Lipids: WaterInsoluble Molecules

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Lipids Water-Insoluble Molecules

• Lipids are insoluble in water.
• This insolubility results from the many nonpolar
  covalent bonds of hydrogen and carbon in lipids.
• Lipids aggregate away from water, which is polar.

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Lipids Water-Insoluble Molecules

• Roles for lipids in organisms include
• Energy storage (fats and oils)
• Cell membranes (phospholipids)
• Capture of light energy (carotenoids)
• Hormones and vitamins (steroids and modified
  fatty acids)
• Thermal insulation
• Electrical insulation of nerves
• Water repellency (waxes and oils)

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Lipids Water-Insoluble Molecules

• Fats and oils store energy.
• Fats and oils are triglycerides, composed of
  three fatty acid molecules and one glycerol
  molecule.
• Aka triacylglycerol
• Glycerol is a three-carbon molecule with three
  hydroxyl (OH) groups, one for each carbon.
• Fatty acids are long chains of hydrocarbons with
  a carboxyl group (COOH) at one end.

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Figure 3.18 Synthesis of a Triglyceride
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Lipids Water-Insoluble Molecules

• Saturated fatty acids
• have only single carbon-to-carbon bonds
• said to be saturated with hydrogens.
• Saturated fatty acids
• rigid and straight
• solid at room temperature
• Animal fats are saturated.

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Lipids Water-Insoluble Molecules

• Unsaturated fatty
• have at least one double-bonded carbon in one of
  the chains
• the chain is not completely saturated with
  hydrogen atoms.
• Double bonds cause kinks that prevent easy
  packing.
• Unsaturated fatty acids are liquid at room
  temperature.
• Plants commonly have unsaturated fatty acids.

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Figure 3.19 Saturated and Unsaturated Fatty Acids
Unsaturated, contains one or more double bonds
between carbons
Saturated with hydrogen
Rigid and straight
Tend to be solid at RT
Kinks in chain prevent packing
Tend to be liquid at RT
Animal fats
Plant fats
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• Trans fatty acids
• Effective January 1, 2006, FDA requires trans fat
  content to be listed in Nutrition Facts panel
• Evidence suggests that consumption of trans fat
  raises LDL (bad) cholesterol and lowers HDL
  (good) cholesterol
• Trans fatty acids are formed when liquid
  vegetable oils go through a chemical process
  called hydrogenation, in which hydrogen is added
  to make the oils more solid.
• Hydrogenated vegetable oils are used because they
  allow longer shelf-life and give food a more
  desirable taste and texture.

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Lipids Water-Insoluble Molecules

• Phospholipids have two hydrophobic fatty acid
  tails and one hydrophilic phosphate group
  attached to the glycerol.
• As a result, phospholipids orient themselves so
  that the phosphate group faces water and the tail
  faces away.
• In aqueous environments, these lipids form
  bilayers, with heads facing outward, tails facing
  inward. Cell membranes are structured this way.

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Figure 3-13(2)Page 52
(b) Phospholipid bilayer
Water
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Figure 3.21 Phospholipids Form a Bilayer
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Lipids Water-Insoluble Molecules

• Carotenoids are light-absorbing pigments found in
  plants and animals.
• One, b-carotene, is a plant pigment used to trap
  light in photosynthesis.
• In animals, this pigment, when broken into two
  identical pieces, becomes vitamin A.

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Figure 3.22 b Carotene is the Source of Vitamin
A
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Lipids Water-Insoluble Molecules

• Steroids are signaling molecules.
• Steroids are organic compounds with a series of
  fused rings.
• The steroid cholesterol is a common part of
  animal cell membranes.
• Cholesterol is also is an initial substrate for
  synthesis of the hormones testosterone and
  estrogen.

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Figure 3.23 All Steroids Have the Same Ring
Structure
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Lipids Water-Insoluble Molecules

• Some lipids are vitamins small organic molecules
  essential to health.
• Vitamin A is important for normal development,
  maintenance of cells, and night vision.
• Vitamin D is important for absorption of calcium
  in the intestines.
• Vitamin E, an antioxidant, protects membranes.
• Vitamin K is a component required for normal
  blood clotting.

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Lipids Water-Insoluble Molecules

• Waxes are highly nonpolar molecules consisting of
  saturated long fatty acids bonded to long fatty
  alcohols via an ester linkage.
• A fatty alcohol is similar to a fatty acid,
  except for the last carbon, which has an OH
  group instead of a COOH group.
• Waxy coatings repel water and prevent water loss
  from structures such as hair, feathers, and
  leaves.

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Nucleic Acids Informational MacromoleculesThat
Can Be Catalytic

• Nucleic acids are polymers that are specialized
  for storage and transmission of information.
• Two types of nucleic acid are DNA
  (deoxyribonucleic acid) and RNA (ribonucleic
  acid).
• DNA encodes hereditary information and transfers
  information to RNA molecules.
• The information in RNA is decoded to specify the
  sequence of amino acids in proteins.

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Nucleic Acids Informational MacromoleculesThat
Can Be Catalytic

• Nucleic acids are polymers of nucleotides.
• A nucleotide consists of
• pentose sugar
• phosphate group
• nitrogen-containing base.
• In DNA, the pentose sugar is deoxyribose in RNA
  it is ribose.

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Figure 3.24 Nucleotides Have Three Components
Nucleotides are composed of three components
1. A nitrogen-containing base.
The nitrogenous bases fall into two categories
Pyrimidines have a single ring.
Base
Purines have two fused rings.
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Figure 3.24 Nucleotides Have Three Components
Nucleotides are composed of three components
1. A nitrogen-containing base (either a
pyrimidine or a purine).
2. A pentose sugar (ribose or deoxyribose).
3. A phosphate group.




Base
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Figure 3.24 Nucleotides Have Three Components
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Table 3.3 Distinguishing DNA from RNA
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Nucleic Acids Informational MacromoleculesThat
Can Be Catalytic

• DNA typically is double-stranded.
• The two separate polymer chains are held together
  by hydrogen bonding between their nitrogenous
  bases.
• The base pairing is complementary At each
  position where a purine is found on one strand, a
  pyrimidine is found on the other.
• Purines have a double-ring structure. Pyrimidines
  have one ring.

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Figure 3.25 Distinguishing Characteristics of
DNA and RNA
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Figure 3.25 Distinguishing Characteristics of
DNA and RNA
Both DNA and RNA contain a series of phosphate
groups and pentoses that form the backbone of
their structure.
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Figure 3.25 Distinguishing Characteristics of
DNA and RNA
In RNA, the bases are attached to the ribose. The
bases are adenine (A) and guanine (G), the
purines, and cytosine (C) and uracil (U), the
pyrimidines.
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Figure 3.25 Distinguishing Characteristics of
DNA and RNA
In DNA, the bases are attached to deoxyribose.
The bases are adenine (A), guanine (G), cytosine
(C), and thymine (T) (thymine is found instead of
uracil).
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Figure 3.25 Distinguishing Characteristics of
DNA and RNA
The numbering of ribose carbons is the basis for
identification of the 5 and 3 ends of DNA and
RNA stands.
5
4
3
2
1
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Figure 3.25 Distinguishing Characteristics of
DNA and RNA
RNA is single-stranded.
5 end
3 end
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Figure 3.25 Distinguishing Characteristics of
DNA and RNA
DNA is double-stranded.
5 end
3 end
5 end
3 end
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Figure 3.25 Distinguishing Characteristics of
DNA and RNA
Hydrogen bonds between purines and pyrimidines
hold the two strands of DNA together.
5 end
3 end
5 end
3 end
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Nucleic Acids Informational MacromoleculesThat
Can Be Catalytic

• The linkages that hold the nucleotides in RNA and
  DNA are called phosphodiester linkages.
• These linkages are formed between carbon 3 of the
  sugar and a phosphate group that is associated
  with carbon 5 of the sugar.
• The backbone consists of alternating sugars and
  phosphates.
• In DNA, the two strands are antiparallel.
• The DNA strands form a double helix, a molecule
  with a right-hand twist.

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Nucleic Acids Informational MacromoleculesThat
Can Be Catalytic

• Most RNA molecules consist of only a single
  polynucleotide chain.
• Instead of the base thymine, RNA uses the base
  uracil.
• Hydrogen bonding between ribonucleotides in RNA
  can result in complex three-dimensional shapes.

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Nucleic Acids Informational MacromoleculesThat
Can Be Catalytic

• DNA is an information molecule. The information
  is stored in the order of the four different
  bases.
• This order is transferred to RNA molecules, which
  are used to direct the order of the amino acids
  in proteins.

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Nucleic Acids Informational MacromoleculesThat
Can Be Catalytic

• Certain RNA molecules called ribozymes can act as
  catalysts.
• Since RNA can be informational and catalytic, it
  could have acted as a catalyst for its own
  replication as well as for the synthesis of
  proteins.

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Nucleic Acids Informational MacromoleculesThat
Can Be Catalytic

• Nucleotides have other important roles
• The ribonucleotide ATP acts as an energy
  transducer in many biochemical reactions.
• The ribonucleotide GTP powers protein synthesis.
• cAMP (cyclic AMP) is a special ribonucleotide
  that is essential for hormone action and the
  transfer of information by the nervous system.

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Table 3.1 The Building Blocks of Organisms
Lipids- not a specific type of polymer, grouped
together because they are insoluble in water.