chapter 2 pt 2 - gavilan college

Copyright © 2009 Pearson Education, Inc..

Including the lecture Materials of

Gregory AhearnUniversity of North Florida

with amendments andadditions by

John Crocker

Chapter 2pt 2

Atoms, Molecules, and Life

Copyright © 2009 Pearson Education Inc.

2.3 Why Is Water So Important To Life?

Water interacts with many other molecules.• Oxygen released by plants during

photosynthesis comes from water.• Water is used by animals to digest food. • Water is produced in chemical reactions that

produce proteins, fats, and sugars.


Many molecules dissolve easily in water.• Water is an excellent solvent, capable of

dissolving a wide range of substances because of its positive and negative poles.

• example NaCl dropped into H2O• The positive end of H2O is attracted to Cl–. • The negative end of H2O is attracted to Na+. • These attractions tend to pull apart the

components of the original salt.


Water as a solvent

Fig. 2-8

Cl–

OCl–

Cl–

H

H

Na+

Na+

Na+


Water-insoluble molecules are hydrophobic• Water molecules repel and drive together

uncharged and nonpolar molecules like fats and oils

• The “clumping” of nonpolar molecules is called hydrophobic interaction


Water molecules tend to stick together.• Surface tension: water tends to resist being

broken• Cohesion: water molecules stick together

Fig. 2-9


Water Molecules Tend to Stick Together

Hydrogen bonding between water molecules produces high cohesion• Water cohesion explains how water

molecules can form a chain in delivering moisture to the top of a tree



Cohesion of water molecules along a surface produces surface tension• Fishing spiders and water striders rely on

surface tension to move across the surface of ponds



Water molecules stick to polar or charged surfaces in the property called adhesion• Adhesion helps water climb up the thin

tubes of plants to the leaves


Water can form ions.• Water dissociates to become H+ and OH–.• Acid solutions have more H+ (protons). • Alkaline solutions have more OH– (hydroxyl

ions).• A base is a substance that combines with H+,

reducing their numbers.• pH measures the relative amount of H+ and

OH– in a solution.


Acid, Basic, and Neutral Solutions

A small fraction of water molecules break apart into ions:

H2O OH- + H+


A water molecule is ionized.

Fig. 2-10

hydrogen ion(H+)

hydroxide ion(OH–)

water(H2O)

+(+)(–)

O

HH

O H

H



Solutions where H+ > OH- are acidic• e.g. Hydrochloric acid ionizes in water:

HCl H+ + Cl-

• Lemon juice and vinegar are naturally produced acids



Solutions where OH- > H+ are basic• e.g. Sodium hydroxide ionizes in water:

NaOH Na+ + OH-

• Baking soda, chlorine bleach, and ammonia are basic



The degree of acidity of a solution is measured using the pH scale• pHs 0-6 are acidic (H+ > OH-)• pH 7 is neutral (H+ = OH-)• pH 8-14 is basic (OH- > H+)


Buffers Maintain Constant pH

• A buffer is a compound that accepts or releases H+ in response to pH change

• The bicarbonate buffer found in our bloodstream prevents pH change



• If the blood becomes too acidic, bicarbonate accepts (and absorbs) H+ to make carbonic acid

HCO3- + H+ H2CO3

bicarbonate hydrogen ion carbonic acid



• If the blood becomes too basic, carbonic acid liberates hydrogen ions to combine with OH- to form water

H2CO3 + OH- HCO3- + H2O

carbonic acid hydroxide ion bicarbonate water


Water stabilizes temperature• Temperature reflects the speed of molecular

motion• It requires 1 calorie of energy to raise the

temperature of 1g of water 1oC (specific heat), so it heats up very slowly

• Because it heats up very slowly water moderates the effect of temperature change

• Very low or very high temperatures may damage enzymes or slow down important chemical reactions


Water Stabilizes Temperature

Water requires a lot of energy to turn from liquid into a gas (heat of vaporization)• Evaporating water uses up heat from its

surroundings, cooling the nearby environment (as occurs during sweating)



• Because the human body is mostly water, a sunbather can absorb a lot of heat energy without sending her/his body temperature soaring



Water requires a lot of energy to be withdrawn in order to freeze (heat of fusion)

Water freezes more slowly than other liquids


Water Forms an Unusual Solid: Ice

• Most substances become denser when they solidify from a liquid

• Water molecules spread apart slightly during the freezing process

• Because of this ice is less dense than liquid water


Water Forms an Unusual Solid: Ice• Ice floats in liquid water• Ponds and lakes freeze from the top

down and never freeze completely to the bottom


Frozen water floats (left) and frozen benzene sinks (right)

Figure 2.13x2


- Lower water is protected by the surface layer of ice.

–Life can survive in cold water underneath ice.

–Spring thaw pushes nutrient-rich bottom water to surface


Like no other common substance on earth, water naturally exists in all three physical states:

Figure 2.10B

• solid

• liquid

• gas


Figure 2.10Bx


Organic refers to molecules containing a carbon skeleton

Inorganic refers to carbon dioxide and all molecules without carbon

Organic vs. Inorganic in Chemistry


2.4 Why Is Carbon So Important To Life?

Carbon can combine with other atoms in many ways to form a huge number of different molecules.

Carbon has four electrons in its outermost shell, leaving room for four more electrons from other atoms (4 covalent bonds).

Carbon atoms are versatile and can form up to four bonds (single, double, or triple) and rings.


Arrangement of atoms determines molecular shape.Shape determines function of molecules

Structuralformula

Ball-and-stickmodel

Space-fillingmodel

Methane

The 4 single bonds of carbon point to the corners of a tetrahedron.


Butane, ball and stick model

Figure 3.1x3


Cyclohexane, ball and stick model

Figure 3.1x5


The great variety of substances found in nature is constructed from a limited pool of atoms.

Organic molecules have a carbon skeleton and some hydrogen atoms.

Much of the diversity of organic molecules is due to the presence of functional groups.

Functional groups in organic molecules confer chemical reactivity and other characteristics


groups of atoms that participate in chemical reactions

determine the chemical properties of molecules

Examples: acidity, solubility

Functional (R) Groups

-OH -COOH -NH2 -CH3


What affects solubility in water?

Molecules with +/- charge are usually hydrophilic or “water-loving”

Molecules with no charge and non-polar are usually hydrophobic and not soluble in water


2.5 How Are Biological Molecules Joined Together Or Broken Apart? Biomolecules are polymers (chains) of

subunits called monomers A huge number of different polymers can be

made from a small number of monomers Biomolecules Are Joined Through

Dehydration and Broken by Hydrolysis


Organic Molecule Synthesis

Monomers are joined together through dehydration synthesis An H and an OH are removed, resulting in the

loss of a water molecule (H2O)



Polymers are broken apart through hydrolysis (“water cutting”) Water is broken into H and OH and used to

break the bond between monomers



All biological molecules fall into one of four categoriesCarbohydratesLipidsProteinsNucleic Acids


2.6 What Are Carbohydrates?

Composition:C, H, and O in the ratio of 1:2:1

Construction: Simple or single sugars are

monosaccharides Two linked monosaccharides are

disaccharides Long chains of monosaccharides are

polysaccharides


Monosaccharides

Basic monosaccharide structure Backbone of 3-7 carbon atoms Many –OH and –H functional groups Usually found in a ring form in cells

Simple sugars provide important energy sources for organisms.

Most small carbs are water-soluble due to the polar OH functional groups


A simple sugar

Fig. 2-13

Glucose, linear form Glucose, ring form(a) (b)H

H

CH2OH

HO

OH

OH

O

H H

OH H

2356 4 1

H H H H

H

H

H

H

H H

H

H

O OOOO

O

CCCCCC


Monosaccharides

Example monosaccharides continued Fructose (found in corn syrup and fruits) Galactose (found in lactose) Ribose and deoxyribose (found in RNA and

DNA)


Most small carbs are water-soluble due to the polar OH functional groups


Disaccharides

Disaccharides are two-part sugars Sucrose (table sugar) = glucose + fructose Lactose (milk sugar) = glucose + galactose Maltose (malt sugar)= glucose + glucose


Manufacture of a disaccharide

Fig. 2-14

glucose fructose sucrose

dehydrationsynthesis

OHO

OHOCH2

OH

HO

CH2OH

H H

OH

H OH

H

H

O HO

OCH2OH

H H

OH

H OH

H

HH

H

H

HOCH2OHH

HOCH2 H

H

H

HOCH2OH

O

OH

O

+

OHH


Polysaccharides

Monosaccharides are linked together to form chains (polysaccharides)

Polysaccharides are used for energy storage and structural components


Polysaccharides

Storage polysaccharides Starch (polymer of glucose)

Formed in roots and seeds as a form of glucose storage

Glycogen (polymer of glucose)Found in liver and muscles


Polysaccharides

Structural polysaccharides Cellulose (polymer of glucose) Found in the cell walls of plants

Indigestible for most animals due to orientation of bonds between glucoses


Polysaccharides

Structural polysaccharides continued Chitin (polymer of modified glucose units)

Found in the outer coverings of insects, crabs, and spiders

Found in the cell walls of many fungi

chapter 2 pt 2 - gavilan college

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