HL Bio - Molecular Bio (II) C1.2: Cell Respiration

Define cell respiration

Cell respiration is a system of metabolic pathways that produces ATP within the cell using energy released from organic compounds such as glucose, fatty acids and proteins

State the three main components of ATP and its functions

Adenosine: the back bone of the molecule; recognisable fo enzyme binding

Ribose: acts as a scaffold to link adenosine and phosphate groups

Phosphate groups: stores high energy in phosphate bonds, released when hydrolysed

Explain 3 properties of ATP that make it ideal as the cellular energy currency

1. Chemically stable at neutral pH of typical cells: so ATP does not break down and prematurely release energy

2. Small and soluble: diffuse freely through cells to move within organelles to power reactions which occur within them

3. Unable to diffuse through phospholipid bilayer of cell membrane: ATP movement can be controlled and there is no leakage out of cells

Outline 3 uses of ATP

1. Synthesising macromolecules: anabolic reactions require high amounts of energy: synthesis of DNA, RNA in transcription and proteins in translation

2. Active transport: energy is required to pump ions against concentration gradient; causes conformational change in channel proteins

3. Movement of a) cells - movement of cilia and flagella b) cell components - chromosome movement during cell division

What is formed when ATP is hydrolysed?

ADP + phosphate group (Pi)

State the factors of cell respiration

1. consumption of inputs - oxygen and glucose

2. production of CO2

3. temperature and pH (aerobic respiration)

Where does glycolysis take place?

Cytoplasm

Outline the process of glycolysis

1. 1 glucose molecule is phosphorylated using 2 ATP molecules to ensure it does not leave the cell, forming a hexose biphosphate molecule

2. Hexose biphosphate molecule becomes unstable, breaks down into 2 (3C) triose biphosphate molecules

3. Both triose biphosphate molecules are phosphorylated again, and reduces 2 NAD molecules to form 2 NADH

4. Both 3C compounds lose its phosphate groups (4 in total), forming 2 pyruvate molecules. The phosphate groups join with ADP molecules to form 4 ATP molecules.

What are the final products of glycolysis?

Net gain of 2 ATP, 2 NADH, 2 Pyruvate

Outline anaerobic respiration

Pyruvate molecules are reduced to form lactate

NADH molecules are oxidised to form NAD+ so that glycolysis can continue

CO2 is produced

Can be produced much more rapidly as there is no need to supply oxygen

Where does anaerobic respiration take place?

Cytoplasm

Where does the link reaction and Kreb's cycle occur?

Mitochondrial matrix

Outline the link reaction using 1 pyruvate molecule + its final products for one pyruvate molecule

1. 1 pyruvate molecules are decarboxylated to form 2C compounds, producing 1 CO2 molecule as waste product

2. 2C compound is oxidised to form acetyl, reducing 1 NAD molecule to form NADH in the process

3. Acetyl is joined with coenzyme A (COA) to form acetyl COA

1 pyruvate = 1 CO2 1 Acetyl COA 1 NADH

Outline the Kreb's cycle (only using 1 acetyl COA)

1. Acetyl in acetyl COA joins with (4C) oxaloacetate, forming (6C) citrate

2. Citrate is decarboxylated twice to form a 4C compound, reducing 2 NAD molecules in the process

3. 4C compound is oxidised to form oxaloacetate by reducing 1 NAD molecule and 1 FAD molecule to form FADH2, forming 1 ATP molecule from ADP in the process

1 acetyl COA = 3 NADH + 1 FADH2 + 1 ATP

1 glucose = 6 NADH + 2 FADH2 + 2 ATP

Where does oxidative phosphorylation occur?

Electron transport chain (ETC) in Inner mitochondrial membrane (IMM)

Outline oxidative phosphorylation

1. NADH and FADH2 transported to ETC in IMM

2. Electron carriers are reduced/donate their electrons to cytochromes so that processes can continue

3. Cytochromes in ETC passes electrons from one protein to another

4. Energy is used to pump protons into inner membrane space (active transport)

5. Accumulation of protons = proton gradient, protons diffuse from inner membrane space into matrix via ATP synthase, synthesising ATP - chemiosmosis

6. Oxygen as final electron acceptors to form H2O

Explain how the structure of ATP synthase allows for chemiosmosis

1. rotor that can spin on its axis - has binding sites for H+ ions, generates energy, spin and allows H+ to diffuse

2. central stalk that projects into matrix - has active sites for ADP, conformational change caused by rotor spinning allows for phosphorylation of ADP to form ATP

How much ATP is formed from 1 NADH and 1 FADH2 molecule?

1 NADH = 2.5 ATP

1 FADH2 = 1.5 ATP

Calculate the total number of ATP molecules produced in aerobic respiration

Total electron carriers formed = 10 NADH + 2 FADH2

Total ATP formed from oxidative phosphorylation = 10 x 2.5 + 2 x 1.5 = 28 ATP

Total ATP formed in aerobic respiration = 28 + 2 (from glycolysis) + 2 (Kreb) = 32 ATP

Outline the role of NAD

Nicotineamide adenine dinucleotide are coenzymes which serve as electron carriers which transport high energy electrons from organic molecules to the electron transport chain in the inner mitochondrial membrane

Outline the differences between the energy released and types of respiration of lipids and carbohydrates

Lipids: 37 kJ per gram, aerobic only

Carbs: 16 kJ per gram, both aerobic and anaerobic