Biological Molecules

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Biological Molecules
2011-08-09 10:48:51

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  1. Carbohydrates
    • Monosaccharides
    • Disaccharides
  2. Monosaccharides
    • Small molecules
    • Soluble in water
  3. Monosaccharides
    • Contain carbonyl functional grp C=O
    • Easily oxidised hence are powerful REDUCING AGENTS
  4. Beta Glucose
  5. Alpha glucose
  6. Reducing Sugars
    • Glucose
    • Galactose
    • Fructose
    • Maltose
    • Lactose
  7. Non Reducing Sugars
    • Sucrose
    • Starch
  8. Fuctions of glucose
    • Respiratory Substrate
    • Synthesis of disaccharides
  9. Disaccharides
    • Carbohydrates made of 2 monosaccharides linked together by Glycosidic bond
    • Glycosidic bond can be broken by HYDROLYSIS (addition of water)
  10. Disachharide synthesis
  11. Combinations
    • Glucose + glucose = maltose + water
    • Glucose + galactose = lactose + water
    • Glucsoe + fructose = sucrose + water
  12. Disaccharides
    • Energy yielding and transport molecules
    • i.e. Lactose for young mammals
    • Sucrose transported in plants
  13. Reducing sugar
    • Free Carbonyl Group -C=O which acts as the reducing grp
    • Benedict's Test (Blue -> Brick Red)
    • Sucrpse must first be hydrolysed into glucose and fructose by heating with HCL then test with Benedict's
  14. Polysaccharides
    • Macromolecules
    • Polymers of sugar units in which a few hundred to a few thousand monosaccharides are linked together by glycosidic bonds
    • Energy storage or structural materials
  15. Storage - Starch
    • Insoluble starch granules
    • Starch polymer of α-glucose

    Amylose and amylopectin
  16. Amylose
    • Condensations btw many α-glucose molecules
    • Unbranched
    • Linked by α(1,4) glycosidic bonds
    • Amylose chain coiled into a helix
    • No cross linking of amylose chain as most hydroxyl groups of glucose residues project into interior of helix
    • Amylose in water - blueblack color with iodine potassium iodide solution
  17. Amylopectin
    • 1,4 linked α-glucose molecules
    • Amylopectin chain shorter than amylose
    • Branched Structure - branches formed by α(1,6) glycosidic linkages
    • Helix
    • No cross linking
    • Amylopectin in water - red-violet color in iodine potassium iodide solution
  18. Function of Starch
    • Food storage
    • Source of carbon and energy when needed
  19. Glycogen
    • Prevalent in skeletal muscles & liver cells
    • Cytoplasmic granules
    • 1,4 linked α-glucose with 1,6 linkages forming branches
    • shorter chain and more highly branched than amylopectin
  20. Function of glycogen
    Carbon and energy storage
  21. *Properties that make starch and glycogen good storage molecules
    • Composed of several thousands of glucose molecules linked by glycosidic bonds
    • Upon hydrolysis, release large amount of energy
    • Insoluble in water
    • Can be stored in large quantities without affecting osmotic potential of cells
    • Can be compacted
    • Branched structure allows for extensive coiling
    • More starch/glucose can be stored per unit volume
    • Easily hydrolysed
    • Branched structure allows many enzymes to act on it at any one time
  22. Structural Polysaccharides - Cellulose
    • Unbranched polymer of β-glucose molecules
    • Successive residues rotated 180
    • β(1,4) linkages make chain straight
    • -OH- groups project outwards from chain in all directions and form H bonds with neighbouring chains
    • Cross-linking
    • Chain form microfibrils which then form macrofibrils
  23. *Cellulose good structural molecule
    • Cellulose chains associate to form microfibrils then macrofibrils
    • Tremendous tensile strength
    • Give cellulose stability and structural properties

    Macrofibrils arranged in several layers in cell walls in a gluelike matrix Gives added strength

    Prevents cell from busting allows development of turgidity

    Fully permeable
  24. Lipids - Triglycerides
    • Condensation between 3 fatty acids and a glycerol molecule
    • Formation of ester bonds
    • Fatty acids - saturated/unsaturated

    • Saturated - no double bonds
    • Unsaturated - have double bonds
  25. Unsaturated fatty acids
    Tend to be liquid at room temp
  26. Saturated fatty acids
    • Solid at room temp
    • Fats
  27. Function of Triglycerides
    Energy store as it has a higher calorific value (38)

    Excellent Insulator

    Provide buoyancy

    • Long term energy store
    • last to be oxidized only after carbo and protein depleted

    mechanical protection (cushion)

    • source of metabolic water
    • release twice as much as water as carbo when oxidized during resp
  28. Lipid - Phospholipids
    • Polar due to ionising of phosphate group (in place of 1 fatty acid)
    • Phosphate head
    • -ve charge
    • Hydrophilic

    Fatty acid chains however are hydrophobic

    Hence it is amphipathic
  29. Functions of Phospholipids
    • Formation of membranes
    • Amphipathic nature enables them to form cell membranes made up of double layer of phospholipids in an arrangement called a phospholipid bilayer

    • Formation of glycolipids
    • oligosaccharides associate with phospholipids to form glycolipids which function as markers for cell cell recognition
  30. Lipids - Cholesterol
    • Insoluble
  31. Functions of cholesterol
    • Maintainence of cell membrane fluidity
    • High temp, makes membrane less fluid by restraining movements of phospholipids
    • Low temp, hinders solidification by disrupting regular packing of phospholipids

    synthesis of other steroids
  32. Proteins
    • Basic unit - Amino Acids
    • 4 functional group
    • Basic amino group -NH2
    • Acidic carboyxl group -COOH
    • Hydrogen atom
    • R group
  33. Amino Acids
    • Exist as zwitterions
    • Both acidic and buffer properties
    • Amphoteric
    • Acts as buffers
  34. Amino acids
    join together forming polypeptide by peptide bond

    • 4 types of other bond that allows polypeptide chain to fold spontaneously to assume functional conformation
    • hydrophobic interactions
    • hydrogen bond
    • ionic bond
    • disulphide bond
  35. Peptide Bond
    • Covalent bond between amino group of the amino acid and carboxyl group of another
    • Condensation
    • Side chains sticking out
    • Polypeptide backbone (bottom)
  36. Ionic Bond
    • formed between acidic and basic R groups
    • Acidic R grps -vely charged
    • Basic R grps +vely charged
    • Groups can be attracted to one another forming ionic bonds
    • Interchain and intrachain
    • Bond is weaker than peptide as it can be broken down by changing pH
  37. Disulphide Bond
    • Amino Acid - Cysteine contains a -SH in its R grp
    • 2 molecules of cysteine
    • Neighbouring sulphydryl grps can be oxidiszed to form disulphide bond
    • Interchain/intrachain
  38. Hydrogen Bond
    • due to unequal sharing of e- in OH- and amino grps
    • Inter/intra chain
    • WEAK but contribute to molecular stability due to frequent occurence
  39. Hydrophobic Interactions
    • Non Polar R groups = hydrophobic
    • Chain will fold so that max no. of hydrophobic grps come into close contact AWAY from water
    • Hydrophobic grps point inwards towards centre
    • Hydrophilic grps face outwards into aq. environment
    • Making protein soluble
  40. From strongest to weakest
    • Disulphide Bond
    • Ionic Bond
    • Hydrogen Bond
    • Hydrophobic Interactions
  41. Each protein has a characteristic 3D shape, specific conformation
    • Primary
    • Secondary
    • Tertiary
    • Quanternary
  42. Primary Structure
    • Unique number and sequence of amino acids in polypeptide chain
    • Specified by DNA in nucleus
    • Determines the overall shape and hence the function of a polypeptide
  43. Secondary Structure (SFS)
    Secondary Fibrous Structural
    • Segments of polypeptide chains repeatedly coiled or folded
    • Protein's overall conformation
    • Result of hydrogen bonds btw repeating constituents of polypeptide backbone not amino acid side chains
    • Proteins (secondary) fibrous in nature
    • Structural functions
  44. Secondary Structure - alpha helix
    • Structure stabilized & maintained by hydrogen bonds btw neighbouring -CO and -NH grps
    • H atom of -NH grp of 1 A.A bonded to the O atom of the -CO grp about 4 A.A away in the SAME chain
    • Alpha helix makes 1 complete turn for every 3.6 A.A
    • Very stable
  45. Secondary Structure - Beta Pleated Sheet
    • Adjacent strands held together by H bonds formed btw -CO and -NH grps to form the sheet
    • Intra/Inter chain sheet
    • All -CO and -NH grps are involved in H bonding so structure is stable and rigid
    • Compact R grps
  46. Tertiary Structure
    • Overall 3D structure of polypeptide
    • Bending twisting folding of secondary structure to form a very specific shape characteristic of the protein
    • Interactions btw R groups (sidechain)
    • Generally globular in nature
    • Soluble in water
    • All 4 bonds btw R grps of A.A maintain tertiary structure of protein
  47. Quaternary Structure
    • Consist of 2 or more polypeptide chains
    • Each chain is known as the subunit of the protein
    • Separate chains held together by interactions btw R grps of different subunits
    • ALL 4 BONDS
  48. Denaturation
    is the loss of the specific three-dimensional configuration of a protein molecule
  49. Denaturation
    • Temporary or permanent
    • BUT Amino Acid sequence [primary structure] is not affected
    • Molecule unfold and no longer perform biological function
  50. Denaturation agents
    Heat/radiation - kinetic energy supplied to protein cause atoms to vibrate disrupt weak H and ionic bonds

    Strong acids/alkalis - ionic bonds disrupted, breakage of peptide bonds possible if exposed fr long time

    Heavy metals - +vely charged ions of heavy metals form strong bonds with -vely charged carboxyl grps on R grps of proteins disrupt ionic bonds

    • Organic solvents/alcohol/detergents - disrupt hydrophobic interactions and form bonds with hydrophobic grps
    • disrupt H bonds
    • Alcohol disinfect by denaturing proteins of bacteria present
  51. Renaturation
    protein spontaneously refold into original structure when conditions are favourable

    evidence that primary structure determined the rest of the struture
  52. Classification of proteins
    • Fibrious protein
    • Globular protein
  53. Fibrous Proteins - Collagen (structural in nature)
    • Secondary Structure
    • No tertiary structure
    • Polypeptide chain cross-linked at intervals to form long fibres/sheets
    • Insoluble in water due to hydrophobic R groups on exterior of molecule
    • Amino acid sequence may differ slightly btw 2 samples of same fibrous protein
    • Length of chain may vary
    • Amino acid seq. regular
    • Structural functions
  54. Globular Proteins - Haemoglobin
    • Tertiary structure!
    • Quanternary may or may not be present
    • Spherical shapre tightly folded
    • Dissolve in water to form collodial solutions due to hydrophilic R grps jutting outwards
    • A.A seq highly specific and never varies btw 2 samples as substituition of just a single A.A residue can cause major alteration in function of protein
    • Length always identical
    • Exhibit irregularities in amino acid seq.
    • Metabolic functions
  55. Collagen
    • basic unit = tropocollagen
    • tropocollagen = 3 polypeptide alpha-chains

    repeating tripeptide seq. of glycine proline hydroxyproline

    3 left handed helical strands wind around to form triple helix

    held together by cross links btw chains (H bonds and covalent bonds)

    Tropocollagen assemble to form collagen fibrils then collagen fibres
  56. *Collagen good structural protein
    • insoluble in water
    • great tensile strength - different tropocollagen molecules staggered and cross linked covalently to form collagen fibril
    • 20-100 collagen fibrils then combine to form collagen fibres - giving collagen additional strength
  57. Globular Protein - Haemoglobin
    • 97% of RBC
    • transport oxygen from lungs to capillaries
    • Tetrameric protein - 4 subunits
    • Quaternary structure - 2 α chains and 2 β chains
    • tetramer compose of 2 identical dimers
    • α1β1 & α2β2
    • bonds involve intrachain: hydrophobic interaction, ionic and hydrogen
    • 2 dimers held by weak polar bonds hence can move wrt each other
  58. Haemoglobin subunit
    • Protein component (globin)
    • Non protein component (haem)
    • Structure is globular with deep hydrophobic cleft (hence hydrophilic R grps jutting outwards)
    • Haem binding pocket lined with hydrophobic AA residues provide hydrophobic environment for haem group
  59. *What makes haemoglobin suited for its function (transport molecule)
    Globular in shape = allows many haemoglobin molecules to be packed into a single RBC, maxmising O2 carrying capacity of each RBC

    Consists of 4 subunits each can bind to 1 O2 molecule = facilitates transport of O2

    Soluble in aq. medium as hydrophilic a.a residues are on the outside thus a good transport protein for O2 in blood

    Binding of O2 is reversible = binding of O2 molecule reversibly to Fe2+ in poryphryin ring ensures oxygen molecule can be released where it is needed

    Exhibits cooperativity = property of proteins where binding of a ligand to 1 site of a protein changes affinity of another site for that ligand

    • When an O2 molecule binds to 1 haemoglobin subunit the binding induces a conformational change in the remaining subunits which increase the affinity for oxygen at the remaining 3 oxygen binding sites
    • Facilitates loading of oxygen in oxygen rich areas such as the lung

    When haemoglobin reaches oxygen-deprived tissues, the unloading of the 1st oxygen molecule induces a conformational change in the other 3 subunits that lowers their affinity for oxygen, result in rapid unloading of other 3 oxygen molecules