Chapter 13: Energy and Respiration Flashcards
Structure of ATP
Adenosine triphosphate:
1. Adenine: nitrogenous base
2. Ribose (pentose sugar)
3. Three phosphate groups
Characteristics of ATP
-Small
-Water-soluble (Easily transported around the cell)
-Readily hydrolysed / lose phosphate to release energy
-Small packets of energy released at one time (Reduced energy wastage)
-ATP can be synthesised and broken down quickly (High turnover rate)
-ATP is a relatively stable molecule in the range of
pH that normally occurs in cells; it does not break
down unless a catalyst such as the enzyme ATPase
is present.
ATP energy release
Removal of 1st phosphate group from ATP → ADP
→ 30.5 kJmol-1 energy released
- Removal of 2nd phosphate group from ADP → AMP
→ 30.5 kJmol-1 energy released - Removal of last phosphate group from AMP → Adenosine
→ 14.2 kJmol-1 energy released
What is respiration?
Process where organic molecules (such as glucose, amino acids, glycerol, fatty acids) are broken down in a series of stages to release energy, which is used to synthesise ATP
4 stages in aerobic respiration of glucose and their locations
1) Glycolysis: Cytoplasm
2) Link Reaction: Mitochondrial matrix:
3) Krebs Cycle: Mitochondrial matrix
4) Oxidative Phosphorylation: Inner mitochondrial membrane / cristae
Why use small, multiple steps in aerobic respiration?
1️⃣ Controlled Energy Release ⚡
- If all the energy in glucose was released at once, it’d be like a huge explosion—🔥💥—too much for the cell to handle!
- Small steps release energy gradually, so cells can efficiently capture it as ATP instead of losing it as heat.
2️⃣ Efficient ATP Production 🏆
- Stepwise reactions allow energy to be transferred to ATP in a controlled way (via oxidative phosphorylation).
- This ensures maximum ATP yield (around 38 ATP per glucose), rather than wasting energy.
3️⃣ Prevents Cell Damage 🚫
- Sudden, massive energy release could overheat and damage proteins & membranes.
- Small steps prevent thermal damage to the cell.
4️⃣ Use of Electron Carriers 🔄
- NADH & FADH₂ pick up electrons at different steps and transport them to the electron transport chain (ETC) for ATP production.
- This wouldn’t work in a single-step reaction!
5️⃣ Allows Metabolic Control 🧠
- Each step is enzyme-controlled, so the cell can regulate respiration depending on energy needs.
- For example, ATP can inhibit phosphofructokinase (in glycolysis) when energy is abundant.
6️⃣ Intermediate Molecules are Useful 💡
- Some intermediates (e.g., pyruvate, acetyl-CoA) are used in other pathways like amino acid or lipid metabolism.
Why doesn’t aerobic respiration of glucose happen easily?
Because glucose is quite a stable substance
→ It requires a high activation energy for reaction to take place
So how do organisms overcome this?
a) Usage of enzymes to lower activation energy
b) Raising energy level of glucose by phosphorylation (More reactive)
Glycolysis steps
1) Glucose (6C) is phosphorylated by 2 ATP
* Form hexose / fructose bisphosphate (6C)
* This raises chemical potential energy of glucose and provides activation energy for split
2) Fructose bisphosphate breaks down to 2 triose phosphate (3C)
3) 2 hydrogen atoms are removed (triose phosphate to intermediate)
* 2 reduced NAD formed
* This is a dehydrogenation / oxidation reaction
4) 4 ATP produced (2 from trios phosphate to intermediates, 2 from intermediates to pyruvate)
* 4 ATP – 2 ATP = net gain of 2 ATP
* Chemical potential energy is released from
intermediate steps
5) 2 pyruvate (3C) produced
What type of phosphorylation occurs in glycolysis?
Substrate-level phosphorylation
Hydrogen Carrier Molecules
- NAD – nicotinamide adenine
dinucleotide
(used in respiration) - NADP – nicotinamide adenine
dinucleotide phosphate
(used in photosynthesis) - FAD – flavin adenine dinucleotide
(used in respiration)
NAD structure
Two linked nucleotides
* Both have ribose sugar and a phosphate group each
* 1 has adenine base, the other nicotinamide ring
* Nicotinamide ring – accepts H
NADP structure
Similar to NAD
* But has a phosphate group instead of H on
carbon 2 on ribose ring with adenine
FAD structure
Two linked nucleotides
* One nucleotide with phosphate, ribose and adenine
* Another nucleotide with phosphate, ribitol and flavin
Link reaction steps
-when there is enough oxygen in matrix, pyruvate moves from cytoplasm into matrix via active transport
-2 pyruvate molecules undergo decarboxylation and dehydrogenation
-and combines with coenzyme A to form 2 acetyl coA (2C)
-2 CO2 waste gas
-2NADH produced by dehydrogenation
Coenzyme A structure
Complex molecule
* Made of a nucleoside (adenine + ribose) and
a vitamin (pantothenic acid)
Krebs Cycle steps
Enzyme controlled
1) Acetyl coenzyme A (2C) combines with oxaloacetate (4C) To form citrate (6C). CoA removed and can be used again in Link Reaction
2) Citrate (6C) goes through series of dehydrogenation and decarboxylation.
3) Oxaloacetate (4C) regenerated. Can combine with another acetyl CoA.
Kreb cycle continues
4) End products of two rounds of Krebs cycle are-
6 NADH
2 FADH2
4 CO2 → waste gas, released
2 ATP
Oxaloacetate (4C) → regenerated twice
Oxidative Phosphorylation steps
- Hydrogen atoms are removed from 10 NADH and 2 FADH₂ (Catalysed by dehydrogenase enzymes) and split into protons and electrons, at the inner mitochondrial membrane in ETC.
-Electron carriers are associated with 4 types of membrane proteins
→ forms a functional unit called a respiratory complex - Electrons pass through the electron transport chain in a series of redox reactions, releasing energy .
- Energy is used to pump protons from the mitochondrial matrix into the intermembrane space, creating a proton gradient. (inner membrane is impermeable to protons, so proton pumps are used)
- Protons diffuse back into the matrix through ATP synthase by facilitated diffusion via chemiosmosis
- The movement of protons through ATP synthase provides energy for the phosphorylation of ADP to ATP.
-Movement of 3 H+ ions back
into matrix = 1 ATP molecule - Oxygen acts as the final electron acceptor, combining with electrons and protons to form water.
-O2 + 4H+ + 4e- → 2 H2O
So previous electron carrier in ETC can be reduced again
-Ensures electrons can keep flowing along ETC
Oxidative phosphorylation products
1 NADH → 3 ATP; 1 FADH2 → 2 ATP
* But bcs some energy may be needed to transport ADP and Pi into
mitochondria and new ATP into cytoplasm * So on average: 1 NADH → 2.5 ATP; 1 FADH2 → 1.5 ATP
Final products per molecule of glucose:
* 102.5 + 21.5 = 28 ATP
* Water
Ways of ATP synthesis in respiration
Substrate-level phosphorylation
Oxidative phosphorylation
Substrate-level phosphorylation
-During glycolysis at cytoplasm → 2 ATP
* During Krebs cycle at matrix → 2 ATP
-4 ATP produced by substrate-level phosphorylation in total
-Transfer of phosphate group from one molecule to another
-Chemical potential energy released
Oxidative phosphorylation
-At inner mitochondrial membrane / cristae
-Requires proton/electrochemical gradient, ATP synthase, ETC
-Electric potential energy released by chemiosmosis is used by ATP
synthase to catalyse formation of ATP
-28 ATP produced by oxidative phosphorylation in total
-Also happens in the chloroplast during photosynthesis
Mitochondria
Structure and Function
Mitochondria are double-membrane organelles known as the powerhouses of the cell because they produce ATP (adenosine triphosphate) through aerobic respiration.
* Typically rod-shaped
* Able to change shape and move in the cell
* 0.5 - 1.0 μm in diameter
* Double membrane
* No. of mitochondria in a cell, no. of cristae and length of crista in mitochondrion – depends on cell
Outer Membrane
-Smooth and permeable to small molecules and ions.
-More permeable to small molecules than inner membrane
-Contains porins (protein channels) that allow the passage of molecules.
e.g to transport pyruvate into the mitochondria for link reaction and Krebs cycle
