Chemical Basis of Life - Damm's Science Page -...

Chapter 2

Chemical Basis of Life

2

Introduction:

A. Chemistry deals with the composition of matter and how it changes.

B. A knowledge of chemistry is necessary for the understanding of physiology because of the importance of chemicals in body processes.

Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

3

Structure of Matter:

A. Elements and Atoms: 1. Matter is anything that has weight and

takes up space. 2. All matter is composed of elements.


4

3. Living organisms require about 20 elements, of which oxygen, carbon, hydrogen, and nitrogen are most abundant.

4. Elements are composed of atoms; atoms of different elements vary in size, weight, and interaction with other atoms.

5. Attractions between two or more atoms are called chemical bonds.


5

B. Atomic Structure: 1. An atom consists of a nucleus

containing protons and neutrons, with electrons in orbit around the nucleus in shells.

2. Protons, with a positive charge, are about equal in size to neutrons, which have no charge.


6

3. Electrons are much smaller and bear a negative charge. 4. An electrically neutral atom has equal numbers of protons and electrons. 5. The number of protons denotes the atomic

number of an element; the number of protons plus the number of neutrons equals the atomic weight.

6. Atoms with the same atomic number, but different weights are isotopes of an element.


7

C. Bonding of Atoms: 1. Atoms form bonds by gaining, losing,

or sharing electrons. 2. Electrons are found in shells around

the nucleus. a. The first energy shell holds a

maximum of two electrons; the other energy shells each hold a maximum of eight electrons when on

the outside. Elements that have their outermost shells filled, are

stable structures that are chemically inert.


8 8

Fig02.02

Lithium (Li) Helium (He) Hydrogen (H)

+ 0 0 +

+ 0

0 + +

0 0 +

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

- -

-

-

-

-

9

3. Atoms with incompletely filled outer shells tend to be reactive to form stable outer shells of 8.

4. When atoms gain or lose electrons, they become ions with a charge. Whether they gain or lose will depend on how many electrons they have in the outer shell to start with.

5. Oppositely-charged ions attract each other and form an ionic bond.


10

Fig02.04 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

+ -

-

11p+!

12n0!

Sodium atom (Na) Chlorine atom (Cl)

Chloride ion (Cl–) Sodium ion (Na+)!

(b) Bonded ions ! These oppositely charged particles attract electrically and join by! an ionic bond

(a) Separate atoms ! If a sodium atom loses an electron to a chlorine atom, the sodium! atom becomes a sodium ion (Na+), and the chlorine atom becomes a chloride ion (Cl–)

Sodium chloride

Na+

Cl–

(c) Salt crystal! Ionically bonded substances form arrays such as a crystal of NaCl.!

17p+!

18n0!

-

11p+!

12n0!17p+!

18n0!

- - -

- - - -

- -

- - - -

- - - -

- - - - -

- - -

-

- - -

- - - - -

- -

- -

- - - - - - -

-

- -

- - -

-

- -

11


6. Covalent bonds are formed when atoms share electrons to become stable with filled outer shells.

a. Two pairs of electrons shared between atoms form a double covalent bond.

7. A polar molecule has a covalent bond in which the electrons are not shared equally.

8. A hydrogen bond forms from a positive H end of a polar molecule to the negative N or O end of another polar molecule.

12

Fig02.05

+ + + +

Hydrogen atom +

H

Hydrogen molecule

H2!

Hydrogen atom


-

-

- -

13

D. Molecules and Compounds:

1. A molecule is formed when two or more atoms combine.

2. If atoms of different elements combine, the molecule can also be called a compound.

a. Compounds always have a definite kind and

number of atoms.


14

E. Formulas: 1. A molecular formula represents the

numbers and types of atoms in a molecule. Ex: Glucose = C6H12O6

2. Various representations, called structural formulas, can be used to illustrate molecules.


15

F. Chemical Reactions: 1. A chemical reaction occurs as bonds are

formed or broken between atoms, ions, or molecules.

2. Those changed by the reaction are the reactants; those formed are the products.

3. Two or more atoms or molecules can be joined during synthesis.


16

4. Larger molecules can be broken into smaller ones in decomposition reactions.

5. Exchange reactions occur as parts of molecules trade places.

6. Reversible reactions are symbolized by using two arrows.

7. Catalysts influence the speed of chemical reactions.


17

G. Acids and Bases: 1. Substances that release ions in water

are called electrolytes. 2. Electrolytes that release hydrogen

ions in water are called acids. 3. Electrolytes that release ions that

combine with hydrogen ions in water are called bases.


18

4. The concentrations of H+ and OH- in

the body is very important to physiology.

5. pH represents the concentration of hydrogen ions [H+] in solution.


19

6. A pH of 7 indicates a neutral solution with equal numbers of hydrogen ions and hydroxyl (OH-) ions.

a. A pH of zero to less than 7 indicates the presence of more hydrogen ions, and thus the solution is more acidic; a pH greater than 7 to 14 indicates more hydroxyl ions, or a basic solution.

b. Between each whole number of the pH scale there is a tenfold difference in hydrogen ion concentration.


20

7. Buffers are chemicals that combine with excess acids or bases to help minimize pH changes in body fluids.

Fig02.11

OH- concentration increases!H+ concentration increases!

Acidic!H+!

Relative!amounts!of H+ (red)!and OH- (blue)!

Basic!OH-!

2.0!gastric!juice!

3.0!apple!juice!

4.2 !tomato!juice!

5.3!cabbage!

6.0!corn!

6.6!cow’s!milk!

7.0!distilled!water!

7.4!human!blood!

8.0!egg!white!

8.4!sodium!bicarbonate!

10.5!milk of!magnesia!

11.5!household!ammonia!

pH 0 1 2 3 4 5 6 7 8 9 10 1 1 12 13 14 Basic (alkaline) Neutral Acidic


21

Chemical Constituents of Cells:

A. Organic compounds contain both hydrogen and carbon.

B. All other compounds are considered inorganic and they usually dissolve in water and release ions, making them electrolytes.

1. Water a. Water is the most abundant

compound in living things and makes up two-thirds of the weight of adults.

Copyright© The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

22

b. Water is an important solvent so most metabolic reactions occur in water.

c. Water is important in transporting materials in the body since it is a major component of blood.

d. Water carries waste materials and can absorb and transport heat.


23

2. Oxygen a. Oxygen is needed to release energy

from nutrients and is used to drive the cell's metabolism.

3. Carbon Dioxide a. Carbon dioxide is released as a waste

product during energy-releasing metabolic reactions.


24

4. Salts a. Salts provide necessary

ions including sodium, chloride, potassium, calcium, magnesium, phosphate, carbonate, bicarbonate, and sulfate.

b. These electrolytes play important roles in many of the body's metabolic processes.


25

C. Organic Substances: 1. Carbohydrates

a. Carbohydrates provide energy for cellular activities and are composed of carbon, hydrogen, and oxygen.

b. Carbohydrates are made from monosaccharides (simple sugars); disaccharides are two monosaccharides joined together; complex carbohydrates (polysaccharides), such as starch, are built of many sugars.

c. Humans synthesize the polysaccharide glycogen.


Fig02.13

O O O O

O O O O O O O

O O O O O

O O O O O CH 2

O O O O

O

CH 2

O O

O

O O O O

O O O O

O O O O

O O O O O O O O O O

O

(a) Monosaccharide! (b) Disaccharide!

(c) Polysaccharide


O O

27

2. Lipids: a. Lipids are organic substances that

are insoluble in water and include fats, phospholipids, and steroids. b. Fats supply energy for cellular

function, and are built from glycerol and three fatty

acids. Fats have a smaller proportion of oxygen atoms than carbohydrates. Fatty acids with hydrogen at every

position along the carbon chain are saturated; those with one or more double bonds are called unsaturated fats.


28

c. Phospholipids contain glycerol, two fatty acids, and a phosphate group, and are important in cell structures.

d. Steroids are complex ring structures, and include cholesterol, which is used to synthesize the sex hormones.


Fig02.14

C O

O H C C H

H

H C H

H C H

H C H

H C H

H C H

H C H

H C H

H C H

H C H

H C H

H C H

H C H

H C H

H C H

H H

C O

O H C C H

H C H

H C H

H C H

H C H

H C H

H C H

H C H

H C H

H C H

H C H

H C H

H C H

H C H

H C H

H C H

H C H

H H

C

H

C

H

H C

H

H C

H

H C

H

H C

H

H C

H

H H

C O

O H C C H

H H C H

H C H

H C H

H C H H

H

C

Glycerol!portion!

Fatty acid!portions!


30

3. Proteins: a. Proteins have a great variety of

functions in the body--as structural materials, as energy sources, as certain hormones, as receptors on cell membranes, as antibodies, and as enzymes to catalyze metabolic reactions.


31

b. Proteins contain C, O, H, and nitrogen atoms; some also contain sulfur.

c. Building blocks of proteins are the amino acids, each of which

has a carboxyl group, an amino group and a side chain called the R group.


32

d. Proteins have complex shapes held together by hydrogen bonds.

e. Protein shapes (conformations), which determine how proteins function, can be altered (denatured) by pH,

temperature, radiation, or chemicals.


Fig02.18

Amino acids

(a) Primary structure—Each! oblong shape in this! polypeptide chain represents! an amino acid molecule. The! whole chain represents a! portion of a protein molecule.!

(b) Secondary structure—The! polypeptide chain of a protein! molecule is often either pleated ! or twisted to form a coil. Dotted ! lines represent hydrogen bonds.! R groups (see fig. 2.17)! are indicated in bold.!

(c) Tertiary structure—! The pleated and coiled ! polypeptide chain of a! protein molecule folds! into a unique three- ! dimensional structure.!

(d) Quaternary structure—Two or more! polypeptide chains may be connected! to form a single protein molecule.


Pleated!structure!

Three-dimensional!folding!

Coiled!structure!

C N N

N N H

H

H O C C C

O O

C C C H O C

C C N C N H O C C

H O C

C N N

N N H

H

H O C

O O

C C C H O C

H R H

R

H R

H R H

R

H R

H R H R

H R

H

H R

H

H R

H R H R

H H R R

H H R R

C H C H

C

C

N H

O H

C C C N

H C C C

N H O

C C

C H C

O

O O

N O

C C C H O

O N

34

4. Nucleic Acids: a. Nucleic acids form genes and take

part in protein synthesis. b. They contain carbon, hydrogen,

oxygen, nitrogen, and phosphorus, which are bound into building blocks

called nucleotides. c. Each nucleotide consists of a 5-

carbon sugar, a phosphate group, and one of many nitrogenous bases.


35

d. Nucleic acids are of two major types: DNA (with deoxyribose) and RNA (with ribose).

e. RNA (ribonucleic acid) functions in protein synthesis; DNA (deoxyribonucleic acid) stores the molecular code in genes.


36

Fig02.21

S P

S P

S P

S P

S P

S P

B

B

B

B

B

B

S P

S P

S P

S P

S P

S P

B

B

B

B

B

B

S

S

S

S

S

P

P

P

P

P

P

B

B

B

B

B

B

(a) RNA (b) DNA


S

Chemical Basis of Life - Damm's Science Page -...

Documents

Transcript of Chemical Basis of Life - Damm's Science Page -...