BioChem Exam #1 Flashcards
Carbon Review
Forms strong, stable covalent bonds;
Bonds up to 4 other atoms (tetrahedral arrangement);
Single, double, and triple bonds
Oxygen Review
Very electronegative (pulls electrons); Final electron acceptor during energy production
Hydrogen Review
H-bonding (very weak but large numbers make them stable);
Electron transport couple with energy production
Nitrogen Review
Makes up proteins and nucleic acids
Phosphorous Review
as (PO4)3-;
High energy compounds, nucleic acids, lipids;
Major buffer in systems
Sulfur Review
Proteins (helps maintain structure and function)
Non-Polar Covalent Bonds
Equal sharing of electrons (No separation of charge)
Polar Covalent Bonds
Unequal charing of electrons (Partial charge separation)
What causes the separation of charge in Polar Covalent bonds?
Differences in electronegativity
Ionic Bonds
Transfer electrons;
Weak bonds in aqueous solution;
Bond formed in attraction of opposite electrical charges of ions;
Total separation of charges
What property allows water to be a major solvent?
The fact that is polar;
H’s are partially positive;
O is partially negative
Hydrogen bonding
Weak dipole-dipole interaction occurring between an electronegative atom and a hydrogen covalently bound to another electronegative atom
What are the major physical properties of water?
High boiling point (liquid at room temp); High heat of vaporization (required for evaporation and why we sweat); High viscosity (responsible for water going up roots); Low density of ice (reason ice expands and floats)
What is meant by “solvent shell”?
Area of partial charges that surround an ionic species that allow the attraction to the partial charges in water causing it to dissolve
What type of compounds are Hydrophillic (water loving)?
Polar and Ionic;
Have separation of charges allowing water to attach to them
What type of compounds are Hydrophobic?
Non-polar;
Lipids;
No partial charges doesn’t allow them to bind to water, but it becomes oriented around them
What are Amphiphilic compounds
They are both hydrophobic and hydrophilic;
Hydrophilic (polar) head and hydrophobic (non polar) tail;
Micelles in the body that allow for digestion = a combo of lipids surrounded by H2O with heads towards water and tails toward lipids;
Cell bilayer
How do proteins react in aqueous solution?
The amino acid side chains will interact;
Water will be on the protein surface interacting with polar and ionic molecules holding them in solution (blood, cells, etc)
What is Osmosis?
Movement of water across a membrane;
A colligative property of solutions;
Based solely on the number of solutes that are in solution;
What is Diffusion?
If a substance is able to pass through a semipermeable membrane, its movement will occur spontaneously DOWN its own concentration gradient;
Water is more concentrated on side with fewer solutes;
(HIGH TO LOW)
What is the main factor in Osmosis?
Movement of H2O molecules depends ONLY on the number of particles dissolved in water – NOT size, charge, etc.
Water’s moment…
Start with more solute on one side of the lipid bilayer than the other using molecules that cannot cross the membrane;
Water will then move to balance out the concentration
What is a HYPOtonic solution?
Has fewer things dissolved in it (lower concentration)
What is a HYPERtonic solution?
Has more things dissolved in it (higher concentration)
What is an ISOtonic solution?
Having the same concentration by comparison between two solutions
How does water dissociate per acid/base?
H+ and OH-
Smaller the pH…
Larger the concentration of [H3O+]
What is an acid?
Proton donor;
MORE H+
What is a based?
Proton acceptor;
Less H+, MORE OH-
What makes a Strong Acid?
Strong tendency to donate protons
What makes a Weak Acid?
(More naturally occurring in biological systems);
Less tendency to donate protons;
Do not totally dissociate in H2O, so do not have as many H+ to give up
What is the relationship between pKa and acidity?
LOWER the pKa;
STRONGER the acid
Stronger acids…
have a HIGHER tendency to ionize which yields MORE products and a HIGHER Ka
A larger Ka means….
a LOWER pKa (stronger acid)
A smaller Ka means…
a HIGHER pKa (weaker acid)
Will a polar or ionic compound pass more readily through a membrane?
Polar;
b/c being Polar is closer to being Non-polar (like dissolves like);
The membrane is Hydrophobic (on polar) so is more accepting of the Polar molecule;
Only a slight separation of charge
As pH is lowered… (add protons)
H+ increases
As pH is increased… (remove protons)
H+ decreases
How does equilibrium shift when the pH is lowered? (add protons)
Shift to the left forming more HA;
Too many H+ so trying to make more reactants that are not dissociated
How does equilibrium shift when the pH is raised? (remove protons)
Shift to the right to break HA apart and gain protons;
Too few H+ so dissociating the reactant into more products
An equilibrium shift of LOWERING pH results in…
HA predominating
At a LOWER pH (more HA)
pK is GREATER than pH
An equilibrium shift of INCREASING pH results in…
A- predominating
At a HIGHER pH (more A-)
pH is GREATER than pK
What are Buffers?
A chemical system that tends to resist changes in pH when a moderate amount of acid or base is added;
Maintains the hydronium ion concentration relatively constant;
Adds or removes H+ when needed
What are the criteria for a good buffer system?
Concentration sufficiently large to compensate for amount of acid/base added (need enough buffer);
pKa near the desired pH (with +/- 1 pH unit, being in the middle allows maintenance of ~ the same pH)
When is a species totally protonated?
100% HA;
When no equivalents of OH- have been titrated
When does the pH=pKa?
When the [HA]=[A-];
Half an equivalence point
When is a species totally deprotonated?
100% A-
What is the Henderson-Hasselbalch equation?
Ka={H+][A-]/[HA]
pH equation
pKa + log[A-]/[HA]
pKa equation
-log_10(Ka)
What is the pKa?
Strength of the acid (lower pKa, stronger acid)
When pH=pKa?
the acid is 50% ionized;
Weak acid is the best at buffering (buffer needs to be +/- 1 unit)
Why is the buffering capacity of the blood important?
Normal blood pH=7.4;
Lower (6.8) = acidosis = death;
Higher (7.8) = alkalosis = death
What are the 4 main buffer systems of the body?
**H2CO3/HCO3-;
H2PO4-/HPO42-;
Plasma protein system;
Hemoglobin (RBCs) = lots of amino acids can be weak acids/bases
Main buffer = H2CO3/HCO3-. Where do the components come from?
CO2 gas in the lungs;
Becomes to CO2 dissolved in the blood plasma;
CO2 (RBC’s) combines with H2O yielding H2CO3 (carbonic anhydrase);
H2CO3 becomes dissolved in the blood plasma;
Then dissociates into H+ and HCO3-
Why is this our main buffer?
Because we have access to so much of it (we can make it), that the high concentration makes up for the pH and pKa difference;
Blood pH = 7.4;
H2CO3 pKa = 6.4
Overall equilibrium for carbonic anhydrase buffer
H20 + CO2 H2CO3 H+ + HCO3-