TL - Amino Acids and Proteins Flashcards
Define amphoteric
A compound that has both acidic and basic properties
What functional groups make amino acids amphoteric?
A basic amino group (NH₂) and an acidic carboxyl group (COOH)
Describe an amino acid
A central carbon atom bonded to:
- A hydrogen atom
- An amino group
- A carboxyl group
- A variable R group
Define zwitterion
A dipolar ion - it has both a positive and a negative charge in different parts of the molecule
Zwitterions only exist near a that molecule’s isoelectric point
Define isoelectric point
The pH at which the average overall charge on a dipolar ion is 0
Describe the structure of an amino acid when the pH is lower than its isoelectric point
The -NH₂ group is protonated (-NH₃⁺)
Describe the structure of an amino acid when the pH is at its isoelectric point
It exists as a zwitterion where both the amino group and the carboxyl group are ionised
Describe the structure of an amino acid when the pH is higher than its isoelectric point
The -COOH group loses its proton (-COO⁻)
Describe how you would identify a mixture of unknown amino acids and name the technique
Paper Chromatography
1) Draw a pencil line near the bottom of a piece of chromatography paper and put a concentrated spot of the mixture of amino acids on it
2) Dip the bottom of the paper (not the spot) into the solvent
3) As the solvent spreads up the paper, the different amino acids move with it, but at different rates, so they spread out
4) When the solvent nearly reaches the top, take the paper out and mark the solvent front with a pencil
5) Amino acids aren’t coloured, so spray ninhydrin solution on the paper to turn them purple
6) Work out the Rᶠ values and compare them to a table of know amino acid Rᶠ values to identify the amino acids
Give the equation to calculate the Retention factor (Rᶠ) using paper chromatography
Rᶠ= Distance moved by spot / distance moved by solvent
What compound is used to show amino acids on a paper chromatograph and what colour do they turn
Ninhydrin solution
Amino acids turn: Colourless → Purple
What are the condensation polymers of amino acids?
Proteins
In what reactions do amino acids:
i) form bonds
ii) break bonds
i) Condensation
ii) Hydrolysis
What bonds are formed between the amine groups and carboxyl groups of amino acids?
Peptide bonds (-CO-NH-)
Give the conditions and reactants required to hydrolyse proteins
Hot aqueous 6moldm⁻³ HCl
Heated under reflux for 24 hours and then neutralised
State and describe the 4 levels of structure for proteins
1) Primary Structure - the sequence of amino acids in a polypetide chain
2) Secondary structure - the hydrogen bonds formed between a polypeptide chain creating Alpha helixes and Beta pleated sheets
3) Tertiary structure - The polypeptide chain is further coiled and folded by different bonds between the R groups of the amino acids
4) Quaternary structure - The structure produced when multiple polypeptide chains bond together
Name and describe the 4 bonds that can hold a tertiary structure together
All these forces exist between the side chains (R-groups) of the amino acids
1) ID-ID forces - weak attractions between 2 non-polar side groups (e.g. CH₃)
2) Ionic interactions between charged side groups (e.g. CO₂⁻ and NH₃⁺)
3) Hydrogen bonding - between groups such as -OH and -NH₂
4) Disulfide bridges - a covalent bond between 2 sulfur-containing side groups (-SH). This type of bonding is stronger than the others
Why are the bonds in the tertiary structure so important to a proteins’ function?
Because it’s the 3D structure that gives proteins their properties
