Topic 2.3 Carbohydrates

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Topic 2.3 Carbohydrates Lipids
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What are carbohydrates?

• Carbohydrates are biological molecules composed
  of carbon, hydrogen and oxygen. They are mainly
  used as a source of energy for living things.
• Animals consume carbohydrates, use them to fuel
  cellular respiration to produce ATP and can store
  a small amount of the ones they do not use.
• Plants produce carbohydrates via photosynthesis,
  use them for cellular respiration to produce ATP
  and store the ones they do not use.

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2.3 (U1) Monosaccharides are linked together by
condensation reactions to form disaccharides and
polysaccharide polymers.

• Monosaccharides are single unit sugars. Common
  monosaccharides are glucose, fructose and
  galactose.

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2.3 (U1) Monosaccharides are linked together by
condensation reactions to form disaccharides and
polysaccharide polymers.

• Disaccharides are double unit sugars composed of
  two monosaccharides held together by an oxygen
  bond created during a process known as a
  condensation reaction.
• Common disaccharides are maltose, sucrose and
  lactose.

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2.3 (U1) Monosaccharides are linked together by
condensation reactions to form disaccharides and
polysaccharide polymers.

• Polysaccharides are many monosaccharides bonded
  together and three examples are starch, glycogen
  and cellulose.

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2.3 (A1) Structure and function of cellulose and
starch in plants and glycogen in humans.

• See handout given in class for specific details
  on the function and structure of both
  polysaccharides.

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2.3 (S1) Use of molecular visualization software
to compare cellulose, starch and glycogen.

• You are responsible to complete an ICA using
  software known as JMol.
• It will help you learn more about the molecular
  structure of polysaccharides.

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Condensation reaction

• A condensation reaction joins two molecules
  together to form a larger molecule and a water
  molecule is formed as a result.
• A monosaccharides loses an OH from one end while
  the other monosaccharide loses an H which then
  combine to form a water molecule.
• Condensation reactions are an anabolic process
  and energy in the form of ATP is used to build
  the polymers.

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Formation of a disaccharide
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Lipids

• Although lipids are a very diverse group of
  carbon containing compounds, they are all
  insoluble in water.
• One of the principal groups are known as
  triglycerides (i.e., fat in adipose tissue in
  humans and the oil in sunflower seeds).
• Lipids can be categorized as fats, oils and
  waxes. Fats are solid at room temperature (20C)
  but liquid at body temp (37C). Oils are liquid
  at both temperatures.

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2.3 (U4) Triglycerides are formed by condensation
from three fatty acids and one glycerol.

• Triglycerides are formed by a condensation
  reaction that includes one glycerol molecule and
  three fatty acids.
• Each fatty acid is bonded to the glycerol
  molecule in three condensation reactions
  therefore three water molecules are produced.
• The bonds are known as ester bonds that form when
  a reaction occurs between the COOH groups of the
  fatty acids and the OH groups of the gylcerol
  molecule.

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Formation of a triglyceride
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Functions of Lipids

• Energy Storage energy can be stored in the form
  of oils in plants and as fat in animals. The
  energy can be release through aerobic cell
  respiration.
• Heat Insulation heat loss for animals is
  reduced by the fat layer located just below the
  skin.
• Buoyancy due to the fact that lipids are less
  dense than water they help animals float.

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2.3 (A3) Lipids are more suitable for long term
storage in humans than carbohydrates.

• Organisms can store energy in the form of
  carbohydrates and/or lipids.
• Living organisms tend to use carbohydrates as a
  short term energy storage while lipids are used
  as the long term energy storage.
• Carbohydrates are stored as glycogen in the
  muscles (2by mass) and liver (up to 150g).
• Lipids are stored as fats in adipose tissue
  directly under the dermis (on top of muscles) and
  also around various organs such as the kidneys.

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2.3 (A3) Lipids are more suitable for long term
storage in humans than carbohydrates.

• Lipid molecules contain 9 calories per gram
  whereas carbohydrate molecules only carry 4
  calories per gram.
• This means that lipid stores are less dense (less
  body mass) for the same amount of energy from
  carbohydrates.
• Stored lipids form pure droplets whereas
  carbohydrates are stored with water so lipids are
  6x more efficient than carbs in the amount of
  energy that can be stored per gram of body mass.

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2.3 (A3) Lipids are more suitable for long term
storage in humans than carbohydrates.

• Stored lipids can also act as insulators.
  Carbohydrates do not have a secondary role.
• Living organisms are able to digest carbohydrates
  easier and more efficiently than lipids which
  means that the energy stored in the molecule can
  be released faster. Consequently it makes carbs
  better for short term storage.
• It is more difficult for lipids to be mobilized
  and used in cell respiration than carbs. They
  are non-polar and can only be used in aerobic
  respiration whereas carbohydrates are polar, can
  be transportted easily and can be used in both
  aerobic and anaerobic respiration.

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2.3 (S2) Determination of body mass index by
calculation or use of a nomogram.

• See handout given in class

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2.3 (U2) Fatty acids can be saturated,
monosaturated or polyunsaturated.

• We covered the structure of fatty acids in topic
  2.1 but lets do a quick review.
• Fatty acids have a carbon chain with hydrogen
  atoms attached by single covalent bonds forming a
  hydrocarbon chain.
• There is a carboxyl group attached at the end of
  the chain which is the acid component of the
  fatty acid.

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Differences in Fatty Acids

• Fatty acids differ in the number of carbon atoms
  in the hydrocarbon chain. Of the fatty acids
  used by living things, most have between 14 and
  20 carbon atoms in the chain.
• Another difference is the bonds that form between
  the carbon atoms. Some are single bonds between
  the carbon atoms leaving room for 2 hydrogen
  atoms to bond to the carbon while others are
  double bonds leaving less room for hydrogen
  atoms.

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Saturated Fatty Acids

• Saturated fatty acids are composed of all single
  covalent bonds between the carbon atoms.
• This means each carbon atom can bond to two other
  carbons plus two hydrogen atoms.
• They are considered saturated fatty acids because
  they hold the maximum amount of hydrogen atoms
  possible.

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Unsaturated Fatty Acids

• Unsaturated fatty acids contain one or more
  double bonds between carbon atoms in the
  hydrocarbon chain. This means they contain less
  hydrogen than they could hold so they are
  considered unsaturated.

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Unsaturated Fatty Acids

• Monounsaturated fatty acid

• Polyunsaturated fatty acid

• Fatty acids that contain one double bond between
  carbon atoms.

• Fatty acids that contain two or more double bonds
  between carbon atoms.

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2.3 (U3) Unsaturated fatty acids can be cis or
trans isomers

• Unsaturated fatty acids are also characterized by
  the location of the hydrogen in relation to the
  double bonded carbon atoms.
• The hydrogen atoms can be located on the same
  side of the two carbon atoms or they can be be
  located on the opposite side.
• The location of the hydrogen atoms change the
  shape and the characteristics of the unsaturated
  fatty acid.

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Cis-fatty Acids

• In cis-fatty acids the hydrogen atoms are on the
  same side of the double bonded carbon atoms.
  This results in a bend in the fatty acid chain
  which does not allow them to pack tightly
  together. This lowers the melting point of these
  fats and they are normally liquid at room
  temperature.

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Trans-fatty Acids

• Trans-fatty acids are artificially produced
  through a process known as hydrogenation.
  Hydrogen is added to unsaturated fats to
  partially saturate them to produce solid fats
  such as shortening and margarine.
• The hydrogen atoms are bonded on either side of
  the double bonds resulting in a straight
  hydrocarbon chain. They can pack tightly
  together and this increases their melting point
  and they are solid at room temperature.

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2.3 (A2) Scientific evidence for health risks of
trans fats and saturated fatty acids.

• See ICA completed in class

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2.3 (A4) Evaluation of evidence and the methods
used to obtain the evidence for health claims
made about lipids.

• See ICA completed in class.