Chapter 2_ Water the Medium of Life Flashcards
With Solvings
Life originated, evolved, and thrives in the
sea
Water and its ionization products,
hydrogen ions and hydroxide
ions, are
critical determinants of
the structure and function of
many biomolecules, including
amino acids and proteins,
nucleotides and nucleic acids,
and even phospholipids and
membranes.
What Are the Properties of Water?
-Water has a substantially higher boiling point, melting point, heat of vaporization, and surface tension
-its maximum density is found in the liquid (not the solid) state, and it has a negative volume of melting (that is, the solid form, ice, occupies more space than does the liquid form, water)
- occur when two atoms in a molecule
have substantially different electronegativity: One atom attracts electrons more than another, becoming more negative, while the other atom becomes more positive.
Permanent Dipoles
Water’s ability to surround ions in dipole interactions and diminish their attraction for each other is a measure of its dielectric constant, D.
(1) Water has a high dielectric constant.
excellent solvent properties of water stem from its ability to readily form hydrogen bonds with the polar functional groups on these compounds, such as hydroxyls, amines, and carbonyls
(2)Water Forms H Bonds with Polar Solutes
- apparent affinity of nonpolar structures for one another
-Because nonpolar solutes must occupy space, the random H-bonded network of water must reorganize to accommodate them.
(3)Hydrophobic Interactions
(Compounds containing both strongly polar and strongly nonpolar groups)
(4) Interaction with amphiphilic molecules
Enumeration: Properties of water
1) Water has a high dielectric constant.
2)Water Forms H Bonds with Polar Solutes
(3)Hydrophobic Interactions
(4) Interaction with amphiphilic molecules
The presence of dissolved substances disturbs the structure of liquid water, thereby changing its properties.
Colligative Properties
Colligative Properties
▪ Freezing point depression
▪ boiling point elevation
▪ vapor pressure lowering
▪ Osmotic pressure effects
The pressure necessary to push water back through the membrane at a rate exactly equaled by the water influx is
the osmotic pressure of the solution
states that when equilibrium is disturbed, the rates of the forward and reverse reactions change to relieve that stress and reestablish equilibrium.
Le Châtelier’s principle
Oxygen–Hemoglobin Equilibrium and Hypoxia
The transport of oxygen involves an equilibrium between hemoglobin (Hb), oxygen, and oxyhemoglobin (HbO2).
We define an aqueous solution as being
neutral when the [H+] = [OH-]
acidic when [H+] > [OH-]
basic when [H+] < [OH-]
is called ionization constant of water and is very small.
-Kw
Kw = [H+][OH-]
The Swedish chemist Svante Arrhenius proposed the first definition of acids and bases
Arrhenius Definition
Arrhenius Definition
“Acids are substances that dissociate in water to produce H+ ions and bases are substances that dissociate in water to produce OHions”
Arrhenius Definition:
But what if the acid/base is not dissolved in water?
- The Arrhenius definition for acids and bases only refers to compounds dissolved in water.
Johannes Brønsted and Thomas Lowry revised Arrhenius’s acid-base theory to
include other solvents besides water.
Brønsted-Lowry Definition
Brønsted-Lowry Definition
“An acid is a hydrogen containing species that donates a proton. A base is any substance that accepts a proton.”
Brønsted-Lowry acids and bases always exist as conjugate acid-base pairs.
Their formulas differ by only one proton.
Conjugate Pairs
What are buffers and what do they do?
Buffers are present to prevent large fluctuations in pH
is one where complete dissociation of the
compound occurs.
A strong acid
is one where incomplete dissociation of the compound occurs.
A weak acid
First Line of Defense against pH:
Chemical Buffer system
- Bicarbonate Buffer system
- Phosphate Buffer system
- Protein Buffer system
Second line of defense against pH:
Physiological Buffer system
- Respiratory Mechanism
- Renal Mechanism
Bicarbonate Buffer system
Maintain a 20:1 ratio : HCO3-
:H2CO3 (bicarbonate to carbonic acid)
-Catalyzed by the enzyme carbonic anhydrase (enzyme found in red blood cells, gastric mucosa, pancreatic cells, and renal tubules)
-Functions with respiratory and urinary systems :to lower pH, kidneys excrete HCO3, to raise pH, kidneys excrete H+ and lungs excrete CO2
is very effective but not found in high
concentrations in extracellular fluid.
Phosphate Buffer
Phosphate Buffer
-Important in the intracellular fluid (ICF) and renal tubules.
-where phosphates are more concentrated
and function closer to their optimum pH of 6.8
– constant production of metabolic acids creates pH values from 4.5 to 7.4 in the ICF, avg. 7.0
Protein Buffers
a) Amino Acids
b) Hemoglobin
a) Amino Acids
free and terminal amino acids
– Respond to pH changes by accepting or releasing H+
-If acid comes into blood, hydronium ions can be neutralized by the –COO- groups
-If base is added, it can be neutralized by the –NH3+ groups
b) Hemoglobin
-Binds CO2
-Binds and transports hydrogen and oxygen
-Maintains blood pH as hemoglobin changes from oxyhemoglobin to deoxyhemoglobin
Physiologic Buffer Systems
Lungs
Kidneys
Physiologic Buffer Systems:
RESPIRATORY REGULATION
-Exhalation of carbon dioxide
* Powerful, but only works with volatile acids
* Doesn’t affect fixed acids like lactic acid
* CO2 + H20 ↔ H2CO3 ↔ H+ + HCO3-
* Body pH can be adjusted by changing rate and depth of breathing
* Provide O2 to cells and remove CO2
Ventilation Rates & Effect on pH Balance
It’s all about CO2 and the bicarbonate buffering system
* Increased ventilation rate causes
Hyperventilation
drives the reaction to the left, causing removal of H+, pH goes up
Hypoventilation
drives the reaction to the right, causing additional H+, pH goes down
Physiologic Buffer Systems:
RENAL REGULATION
-Can eliminate large amounts of fixed acid
* Can also excrete base
* Can conserve and produce bicarbonate ions
* Most effective regulator of pH
* If kidneys fail, pH balance fails
* Only the kidneys can rid the body of acids generated by cellular metabolism (nonvolatile or fixed acids), while also regulating blood levels of alkaline substances and renewing chemical buffer components.
Base Excretion
- Only regulated by the kidney.
- Primary base in the body is HCO3
- The kidney can retain or excrete HCO3- as needed.
Importance of Renal Regulation
-For every hydrogen ion buffered by bicarbonate – a bicarbonate ion is consumed.
-To maintain the capacity of the buffer system, the bicarbonate must be regenerated
Importance of Renal Regulation
◻ Bicarbonate formation can only continue if these hydrogen ions are removed
◻ This process occurs in the cells of the renal tubules where hydrogen ions are secreted into the urine and where bicarbonate is generated and retained in the body
Renal Responses to Acidosis
A. increased reabsorption of the filtered HCO3 −
B. increased excretion of titratable acids, and
C. increased production of ammonia.
Renal Responses to Acidosis: A. increased reabsorption of the filtered HCO3 −
(1)CO2 within renal tubular cells combines with water in the presence of carbonic anhydrase.
(2)The carbonic acid (H2CO3) formed
rapidly dissociates into H+ and HCO3−
(3)Bicarbonate ion then enters the bloodstream
(4)while the H+ is secreted into the renal tubule,
(5)where it reacts with filtered HCO3 − to form H2CO3.
.
Renal Responses to Acidosis: B. Increased Excretion of Titratable Acids
After all of the HCO3− in tubular fluid is
reclaimed, the H+ secreted into the tubular lumen can combine with HPO4 2− to form H2PO4− (the latter is not readily reabsorbed because of its charge and is eliminated in urine). The net result is that H+ is excreted from the body as H2PO4−, and the HCO3−
that is generated in the process can enter the bloodstream.
Renal Responses to Acidosis: C. Increased Formation of Ammonia
In the proximal tubules of the nephrons within the kidneys, glutamine, an amino acid, can be metabolized to produce ammonia. This process is enhanced in response to acidosis. The enzyme responsible for this conversion is glutaminase, which breaks down glutamine into ammonia and other byproducts.
Regulation of Plasma pH - Alkalosis
-When the body is in alkalosis, tubular
cells secrete bicarbonate ions and
reclaim hydrogen ions and acidify the
blood.
-The mechanism is the opposite of
bicarbonate ion reabsorption process
