f212 Biological Molecules

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Carbohydrates

  • All monosaccharides are reducing sugars 
  • Cn(H2O)n
  • Alpha glucose (plants & animals can break down) - starch & glycogen 
  • Beta glucose (plants & animals cannot break down) - cellulose
  • Structural isomers = different shaped forms of the same molecule
  • Disaccharides formed by 2 monosaccharides joining together to form a disaccharide
  • Glucose + glucose = maltose
  • New covalent bond - glycosidic bond formed
  • Glucose molecules contain a large number of bonds that can be broken to form simpler molecules
  • Breaking down of glucose in respiration releases energy
  • This energy can be used to make ATP 
  • In living organisms glucose is broken down in many steps by enzymes
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Monosaccharides

Glucose

  • Small, sweet, soluble & crystalline
  • Energy via respiration 
  • Deoxyribose (5C) 
  • Information molecule
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Disaccharides

Maltose

  • Glucose + glucose = maltose
  • Further condensation reactions - amylose - coil into spring - insoluble
  • Sugar obtained when starch broken down in hydrolysis reaction
  • Split glucose during respiration
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Polysaccharides

Starch

  • Long, straight chain amylose 
  • Branched amylopectin (1,4 glycosidic bond - helical and 1,6 glycosidic bond - branched)
  • Chloropasts in membrane bound starch grains
  • Energy-storage carbohydrate in PLANTS. 
  • Starch - glucose - ATP

Cellulose

  • Large molecules 
  • Many beta-glucose molecules
  • Insoluble in water 
  • Very strong 
  • Structural 
  • Plant cell walls 
  • Cross-linked by H bonds- microfibrils & macrofibrils
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Proteins from amino acids

Function

  • Structural 
  • Enzymes
  • Hormones
  • Antibodies
  • Membrane carriers & pores - active transport & facilitated diffusion 

Primary structure

  • Specific sequence of amino acids that make up the protein

Secondary structure

  • Coiling & pleating of parts of the polypeptide molecule 

Tertiary structure

  • Overall 3D structure of the final polypeptide or protein molecule
  • Hydrophobic, hydrophilic interactions, disulfide bonds & ionic interactions
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Haemoglobin

Quaternary structure

  • 4 polypeptide subunits: 2 alpha & 2 beta chains
  • 4 subunits form one haemoglobin molecule which is water-soluble globular protein
  • Haemoglobin's function is to carry oxygen from the lungs to the tissues
  • Binds oxygen in the lungs & releases it in the tissues
  • Haem group (prosthetic group) contains Fe2+ ion
  • An oxygen molecule can bind to iron in haem group 
  • One complete haemoglobin molecule can bind up to 4 oxygen molecules
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Collagen

Quaternary structure

  • Fibrous protein 
  • Insoluble in water
  • 3 polypeptide chains wound around each other
  • Each of the 3 chains is itself- made up of 1000 amino acids
  • Hydrogen bonds form between the chains - structure strength
  • Each collagen molecule forms covalent bonds - cross-links with other colagen molecules.
  • Cross-links are staggered along the collagen molecules - adding strength
  • Collagen fibril
  • Collagen fibre
  • Approximately 35% molecule's primary structure os glycine
  • Collagen's functions:
  • Walls of arteries preventing blood that is being pumped from the heart at high pressure from bursting walls
  • Tendons form strong connection that allows muscles to pull bones for movement
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Lipids

Triglyceride

  • Glycerol 
  • 3 fatty acids
  • Compact energy store
  • Insoluble in water - no effect on water potential 
  • Stored as at 
  • Thermal insulation 
  • Protective properties

Phospholipid

  • Phosphate head - hydrophilic
  • Glycerol 
  • 2 fatty acids - hydrophobic
  • Perfect for cell membranes
  • Phosphate group may have carbohydrate attached - glycolipids involved in cell signalling

 

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Polysaccharides

Glycogen

  • Alpha glucose subunits
  • Large branched molecule
  • Different from amylopectin 
  • 1,4 glucose chain shorter & branched more
  • More compact than starch
  • Energy-storage carbohydrate in ANIMALS. 
  • Glycogen granule in animal cells
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Lipids

Cholesterol

  • 4-C based ring structures joined together
  • Forms small, thin molecule that fits into lipid bilayer
  • Strength & stability
  • Steroid hormones
  • Excess cholesterol: bile (cholesterol sticks together forming lumps - gallstones) & blood (deposited in innter lining of blood vessel - atherosclerosis - circulatory problems)
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