Chemical Basis of Life - Mt. Hood Community Collegestream.mhcc.edu/videos/thatchev/Bi100_ch2.pdf ·...
Transcript of Chemical Basis of Life - Mt. Hood Community Collegestream.mhcc.edu/videos/thatchev/Bi100_ch2.pdf ·...
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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
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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.