1

The chemicals of Life

Lesson 3

2

Learning Focus• Describe the structure of important biochemical

compound – carbohydrates, protein, lipids, and nucleic acids and explain their function within the cells

• Identify common functional groups within biological molecules, and explain their contributions to the function of each molecule.

• Identify and describe the main types of biochemical reactions: oxidation-reduction, hydrolysis, and condensation

• Draw 3D molecular models of important biochemical compounds.

3

Functional groups

• A group of atoms within an organic compound that give it characteristic chemical and physical properties

• Are reactive clusters where much of the bonding takes place in biological molecules.

• They are attached to the carbon backbone of organic molecules

4

5

Bonding Capacity• The structure of each of the functional groups

show that they will always form the same number of covalent bonds with adjacent molecules. Therefore bonding capacity is the number of covalent bonds an atom can form with neighbouring atoms.

• Hydrogen can bond with one other molecule, oxygen and sulphur with two, nitrogen with three, carbon with four and phosphorous with five.

6

Bonding capacity - Tip

• One way to remember the bonding capacity of the 4 most common elements in order is through the acronym HONC (pronounced “HONK”). H = 1, O = 2, N = 3, C = 4

7

Redox reactions• Reactions that involve the transfer of electrons

from one reactant to another• Oxidation occurs when there is a loss of

electrons,• Reduction occurs when there is a gain of

electrons (important in photosynthesis and cellular respiration)

• Use mnemonic: LEO GER– LEO = loss of electrons = Oxidation– GER = gain of electrons = Reduction

8

Redox Reactions

9

Biological Macromolecules

• Most important biological molecules are macromolecules.

• They are large molecules which are usually composed of many repeating subunits

10

Class or Group

Macromolecule(Polymer)

Specific Examples

Subunit(Monomer)

Examples

Carbohydrate Oligosaccharide,Polysaccharide

Complex carbohydrates (starch, Cellulose)

Monosaccharide Simple sugar(glucose, fructose)

Fats/Lipids Di or Triglyceride Phospholipid Glycerol and fatty acids

Glycerol; Oleic acid (in vegetable oil)

Protein Protein Enzymes Amino acid 20 different ones

Nucleic Acid DNA, RNA DNA, mRNA, tRNA

Nucleotide Phosphate Group + sugar + one of 5 nitrogenous bases

11

Condensation (dehydration synthesis) and Hydrolysis Reaction

• Various molecules are assembled and disassembled the same way

• Condensation and hydrolysis reactions require enzymes to take place

• Involves two different types of reactions– Condensation/dehydration –removal of water this

is an anabolic reaction (build up of molecules)– Hydrolysis – addition of water this is a catabolic

reaction (break down of molecules)

12

Condensation or dehydration synthesis reactions (Anabolic)

• Creates a covalent bond between 2 interacting subunits,

• Link the 2 subunit at their functional groups• Involves the removal of H+ from the functional

group of one subunit and a OH- from the other subunit’s functional group to form water.

• Reaction produce larger molecules from smaller subunits and require energy to take place.

13

Condensation of a glucose and Fructose molecule

14

Hydrolysis Reactions (Catabolic)

• Break molecules into their subunits• It is the reverse of condensation reactions• Water molecule is used to break a covalent bond –

(hydro-lysis).• Water provides an “H” to one subunit and an “OH”

to the other• Energy is released during the reaction• can break a triglyceride into its subunits by

breaking the ester linkages

15

• http://www.tvdsb.on.ca/westmin/science/sbioac/biochem/condense.htm

16

Carbohydrates• Contain C, H, and O in a 1:2:1 ratio, i.e. (CH2O)n

• Most common organic materials on earth• Produced by photosynthesis• Used by organisms for energy, and building materials

within the cell,• Used for cell-to-cell identification during metabolic

processes• Classified into: monosaccharides, oligosaccharides and

polysaccharides

17

Monosaccharides

• Are simple sugars, mono – one, saccharum – sugar• Consist of a single chain of carbon atoms with an

“OH” or hydroxyl group attached• They are distinguished by their carbonyl group, either

an aldehyde (functional group CH=O) or Ketone (functional group C=O) and the number of carbons in their carbon backbone

• E.g. a 5-carbon chained monosaccharide is called a pentose, 6-carbon is called a hexose

18

Monosaccharide

• Glucose a monosaccharide can be linear in its dry state or forms a ring in water.

• If the OH group at carbon #1, is below the plane of the ring it is called α-glucose(alpha-glucose). If the OH group is above the plane of the ring, it is called β-glucose (beta-glucose)

19

Alpha glucose

• If the OH group at carbon #1, is below the plane of the ring it is called α-glucose (alpha-glucose)

20

Beta Glucose

• If the OH group is above the plane of the ring, it is called β-glucose (beta-glucose)

21

• If the OH group at carbon #1, is below the plane of the ring it is called α-glucose (alpha-glucose)

• If the OH group is above the plane of the ring, it is called β-glucose (beta-glucose)

22

Figure 3: Glucose

Common Saccharides

Function of CarbohydratesSimple sugars (Mono and Disaccharides)• Primary function = energy source for the cell• Produced by photosynthesis• Converted into ATP by respiration

Source: http://en.wikipedia.org/wiki/Image:CellRespiration.svg

25

Oligosaccharides• Contains 2 or 3 simple sugars bonded together.• The covalent bond linking the two molecules is a

glycosidic linkage. These bonds are formed by condensation reactions

• E.g. maltose (2 α-glucose molecules joined), for sucrose ( α-glucose and α-fructose joined)

26

27

Condensation of 2 alpha molecules to form Maltose

28

Polysaccharides• They are complex carbohydrate composed of

hundred to several thousand monosaccharide subunits,

• They are joined by glycosidic linkages.• E.g. starch and glycogen used as energy storage• Cellulose and chitin used for structural support

29

Glycogen• Stored in small amounts in humans and other

animals in muscles and liver cells• Enzymes can hydrolyze glycogen into glucose

for energy during physical activity.

30

Cellulose

• Primary structural unit of plants cell walls.• Plants produce 200billion kg/yr – the most abundant

organic substance on earth.• Consist of straight chain polymer of β-glucose molecules• Hydrogen bonding occurs between several straight chains

to produce tight bundles called microfibrils.• Microfibrils intertwine to form tough, insoluble cellulose

fibres• Humans cannot digest glycosidic linkages between β–

glucose in cellulose.• We can digest starch, cellulose is a part of a healthy diet

in humans

31

Cellulose

• Ruminants' have bacterial and protists in their guts that produce enzymes that break down β–glucose linkages

• Therefore can digest cellulose, and use as energy source.

32

Chitin• Makes up the exoskeleton of insects and

crustaceans.• The second most abundant organic material on

earth.• Use in contact lenses and biodegradable

stitches.

Polysaccharides• Energy storage molecules

Example:– starch in plants– glycogen in animals

• Structural moleculesExampleCellulose = plant cell wallChitin = Insect and Arthropod exoskeletons

Source:http://en.wikipedia.org/wiki/Image:Chloroplasten.jpg

Source:http://en.wikipedia.org/wiki/Image:Lyristes_plebejus.jpg

Complex carbohydrates:Examples:

• Amylose (straight chain plant starch)• Amylopectin (branching plant starch)• Cellulose (plant cell walls)• Glycogen (animal starch)• Chitin (insect exoskeleton)

Usually glucose molecules are bonded between C1 and C4 (straight chains). But bonding between C1 and C6 is possible (branching).

AmyloseSource:http://en.wikipedia.org/wiki/Image:Amylose.svg

AmylopectinSource:http://en.wikipedia.org/wiki/Image:Amylopektin_Sessel.svg

GlycogenSource:http://en.wikipedia.org/wiki/Image:Glykogen.svg

35

36

review

• Textbook work for review• Page 34 #s – 2, 3, 5, 6, 8, 10

37

Fats and Lipids• The most common energy storing molecule in

organisms, 1g of fat =38kj (17kj of carbohydrates and proteins)

• Excess carbohydrate is converted to fats for later energy usage.

• Most common form of fat in plants and animals are Triglycerides. Fats are solid, and oils are liquid at room temp.

• Lipids are hydrophobic, they are non polar, composed of C, H, O

• Lipids are soluble in other non polar substances. (like-dissolves-like).

38

Fats and Lipids

• Lipids are energy storing like fats,• Used for building membranes and cell parts,• They are chemical signalling molecule because

they transmit information between cells.• Also activate enzyme actions• Used as insulation layer for protection of organs• Are grouped into four:

1) fats, 2) phospholipids, 3) steroids, 4) waxes.

39

Glycerol

• It is a 3 carbon alcohol containing a hydroxyl (OH) group attached to each carbon.

• Glycerol forms the backbone of triglyceride molecules.

40

Fatty Acids

• They are long hydrocarbon chains with a single carboxyl group (COOH) at one end.

• They could be saturated, i.e. do not have double bonds between the carbon atoms in the chain. E.g. animal fat (butter, lard)

• Mono-unsaturated – have one double bond (plant oils, e.g. oleic acid – liquid at room temp.)

• Poly-unsaturated – have 2 or more double bonds. (plant oils – liquid at room temp)

41

Page 43 diagram of stearic acid and Oleic Acid

42

43

Hydrolysis of a triglyceride

44

Phospholipids

• They make up the cell membrane• Consist of a glycerol, 2 fatty acids and a polar

phosphate group• Polar head is hydrophilic,• 2 non-polar tails are hydrophobic• When added to water, phospholipids form

spheres called micelles

45

phospholipids

46

Phospholipids

47

Steroids

• Compact hydrophobic molecules made of 4 fused hydrocarbon rings, and different functional groups.– Cholesterol: important component of cell membranes

and building block for other steroids in the body– High concentration of cholesterol in the bloodstream

and a diet rich in saturated foods have been linked to atherosclerosis (blocking of blood vessels) which can lead to heart attack or stroke.

48

Cholesterol

49

Waxes

• These are lipids containing long fatty acids linked to alcohols.

• They are hydrophobic, firm and pliable.• Used by plants (cutin) and animals for water

proofing.

50

Proteins

• They are the most diverse molecules in living organisms and among the most important

• Act as structural building blocks, as functional molecules,

• Involved in almost everything that a cell does• Different proteins perform specific task• More than 50% of the dry mass of cells is made up

of protein• All enzymes (biological catalysts) are proteins

51

Protein Shape

• Proteins are amino acid polymers folded into 3D shape

• The function of a protein is directly related to the specific shape of the protein

• There4 a protein shape depends on the sequence of amino acids that make up the protein

• There are 4 basic structures to a protein

52

53

Proteins

• There are 20 amino acids • Each is made up of a central carbon, an amino

group, a carboxyl group, a hydrogen and one of 20 different “R” groups.

• The “R” group represents the grouping that is unique to each amino group

54

Structure of an Amino Acid

55

56

57

58

Primary Structure

• The amino group on one amino acid can react with the carboxyl group on another amino acid to form a peptide bond.

• This way amino acids can join to form a polypeptide chain.

• The specific sequence of amino acids in a polypeptide is known as the primary structure

• the 10 structure determines the shape and therefore function of the protein.

59

Secondary Structure

• In a secondary structure protein, the hydrogen bonding affects the orientation

• The backbone of a polypeptide chain contains both N-H groups and C=O groups

• These groups can form hydrogen bonds with each other, resulting in 2 arrangements– Alpha-helix: right handed coil (e.g. hair protein almost

complete alpha helix shape)– Beta-sheet: pleated sheet (e.g. silk contains a large

amount of beta sheets)

60

Tertiary Structure Protein

• Structure is maintained by the interactions between the amino acids’ R groups to each other and to their surroundings

• Examples:– Some R groups are non-polar (hydrophobic). These

groups tend to move to the middle of the molecule – away from water

– Some R groups are polar (hydrophilic), these groups will be oriented toward the water (edges of the molecule)

61

Examples of tertiary structure Protein

• Some R-groups can form hydrogen bonds• Other R-groups containing sulphur atoms can

form disulphide bridge between different areas of a protein.

• Disulphide bridges are strong stabilizers of tertiary structure.

62

63

Quaternary Structure Protein

• They have more than one polypeptide chain• It is the interactions between 2 or more polypeptide

chains in a protein that maintain the quaternary structure.

• Examples:– Collagen is made up of 3 polypeptide chains in a rope-like

structure– Haemoglobin is a globular protein made up of polypeptide

chains

64

Structure is Function• The final shape of a protein is dependent

upon the primary structure.– E.g.– Haemoglobin protein a single amino acid can be

substituted: i.e. valine for glutamic acid.– This non-polar amino acid substitution

dramatically changes the protein shape and causes the disease sickle cell anaemia

65

66

Denaturation of Proteins

• Change in pH or temperature can change a protein’s shape

• If a protein loses its normal shape it is said to be denatured, and it will not function properly

• If gently denatured the protein may regain its proper shape and function when conditions return to normal, as long as the primary structure is not changed.

67

Hydrolysis and Condensation Reactions Involving Proteins

• When two amino acids bind together, resulting covalent bond is called a peptide bond.

• The resulting molecule is called dipeptide• when an amino acids are joined together it is

called polypeptide

68

• http://www.youtube.com/watch?v=KH-LQSr7rHs

http://www.youtube.com/watch?v=MG8ziGyattk&feature=related

70

Nucleic Acids• Used by all organisms to store heredity

information that determines the structural and functional characteristics of an organism.

• There are 2 types:– DNA– RNA

71

DNA Nucleotide Structure

72

Home-Work

• Page 50 # 19, 21, 22, 24, 25 27

• Quiz to Follow at a determined date.

• Thanks.