C1.2 CELL RESPIRATION

Outline the structure, and special properties of ATP

ATP is the molecule that distributes energy within cells – energy source

STRUCTURE:
Adenosine triphosphate consists of a nucleotide:
- sugar (ribose)
- base (adenine)
- phosphate (3 groups)

PROPERTIES:
1. has three phosphates linked by covalent bonds
2. ATP can be interconverted (hydrolysed) to ADP + Pi – the energy stored in the phosphate bond is released & used by the cell
3. ATP can be recycled in mitochondria – ADP or AMP can gain phosphates to regenerate ATP

Recall the life processes within cells that ATP supplies with energy

1. Active transport across membranes

2. Synthesis of macromolecules (anabolism)

3. Movement of the whole cell or cell components like chromosomes

Outline the transfer of energy during interconversions between ATP and ADP

1. Energy is RELEASED by HYDROLYSIS of ATP to ADP + phosphate

2. Energy is REQUIRED to SYNTHESISE ATP from ADP and Phosphate

Outline cell respiration

1. Controlled release of energy from organic compounds to produce ATP

2. Series of metabolic pathways and cycles of enzymatically controlled reaction – glycolysis, link reaction, krebs cycle, and electron transport chain

3. Breaks down a range of organic compounds, primarily glucose and fatty acids

Write down the word equation for aerobic cell respiration

C6 H12 O6 + 6O2 –> 6CO2 + 6H2O + ATP(energy)

Review the location all the processes of cell respiration (both aerobic and anaerobic)

Cytoplasm: glycolysis
Mitochondria: Krebs cycle (matrix) electron transport chain

Compare aerobic and anaerobic cell respiration in humans

AEROBIC:
1. use ALL respiratory substrates (carbohydrates, glucose, lipids, proteins)
2. Requires oxygen
3. High yield of ATP (36-38)
4. CO2 + H2O waste products
5. Occurs in cytoplasm and mitochondria

ANAEROBIC:
1. Uses carbohydrates (glucose) as respiratory substrate
2. Doesn’t require oxygen
3. Low yield of ATP (2)
4. Lactate/lactic acid as waste product
5. Occurs in cytoplasm

Outline glycolysis

1) Occurs in the cytoplasm
2) Converts glucose into pyruvate — net production of 2 pyruvate, 2 NADH/reduced NAD, and 2 ATP
3) Is a chain of 4 enzymatically controlled reactions including:

1. PHOSPHORYLATION:
   - 2 ATP is used
   - Makes substrate less stable & more reactive

2. LYSIS
   - substrate is lysed
   - substrate (fructose 1,6 biphosphate) is split into 2 G3P (triose phosphate or glyceraldehyde 3 phosphate)

3. OXIDATION
   - substrate is oxidised: 2 electrons and hydrogens are removed
   - NAD+ is reduced (2 electrons and hydrogens are GAINED) to form reduced NAD ( NADH + H+)
   - is a redox reaction

4. ATP FORMATION
   - 4 ATP is produced by substrate-level phosphorylation
   - net yield is 2 ATP (4 produced, 2 used)

Outline glycolysis in anaerobic respiration in humans

1. Pyruvate is converted to lactate

2. NADH is oxidised (loses electrons & hydrogens), and pyruvate is reduced (gains electrons & hydrogens)

3. NAD is thus regenerated

4. Lactate is produced as waste product (oxygen is required to remove it)

5. Normally low yield of ATP (2), but can also generate large amount for ATP rapidly for burst of energy – sprinting

Outline anaerobic respiration in yeast

1. YEAST, water, sugar, and flour is added to produce bread or YEAST, malt, h2o, and hops is added to produce beer

2. Yeast respires anaerobically AND aerobically – once oxygen is used up, it will respire aerobically

3. Glucose converts into 3-C pyruvate and NAD is reduced n glycolysis

4. 3-C pyruvate is decarboxylated and reduced (removal of Co2) to produce 2-C ethanol and Co2

5. NADH is oxidised to regenerate NAD

6. CO2 causes bread to rises and ethanol evaporates

Outline the link reaction

1. Occurs in matrix of mitochondria

2. Converts pyruvate to acetyal CoA – net production of 2 acetyl CoA, 2 NADH + H+

3. Decarboxylation of pyruvate (CO2 is removed)

4. Oxidation of substrate (2 electrons & hydrogens are lost)

5. Addition of coenzyme A (CoA)

Outline the krebs cycle

1) Occurs in the matrix of the mitochondria
2) Acetyl CoA enter krebs cycle – net production of 4 CO2, 6 NADH + H+, 3 FADH2, and 2 ATP (by substrate level phosphorylation)

THE PROCESS!!!
1. 2-C Acetyl CoA/acetate + 4-C oxoaloacetate -> 6-C compound

2. Oxidative decarboxylation of 6-C substrate occurs 2 times to form 4-C and 5-C molecules:
   - Substrate is oxidised (2 electrons & hydrogens are lost)
   - NAD is reduced (2 electrons & hydrogens are gained) -> reduced NAD

3. ATP is produced by substrate level phosphorylation

4. Oxidation of 4-C substrate & reduction of NAD and FAD -> oxoalocetate and reduced NAD and FAD

Describe the transfer of energy by reduced NAD to the electron transport chain

IN MITOCHONDRION’s CRISTAE/INTERMEMBRADE SPACE:

1. All reduced NAD (NADH + H+) transfers electrons, hydrogen, and energy to the electron transport chain

2. NAD+ is reduced to form NAD or NADH + H+ ( gains 2 electrons/energy and 2 hydrogens)

3. FAD is reduced – gains 2 electrons and hydrogens to form FADH2

Outline the generation of a proton gradient by the flow of electrons

1. Electrons are passed from electron carrier to electron carrier

2. Energy is released from the movement of electrons

3. The energy is coupled to the pumping of protons from the matrix to the inter membrane space

4. The proton gradient is formed from the flow of electrons

Outline chemiosmosis

1. Electron transport chain performs chemiosmosis

2. Generates ATP

3. is the coupling of movement of electrons – forms proton gradient to the synthesis of ATP

4. Energy is released from the movement of electrons along the transport chain -> used to pump protons from matrix to intermenbrane space

5. Forms proton gradient

6. Protons diffuse through ATP synthase from intermembrane space back to matrix

7. ATP production is coupled to the flow of protons through oxidative phosphorylation

Describe the role of oxygen as the terminal electron acceptor

1. Oxygen is the final electron acceptor

2. Is highly electronegative -> electrons are attracted to oxygen

3. 1/2 O2 joins with 2H+ to form water

4. Maintains hydrogen ion concentration gradient and prevents the buildup of lactic acid

5. Allows the movement of electrons along the ETC, regeneration of NAD, and maximum release of energy from glucose

Compare lipid and carbohydrates as respiratory substrates

LIPIDS:
1. Transfer/release 2x the energy as compared to carbohydrates – less oxygen
2. Difficult to digest
4. Transported as lipoproteins (HDL/LDL)
3. Not soluble, doesn’t affect osmotic pressure
4. Found in seeds in plants and adipose tissue in animals
5. Enter the respiratory pathway in the Krebs cycle

CARBOHYDRATES:
1. Transfer/release half the amount of energy – more oxygen
2. Easier to digest
3. Transported by its dissolved
4. Found in starch in plants and glycogen (triglycerides) in animals
5. Enter respiratory pathway in glycolysis

Outline the variables affecting the rate of cell respiration

1. Temperatures - high temps increase metabolism & enzyme activity → increases rate

2. pH - too acidic/alkaline -> lowers rate

3. Oxygen supply - less oxygen -> lowers rate

4. Substrate supply - type & concentration of substrate -> affects rate

5. Size of organism - smaller organisms lose heat faster -> higher rate

6. Metabolic rate of cell: muscle cells require more energy -> higher rate

Homeotherms: maintain central body temperature internally

Poikilotherms: do not regulate body temperature internally – regulate it behaviourly

Outline the overall process of the electron transport chain

IN CRISTAE/INTERMEMBRANE SPACE:

1. Reduced NAD/FAD transfer electrons, energy and hydrogen to the electron transport chain

2. Generation of proton gradient due to movement of electrons

3. Energy is used for the pumping of protons into the intermembrane space

Outline characteristics of anaerobic respiration in humans

1. No oxygen

2. Low yield of ATP

3. Only uses glycolysis in cytoplasm to convert glucose to pyruvate (net production of 2 ATP, 2 pyruvate, and 2 NADH)