Structure and function of cell components

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Structure and function of cell components

1. Carbohydrates
2. Lipids
3. Proteins
4. Nucleic Acids
5. Membranes
6. Cytoskeleton

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Lipids

• All relatively insoluble in water
• Made of C, H, O (with less O in proportion to C
  and H compared to carbohydrates)
• Fats and oils are familiar lipids
• Fats tend to be solid at room temperature
• Oils tend to be liquid at room temperature
• 3 lipids are of importance to cells
• Triglycerides (triacylglycerol)
• Phospholipids
• Steroids

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Structure of glycerol

• Glycerol is a three carbon alcohol that contains
  3 OH (hydroxyl) groups

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Structure of Fatty Acids

• Fatty acids are hydrocarbon chains ending in a
  carboxyl group (COOH)

• R is an abbreviation for any organic group
• About 30 different fatty acids are commonly found
  in lipids (they nearly always have an even number
  of carbon atoms).

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Structure of Fatty Acids cont

• Saturated fatty acids
• All available bonds are occupied by hydrogens
• E.g
• Palmitic acid CH3(CH2)14COOH
• Stearic acid CH3(CH2)16COOH

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Structure of fatty acids cont

• Unsaturated fatty acids
• Some carbon atoms are double bonded with one
  another, therefore they are not fully saturated
  with hydrogen
• E.g. Oleic Acid CH3(CH2)7 CH (CH2)7COOH
• Note - this is monounsaturated (1 double bond)

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Structure of fatty acids cont

• E.g. Linoleic acid CH3(CH2CHCH)3(CH2)7COOH
• Note this is polyunsaturated (more than 1
  double bond)

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Formation of Ester Linkages

• Glycerol and fatty acids are joined together by
  dehydration (condensation) reactions
• The bond linking glycerol and fatty acids is
  called an ester bond

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Formation of ester linkages cont
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Formation of ester linkages cont
Ester bond
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Structure of Triglycerides

• A triglyceride molecule is the result of a
  glycerol molecule forming ester linkages with 3
  fatty acids
• The type of triglyceride formed is dependent on
  the fatty acids present

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Structure of Phospholipids

• A phospholipid consists of a glycerol molecule
  attached to 2 fatty acids, and a phosphate group
  which is linked to an organic compound (e.g.
  choline)

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Structure of phospholipids cont

• The fatty acid portion of a phospholipid is not
  soluble in water (hydrophobic)
• The glycerol and organic base of a phospholipid
  is water soluble (hydrophilic)
• In water phospholipids form a bilayer with the
  hydrophilic head pointing outwards and
  hydrophobic tail inwards

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Structure of Steroids

• Steroids consist of 4 hydrocarbon rings with
  slightly different side chains.
• The length and structure of the side chains
  distinguish one steroid from another.

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Functions of Lipids

• Structural
• Membranes
• Phospholipid bilayer
• Cholesterol is part of animal cell membranes
  (plants have a similar molecule)
• Adipose tissue cells (contain lipid droplets)
• Cushions vital organs
• Insulation
• Endothermic animals have layers of fat cells
  below the skin to prevent heat loss

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Functions of lipids cont

• Storage
• Energy storage
• Triglycerides insoluble therefore has no
  influence on osmosis
• Fat and lipid molecules are very compact
• Release large amounts of energy
• Water storage
• Fat in camel humps releases water (as well as
  energy) when respired.

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Functions of lipids cont

• Hormones
• Steroid hormones regulate metabolism in a variety
  of animals including vertebrates, insects and
  crabs
• Cholesterol reduces the fluidity of the membrane
• Cholesterol prevents solidification at low
  temperatures

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Learning Activities

• Read and take notes from DART pg 32 37
• Scholar (section 4.3)
• Lipids worksheet
• Use the internet to familiarise yourself with
  different ways of presenting the chemical
  formulae / structures
• Posters and diagrams (compare / contrast)
• Advanced Higher Questions