3.2 Carbohydrate and Fat Metabolism
METABOLISM
• Metabolism is all the biochemical reactions that occur within
an organism, including anabolic and catabolic reactions.
• Anabolism
• Energy requiring reactions whereby small molecules are built
up into larger ones.
– Eg. For example, glucose molecules convert to glycogen.
• Catabolism
• Chemical reactions that break down complex organic
compounds into simpler ones, with the net release of energy.
• This can be aerobic (“with oxygen) or anaerobic (“without
oxygen)
– Eg. digestive enzymes break down food  release energy
– respiration
Anabolism and Catabolism
Energy storage by lipids and carbohydrates
Wallet
(Glycogen)
An analogy:
easy to get to,
would be too big if you put
in all your money
You are
paid in cash
(Glucose)
Bank
(Fat)
Spend it!
(Respiration)
Can put lots of money here, more
of a hassle to get it back out
Storage sites for glycogen and triglyceride
Humans store excess glucose as
glycogen.
Glycogen can have
up to 60, 000
glucose molecules
in it
The major sites for storage
of triglyceride is the
adipose tissue and skeletal
muscles
Glycogen is stored as small granules,
particularly in muscles and liver.
Glycogen is stored up to about 10 hours. Any
unused glycogen is converted to triglyceride
Carbohydrate Metabolism
Blood glucose levels
Blood glucose rises just after eating, but quickly returns to normal.
Where does the sugar go? Why is it not left in the blood?
140
blood glucose
(mg/100cm3)
120
100
80
60
40
20
0
normal
after meal
after vigorous exercise
The role of Insulin
Role of Insulin
Both insulin and muscle contraction stimulate glucose
uptake from the blood into skeletal muscle.
EXERCISE
Functions of glucagon and adrenaline during fasting
and exercise
Pathways in carbohydrate metabolism
Lysis means
breakdown
When the energy stored
in the glycogen is
needed it is turned back
into
glucose. This process is
known as
glycogenolysis
Glucose is broken down to provide
energy. This process is known
as glycolysis
genesis means
production
Glucose that is not used
immediately is stored as
glycogen. This
conversion of glucose
to glycogen
is called glycogenesis.
Lipolysis
Lipolysis is the process of releasing triglycerides
from the body’s fat stores.
Triglyceride breaks down to form glycerol and three
fatty acids
+
triglyceride
glycerol
fatty acids
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15