Medical Biochem Lecture 2

What makes water a good medium for life?

it is an excellent solvent since reactions occur in aqueous solutions, water takes part in reactions, it acts as a heat buffer to maintain internal temperatures, water is denser than ice, water determines structure/functions of proteins, nucleic acids, and membranes.

What is unique about a water molecule’s chemistry?

Water is a sp3 hybridized molecule, the electronegativity of the oxygen atom induces a net dipole moment allowing water to be a hydrogen bond donor and acceptor

How does water’s molecule affect hexagonal ice?

creates a regular lattice=low entropy, contains more hydrogen bonds= causes it be denser, absorbs heat when melting (delta H is positive), but delta S increases when water

When is water a good solvent? Examples?

for charged and polar substances that form H-bonds

ex) amino acids, peptides, alcohols, carbs, nucleic acids (these can disrupt water lattice so limited solubility even for some polar molecules)

When is water a poor solvent? Examples?

nonpolar substances (like-dissolves like)- can’t form H-bonds and disrupt water lattice

ex) nonpolar gases, aromatic rings, aliphatic chains, lipids

What is water’s role in osmotic pressure of cells?

water can put stress on the plasma membrane and cause lysis during a hypotonic environment (water moves into cell) it’ll want to follow the solutes.

How do multicellular animals maintain their osmolarity?

they pump out ions into interstitial fluid

or pump water directly using aquaporins

What is it called when water is produced in a reaction?

condensation

What is it called when water is consumed in a reaction?

hydrolysis

What molecules can form weak bonds?

all molecules can create van der waals

hydrogen and ionic can only form between molecules with a net charge, or a dipole

What is unique about weak bonds?

they don’t share electrons, they are broken by thermal energy, combined they influence 3D structures

How are hydrogen bonds formed?

between dipole moments of NH/OH molecules

How are ionic interactions specifically formed?

electrostatic interactions between permanently charged species or an ion and a permanent dipole

How are hydrophobic effects specifically formed?

water molecules form around nonpolar substances. Nonpolar substances will cluster together to allow for the water to interact with itself more.

Why are hydrogen bonds highly directional?

The angle and orientation of the electronegative atom with hydrogen determines the strength of the bond. Hydrogen is strongest when the angle of the bond is in a line.

What is the biological relevance of hydrogen bonds?

1. H-bonds create the unique properties of water

2. It helps determines the structure and functions of DNA, proteins, lipids, and sugars

3. It is involved in enzyme/substrate, hormone/receptor interactions, mRNA with tRNA

How is entropy affected during hydrophobic interactions?

Entropy is initially reduced due to the water surrounding the nonpolar molecules. When they cluster together entropy increases as water has more room to interact with one another again.

How does hydrophobic interactions stabilize macromolecules?

hydrophobic amino acids are buried within proteins and packed through van der Waals interactions, this helps with folding and stability

What is ionization of water?

pure water polar bonds can dissociate into hydrogen ion and a hydroxide ion. This creates the pH scale and what determines molecules acidity and basicity.

What is proton hopping and its role in a cell?

covalent and hydrogen bonds are interchangeable and allow movement of their protons in water. This allows for biological proton-transfer reactions (e.g. photosynthesis)

What is the equilibrium constant and pH formula?

Keq= ([H+] x [OH-])/([H2O]) pH= -log[H+]

What does pKa measure?

Acidity: strong acid will have a large Ka and a small pKa

What is a buffer?

A weak acid and conjugate base are used to resist change in pH

How does a weak acid and its conjugate base act as a buffer?

When the acid dissociates it releases some hydrogen ions. Its conjugate base will be able to react to absorb the ions due to the dynamic equilibrium. This means when the conjugate base reacts the solutions will not have much increase in the pH level.

Why are buffers important in biological system, examples?

Some parts of the body are affected by pH levels by changing the pH levels it may affect enzyme-catalyzed reactions. pH would change the h-bond donors/acceptors, change solubility of polar molecules, change active sites, and destabilize the structure.

ex) co2 gas and hCO3 depends on pH. Having extra CO2 can allows for the formation of more H2CO3

What is acidosis and alkalosis?

acidosis: blood pH below 7.4, may cause CO2 build-up

alkalosis: blood pH above 7.4, may cause hyperventilation (loss of CO2)