Chemical Basis of Life

Ionic Bonding

http://www.es.ucsc.edu/~es10/classnotes/lectures/ionic.bond.jpg

Covalent Bonding

http://www.gcsescience.com/Methane-Molecule.gif

http://media-2.web.britannica.com/eb-media/04/96904-004-C880B85D.gif

Hydrogen Bonding

http://upload.wikimedia.org/wikipedia/commons/f/f9/3D_model_hydrogen_bonds_in_water.jpg

http://schools-wikipedia.org/images/646/64609.png

Properties of Water1. Strong Polarity:• Polar water molecules attract other polar

compounds causing them to dissociate– Water is a great solvent

• Many molecules can dissolve in cells (mostly water)– Allows for chemical reactions and transportation

Properties of Water2. High Specific Heat• Hydrogen bonds absorb heat when broken and

release heat when formed– This minimizes temperature changes in the body– Body temp remain relatively constant

3. High Heat of Vaporization• Energy needed to break H+ bonds• Body can dissipate excess heat & maintain a

normal body temperature by evaporation

Properties of Water

4. Cohesion• Water molecules provide lubrication or

cushioning to protect against damage from friction or trauma

Electrolytes

Substances that dissociate (break up) in solution to form charged particles or ions.

– Examples: Acids, bases, salts– Cations: positive charged ions– Anions: negative charged ions

Acids & Bases

Acid – any substance that releases H+ when in solution– “proton donor”– Ex: HCl (stomach acid)

Base – any substance that increases the OH- concentration when dissociated in solution– “proton acceptor”– “Ex: NaOH

pH ScaleRepresents the H+ ion concentration

in a solution7 = neutral0-6 = acidic 8-14 = basic/alkaline

Buffers

Any molecule that moderates changes in pH. – Key role in the body’s ability to maintain

a normal pH (homeostasis)

Many buffers are anions that have a strong affinity for H+ – bicarbonate ion (HCO3

-) is an important buffer in the human body

Carbohydrates

Building Block – MonosacchrideDisaccharides – 2 monosacchrides

covalently bondedPolysaccharides – complex

carbohydrates

Carbohydrates

• Structure:– Contains the elements C, H, O

• H and O always in 2:1 ratio

– Monosaccharides form short carbon chain• Ex: Glucose (C6H12O6)

• Function:– Provide energy for cellular activities – Structural support in DNA (deoxyribose)

and RNA (ribose)

LipidsIncludes: fats, phospholipids, steroids

and prostaglandins – Water insoluble

1. Fats/Triglycerides:– Structure: glycerol & 3 fatty acid tails– Function: concentrated energy source

http://www.future-of-technology.com/web_images/triglyceride.jpg

Lipids cont….2. Phospholipids

– Structure: glycerol, 2 fatty acid tails & a phosphate group• Head: water soluble (“hydrophilic”)• Tails: fat soluble (“hydrophobic”)

– Function: main component of cell membrane

http://www.fz-juelich.de/isb/isb-1/datapool/page/28/Figure1-500.jpg

Lipids cont….

3. Steroids– Cholesterol: Provides stabilization

function in cell membrane– Other examples: estrogen &

testosterone

4. Prostaglandins

Proteins

• Wide range of functions:– Defense system (antibodies)– Serve as receptors or binding sites– Structural (skin, tendons, nails)– Catalyze chemical reactions (enzymes)– Communication (insulin – protein

hormone)

Amino Acids

Building blocks of proteins– 20 amino acids– 8 are essential (must be obtained

through diet)– Structure:

• Amine group• Carboxyl group• Side chain (determines

unique properties of amino acid)

http://www.aloeveraibs.com/wp-content/uploads/2008/08/aminoacidstruc.jpg

Enzymes

• Largest group of proteins in the body.

• Chemical catalyst– Assist in chemical reactions but are not

products nor reactants – Not changed by the reaction – Usually end in -ase

Nucleic Acids • Form genes and take

part in protein synthesis

• Building block – nucleotide – Phosphate– Nitrogen Base (Adenine,

Guanine, Cytosine, Thymine)

– 5-carbon sugar (deoxyribose in DNA)

• Ex: DNA, RNAhttp://bbruner.org/bitn/bitn_fig/dna.gif

Metabolism All the chemical reactions that take place

in our body’s cells.– Catabolism: Chemical reaction that breaks

down large molecules into smaller units. This type of reaction releases energy. Also called a hydrolysis reaction because a water molecule is added for the reaction to occur.

– Anabolism: Chemical reaction that combines smaller molecules to form larger molecules. This type of reaction requires energy, usually ATP. Also called a dehydration synthesis reaction because a water molecule is removed during the reaction.

– Fig 2-25, p. 61