Lecture 5: Lipids and Carbohydrates

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Lecture 5 Lipids and Carbohydrates

• Craig Kasper
• Aquaculture
• FAS 1012

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Part 1 Lipid Characteristics

• Lipid a compound that is insoluble in water,
  but soluble in an organic solvent (e.g., ether,
  benzene, acetone, chloroform)
• lipid is synonymous with fat, but also
  includes phospholipids, sterols, etc.
• chemical structure glycerol fatty acids

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Lipid Molecule
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Nutritional Uses of Lipids

• We already know that lipids are concentrated
  sources of energy (9.45 kcal/g)
• other functions include
• 1) provide means whereby fat-soluble nutrients
  (e.g., sterols, vitamins) can be absorbed by the
  body
• 2) structural element of cell, subcellular
  components
• 3) components of hormones and precursors for
  prostaglandin synthesis

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Lipid Classes

• simple FAs esterified with glycerol
• compound same as simple, but with other
  compounds also attached
• phospholipids fats containing phosphoric acid
  and nitrogen (lecithin)
• glycolipids FAs compounded with CHO, but no N
• derived lipids substances from the above
  derived by hydrolysis
• sterols large molecular wt. alcohols found in
  nature and combined w/FAs (e.g., cholesterol)

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Saturated vs. Unsaturated Fatty Acids

• saturated the SFAs of a lipid have no double
  bonds between carbons in chain
• polyunsaturated more than one double bond in
  the chain
• most common polyunsaturated fats contain the
  polyunsaturated fatty acids (PUFAs) oleic,
  linoleic and linolenic acid
• unsaturated fats have lower melting points
• stearic (SFA) melts at 70oC, oleic (PUFA) at 26oC

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Fatty Acids Commonly Found in Lipids
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Saturated vs. Unsaturated Fats

• saturated fats tightly packed, clog arteries as
  atherosclerosis
• because of double bonds, polyunsaturated fats do
  not pack well -- like building a wall with bricks
  vs. irregular-shaped objects
• plant fats are much higher in PUFAs than animal
  fats

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Saturated vs. Unsaturated FAs Plant vs. Animal
Fat
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Lipid Digestion/Absorption

• Fats serve a structural function in cells, as
  sources of energy, and insulation
• the poor water solubility of lipids presents a
  problem for digestion substrates are not easily
  accessible to digestive enzymes
• even if hydrolyzed, the products tend to
  aggregate to larger complexes that make poor
  contact with the cell surface and arent easily
  absorbed
• to overcome these problems, changes in the
  physical state of lipids are connected to
  chemical changes during digestion and absorption

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Lipid Digestion/Absorption

• Five different phases
• hydrolysis of triglycerides (TG) to free fatty
  acids (FFA) and monoacylglycerols
• solubilization of FFA and monoacylglycerols by
  detergents (bile acids) and transportation from
  the intestinal lumen toward the cell surface
• uptake of FFA and monoacylglycerols into the cell
  and resynthesis to triglyceride
• packaging of TGs into chylomicrons
• exocytosis of chylomicrons into lymph

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Enzymes Involved in Digestion of Lipids

• lingual lipase provides a stable interface with
  aqueous environment of stomach
• pancreatic lipase major enzyme affecting
  triglyceride hydrolysis
• colipase protein anchoring lipase to the lipid
• lipid esterase secreted by pancreas, acts on
  cholestrol esters, activated by bile
• phospholipases cleave phospholipids, activated
  by trypsin

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What about Bile???

• These are biological detergents synthesized by
  the liver and secreted into the intestine
• they form the spherical structures (micelles)
  assisting in absorption
• hydrophobic portion (tails of FA) are located to
  the inside of the micelle, with heads
  (hydrophillic portion) to the outside
• they move lipids from the intestinal lumen to the
  cell surface
• absorption is by diffusion (complete for FA and
  monoglycerides, less for others)

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Factors Affecting Absorption of Lipids

• amount of fat consumed (? fat ? digestion ?
  absorption)
• age of subject (? age ? digestion)
• emulsifying agents
• chain length of FAs (gt 18C ? digestibility)
• degree of saturation of FA (? sat ?
  digestibility)
• overheating and autooxidation (rancidification at
  double bond)
• optimal dietary calcium optimal FA absorption
  (high Ca ? absorption)

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Lipid Metabolism/Absorption

• short chain FAs are absorbed and enter the
  portal vein to the liver
• those FAs with more than 10 carbons are
  resynthesized by the liver to triglycerides
• they are then converted into chylomicrons and
  pass to the lymphatic system
• some FAs entering the liver are oxidized for
  energy, others stored
• blood lipids 45 P-lipids, 35 triglycerides,
  15 cholestrol esters, 5 free FAs

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Lipid Digestion/Absorption
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Lipid Digestion/Absorption
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Characteristics of Fat Storage

• Most of the bodys energy stores are
  triglycerides
• storage is in adipose, source is dietary or
  anabolism (synthesis) from COH or AA carbon
  skeletons
• remember obesity?
• adipose can remove FAs from the blood and
  enzymes can put them back

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Fatty Acid Nomenclature

• Nomenclature reflects location of double bonds
• also used are common names (e.g., oleic, stearic,
  palmitic)
• linoleic is also known as 182 n-6
• this means the FA is 18 carbons in length, has 2
  double bonds, the first of which is on the 6th
  carbon
• arachidonic 204 n-6

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Essential Fatty Acids

• Only recently determined as essential (1930)
• body can synthesize cholesterol, phospholipids
• research same as AAs but via addition (EFAs
  added improved growth, NEFAs didnt)
• requirement determined by depleting fat reserves
  of subject animal difficult

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Essential Fatty Acids (fish)

• Most NEAA found in marine food webs
• Essential fatty acids (to date)
• linoleic (182 n-6 terrestrials fish - not
  really)
• linolenic (183 n-3 terrestrials fish)
• arachidonic (204 n-6 marine maybe)
• eicosopentaenoic acid (205 n-3, marine)
• docosohexaenoic (226 n-3, marine)
• Why? Because elongation beyond 18 carbons is
  very difficult in marine fish (lack pathways)
• actual EFA requirement is a matter of whether the
  fish is FW/SW or WW/CW

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Essential Fatty Acids (most animals)

• salmonids need n-3 FAs for membrane flexibility
  in cold water
• trout can elongate and desaturate n-3 FAs
• Linoleic acid (182 n-6) is the most essential
• addition of arachidonic is also helpful in
  deficient diets, but can be synthesized from
  linoleic (maybe sparing effect)
• EFAs, like EAAs, must be dietary

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Essential Fatty Acids
LINOLEIC CH3(CH2)4CHCHCH2CHCH(CH2)7COOH 182
n-6 LINOLENIC CH3CH2CHCHCH2CHCHCH2CHCH(CH2)7CO
OH 183 n-3 EICOSOPENTAENOIC
ACID CH3CH2CHCHCH2CHCHCH2CHCHCH2CHCHCH2CHCH(C
H2)3COOH 205 n-3 DOCOSOHEXAENOIC ACID - YOU
CAN DO THIS ONE!
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Lipids as Crustacean Energy Sources

• Largely, n-6 FAs (linoleic) used for energy
• as temperature drops, requirement for
  monounsaturated and PUFAs increases
• change in temperature change in diet
• cold water species increased dietary HUFAs
• maturation animals increased requirement for
  204 n-6, 205 n-3 and 226 n-3 for proper
  spawning

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Part 2 Carbohydrate Characteristics

• From Lovell DAbramo et al.

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General Comments

• Carbohydrates often written as COH
• much of what we need to know about them, besides
  their structure, was covered in Bioenergetics,
  Parts 12
• here, we cover structure

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Carbohydrate Structure

• Basic chemical structure consists of sugar units
• found as aldehydes or ketones derived from
  polyhydric alcohols
• contain C, H, O
• often shown as aliphatic or linear structures,
  but exist in nature as ringed structures

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Glucose Structure
O C-H H- C-OH HO-C-H
H-C-OH H-C-OH CH2OH
CH2OH
O
H
H
OH
H
OH
HO
H
OH
Haworth perspective
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Carbohydrate Classification

• Usually by the number of sugar units in the
  molecule
• monosaccharides (glucose)
• disaccharides (2 units)
• maltose (2 glucose units)
• sucrose (glucose fructose)
• polysaccharides (long chain polymers of
  monosaccharides
• most important polysaccharides to animals are
  starch and cellulose

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Starch and Cellulose
CH2OH
CH2OH
O
O
H
H
H
H
starch
OH
H
OH
H
O
O
O
H
OH
H
OH
CH2OH
CH2OH
H
O
O
H
O
O
O
OH
H
OH
H
H
H
cellulose
H
OH
H
OH
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Starch and Cellulose

• Starch contains ?-D-glucose linkage
• Cellulose has a ?-D-glucose linkage
• we store starch in muscle tissues as glycogen,
  peeled off by enzymes when needed
• cellulose is primary component of plant tissue,
  largely indigestible to monogastrics
• must have enzyme, cellulase