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BioMolecules
continued
Polysaccharides
• Polysaccharides are carbohydrates
composed of many monosaccharides.
• There are two types of
polysaccharides
ÖStorage Polysaccharides: They
store energy
ÖStructural Polysaccharides: These
are use for building cell structures.
Polysaccharides are long chains of sugar
units
• These large molecules are polymers of
hundreds or thousands of monosaccharides
linked by dehydration synthesis
Energy
1. Glucose + Glucose
H 2O
Enzyme
Energy
Maltose
n(H2O)
2. Maltose + n(Glucose)
Polysaccharide
Enzyme
n = many
• Starch and glycogen are storage polysaccharides
that store sugar for later use
• Cellulose is a structural polysaccharide in plant
cell walls
Starch granules in
potato tuber cells
Glycogen granules
in muscle tissue
Cellulose fibrils in
a plant cell wall
Cellulose
molecules
Glucose
monomer
STARCH
GLYCOGEN
CELLULOSE
• Starch is a storage polysaccharide composed entirely of
glucose monomers.
• One unbranched form of starch, amylose, forms a helix.
• Branched forms, like amylopectin, are more complex.
• Animals that feed on plants, especially parts rich in starch,
can also access this starch to support their own
metabolism.
Fig. 5.6a
• Animals also store glucose in a
polysaccharide called glycogen.
• Glycogen is highly branched, like
amylopectin.
• Humans and other vertebrates store
glycogen in the liver and muscles but only
have about a one day supply.
Insert Fig. 5.6b - glycogen
How do we use sugars?
• Pancreatic Hormones Control Glucose Levels in the
Blood. Figure 23.8 The pancreas controls blood
glucose levels (p. 457) .
• When sugar in the blood stream is too high, the
pancreas produces the hormone (regulator) insulin that
removes sugar from the blood stream and sends it to the
liver where it becomes GLYCOGEN.
• When sugar in the blood stream is low, the pancreas
produces glucagon, a second hormone (another
regulator), that makes the liver cells hydrolyse some
glycogen into glucose and some glucose is released
until the concentration of sugar in the blood stream is
back to normal.
Chapter 23
eating
hunger
insulin-producing
cells
pancreas
high blood
glucose
low blood
glucose
glucagon-producing
cells
glucagon
insulin
glucose
body cells
body cells
burn
burn fat converts glycogen
converts glucose
instead ofto glucose glycogen to glycogen glucose
glucose
raises blood
glucose
liver
lowers blood
glucose
•Other polysaccharides, structural polysaccharides serve
as building materials for the cell or whole organism. This is
the case of cellulose commonly known as fiber. Cellulose
is the main component of the cell wall of plants.
wood is mostly cellulose
plant cell with cell wall
close-up of cell wall
individual
cellulose
molecules
bundle of
cellulose
molecules
cellulose fibe
• The enzymes in our body cannot hydrolyze the
bonds in cellulose.
• Cellulose in our food passes through the digestive
tract and is eliminated in feces as “insoluble fiber”.
• As it travels through the digestive tract, it abrades
the intestinal walls and stimulates the secretion of
mucus.
• Some microbes can digest cellulose to its glucose
monomers through the use of cellulase enzymes.
• Many eukaryotic herbivores, like cows and
termites, have symbiotic relationships with
cellulolytic microbes, allowing them access to this
rich source of energy.
• Another important structural polysaccharide
is chitin, used in the exoskeletons of
arthropods (including insects, spiders, and
crustaceans).
• Chitin also forms
the structural
support for the
cell walls of
many fungi.
What Are Lipids?
• They are grouped together because
they do not mix with water.
• They comprise Oils, Fats, Waxes,
Phospholipids and Steroids.
• Contain Only Carbon, Hydrogen, and
Oxygen
• Lipids are classified into two groups
• 1. Lipids with fatty acids: Triglycerides
Phopholipids
• 2. Lipids without fatty acids: Steroids.
What is a fatty acid?
A fatty acid consists of a carboxyl group attached to a
long carbon skeleton, often 16 to 18 carbons long.
Carboxyl or Acid Group
If the carbon chain is single bonded: Saturated. Saturated fatty
acids are solid at room temperature and are found mainly in
animals.
If the carbon chain has one or more double or triple bonds, then
the fatty acid is unsaturated. Unsaturated fatty acids are liquid
at room temperature and are more commonly found in plants.
Triglycerides
• Commonly
known as fats
oils and waxes.
• They are formed
by dehydration
synthesis
• How? By
adding three
fatty acids and
one molecule of
glycerol.
glycerol
fatty acids
triglyceride
3 water
molecules
The functions of triglycerides include:
•
•
•
•
Storage of energy
Insulation
Cushioning
Help to prevent
dehydration
• Help to maintain the
internal temperature.
Plenty of storage and
cushioning here!
Phospholipids
• Consist of a polar head, a glycerol and two
fatty acids. These are the main
components of the cell membrane.
polar head
glycerol
backbone
fatty acid tails
(hydrophobic)
(hydrophilic)
Steroids
• Steroids Consist of Four Carbon Rings
Fused Together
Steroids functions include:
• Structural molecules: Steroids are part of
the cell membrane. For example in animal
cells we find cholesterol (never found in
plants).
• Some hormones (regulators) are
chemically steroids. For example
Estrogen, Progesterone and Testosterone.
• Vitamin D is a steroid.
Synthetic (man made) steroids
include:
• Cortisones : antinflamatories
• Birth control pills: usually synthetic variants of
estrogen.
• Anabolic steroids. Anabolic steroids
• are usually synthetic variants
• of testosterone