1. Protein Synthesis
Section 12.3

2. DNA’s Purpose
DNA has genes that code for the synthesis (creation) of specific PROTEINS
Here’s the problem…
Where is DNA located?
Nucleus

3. DNA’s Purpose Where does Protein synthesis occur?
At ribosomes in the cytoplasm
Can DNA ever leave the nucleus?
NO!

4. RNA –Ribonucleic Acid 3 major types of RNA: Messenger RNA (mRNA)
carries information from DNA to ribosome
Transfer RNA (tRNA)
Carries amino acids to ribosome to make protein
Ribosomal RNA (rRNA)
Makes up ribosomes; site of protein synthesis.
located on Rough ER and in cytoplasm

5. 3 Differences between DNA and RNA
Structure: Double stranded
Sugar: Deoxyribose
Bases: Adenine
Guanine
Cytosine
Thymine
RNA
Structure: Single-stranded
Sugar: Ribose
Bases: Adenine
Guanine
Cytosine
Uracil

6. Copy the question to your notes!
What are the three main types of RNA?
What are three differences between RNA and DNA?
messenger RNA, transfer RNA, ribosomal RNA
Single stranded
Ribose sugar
Uracil replaces Thymine

7. How do you get from DNA to Proteins?
TRANSCRIPTION – the synthesis of RNA under the direction of DNA
TRANSLATION – the synthesis of a protein, under the direction of mRNA

8. Transcription
From DNA to RNA

9. Transcription - Where does this happen?
Where is the DNA?
In the nucleus

10. Transcription - how RNA is made
Location = nucleus
RNA polymerase runs along DNA strand and makes messenger RNA (mRNA).
Adds nucleotides in 5’ to 3’ direction.

11. Transcription – how RNA is made
Adenine on DNA pairs with Uracil on RNA
mRNA leaves nucleus through a nuclear pore and meets up with a ribosome (rRNA) in the cytoplasm

12. Practice making mRNA Transcript
DNA code: TAC GTA AAC TTC ATT mRNA strand : AUG CAU UUG AAG UAA

13. RNA Processing
Messenger RNA

14. RNA processing
mRNA must be altered before it can be used to make a protein.
3 steps :
Remove introns
Add 5’ cap
Add 3’ Poly A tail

15. Introns and Exons Exons – code for proteins
Introns – intervening sequences that must be removed.

16. Translation
From mRNA to Protein

17. Translation- Where does this happen?
Protein synthesis – the manufacture of proteins
Where are proteins made in the cell?

18. Translation - how proteins are made
location= ribosome in cytoplasm
Once mRNA is at a ribosome, amino acids are assembled to make proteins

19. Translation - how proteins are made
Transfer RNA (tRNA) brings the correct amino acid to the growing protein chain

20. tRNA reads codons tRNA reads codons to assign the correct amino acid.
Codon - found on mRNA; consists of three bases (triplet codon)
64 codons for
20 amino acids

21. Codons AUG – start codon or Methionine
UAA, UAG, UGA – stop codons; code for nothing. Like the period on the end of a sentence.

22. Practice using codons mRNA: AUGCAUUUGAAGUAA Separate the codons
Copy the codons to your notes then use Codon table to find amino acids!

24. Practice using codons Met (start) - His - Leu - Lys - STOP
AUG – CAU – UUG – AAG – UAA Resulting amino acids:
Met (start)
- His
- Leu
- Lys
- STOP

25. Protein formation
Amino acids link together to form a protein

26. SUMMARY
1) mRNA is transcribed in the nucleus by RNA polymerase 2) mRNA is processed 3) mRNA attaches to the ribosome 4) tRNA brings the amino acid as it reads mRNA codons 5) The amino acids are joined together 6) When a stop codon is reached the protein synthesis ends.