Amino Acids, Peptides and Proteins

  • Created by: LBCW0502
  • Created on: 13-10-17 12:35
Proteins are linear polymers consisting of which monomers?
L-alpha amino acids
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Give 7 biological functions of proteins
Hormones, enzymes, transporters, receptors, carriers, defence agents and contractile structures
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Give 3 pharmaceutical uses of proteins
Targets for drugs, drug synthesis, bio-markers
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What are the main groups in an L alpha amino acid?
Carboxyl group, central carbon, amino group, hydrogen atom and R (side group)
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Why is the L alpha amino acid described as zwitterionic?
A positive charge from the amino group and a negative charge from the carboxyl group can be present within the molecule
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How many different L-alpha amino acids are used in mammalian peptides and proteins?
20
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How do you distinguish between an L amino acid and a D amino acid?
CO-R-N clockwise gives L and CO-R-N anticlockwise gives D
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Why are D-alpha amino acids used in drugs?
Cannot be broken down easily (last longer in the body)
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How many amino acid side groups do you need to know?
10 (see table in lecture slide)
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Which chemical agent is used for amino acid detection?
Ninhydrin (turns purple)
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How is a peptide bond formed?
Through a condensation reaction (peptide bond between CO and NH)
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How many amino acids are in a dipeptide?
2 amino acid residues
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How many amino acids are in a tripeptide?
3 amino acid residues
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How many amino acids are in a tetrapeptide?
4 amino acid residues
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How many amino acids are in a oligopeptide?
A few amino acid residues
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How many amino acids are in a polypeptide?
Many amino acid residues
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Almost all bonds in peptides and proteins are trans or cis?
Trans (60%)
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What is the primary structure of a protein?
Specific sequence of amino acids residues (ordered list) written from N terminus to C terminus. There are peptide bonds and disulfide bonds (topology)
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What is the secondary structure of a protein?
Local folding of peptide chain stabilised by hydrogen bonds between CO and NH
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What are the three types of secondary structures?
Helices, beta pleated sheets and turns
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Describe the structure of helices
Helices are characterised by the number of residues per turn (most common - right hand alpha helix). 3.65 amino acid residues per turn wound in a clockwise sense
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What are the two types of beta pleated sheets?
Parallel and anti-parallel
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What is the difference between the two types of beta pleated sheets?
In a parallel beta pleated sheet, the order of amino acid residues are in the same direction with non-parallel hydrogen bonds. In anti-parallel, the order of amino acids are in different directions on the two chains, leading to parallel H bonds
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Are beta pleated sheets flat?
No
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Describe the structure of reverse turns
Involves 4 amino acid residues joined by peptide bonds and stabilised by H bonds between CO and NH of first and third amino acid (involves Gly and Pro)
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What is BCA?
Bicinchonic acid
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What is the purpose of BCA?
Reacts with copper ions to form a complex (colour changes from green to purple)
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What are protein assays?
Proteins extracted from cells separated by electrophoresis & stained with Coomassie Blue
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What can oxytocin be used to treat?
Postpartum haemorrhage (but oxytocin is not compatible with bisulfites a preservatives
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What has been used to overcome the issue of oxytocin becoming ineffective due to temperature?
Put in a solid state (dry powder) to be inhaled - there is a higher thermal stability
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Describe the tertiary structure of a protein
Overall folding of polypeptide chain in protein, stabilised by non-covalent interactions between residue side chains
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What are the three interactions in the tertiary structure?
Electrostatic, van der Waals and hydrogen bonding
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How do amino acid residues distribute themselves in a globular protein?
Polar surface on the outside with a hydrophobic core
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What is the major driving force for protein folding?
Hydrophobic effect (protein folding occurs spontaneously)
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How do amino acids residues arrange themselves in an enzyme?
In two domains (e.g. pancreatic trypsin)
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Give two examples of proteins with quaternary structures
Insulin (hexamer with 6 identical sub units) and haemoglobin (tetramer with 2 alpha and 2 beta sub units)
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Non-covalent association of sub units forms which structure?
Oligomeric structure
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What are the advantages of a quaternary structure?
More efficient storage, efficiency in synthesis, economy of DNA allosteric interactions
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Describe the structure of immunoglobulins
4 polypeptide chains, 12 domains, 4 per heavy chain, 2 per light chain, constant region, variable region and disulfide bridges
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What are supersecondary structures?
Preferred arrangement of secondary proteins, found in unrelated proteins, more energetically stable, associated with DNA binding, calcium binding and nucleotide binding
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What are fibrous proteins?
Structure which form fibres, they have repeating amino acid sequences e.g. collagen (triple helix), keratin (coil)
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What are the two known structural classes of membrane proteins?
Alpha helical bundle and beta barrel
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Which factors cause protein denaturation?
High temperature (disrupt H bonds) and extreme pH (changes electrostatic interactions between side chains) - leads to unfolding of protein
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Card 4

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What are the main groups in an L alpha amino acid?

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Card 5

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Why is the L alpha amino acid described as zwitterionic?

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