1. LAST UNIT! Energetics

2. From molecules to energy

3. Essential questions How do plants and animals gain and use energy?
How can Venezuela utilize its energy resources to improve the wellbeing of society?
3.5 Transcription & Translation, 3.7 Cellular Respiration, 3.8 Photosynthesis
HL: 7.3 Transcription, 7.4 Translation, 8.1 Cellular respiration, 8.2 Photosynthesis
Important assessments: Unit Test, Project

4. 3.5 Transcription & 7.3 Transcription (HL)

5. The big picture: from gene to protein
mRNA
Protein

6. 3.5.1 DNA and RNA DNA RNA Sugar Deoxyribose Ribose Pyrimidine
Thymine, cytosine
Uracil
Strands
Double
Single

7. 7.3.1 Transcription (HL)
Transcription is carried out in a 5’  3’ direction

8. 7.3.2 Sense vs. Anti-sense strand (HL)
Anti-sense strand = strand that is transcribed
Sense strand = the coding strand, has the same base sequence as mRNA (uracil instead of thymine)

9. Transcription
A. Initiation: RNA polymerase is an enzyme complex which:
unwinds and unzips DNA double strand
attaches to promoter region of gene, which marks the beginning point for transcription
attaches with assistance of transcription factors
binds to DNA anti-sense strand
B. Elongation: RNA polymerase:
uses DNA anti-sense strand as a template to synthesizes a complementary RNA strand from nucleoside triphosphate taken from the surrounding solution in 5’ to 3’ direction
adds nucleoside triphosphates using base pairing rules
A = U T = A G = C C = G
C. Termination: RNA polymerase :
reaches termination region of the gene, which marks the end of the coding sequence
terminates transcription by releasing both DNA and mRNA

10. 3.5.2 Transcription

11. 3.5 Translation & 7.4 Translation (HL)

12. The big picture: from gene to protein
mRNA
Protein

13. 7.3.4 Post transcriptional modification
Introns = non coding, intervening sequence
Exons = coding region
RNA needs removal of introns to form mature mRNA

14. 3.5.3 Triplet code
triplet code = 3 nucleotide bases code for one amino acid
codon = a group of 3 nucleotide bases

15. 3.5.3 Triplet Code
universal: all living organisms use the same genetic code  common ancestry
degenerate: two or more codons can code for the same amino acid  buffer for mistakes

16. 7.4.2 Major players mRNA contains codon Ribosome tRNA
Protein (40% of weight) + rRNA (60% of weight)
Large subunit ribosome = three binding sites
Small subunit ribosome
tRNA
Anticodon = a group of 3 nucleotide bases with complementary base pairs to the codon
Amino acid attached to tRNA

17. 3.5.4 Initiation Occurs in 5’  3’ Direction
mRNA binds to the small subunit of the ribosome
AUG is universal start codon. tRNA with anticodon UAC and carrying AA methionine enters the P-site during translation
tRNA anticodon binds to mRNA codon by complementary base pairing
large ribosomal subunit binds and produces three binding sites: P site, A site and E site

18. Elongation
tRNA with anticodon complementary to second mRNA codon binds to A site, with appropriate amino acid attached to tRNA
Enzymes in ribosome catalyze formation of peptide bond between P site A site amino acids to create a polypeptide
P site tRNA is separated from amino acid and exits ribosome
Ribosome moves one codon along the mRNA, thus shifting previous A-site tRNA to P-site, and opening A-sites

19. 3.5.4 Termination
When ribosomal A-site reaches a stop codon, no tRNA has a complementary anticodon. Release factor protein binds to A-site stop codon.
Release: polypeptide, mRNA. Separate large and small ribosomal subunits

20. HL ONLY: READ ON

21. 7.4.1 tRNA all tRNA molecules have:
a) a triplet of bases called the anticodon, found in the anticodon loop of 7 nucleotides
b) two other loops
c) a CCA base sequence at the 3’ terminal, a site for amino acid attachment
d) sections that become double-stranded by base pairing

22. 7.4.1 tRNA
tRNA activating enzyme attaches a specific amino acid to the 3’ end of a tRNA
20 different tRNA activating enzymes, one for each of the 20 amino acids
each enzyme attaches one specific amino acid to all tRNA molecules that have an anticodon corresponding to that amino acid

23. 7.4.1 tRNA
ATP hydrolysis provides the energy for amino acid attachment to tRNA
stored energy is also used later to link the amino acid to the growing polypeptide chain during translation

24. 7.4.7 Ribosomes
Polysomes: several to many ribosomes translating the same mRNA into protein; each moving in the 5’ to 3’ direction
Which ribosomes?
Free ribosomes synthesize proteins for use within the cell itself
Bound ribosomes synthesize proteins primarily for secretion or for lysosomes