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Bi100 Chapter 2

Chemical Basis of Life

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.

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.

B

Yeah, I’m made of elements.

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Structure of Matter:

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.

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.

-

-

+ +

Atomic Structure: 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 numbers of neutrons are isotopes of an element.

-

-

+ +

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

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

the nucleus.

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

+ 0 0 +

+ 0

0 + +

0 0 +

- -

-

-

-

-

Fig02.02

Atomic Structure

3. 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.

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

+ + +

+ +

-

-

+ + + -

-

-

-

Atomic Structure:

5. Covalent bonds are formed when atoms share electrons

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

+ - + -

-

-

+ +

+

-

-

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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.

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.

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.

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

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Acids and Bases:

1. Substances that release ions in water are called electrolytes.

2. Electrolytes that release hydrogen ions (H+) in water are called acids.

3. Electrolytes that release hydroxide (OH-) ions are called bases.

Acids and Bases:

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.

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!cowʼs!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

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Acids and Bases:

•  A pH of 7 indicates a neutral solution with equal numbers of hydrogen ions and hydroxyl (OH-) ions. – a. a solution with a pH of 0-7 is acidic and

has more H+ ions than OH- – b. a solution with a pH of 7-14 is basic and

has more OH- ions than H+. •  *note that the pH scale is an exponential scale (that

means small changes in pH represent large numbers in concentration)

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Acids and Bases: 7. Buffers are chemicals that combine with excess

acids or bases to help minimize pH changes in body fluids.

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. – Water:

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

Organic Substances:

•  Carbohydrates – Carbohydrates provide energy for cellular

activities and are composed of carbon, hydrogen, and oxygen.

– Carbohydrates are made from monosaccharides (single sugars);

– disaccharides are two monosaccharides joined together;

– polysaccharides, such as starch, are built of many sugars.

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Organic Substances:

•  Lipids: – Lipids are organic substances that are

insoluble in water and include fats, phospholipids, and steroids.

Organic Substances:

•  Proteins: – 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 facilitate (or catalyze) metabolic reactions.

Organic Substances

•  Proteins contain C, O, H, and N atoms; some also contain S.

•  Building blocks of proteins are the amino acids

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Organic Substances

•  Proteins have complex shapes or conformations: –  primary structure

•  order of amino acids

–  secondary structure •  pleats or helices

–  tertiary structure •  complex 3-D folding

–  quaternary structure •  multiple proteins interacting

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.

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

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

1o

2o

3o

4o

Organic Substances:

Nucleic Acids: a. Nucleic acids form DNA and RNA.

b. Nucleic acids are of two major types: DNA (with deoxyribose) and RNA (with ribose). c. RNA (ribonucleic acid) functions in protein synthesis; DNA (deoxyribonucleic acid) stores the molecular code in genes.