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METABOLISM OF FOOD
Dr. Daxaben N. Mehta
Principal
Smt. S.C.U.Shah Home Science and
C.U.Shah Arts & Commerce Mahila College
Wadhwancity – Dist: Surendranagar
METABOLISM
Dr. Daxa N. Mehta
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Why do we need food ?
The main nutrients the body needs are:
carbohydrates for energy;
proteins for growth and repair;
fats to store energy;
vitamins and minerals to keep the body healthy.
The amount of each food type needed is related to the
proportions in the food pyramid.
Which food type does the body need the most of?
METABOLISM
Dr. Daxa N. Mehta
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METABOLISM
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Metabolite = Biological compound
Catabolism: All the reactions concerned
with breaking down compounds and
generating and storing energy for the needs
of the cell and organism. Energy = ATP
Anabolism: All the reactions concerned
with the biosynthesis of complex compounds
from simpler compounds. Usually use ATP.
METABOLISM
Dr. Daxa N. Mehta
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What is digestion?
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The body carries out digestion of food to convert large
insoluble food molecules into smaller soluble ones.
carbohydrate
molecule
protein
molecule
fat
molecule
Small food molecules can pass through the walls of the
small intestine and then dissolve into the blood stream.
Large food molecules cannot do this.
METABOLISM
Dr. Daxa N. Mehta
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The stomach
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After food is swallowed it enters the stomach, which is
basically a muscular bag filled with hydrochloric acid.
food enters
from the gullet
the chemical breakdown of
food begins;
microbes are destroyed.
muscle
tissue
food leaves
the stomach
METABOLISM
Dr. Daxa N. Mehta
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The small intestine
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From the stomach, food enters the small intestine
where digestion is completed and the small digested food
molecules are absorbed into the bloodstream.
METABOLISM
Dr. Daxa N. Mehta
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The large intestine
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After the small intestine, the remains
of any undigested food travel to the
large intestine.
All that is left of the food is
water and waste material.
The water is valuable and so is absorbed in the large
intestine into the blood stream.
The waste material cannot be digested or used by the body.
This undigested waste travels to the rectum where it is
stored until leaving the body through the anus.
METABOLISM
Dr. Daxa N. Mehta
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Types of digestive enzymes
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Digestive enzymes are the chemicals
that break large insoluble food molecules
into smaller soluble molecules.
Digestive enzymes are classified by the type of food that
they affect, so there are three main types:
carbohydrase – breaks carbohydrate into smaller sugars.
protease – breaks protein into amino acids.
lipase – breaks fat into fatty acids and glycerol.
METABOLISM
Dr. Daxa N. Mehta
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carbohydrate digestion
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Carbohydrates are chains of identical sugar
molecules.
The digestive enzymes called carbohydrases break
the chemical bonds between the individual sugar
molecules in each carbohydrate chain.
carbohydrase
long
carbohydrate
molecule
METABOLISM
sugar
molecules
Dr. Daxa N. Mehta
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protein digestion
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Proteins are made up of amino acids. There are 20 different
types of amino acids.
Proteins are digested by digestive enzymes called proteases.
These enzymes work in an acidic environment to break
proteins into smaller amino acids.
protease
long
protein molecule
METABOLISM
amino acid
molecules
Dr. Daxa N. Mehta
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fat digestion
Firstly, bile (released by the gall bladder) allows the fat to “mix”
with water by breaking the fat into smaller droplets. This is called
emulsification.
bile
Secondly, the digestive enzyme lipase breaks each fat
molecule into the smaller glycerol fatty acid molecules .
lipase
fat molecule
METABOLISM
+
glycerol
fatty acids
Dr. Daxa N. Mehta
24. Catabolism
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Breakdown of macromolecules to
building blocks -- generally hydrolytic
protein polysaccharide lipid nucleic acids
amino glucose,
glycerol ribose,het
acids other sugars fatty acids bases,
phosphate
no useable energy yield here- only building
blocks obtained
METABOLISM
Dr. Daxa N. Mehta
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Breakdown of monomers
to common intermediates
amino
acids
glucose,
other sugars
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glycerol,
fatty acids
pyruvate
NH4+
acetyl CoA
citric acid cycle ETS/Ox Phos ATP
CO2
Oxidative processes- ATP & NADH
METABOLISM
Dr. Daxa N. Mehta
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3-Breakdown of intermediates to CO2
and electrons is accomplished
through a central oxidative pathway:
the Citric Acid Cycle or TCA or the Krebs Cycle.
This cycle leads to the production of ATP by
processes called electron transport and oxidative
phosphorylation.
METABOLISM
Dr. Daxa N. Mehta
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Isomerization of glucose 6-phosphate
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phosphoglucoisomerase
glucose 6-phosphate
fructose 6-phosphate
aldose to ketose isomerization reversible
METABOLISM
Dr. Daxa N. Mehta
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Cleavage to two triose phosphates
aldolase
HC=O
H2COP
HCOH
O=C
HCOP +
CH2OH
H
glyceraldehyde
3-phosphate
dihydroxyacetone
phosphate
where P = phosphate
cleaves a 6C sugar to 2 3C sugars
METABOLISM
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Oxidation of glyceraldehyde
3-phosphate
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glyceraldehyde-3-phosphate dehydrogenase
OH
+ OPOH
NAD NADH
O-
glyceraldehyde 3-phosphate
METABOLISM
O
HOPO
O
C=O
HCOH
H2C
O- P
1,3 bisphosphoglycerate
Dr. Daxa N. Mehta
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Transfer phosphate to make ATP
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phosphoglycerate kinase
-
O=C-O- P
HC-OH + P
H2C-O-P P
Adenosine
1,3PG
ADP
METABOLISM
O=C-OH P
HC-OH + P
H2C-O-P P
Adenosine
3-phosphoglycerate ATP
Dr. Daxa N. Mehta
39. Generation of second very high
energy compound by a dehydration
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enolase
METABOLISM
Dr. Daxa N. Mehta
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Final generation of ATP
pyruvate kinase
P
O H
-OOC-C=CH
ADP
phosphoenolpyruvate
METABOLISM
ATP
O
-OOC-C-CH
3
pyruvate
Dr. Daxa N. Mehta
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Input = 2 ATP
1. glucose + ATP
glucose-6-P
2. fructose-6-P + ATP fructose 1,6 bisphosphate
Output = 4 ATP + 2 NADH
1. 2 glyceraldehyde 3-P + 2 Pi + 2 NAD+
2 (1,3 bisphosphoglycerate) + 2 NADH
2. 2 (1,3 bisphosphoglycerate) + 2 ADP
2 (3-P-glycerate) + 2 ATP
3. 2 PEP + 2 ADP
2 pyruvate + 2 ATP
Net = 2 ATP and 2 NADH
METABOLISM
Dr. Daxa N. Mehta
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Oxidation of pyruvate
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Intermediate step between
glycolysis and the kreb’s cycle
METABOLISM
Dr. Daxa N. Mehta
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FAD+, lipoic acid + NAD+ CoA
and thiamine pyrophosphate CO2
+ acetyl-CoA + NADH + H+
METABOLISM
Dr. Daxa N. Mehta
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