Lecture 2 - Water

Water

• most abundant biomolecule in the body

• 60-95% of living cells

Intracellular fluids

55% of the water in the human body

8%

Plasma

Plasma

Water dissolves water-soluble nutrients so they can be brought by the blood to the different parts of the body

22%

Interstitial and lymph

Interstitial fluid

fluid that surrounds the cells helps deliver nutrients from the inside to the outside of the cells

Lymphatic fluid

travels through the lymphatic system and carries cells that help fight infections and other diseases

Lymphatic fluid

helps carry infection fighting cells all over our body

15%

Connective tissue, bone and cartilage

Connective tissue, bone and cartilage

Lubrication

Normal metabolic activity

occur only when the cells are at least 65% H2O

1. Transport medium across membranes

2. Maintain temperature

3. Solvent

Function of Water as Solvent for Biochemical Reactions:

transport medium across membranes

Due to different water moving capability, such as diffusion and osmotic pressure

maintain temperature

Sweating → water with other ions; one of the homeostatic activities/processes in the body

solvent

(carrying dissolved chemicals) in the digestive and waste excretion systems

water balance

must be maintained within the body

dehydration

loss of water in the body significantly exceeds the intake

edema

loss of water in the body is significantly less the intake

Overhydration

experienced when someone drinks too much water

• boiling point

• melting point

• heat of evaporization

• surface tension

Water has substantially higher:

maximum density of water

found in the in the liquid state

bent structure

2 hydrogens of water are covalently linked to the oxygen atom giving a non-linear arrangement

oxygen atom

partial positive charge

hydrogen atom

partial negative charge

polar bonds

positive and negative side

Hydrogen bond

water molecules attract one another through the formation of

Hydrogen bond

• non-covalent interaction

• a dipole-dipole interaction

hydrogen donor

hydrogen atom covalently bonded to one electronegative atom

hydrogen acceptor

a lone pair of electrons on another electronegative atom

hydrogen donor

hydrogen atom that is covalently bonded to its oxygen

hydrogen acceptor

lone pair in the oxygen atom of another water molecule

hydrogen acceptor

oxygen

hydrogen donor

hydrogen

hydrogen donors and hydrogen acceptors

Water can then be both

• high viscosity

• surface tension

• boiling point

Hydrogen bonding favors the self-association of water molecules

Hydrogen bonding

enables water to dissolve many organic biomolecules

hydrophilic

ionic substances and polar substances, that can be dissolved in water

Ion-dipole Interaction

• negative oxygen atoms of the water molecules are oriented towards the cations

• positive hydrogen atoms are oriented towards the anions

Dipole-dipole interaction

• interaction between water and another polar molecule

• dissolution of both polar substances

hydrophobic effect

• water molecules exclude non-polar substances forcing them to associate with each other

• critical for folding of proteins and the self-assembly of biological membranes

amphipathic; amphiphiles

non-polar hydrocarbon tail and an ionic or polar end

hydrophilic head (polar)

tends to be hydrated

hydrophobic tail (non-polar)

tends to be excluded

auto-ionization of water

highly electronegative oxygen atoms strips the electrons from one of its hydrogen atoms

Bronsted-Lowry definition

acid is a proton donor, and a base is proton acceptor

Acid strength

amount of hydrogen ion (proton) released when a given amount of acid is dissolved in water

conjugate base

one that is left when a H+ leaves an acid

conjugate acid

one that is formed when a base accepts a H+

buffer

solution that tends to resist pH changes when small amount to moderate amounts of strong acid or strong base are added

buffer

keeps the pH within this range

buffer

used to resist pH changes

buffer

composed of a mixture of a weak acid and its conjugate base

acid (H+ ) is added to a buffer solution

reacts with the conjugate base to form the weak acid

base is added to the buffer

reacts with the weak acid to form water and the conjugate base

Maximum buffering

buffer pH is approximately equal or near to the pKa of its weak acid

Bicarbonate Buffer System

most important type of buffer present in the plasma of the blood

7.35- 7.45

normal pH range of the blood

acidic

Below this range means there’s abundant hydrogen ions (H + ) in the blood

basic

above this pH means there’s little H

acidosis

blood pH is low

alkalosis

pH is high

7.4

pH of blood

pH of blood

regulated by the carbon dioxide-carbonic acid-bicarbonate buffer system

• lungs

• kidneys

2 key organs involved in this specific buffer system

acidosis

decrease in blood pH (increase in H+ )

alkalosis

increase in blood pH (decreases in H+ )

Respiratory Acidosis

Increase of CO2

Respiratory Alkalosis

Decrease of CO2

Metabolic Acidosis

Decrease of HCO3 -

Metabolic Alkalosis

Increase of HCO3 -