Unit 3

The Chemistry of Living Things

(“Biochemistry”)

1

Slide 2.1

Atoms

• “atom” means “can’t be cut” – coined by Greeks 2500 years ago.

• The atom is the smallest functional unit of an element.

• Atoms are made of: (see next slide)

Atoms are made of

• Protons: positive charge, in nucleus, are heavy, “p+”

• Neutrons: no charge, in nucleus, are heavy, “n0”

• Electrons: negative charge, outside nucleus “electron cloud”, very light (1/1840 of a proton or neutron), “e-”

Only copy red diagram in upper left. No caption needed.

Charges in an Atom

• The + charge on a proton is equal to the - charge on an electron.

• Atoms are neutral (have no overall charge)• Therefore, the # of protons = # electrons in an

atom.

Slide 2.2

Atomic number– determines the identity of the atom. – It tells us the number of protons in the atom. – It also tells us the number of electrons (b/c an atom is neutral in charge.)

– Ex: atomic number of carbon, C = 6– Question: how many protons? How many electrons? How many neutrons?

6

ELECTRONS

• Electrons are in constant motion around the nucleus.

• e-s in the highest occupied level are called valence e-s.

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Slide 2.3.

BONDING: • (Definition) atoms combining to form

molecules

• It occurs when valence electrons rearrange themselves– There are 2 ways to get the e-’s you need.

Sharing electrons (COVALENT BONDING)Gain/lose electrons (IONIC BONDING)

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COVALENT BONDS

Formation of SALT, NaCl

IONIC BONDS

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The Most Common Elements in Living Things

• Carbon• Hydrogen• Oxygen• Nitrogen• Phosphorus• Sulfur

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Elements of Living Organisms(DON’T COPY)

21Table 2.2Slide 2.5

Life Depends on Water• Water molecules are polar (they have slight

electrical charges, like little magnets)o Biological solvent-ex: K+ for muscle contractiono Hydrogen bonds make it expand when frozen

(animals in lakes can survive winter)oWater is liquid at body temperatureoWater can absorb and hold heat energyoWater helps regulate body temperature

22Slide 2.6

IMPORTANT FACTS ABOUT WATER

Properties of Water (b/c of hydrogen bonding)

1. Cohesion- attraction between molecules of the same substance. (water-water attraction)

Examples– Drops of water– Surface tension (Fig 2-8 p 41 of text)

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Properties of Water (b/c of hydrogen bonding)

2. Adhesion-attraction btwn molecules of different substances (water-other substance attraction)

Examples– Capillary action-water drawn up a tube– “Meniscus”= the curve shape water has when in a

tube

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Water forms Important Mixtures• Solutions

• (DEFINITION) when a substance dissolves in water

• Ex: Salt-water.

• NaCl is pulled apart into IONS by the water.

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Water forms Important Mixtures(cont.)

• Suspensions

• Material does NOT dissolve, but separates into small pieces that remain floating

• Ex: blood w/red blood cells

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ACIDS & BASES

• Water can form ions too!

• H2O H+ + OH-

• When by itself, water makes equal amounts of H+ + OH-

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ACIDS & BASES (cont.)

• Some things cause water to release many H+ ions. These are acids.

• Some things cause water to release many OH- ions. These are bases.

• pH is a measure of the H+ concentration in a solution.

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Figure 2.10Slide 2.10

The pH Scale

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BUFFERS

(DON’T WRITE THIS) Remember homeostasis?

WRITE THIS:• All living things need to maintain a stable pH.– Humans need a pH between 6.5 & 7.5– Otherwise, chemical reactions get messed up.

• They do this through buffers: weak acids or bases that prevent sharp, sudden changes in pH– Ex: ______ for an upset stomach. It absorbs extra H+ ions.

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(Section 3): Carbon “Organic” Compounds

• Why is carbon so special?• Carbon has 4 valence electrons, • Allows it to bond to many other things at

once.

• Pix of organic compounds important to living things

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Section 3: Carbon (Organic) Compounds of Living Organisms• Is 18% of human body by weight• Forms four covalent bonds• Can form single or double bonds• Can build micro- or macromolecules (big

chains)

Slide 2.11

Carbon is the building block of living things:

Figure 2.12Slide 2.12

Carbon Can Bond in Many WaysDon’t Copy Diagrams. Leave room for 2-3 sentences.

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Figure 2.14Slide 2.15

1: Carbohydrates MADE OF: C, H, O

(don’t copy diagrams)

FUNCTION: energy & structure

1. Sugars: short chains of – Monosaccharides- 1 sugar ring

Ex: glucose, galactose– Disaccharides-2 attached sugar rings

Ex: sucrose, fructose, lactose

2. Polysaccharides: thousands of monosaccharides joined in chains and branches– Starch: made in plants; stores energy– Glycogen: made in animals; stores energy– Cellulose: undigestible polysaccharide made in plants

for structural support

Slide 2.16

Types of Carbohydrates

Lipids: Insoluble in Water

TYPES OF LIPIDS• Triglycerides: energy storage molecules– Fatty acids: saturated and unsaturated

• Phospholipids: cell membranes

• Steroids: carbon-based ring structures– Cholesterol: used in making estrogen and

testosterone36Slide 2.17

2: LipidsMade of: C,H,(O)

Function: energy storage, waterproof coverings

Proteins: Complex Structures Contructed of Amino Acids

• Made of: C,H, O, N• Function: building materials, enzymes• Structure– Made of monomers called amino acids – The instructions for building proteins are in DNA

Slide 2.18

Proteins

Copy only bottom diagram & leave room for examples

Don’t copy, but Leave room for examples

Hemoglobin (4 protein strands held together)

Don’t copy, but Leave room for examples

Enzyme FunctionEnzymes:– are proteins– function as catalysts (something that speeds up

chem rxns)– facilitate chemical reactions

• Lower the activation energy (energy required to start a rxn.)

The function of an enzyme is dependent on:– temperature – pH – ion concentration– presence of inhibitors

41Slide 2.19

Enzyme Action

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Structure and Function of Nucleic Acids• Functions

– Store genetic information– Provide information used in making proteins

• Structure– Nucleotides consist of a phosphate group, a sugar,

and a nitrogenous base– DNA structure is a double helix: two associated

strands of nucleic acids– RNA is a single-stranded molecule

43Slide 2.20

Structure of DNA and RNA• DNA: double-stranded– Sugar: deoxyribose– Nitrogenous bases: adenine, thymine, cytosine,

guanine– Pairing: adenine-thymine and cytosine-guanine

• RNA: single-stranded– Sugar: ribose– Nitrogenous bases: adenine, uracil, cytosine,

guanine– Pairing: adenine-uracil, cytosine-guanine

44Slide 2.21

Nucleic Acids

.

Figure 2.25Slide 2.22Copyright © 2001 Benjamin Cummings, an imprint of Addison Wesley Longman, Inc.

Structure and Function of Adenosine Triphosphate (ATP)

Copy diagram on right,