Download Buffers - Philadelphia University

Buffers
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Buffers are solutions that resist changes in their pH as acid (H+) or base (OH-) is added.
Typically, buffers are composed of a weak acid and its conjugate base.
Acids = Proton (H+) donors
Bases = Proton Acceptors
HA
Acid
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H+ + Aconjugate base
Acids and their conjugate bases are in equilibrium. Equilibria are related to the properties of the
reactants and products, so for weak acids, the tendency to give up its proton determines its
buffering property
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The tendency to ionize can be put in an equilibrium equation
Ka=
[H ][A ]
[HA]
A solution of a weak acid that has a pH near to its pKa has an equivalent amounts of conjugate
base and weak acid.
Typically a weak acid is in its useful buffer range within 1 pH unit of its pKa.
Polyprotic acids
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Have more than one acid-base group
H3PO4 and H2CO3
The pK’s of two closely associated acid-base groups are not independent - the closer
they are, the greater the effect.
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Examples: oxalic acid and succinic acid
OO
H-O-C-C-O-H
pK differs by 3 pH units
O
O
H-O-C-CH2CH2-C-O-H
pK differs by 1.4 pH units
Polyprotic acids
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The effect of having
successive ionizations
from the same center is
even greater.
However if pK’s of
polyprotic acid differ by
less than 2 pH units, this
reflects the average
ionization of all of the
groups.
Universal features of cells
• “Life possesses the properties of replication, catalysis, and
mutability.” - Norman Horowitz
• Life requires free energy.
– Main energy currency is
• ATP (bond energy, G)
• NADH, NADPH (redox energy)
– All cells obey the same laws of thermodynamics (see Ch.3).
 G (Gibbs free energy) must be negative (spent)
 S (Entropy) increases
– Sources of energy may vary
• Purple sulfur bacteria
• Humans
• Plants
H2S
CH2O
h
So
H2O + CO2
Universal features of cells (cont.)
• Most organisms are composed of only 16 chemical elements
• (H,C,N,O,P,S,Mn, Fe, Co, Cu, Zn, Na, Mg, Cl, K, Ca).
– Chemical makeup appears to be determined partly by the availability of
raw materials and the specific roles of of molecules in life processes.
– Do not reflect the composition of the biosphere
– Examples on per atom basis, H in organisms = 49%, H in Earth’s crust
= 0.22 %, Si in organisms = 0.033%, Si in Earth’s crust = 28%)
• H, O, N, and C, make up >99% by weight of living matter are the
smallest atoms that can share 1, 2, 3, and 4 electrons
respectively.
• O, N, and C are the only elements that easily form strong
multiple bonds.
• O2 is soluble in water and readily available to all organisms.
• Phosphorous and sulfur are unstable in the presence of water.
– Require a large amount of energy to form.
– Energy released when they are hydrolyzed.
MW
18-44
N2, H2O, CO2
20 amino
acids
100-250
100-800 Amino acids
104-109
106-1010
Proteins
5 aromatic
bases,
ribose
Nucleotides
Nucleic acids
Glucose
Palmitate, glycerol,
choline
Sugars
Phospholipids
Polysaccharides
Multienzyme complexes, ribosomes, chromosomes,
membranes, structural elements
Organelles, Cells, Tissues, Organs,
Organsims
Universal features of cells (cont.)
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All cells function as biochemical factories and use the same basic
molecular building blocks.
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Proteins (amino acids
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polypeptides
proteins)
Can be structural or catalytic
Enzymes
Transport (Na+/K+ pump)
Storage (ferritin)
Signals (hormones/toxins), examples insulin or botulinum toxin
Receptors –
Structure (collagen, elastin) –
lipids)
Lipids (fatty acids
Membranes
Triglycerides (energy storage)
Phospholipds (membrane structure)
Sphingolipids (found in nerve cells and brain tissue)
Sterols (hormones and membranes)
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Universal features of cells (cont.)
• Carbohydrates
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Monosaccharides (glucose, fructose)
Disaccharides (sucrose, maltose)
Trisaccharides (raffinose)
Complex carbohydryates
• Starch (energy storage)
• Cellulose (structure, cell wall)
• Cell-cell recognition
• Nucleic acids
– DNA (genetic material)
– RNA (mRNA, tRNA, pre-mRNA or hnRNA, rRNA)
• Proteins and nucleic acids are produced by the same rules
– Central dogma
DNA
RNA
• A living cell can exist with fewer than 500 genes!
Protein
Types of cells
• There are two major cell types: eukaryotes and prokaryotes.
• Eukaryotes have a membrane enclosed nucleus encapsulating
their genomic DNA.
• Prokaryotes do not have a nucleus.
Prokaryotes
Eukaryotes
Bacteria,
Archaea
Fungi, Protists,
Animals, Plants
1-10 µm
10-100 µm
Prokaryotes
• Most numerous and
widespread organisms
on Earth
• Wide variety of
metabolic energy
sources
• Relatively simple
anatomy
• Shape is sometimes
used to determine a
particular type of
bacteria