Respiration: ATP and Coenzymes

Respiration: ATP and Coenzymes

What do you already know? • What is ATP? • Where do we get energy from? • If you compared the rate of respiration of a bacterial cell at 20oC and 35 oC what would you expect to find? What would you expect to find at 70 oC? Explain • What is cellular respiration, where does it occur and why is it important to living organisms? • How is respiration similar to burning fuel? How is it different? • Can enzymes respire? Explain • What is aerobic respiration? • What is anaerobic respiration? • Why do yeast cells sometimes respire to produce alcohol but at other times just produce carbon dioxide and water? • When substances cross biological membranes energy is either released or used. How is membrane transport by diffusion and by active transport a) different and b) similar?

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What is energy?

Uses of ATP Cells need a supply of ATP molecules to act as an immediate energy source for : • Active transport, secretion, exocytosis, endocytosis • Maintaining nerve cell membrane potential • Movement: Muscles, Flagella, Microtubules • Mitosis • DNA replication • Synthesis of new organelles • Metabolic synthesis and chemical activation • Bioluminescence • Maintenance of body temperature

ATP = source of energy

HOMEWORK Read pages 80 – 81 Answer questions 1-4 page 81 (full sentences, key terminology, logical argument / explanation) Read Bio Science Review Article: ATP Highlight key points and add to file This will not be marked, but will be looked at when files are taken in

http://www.worldofmolecules.com/3D/atp_3d.htm Structure of ATP ATP 3 phosphate groups Adenine ribose P P P P P ADP 2 phosphate groups Adenine ribose

Synthesis of ATP from ADP Phosphoric acid and ADP undergo a condensation reaction Water is eliminated and ATP is formed ReplayClose window

ATP is made of adenine, ribose and phosphate therefore it is classed as a…… • ATP is a small water soluble molecule therefore it easily transported inside cells. • When each of the first two phosphates is hydrolysed from ATP approx 30kJ/mol of energy is released • Usually just the first phosphate is removed resulting in ADP and phosphate • This is a reversible reaction and ATP can be resynthesised from ADP and phosphate if energy is put back in.

ATP + H2O ADP + Pi + 30kJ

Energy currency • ATP is called an energy currency not an energy storage molecule because it is an immediate source of energy • Short term energy stores could be … • Long term energy stores could … • There are only about 5g of ATP in your body, but… at rest you will hydrolyse about 40kg of ATP per day! • Because ATP is synthesised from ADP by the addition of a phosphate we say it is produced by phosphorylation • The enzyme that does this is called ATP synthase.

Synthesis of ATP ADP can be phosphorylated in 3 ways; • By reorganising chemical bonds and transferring phosphate directly from a substrate to ATP. This is called substrate level phosphorylation and occurs during respiration. • By photophosphorylation which takes place in chloroplasts during photosynthesis and is linked to the absorption of light energy. • By oxidative phosphorylation which takes place in mitochondria and is linked to the oxidation of substrates in respiration. • http://highered.mcgraw-hill.com/olc/dl/120071/bio11.swf

Chemiosmotic theory of ATP synthesis • In both photophosphorylation and oxidative phosphorylation ATP is synthesised during the transfer of electrons along a chain of carrier molecules in either mitochondrial or chloroplast membranes. • The electrical potential energy of the electrons is used to create a difference in hydrogen ion concentration across the membrane.

Essentially the flow of these hydrogen ions back across the membrane down their conc gradient releases energy which is used to phosphorylate ADP.

ATP synthase • ATP synthase is a protein that spans the inner membrane of mitochondria and the thylakoid membrane of chloroplasts. • It is through this protein that the hydrogen ions flow back into either the mitochondrial matrix or the chloroplast stroma • http://www.dnatube.com/video/104/ATP-synthase-structure-and-mechanism

ATP synthase has three binding sites and a part of the molecule that rotates as the hydrogen ions pass through • When the hydrogen ions pass through the ‘stalk’ part of the molecule rotates • This produces the structural changes in the binding sites in the ‘knob’ as shown opposite • The three phases are ; • Loosebinding of ADP and phosphate (L) • Forming tightly bound ATP(T) • Releasing ATP byopening (O) • An animation of this can be seen at the following address • http://www.stolaf.edu/people/giannini/flashanimat/metabolism/atpsyn2.swf

Synoptic Questions

1 Calculate the percentage decrease in bone density for women who drank more than seven fizzy drinks per week, compared with those women who drank none. 2 Describe the results. 3 A news story on this study said that scientists had found that fizzy drinks cause osteoporosis. Evaluate the evidence for this claim. You should consider the data and the methodology.

COENZYMES • Organic molecules, essential for enzyme controlled reaction • Usually bind temporarily to the enzyme molecule • Carry a chemical group needed in or produced by the enzyme-controlled reaction • Coenzyme exists in 2 forms – with and without the chemical group – so they are re-cycled • Chemical group is removed by another enzyme-controlled reaction • Coenzymes are often formed from vitamins • On their own they are catalytically inactive, but act as “handles” for enzymes to attach

Molecular structure of NAD 2 linked nucleotides= 5-carbon sugar, ribose, Adenine, Phosphate group

The structure of coenzyme A Derived from:- Pantothenic acid (B vitamin) Adenosine (adenine + ribose) 3 phosphates Cysteine (an amino acid)

Chemical groups carried by coenzymes

The stages of respiration Pyruvate dehydrogenase

Coenzymes in respiration • NAD acts as a H carrier with the enzyme pyruvate dehydrogenase. • Coenzyme A also works with pyruvate dehydrogenase to form acetyl coenzyme A. • Pyruvate dehydrogenase is inhibited by high NADH, ATP and acetyl coenzyme A. Can you think why this is useful?

Respiration: ATP and Coenzymes