Module 4 Proteins S22 PDF

 small Large monomer: polymer: amino acid (aa) polypeptide (50-100 AA’s) dimer: → linear, smaller than dipeptide “biological proteins”...

 small Large monomer: polymer: amino acid (aa) polypeptide (50-100 AA’s) dimer: → linear, smaller than dipeptide “biological proteins” trimer: biological protein tripeptide (100’s to 1000’s of aa’s) oligomer: complexly folded, usually oligopeptide (4-50 aa’s) globular *may or may not be present  R → side chain: different for each aa defines which aa it is determines chemical properties can be simple (glycine → H) complex (phe → benzene ring) You must be able to draw the general chemical structure of an aa  H H H O H O H N–C–C OH + H N–C–C OH R R AA1 AA2 Condensation H H O H O reaction: H N–C–C–N–C–C OH + H2O loss of water and R H R joining of 2 Dipeptide Peptide bonds (AA1–AA2) molecules … amino H O carboxyl N–AA1–AA2–AA3–AA4–…–AAn–C terminal H OH terminal Polypeptide(n) R groups In biological proteins, peptide bonds are most often (1000:1) found in the trans form protein dimers, trimers and oligomers “condensation” cis/trans?  “condensation” many condensations 50 to 100 aa’s Peptide bonds  “amino terminus” “carboxy terminus” (for this end of the (for this end of the AA/protein) AA/protein) H H O amine functional N–C–C carboxylic acid group H OH functional group R R → side chain determines which aa it is variable composition may or may not contain functional group(s)  Zwitterion: molecule that has both +ve and –ve charges simultaneously amino acid amine group carboxylic H acid H H O group H cation O N–C–C H – +N – C–C H OH H O– R R anion un-ionized form ionized form (Zwitterion) at our neutral (cellular) pH: (always) amino group accepts H+, carboxyl group donates H+  δ+ H δ– H δ– δ+ O N – C – Cδ+ Hδ+ O – H R δ– δ+ the R side chain determines: The overall properties of the amino acid, including polarity  classification based on: side chain polarity: → non-polar and polar aa’s polar side chains can be neutral, acidic, or basic → polar acidic, polar basic, and polar neutral aa’s You do NOT need to memorize each amino acid, however once we are finished this section you should be comfortable discussing/recognizing what it is that makes an amino acid acidic/basic/polar  Amino acids (non-polar) non-polar aa side chains: consist mostly of C and H atoms (i.e. hydrocarbons) have neutral charge Sulfur-containing AAs another term would be: hydrophobic  Amino acids (polar, neutral) polar neutral aa side chains: contain polar functional groups (e.g. –OH, some NH2 , =O) can occur in both ionized (if at acidic/basic pH) and non-ionized forms (our normal neutral pH)  Amino acids (polar, basic or acidic) polar basic: polar acidic: have a positive charge at neutral pH negative charge at neutral pH amine group (–NH2) accepts a H+ carboxylic acid group (–COOH) ion donates a H+ ion  adults: 8 children: 10 children adults Essential aa’s: Non-essential aa’s: body can’t make can be synthesized by so must be obtained the body from diet *Arginine and histidine: Essential only in children neurotransmitter vasoconstictor hormone: part of circadian rythym Vitamin B  H H Amino acids (aa’s) are joined via H O H O H N–C–C OH + H N – C – C OH successive condensation reactions at R R Carboxyl terminus of new peptide: AA1 AA2 H H O H O 2 or 3 aa’s → di- or tripeptide N–C–C–N–C–C + H2O H OH R H R 4-50 aa’s → oligopeptide Dipeptide Peptide bonds (AA1–AA2) multiple (50+) linear aa’s → … H O polypeptide N–AA1–AA2–AA3–AA4–…–AAn–C H OH Polypeptide(n) single or multiple folded polypeptides (100-1000’s of aa’s) Complex 3-D biological protein (functional) → biological protein  α-helixes X β-sheets w/ connecting loops  side view top view 3.6 aa’s ~10 aa’s hydrogen-bonds  R R R R R hydrogen-bonds R R R R superoxide dismutase catalase “subunit(s)” Disulfide bonds: between two Sulphur atoms on adjacent cysteine aa’s  inactive enzyme active enzyme (subunits dissociated) (subunits associated) superoxide ion Subunits  denaturation disrupts the 2o, 3o, and 4o structure of proteins 1o structure is unaffected due to strong covalent peptide bonds which are not broken by the treatments below: denaturation can occur by: heating (such as when cooking) treatment with acids or bases treatment with organic compounds treatment with heavy metals but… 1o structure is broken by acid AND heat Heat denatures the egg proteins…  main characteristic/function: maintain osmotic pressure/transport non polar molecules  transferrin Immunoglobulin G (IgG) main characteristic/function: transport metal ions/eliminate foreign particles  Fe2+ Hemoglobin 4o structure main characteristic/function: transport of oxygen from lungs to tissues thru blood  main characteristic/function: binding oxygen in muscle cells myoglobin  a) 4o hemoglobin b) 3o myoglobin c) 2o a-helix monomer (active) hormone produced when blood glucose levels are high (stored as inactive hexamer, in pancreatic b-islet cells), released as active hexamer monomer which binds to insulin receptor (inactive) phosphorylation signaling cascade glucose uptake main characteristic/function: vesicle regulate blood glucose levels translocation a cascade of signaling events takes place leading to the translocation of GLUT4 glucose transporter proteins to cell membrane and glucose uptake into cell (and subsequent decrease in blood glucose levels) T3 and T4 are produced in thyroid gland and circulated in blood normally TH’s inhibit the brain pathways that cause their own production low TH levels remove inhibition → greater production main characteristic/function: control of metabolic rate also known as human growth hormone, and is produced in pituitary gland and circulated in blood main characteristic/function: regulate cell/tissue growth promotes lipolysis and gluconeogenesis promotes protein synthesis, increase in muscle cells, bone growth too much: acromegaly too little: dwarfism main characteristic/function: tensile strength ageing → accumulative loss of all body proteins* collagen makes up 25% of body’s protein → filler collagen can be replaced in small amounts by injecting it into areas such as the mouth. note: while collagen DOES act as filler protein it’s main role in body is still tensile strength main characteristic/function: elasticity Elastin gives skin its elastic It is lost with ageing and the properties skin sags as a result found in many tissues: blood vessels, skin, cartilage → consist of a core protein with many polar CHO sidechains carbohydrate chains main characteristic/function: (highly polar) hydration core protein carbohydrate sidechains trap water → hydrated gels Fibronectins are extracellular matrix proteins that crosslink other matrix proteins such as collagen and proteoglycans crosslinks main characteristic/function: adhesion levels actually increase* with age making connective tissue less flexible → skin becomes brittle and wrinkled, joints get stiffer poor lifestyle choices like smoking and excessive alcohol can hasten the loss of extracellular matrix proteins, such as: collagen, elastin, proteoglycans, while increasing fibronectin  both… main characteristic/function: muscle contraction ATP ATP ATP ATP ATP muscle contraction video: https://www.youtube.com/watch?v=7O_ZHyPeIIA  an illustration of how extracellular and intracellular proteins can allow a cell to do many interesting things (just for fun…) structural proteins:  Dietary protein every living cell in our body contains protein On a dry matter basis,~50 % of our body mass comes from protein of the 20 amino acids, our body can only make 10-12 and unlike fats and carbohydrates, the body does not store protein in an easily accessible way → we need a significant amount of protein every day (ideally complete protein) 31% 28% 3% 25% 9% 8% 10–35% (taken from Health Canada website) Cohort Recommended Daily Allowance (g protein/kg BM per day) Average sedentary adult 0.75 → 0.8 Active adult 0.8 → 1.3 Growing athlete 1.3 → 1.9 Adult building muscle mass 1.3 → 1.9  70.5 kg 1.3–1.9 92–134 g/d  Dietary protein sources Protein content (g) 1.5 cups Mini Wheats cereal (1.5 c) x (4 g/0.5 c) = 12 g Breakfast 1.5 cups 1% milk (1.5 c) x (8 g/c) = 12 g 0.75 cups snow peas (0.75 c) x (2 g/0.5 c) = 3 g 2 slices rye bread (2 slices) x (4 g/slice) = 8 g Lunch 2 oz cheddar cheese (2 oz) x (7 g/oz) = 14 g 2 oz pancetta (lunch meat) (2 oz) x (7 g/oz) = 14 g 1.25 cups vegetables (mixed) (1.25 c) x (2 g/0.5 c) = 5 g Supper 6 oz black beans (6 oz) x (6 g/oz) = 36 g 3 oz fresh mozzarella cheese (3 oz) x (7 g/oz) = 21 g Total: 125 g protein  190g it can be difficult to get all the amino acids we need (plants are low in Lys, Met, Trp) low Lys/Met/Trp (all essential AA’s) Vegan diets tend to be low in calcium, Vit D and Vit B-12 (some soy milk and breakfast cereals are fortified with these)