Energy Transfer In And Between Organisms: - Oxidative Phosphorylation

Oxidative Phosphorylation

Oxidaive phosphorylation and mitochondria 

Mitochondria is the site for oxidative phosphorylation // occur in great numbers in metabolic active cells - muscles, live and epithelial cells. 

Electron transfer chain and the synthesis of ATP

Electrons transfers down a series of electron carrier molecules // forms electron transfer chain.

- Hydrogen from glycolysis & krebs cycle combine with coenzyme NAD & FAD.
- Reduced NAD & FAD give electron from hydrogen atom they gained into the electron transfer chain
- Electrons pass through series of oxidation-reduction reactions // as electrons pass releasing energy // actively transport protons into inter-membranal space.
-  Before they are transported back into the inter-mitochodrial matrix by ATP synthase channels, protons accumulate in the inter-membranal space.
- End of the chain // protons and electrons combine with oxygen to form water // oxygen is the final acceptor of electrons in the electron transfer chain.



Releasing energy in stages





Alternative respiratory susbstrates:

Sugars and lipids and proteins can be oxidised // used a respiratory substrate without being converted into carbohydrates.

Respiration of lipids

Lipids are hydrolysed to glycerol and fatty acids.
Glycerol is phosphorylation and converted into triose phosphate // enters glycolysis pathway into 2-carbon fragments // converted to acetyl coenzyme A // enters the Kreb Cycle.
Oxidation of lipids produces 2-carbon fragment of carbohydrates and many hydrogen atoms.

Hydrogen atoms produce ATP during oxidative phosphorylation // lipids release more than double the energy for the same mass of carbohydrates.

Respiration of protein

Protein source of energy // hydrolysed to amino acids // amino group removed (deamination)
Enter the respiratory pathway at different points // 3-carbon compounds converted into pyruvate // 4- and 5-carbon compounds are converted to intermediates in the Krebs cycle.

Energy Transfer In And Between Organisms: - Link Reaction And Krebs Cycle.

- Link reaction and Kreb cycle - 

Link reaction: 

Pyruvate is oxidised to acetate // pyruvate loses a CO₂ and (X2) H // H is accepted by NAD to reduced NAD later used to produce ATP. 

2-Carbon acetate combines coenzyme A (CoA) = acetylcoenzyme A 

Krebs cycle

2-Carbon acetylcoenzyme A from link reaction combined with the 4-carbon molecule to produce a 6-carbon molecule. 

6-Carbon molecule loses carbon dioxide and hydrogen to give 4-Carbon molecules and single molecule of ATP produced as result of substrate-level phosphorylation 

4-Carbon molecule combines with new molecule of acetylcoenzyme A // cycle starts again. 

Pyruvate, link reaction and krebs cycle produces 

- Reduced coenzymes NAD and FAD // by oxidative phosphorylation potential to provide energy to produce ATP 

- 1 ATP molecule 

- 3 CO₂ molecules

2 Pyruvate molecules produced for each original glucose molecule. 

Coenzymes = molecules that enzymes require to function, includes:

NAD - important throughout repsiration 

FAD - important in the Kreb cycle 

NADP - important in photosynthesis

Respiration NAD important carrier // works with dehydrogenase enzymes catalyse removal hydrogen atoms from substrates transfer them to the other molecules involved in oxidative phosphorylation. 

Kreb cycle is important for: 

Breaking down pyruvate into CO₂ 

Producing hydrogen atoms carried by NAD to electron transfer chain prodivde energy for oxidative phosphorylation = ATP produced 

Regenerates 4 carbon molecule combines with acetylcoenzyme A 

Source of intermediate compounds used by cells - fatty acids, amino acids and chlorophyll. 

Energy Transfer In And Between Organisms: - Glycolysis

- Glycolysis -

2 Different forms of cellular respiration =

Aerobic respiration = requires O₂ produces CO₂, H₂O, ATP 

Anaerobic respiration = takes place absence of O₂ produces lactate or ethanol and CO₂ // little ATP. 

Aerobic respiration summeriesed into 4 stages 

1. Glycolysis 
2. Link reaction 
3. Kreb cycle 
4. Oxidative phosphorylation 

Glycolysis 

1. Phosphorylation of glucose to glucose phosphate = glucose is made reactive with the addition of 2 phosphate molecules (phosphorylation) // Phosphate molecules come from hydrolysis of ATP (X2) ⇒ ADP. // Energy provided to activate glucose lowering activation energy for enzyme controlled reactions 

2. Phosphorylated glucose is split = Glucose is split into 3-carbon triose phosphate (X2) 

3. Triose phosphate is oxidised = H₂ removed from triose phosphate (X2) transformed into hydrogen-carrier molecule NAD to form reduced NAD

4. Production of ATP = enzyme controlled reaction converts triose phosphate into 3-carbon molecule Pyruvate // (X2) molecules of ATP are regenerated from ADP.

From ONE molecule of glucose =

2 ATP molecules // was 4 but 2 was used in initial phosphorylation of glucose - net increase of 2 molecules. 

2 reduced NAD molecules 

2 Pyruvate molecules 

Energy Transfer In And Between Organisms: - Light Independent Reaction

- Light Independent Reaction -

The Calvin Cycle - 

The products of the light dependent reaction is ATP and reduced NADP // both used to reduce glycerate-3-phosphate. 

This would have occur with or without light. 

1. The CO₂ diffuses into the leaf through the stomata // dissolves in water around the walls of mesophyll cells // diffuses through the cytoplasm and chloroplast membrane into the stomata of chloroplast. 

2. In stroma CO₂ reacts with 5 carbon compound   // catalysed by enzyme ribulous bisphosphate carboxylase (Rubisco)

3. Reaction CO₂ + RuBP = 2X 3-carbon glycerate 3-phosphate.

4. Reduced NADP from light dependent reaction, reduces glycerate 3-phosphate ⇒ triose phosphate using energy supplied by ATP. 

5. NADP is re-formed // goes back into the light dependent reaction = gaining protons. 

6. Triose phosphate converted into organic substances // starch, cellulose, lipids, glucose, amino acids, and nucleotides. 

7. Most triose phophate is used to generate ribulose bisphosphate // ATP is used from Light Dependent Reaction . 

Site of the light-independent reaction -

Chloroplast is adapted in carrying out the light independent reaction of photosynthesis. 

The stroma contains a fluid with all the enzymes needed for the light independent reaction. Stromal fluid is membrane-bound in the chloroplast. 

The stroma fluid surrounds the grana // products of light dependent stage in grana can diffuse into stroma 

Contains DNA and ribosomes // can quickly and easily manufacture some of the proteins involved in the light-independent reaction. 

Energy Transfer In And Between Organisms: - Light Dependent Reaction

- Light Dependent Reaction -

Oxidation and Reduction 

Oxidation is when the substance gains oxygen or loses hydrogen. 

Reduction is when the substance loses oxygen or gains hydrogen.

Oxidation results in energy being given out, whearas reduction results in it being taken in. 

Making of a ATP

Photoionisation is a result of the chlorophyll molecule becoming ionised. 

The electrons leave the chlorophyll are taken up by a molecule electron carrier // the chlorophyll is oxidised // electron carrier is reduced. 

Electrons are passed along a series of oxidation-reduction chain reactions. // A transfer chain that is located in membrane of the thylakoids. 

With each carrier the energy level is lowered in the electron, the energy released is used to combine the inorganic phosphate and the ADP molecule to create ATP. 

Chemiosmotic theory

This explains the ATP production 

1.  Proton pumps // protein carrier are used to pump the protons (H+) from the stroma in the thylakoid membrane. 
2. Electrons released from photolysis drives the process as it produces protons // further increase of concentration in the thylakoid space.
3. A concentration gradient is maintained // higher concentration = in the thylakoid space, lower concentration = in the stroma 
4. Protons can only cross the thylakoid membrane through ATP synthesised channel proteins. 
5. The channels for small granules on the membrane surface = stalked granules. 
6. Protons pass through these ATP synthase channels they can cause changes to the structure of the enzyme // catalyse combination of ADP with inorganic phosphate to form ATP. 

Photolysis of water 

2H₂O → 4H+ + 4e⁻  + O² 

Protons are passed out of the thylakoid space through ATP synthase channels taken up by electron carrier = NADP.
On taking up the protons the NADP reduced // the reduced NADP = main product of the light dependent stage and enters the light independent reaction.

Reduced NADP is important because it is further potential source of chemical energy to the plant.
Oxygen is a by-product from the photolysis of water is either used in respiration or diffuses out of the stomata as waste product of photosynthesis.

Site of the light-dependent reaction: 

Chloroplasts are structurally adapted to their functions of capturing sunlight. 

Thylakoid membranes have a large surface area for attachment of chlorophyll, electron carriers and enzymes carry out light-dependent reaction. 

Network of proteins in grana holds the chlorophyll // precise to allows maximum absorption. 

Granal membranes have ATP synthase channels which catalyse the production of ATP // also selectively permeable which allows establishment of proton gradient. 

The chloroplast contain both DNA and ribosomes can quickly and manufacture some of the proteins involved in light-dependent reactions.  

Energy Transfer In And Between Organisms: - Photosynthesis

- Photosynthesis - 

Site of Photosynthesis. 

Within eukaryotic plants this is the main site of photosynthesis // Within the chloroplast of cellular organelles. 

Structure of the leaf.

1. Large surface area = more sunlight is absorbed
2. Arrangement of leaves = avoids overlapping // leaves do not overshadow each other. 
3. Thin // diffusion distance is kept short = light absorbed within few micrometers 
4. Transparent cuticle and epidermis let light through to photosynthetic mesophyll cells 
5. Long, narrow upper mesophyll cells packed with chloroplast = collecting sunlight. 
6. Numerous stomata = gas exchnage // short diffusion pathway from the mesophyll cells 
7. Stomata open and closes = result of light intensity 
8. Many air spaces in lower mesophyll layer to allow rapid diffusion in the gas phase of carbon dioxide and oxygen. 
9. Network of xylem = brings water to leaf cells // Phloem = carries away the sugar (product of photosynthesis) 

There are 3 stages in photosynthesis. 

- Capturing the light energy 

- Light-dependent reaction 

- Light Independent reaction 

Structure of chloroplast and its role.

The grana = 100 discs-like structure = thylakoids // light dependent stage takes place here. 

The stroma = fluid filled matrix // light independent stage occurs here // number of other structures, for example, starch grains.