1. Summary 1.Eukaryotic cells keep genetic information in DNA enclosed in cell nucleus and mitochondria and chloroplasts (plants); 2.The genomes of several model organisms are completely sequenced; 3.Long DNA molecules are efficiently packed in chromosomes; 4.Cell nucleus is a highly organized structure; 5.Different sets of genes are expressed in different tissues; 6.Epigenetic regulation of gene expression. 44 More about cell nucleus later…

2. Lecture 2 Cell chemistry and biosynthesis 1

3. 70% of a cell’s weight is water the most abundant substance in cells Life on Earth began in the ocean Hydrogen bond link water molecules together so that water is a liquid form at room temperature (RT) 2

4. Cells contain four major families of small organic molecules They can also exist in monomers and be broken down in metabolic pathways 3

5. Glucose monomer 4

6. Monosaccharide to disaccharide 5

7. Polysaccharide- Glycogen 6

8. Fatty acids are usually covalently linked other molecules by their carboxyl group in a cell 7

9. Some fatty acids contain double bonds between carbons Essential structure of a cell!!! 9

10. Lipids: a loosely defined collection of biological molecules which are insoluble in water while being soluble in fat and organic solvents such as benzene. They either contain long hydrocarbon chains, as in the fatty acids and isoprenes, or multiple linked aromatic rings, such as in the steroids. Examples: fatty acids and their derivative such as triacylglycerols Phospholipids: amphipathic Lipids and phospholipids 8

11. Amino acids and proteins 10

12. Nucleotides and nucleic acids 11

13. Macromolecules are abundant in cells 12

14. Noncovalent bonds specify both the precise shape of a macromolecule and its binding to other molecules 13

15. Metabolic pathways and their interconnections 500 reactions 14

16. Two opposing streams of chemical reactions 15

17. Second law of thermodynamics Greater entropy 16

18.  G=  G o +0.616ln[B]/[A] AB 17  G Positive--no Negative--yes

19. A peptide bond 18

20. 19

21. The 20 amino acids found in proteins 20

22. Three types of noncovalent bonds driving protein folding 21

23. Polar amino acid side chains gather on the outside 22

24. Secondary structure:  helix Formed by hydrogen bonds in the polypeptide backbone 23

25. Secondary structure:  sheet Formed by hydrogen bonds in the polypeptide backbone 24

26. Coiled-coil: from hydrophobic  helices 25

27. Protein domains (40-350 aa): modular units 26

28. A protein “dimer” 27

29. A “tetramer” 28

30. A tetramer of two different subunits 29

31. Sizes and shapes of domains and proteins 30

32. Actin polymers: important components of cytoskeleton! 31

33. Self-assembly of a macromolecule aggregate 32 First example Bacterial ribosome: 55 proteins, 3 rRNAs

34. Proteins don’t work alone: Protein-protein interactions between functional groups of proteins-- challenges in “post-genome” era 33

35. Summary 34 1.Cells follow rules of chemistry; 2.Water is the most abundant substance proteins constitutes most of a cell’s dry mass; 3.Four major classes of small organic molecules make macromolecules; 4.Living cells undergo metabolism; 5.A reaction will happen if it can result in lower free energy in the system; 6.Proteins and protein complexes execute almost all cell functions.