The Molecules of Cells

1. The Molecules of Cells Chapter 3

2. Overview • Introduction to Organic Compounds • Categories of Reactions • Molecules of Life • Carbohydrates • Lipids • Proteins • Nucleotides

3. What Are Organic Compounds? Unique to living systems Contain C & at least one H atom Each has a functional group: • Specific atoms/groups of atoms covalently bonded to C • Have specific physical & chemical properties

4. Why Carbon? Versatile bonding Can covalently bond with up to 4 atoms Forms stable bonds Helps form backbone for other elements to bond with

5. How Do Cells Build Organic Compounds? Monomer: Individual subunit of larger molecules needed to maintain cell structure & function e.g. amino acids

6. Polymer: Combination of 3 to millions of subunits e.g. proteins

7. Hydrocarbons H covalently bonded to C e.g. gasoline, other fossil fuels All 2 million+ are non-polar Some of Earth’s most important energy sources (electric & heat energy)

8. Functional Groups Specific atoms or groups of atoms covalently bonded to carbon atoms in organic compounds More reactive than hydrocarbon groups Can affect how structurally similar molecules work e.g. estrogens & testosterone (different positions of functional groups determines sexual traits)

9. Hydroxyl Alcohols, sugars, amino acids Water-soluble Methyl Fatty acid chains Insoluble in water H C H H Types of Functional Groups —OH

10. Carbonyl Sugars, amino acids, nucleotides Water-soluble Aldehyde if at end of carbon backbone Ketone if within carbon backbone C C H O CO O Types of Functional Groups continued —CHO (aldehyde) (ketone)

11. C OH C O- O O Types of Functional Groups continued Carboxyl • Amino acids, fatty acids • Water-soluble • Highly polar • Acts as acid by giving up H+ —COOH —COO- (non-ionized) (ionized)

12. Amino Amino acids, some nucleotide bases Water-soluble Acts as weak base by accepting H+ H N H N H+ H H Types of Functional Groups continued —NH2 —NH3+ (non-ionized) (ionized)

13. Phosphate Nucleotides (e.g. ATP), DNA, RNA, some proteins, phospholipids Water-soluble Acidic O- O P O- — P O Types of Functional Groups continued

14. Sulfhydryl Cysteine (an amino acid) Helps stabilize protein structure via disulfide bridges —S —S— Types of Functional Groups continued —SH (disulfide bridge)

15. Categories of Reactions (1) Functional Group Transfer a.k.a. exchange reaction AB + CD → AD + BC 1 molecule gives up group to another Making & breaking of bonds e.g. ATP gives phosphate group to glucose in cellular respiration

16. (2) Electron Transfer a.k.a. redox reaction One molecule loses e-s Another gains them e.g. cellular respiration, where glucose is oxidized (loses e-s) to CO2 & O is reduced (gains e-s) to H2O

17. (3) Rearrangement Internal bonds reform to turn one organic compound into another = structural isomer of original (same molecular formula, different order of bonding)

18. (4) Condensation a.k.a. synthesis reaction A + B → AB 2 molecules covalently bond to form a larger molecule (1 water molecule produced for each joining) Making of bonds (= anabolic) e.g. Na & Cl forming NaCl, amino acids forming a protein

19. (5) Cleavage a.k.a. decomposition reaction AB → A + B Molecule is split into 2 smaller ones Breaking of bonds (= catabolic) e.g. glycogen being broken down into glucose, carbs being broken down into simpler sugars

20. e.g. hydrolysis Cleavage reaction Molecule split by enzyme action OH & H from H2O attached to exposed sites e.g. hydrolysis of sucrose into glucose & fructose

21. Factors Influencing Reaction Rates For reactions to occur, atoms & molecules must collide with enough force to overcome repulsion between e-s Temperature • ↑ temp, ↑ rxn rate • ↑ kinetic energy, ↑ collisions Concentration of reactants • ↑ concentration, ↑ frequency of collisions

22. Particle size • Smaller move faster so collide more frequently Catalyst • Substance that speeds up chemical rxns • Does not become chemically changed or part of product

23. Molecules of Life • Carbohydrates • Lipids • Proteins • Nucleotides

24. (1) Carbohydrates Sugars & starches Make up 1-20% of cell mass Contain C, H, O Important source of energy Also serve some structural purpose e.g. ribose & deoxyribose in RNA & DNA Classified by size & solubility

25. CO (a) Monosaccharides “1 sugar” Building blocks of other carbs Most water-soluble sugars 2 or more –OH groups bonded to C backbone 1 aldehyde or ketone (carbonyl) group Most have a 5-C or 6-C ring —CHO

26. Monosaccharide Structure glucose fructose galactose ribose deoxyribose

27. (b) Disaccharides Double sugar Consist of 2 monosaccharides Must be broken down to be absorbed

28. (c) Oligosaccharides “Few” or short-chain sugars Includes disaccharides Often found as side-chains on lipids & proteins

29. (d) Polysaccharides “Many sugars” Chains of glucose Least water-soluble of carbs More complex = less soluble Good energy storage product Must be broken down to be absorbed

30. Polysaccharide Structure: Starch Spiral structure OH groups stick out from coils Storage carbohydrate of plants

31. Polysaccharide Structure: Glycogen Filamentous (branched) chains Storage carbohydrate of animal tissues Equivalent to starch in plants Stored in muscle & liver cells

32. Polysaccharide Structure: Cellulose Every other sugar is “upside-down” Sheets form by H-bonding between chains Structural carbohydrate of plants Makes up cell walls

33. Polysaccharide Structure: Chitin Modified polysaccharide Nitrogen groups attached to glucoses Strengthens cuticle of arthropods & cell walls of fungi =structural carbohydrate of animals & fungi

34. Simple Carbohydrates a.k.a. simple sugars Monosaccharides & disaccharides Taste sweet Few essential nutrients & high in calories e.g. candy, milk products, fruit

35. Complex Carbohydrates a.k.a. starches & fibres Oligosaccharides & polysaccharides Taste pleasant but not sweet e.g. whole grains, legumes, starchy vegetables (potatoes, etc.)

36. Fibre = cellulose ↑ fibre in diet = ↓ risk of cancer, diabetes, hypertension, etc. Processing plant foods decreases the amount of fibre & vitamins

37. In excess, carbs can lead to: • Increased blood sugar • Excess sugar being stored as fat • Increased risk of heart disease, etc. Diet rich in whole grains, fruits, & vegetables may reduce risk of heart disease & some cancers

38. (2) Lipids Fats & oils Contain C, H, O Less O than carbs Some also have P Non-polar Insoluble in water

39. (a) Fatty Acids Carboxyl group attached to backbone of up to 36 atoms Each C is covalently bonded to 1-3 H atoms

40. (i) Saturated fatty acids C backbones completely filled with attached H atoms Single covalent bonds only Animal fats: Usually solid at room temperature Associated with heart disease, clogged arteries, etc. = bad fats e.g. palmitic acid, stearic acid

41. (ii) Unsaturated fatty acids Not all Cs have H attached ≥1 double covalent bond Causes kinks in tails Plant fats: Usually liquid at room temperature

42. Mono- vs. polyunsaturated fats Mono-unsaturated e.g. oleic acid • Only 1 double bond • Thought to lower cholesterol Polyunsaturated e.g. linoleic acid • More than 1 double bond

43. Partial hydrogenation of vegetable oils Artificial saturation Turns liquid oils into solids (e.g. margarine) Oil is heated; H2 gas & nickel catalyst added Breaks C double bonds & attaches H

44. Partial hydrogenation & trans-fatty acids Partial hydrogenation = bad! Fat is now saturated Trans-fats created by heat (e.g. deep frying) & hydrogenation Double bonds fold in unnatural direction Enzymes that process fat are unable to process trans-fatty acids in a normal way Domino effect: Because trying to process trans-fatty acids, don’t process essential fatty acids properly

45. Essential fatty acids Body can manufacture some (palmitic acid, oleic acid, etc.) Others must be ingested via foods (omega-3 & omega-6 fatty acids)

46. (b) Neutral Fats 3 fatty acid tails attached to glycerol backbone = triglycerides Large & found throughout entire body “Body fat” used for insulation, protection, energy production Yield > double the energy of complex carbs e.g. butter, lard, veg. oils

47. (c) Phospholipids Glycerol backbone with phosphorus group & 2 fatty acid tails • Tails are non-polar • Head is polar Make up double-layered cell membranes Help regulate what crosses boundary of cell

48. (d) Waxes Long-chained fatty acids bonded to long-chain alcohols or carbon rings Repel water Protect Lubricate Add pliability to hair, skin, etc.

49. (e) Sterols Backbone of 4 C-rings Differ in functional groups In all eukaryotic cell membranes Steroids are essential for human life (homeostasis, vitamin D, sex & metabolic hormones)

50. Cholesterol Found only in animal foods Made in liver Can’t dissolve in blood Is carried to & from cells by lipoproteins (LDL & HDL) Note: cholesterol itself is not bad