Carbohydrate Metabolism & Glycolysis
Introduction to Metabolism
1. Metabolism is the total amount of biochemical reactions involved in maintaining the living
conditions of cells in an organism. All living organisms require energy for different essential
processes and for producing new organic substances.
2. Metabolism helps with:
a. Growth
b. Repair
c. Reproduction
d. Maintaining structures of living organisms
e. Providing energy and providing internal heat to maintain body temperature and warmth
3. Metabolism is of 2 types:
4. Bioenergetics is a branch of biochemistry that focuses on how cells transform energy, often by
producing, storing or consuming adenosine triphosphate (ATP). ATP is also called the energy
currency of the cells.
Metabolism
Anabolism Catabolism
Process involves breaking down Process involves synthesizing
larger organisc molecules into compounds from simpler
smaller molecules. Process releases substances required by the cells.
energy. Process requires and stores energy.
5. Pathway for carbohydrate catabolism:
Electron
Glycolysis Krebs cycle
transport chain
, 6. 2 critical parameters monitored during a medical emergency are:
a. Blood sugar level
b. Blood pressure (and blood volume)
7. Monitoring these parameters is important because blood glucose is the only energy source for:
a. Brain
b. Red blood cells
c. Central nervous system
8. Carbohydrates are the fastest source of energy for the body.
Glycolysis
1) Glycolysis can be defined as the breakdown of glucose (6-carbon compound) into pyruvate (3-
carbon compound) or lactate (3-carbon compound) via aerobic or anaerobic respiration,
respectively, to generate ATP.
2) The process takes place in the cytoplasm.
3) Pyruvate is produces as the end product of aerobic glycolysis (~presence of oxygen). Lactate is
produced as the end product of anaerobic glycolysis (~absence of oxygen).
4) Salient features of glycolysis:
a. Glycolysis takes place in the cytoplasm.
b. It is the only pathway that can take place in the presence or absence of oxygen.
c. It is the pre-requisite for oxidative pathways as it provides the substrate Glucose-6-
phosphatecentral molecule needed for other biochemical pathways.
d. It is a pathway that can operate even without mitochondria. Example:
i. Kidney medulla
ii. Cornea Have only few mitochondria
iii. Testis
iv. Red blood cells Do not have mitochondria!
e. It is useful in the synthesis of non-essential amino acids.
f. Glycolysis provides glycerol for triglyceride synthesis.
5) Steps of glycolysis:
a. Glycolysis is a linear pathway.
b. It is a 10 steps process.
i. Reversible steps: Steps 2, 4 to 9
ii. Irreversible steps: Steps 1, 3, and 10
, Irreversible steps are very important and are also called Regulatory Steps since
they can regulate when to turn the ATP production on/off., using enzymes and
hormones based on body signals and demands.
c. The 10 steps occur in 3 stages:
Stage 1: ATP is used up.
Energy Investment Involves step 1, 2,
Phase 3
Stage 2:
3 stages of Involves step 4
glycolysis Doubling/splitting and 5
phase
Stage 3:
Involves step 6 to
Energy generation 10
phase
Step 0: Glucose enter cells
Glucose is a small and polar molecule. It can enter the cells via 2 methods:
Method 1: Secondary active transport in which the transport can take place against the glucose
concentration gradient.
Method 2: Through a group of glucose transporter proteins (GLUT) that assist in facilitated
diffusion of glucose.
Step 1: Phosphorylation of glucose
The moment glucose enters the cell, the enzyme Hexokinase/Glucokinase catalyzes the
phosphorylation of glucose to produce Glucose-6-phosphate. Hexokinase has broad specificity
for substrates.
This step uses up the phosphate from the ATP molecule.
The step also uses magnesium (Mg2+). Mg2+ is needed to shield the negative charges on the
phosphate of ATP, thereby allowing the nucleophilic attack of carbon-6 of glucose. Magnesium
deficiency can inhibit hexokinase activity.
Glucose-6-phosphate is more reactive form as it is negatively charged. This reaction prevents
the phosphorylated glucose molecule from continuing to interact with the GLUT proteins, and it
can no longer leave the cell because the negatively charged phosphate will not allow it to cross
the hydrophobic interior of the plasma membrane.
Step 2: Isomerization of glucose-6-phosphate
This step involves the isomerization of glucose-6-phophate to fructose-6-phosphate by the
enzyme Phosphoglucose Isomerase.
Introduction to Metabolism
1. Metabolism is the total amount of biochemical reactions involved in maintaining the living
conditions of cells in an organism. All living organisms require energy for different essential
processes and for producing new organic substances.
2. Metabolism helps with:
a. Growth
b. Repair
c. Reproduction
d. Maintaining structures of living organisms
e. Providing energy and providing internal heat to maintain body temperature and warmth
3. Metabolism is of 2 types:
4. Bioenergetics is a branch of biochemistry that focuses on how cells transform energy, often by
producing, storing or consuming adenosine triphosphate (ATP). ATP is also called the energy
currency of the cells.
Metabolism
Anabolism Catabolism
Process involves breaking down Process involves synthesizing
larger organisc molecules into compounds from simpler
smaller molecules. Process releases substances required by the cells.
energy. Process requires and stores energy.
5. Pathway for carbohydrate catabolism:
Electron
Glycolysis Krebs cycle
transport chain
, 6. 2 critical parameters monitored during a medical emergency are:
a. Blood sugar level
b. Blood pressure (and blood volume)
7. Monitoring these parameters is important because blood glucose is the only energy source for:
a. Brain
b. Red blood cells
c. Central nervous system
8. Carbohydrates are the fastest source of energy for the body.
Glycolysis
1) Glycolysis can be defined as the breakdown of glucose (6-carbon compound) into pyruvate (3-
carbon compound) or lactate (3-carbon compound) via aerobic or anaerobic respiration,
respectively, to generate ATP.
2) The process takes place in the cytoplasm.
3) Pyruvate is produces as the end product of aerobic glycolysis (~presence of oxygen). Lactate is
produced as the end product of anaerobic glycolysis (~absence of oxygen).
4) Salient features of glycolysis:
a. Glycolysis takes place in the cytoplasm.
b. It is the only pathway that can take place in the presence or absence of oxygen.
c. It is the pre-requisite for oxidative pathways as it provides the substrate Glucose-6-
phosphatecentral molecule needed for other biochemical pathways.
d. It is a pathway that can operate even without mitochondria. Example:
i. Kidney medulla
ii. Cornea Have only few mitochondria
iii. Testis
iv. Red blood cells Do not have mitochondria!
e. It is useful in the synthesis of non-essential amino acids.
f. Glycolysis provides glycerol for triglyceride synthesis.
5) Steps of glycolysis:
a. Glycolysis is a linear pathway.
b. It is a 10 steps process.
i. Reversible steps: Steps 2, 4 to 9
ii. Irreversible steps: Steps 1, 3, and 10
, Irreversible steps are very important and are also called Regulatory Steps since
they can regulate when to turn the ATP production on/off., using enzymes and
hormones based on body signals and demands.
c. The 10 steps occur in 3 stages:
Stage 1: ATP is used up.
Energy Investment Involves step 1, 2,
Phase 3
Stage 2:
3 stages of Involves step 4
glycolysis Doubling/splitting and 5
phase
Stage 3:
Involves step 6 to
Energy generation 10
phase
Step 0: Glucose enter cells
Glucose is a small and polar molecule. It can enter the cells via 2 methods:
Method 1: Secondary active transport in which the transport can take place against the glucose
concentration gradient.
Method 2: Through a group of glucose transporter proteins (GLUT) that assist in facilitated
diffusion of glucose.
Step 1: Phosphorylation of glucose
The moment glucose enters the cell, the enzyme Hexokinase/Glucokinase catalyzes the
phosphorylation of glucose to produce Glucose-6-phosphate. Hexokinase has broad specificity
for substrates.
This step uses up the phosphate from the ATP molecule.
The step also uses magnesium (Mg2+). Mg2+ is needed to shield the negative charges on the
phosphate of ATP, thereby allowing the nucleophilic attack of carbon-6 of glucose. Magnesium
deficiency can inhibit hexokinase activity.
Glucose-6-phosphate is more reactive form as it is negatively charged. This reaction prevents
the phosphorylated glucose molecule from continuing to interact with the GLUT proteins, and it
can no longer leave the cell because the negatively charged phosphate will not allow it to cross
the hydrophobic interior of the plasma membrane.
Step 2: Isomerization of glucose-6-phosphate
This step involves the isomerization of glucose-6-phophate to fructose-6-phosphate by the
enzyme Phosphoglucose Isomerase.
