CELLULAR RESPIRATIONCHAPTER 7- CFE HIGHER

HUMAN BIOLOGY

CELLULAR RESPIRATION

•THIS IS A SERIES OF METABOLIC PATHWAYS THAT BRING ABOUT THE RELEASE OF ENERGY FROM A FOODSTUFF AND THE REGENERATION OF THE HIGH-ENERGY COMPOUND ADENOSINE TRIPHOSPHATE (ATP)

ADENOSINE TRIPHOSPHATE (ATP)

A molecule of ATP is composed of adenosine and three inorganic phosphate groups. Energy held in ATP is released when the bond attaching the terminal phosphate is broken by enzyme action. This results in the formation of Adenosine diphosphate (ADP) and inorganic phosphate (Pi). Energy is required to regenerate ATP from ADP and inorganic phosphate.

TRANSFER OF ENERGY VIA ATP

FIXED QUANTITY OF ATP

THREE STAGES OF CELLULAR RESPIRATION

• 1. GLYCOLYSIS

• 2. CITRIC ACID CYCLE

• 3. ELECTRON TRANSFER CHAIN

The first stage of Cellular Respiration is called Glycolysis and occurs in the cytoplasm.

In this stage glucose is ‘split’ to form Pyruvate.

Glycolysis consists of a series of enzyme-controlled steps.Those in the first half of the chain make up the energy investment phase where 2ATPs are needed to start the process off.

Those in the 2nd half of the chain make up the energy payoff phase where 4ATPs are produced. By the time the original 2ATPs are paid back, a net gain of 2ATPs are left.

Phosphorylation of intermediates occurs twice in the first phase, in step 1 and in step 3. Step 3 is catalysed by an enzyme phosphofructokinase.

Hydrogen ions are released from the substrate by an enzyme called dehydrogenase. These hydrogen ions are added to a coenzyme called NAD and becomes NADH.

The process of glycolysis does not need oxygen however the production of further ATPs from NADH only occurs at the later stage in respiration if oxygen is present. So far however only 2ATPs have been generated.

CARBOHYDRATES AS RESPIRATORY SUBSTRATES

FATS AS RESPIRATORY SUBSTRATES

PROTEINS AS RESPIRATORY SUBSTRATES

Proteins in the diet are broken down to their component amino acids by the action of digestive enzymes. Amino acids in excess of the body’s requirements for protein synthesis undergo deamination, forming urea and respiratory pathway intermediates as shown opposite. These intermediates then enter the metabolic pathway and act as respiratory substrates regenerating ATP as before.

The third step in glycolysis can be regarded as a key regulatory point as it can be controlled by enzymes

When a cell contains more ATP than is needed the high concentration of ATP has an inhibitory effect on phosphofructokinase and this slows down glycolysis. When ATP levels drop again the phosphofructokinase is no longer inhibited and glycolysis speeds up again

When there is a high concentration of citrate this also has an inhibitory effect on phosphofructokinase and slows down glycolysis

When citrate levels fall again glycolysis speeds up again as there is no longer an inhibitory effect on phosphofructokinase

CREATINE PHOSPHATE SYSTEM

CREATINE PHOSPHATE SYSTEM

Much of the energy needed for repetitive muscular contraction comes from a chemical creatine phosphate

CREATINE PHOSPHATE SYSTEM

CREATINE PHOSPHATE SYSTEM

LACTIC ACID METABOLISM

LACTIC ACID METABOLISM

OXYGEN DEBT

ATP TOTALS

TYPES OF SKELETAL MUSCLE FIBRE

MYOGLOBIN

DIFFERENT FIBRES FOR DIFFERENT EVENTS

DIFFERENT FIBRES FOR DIFFERENT EVENTS

• SKELETAL MUSCLES CONTAIN A GENETICALLY DETERMINED MIXTURE OF SLOW-TWITCH AND FAST-TWITCH FIBRES. IN MOST MUSCLES, A FAIRLY EVEN BALANCE EXISTS BETWEEN THE TWO BUT IN SOME MUSCLES, ONE TYPE PREDOMINATES OVER THE OTHER.

• FOR EXAMPLE, THE MUSCLES IN THE BACK RESPONSIBLE FOR MAINTAINING POSTURE CONTAIN MOSTLY SLOW-TWITCH FIBRES, WHEREAS THE MUSCLES THAT MOVE THE EYEBALLS ARE MADE UP MAINLY OF FAST-TWITCH FIBRES.