Chapter 2 pt 2. Atoms, Molecules, and Life. Gregory Ahearn. John Crocker. Including the lecture Materials of

Transcription

1 Chapter 2 pt 2 Atoms, Molecules, and Life Including the lecture Materials of Gregory Ahearn University of North Florida with amendments and additions by John Crocker Copyright 2009 Pearson Education, Inc..

2 2.4 Why Is Carbon So Important To Life? Carbon can combine with other atoms in many ways to form a huge number of different molecules. Carbon has four electrons in its outermost shell, leaving room for four more electrons from other atoms (4 covalent bonds). Carbon atoms are versatile and can form up to four bonds (single, double, or triple) and rings.

3 Arrangement of atoms determines molecular shape. Shape determines function of molecules Structural formula Ball-and-stick model Space-filling model Methane The 4 single bonds of carbon point to the corners of a tetrahedron.

4 The great variety of substances found in nature is constructed from a limited pool of atoms. Organic molecules have a carbon skeleton and some hydrogen atoms. Much of the diversity of organic molecules is due to the presence of functional groups.

5 Functional (R) Groups Confer chemical reactivity Participate in chemical reactions Determine the chemical properties of molecules including acidity and solubility

6

7 What affects solubility in water? Molecules with +/- charge are usually hydrophilic or water-loving Molecules with no charge and non-polar are usually hydrophobic and not soluble in water

8 2.5 How Are Biological Molecules Joined Together Or Broken Apart? Biomolecules are polymers (chains) of subunits called monomers A huge number of different polymers can be made from a small number of monomers Biomolecules are joined by removing water (dehydration) and broken by adding water (hydrolysis)

9 Organic Molecule Synthesis Monomers are joined together through dehydration synthesis An H and an OH are removed, resulting in the loss of a water molecule (H 2 O)

10 Organic Molecule Synthesis Polymers are broken apart through hydrolysis ( water cutting ) Water is broken into H and OH and used to break the bond between monomers

11 Organic Molecule Synthesis All biological molecules fall into one of four categories Carbohydrates Lipids Proteins Nucleic Acids

12

13

14 2.6 What Are Carbohydrates? Composition: C, H, and O in the ratio of 1:2:1 Construction: Simple or single sugars are monosaccharides Two linked monosaccharides are disaccharides Long chains of monosaccharides are polysaccharides

15 Monosaccharides Basic monosaccharide structure Backbone of 3-7 carbon atoms Many OH and H functional groups Usually found in a ring form in cells Simple sugars provide important energy sources for organisms. Most small carbs are water-soluble due to the polar OH functional groups

16 A simple sugar H H H H H O H C C C C C C H H CH 2 OH H O H O O O H O O HO OH H OH (a) H H H H Glucose, linear form (b) H OH Glucose, ring form Fig. 2-13

17 Monosaccharides More monosaccharides Fructose (found in corn syrup and fruits) Galactose (found in lactose) Ribose and deoxyribose (found in RNA and DNA)

18

19 Disaccharides Disaccharides are two-part sugars Sucrose (table sugar) = glucose + fructose Lactose (milk sugar) = glucose + galactose Maltose (malt sugar)= glucose + glucose

20 Manufacture of a disaccharide glucose fructose sucrose H HO CH 2 OH O H OH H H OH + HOCH 2 HO H O HO H CH2 OH dehydration synthesis H HO CH 2 OH O H OH H H O HOCH 2 H O HO H CH2 OH H OH OH H H OH OH H H O H Fig. 2-14

21 Polysaccharides Monosaccharides are linked together to form chains (polysaccharides) Polysaccharides are used for energy storage and structural components

22 Polysaccharides Storage polysaccharides Starch (polymer of glucose) Formed in roots and seeds as a form of glucose storage Glycogen (polymer of glucose) Found in liver and muscles

23

24 Polysaccharides Structural polysaccharides Cellulose (polymer of glucose) Found in the cell walls of plants Indigestible for most animals due to orientation of bonds between glucoses

25

26

27 Polysaccharides Structural polysaccharides continued Chitin (polymer of modified glucose units) Found in the outer coverings of insects, crabs, and spiders Found in the cell walls of many fungi

28

29

30

31 2.7 What Are Lipids? Molecular characteristics of lipids Lipids are molecules with long regions composed almost entirely of carbon and hydrogen. The nonpolar regions of carbon and hydrogen bonds make lipids hydrophobic and insoluble in water.

32 What Are Lipids? Lipids are diverse in structure and serve in a variety of functions Energy storage Waterproofing Membranes in cells Hormones

33 What Are Lipids? Lipids are classified in 3 groups Group 1: Oils, fats, and waxes Group 2: Phospholipids Group 3: Steroids

34 Group 1: Oils, fats, and waxes Formed by dehydration synthesis 3 fatty acids + glycerol triglyceride Contain only carbon, hydrogen, and oxygen Contain one or more fatty acid subunits in long chains of C and H with a carboxyl group ( COOH) Triglycerides are used for long-term energy storage in both plants and animals. Ring structure is rare

35

36 Group 1: Oils, fats, and waxes (continued) Characteristics of fats Fats are solid at room temperature. Solidity is due to the prevalence of single carbon bonds Fats have all carbons joined by single covalent bonds. The remaining bond positions on the carbons are occupied by hydrogen atoms.

37 Group 1: Oils, fats, and waxes (continued) Fatty acids of fats are said to be saturated and are straight molecules that can be stacked. (a) Beef fat (saturated) Fig. 2-18a

38 Group 1: Oils, fats, and waxes (continued) Characteristics of oils Oils are liquid at room temperature. Some of the carbons in fatty acids have double covalent bonds. There are fewer attached hydrogen atoms, and the fatty acid is said to be unsaturated.

39 Group 1: Oils, fats, and waxes (continued) Unsaturated fatty acids have bends and kinks in fatty acid chains and can t be efficiently stacked. (b) Peanut oil (unsaturated) Fig. 2-18b

40 Group 1: Oils, fats, and waxes (continued) Characteristics of waxes Waxes are solid at room temperature. Waxes are highly saturated. Waxes are not a food source. Waxes are composed of long hydrocarbon chains and are strongly hydrophobic

41 Group 1: Oils, fats, and waxes (continued) Waxes form waterproof coatings Leaves and stems of plants Fur in mammals Insect exoskeletons Used to build honeycomb structures

42 Group 1: Oils, fats, and waxes (continued) Bees use waxes to store food and honey. Fig. 2-17b

43 Group 2: Phospholipids Phospholipids: form dual layered plasma membranes around all cells Construction like oils except one fatty acid is replaced by a phosphate group attached to glycerol. 2 fatty acids + glycerol + a short polar functional group water-soluble heads and water-insoluble tails.

44 Group 2: Phospholipids (continued) The phosphate end of the molecule is water soluble; the fatty acid end of the molecule is water insoluble. CH 3 O H 3 C-N + - CH 2 - CH 2 -O-P-O-CH 2 O CH CH 2 CH 3 O HC-O-C-CH 2 -CH 2 - CH 2 -CH 2 - CH 2 - CH 2 - CH 2 -CH O CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 H 2 C-O-C-CH 2 -CH 2 - CH 2 -CH 2 - CH 2 - CH 2 - CH 2 - CH 2 -CH 2 -CH 2 - CH 2 - CH 2 - CH 2 -CH 2 -CH 2 -CH 3 polar head (hydrophilic) glycerol fatty acid tails (hydrophobic) Fig. 2-19

45 Group 3: Steroids Steroids contain four fused carbon rings. Various functional groups protrude from the basic steroid skeleton. Examples of steroids Cholesterol Found in membranes of animal cells Male and female sex hormones

46

47 2.8 What Are Proteins? Functions of proteins Proteins act as enzymes to catalyze (speed) many biochemical reactions. They provide structure (ex/ elastin) They can act as energy stores. They are involved in carrying oxygen around the body (hemoglobin). They are involved in muscle movement.

48

49 Some proteins are structural and provide support in hair, horns, spider webs, etc. Fig. 2-21

50 Proteins are formed from chains of amino acids. All amino acids have the same basic structure: A central carbon An attached amino group An attached carboxyl group An attached variable group (R group) Some are hydrophobic Some are hydrophilic amino group variable group carboxylic acid group hydrogen

51

52 Amino acid monomers join to form chains by dehydration synthesis. Proteins are formed by dehydration reactions between individual amino acids. The NH 2 group of one amino acid is joined to the COOH group of another release of H 2 O and the formation of a new peptide (two or more joined amino acids). The resultant covalent bond is a peptide bond

53 Long chains of amino acids are known as polypeptides or just proteins

54 The sequence of amino acids in a protein dictates its three dimensional structure This structure gives proteins their functions. Long chains of amino acids fold into threedimensional shapes in cells, which allows the protein to perform its specific functions. When a protein is denatured, its shape has been disrupted and it may not be able to perform its function.

55 Four Levels of Structure Proteins exhibit up to four levels of structure Primary structure is the sequence of amino acids linked together in a protein Secondary structures are helices and pleated sheets Tertiary structure refers to complex foldings of the protein chain held together by disulfide bridges, hydrophobic/hydrophilic interactions, and other bonds Quaternary structure is found where multiple protein chains are linked together

56

57

58

59 Three Dimensional Structures The type, position, and number of amino acids determine the structure and function of a protein Precise positioning of amino acid R groups leads to bonds that determine secondary and tertiary structure Disruption of these bonds leads to denatured proteins and loss of function

60 2.9 What Are Nucleic Acids? Structure of nucleic acids Nucleic acids are long chains of similar (not identical) subunits called nucleotides. All nucleotides have three parts. A five-carbon sugar (ribose or deoxyribose) A phosphate group A nitrogen-containing molecule called a base In nucleotide polymers the phosphate group of one nucleotide bonded to the sugar group of the next.

61 Nucleic Acids Nucleotide chain base sugar phosphate Fig. 2-26

62 Molecules of Heredity Two types of polymers of nucleic acids DNA (deoxyribonucleic acid) found in chromosomes Carries genetic information needed for protein construction Deoxyribonucleotide monomers(a, G, C, T) RNA (ribonucleic acid) Copies of DNA used directly in protein construction Ribonucleotide monomers (A, G, C, U)

63 Deoxyribose nucleotide base phosphate NH 2 HO OH P O CH 2 O HC N N C C C N N CH O sugar H H H H OH H Fig. 2-25

64 Molecules of Heredity Each DNA molecule consists of two chains of nucleotides that form a double helix

65 Other Nucleotides Nucleotides act as messengers in the cell Adenosine monophosphate (AMP) carries information to other molecules Nucleotides as energy carriers Adenosine triphosphate (ATP) carries energy stored in bonds between phosphate groups NAD + and FAD carry electrons Nucleotides as enzyme assistants Coenzymes help enzymes promote and guide chemical reactions

66