1. Gene Expression
aka
Protein Synthesis

2. Transcription
Transcription begins when RNA polymerase unwinds and separates the 2 strands of the double helix, exposing the DNA nucleotides on each strand.
RNA polymerase adds and then links complementary RNA nucleotides as it reads the gene.
Transcription follows the base-pairing rules for DNA replication except that in RNA, uracil, rather than thymine, pairs with adenine.
U – A
G – C

3. Transcription DNA: ATA-GGC mRNA: UAU-CCG
Enzyme unwinds & separates DNA strands.
Gene
Promoter
One strand is used as a template to make mRNA
DNA: ATA-GGC
mRNA: UAU-CCG m m

4. Transcription
Transcribe the following DNA strand into an mRNA molecule. U G C U A
DNA
RNA

5. Three-Nucleotide “Words”
mRNA – (messenger RNA) carries the instructions for making a protein from a gene and delivers it to the site of translation (ribosome); the information is translated into the amino acids that make the protein
Codon – a series of 3 nucleotide sequences on the mRNA; each codon corresponds to an amino acid or start and stop signal for translation
Genetic Code – are the amino acids or “start” and “stop” signals that are coded for by each of the possible 64 mRNA codons
(Genetic Code = Codon Chart)
Three-Nucleotide “Words”

6. Genetic Code
codon

7. Genetic Code Examples
ALL organisms use the same genetic code to translate nucleic acid sequences into proteins. This strongly suggests that all life forms have a common ancestry.

8. II. Translation
Translation takes place in the cytoplasm. During translation, the mRNA molecule binds to a ribosome, and the tRNA’s carry amino acids to the ribosome according to the codons on the mRNA. Each codon codes for a specific amino acid. The amino acids are then joined to make a protein.
tRNA – (transfer RNA) is a small strand of RNA that carries a specific amino acid on one end; each tRNA is folded into a compact shape and has an anticodon
anticodon – a 3 nucleotide sequence on a tRNA that is complementary to an mRNA codon
rRNA – (ribosomal RNA) are RNA molecules that are part of the structure of ribosomes

9. Codons & Anticodons (mRNA) (tRNA) Amino Acids Anticodons Codons tRNA

10. Transcription & Translation
Transcription occurs in the nucleus!
Translation occurs on a ribosome in the cytoplasm!

11. Transcription vs. DNA Replication
*makes copies of DNA
molecules
*both strands of DNA
are used as a template
*makes RNA
molecules
*only 1 strand is
used as template

12. 2
1. Which step below represents transcription? 2. Which step below represents translation? 3. Which step below represents DNA replication? 3 1
(Proteins)

13. Anticodons: AAU AUG GUC
5. What are the codons that correspond to the following segment of DNA? DNA: CAG TAT GAT 6. What are the anticodons that correspond to the following segment of mRNA codons? mRNA: UUA – UAC – CAG
Codons: GUC AUA CUA
Anticodons: AAU AUG GUC