જ⁀➴ water, pH, buffers

water

active molecule that is essential to maintain the 3D structure and proper functioning of biochemical molecules and is an active participant in biochemical reactions

is water a neutral medium?

no. it’s an active molecule that shapes biomolecules, stabilizes their structures, and participates in biochemical reactions

how does water help maintain the 3D structure of biomolecules?

water forms hydrogen bonds with molecules like dna and proteins, stabilizing their proper 3D shape for correct function

what would happen to biomolecules without water?

they might lose their proper structure and functionality, disrupting biochemical processes

how does water participate in biochemical reactions?

water is involved in hydrolysis and condensation reactions

compared to similar liquids, water has a higher what?

1. boiling point

2. melting point

3. heat of vaporization

4. surface tension

name one way hydrogen bonds in water are dynamic

hydrogen bonds constantly form and break, making a rapidly changing network

what kind of molecule is water?

polar

what is responsible for water’s unusual properties?

it’s molecular structure and the intermolecular attractions

how do hydrogen bonds form between water molecules?

the slightly positive hydrogen of one water molecule is attracted to the slightly negative oxygen of another molecule

what does it mean that water is a polar molecule?

the oxygen is slightly negative, hydrogen is slightly positive and it create a dipole.

how many hydrogen bonds does each water molecule form on average?

about 3.4

what is the relationship between water’s polarity and its ability to form hydrogen bonds?

polarity creates partial charges that allow water molecules to attract each other and form hydrogen bonds

What kind of bond is the O—H bond in water?

mostly covalent, but with ~33% ionic character because oxygen pulls much harder on the shared electrons

What gives the O—H bond its partial ionic character?

oxygen is highly electronegative, creating partial charges 

Why are hydrogen bonds stronger than regular van der Waals interactions?

the special closeness between atoms creates stronger intermolecular attraction

Why do hydrogen bonds give water unusual properties (high boiling point, surface tension, etc.)?

They are strong enough to resist easy breaking but not as permanent as covalent bonds

How do hydrogen bonds behave in liquid water?

they constantly break and reform, creating a dynamic and flexible network

How do hydrogen bonds behave in ice?

they form a fixed, rigid three dimensional network

How many hydrogen bonds does each H₂O molecule form in ice?

4

What kind of structure do hydrogen bonds in ice create?

An open lattice structure with empty spaces

Why does ice have lower density than liquid water?

the lattice holds molecules farther apart, increasing the volume without increasing the mass

What is the average lifetime of an H bond between two H2O molecules?

9.5 picoseconds

what is a hydration shell?

a layer of water molecules that surrounds an ion, with the oxygen side facing positive ions and the hydrogen side facing negative ions.

Why do water molecules form hydration shells around ions?

because of its polarity

What is the dielectric constant?

A measure of how well a solvent reduces the attraction between oppositely charged ions

How does water’s high dielectric constant help ions dissolve?

weakens the electrostatic forces between positive and negative ions, making it easier for them to stay separated in solution. and possibly dissolve.

What is a hydrophobic molecule?

A nonpolar molecule that does not interact well with water because they have no partial charges

how does water interact with hydrophobic moleciles?

they form a cage-like (clathrate) structure around the hydrophobic solute.

What are hydrophobic interactions?

The tendency of nonpolar molecules to cluster together in water, minimizing disruption of water’s hydrogen-bonded network.

Can water bonds with other polar molecules?

Yes, because they also have partial negative and positive charges.

what lipid forms a lipid bilayer when in water?

glycerophospholipids

what is a lipid bilayer?

contains a larger or two nonpolar tails; is the structure of the outer cell membrane

how does the lipid bilayer apply in cells?

It works as a barrier to maintain the different concentrations of sodium, potassium and chlorine ions inside and outside the cell

what is a micelle?

Amphiphilic molecules that cluster together to form a sphere to minimize unfavorable interactions

what are amphiphilic or amphipatic molecules?

molecules with two parts, a polar head and nonpolar tail.

what group is the polar part of an amphiphilic molecule?

carboxyl group

what part is the nonpolar part of an amphiphilic molecules?

long hydrocarbon tail

what is a colligative property?

property of a solution that depends only on the number of solute particle and not the chemical structure

exmples of colligative properties

1. osmotic pressure

2. freezing point depression

3. boiling point elevation

4. vapor pressure lowering

what is osmotic pressure?

its when wate moves from high water concentration to low water concentration

what happens to a cell that has too much solute inside?

water will rush in and cause the cell to swell and rupture

what is pH?

A measure of the hydrogen ions concentration and is defined by the equation 

what is a buffer system?

a solution that resists change in pH when acids or bases are added. they maintain stable pH

what are two important systems of cells and blood?

1. phosphate buffer system

2. carbonate buffer system

what does the phosphate buffer system consist of?

1. H2PO4^-

2. HPO₄^-2

H₂PO_4-

dihydrogen phosphate ion

HPO₄^-2

monohydrogen phosphate ion

what happens when theres excess OH in the phosphate buffer system?

H₂PO₄^- + OH^- → HPO₄^-

what happens when theres excess H in the phosphate buffer system?

HPO₄^- + H → H₂PO₄

whta does the carbonate buffer system consist of?

1. HCO₃^-

2. H₂CO₃

HCO₃^-

bicarbonate

H₂CO₃

carbonic acid

What happens when there’s extra H in the carbonate buffer system?

HCO₃^- + H → H₂CO₃

What happens when there‘s extra OH in the carbonate buffer system?

H₂CO₃ + OH → HCO₃^- + H₂O

Why is carbonic acid eliminated from the body?

it’s unstable and breaks down into carbon dioxide and water 

How is the CO₂ produced from carbonic acid removed from the body?

exhaled through the lungs, and hyperventilation can increase the removal if needed.

Summarize how excess H⁺ in the blood is removed via the carbonic acid system.

H⁺ + HCO₃⁻ → H₂CO₃ → CO₂ + H₂O → CO₂