Proteins Flashcards
What are proteins?
Proteins are heteropolymers of alpha amino acids, most functionally diverse and abundant molecules in living systems.
How many amino acids in Mammalian systems and how are they found?
20 Amino acids in the body, some made in body, essential amino acids are gained from food.
Why are proteins so complex?
Proteins can exist as a single polypeptide, others have same polypeptide (Homomeric) or different polypeptides (heteromeric)
What non protein factors can be added onto proteins?
Lipids, carbs, and metal ions
Also amino acids can be modified
The structure for all Alpha amino acids are the same but one? Which one?
Proline
How are proteins named?
From the central carbon down the R group in the Greek alphabet
How are AAs classified?
AAs are classified by their R group.
R group can be as simple as H (Glycine) to a carbon skeleton with various functional groups.
R groups have four categories of what can affect an amino acid, what are they?
1.Non-charged polar side chains (aliphatic-aromatic)
2.Uncharged polar side chains
3.Acidic
4.Basic
Why can Glycine be hydrophobic and hydrophilic?
Glycine can be polar or non-polar
Why are non polar side chains hydrophobic?
Because hydrogen and carbons make the hydrophobic
Give two points about Proline that makes it different
1.Proline R group is bonded to the amine making its amine group secondary
2.Cyclic structure allows bends within resulting polypeptide
Give two facts about uncharged polar side chains
- They are hydrophilic (good for being on the surface of proteins for aqueous solution)
- They can make H bonds as some have hydroxyl groups, or amide and carbonyl groups (glutamine)
What can Two Cysteines do?
Two Cysteines have -SH groups which can form a disulphide bond to stabilise many extracellular proteins (albumin)
Four main points about acidic side chains
1.Extra COO- group
2.polar
3.Negative charge
4.Hydrophilic
What are aspartate and glutamate (pH 7)
They are amides of asparagine and glutamine
Three main points about basic side chains
- Polar
- Hydrophilic
- Positive charge
3 facts about Histidine (basic)
- Switches between neutral and positive charge and physiological pH
- Found at enzyme active sites
- Helps catalyse making and breaking bonds
Name three amino acids with special properties
Glycine (Adds flexibility and is amphipathic), Proline (ring structure adds kinks), Cysteine (Two can form a disulphide bond within)
Give a couple optical properties about AAs
1.Bonded to four groups (except gly)
2.Chiral Centre
3.Enantiomers of Alpha AAs are labelled either as D- or L-
4.Most in humans are L- configuration
5.D- are rare can be found in bacterial cell walls.
Give a couple spectral properties about AAs
- Do not absorb light so colourless
- Aromatic side chains absorb UV (Phe,Trytophan,Tyrosine 280 nm) allowing spectroscopy of protein concentration.
Post transitional modification of AAs allow addition of:
- Hydroxyl -OH
- Phosphoryl -PO4^3-
- Methyl -CH3
- Acetyl -COCH3
- Carboxylation - COOH
Give 2 points about hydroxylation
1.Added -OH stabilises collagen fibres via H bonds
2.Vitamin C deficiency stops hydroxylation of collagen leading to scurvy.
Give 3 points about methylation
1.Lysine can be methylated up to 3 times at its amino group
2.Histone methylation regulates gene expression
3.N-Methyllysine is found in myosin, a contractile component of muscle.
