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Chapter 5

BIOLOGY 1A03 Chapter Notes - Chapter 5: Unsaturated Hydrocarbon, Lactose Intolerance, Hydrogen Breath Test


Department
Biology
Course Code
BIOLOGY 1A03
Professor
Lovaye Kajiura
Chapter
5

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Chapter 5: An Introduction to Carbohydrates
Functions of Carbohydrates
Energy source- glucose is rapidly metabolized
Energy storage- starch and glycogen
Structural support- cellulose, chitin and cartilage
Transport of energy source- sucrose (plants), lactose (milk)
Cell surface signals- cell communication and cell-cell recognition
An organ is identified as belonging to the body by carbohydrates
Monosaccharides- are single sugars (simple sugars)
Ribose- present in RNA
Deoxyribose- present in DNA
Glucose- present in starch, cellulose and glycogen
Galactose- present in cartilage (cartilage is found in fish and part of the human body)
The carbonyl group that serves as one of the monosaccharide’s distinguishing features can
be found either at the end of the molecule, forming an aldehyde sugar (aldose), or within the
carbon chain, forming a ketone sugar (ketose). The presence of the carbonyl group along with
multiple hydroxyl groups provides an array of functional groups in sugars. Glucose and
Galactose are both 6-carbon sugars that only differ by their variation in the spatial orientation
of their hydroxyl groups (however, they are not mirror images).
Fig. 5.3 Sugars Exist in Linear and Ring Forms
Although the linear form of glucose is rare, in solution almost all glucose molecules
spontaneously bend into one of two ring structures, called the alpha and beta forms of glucose.
The difference between the two forms lies in whether the hydroxyl group on carbon #1 is above
or below the plane of the ring. The two forms exist in equilibrium, but the beta form is more
common because it is slightly more stable than the alpha form.
The ring structure forms when the oxygen from the hydroxyl group bonds with the
carbon from the carbonyl group.
Alpha glucose- OH group at carbon number 1 is below the plane of the ring
Beta glucose- OH group at carbon number 1 is above the plane of the ring
Fig. 5.4 Monosaccharides Polymerize through Formation of Glycosidic Linkages
A Glycosidic linkage occurs when hydroxyl groups on two monosaccharides undergo a
condensation reaction to form a bond. The linkage between carbon 1 and carbon 4 (for both
maltose and lactose), the formation of different monosaccharides form these new
disaccharides, creating alpha- 1,4- Glycosidic linkages.
Disaccharides

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Are double sugars that consist of two monosaccharides, which are joined through a
condensation (dehydration) reaction.
GLUCOSE + GLUCOSE=MALTOSE & GLUCOSE + FRUCTOSE=SUCROSE & GLUCOSE +
GALACTOSE=LACTOSE
The liquid form of sucrose is now used as a type of sweetner; it is good for the quick
production of food and for making candy.
Be sure to know which carbons the Glycosidic linkages form between.
Real World Examples
Lactose Intolerance and Galactosemia (Box 5.1)
Lactose intolerance is the inability for people to digest lactose, which is common in milk,
cheese, yogurt, ice cream, candy, cake, etc.
It is an autosomal recessive trait
Symptoms: gas, flatulence, bloating, diarrhea, dehydration and cramps in the stomach.
Diagnosis: hydrogen breath test, blood glucose test, small bowel biopsy, etc.
Ways to prevent these symptoms are: to not eat any products with lactose or to take
lactase pills 30 minutes prior to eating dairy.
Supplementary information: growth hormones were given to cows for mass milk
production but they turned out being responsible for students developing a lot of acne.
When humans are born they are able to digest lactose (breast feeding, mammals) because
they produce the enzyme lactase which allows them to break down lactose into glucose and
galactose and digest them. However, many lose this ability to produce the enzyme as they get
older, even if they could digest it as young adults (not preventable).
Summary Table 5.1 Polysaccharides Differ in Structure
Polysaccharide
Function
Chemical Structure
Three-
Dimensional
Structure
Starch
Example:
potatoes
Used for energy
storage in plant cells.
Amylose
(unbranched
helix)
Amylopectin
(branched
helices)
Glycogen
Used for energy
storage in animal cells
(liver and muscles).
Highly
branched
helices

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Cellulose
Example:
celery, fiber
Used for structural
support in cell walls
of plants and many
algae.
Parallel
strands joined
by hydrogen
bonds
Chitin
Example: crab,
mushrooms
Used for structural
support in the cell
walls of fungi and the
external skeletons of
insects and
crustaceans.
Parallel
strands joined
by hydrogen
bonds
Peptidoglycan
Used for structural
support in bacteria
cell walls.
Parallel
strands joined
by peptide
bonds
Polysaccharides
Are polymers that consist of many sugar monomers
Hand sanitizer kills off the bacteria that make up peptidoglycan
Fig. 5.6 Cellulose, Chitin and Peptidoglycan can Form Tough Fibers or Sheets
Note the diagrams of what each carbohydrate looks like under a microscope.
Fig. 5.7 Carbohydrates are an Identification for Cells
Glycoproteins contain sugar groups that project from the surface of the plasma
membrane. These sugar groups have distinctive structures that identify the type or species of
the cell.
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