1. Protein Synthesis: Transcription
How is mRNA created from DNA?

2. Chromosome
DNA
Prentice Hall Biology textbook
Gene

3. IMPORTANT VOCABULARY:
Protein Synthesis is when DNA’s code is used by the cell to make proteins. This is also known as gene expression.
The genes “express themselves” when the proteins they code for are made.
IMPORTANT VOCABULARY:
GENE
BASE TRIPLET
CODON
ANTICODON
AMINO ACID
PROTEIN

4. Gene Expression
GENE: sequence of DNA that codes for a protein and thus determines a trait
BASE TRIPLET: nucleotide triplet on DNA
CODON: nucleotide triplet on mRNA that codes for a specific amino acid
ANTICODON: nucleotide triplet on tRNA that pairs with a codon
AMINO ACIDS: amino acids make up proteins
PROTEIN: biomolecule made up of a chain of amino acids

5. Sections within a gene Stop Triplet Start Triplet Codes for protein
TAC
ATT, ATC, or ACT
Base Triplets
Prentice Hall Biology textbook
Examples ATC CCG

6. Overall Process of Protein Synthesis (Gene Expression)
DNA
Transcription
Translation
mRNA
Protein
DNA contains the code for all traits/ proteins
Translation
Protein is made by mRNA and tRNA
Information is “deciphered” to build a protein.
Transcription
mRNA is made by copying DNA’s code for a protein
Information in DNA is “rewritten” as a molecule of mRNA

7. TRANSCRIPTION TRANSCRIPTION: mRNA is made copying DNA’s code
Occurs in the nucleus
Makes mRNA from DNA template
click to play animation

8. TRANSCRIPTION A G C A T C G
1. The enzyme helicase break the hydrogen bonds between the nitrogen bases, unzipping a gene portion of the DNA.

9. TRANSCRIPTION A T
1. (continued) a gene portion of the DNA strand separates A T G C G C A T G C

10. A T G C A T C G

11. TRANSCRIPTION 2. mRNA is made from the DNA templateG T
2. mRNA is made from the DNA template
The enzyme RNA polymerase brings in mRNA nucleotides and matches them with their DNA complement A G C A G

12. Base Pairing Rule mRNA nucleotides match by the base pairing rule.
A - T (RNA has U)
C - G A T C G U T G C A

13. U T A A A T G G C C A A T G G C

14. A T C G U T A G
mRNA
DNA C A G

15. 3. mRNA separates from DNA and (after editing) leaves the nucleus

16. G A C U T A T C G A G C A G

17. 4. The two DNA strands move back together and…..

18. 4. …an enzyme helps the DNA strands rezip.G C A T C G
4. …an enzyme helps the DNA strands rezip.

19. REVIEWING TRANSCRIPTION
TRANSCRIPTION: mRNA is made copying DNA’s code
1. DNA unzips
2. mRNA is made from the DNA template
3. mRNA separates from DNA and (after editing) leaves the nucleus
4. The DNA molecule rezips (closes back up.)
click to play animation

20. mRNA Editing Pre-mRNA is processed to remove non- coding segments
exons = coding segments
introns = non-coding segments
inbetween sequence (junk)
introns come out!
intron = noncoding (inbetween) sequence
eukaryotic DNA
exon = coding (expressed) sequence 22

21. RNA splicing enzymes Spliceosome
snRNPs
exon
intron
snRNA 5' 3'
Spliceosome
Enzyme that recognizes introns and removes them
cut & paste enzyme
spliceosome
exon
excised
intron 5' 3'
lariat
mature mRNA 23

22. More mRNA editing
Need to protect mRNA on its trip from nucleus to cytoplasm
enzymes in cytoplasm attack mRNA so we need to protect the ends of the molecule
add 5 GTP cap
add poly-A tail
longer tail, mRNA lasts longer A
3' poly-A tail
mRNA 5'
5' cap 3' G P
A’s
eukaryotic RNA is about 10% of eukaryotic gene. 24

23. Now mRNA is ready to leave the nucleus!
3' poly-A tail
mRNA 5'
5' cap 3' G P
A’s

24. TRY THIS! TACAACCGATGA Transcribe this segment of DNA:
You can have them do this on white boards or in their notes. If you are using the interactive notebook this will go on the left page.

25. Predict the corresponding amino acids for each codon. AUG UUG GCU ACU