Proteins

While their name implies that amino acids are compounds that contain an —NH2 group and a —CO2H group, these groups are actually present as —NH3

+ and —CO2

– respectively.

Living organisms always synthesize proteins from N to C terminus

Amino acids

The 20 Key Amino Acids

More than 700 amino acids occur naturally, but 20 of them are especially important.These 20 amino acids are the building blocks of proteins. All are -amino acids.They differ in respect to the group attached to the carbon.

Essential amino acids are those that are "essential" in the diet. In other words, we cannot create them. For example Phenylalanine

Non-essential amino acids are those which can be produced from other amino acids and substances in the diet and metabolism. For example Serine

Essential and Non Essential aminoacids

Essential amino acids•arginine •histidine •isoleucine •leucine •lysine •methionine •phenylalanine •threonine •tryphtophan •valine

Non-essential amino acids•alanine •asparagine •aspartate •cysteine •glutamate •glutamine •glycine •proline •serine •tyrosine

Aminoacids are aliphatic and aromatic. In which aromatic has ability to absorb UV light

Peptides Peptides are compounds in which an amide bond links

the amino group of one -amino acid and the carboxyl group of another.

An amide bond of this type is often referred to as a peptide bond.

Living organisms always synthesize proteins from N to C terminus.

Alanine and Glycine

CHCH33

OO

CC++

HH

CC OO––

HH33NN

OO

CC

HH

HH

CCHH33NN++

OO––

Alanylglycine

Two -amino acids are joined by a peptide bond in alanylglycine. It is a dipeptide.

CHCH33

OO

CCHH33NN++

HH

CC

OO

CCNN

HH

HH

CC OO––

HH

Assignment

Isoelectric point of aminoacids

Protein purification – column chromatography

-Protein mixture applied to column

-Solvent (buffer) applied to top, flowed through column

- Different proteins interact with matrix to different extents, flow at different rates

-Proteins collected separately in different fractions

Strategy for purification of a protein:

Once the protein extract is prepared, in order to prify a single protein from this extract different fractionation methodologies can be used.

•pHH dependent precipitation

•Protein charge based methods: Ion exchange chromatography, electrophoresis, and isoelectric focussing

•Protein size based methods: Dialysis, ultrafiltration, gel Electrophoresis, gel filtration chromatography and ultrafiltration

•Polarity based methods: Reverse phase chromatography, Hydrophobic interaction chromatography, adsorption chromatography

Column Chromatography

1. SIZE—Gel filtration

2. CHARGE—Ion exchange

3. SPECIFIC BINDING—Affinity

Molecules can be separated on the basis of:

Gel filtration chromatography - separation by size

Beads have different size pores

As column flows:

• large proteins excluded from pores and therefore flow rapidly

• small proteins enter pores and flow slowly

Ion exchange chromatography – separation by charge

Beads have charged group: + charge binds acidic amino acids - charge binds basic amino acid

Different proteins bind with different affinity

Eluted with increasing amount of salt (NaCl or KCl)

Different proteins elute at different salt concentrations

Affinity chromatographyseparation by biological binding interactions

washporousbead

glutathione

elute

GST apply sample

thrombin siteprotein of interest

Example: GST - Glutathione

GST-tagged proteins bind to gluthatione on beads

Non-specifically or weakly bound proteins washed off

GST-tagged proteins eluted with glutathione (competitor) or thrombin (protease)

The Battery

The Battery

Main Entry: storage battery Function: noun Date: 1881 : a cell or connected group of cells that

converts chemical energy into electrical energy by reversible chemical reactions and that may be recharged by passing a current through it in the direction opposite to that of its discharge -- called also storage cell.

Battery

HAZARDOUSCONSTITUENT

POSSIBLEEFFECTS

SULFURIC ACID

Corrosive, causessevere skin burns,

and can causeblindness.

LEAD

Causes nerve andkidney damage,

suspectedcarcinogen

Lead Acid Battery

Electrolyte for the most part distilled (pure) water, with some sulfuric acid mixed with the water.

Electrodes must be of dissimilar metals.

An active electrolyte.

Charging

In the charged state, each cell contains negative plates of elemental lead (Pb) and positive plates of lead(IV) oxide (PbO2) in an electrolyte of approximately 33.5% v/v (4.2 Molar) sulfuric acid (H2SO4). The charging process is driven by the forcible removal of electrons from the positive plate and the forcible introduction of them to the negative plate by the charging source. Negative plate reaction: PbSO4(s) + H+(aq) + 2-e → Pb(s) + HSO−4(aq) Positive plate reaction: PbSO4(s) + 2H2O(l) → PbO2(s) + HSO−4(aq) + 3H+

(aq) + 2e

Discharging

In the discharged state both the positive and negative plates become lead(II) sulfate (PbSO4) and the electrolyte loses much of its dissolved sulfuric acid and becomes primarily water. The discharge process is driven by the conduction of electrons from the negative plate back into the cell at the positive plate in the external circuit.

Negative plate reaction(Anode Reaction):Pb(s) + HSO−4(aq) → PbSO4(s) + H+(aq) + 2-e

Positive plate reaction(Cathode Reaction):PbO2(s) + HSO−4(aq) + 3H+(aq) + 2-e → PbSO4(s) + 2H2O(l)

Discharging

The total reaction:

Pb(s) + PbO2(s)+2H2SO4(aq) → 2PbSO4(s) + 2H2O(l)

Copper

Uses of copper Amongst other things copper is used for: electrical wiring. It is a very good conductor of electricity and is easily

drawn out into wires. domestic plumbing. It doesn't react with water, and is easily bent into

shape. boilers and heat exchangers. It is a good conductor of heat and doesn't

react with water. making brass. Brass is a copper-zinc alloy. Alloying produces a metal

harder than either copper or zinc individually. Bronze is another copper alloy - this time with tin.

coinage. In the UK, as well as the more obvious copper-coloured coins, "silver" coins are also copper alloys - this time with nickel. These are known as cupronickel alloys. UK pound coins and the gold-coloured bits of euro coins are copper-zinc-nickel alloys.

Purification of copper

When copper is made from sulphide ores then it is impure. The blister copper is first treated to remove any remaining sulphur (trapped as bubbles of sulphur dioxide in the copper - hence "blister copper") and then cast into anodes for refining using electrolysis.

The purification uses an electrolyte of copper(II) sulphate solution, impure copper anodes, and strips of high purity copper for the cathodes.

At the cathode, copper(II) ions are deposited as copper.

At the anode, copper goes into solution as copper(II)

ions. For every copper ion that is deposited at the cathode,

in principle another one goes into solution at the anode. The concentration of the solution should stay the same.

All that happens is that there is a transfer of copper from the anode to the cathode. The cathode gets bigger as more and more pure copper is deposited; the anode gradually disappears.

In practice, it isn't quite as simple as that because of the impurities involved.

Any metal in the impure anode which is below copper in the electrochemical series (reactivity series) doesn't go into solution as ions. It stays as a metal and falls to the bottom of the cell as an "anode sludge" together with any uncreative material left over from the ore. The anode sludge will contain valuable metals such as silver and gold.

The concentration of ions like zinc will increase with time, and the concentration of the copper(II) ions in the solution will fall. For every zinc ion going into solution there will obviously be one fewer copper ion formed. (See the next note if you aren't sure about this.)

The copper(II) sulphate solution has to be continuously purified to make up for this.