PROTEINS Organic compounds Acid and amino group * nitrogen**** * side group.
Proteins Major group of biological molecules. Proteins Monomers: amino acids ▫Always contain an...
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Transcript of Proteins Major group of biological molecules. Proteins Monomers: amino acids ▫Always contain an...
![Page 1: Proteins Major group of biological molecules. Proteins Monomers: amino acids ▫Always contain an amino group and carboxylic acid group Polymers: peptides.](https://reader035.fdocuments.us/reader035/viewer/2022070407/56649e415503460f94b33fcc/html5/thumbnails/1.jpg)
ProteinsMajor group of biological molecules
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Proteins
•Monomers: amino acids▫Always contain an amino group and
carboxylic acid group•Polymers: peptides
▫Each different sequence of amino acids is a different peptide
•Polymerization Rxn: Condensation Reactions
•Examples: meat, skin, hair, nails, casein
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Amino Acids
•The “R” can be an H or any hydrocarbon or organic functional group
•Amino acids are classified based on properties of R group
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Amino Acid ClassificationsType of Amino Acid R group contains
Non-polar/hydrophobic Hydrocarbon
Polar but charges Alcohol, sulfhydryl (-SH), or amide (-CONH2)
Basic Amino (–NH2)
Acidic Carboxylic Acid (-COOH)
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Zwitterions• Amino acids(AA) can become charged in two
places – thus making them dipolar ions
• Zwitterions result from internal acid/base reaction where the carboxylic acid group on the AA transfers an H to the amino group on the same AA
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Amino Acids are Amphoteric
•AA contain both an acid and base group and are therefore amphoteric (able to act as either and acid or a base)
•As a result, amino acids are very good buffers – resist changes in pH
•pH changes just affect the charge of the AA
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Isoelectric Point
•Isoelectric point is when the AA is neutral – it is a zwitterion
•The isoelectric point of each AA is different
•Changes in pH cause differing charges on the AA
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Condensation to make Proteins
• The bond that results from the condensation reaction of AA to make a protein is called a peptide bond
• The carboxylic acid group on one AA reacts with the amino group on another AA
• Literally millions of possible AA sequences of varying lengths
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4 Levels of Structure for Proteins• Primary-
▫amino acid sequence connected through peptide bonds to form a polypeptide
• Secondary- ▫ through hydrogen bonds between carboxylic
groups and amino groups• Tertiary-
▫ further twisting and folding of polypeptide on itself via interactions of R groups
• Quaternary-▫ Interactions between polypeptide chains
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Primary Structure
•Dictates rest of protein structure
•Forms the covalent backbone of the molecule
•All polypeptide bonds
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Secondary Structure
•Influenced by R groups
•All hydrogen bonding
•Types:▫α-helix▫β-pleated sheet
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Alpha(α) Helix• looks like a spiral-
forms via hydrogen bonding between AA 4 units apart
• It’s flexible and elastic
• Folding of 1 polypeptide (intra-chain H bonds)
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Beta (β)- pleated sheets• Hydrogen bonding
between polypeptides (inter-chain hydrogen bonds)
• Looks like waves stacked on each other
• Are inelastic and therefore well defined
• Aka Fibrous proteins
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Tertiary Structure = conformation•Results from interactions of R groups•All with in the same polypeptide
•Globular conformations are very common and important▫Include all enzymes and hormones▫Water soluble because hydrophilic R
groups on outer surface and hydrophobic on interior
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Stabilization of Globular Proteins•In order of strength:•Hydrophobic interactions
▫– between nonpolar side chains•Hydrogen bonding –
▫between polar side chains•Ionic Bonds –
▫between charged side chains•Disulfide bridges –
▫ covalent bonds between sulfur atoms in cysteine
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Denaturing of Proteins
•Denaturing – when a protein loses its tertiary structure
•Results in protein being inactive/ losing its function
•Caused by:▫Temperature changes▫pH changes
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Quaternary Structure
•Association between different polypeptides
•Ex: ▫Collagen – triple helix of chains▫Haemoglobin – 2 alpha and 2 beta chains
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Hydrolysis of Proteins
•Proteins are analyzed by knowing its amino acid composition
•To do this, the peptide bonds in the polypeptide must be broken
•Are broken through hydrolysis reaction – adding water back onto the amino acids (OH onto carboxyl group and H onto amino end)
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Separation of AA Sequence
•Chromatography▫Particularly useful with colorful substances▫http://www.youtube.com/watch?v=J8r8hN0
5xXk•Electrophoresis
▫Based on movement of charged particles in an electric field
▫http://video.mit.edu/watch/gel-electrophoresis-10949/
▫http://learn.genetics.utah.edu/content/labs/gel/
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Let’s Build…
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