BY4

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BY4 Metabolism, Microbiology and
HomeostasisLearning objectives

• To know the importance of chemical energy in
  biological processes
• To understand the role of ATP
• To draw the structure of ATP
• To understand the stages in aerobic respiration
  glycolysis, link reaction, Krebs cycle and the
  electron transport chain

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What processes do cells need energy for?

1. Movement e.g. movement of cilia and flagella,
   muscle contraction

2. Maintaining a constant body temperature to
provide optimum internal environment for enzymes
to function
3. Active transport to move molecules and ions
across the cell surface membrane against a
concentration gradient
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4. Anabolic processes e.g. synthesis of
polysaccharides from sugars and proteins from
amino acids
5. Bioluminescence converting chemical energy
into light e.g. glow worms
6. Secretion the packaging and transport of
secretory products into vesicles in cells e.g. in
the pancreas
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Respiration

• Energy is released in respiration
• A series of oxidation reactions taking place
  inside living cells which releases energy to
  drive the metabolic activities that take place in
  cells

Aerobic respiration takes place in the presence
of oxygen
Anaerobic respiration takes place in absence of
oxygen
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The role of ATP (adenosine triphosphate)

• The short term energy store of the cell
• Often called the energy currency of the cell
  because it picks up energy from food in
  respiration and passes it on to power cell
  processes.

ATP made up of Adenine (a base) Ribose (a
pentose sugar) 3 phosphate groups
Draw the structure of ATP on page 286
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How ATP releases energy

• The 3 phosphate groups are joined together by 2
  high energy bonds
• ATP can be hydrolysed to break a bond which
  releases a large amount of energy
• Hydrolysis of ATP to ADP (adenosine diphosphate)
  is catalysed by the enzyme ATPase

(ATPase) ATP ADP
Pi 30 KJ mol-1 (H2O)
Draw the hydrolysis of ATP on page 286
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• The 2nd phosphate group can also be removed by
  breaking another high energy bond.
• The hydrolysis of ADP to AMP (adenosine
  monophosphate) releases a similar amount of energy

(ATPase) ADP AMP Pi 30 KJ
mol-1 (H2O)
AMP and ADP can be converted back to ATP by the
addition of phosphate molecules
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The production of ATP by phosphorylation

• Adding phosphate molecules to ADP and AMP to
  produce ATP

Phosphorylation is an endergonic reaction
energy is used Hydrolysis of ATP is exergonic -
energy is released
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Advantages of ATP

• Instant source of energy in the cell

• Releases energy in small amounts as needed

• It is mobile and transports chemical energy to
  where it is needed IN the cell

• Universal energy carrier and can be used in many
  different chemical reactions

Answer sample past paper question on sheet
10
Aerobic respiration to release energy 4 main
stages
CO2
glucose
Krebs cycle
Glycolysis
FADH2
NADH
pyruvate
Electron transport chain
Link reaction
Hydrogen atoms
Acetyl coenzyme A
oxygen
water
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Glycolysis -the splitting of glucose
1. Glucose (6C) phosphorylated to Glucose
phoshate (6C)
The phosphate comes from ATP
3. Glucose phosphate (6C) phosphorylated to
fructose biphosphate (6C)
4. Fructose biphosphate (6C) is split into two
molecules of glycerate 3 phosphate
6. H is removed and transferred to the hydrogen
acceptor NAD (nicotinamide adenine dinucleotide)
5. Each Glycerate 3 phosphate (3C) is converted
to pyruvate (3C)
7. 2 x 2 ATP produced
Draw glycolysis reaction on page 287
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Glycolysis in detail

• Takes place in cytoplasm of cells

• Does not need oxygen first stage of aerobic
  respiration and only stage of anaerobic
  respiration

• Although glycolysis yields energy it does need an
  input of energy to get the reaction started

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Glycolysis overview

• Glycolysis produces from 1 molecule of glucose
• 2 molecules of ATP in total (4 ATP are produced
  but 2 are used at the start)
• 2 molecules of NADH2 (reduced NAD)
• 2 molecules of pyruvate to enter the link
  reaction

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The link reaction in mitochondria in presence of
oxygen
Pyruvate (3C)
2. Pyruvate dehydrogenated hydrogen removed
1. Pyruvate decarboxylated - CO2 removed
NAD
CO2
NADH H
Acetate (2C)
3. Acetate (2C) combines with coenzyme A
Coenzyme A
Acetyl coenzyme A
Dont forget this happens TWICE as 2 molecules of
pyruvate are formed from each glucose molecule
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Krebs cyclein matrix of mitochondria
Draw Krebs cycle on page 288