The TCA cycle Dr. S. Picksley H17, ext 5935. Petrol or diesel (hydrocarbons) + oxygen (O 2 ) + spark Energy + C0 2 + H 2 0 Combustion releases energy.

Slides:



Advertisements
Similar presentations
Fig. 7-2a, p.108. Fig. 7-2b, p.108 a All carbohydrate breakdown pathways start in the cytoplasm, with glycolysis. b Fermentation pathways are completed.
Advertisements

Chapter 13 How Cells Obtain Energy from Food. From Chapter 3 (Energy) Sun is source of all energy Through photosynthesis/dark reactions, plants convert.
Chapter 9: Cellular Respiration
Unit 7 – ENERGY PROCESSING IN LIVING ORGANISMS
4.2 Link Reaction and Krebs Cycle
Krebs Cycle state that the Krebs cycle takes place in the mitochondrial matrix; outline the Krebs cycle, with reference to the formation of citrate from.
Cellular Respiration Chapter 9.
Lesson 7: Harvesting of Energy “Cellular Respiration”
Cell Respiration Chapter 5. Cellular Respiration Release of energy in biomolecules (food) and use of that energy to generate ATP ENERGY (food) + ADP +
Metabolism and Energy Production
Carbohydrate Metabolism Turning Sugar into Energy.
Biol 105 Lecture 6 Read Chapter 3 (pages 63 – 69)
Cellular Respiration.
Cellular Respiration 7.3 Aerobic Respiration.
Cellular Respiration Chapter 08. Cellular Respiration 2OutlineGlycolysis Transition Reaction Citric Acid Cycle Electron Transport System Fermentation.
Chapter 5 Bacterial MetabolismBacterial Metabolism Metabolism is sum total of all biochemical processes taking place in an organism. Two categories –Anabolism.
TCA Cycle.
Key Area 1: Cellular respiration Glycolysis, Citric Acid Cycle, Electron Transport Chain Unit 2: Metabolism and Survival.
Cellular Respiration AP Biology Photosynthesis….then Photosynthesis captures the sun’s energy and converts it to glucose Cellular respiration is the.
1 Respiration Cellular respiration is a series of reactions that: -are oxidations – loss of electrons -are also dehydrogenations – lost electrons are accompanied.
 Organisms must take in energy from outside sources.  Energy is incorporated into organic molecules such as glucose in the process of photosynthesis.
Cellular Respiration 3.7 & 8.1. Redox = oxidation/reduction reaction  Oxidation- loss of electrons - oxidized when it loses one or more e -  Reduction.
CITRIC ACID CYCLE- discovered by Sir Hans Krebs in He was awarded Nobel Prize in Medicine Sir Hans KrebsSir Hans Krebs 1. The citric acid cycle (also.
The Krebs Cycle Biology 11 Advanced
Respiration. Learning Outcomes Discuss the role and production of ATP with particular reference to the transfer of chemical energy, the role of ATP in.
Cellular Respiration.
Glycolysis 1. From glucose to pyruvate; step reactions; 3
M. Saadatian Cellular respiration 1.
Cellular Respiration. Energy Flow photosynthesis –carried out by plants uses energy from sunlight converts into glucose & oxygen used in cellular respiration.
How Do Organisms Supply Themselves With Energy? Key Questions How do organisms supply themselves with energy? How do organisms extract energy from glucose?
Chapter 7: Cellular Pathways That Harvest Chemical Energy Cellular Pathways That Harvest Chemical Energy Obtaining Energy and Electrons from GlucoseObtaining.
Oxidative Decarboxylation of Pyruvate
The Krebs Cycle 9-2.  At the end of glycolysis, about 90% of the chemical energy available in glucose is still unused  To extract the rest, cells need.
Cellular Respiration Chapter 08. Cellular Respiration 2OutlineGlycolysis Transition Reaction Citric Acid Cycle Electron Transport System Fermentation.
Respiration Things to cover: Structure and the mitochondria
Cellular Respiration Obtain energy from the degradation of sugars Uses Oxygen and produces CO 2 Many steps take place in the mitochondria of cells Complementary.
After pyruvate is oxidized, the citric acid cycle completes the energy-yielding oxidation of organic molecules. Chapter 9, Section 3.
9.2 The Process of Cellular Respiration
CELLULAR RESPIRATION (The process of converting glucose into ATP)
Cellular Respiration Chapter 8.
Aerobic Respiration Section 9:2. Overview Krebs Cycle: In the presence of O2, Pyruvic Acid oxidizes, the reduction of NAD + to NADH, and FAD to FADH,
Glucose + Oxygen  Carbon Dioxide + Water (+38 ATP) CELLULAR RESPIRATION VIDEO: CRASHCOURSE RESPIRATION SUMMARY.
Chapter 9 Cellular respiration: Harvesting Chemical energy
The Citric Acid Cycle.
Aerobic Cellular Respiration
Cellular Respiration Campbell Ch. 9. Life Requires Energy Energy flows into an ecosystem as sunlight and leaves as heat Photosynthesis Cells use chemical.
Higher Biology Unit Cellular Respiration. Respiration Respiration is a catabolic pathway that is controlled by different enzymes. It releases energy.
4.2 Link Reaction and Krebs Cycle
School of Sciences, Lautoka Campus BIO509 Lecture 27: Respiration
Glycolysis and Cellular Respiration
Aerobic Metabolism: The Citric Acid Cycle
Biology, 9th ed,Sylvia Mader
Respiration.
Glycolysis, Link Reaction, and Krebs
The test has been postponed until Wednesday, November 1st
Cellular Respiration: The Details
The Krebs Cycle Biology 11 Advanced
3.5 Energy transfer in and between organisms Respiration
Cellular Metabolism Chapter 4
Cellular Respiration.
Breakdown of glucose to carbon dioxide and water
Chapter 18 Metabolic Pathways and Energy Production
Cellular Respiration Part III:
AP Biology Ch. 9 Cellular Respiration
Aerobic Respiration Section 9:2.
Aerobic Respiration: Overview
Energy in food is stored as carbohydrates (such as glucose), proteins & fats. Before that energy can be used by cells, it must be released and transferred.
4.2 Link Reaction and Krebs Cycle
Presentation transcript:

The TCA cycle Dr. S. Picksley H17, ext 5935

Petrol or diesel (hydrocarbons) + oxygen (O 2 ) + spark Energy + C0 2 + H 2 0 Combustion releases energy very fast & explosively. We need to release energy from food slowly and discretely, This is done by the TCA cycle and oxidative phosphorylation. THE PROBLEM

Learning objectives 1. Understand how complex foodstuffs (carbohydrate, fat & protein) are converted into energy (ATP). 2. The conversion of food to ATP is a two step process, in which catabolites (breakdown products of carbohydrate, fat & protein) are channelled into the TCA cycle and oxidised to produce C02 and energy rich (reduced) molecules of NADH and FADH2 (nucleoside cofactors) and GTP.

Learning objectives cont. 3. NADH and FADH2 then transfer their energy to ATP by electron transport / oxidative phosphorylation (the subject of the next lecture!). 4. In effect these two processes represent RESPIRATION - the process by which aerobic cells obtain energy from the oxidation of food by oxygen. 5. The TCA cycle is also a starting point for some biosynthetic pathways (anabolic metabolism, - from simple to complex molecules).

Recommended texts ‘Instant notes in biochemistry’ Section L1 The Citric acid cycle. By Hames et al. p ‘Biochemistry’ by Campbell. p

Overview We derive all our cellular energy from carbohydrates, fat and proteins. Carbohydrates, fat and proteins, are catabolised (broken down) to a common intermediate, acetyl CoA, that enters the TCA cycle. CoA stands for a co-enzyme A (an essential enzyme activator). By a series of enzyme catalysed reactions the two carbon atoms of acetyl CoA is oxidised (loses electrons) to C02 to produce GTP (from GDP) and four pairs of electrons. These electrons are transferred to nucleotide derived coenzymes, NAD + and FAD, which finally transfer them to O 2 (oxygen).

Overview cont. Energy is produced and trapped as ATP by oxidative phosphorylation. Energy is also produced during the TCA cycle in the form of GTP (which is formally equivalent to ATP). Energy use in man At rest we will consume half our body weight in ATP per day! Of course we cannot store this amount of ATP. As we consume energy, ATP --> ADP + Pi, we replace it by oxidising food molecules, and regenerating ATP molecules. The production of ATP is initially carried out by enzymes of the TCA pathway and finally by an electron transport chain.

The TCA or Citric acid or Krebs Cycle Its called a cycle because the acetyl CoA reacts with a metabolite (oxaloacetate), that is regenerated by a series of enzyme catalysed reactions. Oxaloacetate + acetyl Coa > citrate Hence the alternative name, the Citric Acid Cycle. Citrate has three COO - groups, TriCarboxylic Acid. The cycle takes place in the mitochodria in all mammalian cells.

TCA cycle Location: occurs in the mitochondria of eukaryotic cells and in the cytosol of bacteria. Glycolysis Glucose ---> Pyruvate > Acetyl CoA Fats, Proteins > Acetyl CoA Acetyl CoA is the form in which fuel molecules enter the cycle. This cycle has eight well-characterised stages. We will only consider an overview of the cycle.

TCA cycle Acetyl CoA (C2) + oxaloacetate (C4) --> Citric acid (C6) Oxaloacetate (C4) + 2CO 2 And then the cycle begins again. 2 carbon atoms enter and 2 leave. Yields per cycle: 1 GTP, 3NADH, 1FADH2, CoA + 2CO 2

In the text books it will describe the TCA cycle as follows: AcetylCoA Citrate Isocitrate A-ketoglutarate Succinyl CoA Succinate Fumarate Malateoxaloacetate THIS LEVEL OF DETAIL IS NOT REQUIRED. THE AIM IS TO UNDERSTAND THE PRINCIPLES.

TCA cycle key points Acetyl CoA + oxaloacetate -----> Citric acid 2 Carbons+ 4 Carbons 6 Carbons 2 CO 2 Yields: 1 GTP, 3 NADH, 1 FADH2, CoA + 2CO 2 Acetyl CoA is oxidised to CO 2 This does not involve oxygen

Oxidation of acetyl CoA Acetyl CoA is oxidised to CO 2 by the donation of electrons (e-) along with the hydrogen (H+) or hydride (H-)ion. H atom = H+ + e- (electron) Hydrogen ion or proton is H+ Hydride ion is H-, H- = H+ + 2e- Oxidation = loss of electrons. Reduction = gain of electrons. Oxidation and reduction occur side by side, as electrons are not created or destroyed

Electrons are donated to NAD + or FAD NAD is nicotinamide adenine di-nucleotide. It is a co-enzyme, i.e. a chemical that is essential for enzyme activity but is easily dissociated from the protein with the loss of activity. NAD + + 2H + + 2e - = NADH + H + (oxidised form) (reduced form) FAD is flavin adenine di-nucleotide. It is a prosthetic group, i.e. a chemical that is essential for activity and that is physically linked to an enzyme. FAD + 2 H + + 2e - = FADH 2 (oxidised form) (reduced form)

Oxidised and reduced forms of NAD + and FAD

The TCA reaction Acetyl CoA + 3NAD + + 1FAD + GDP + Pi + 2H 2 0 CoA + 2CO 2 + 3NADH + 3H + + 1FADH 2 + GTP. One complete cycle yields in energy terms: 1 GTP + 3NADH + 1FADH 2. (=ATP) GTP is a nucleotide and an energy source just like ATP and is equivalent to ATP. The production of GTP during the TCA cycle is referred to as substrate level phosphorylation, i.e. it is directly produced from GDP + Pi, without an intermediate.

NADH & FADH 2 are energy-rich carrier molecules NADH and FADH2 are energy-rich molecules, which transfer their energy to ATP molecules by an indirect route of transfering electrons via the electron transport chain to oxygen (oxidative phosphorylation). 1 molecule of NADH > 2.5 molecules of ATP (3 molecules of ATP in older textbooks) 1 molecule of FADH > 1.5 molecules of ATP (2 molecules of ATP in older textbooks)

Regulation of the TCA cycle by respiratory control The flow of intermediates through the TCA cycle is regulated by the demand for ATP. If energy demand is high as indicated by low [ATP]:[ADP] and [NADH]:[NAD + ] there will be a high flow of intermediates through the TCA cycle to produce the required energy.

TCA cycle as a source of biosynthetic precursors The TCA cycle in addition to generating energy rich molecules also has a role in generating important precursors for: 1.Synthesis of some amino acids 2.Synthesis of glucose 3.Synthesis of proteins 4.Synthesis of nucleic acids 5.Syntheis of fats 6.Synthesis of pophyrins (used to make haem for haemoglobin).