carbohydrate metabolism 1 l Biochemistry MCQs (multiple choice question) for dental students
-Definition:
- Aldehyde or Ketone derivatives of the
higher polyhydric alcohols or compounds which yield
these derivatives on hydrolysis
Classification:
- (mono, di, oligo, poly)
saccharide Monosaccharides: Trioses (3-C), Tetroses(4-C),
Pentoses(5- C),Hexoses(6-C) depending upon the number of carbon atoms
The Simple Carbohydrates
• Monosaccharrides are single sugars (most are hexoses).
- Glucose serves as the essential energy source, and is
commonly known as blood sugar .
- Fructose is the sweetest, occurs naturally in honey and
fruits, and is added to many foods in the form of high-fructose corn
syrup.
- Naturally ;Galactose rarely occurs as as single
molecule (free).
- monosaccharaides exist in the cyclic acetal form (Haworth projection). This structure
will be more stable: A new chiral center is created
and monosaccharaides exist as α(alpha when OH group of C-1
below the ring ) or β(beta when OH group of C-1 upper the
ring ) called anomers.
- All the monosaccharide except dihydroxyacetone contain
one or more asymmetric C-atoms and thus forms isomers .The open chain
form of monosaccharide represented by Fisher projection formulas
which assign to either the D or L family according to the
configuration of the chiral C-atom most sugars in nature are
D))farthest from the carbonyl group.
Epimers and epimerization:
- Two sugars which differ from one another only in the
configuration around a single C-atom such as glucose and galactose
which differ only in the position of OH at C4 (glucose and mannose
which differ only in the position of OH at C2)
Epimerization:
- Process by which one epimer is converted to other is
epimerization and it requires the enzyme epimerase ,e.g. conversion
of galactose to glucose in liver.
The Simple Carbohydrates
- Disaccharides are pairs of
monosaccharides, one of which is always glucose
1.
Condensation reactions link monosaccharides together.
2.
Hydrolysis reactions split molecules and commonly occur during
digestion.
3.
Maltose consists of two glucose units. It is produced during the
germination of seeds and fermentation.
4.
Sucrose is fructose and glucose combined. It is refined from
sugarcane and sugar beets, tastes sweet, and is readily available.
5.
Lactose is galactose and glucose combined. It is found in milk and
milk products.
The Complex Carbohydrates
- Few (oligosaccharides) or many (polysaccharides)
glucose units bound/linked together in straight or branched chains.
- Glycogen
1.
Storage form of glucose in the body
2.
Provides a rapid release of energy when needed
- Starches
- storage form of glucose in plants
- Found in grains, tubers, and legumes
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