bio cell respiration

energy

• ATP (adenosine triphosphate) is a molecule that functions to distribute energy within cells

• ATP is a ribonucleotide because it consists of the base adenine, a ribose sugar, and 3 phosphate

• It is used for temporary storage of energy and energy transfer between processes

characteristics of ATP

• Soluble in water so it can easily move in the cytoplasm

• Stable at pH levels close to neutral, same as in cytoplasm

• Third phosphate can be easily removed and reattached by hydrolysis and condensation reactions

• Cannot freely move across the cell membrane so movement is controlled

what is ATP needed for

• Active transport: pumping particles across the membrane against it's concentration gradient requires energy, energy used to cause reversible changes in the conformation of the pump

• Synthesizing macromolecules: anabolic reactions that link monomers into large polymers require the use of ATP

• Movement: components of cells are all the time moving (chromosomes during mitosis)

energy transfers

• ATP stores chemical energy in the covalent bonds between the phosphate groups

• When ATP is hydrolyzed, the terminal phosphate is released and ATP is converted to ADP

• Energy is required to regenerate ADP to ATP. this energy can come from

  • Cell respiration: energy produced by oxidizing sugars, lipids, or proteins

  • Photosynthesis: light energy is converted to chemical energy

  • Chemosynthesis: energy is released by oxidising inorganic molecules

• Energy transfers during the conversion of ATP into ADP are not 100% efficient so some of the energy is converted to heat

cell respiration

• The controlled release of energy from the breakdown of organic compounds to produce ATP

• In many cells, respiration uses energy and produces ATP and CO2

• The main organic compound used for this process is glucose although lipids and proteins can be used

types of cell respiration

• Cell respiration can be anaerobic (does not require oxygen) or aerobic (requires oxygen)

• aerobic respiration in humans, animals, and plants: glucose + oxygen → water + CO2

• Anaerobic respiration in yeast and fungi: glucose → ethanol + CO2

• anaerobic in humans: glucose —> lactic acid

difference between aerobic and anaerobic

	Aerobic (mitochondria)	Anaerobic (cytoplasm)
O2	present	Not present
ATP yield	More than 30	2
substrate	Carbs such as glucose, lipids including fats and oils, and amino acids after deamination	Carbs only
products	CO2 and water	Humans: lactase plants/yeast: ethanol and CO2
location	mitochondria	cytosol
Reactions	Glycolysis, link reaction, Krebs cycle, ETC	Glycolysis, fermentation

limiting factors of cell respiration

• Temp: impacts the frequency of successful enzyme-substrate collisions

• pH: changes the charge and solubility of the enzymes involved

• Glucose: is the main respiratory substrate and hence its levels will determine the rate of cell respiration (higher glucose levels→ higher respiration rate)

• Oxygen: required for aerobic respiration and its levels will determine the type of reaction

• Presence of inhibitors: disrupts the normal reaction pathway between an enzyme and a substrate

meausring the rate of respiration

A respirometer is a device that determines an organism’s aerobic respiration rate by measuring the rate of oxygen consumption

hydrogen carriers

• Oxidation is the loss of electrons or H+ or the gain of oxygen

• Reduction is the gain of electrons or H+ or the loss of oxygen

• Electron carriers are molecules that can accept and lose electrons reversibly

• The main electron carrier in respiration is NAD (nicotinamide adenine dinucleotide)

  • NAD⁺ + 2H⁺+ 2e → NADH + H⁺

• The hydrogen carriers function like taxis, transporting the electrons and protons to the cristae of the mitochondria

  • At the cristae, the electrons and protons of the hydrogen atom are donated to the ETC

glycolysis

• The first step in the controlled breakdown of carbs is glycolysis which occurs in the cytosol of the cell

• In glycolysis glucose (6C) is broken down into two molecules of pyruvate (3C) in 4 steps 

glycolysis steps

• Phosphorylation of glucose: glucose is phosphorylated by two molecules of ATP to make it less stable and more reactive

• Lysis: the hexose biphosphate (6C sugar) is split into two triose phosphates (3C sugars)

• Oxidation: hydrogen atoms are removed from each of the 3C sugars (via oxidation) to reduce NAD

  • Two molecules of NADH are produced in total (one from each 3C sugar)

• ATP formation: some of the energy released from the sugar intermediates is used to synthesize ATP

  • 4 molecules of ATP are generated 

  • net gain (2 atp, 2 nadh, 2 pyruvate)

fermentation

• Fermentation involves the conversion of pyruvate into a carbon compound via a reaction that oxidizes the hydrogen carrier NAD

  •  this restores the stocks of NAD needed for glycolysis allowing ATP production to continue in the absence of oxygen

•  products of anaerobic respiration:

  •  in animals, the pirate is converted into lactic acid,  lactase

  •  in plants and yeast, pyruvate is converted into CO2 and ethanol

link reaction

• The first stage of aerobic respiration is the link reaction which transports pyruvate into the mitochondria

• aerobic respiration uses available oxygen to further oxidize the sugar molecule for a greater yield of ATP

• Pyruvate is transported from the cytosol into the mitochondria matrix

• The pyruvate loses a carbon atom (decarboxylation) which forms a carbon dioxide molecule

• NAD is reduced to NADH

• The acetyl compound (2C)  is transferred to coenzyme A to form acetyl coA

• As glycolysis splits glucose into two pyruvate molecules, the link reaction occurs twice per molecule of glucose

• Per glucose molecule, the link reaction produces coA (x2), NADH (x2), and CO2 (x2)

krebs cycle

• The second stage of aerobic respiration is the Krebs cycle, also called the citric acid cycle which occurs in the matrix of the mitochondria

• 2 carbon atoms are released via decarboxylation to form 2 molecules of CO2

• 4 oxidation reactions result in the reduction of hydrogen carries ( 3 NADH and 1 FADH₂)

• One molecule of ATP is produced

• As the link reaction produced 2 molecules of acetyl coA (one per each pyruvate) the krebs cycle occurs twice

• Per glucose molecule the krebs cycle produced ATP (x2), CO2 (x4) and a large yield of hydrogen carriers (x8)

ETC

• The final stage of aerobic respiration is the ETC which is located in the inner mitochondrial membrane

• Within the inner membrane of the mitochondria, there are groups of proteins that act as electron carriers by accepting and passing on pairs of electrons. These carriers form the electron transport chain

• The three main steps of the ETC are

  • Generating a proton gradient

  • Chemiosmosis

  • Reduction of O2

step 1: generating proton gradient

1. The hydrogen carriers NADH and FADH2 are oxidized and release high-energy electrons and protons

2. The electrons are transferred to the ETC, consisting of several transmembrane carrier proteins

3. as electrons pass through the chain, they lose energy which is used to pump protons from the matrix 

4. The accumulation of H+ ions within the intermembrane space creates an electrochemical gradient

step 2: chemiosmosis

1. H+ ions move down the gradient and diffuse back into the matrix

2. This diffusion of protons is called chemiosmosis and is facilitated by the transmembrane enzyme ATP synthase

3. As the H⁺ ions move through ATP synthase they trigger the molecular rotation of the enzyme, synthesising ATP

step 3: reducing oxygen

1. In order for the electron transport chain to continue functioning, the de-energised electrons must be removed

2. Oxygen acts as the final electron acceptor, removing the de-energised electrons to prevent the chain from becoming blocked

3. Oxygen also binds with free protons in the matrix to form water – removing matrix protons maintains the hydrogen gradient

4. In the absence of oxygen, hydrogen carriers cannot transfer energised electrons to the chain, and ATP production is stoped

mitochondria

• Outermembrane: contains transport proteins that enable the shuttling of key materials from the cytosol

• Inner membrane: contains the ETC and ATP synthase used for oxidative phosphorylation

• Cristae:The inner membrane is arranged into folds that increase the surface area to volume ratio

•  intermembrane space:  small space between membrane that maximizes hydrogen gradients upon proton accumulation

•  Matrix;  Central cavity that contains appropriate enzymes and is suitable pH for the Krebs cycle to occur

Energy sources

• Carbohydrates are the most commonly used respiratory substrates because they are easier to digest and transport

•  fatty acid chains are broken down into 2C compounds to form acetyl-coa so they can only be digested aerobically 

• Lipids also produce more energy per gram as the carbon chain possesses less oxygen and have more oxidizable hydrogen and carbon