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)

• 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)

Translation4. 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)