Chapter 2 A&P Lecture, the Chemistry of Life

Element

The simplest form of matter to have unique chemical properties.

Chemical Elements

91 naturally occurring elements

24 play a role in normal physiology in humans

6 account for 98.5% of the body’s weight (O, C, H, N, Ca, P)

Chemical symbols

Letters that represent the elements.

Hydrophilic

Substances that dissolve in water.

Water

Polar Covalent Bonds

Your body is 50-75% water

It has properties of solvency, cohesion, adhesion, chemical reactivity, and thermal stability

Solvency is the ability to dissolve other chemicals, water is the universal solvent

Chemical Reactivity is water’s ability to a participate in chemical reactions

• It ionizes many other chemicals like salts and acids

• It can also ionize itself into H+ and OH-

• These ions can be incorporated into other molecules (hydrolysis) or released form them (condensation)

Hydrophobic

Substances that do not dissolve in water.

Acid

A proton donor

Base

A proton acceptor

pH

A measure of acidity derived from the molarity of H⁺ and is symbolized in brackets [H⁺]

Solution with a pH of 7 is

neutral

Solutions with a pH of 1-6 are

acidic

Solutions with a pH of 8-14 are

basic (alkaline)

pH scale is

logarithmic, so a change in one number on the scale is actually a tenfold change

Buffers

Chemical Solutions that resist changes in pH

Energy

The ability or capacity to do work

Potential Energy

the energy stored in an object

Kinetic Energy

the energy of motion

Chemical Energy

Potential energy stored in the bonds of molecules

Heat

kinetic energy of molecular motion

electromagnetic energy

the kinetic energy of moving ‘packets’ of radiation called photons

-the most familiar form of this is light

electrical energy

potential and kinetic forms

it is potential when charged particles accumulate on one side of a cell membrane

it becomes kinetic when these particles move across and create an electrical current

free energy

potential energy available in system to do useful work

-in human physiology the most relevant free energy is the energy stored in chemical bonds or organic molecules

A chemical reaction

a process in which covalent or ionic bonds are formed or broken

Chemical Equation

shows reactants on the left and products on the right, with an arrow pointing from reactants to products

Reversible reactions

have a double arrow indicting it can go in either direction (A + B↔ AB)

Typically follows the law of mass action and proceed from reactants in greater quantity to substances with the lesser quantity

Decomposition reactions

occur when a large molecule is broken down into two or more smaller ones (A→A+B)

Synthesis reactions

Occur when two or more small molecules combine into a large one (A + B → AB)

Molecules are

in constant motion

Rate of reaction

depends on nature of reactants and the frequency and force of the collisions between molecules

Things that affect reaction rates are:

o   Concentration (more concentration will increase rate of reaction)

o   Temperature (higher temperature will increase the rate of reaction)

o   Catalysts (biological catalysts or enzymes speed up reactions)

Metabolism

The sum of all chemical reactions in the body.

Anabolism

The process that builds small molecules into larger ones and stores energy (endergonic reactions)

Catabolism

The process that breaks down large molecules into smaller ones and releases energy. (exergonic reactions)

Oxidation

Process where electrons are given up and energy is released (LEO)

-  Electron donor or reducing agent

Reduction

Process where electrons are gained, and energy is stored (GER)

- Oxidizing agent or electron acceptor

Organic Compounds

substances that contain carbon

Unsaturated fats

(like linoleic acid) have some double covalent bonds in between carbons, so they are not completely saturated with hydrogens

-        -these are liquid at room temperature and come from plants, and are more healthy

-        -polyunsaturated fats have two or more double bonds

-        monounsaturated fats have one double bond

-        -triglycerides have a glycerol and 3 fatty acid chains

formed by dehydration synthesis (lose water)

stored in adipose

-        essential fatty acids must be obtained from the diet

Phospholipids

Molecules with hydrophilic heads and hydrophobic tails important in cell membrane construction.

Enzyme

- A modified protein that acts as a catalyst and speeds up metabolic reactions

-        Enzymes bind to substrate at the active site and form an enzyme-substrate complex

-        Enzymes usually end in the suffix ‘ase’

-        Factors that change the shape of the enzyme (temperature and pH can alter or destroy the enzyme’s ability to bind to its substrate

-        Cofactors-enzymes need ‘helpers’ that are nonprotein (inorganic like minerals)

-        If the cofactor is organic and derived from a vitamin like riboflavin they are called coenzymes

-        NAD, FAD, CoA are all coenzymes that are necessary for cellular respiration-

ATP

Adenosine triphosphate

the body’s most important energy transfer molecule

Require enzymes called ATPases to hydrolyze the 3^rd phosphate

ATP↔ADP + P

GTP is another nucleotide involved in energy reactions

cAMP is a nucleotide formed by the removal both the 2^nd and 3^rd phosphate groups from ATP

Nucleic acids

These are necessary to give instruction to cells, form genes, and protein synthesis

Includes DNA or deoxyribonucleic acid and RNA or ribonucleic acid

Carbohydrates

provide energy for the cell

these are necessary for cell structures (glycoprotein)

they are water soluble molecules containing carbon, hydrogen, and oxygen in a 1:2:1 ration

carbs are classified by size

Simple Sugars

Monosaccharides with 3-7 in a ring or a chain

-        pentoses have 5 carbons (ribose and deoxyribose)

-        hexoses have 6 carbons (the examples below are isomers)

These include glucose or dextrose (blood sugar), fructose (fruit sugar), and galactose (C₆H₁₂O₆)

Disaccharides

are composed of two, six carbon units and include sucrose (table sugar) which is glucose and fructose, lactose (milk sugar)  which is glucose and galactose, and maltose (malt sugar) which is glucose and glucose

Complex Carbohydrates

also known as polysaccharides

-        One is called cellulose is found in plants.  Humans need this for fiber, but can’t digest it

-        Plant starch is easily digested (potatoes for example)

-        Animals have starch too, but it is called glycogen, and it is stored in the muscles and liver

 

Lipids

fatty acids, triglycerides, phospholipids, eicosanoids, and steroids

-organic chemicals that are insoluble in water so are hydrophobic (won’t dissolve)

  -these are vital for homeostasis, but should be limited to 30% of the diet

  -most common type of lipid is fat, which is used for energy (at least twice the energy from sugar)

-fat is composed of carbon, hydrogen, and oxygen, but in different proportions than sugar

  -the building block of fat is the fatty acid molecule and the glycerol molecule

  -all fats have a carboxyl group (COOH) at the end of a chain of carbons

Saturated Fatty Acids

Linked by a single carbon-carbon bond and are saturated with hydrogen molecules

-        these are solid at room temperature and come from animals

-        limit consumption of this type of fatty acid to <10% of your total fat intake per day.

trans fats and cardiovascular health

-        trans fats can pack together and are solid at room temperature

-        cis fats can’t pack closely together and are oils

Phospholipids

Have 2 fatty acid chains and a portion containing a phosphate group

·       -the phosphate group is hydrophilic (water loving) and is called the head

·       -the fatty acid portion is hydrophobic (water fearing) and is called the tail, because of this they are called amphipathic

·       -phospholipids are important in cell membrane construction

Eicosanoids

Are modified 20 carbon fatty acids that are synthesized as needed from arachidonic acid

-        classes include prostaglandins, and leukotrienes

Prostaglandins

Play a role in inflammation, blood clotting, hormone action, labor contractions, control of blood vessel diameter, etc

Steroids

Are complex rings of carbon and include cholesterol, sex hormones, and adrenal hormones

-        medical condition:  hypercholesterolemia, not enough LDL receptors

-        see Deeper insight 2.4 (good and bad cholesterol)

Glycolipids

Associated with plasma membranes and serve as cellular binding sites

What are also lipids?

fat soluble vitamins (A,D,E, and K)

Proteins

• may function as antibody, as receptors on cell surfaces, as energy sources, as chemical messengers, membrane transport, etc.

• there are structural and functional proteins

• an enzyme is a type of protein

• proteins are made from building blocks called amino acids (20 different kinds)

• -all proteins have an amino group (NH₂), a central carbon (C), a carboxyl group (COOH), and an ‘R’ group

•    peptide bond links amino acids

•   an oligopeptide is a chain of fewer than 10 or 15 amino acids

• a polypeptide is a chain of 16- or more amino acids

• protein is a chain of 50 or more amino acids

• we have primary, secondary, tertiary, and quaternary structures (see figure 2.24)

• proteins can be denatured (destroyed) by high temperatures, radiation, extremes in pH, and some types of chemicals