Cell Respiration and Metabolism

• Glycolysis

• Lactic Acid Pathway

• Krebs Cycle

• ATP Production

• Basal Metabolic Rate (not in your book)

CHAPTER 5

Metabolism

Metabolism = all of the reactions in the body that involve energy transformation are collectively termed metabolism.

Metabolism:

1- Anabolism = the process of using energy to build up larger molecules. Here some of the energy used is stored in the new molecule. e.g. synthesis of glycogen, fat, and protein.

2- Catabolism = the process of releasing energy from larger food molecules by converting them into smaller molecules. e.g. breakdown of glucose, fatty acids, and amino acids and formation of ATP in the process.

Glycolysis

Glycolysis = Breakdown of glucose to obtain energy.

Glucose + 2NAD + 2ADP + 2 Pi

2 Pyrovic Acid + 2NADH + 2ATP

Nicotinamide Adenine Dinucleotide

Adenosine Diphosphate

Adenosine Triphosphare

Glycolysis cccurs in cell cytoplasm

Glycolysis

-1

-1

+2

+2

Activa

tion

Glucose

+ 2 ADP + 2 Pi

+ 2NAD

2 Pyrovic Acid

E N

E R

G Y

L E

V E

L

2 NADH2 ATP

Glycolysis

Phosphorylation of glucose toglucose-6 phosphate traps

glucose inside the cell.

Lactic Acid Pathway

• Anerobic respiration or Lactic acid Fermentation

GlucoseGlycolysis

In the absence of oxygent

Glycogenesis and Glycogenolysis

• Cells can not accumulate free glucose because of osmotic effect which causes the water to enter the cell.

• So glucose is stored in the form of glucose polymeres (Glycogen), particularly in liver, skeletal muscle and heart.

• Formation of glycogen from glucose is called glycogenesis.

Glucose Glucose-6-phosphate Glucose-1-phosphate

Glycogen

ATP ADP

Pi EnzymeEnzymeEnzyme

Enzyme

Breakdown of glycogen to glucose is called glycogenolysis.

Glycogen Glucose-1-phosphate Glucose-6-phosphate

Glucose

Pi

Enzyme Enzyme

Only in LIVER

Glycogenesis and Glycogenolysis

Blood glucose that enters tissue cells is rapidly converted to glucose-6-phosphate. This intemediate can be metabolized for energy in glycolysis, or it can be converted to glaycogen (1) in a process called glycogenesis. Glycogen represents a storage form of carbohydrates which can be used as a new source of glucose (2) by glycogenolysis.

Cori Cycle

2 ATPGlycolysis

Lactic Acid Pathway

Gluconeogenesis

Aerobic Cell Respiration

• Conversion of molecules such as glucose or fatty acid to CO2 & H2O in the presence of O2 is called aerobic cell respiration.

Glucose CO2 + H2O + ATP + HEAT

O2

ENZYMES

Aerobic Respiration

Glucose

Glycolysis

• 1- One guanosin triphosphate (GTP) is produced, which gives a

phosphate group to ADP to produce one ATP.

• 2- Three molecules of NAD are reduced to NADH

• 3- One molecule of FAD is reduced to FADH2.

• The production of NADH and FADH2 are far more significant in terms of energy production than GTP production.

Main Events in Krebs Cycle

2ATP/glucose

6NADH/glucose

2FADH2/glucose

Flavin Adenine Dinucleotide

Chemiosmotic Theory

• ATP is formed during oxidative phosphorylation by the flow of hydrogen ions across the inner mitochondrial membrane.

• Two or three molecules of ATP are produced per pair of electrons donated, depending on the point at which a particular coenzyme enters the electron-transport chain.

Oxidative Phosphorylation

Net ATP production from Glucose

Heat Production in the Body

- Metabolic activity occurs in all cells of the body, therefore all cells are involved in the production of heat but there are certain tissues which produce more heat than others:

- Tissues with highest heat production:

- Liver

- Brain

- Endocrine Glands

- Skeletal muscle during exercise

Metabolic rate

-Metabolic rate = the total rate of body metabolism. Body metabolism is measured by Calories.

- One calorie is defined as the amount of heat required to raise the temperature of one cubic centimeter of water from 14.5 degrees to 15.5 degrees centigrade.

In an aerobic respiration one L of O2:

+ Carbohydrates 5.06 Calories+ Proteins 4.60 Calories+ Fat 4.70 Calories

Therefore 1L of O2 + mixed food 4.825 Calories

Basal Metabolic rate (BMR)

-The metabolic rate of an awake, relaxed person 12-14 hours after eating and at a comfortable temperature is known as Basal Metabolic Rate (BMR).BMR is determined by: age, sex, body surface area, and thyroid hormone secretion.

Basal conditions can be achieved by:

1- Avoiding exercise for at least 30 minutes before measuring BMR.

2- Complete mental rest.

3- Comfortable temperature.

4- Fasting for at least 12 hours.

5- Body temperature must be normal.

Methods for Measuring Metabolic rate

1- Direct Method:

Thermometer

Calorimeter

Methods for Measuring Metabolic rate

2- Indirect Method:

Units of Metabolic rate- Metabolic rate is measured as:

Calories per square meter per hour (Calories/m2/hr)

-m2 is the measure of body surface area.

As an example BMR can be calculated from the amount of O2 consumption:

A subject consumes 15 L of O2 in 1 hour at basal conditions, Caloric equivalent of O2 is 4.8 Calories/L. the subject’s body surface area is 1.5 m2,

What is this subject’s BMR?15 x 4.8 = 72.4 Calories/hr

72.5

1.5= 48.3 calories/m2/hr

Means for each L of O2 4.8 Calories heat is produced

Heat loss from the Body

- Heat is lost from the body by: Radiation, Conduction and Evaporation

Body Temperature

- The body maintains its temperature around 37 oC which is the optimum for enzymes and biological reactions.

- To achieve this body must balance between heat production and heat loss.