1. From Gene to Protein
Chapter 2 and 7 of IB Bio book

2. Protein Synthesis: overview
DNA has instructions for building proteins
Transcription: the synthesis of RNA (especially mRNA) using the code of DNA as a template (pattern)
Translation: actual synthesis of a polypeptide under the direction of mRNA
From “language” of nucleic acids to “language” of proteins

3. The Triplet Code DNA has 2 strands: Codons mRNA base triplets
antisense strand (template strand) gets transcribed to make mRNA (complementary to mRNA)
sense strand (coding strand) has the same base sequence as the mRNA that is transcribed (with thymine instead of uracil).
Codons
mRNA base triplets
Each codon codes for one amino acid.

4. Transcription: overview
F:\Desktop\animations from bio powerpoints\Chapter 11 BDOL IC

5. Transcription, Details
Gene: stretch of DNA transcribed into an mRNA molecule
Promoter : region on DNA where RNA polymerase attaches and where initiation of transcription begins
RNA polymerase:
pries DNA apart
hooks RNA nucleotides together (in 5’3’ direction) as specified in the DNA code
Terminator region: sequence that signals the end of transcription

6. Transcription animation with more detail

7. Eukaryotic cells modify mRNA after transcription
RNA splicing (note: ONLY occurs in EUKARYOTES):
exons (expressed sequences) kept,
introns (intervening sequences) cut out;
exons joined to form mature mRNA.
Increases the number of different proteins that can be produced
The human genome contains about 21,000 protein-encoding genes, but the total number of proteins in human cells is estimated to be between 250,000 to one million. (source: National Cancer Institute
Other stuff (interesting but not important to IB):
5’ cap: modified guanine; protection from degradation by enzymes; recognition site for ribosomes
3’ tail: poly(A) tail (adenine); protection; recognition; transport

8. Translation
Production of a polypeptide (protein).

9. Translation: Important components
mRNA is the instructions for how to build the protein.
Each codon codes for 1 amino acid.

10. Translation: Important components
tRNA
Each tRNA can only bind one amino acid
tRNA activating enzyme binds a specific amino acid to the tRNA, using ATP for energy.
note: illustrates enzyme -substrate specificity and role of phosphorylation (new syllabus)
The amino acid attaches to the side of tRNA opposite the anticodon.
Anticodon = nucleotide triplet on tRNA
note: CCA at 3’ end

11. Translation: Important components
The Ribosome (made of proteins and rRNA)– consists of two subunits, small and large
rRNA – a component of the ribosome that helps with making proteins.
A site-- holds the tRNA carrying the next amino acid to be added to the chain
P site -- holds the tRNA carrying the growing polypeptide chain
E site- exit site where tRNA’s are released

12. Translation (animations)
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13. Translation (the process)
Initiation~ involves assembly of components
Start codon
mRNA binding site-mRNA attaches to small ribosomal subunit
tRNA also attaches small
followed by large ribosomal subunit
Elongation ~
codon recognition by anticodons
peptide bond formation (catalyzed by rRNA)
5’ 3’ (ribosome moves along mRNA toward the 3’ end)

14. Translation (the process)
Translocation– tRNAs move from A site to P site to E site
Termination~ ‘stop’ codon reaches ‘A’ site
After termination, disassembly of components occurs.

15. Translation in Prokaryotes Note…
Translation can occur immediately after transcription in prokaryotes due to the absence of a nuclear membrane.

16. Skill: ID Polysomes on micrographs
Polysome: a complex of an mRNA molecule and two or more ribosomes that is formed during translation.
many copies of a polypeptide can be made very quickly
A portion of an E. coli chromosome being transcribed (left to right) and being simultaneously translated. The arrow points to the putative site where RNA polymerase is first bound to the DNA. The chains of dark bodies are polysomes, that is, several ribosomes on the same mRNA molecule.

17. Skills: Using tables of mRNA codons (codon charts)
Use a table of the genetic code to deduce which codon(s) corresponds to which amino acid.
Deduce the sequence of amino acids coded by an mRNA molecule using a table.
See next page for charts…

18. Table of Codons and Amino Acids

20. Translation (animations)
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21. Peptide Bond

22. From Polypeptide to functional Protein
Posttranslational Modifications occur to polypeptides after translation
Folding to get secondary, tertiary structure
Joining to other polypeptides and/or prosthetic groups (Quaternary structure)

23. Free Ribosomes vs. Bound Ribosomes…
Free– proteins within cell
Bound– secretory proteins

24. Summary of Central Dogma (including RNA processing) Good animation

25. RNAi video

26. Mutations: genetic material changes in a cell
Note: new alleles are formed by mutation!
Base substitution Mutations (Point mutations):
Changes in 1 or a few base pairs in a single gene
This alters mRNA
May result in altered protein due to amino acid difference

27. Important Point Mutation example: Sickle cell anemia
GAG mutates to GTG
So for the 6th amino acid…
Glutamic Acid = replaced by Valine
Causes shape change, resulting in disease.

28. Mutations (continued) not in IB syllabus
Base-pair insertions or deletions: additions or losses of nucleotide pairs in a gene
frameshift mutation
alters the ‘reading frame’ of triplets~
Mutagens: physical and chemical agents that change DNA

29. Theory of knowledge: Discuss
•The nature versus nurture debate concerning the relative importance of an individual’s innate qualities versus those acquired through experiences is still under discussion. Is it important for science to attempt to answer this question?

30. Don’t use next slides

31. The Triplet Code
The genetic instructions for a polypeptide chain are ‘written’ in the DNA as a series of 3-nucleotide ‘words’
The two strands of DNA:
antisense strand (template strand) gets transcribed to make mRNA (complementary to mRNA)
sense strand (coding strand) has the same base sequence as the mRNA that is transcribed (with thymine instead of uracil).
Codons (mRNA base triplets) Each codon codes for one amino acid.
‘U’ (uracil) replaces ‘T’ in RNA