1. Molecular Biology

2. DNA Replication…review
strands are complementary; nucleotides line up on template according to base pair rules.
SEMI-CONSERVATIVE?

3. DNA Replication

4. Replication - DNA doubles, and the cell divides.
The DNA doubles during INTERPHASE
The cell divides in MITOSIS – when it goes through the phases PMAT
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5. Leave Replication behind us…

6. CENTRAL DOGMA of Molecular Biology PROTEIN SYNTHESIS

7. Protein Synthesis: overview
Transcription: synthesis of RNA under the direction of DNA
(DNA mRNA)
Translation: actual synthesis of a polypeptide under the direction of mRNA
(mRNA  Protein)
PROTEINS determine TRAITS

8. The Triplet Code
The genetic instructions for a polypeptide chain are ‘written’ in the DNA as a series of nucleotide ‘words’
Codons (3 mRNA bases)
Remember : ‘U’ (uracil) replaces ‘T’ in RNA

9. Transcription: overview

10. Translation vocabulary
mRNA from nucleus is ‘read’ along its codons by tRNA’s anticodons at the ribosome
tRNA has an amino acid attached to one side, an anticodon on the other

11. Translation

13. Why Do We Need Proteins? Cell Structure Cell = 80% protein
Cell membrane

14. Why Do We Need Proteins? Cell Processes Hormones (signals)
Enzymes (speed up reactions)

15. Why Do We Need Proteins? Membrane Channels (remember transport?)
Neurotransmitters (carry nerve/brain messages)

16. What Do We Need For Protein Synthesis?
2. RNA
mRNA = (messenger RNA) makes and takes copy of DNA to cytoplasm
tRNA = (transfer RNA) Matches w/ mRNA on ribosome and carries AA to add to protein chain

17. What Do We Need For Protein Synthesis?
3. Ribosome
Reads mRNA
Directs tRNA
Creates peptide bonds between AAs
(makes polypeptide chain)

18. What Do We Need For Protein Synthesis?
4. Amino Acids (AAs)
Building blocks of proteins
(20 AAs exist)
Protein = AA chain
= polypeptide chain
ORDER MATTERS!
AA order determines function of protein

19. Steps of Protein Synthesis
Transcription (writing the “message”)
DNAmRNA
messenger carries code to cytoplasm
Translation (reading the “message”)
mRNA tRNA protein (AA chain)
message translated into a protein

20. Steps of Protein Synthesis
(Nucleus)
(Cytoplasm)

21. Transcription DNA to mRNA Location = nucleus Steps
a. Enzyme binds to DNA, unzips it
b. mRNA copy of gene made from DNA template
*U replaces T in RNA

22. 3 DNA nucleotides (triplet) to mRNA codon
Transcription
3 DNA nucleotides (triplet) to mRNA codon
Codons

23. Translation mRNA to tRNA to protein (AA chain) Location = cytoplasm
(first codon in mRNA is the start codon)

24. Translation Steps of Translation
1. mRNA moves to cytoplasm, binds to ribosome
2. tRNA anticodon UAC brings AA (methionine) to mRNA codon on ribosome

25. Translation 3. Ribosome moves down mRNA to next codon
4. tRNA anticodon brings & attaches next AA with peptide bond

26. Translation 5. tRNA leaves ribosome once AA attached Protein chain AA
mRNA

27. Translation 6. Steps 1-5 repeated, adding AAs
until STOP CODON signals end of protein
7. Polypeptide chain released from ribosome

28. Synthesis Practice TAC AUG UAC GGA CCU GGA CCT GGA CCU TAT AUA UAU AGA
DNA
(triplet)
mRNA
(codon)
tRNA
(anti-codon)
TAC
AUG
UAC
GGA
CCU
GGA
CCT
GGA
CCU
TAT
AUA
UAU
AGA
UCU
AGA
ACT
UGA
ACU

29. Synthesis Practice ACT AGA TAT CCT GGA TAC ACU UGA UCU UAU AUA CCU UAC
DNA
(triplet)
ACU
UGA
UCU
UAU
AUA
CCU
UAC
AUG
tRNA
(anti-codon)
mRNA
(codon)
Amino
Acid
Met (Start)
Methionine
Pro
Proline
Gly
Glycine
Ile
Isoleucine
Ser
Serine
Stop