Biochemistry forAnatomy & Physiology Students

BIO 351Our Lady of Holy Cross College

Elements

All matter is composed of elements – unique substances that cannot be broken down into simpler substances

Four elements – carbon, oxygen, hydrogen, and nitrogen – make up 96% of our body weight

Each element is composed identical particles or building blocks called atoms

Atoms

Periodic Table of Elements

Elements Different elements are composed of different #s of

protons, neutrons and electrons, and that is what determines the unique properties of each element

Atomic number = # of protons. It determines the identity (name) of the element

Atomic mass = sum of the masses of all of an element’s protons and neutrons

Isotopes of an element have the same # of protons but different #s of neutrons

Radioactive isotopes are unstable and disintegrate spontaneously. Half-life is the amount of time for half of the atoms to disintegrate

Atomic weight = average of the mass #s of all isotopes of an element, taking into account the relative abundance of the isotopes

Elements in the Human Body 26 of the elements are normally found in

the body Of these 11 are listed as major elements

because they are present in large amounts 15 are called trace elements because they

are only present in tiny quantities H, O, N, and C are the most common

elements in the body. H forms 1 bond, O forms 2 bonds, N forms 3 bonds, and C forms 4 bonds

Subatomic Particles Proton is positively charged Neutron has no electrical charge Protons and neutrons have approximately

the same mass and are located in the nucleus of the atom

Electron has a negative charge and has essentially no mass

Atoms are electrically neutral. The positive and negative charges (on protons and electrons) are balanced

Atomic Model Planetary model – older model, electrons

orbit nucleus, are depicted in shells. Each shell represents an energy level.

Orbital model – more modern model, shows an electron cloud which depicts probability of finding an electron or electrons in a particular region. Each electron shell contains one or more orbitals.

Molecules Two or more atoms may combine to

form a distinctive type of particle called a molecule

If atoms of the same element combine, they produce molecules of that element

2 or more different elements can combine to form molecules of a compound.

Exs: The chemical formula for water is H2O. (Two atoms of hydrogen and one atom of oxygen form each molecule.) CO2 is carbon dioxide.

Chemical Bonds Reactivity of an atom is related to the # of

electrons in outermost shell Shell 1 can hold a maximum of 2 electrons. Octet rule – all other shells hold a maximum

of 8 electrons. When the outermost shell of an atom is full,

the atom is stable, i.e. chemically inert 3 types of bonds: ionic, covalent, hydrogen

Ionic Bonds

Covalent Bonds

Water--H2O Water makes up 60—80% of the volume of most

living cells. It is a polar molecule, meaning that it has unequal

electron bond sharing. Water is the universal solvent. (Substance

dissolved in a solvent is called a solute.) Hydrogen bonds form between water molecules

as well as between other strongly polar molecules. Hydrogen bonds are responsible for the high

surface tension of water and are responsible for the three-dimensional

shape of proteins and DNA.

Water molecules showing the hydrogen bonding that exists between negatively charged oxygen and positively charged hydrogen.

Acids and Bases Electrolytes are substances that dissociate (break up) in

solution to form charged particles called ions. These include acids, bases, and salts.

Acids dissociate in water to yield hydrogen ions (which is a bare proton) and anions (negatively charged particles). They are proton donors

Bases absorb hydrogen ions. (They are proton acceptors.)

The relative concentration of hydrogen ions is measured in concentration units called pH units.

The pH scale extends from 0—14; a pH of 7 is neutral; a pH below 7 is acidic; a pH above 7 is basic or alkaline.

Acids and bases neutralize each other. When mixed together they form a salt and water.

Buffers are substances which resist large fluctuations in pH that would damage living tissues.

What is the pH range of urine?

Of human blood?

Of saliva?

Of gastric juice?

Why is the pH of gastric juice so acidic?

Why is the pH of distilled water 7?

Organic Compounds Carbon containing compounds that

have C – C or C – H bonds The 4 kinds of organic compounds we willstudy are:

Carbohydrates Lipids Proteins Nucleic Acids

Proteins, nucleic acids, polysaccharides andlipids are the most abundant biomolecules

Carbohydrates This group of molecules includes sugars and

starches. All carbohydrates contain carbon, hydrogen,

and oxygen in a 1:2:1 ratio. Represent 1—2% of cell mass. Major function: to provide energy for cellular

work. Monosaccharides: simple sugars with 5 or 6

carbons in a single ring structure. Examples are glucose (blood sugar), fructose (fruit sugar), and galactose.

Examples of Monosaccharides

Glucose, fructose, and galactose have the same chemical formulas (therefore they are isomers), but differ in their structure (3 dimensional arrangement of their atoms). They all have 6 carbons, so they are called hexoses.

Deoxyribose and ribose are both 5 carbon sugars. They are called pentoses.

Carbohydrates, continued Disaccharides are formed when two

monosaccharides are joined in a chemical reaction called dehydration synthesis.

Biologically important disaccharides are lactose (milk sugar), sucrose (table sugar), and maltose.

Polysaccharides are long chains of monosaccharides linked together by dehydration synthesis.

Examples are glycogen (animal starch) and cellulose. Where is glycogen found in the body?

Glycogen is stored in the liver and in skeletal muscle tissue.

Sucrose: a disaccharide

Lactose: milk sugar

The top reaction is the one that you will model in the laboratory. Notice that a water molecule is lost when the two monosaccharides are combined in the synthesis reaction.

Note the branching in the polysaccharide chain shown above.

Plant starch, a digestible polysaccharide

The cellulose of plant cell walls is indigestible.

Hydrolysis Larger molecules are broken down

into smaller molecules in a process called hydrolysis, literally to “break with water.”

When this occurs in the digestive tract and is catalyzed by enzymes we call it chemical digestion.

Lipids Insoluble in water but dissolve readily in

nonpolar solvents. Contain carbon, hydrogen, and oxygen, but

much less oxygen than carbohydrates. Some lipids, called phospholipids, contain P.

Types of lipids: neutral fats, phospholipids, and steroids.

Neutral fats are also called triglycerides and are called fats when solid at room temperature and oils when liquid at room temperature. They are used for energy storage and pad and protect organs.

Triglycerides are made up of glycerol and three fatty acids. If the chemical bonds between the carbon chains in the fatty acids are single, the fat is saturated. They are solid at room temp. If at least one double bond is present, the fat is unsaturated. They tend to be liquid at room temp.

Functions and Locations of Neutral Fats Serve as energy reserves. Protect the body from temperature

extremes. Cushion vital organs. Fats are located in the subcutaneous

tissue and around body organs.

Section through the abdomen (Visible Human Project)

Phospholipids have a phosphate-containing group that substitutes for a fatty acid, giving the molecule a polar “head.” They are amphipathic, meaning they have polar and nonpolar regions. These molecules are important constituents of cell membranes.

Chemical Structure

Nonpolar tails

Polar head

Steroids Classified with fats, but very different in structure

—made up of four interlocking hydrocarbon rings.

Fat soluble Examples: cholesterol, cortisol, aldosterone,

estrogen, testosterone, progesterone Cholesterol is the most important of the steroids.

Only found in foods of animal origin It is an important component of cell

membranes. It is the raw material of vitamin D synthesis. It is the raw material for the synthesis of

steroid hormones.

cholesterol

Some common chemical groups Hydroxyl –OH-

Methyl -CH3

Ethyl -CH2CH3 Carboxyl –COOH Phosphate group –PO4

-3

Cholesterol’s Function in the Cell Membrane It makes the lipid

bilayer less deformable and decreases its permeability to small water-soluble molecules.

The other molecules shown are the phospholipids.

Questions Which organic molecules are the most readily

and used source of cellular fuel? Sucrose is classified as a __________. Glucose is classified as a __________. A chemical reaction in which two smaller

molecules unite to form a larger molecule (with the loss of water) is called _____________.

A solution with a pH of 3 is considered ________(acidic, alkaline).

The molecules important in cell membranes include ________________.