principles of human anatomy and physiology, 11e1 chapter 2 the chemical level of organization...

Principles of Human Anatomy and Physiology, 11e 1

Chapter 2

The Chemical Level of Organization

Lecture Outline


Basic Principles

• Chemistry is the science of the structure and interactions of matter.

• Matter is anything that occupies space and has mass.– Mass is the amount of matter a substance contains– weight is the force of gravity acting on a mass.


HOW MATTER IS ORGANIZED

• Chemical Elements– Elements are given letter abbreviations called chemical

symbols.• Oxygen (O), carbon (C), hydrogen (H), and nitrogen

(N) make up 96% of body weight.

– Trace elements are present in tiny amounts

• copper, tin, selenium & zinc


Structure of Atoms

• Atoms are the smallest units of matter that retain the properties of an element

• 3 types of subatomic particles

• Nucleus: protons (p+) & neutrons (neutral charge)

• Electrons (e-) surround the nucleus as a cloud


Electron Shells

• Most likely region of the electroncloud in which to find electrons

• Each electron shell can hold onlya limited number of electrons

• Number of electrons = number of protons• Each atom is electrically neutral; charge = 0


Atomic Number & Mass Number

• Atomic number is number of protons in the nucleus. .• Mass number is the sum of its protons and neutrons.


Atomic Number and Mass Number

• The mass number of an atom

– Isotopes

• Isotopes– Stable isotopes do not change their nuclear structure

over time.– radioactive isotopes


Ions, Molecules, Free Radicals, and Compounds

• Ions• Molecules (Fig 2.3a)


CHEMICAL BONDS

• The atoms of a molecule are held together by forces of attraction called chemical bonds.

• The likelihood that an atom will form a chemical bond with another atom depends on the number of electrons in its outermost shell, also called the valence shell.


CHEMICAL BONDS

• An atom with a valence shell holding eight electrons (2 electrons for hydrogen and neon) is chemically stable, which means it is unlikely to form chemical bonds with other atoms.

• To achieve stability, atoms that do not have eight electrons in their valence shell (or 2 in the case of H and He) tend to empty their valence shell or fill it to the maximum extent.

• octet rule


Ionic Bonds

• When an atom loses or gains a valence electron, ions are formed (Figure 2.4a).

– Opposites attract

– Cations

– Anions


Ionic Bonds

• When this force of attraction holds ions having opposite charges together, an ionic bond results.– Sodium chloride is formed by ionic bonds (Figure 2.4)

• In general, ionic compounds exist as solids but some may dissociate into positive and negative ions in solution. Such a compound is called an electrolyte.

• Table 2.2 lists the names and symbols of the most common ions and ionic compounds in the body.


The Ionic Bond in Sodium Chloride

• Sodium loses an electron to become Na+ (cation)

• Chlorine gains an electron to become Cl- (anion)

• Na+ and Cl- are attracted to each other to form the compound sodium chloride (NaCl) -- table salt

• Ionic compounds generally exist as solids


Covalent Bonds

• Atoms share electrons to form covalent bonds

• Electrons spend most of the time between the 2 atomic nuclei

• Polar covalent bonds


Polar Covalent Bonds

• Unequal sharing of electrons between atoms. (Figure 2.6).

• In a water molecule, oxygen attracts the hydrogen electrons more strongly– Oxygen has greater electronegativity


Hydrogen Bonds

• Weak


CHEMICAL REACTIONS

• A chemical reaction occurs when new bonds are formed or old bonds break between atoms (Figure 2.8).

• Law of conservation of mass.

• Metabolism


Forms of Energy and Chemical Reactions

• Energy• Kinetic energy

– Temperature is an indirect measure of molecular motion.• Potential energy

– Chemical energy is a form of potential energy stored in the bonds of compounds or molecules.

• Law of conservation of energy


Energy Transfer in Chemical Reactions

• Reactions in living systems usually involve both kinds of reactions occurring together.– exergonic reactions release energy– endergonic reactions absorb energy

• You will learn of many examples in human metabolism that involve coupled exergonic and endergonic reactions; the energy released from one reaction will drive the other.– Glucose breakdown releases energy, which is

used to build ATP molecules (that store the energy for later use in other reactions.)


Activation Energy• Activation energy is the

collision energy needed to break bonds & begin areaction.

• Increases in concentration &

temperature, increase the

probability of collision– more particles are in a given space when the concentration

is higher– particles move more rapidly when temperature is raised


Effectiveness of Catalysts

• Catalysts speed up chemical reactions by lowering the activation energy.


Catalysts or Enzymes

Example:

• Normal body temperatures and concentrations are low enough that many chemical reactions are effectively blocked by the activation energy barrier.– Lactose typically reacts very slowly with water to break down

into two simple sugars called glucose and galactose.– Lactase, an enzyme (catalyst) orients the colliding particles

(lactose and water) properly so that they touch at the spots that make the reaction happen.

– Thousands of lactose/water reactions may be catalyzed by one lactase enzyme.

– Without lactase, the lactose will remain undigested in the intestines and often causes diarrhea and cramping.


Synthesis Reactions--Anabolism

• Two or more atoms, ions or molecules combine to form new & larger molecules

• All the synthesis reactions in the body together are called anabolism

• Usually are endergonic because they absorb more energy than they release

• Example– combining amino acids to form a protein molecule


Decomposition Reactions--Catabolism

• Large molecules are split into smaller atoms, ions or molecules

• All decomposition reactions occurring together in the body are known as catabolism

• Usually are exergonic since they release more energy than they absorb


Reversible Reactions

• Chemical reactions can be reversible.– Reactants can become products or products can revert to

the original reactants


Oxidation-Reduction Reactions

• Oxidation is the loss of electrons from a molecule

• Reduction is the gain of electrons by a molecule

• In the body, oxidation-reduction reactions are coupled & occur simultaneously


INORGANIC COMPOUNDS AND SOLUTIONS

• Inorganic compounds

• Organic compounds


Water in Chemical Reactions

• Water is the ideal medium for most chemical reactions in the body and participates as a reactant or product in certain reactions.

• Hydrolysis

• Dehydration synthesis


Water as a Solvent• Most versatile solvent known

– polar covalent bonds (hydrophilic versus hydrophobic)

– its shape allows each watermolecule to interact with 4 ormore neighboring ions/molecules

• oxygen attracts sodium• hydrogen attracts chloride• sodium & chloride separate as ionic

bonds are broken• hydration spheres surround each ion and

decrease possibility of bonds being reformed

• Water dissolves or suspends many substances


High Heat Capacity of Water

• Water has a high heat capacity.

• Heat of vaporization is also high


Cohesion of Water Molecules

• Hydrogen bonds link neighboring water molecules giving water cohesion

• Creates high surface tension– difficult to break the surface of liquid if molecules

are more attracted to each other than to surrounding air molecules

– respiratory problem causes by water’s cohesive property

• air sacs of lungs are more difficult to inflate


Water as a Lubricant

• Water is a major part of mucus and other lubricating fluids.– mucus in respiratory and digestive systems– synovial fluid in joints– serous fluids in chest and abdominal cavities

• organs slide past one another • It is found wherever friction needs to be reduced or

eliminated


Inorganic Acids, Bases & Salts. Acids, bases and salts always dissociate into ions if they are

dissolved in water (Fig 2.12)– acids dissociate into H+

and one or more anions– bases dissociate into OH-

and one or more cations– salts dissociate into anions

and cations, none of whichare either H+ or OH-

• Acid & bases react in the body to form salts

– Electrolytes are important salts in the body that carry electric current (in nerve or muscle)


Concept of pH

• pH scale runs from 0 to 14 (concentration of H+ in moles/liter)• pH of 7 is neutral

(distilled water -- concentration of OH- and H+ are equal)• pH below 7 is acidic ([H+] > [OH-]).• pH above 7 is alkaline ([H+] < [OH-]).


Acid-Base Balance: The Concept of pH

• Biochemical reactions are very sensitive to even small changes in acidity or alkalinity.– pH of blood is 7.35 to 7.45


Carbon and Its Functional Groups

• The carbon that organic compounds always contain has several properties that make it particularly useful to living organisms.


• Many functional groups can attach to carbon skeleton– esters, amino, carboxyl, phosphate groups (Table 2.5)

• Very large molecules are called macromolecules (or “polymers” if all the monomer subunits are similar)

• Isomers have the same molecular formulas but different structures (glucose & fructose are both C6H12O6)

• STRUCTURALFORMULA OFGLUCOSE (Fig 2.14)

Carbon & Its Functional Groups


Carbohydrates

• formed from C, H, and O– ratio of one carbon atom for each water molecule

• glucose is 6 carbon atoms and 6 water molecules (H20)• 2-3 % of total body weight

– glycogen is stored in liver and muscle tissue– sugar building blocks of DNA & RNA

(deoxyribose & ribose sugars)• Only plants produce starches or

cellulose for energy storage


Monosaccharides and Disaccharides: Sugars

• Monosaccharides – Humans absorb only 3 simple sugars without further

digestion in our small intestine• glucose found syrup or honey• fructose found in fruit• galactose found in dairy products

• Disaccharides are formed from two monosaccharides by dehydration synthesis; they can be split back into simple sugars by hydrolysis (Figure 2.15). Glucose and fructose combine, for example, to produce sucrose.


Disaccharides

• Combining 2 monosaccharides by dehydration synthesis releases a water molecule.– sucrose = glucose & fructose– maltose = glucose & glucose– lactose = glucose & galactose (lactose intolerance)


Polysaccharides

• Polysaccharides are the largest carbohydrates and may contain hundreds of monosaccharides.

• The principal polysaccharide in the human body is glycogen, which is stored in the liver or skeletal muscles. (Figure 2.16)– When blood sugar level drops, the liver hydrolyzes

glycogen to yield glucose which is released from the liver into the blood


Lipids

• Lipids, like carbohydrates, contain carbon, hydrogen, and oxygen; but unlike carbohydrates, they do not have a 2:1 ratio of hydrogen to oxygen.

• They have few polar covalent bonds – hydrophobic– mostly insoluble in polar solvents such as water– combines with proteins (lipoproteins) for transport in

blood


Lipids = fats

• Formed from C, H and O– fats– phospholipids– steroids– eicosanoids– lipoproteins – some vitamins

• 18-25% of body weight


Triglycerides

• Triglycerides – At room temperature, triglycerides may be either solid

(fats) or liquid (oils).– Excess dietary carbohydrates, proteins, fats, and oils will

be deposited in adipose tissue as triglycerides.– Neutral fats composed of a single 3-carbon glycerol

molecule and 3 fatty acid molecules (Figure 2.17).– 9 calories/gram compared to 4 for proteins &

carbohydrates


Triglycerides

• 3 fatty acids & one glycerol molecule• Fatty acids attached by dehydration systhesis


Chemical Nature of Phospholipids

head tails


Phospholipids

• Phospholipids are important membrane components.• They are amphipathic (Figure 2.18).

• a phosphate group (PO4-3) & glycerol molecule• forms hydrogen bonds with water

• interact only with lipids


Steroids

• Steroids have four rings of carbon atoms (Figure 2.19a).• Steroids include

– sex hormone– bile salts– cholesterol, with cholesterol serving as an important

component of cell membranes and as starting material for synthesizing other steroids.


Four Ring Structure of Steroids


Other Lipids

• Eicosanoids include prostaglandins and leukotrienes.– Lipid type derived from a fatty acid called arachidonic acid– prostaglandins = wide variety of functions

• modify responses to hormones• contribute to inflammatory response• prevent stomach ulcers• dilate airways• regulate body temperature• influence formation of blood clots

– leukotrienes = allergy & inflammatory responses

• Body lipids also include fatty acids; fat-soluble vitamins such as beta-carotenes, vitamins D, E, and K; and lipoproteins.


Proteins

• Proteins give structure to the body, regulate processes, provide protection, help muscles to contract, transport substances, and serve as enzymes (Table 2.8).

• Contain carbon, hydrogen, oxygen, and nitrogen• 12-18% of body weight


Proteins

• Constructed from combinations of 20 amino acids.


Amino Acid Structure

• Central carbon atom

• Amino group (NH2)

• Carboxyl group (COOH)• Side chains (R groups) vary

between amino acids


Levels of Structural Organization

• Levels of structural organization include – primary– secondary– tertiary– quaternary (Figure 2.22)

• Importance of shape• Denaturation


Levels of Structural

Organization

• Primary is unique sequence of amino acids• Secondary is alpha helix or pleated sheet folding• Tertiary is 3-dimensional shape of polypeptide chain


Levels of Structural Organization

• Primary…• Secondary …• Tertiary…• Quaternary is relationship of

multiple polypeptide chains


Protein Denaturation

• The function of a protein depends on its ability to bind to another molecule

• Hostile environments such as heat, acid or salts will change a protein’s 3-D shape and destroy its ability to function– raw egg white when cooked is vastly different


Enzymes

• Catalysts in living cells are called enzymes.• Enzymes are highly specific in terms of the “substrate” with

which they react.

• Enzymes speed up chemical reactions by increasing frequency of collisions, lowering the activation energy and properly orienting the colliding molecules (Figure 2.23).


Enzyme Functionality

• Highly specific• Very efficient• Under nuclear control


Nucleic Acids: Deoxyribonucleic Acid (DNA) and Ribonucleic Acid (RNA)

• Nucleic acids are huge organic molecules that contain carbon, hydrogen, oxygen, nitrogen, and phosphorus.– Deoxyribonucleic acid (DNA)

– Ribonucleic acid (RNA)

– Nucleotides (Figures 2.24a, b).


DNA Structure

• Contains C, H, O, N and phosphorus.

• A molecule of DNA is a chain of nucleotides.

• A nucleotide includes:– nitrogenous base (A-G-T-C)– pentose sugar– phosphate group


DNA Fingerprinting

• Used to identify criminal, victim or a child’s parents– need only strand of hair, drop of semen or spot of blood

• Certain DNA segments are repeated several times– unique from person to person


RNA Structure

• Differs from DNA– single stranded– ribose sugar not deoxyribose sugar– uracil nitrogenous base replaces thymine

• Types of RNA within the cell, each with a specific function– messenger RNA– ribosomal RNA– transfer RNA


Adenosine Triphosphate (ATP)

• Temporary molecular storage of energy as it is being transferred from exergonic catabolic reactions to cellular activities

• Consists of 3 phosphategroups attached toadenine & 5-carbonsugar (ribose)

• (Figure 2.25).


Formation & Usage of ATP

• Hydrolysis of ATP

• Synthesis of ATP

– energy from 1 glucose molecule creates 36 molecules of ATP

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