Chapter 6 Cellular Respiration



Chapter 6 Cellular Respiration

C6H12O6 + 6O2 6CO2 + 6H2O + 36 ATP

glucose + oxygen ( carbon dioxide + water + energy

• Living things need energy to carry on life activities

o making complex compounds from simpler ones.

o moving some materials across membranes

o cells need energy just to stay alive.

• chemical energy is stored in food

• carbohydrates most commonly broken down for energy

• some energy is released as heat

• rest of energy from food stored in chemical form

• cellular respiration is an energy releasing process which takes place in all living things.

o both autotrophic and heterotrophic organisms

• ATP and ADP

• Adenosine triphosphate – high energy

• adenosine diphosphate – low energy

• structure of ATP

• Energy cycle of the cell

• ATP supplies the cell with the energy needed for cell work

• glucose is broken down

• energy is released

• energy used to attach a third phosphate to ADP

• energy is released when the third phosphate is detached from ATP

• ADP is regenerated for reuse.[pic]

ENERGY:

• A continuous supply is needed for cells to stay alive

• carbohydrates – glucose- foods most commonly broken down for energy

• energy is released when food(fuel) is burned

• energy is released by chemical changes

• energy is released partially as heat – maintains body temperature

• energy releasing process is called cellular respiration

• energy is used by cells in the form of ATP

• ATP is packaged for slow gradual use

• ATP is adenosine triphosphate

• high energy bonds link phosphates to each other

• energy is transferred to another compound when the last phosphate group is removed and bonds to another compound

• Phosphorylation = transfer of energy from one compound to another – it is how energy is transferred in living cells

• when ATP is hydrolyzed (broken down ) – energy is released

• ADP has less energy than ATP

• Cellular respiration is a biochemical pathway

o a biochemical pathway is a sequence of chemical reactions that leads to a particular result in a living cell.

• Chemical reactions of cellular respiration require specific enzymes

• each enzyme requires the action of a COENZYME.

• the coenzyme acts as a hydrogen acceptor

• the coenzyme gains energy because it is carrying an extra hydrogen and electrons.

• Coenzymes of cellular respiration are:

o NAD+ nicotinamide adenine dinucleotide

o FAD flavin adenine dinucleotide

o each accepts hydrogen atoms

o in cellular respiration glucose is oxidized (loses electrons)

• Stages of cellular respiration

o glycolysis – does not require the presence of oxygen ever!

▪ takes place in the cytoplasm in ALL living things

▪ requires an investment of 2 ATP

▪ glucose is split into 2 three carbon sugars called PGAL (phosphoglyceraldehyde)

▪ through a series of enzyme catalyzed reactions, PGAL is converted to pyruvic acid and generates NADH and ATP during these reactions.

▪ produces as end products

• 2NADH ( hydrogen acceptors – coenzymes – energy carriers to the electron transport chain in the mitochondria)

• 2ATP (net gain)

• 2 pyruvic acid molecules

IF OXYGEN IS PRESENT PYRUVIC ACID ALONG WITH OXYGEN GOES TO THE MITOCHONDRIA FOR THE COMPLETION OF AEROBIC RESPIRATION:

• Aerobic cellular respiration

o oxygen present

▪ pyruvic acid along with oxygen enter the mitochondria

▪ pyruvic acid molecules are broken down to yield CO2, and acetyl coenzyme A (acetyl CoA)

▪ Acetly Co A enters the Krebs cycle reacting with oxaloacetate in the matrix of the mitochondria.

KREBS CYCLE: takes place in the mitochondrial matrix.

▪ each turn of krebs needs 1 molecule of aceyl Co A and yields 2 molecules of CO2 and 4 pair of H+ atoms

▪ H+ atoms are picked up by NAD+ and another energy carrier (hydrogen acceptor) FAD.

▪ NAD+ ( NADH

▪ FAD ( FADH2

▪ both of these hydrogen acceptors carry energy to the electron transport chain.

▪ Yields: 2 turns (one for each pyruvic acid)

• 2 ATP

• NADH

• FADH2

• CO2

ELECTRON TRANSPORT CHAIN: takes place in the inner membrane of the mitochondria.

• energy releasing reactions

• organized system of enzymes and coenzymes in the inner mitochondrial membrane are involved

• NADH and FADH2 carry H+ into the ETC

• electrons from H+ are passed from one compound to another

• hydrogens give up electrons along the chain and molecules of ATP are formed from the energy released.

• H+ gradient formed and as they fall through ATP ase , an enzyme complex in the mitochondrial inner membrane, down the concentration gradient – the energy is used to convert ADP to ATP.

• oxygen is the final hydrogen acceptor at the end of the chain forming water. This is the “water of metabolism”.

• net result is a total gain of 32 molecules of ATP

o 32 ATP from electron transport

o 2 from Krebs

o 2 from glycolysis

o total = 36 molecules from aerobic cellular respiration

IF OXYGEN IS ABSENT AND NO MITOCHONDRIA ARE PRESENT :

Pyruvic acid undergoes fermentation.

• Anaeorbic respiration – fermentation

• fermentation is the process where is no further release of energy after glycolysis.

• takes place in the absence of oxygen

• bacteria, yeast and muscle cells depleted of oxygen

o Two Types of anaerobic respiration/ fermentation:

▪ lactic acid fermentation – pyruvic acid in the absence of oxygen is converted to lactic acid.

• bacteria – yogurt

• muscle cells - cramps

▪ ethyl alcohol fermentation – pyruvic acid in the absence of oxygen is converted to ethyl alcohol and carbon dioxide.

• yeast – beer and wine

• yeast – bread

• does not involve oxygen

• only ATP produced is the result of glycolysis

Tremendous amount of stored potential energy still locked up in the products of fermentation. Not as efficient as aerobic respiration.

[pic]

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breakdown of glucose

ADP + P

ATP

Cell Activities

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