Amino Acids & Peptides Flashcards
What do all AAs (excluding Pro) have in common structurally?
- An acidic carboxyl group connected to the alpha carbon
- A basic amino group connected to alpha carbon
- An alpha hydrogen connected to the alpha carbon
What is unique about the R group in Glycine
The fourth substituent (R group) is also a hydrogen. It’s the simplest AA.
What do neutral AAs have
One COOH & one NH2 group
What do acidic AAs have
Two COOH and one NH2 groups
What do basic AAs have
One COOH group and two NH2 groups
Which 3 AAs are basic
- Lysine (Lys)
- Arginine (Arg)
- Histidine (His)
Which 2 AAs are acidic
- Aspartic acid (Asp)
- Glutamic Acid (Glu)
What do AAs with non polar side chains not participate in
Hydrogen or ionic bonding
Why is Cysteine a special AA
The SH group of two cysteines can be oxidised to form a covalent cross link called a disulphide bond
Why is Glycine a special AA
It’s R group is a hydrogen molecule
Why is Proline a special AA
Its side chainand alpha amino N form a rigid ring structure. Proline is therefore often found at bends or turns in protein structure.
What is desmosine (elastin) formed from
4 Lysine residues
Ubiquitination
- Ubiquitin (a protein) attaches to Lysine via an isopeptide bond
- Mediates protein degradation (tidies AAs before degradation), signalling, trafficking
To which AAs does the process of methylation occur
- Attachment of a methyl group to Lys/Arg
- This regulates RNA processing, transcription, DNA damage repair
To which AAs does phosphorylation occur
- Attachment of a phosphate group to Ser/Thr/Tyr residues
- Done by kinases, reversible process
- Regulates enzymatic activity
To which AAs does Glycosylation occur
- Attachment of glycans (sugars?) to Asn/ Ser/ Thr/ Tyr residues
- Involved in cell-cell interaction and recognition, protein folding and chaperone recruitment
To which AAs does Acetylation occur
- Attachment of an acetyl group to Lysine
- Mediates protein-protein interaction
What form do AAs exist as at low pH
They exist in a positively charged form (cation) at low pH
What form do AAs exist as at high pH
They exist in a negatively charged form (anion) at high pH
When the molecule has both a positive and negative charge, what does the AA exist as
The AA exists in zwitterion form (- carboxyl group & + amino group)
What is the Isoelectric Point of an AA
The point when the net charge of the AA is zero.
What happens to the AA at its isoelectric point
- AA is least soluble in water
- AA doesn’t migrate in electric field
What AA can act as a buffer in two pH ranges
Glycine
What type of reaction is involved in peptide bond formation
Dehydration/condensation reaction (requires ATP)
Where to start when naming peptides
At the N-terminal (Amino Terminal)
4 Functions of peptides
- Hormones & Pheromones: insulin, oxytocin
- Neuropeptides: substance p (pain mediator)
- Antibiotics: polymyxin B (for gram neg), bacitracin (for gram pos)
- Protection: e.g: toxins
3 things proteins could be comprised of
Polypeptides & possibly:
1. Cofactors
2. Coenzymes
3. Prosthetic groups
What differences does separation of proteins rely on
- Charge
- Size
- Affinity for a ligand
- Solubility
- Hydrophobicity
- Thermal Stability
The 7 AAs with ionizable side groups
- Aspartic Acid
- Glutamic Acid
- Histidine
- Cysteine
- Tyrosine
- Lysine
- Arginine
Which of the 7 have terminal alpha carboxyl group (3)
- Aspartic acid
- Glutamic acid
- Histidine
Which of the 7 have terminal alpha amino group (4)
- Cysteine
- Tyrosine
- Lysine
- Arginine
