Molecules

physical properties of water and its importance.

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  • Created by: Brieanna
  • Created on: 04-11-13 18:23

Physical properties of water

SOLVENT PROPERTIES:

  • Dipolar molecule - it has electronegative O ions and electropositive H ions
  • THEREFORE - substances can be easily attracted to the molecule and dissolved into it as they will be attracted to one of the charged ions.
  • Hydrogen bonds - collectively hydrogen bonds make a stable substance and so dissolving other molecule into it does not affect it.
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Physical properties of water

HIGH SPECIFIC HEAT CAPACITY:

  • Very high and much of the heat is used to break hydrogen bonds.
  • This means water does not rapidly change temperature and so can sustain life because an organism would not have to keep adapting or using its own resources to cool down/warm up

HIGH LATENT HEAT OF VAPORIZATION:

  • Hydrogen bonds attract water molecules together so vapour finds it hard to escape
  • It requires a lot of energy for water to vapourize 
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Biological importance of water

SOLVENT PROPERTIES:

  • Allows water to be transport medium (e.g. removal of urea and ammonia in urine).

TRANSPIRATION STREAM:

  • Water continuously able to move up xylem because of COHESION between water molecules and adhesion between water and walls of xylem.

MOLECULAR ABILITY:

  • Hydrogen bonds weakness means water constantly moves -  necessary for osmosis.
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Biological importance of water

METABOLIC FUNCTIONS:

  • Water is used as a reagent in photosynthesis
  • Water hydrolyses macromolecules
  • Water is a medium for all biochemical reactions

TRANSPARENCY:

  • Visible light can pass through so photosynthesis is possible in relatively shallow aquatic environments.

THERMOREGULATION:

  • High specific heat capacity means bodies that are mainly water are stable so less likely to be damaged by environmental changes
  • High latent heat of vaporization means body can be cooled with little water loss
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Monosaccharides and disaccharides

MONOSACCHARIDE:

  • Simple sugar - GF - (CH2O)n
  • It is a monomer

DISACCHARIDE:

  • 'double sugar' 
  • formed by two monosaccharides by a glycosidic bond
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Glucose

GLUCOSE:

  • six carbon atoms - HEXOSE SUGAR
  • C6H12O6
  • energy source
  • highly soluble
  • two forms : alpha and beta glucose 
  • These are structural isomers - the difference is the position of the OH group on the first Carbon
  • Glucose can bond to other sugars to make disaccharides and polysaccharides (starch and glycogen)
  • Soluble so affects osmosis and water movement in cells
  • lots of energy stored in the bonds
  • can be broken down in aerobic respiration to produce ATP 
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Monosaccharides and disaccharides

ALL MONOSACCHARIDES ARE REDUCING SUGARS

DISACCHARIDES:

  • Formed when two monosaccharide molecules join together with a glycosidic bond
  • The glycosidic bond forms between a hydroxyl (OH) group and another OH group on another molecule.

IT IS CALLED A 1,4 GLYCOSIDIC BOND

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Polysaccharides

  • Polymers made from monomers (monosaccharides)
  • GF - C6H10O5
  • Held together by 1,4 or 1,6 glycosidic bonds
  • 1,6 = O - CH2 - C (last carbon)
  • 1,4 is OH and OH
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Starch (Polysaccharide)

STARCH

 AMYLOSE  - 1,4 glycosidic - alpha glucose - unbranched - helical - compact -storage -               respiratory substrate.

AMYLOPECTIN  - 1,4 and 1,6 glycosidic - alpha - highly branched

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Glycogen

  • 1,4 and 1,6 glycosidic (lots)
  • alpha glucose
  • very branches (more than amylopectin) 
  • more soluble than starch
  • easily broken
  • stored as granules in liver and muscles
  • dense
  • create energy for metabolic processes
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Cellulose

  • 1,4 glycosidic
  • beta glucose
  • every other molecule rotates 180 to make adjacent hydroxyl groups
  • unbranched
  • microfibrils
  • hydrogen bonding
  • for tensile strength in cell walls to prevent cell bursting when full of water
  • structural support
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Lipids

  • Insoluble in water
  • Soluble in organic solvents
  • contain hydrogen, carbon, oxygen
  • Triglycerides are the most common form

TRIGLYCERIDES:

  • Formed by esterification ( condensation ) - ESTER BOND
  • Between 3 fatty acids and a glycerol

Fatty Acids:

  • Carboxyl group (-COOH) and general formula CH3(CH2)nCOOH
  • Separates from water

ESTERIFICATION:

  • Each glycerol end (H part of OH) joins to HO of fatty acid = water
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Fatty Acids

SATURATED:

  • single bonds
  • straight chains

UNSATURATED:

  • kinked chain
  • some double bonds
  • cis and trans
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Phospholipids

  • major component of cell membranes
  • contain glycerol, fatty acids and a phosphate group with an alcohol group ('x')

- Phospholipids are amphiathic

  • they have both hydrophillic and hydrophobic parts
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Structure of proteins

What are proteins?

  • diverse groups of large and complex polymer molecules
  • made from chains of amino acids
  • proteins are main components in body tissues
  • catalysts
  • 20 different amino acids
  • General structure:
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Bonding in amino acids

- Condensation reaction

- Peptide bond 

- Water released

- Reversible reaction

- Covalent bond

- Two amino acids = dipeptide

- A long chain = polypeptide

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Protein Structure

PRIMARY:

  • sequence of different amino acids along a polysaccharide chain

SECONDARY:

  • shape formed by amino acid chain as it bends and twists to form the most stable arrangement
  • alpha helix 
  • beta pleated sheet

TERTIARY:

  • 3D form of the amino acid as the polypeptide chain folds and bends
  • bonds: hydrogen, ionic and disulfide bridges
  • hydrophobic - inside, hydrophillic - outside
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Fibrous Proteins

  • formed from parallel polypeptide chains held together by cross links
  • long
  • rope-like
  • high tensile strength
  • generally insoluble in water

COLLAGEN:

  • fibrous, insoluble
  • each molecule has 3 polypeptide chains wound round each other
  • hydrogen bonds between chains
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Globular Proteins

  • spherical shape (tightly folded polypeptide chains)
  • hydrophobic on inside and hydrophillic on outside
  • soluble
  • transport proteins

HAEMOGLOBIN:

  • 4 polypeptide chains
  • 2 alpha, 2 beta
  • carries oxygen from lungs to tissues (oxyheamoglobin)
  • each polypeptide has a haem prosthetic group which contains an iron ion
  • ENZYMES ARE GLOBULAR PROTEINS
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