Chapter 13 .Chemicals of life

No molecule in a living organism is a permanent resident. Within 7 years, most of the molecules in a human body have been replaced by new one!

Individual? Decided completely by the genetic code? No! An individual’s identity is continually re-established each and every moment.

13.1 Biomolecules are produced and utilized in cells

• Plasma membrane: 细胞膜

• Cell wall: 细胞壁• Cell nucleus ：细胞核• Cytoplasm: 细胞质• Organelles: 细胞器

• Carbohydrate: 碳水化合物• Lipid: 脂类• Protein: 蛋白质• Nucleic acid: 核酸

Plant cell

Animal cell

13.2 Carbohydrates give structure and energy

• Carbohydrates are molecules of carbon, hydrogen and oxygen produced by plant through photosysthesis ( 光合作用 ).

• Saccharide: 糖类• Glucose: 葡萄糖• Fructose: 果糖

OH

OHOH

H

H

OH

H

OH

CH2OH

H

OCH2OH

HOH

OH

OH

H

H

CH2OH

Glucose Fructose

Honey

Sucrose: 蔗糖

Lactose: 乳糖Lactase: 乳糖酶

Polysaccharides ( 多糖 ) are complex carbohydrates

Hyaluronic acid: 透明质酸Glucuronic acid: 葡萄醛酸Chitin: 甲壳素

The polysaccharides of the human diet are made only of glucose. These polysaccharides include starch ( 淀粉 ), glycogen （糖原） and cellulose （纤维素） , which differ from one another in how the glucose units are chained together.

Amylose: 直链淀粉 20%

Amylopectin: 支链淀粉 80%

Glycogen is found in animal tissue

Cellulose is consisted of β–glucose and has a straight conformation.Cellulose is by far the most abundant organic compound on earth. But most animals, including humans, are not able to break

cellulose down to glycose.

• Fats are used for energy and insulation• A fat is any biomolecule formed from the reaction of a glycerol

molecule, attached to three fatty acid molecules. Fatty acid can be saturated or unsaturated.

• Fats are used to reserve energy. 1 gram of fat contains about 9 calories of energy, while a gram of carbohydrate and protein contains only 4 calories of energy.

• Fats are also used to insulate us from cold.

13.3 Lipids are insoluble in water

Saturated fat and unsaturated fatThe molecules of saturated fats can pack together, leading to high melting points.The molecules of unsaturated fats can not pack together, leading to low melting points.

stearic acid ， m.p.69℃ oleic acid ， m.p.13℃

Fats from animals and plants are mixture of different fat molecules

Table 13.1 degree of unsaturation in some common fats

Fat Percentage of total fatty acid content

Saturated Monounsaturated polyunsaturated

Coconut 93 6 1

Palm 57 36 7

Lard 44 46 10

Cottonseed 26 22 52

peanut 21 4 30

Olive 15 73 12

Corn 14 29 57

Soybean 14 24 62

Sunflower 11 49 70

Safflower 10 14 76

Canola oil 6 58 36

Steroids ( 类固醇 ) contain four carbon rings

• Cholesterol: 胆固醇• Testosterone: 睾酮• Estradiol: 雌甾二醇

13.4 Proteins are polymers of amino acids ( 氨基酸 )

• 20 amino acids differ from one another by the chemical identity of their side groups.

• Amino acids are linked through peptide bonds ( 肽键 ). A group of amino acids linked together through peptide bonds is called peptide. Peptides containing more than ten amino acids are generally called polypeptides.

There are many kinds of proteins

Protein structure is determined by attractions between neighboring

amino acids

The proteins in hair and fingernails contain a lot of disulfide bonds

Many proteins consist of two or more polypeptide chains.

血红蛋白

The proteins can be denatured with the change in conditions.

Enzymes are biological catalysts

Figure 13.25

Upon binding to the receptor site on the enzyme sucrase, the substrate sucrose is split into its two monosac-charide units, glucose and fructose.

13.5 Nucleic acids code for proteins• Our bodies are built of proteins. Our bodies are able to assemble ami

no acids in just the right order to build proteins that have highly functional structures.

• A nucleotide ( 核苷 ) consists of a phosphate ( 磷酯 ), a ribose sugar ( 核糖 ), and a nitrogenous base ( 碱基 ).

• A nucleic acid is a polymer made up to nucleotide monomers.

• Two types of nucleic acids: deoxyribonucleic acid ( 脱氧核糖核酸 ) and ribonucleic acid ( 核糖核酸 ).

• Deoxyribonucleic acids are the primary source of genetic information and are found in the cell nucleus.

• Ribonucleic acids occur mostly outside the cell nucleus in the cytoplasm, where they piece together amino acids to make proteins.

DNA is the template of life

• Gregor Mendel’s work rose the idea of heredity. The unit containing the heritable information is called genes. In 1900s, genes have been related to chromosomes ( 染色体 ), which consist of DNA and proteins.

• In 1953, James Watson and Francis Crick proposed the double helix structure of DNA. The most critical point of double helix model is the hydrogen bonding between guanine and cytosine, and also between adenine and thymine.

Replication of DNA

• One gene codes for one polypeptide• Gene controls the protein’s amino acid

sequence. Each gene codes for the synthesis of a particular protein.

• The number of human gene is 30000-100000.• Each chromosome contains 1000-2000 genes.• Each DNA molecule contains about 3.1 billion

base pairs.• Genes make up only about 20% of a DNA

molecule.

• RNA is largely responsible for protein synthesis• The manufacturing of proteins involves two proc

esses: transcription ( 转录 ) and translation ( 转译 ).

• These steps are mediated by the three forms of RNA: messenger RNA ( 信使 RNA ， mRNA), ribosomal RNA ( 核糖体 RNA ， rRNA) and transfer RNA ( 转移 RNA ， tRNA).

Codon （密码子、三联体）

Translation

Ribosome

Ribosome

• Genetic engineering• Restriction enzyme ( 限制酶 ) ban cleave long strands of

DNA into small fragments.• Gel electrophoresis is used to separate fragmented DNA.

Gel electrophoresis

Recombinant （重组） DNA

Gene cloning ( 基因克隆 )

13.6 Vitamins are organic, minerals are inorganic

• Lipid-soluble vitamins and water-soluble vitamins

• Lipid-soluble vitamins can be stored in body for long time, but not for children.

• Over-dose of vitamins A and D are harmful.

• Vitamins B and C are washed away by water.

Table 13.2 Some Vitamins Needed by the Human BodyVitamin Function Deficiency syndrome

Lipid-soluble

Vitamin A (retinol) Precursor to rhodopsin, a chemical used for vision; assists in inhibiting bacterial and viral infectio

ns

Night blindness

Vitamin D (calciferol) Helps incorporate calcium into body

Weak bones

Vitamin E (tocopherol) Inhibits oxidation of polyunsaturated fats;

free radical scavenger;

Diminished hemoglobin

Vitamin K ( phylloquinone) helps maintain ability to form blood clots

Abnormal bleeding

Water-soluble

B vitamins Coenzymes in biochemical reactions for growth

and energy production

Various nerve and skin disorders, anemia

Vitamin C (ascorbic acid) Antioxidant; asisits in inhibiting bacterial and viral

infections

scurvy

Minerals

Macromineral (ionic form) Some functions Deficiency syndrome

Sodium (Na+) Transportation of molecules across cell membrane,

nerve function

Muscle cramps, reduced appetite

Potassium(K+) Transportation of molecules across cell membrane,

nerve function

Muscular weakness, paralysis, nausea, heart failure

Calcium(Ca2+) Bone and tooth formation, nerve and muscle function

Retarded growth, possibly loss of bone mass

Magnesium(Mg2+) Enzyme function Nervous system disturbances

Chlorine(Cl-) Transportation of molecules across cell membrane, digestive fluid, nerve

function

Muscle cramps, reduced appetite

Phosphorus(H2PO4-) Bone and tooth formation, nerve and muscle function

Weakness, calcium loss

Sulfur(SO42-) Amino acid component Protein deficiency

Table 13.3 Some Macrominerals Needed by the Human Body

ATP&ADP

13.7 Metabolism ( 代谢 ) is the cycling of biomolecules through the body catabolism and metabolism

13.8 The food pyramid summarizes a healthful diet

CarbohydratesGlycemic Index （血糖指数）

Glucose 100 Honey 58

Baked potato 85 Sweet corn 55

Cornflakes 83 Brown rice 55

Microwaved potato 82 Popcorn 55

Jelly beans 80 Oatmeal cookies 55

Vanilla wafer 77 Sweet potato 54

French fries 75 Banana 54

Cheerios 74 Milk chocolate 49

White bread 71 Orange 44

Mashed potato 70 Snickers candy bar 40

Life-savers candy 70 Pinto beans 39

Shredded wheat 69 Apple 38

Wheat bread 68 Spaghetti, boiled 5minutes 36

Sucrose 64 Skim milk 32

Raisins 64 Whole milk 27

Mars candy bar 64 Grapefruit 25

High-fructose corn syrup 62 soybean 18

White rice 58 peanuts 15

Table 13.4 Glycemic Index for Select Foods

source: Jennie Brand Miller et al., the Glucose Revolution: the authoritative guide to the Glycemic index.Sydney: Marlowe & company, 1999

• Unsaturated fats are generally more healthful than saturated fatsSaturated fats are used to synthesize cholesterol.Fats are also packaged with water soluble proteins (Lipoproteins) to move through bloodstream.

• Hydrogenation of unsaturated fats can be used to prepare margarine and also in the process of making chocolates.

Lipoprotein Percent protein

Density(g/ml) Primary function

Very-low-density(VLDL) 5 1.006-1.019 Fat transport

Low-density(LDL) 25 1.019-1.063 Cholesterol transport(to cells to build cell walls)

High-density(HDL) 50 1.063-1.210 Cholesterol transport(to liver for processing)

Table 13.5 The Classification of Lipoproteins

Essential for adults

Essential for children