(7) Cellular Respiration (E) Regulation of pathways through feedback inhibition (A) Role of ATP & Phosphorylation (B) The metabolic pathway of respiration: Glycolysis and the citric acid cycle (C) The metabolic pathway of respiration: electron transport chain & ATP synthesis (D) Substrates for Respiration

Cellular Respiration (b) Describe the process of Glycolysis Using the terms phosphorylation energy investment, energy pay-off Name the enzymes involved in Glycolysis State the role of these enzymes

Re-cap from last year! What molecule do we start with? What gas do we need? What gas is made? How many stages are there? What is the 1st stage called? Where does each stage take place? How much ATP is made in stage 1 compared to stage 2?

What is Cellular Respiration? Cellular respiration is a process where the cell breaks down glucose through a series of enzyme controlled reactions in order to release energy. More energy is released if oxygen is present compared to if a cell carried out respiration in the absence of oxygen (more on this type of respiration in the LAST Key Area!)

Why is respiration so important? The metabolic pathways of cellular respiration are central to metabolism. They yield energy and are connected to many other pathways.

Checklist for each stage of respiration Name of stage Location Starting molecule(s) Intermediate molecule(s) Final molecule(s) ATP Carbon dioxide Hydrogen Oxygen Any other points?

Cellular Respiration 1. Glycolysis Cytoplasm 2. Citric Acid Cycle Stage Location 1. Glycolysis Cytoplasm 2. Citric Acid Cycle Matrix of the Mitochondria 3. Electron Transport Chain Mitochondrial membrane

Mitochondria Mitochondria are found in the cell cytoplasm and if oxygen is present aerobic respiration occurs here They are the site of ATP production in cells. The inner membrane has many folds (called cristae) to increase the surface area for respiration to take place – ELECTRON TRANSPORT CHAIN The fluid filled central matrix contains many enzymes – CITRIC ACID CYCLE Therefore, cells requiring much energy such as sperm, liver, muscle and nerve cells contain numerous mitochondria. Pupils should label the diagram too!

Stage 1…

Glycolysis (occurs with or without oxygen) Glucose ATP ADP (able to continue to other pathways) Intermediate Energy investment stage (2 ATP per glucose molecule are REQUIRED) Intermediate ATP ADP Irreversible Carried out by phosphofructokinase Intermediate 2ADP 2ATP Energy PAY-OFF stage (4 ATP per glucose molecule are PRODUCED) 2NAD 2NADH 2ADP 2ATP Pyruvate (progresses to the citric acid cycle if oxygen is available)

Phosphofructokinase There are 2 phosphorylations during Glycolysis The 2nd phosphorylation of glucose is catalysed by an enzyme called phosphofructokinase This reaction is an irreversible reaction which only leads to the glycolytic pathway.

Dehydrogenase During the energy pay off stage, H+ ions (hydrogen ions) are released from the substrate by a dehydrogenase enzyme. Dehydrogenase also remove high energy electrons. Both the H+ ions and high energy electrons are then passed to a coenzyme molecule called NAD.

Hydrogen Carriers Hydrogen is a gas To keep it in the cell and allow it to be transferred between one substrate and another, it becomes attached to a HYDROGEN CARRIER (or hydrogen acceptor) In RESPIRATION the main hydrogen acceptor is Nicotinamide Adenine Dinucleotide (NAD) When it is reduced (ie adds hydrogen) it is NADH NAD + H NADH

Hydrogen Carriers During glycolysis, hydrogen released from the glucose is temporarily bound to NAD NAD is a coenzyme that acts as a hydrogen acceptor and carrier NAD becomes reduced with the addition of hydrogen to form NADH NAD + H NADH NADH is transferred to the last stage of respiration – known as the electron transport chain and then goes back to the stage 1 and 2 as NAD and picks up more hydrogen

Use the following checklist AND your flow diagram to see if you can describe Glycolysis

Checklist Name of stage Location Starting molecule(s) Intermediate molecule(s) Final molecule(s) ATP Carbon dioxide Hydrogen Oxygen Any other points?

Pyruvate progresses to the citric acid cycle if oxygen is available. Glycolysis involves the breakdown of glucose to pyruvate in the cytoplasm. This progression of pathways can occur in the presence or absence of oxygen (fermentation). The phosphorylation of intermediates in glycolysis occur in an energy investment phase, where 2 ATP are used up per glucose molecule. The first phosphorylation leads to a product that can continue to a number of pathways. The second phosphorylation, catalysed by phosphofructokinase, is an irreversible reaction leading only to the glycolytic pathway. During the energy pay off stage, 4 ATP molecules are produced per glucose molecule, therefore generating the cell a net gain of 2 ATP molecules per glucose molecule. 2 Hydrogen ions are also released during the energy pay-off stage and are picked by the co-enzyme NAD to form NADH2. Pyruvate progresses to the citric acid cycle if oxygen is available. 1 2 3 4 5 6 7 8 9 This is a handout 10 11 12 13 14

Cellular Respiration (b) Describe the process of Glycolysis Using the terms phosphorylation energy investment, energy pay-off Name the enzymes involved in Glycolysis State the role of these enzyme