UGA
* Note Uracil (U) replaces Thymine
(T) in RNA
Translation
• Translation is the process of making a
protein from the information on the
mRNA strand
• Translation switches from the RNA
“language” to the protein “language”
• DNA base sequence is thereby
“decoded”
Translation
1. A ribosome attaches to the mRNA
made during transcription.
2. The ribosome will read a 3-letter
base sequence called a codon on
the mRNA molecule.
3. Each codon on the mRNA codes for
a specific amino acid (monomer of
proteins)
Translation
4. As the ribosome translates each
codon, a molecule of tRNA (t =
transfer) brings the complimentary
anti-codon to the ribosome.
5. Each molecule of tRNA has the
correct amino acid that is needed to
complete the protein.
6. The codon on the mRNA and the
anti-codon on the tRNA bond
putting the amino acid into place.
Translation
7. As the ribosome continues to
translate the mRNA, a protein is
simultaneously made.
8. Each amino acid is bonded to the
next by a peptide bond forming the
finished protein.
9. The finished protein is released
when a stop codon is reached
Practice
Using the molecule of mRNA in your
notes, write the corresponding tRNA
Answers
tRNA: UAC ACC UUG
AAG GGA CCC AGC
CGC UUC ACU
Find the corresponding amino acids for
each codon.
*Use the codon chart in your notes…
Answers
Amino Acids: (start)
tryptophan – asparagine –
phenylalanine – proline –
glycine – serine – alanine –
lysine (stop)