Cellular

Respiration

May 2017

What is cellular respiration

– Is the gradual release of energy by the stepwise breakdown of energy-rich fuel

molecules, example glucose within a plant or animal cell to keep it alive.

– The process takes place by a series of reactions controlled by enzymes.

Oxygen usually used and carbon dioxide, water and energy released during

the process.

– Glucose comes from the food produced during photosynthesis. Oxygen comes from the air which the organism breathes in. carbon dioxide and water vapour are got rid of in the air breathed out. Most of the energy is lost as heat, but some is channelled into molecules of the energy carrier ATP.

– Cellular respiration comprises of series of reactions carried out by groups of soluble enzymes located in the cytosol and mitochondria of plant and animal cells.

❖ Cellular respiration occurs in all living cells and is the only

way in which cells can obtain energy for their activities.

❖ The Chemical Energy released when fuel molecules like

glucose are broken down is not used directly in the cell.

❖ Instead it is transferred to and stored in ATP which provides

the energy for all Metabolic Processes.

❖ These processes include muscle contraction, nerve

transmission, synthesis of new materials for growth like

protein synthesis, regulation of body temp and other

homeostatic processes

Cellular Respiration

Three types – aerobic and anaerobic respiration and anaerobic fermentation

1. Aerobic respiration – glucose is broken down in the presence of oxygen (a lot of energy is released)

❖WHEN OXYGEN ACCEPTS THE ENERGY DEPLETED HYDROGEN ATOM

2. Anaerobic respiration – glucose is broken down in the absence of oxygen (a small amount of energy is released)

❖WHEN AN INORGANIC MOLECULE OTHER THAN OXYGEN ACCEPTS THE HYDROGEN; many bacteria use sulphur, nitrate and carbon as hydrogen acceptors

3. Anaerobic fermentation – occurs without involvement of oxygen

❖WHEN AND ORGANIC MOLECULE ACCEPTS THE LOW ENERGY HYDROGEN e.g. ACETALDEHYDE

Aerobic Respiration❖ Enzymes

C6H12O6 + 602 6H20 + 6CO2 + 38 ATP

❖ glucose + oxygen water + carbon + heat

dioxide

❖ One glucose molecule produces 38 ATP molecules

❖ This energy is used for life processes of cells such as

growth, movement and transporting substances across

membranes (active transport)

❖ Occurs in the presence of oxygen - Figure 6.2 pg 185

❖ Divided into three stages

1. Glycolysis (Anaerobic Process as well)

❖ Occurs in cytoplasm

❖ Glucose is broken down into pyruvic acid

❖ Energy-rich hydrogen atoms are given off and these move into the

mitochondria for the 3rd stage

❖ 2 ATP Molecules are produced

– THE NET PRODUCT OF GLYCOLYSIS:

– ONE MOLECULE OF GLUCOSE IS CONVERTED INTO TWO MOLECULES OF PYRUVATE,

TWO MOLECULES OF ADP INTO TWO MOLECULES OF ATP, AND TWO MOLECULES

OF NAD+ INTO TWO MOLECULES OF NADH (reduced from NAD+ )

1. PHOSPHORYLATION OF GLUCOSE

2. REARRANGEMENT OF GLUCOSE

3. SECOND ATP PHOSPHORYLATION

4. FORMATION OF GLYCERALDEHYDE PHOSPHATE

5. FORMATION OF BIPHOSPHOGLYCERATE

6. FORMATION OF PHOSPHOGLCERATE

❖ 2. Krebs Cycle

❖ Occurs in the mitochondria

❖ Pyruvic acid is completely broken down into energy rich hydrogen atoms and carbon dioxide

❖ The carbon dioxide is given off as a gas that is breathed out

❖ The energy-rich hydrogen atoms are used in the 3rd stage

– THE NET PRODUCT OF KREBS CYCLE:

– IT TAKES TWO PREPARATORY REACTION SEQUENCES AND TWO TURNS OF THE KREBS CYCLE TOUSE UP THE TWO PYRUVATE MOLCULES FORMED FROM ON MOLECULE OF GLUCOSE.

– ALTHOUGH THE TWO TURNS OF THE CYCLE GENERATE ONLY 2 ATP MOLECULES MUCH MORE ENERGY IS STORED IN THE RELEASED CO ENZYMES. THE CARBON DIOXIDE FORMED LEAVES THE CELL AS A PRODUC OF CELLULAR RESPIRATION

❖ 3. Oxidative Phosphorylation

❖ Occurs in the mitochondria

❖ The energy rich hydrogen atoms from the 1st and the 2nd stage lose

their energy and this energy is used to make energy rich ATP (a

phosphate is added ADP – Known as phosphorylation)

❖ Once the hydrogen atoms lose their energy , they combine with

oxygen to form water which is either breathed out as water vapour

or excreted by the kidneys

– THE NET PRODUCT OF ELECTRON TRANSPORT SYSTEM (ETC):

– O2 + 4H+ + 4e - 2H2O

Factors that affect the rate of aerobic respiration

❖Aerobic respiration depends on enzymes

❖Enzymes are affect by temperature

❖However; in the human body temperature is not a factor as the

body temperature remains constant at 37 degrees Celsius

❖Metabolic rate refers to the rate at which all the chemical

reactions in the body cells are occurring

❖When we need more energy the body increases the rate of

aerobic respiration and hence we say the metabolic rate

increases

❖When these increase we breathe more often and more deeply

and produce more heat due to ATP being used

Anaerobic Respiration

❖Occurs when no oxygen is present and in all living organisms

❖Organisms that live in places where there is no oxygen respire

anaerobically – this is called alcoholic fermentation

❖When it occurs in animal cells it is called lactic acid

fermentation

❖Lactic acid fermentation occurs in animal cells that require a lot

of energy such as muscle cells when they do not get enough

oxygen

❖The breakdown of one glucose molecule only produces 2 ATP

molecules as glucose is not completely broken down

❖Table 6.1 pg 191

❖Alcoholic Fermentation

❖Alcohol, carbon dioxide and energy is produced

❖C6H1206 2C2H5OH + 2CO2 + 2ATP

Glucose Alcohol + Carbon Dioxide + Energy

❖Lactic Acid Fermentation

❖Lactic acid and energy is produced

❖ C6H1206 2C3H603 + 2ATP

Glucose Lactic Acid + Energy

Anaerobic Respiration in Humans

❖Muscle cells need a lot of energy when one is

exercising

❖If there is not enough oxygen getting to these muscle

cells glucose cannot be broken via aerobic respiration

❖Hence glucose will be broken down anaerobically

which will give rise to lactic acid

❖Lactic acid builds up and prevents one’s muscles from

contracting as much – this is called muscle fatigue

❖Extra oxygen is needed to break down lactic acid – this is

known as oxygen debt

❖In order to pay this debt we breathe deeply and quickly after

exercising

❖When the debt is paid back one’s breathing turns to normal

Anaerobic Respiration in Industry

❖Biotechnology – the industrial use of living organisms to manufacture food and other products

❖Yeast occurs naturally on different kinds of plants

❖Yeast is used to make alcoholic drinks such as beer and wine by breaking down the glucose anaerobically

❖Yeast is also used to make bread

❖Flour, water, sugar and yeast are mixed together

❖The yeast breaks down the sugar in the process of alcoholic fermentation which gives off carbon dioxide and alcohol

❖The carbon dioxide is trapped in the dough causing it to rise

❖Baking the dough kills the yeast and causes the alcohol to evaporate