Chapter 8 Topic 8: Cell Respiration and Photosynthesis Mrs. Ragsdale Biology SL/HL Chapter 8 Topic 8: Cell Respiration and Photosynthesis

8.1 Cell Respiration

Lil bit of chemistry review Oxidation and Reduction reactions Oxidation – loss of an electron Reduction – gain of an electron Typically involve trading H⁺ ions

Oxidation vs Reduction Oxidation reactions Reduction reactions Loss of electrons Gaining oxygen Loss of hydrogen Gain of electrons Losing oxygen Gain of hydrogen

Major Lingo Used: Phosphorylation: addition of phosphate groups Makes reactions that occur in a chain or pathway easier by adding energy Dephosphorylation: removal of phosphate Oxidation: loss of hydrogen Reduction: gain of hydrogen If compound A is oxidized, then compound B is reduced

Cell Respiration: 3 Step Process Glycolysis – Sugar is converted into pyruvate Can be aerobic (with oxygen) or anaerobic (without oxygen) Krebs Cycle – pyruvate is used to charge electron carriers Link Reaction (happens before Kreb’s Cycle) Electron Transport Chain – electrons create a hydrogen proton gradient that fuels ATP pumps

Cellular Respiration Overview

Cytoplasm Glycolysis – Breakdown of glucose into pyruvate

Glycolysis – Converting glucose into pyruvate 4 Step Process: Two phosphate groups added to one molecule of glucose Phosphorylation – adding a phosphate group This raises the energy level and powers the rest of the reaction Hexose biphosphate is split to form two molecules of triose phosphate.

Glycolysis continued Two atoms of hydrogen are removed from each triose phosphate molecule (oxidation). When hydrogen bonds break, a large amount of energy is released carrying into the next step. NAD⁺ is converted into NADH Extra phosphates that were added are then removed  Pyruvate End result: 2pyruvate + 2NADH + 2H⁺

Breakdown of Steps Add 2 Phosphate to glucose (phosphorylation) Split this in half and make triose phosphate Remove 2 hydrogen (oxidation) and make glycerate 3-phosphate Remove extra phosphates Net: 2 ATP and 2 NADH + 2H⁺

Glycolysis Summary One glucose molecule (C₆H₁₂O₆) Breaks down into two pyruvate molecules Two ATP molecules are used per glucose but 4 are produced => net yield of 2 ATP Two NAD⁺ molecules converted into NADH + H⁺ http://www.youtube.com/watch?v=mmACA_eVLTE

Aerobic vs Anaerobic Respiration At the end of glycosis a choice must be made! Oxygen present = pyruvate proceeds to the mitochondria Oxygen absent = pyruvate is turned into some form of waste 2 ATP is all the energy created

Pyruvate’s Fate WITHOUT Oxygen Anaerobic respiration – when no oxygen is present. Occurs In the cytoplasm After glycolysis, pyruvate is converted to a waste product NO ENERGY IS OBTAINED OR USED Waste in humans is Lactate (Lactic Acid) Waste in Yeast is Ethanol and Carbon dioxide

Pyruvate’s Fate WITH Oxygen Aerobic Respiration- when oxygen is present Occurs in mitochondria After glycolysis, pyruvate is broken down in the mitochondria LARGE yield of energy (34 ATP) Waste products are CO2 and H2O

The Mitochondria Link Reaction, Kreb’s Cycle and Electron Transport Chain

Draw and Label: Electron micrograph of Mitochnodria Outer mitochondrial membrane Inner mitochondrial membrane Space between inner and outer membrane Matrix 70s ribosomes Cristae

Link Reaction: Beginning of the Kreb’s Cycle Pyruvate is decarboxylated once (CO2 is removed) and oxidized once (H⁺ is removed) Forms an acetyl group

Kreb’s Cycle Involves 2 additional decarboxylations and four more oxidations Product gained: high energy electron carrier = NADH and FADH₂

Types of Reactions in Kreb’s Cycle Decarboxylation – carbon dioxide is removed Remember, CO₂ is a waste product! Oxidation – hydrogen removed NAD⁺ becomes NADH FAD⁺ becomes FADH₂ Both of these reactions release/store energy Substrate-level phosphorylation Requires the addition of ATP

Kreb’s Cycle

Electron Transport Chain A series of electron carriers located in the inner membrane of the mitochondrion Oxidative Phosphorylation – the energy released by oxidation turning causing ADP to be phosphorylated into ATP Chemiosmosis – the coupling of ATP synthesis to electron transport via a concentration gradient of protons

Electron Transport Chain – in a nutshell NADH and FADH₂ donate H⁺ protons along the inner membrane wall creating a high concentration gradient of protons within that small space An ATP synthase pump works to phosphorylate the ADP into ATP using the H⁺ ions to fuel the pump

Oxygen’s Big Star Role So what happens to the extra H⁺ ions and why is it so important that oxygen be there? After the ATP synthase “pump” is turned and ATP is created, the H⁺ protons must bond with something Only if Oxygen is present and available to bind with H⁺ creating H₂O can the additional 30 ATP be made. If no oxygen is present, the extra H⁺ build up will trigger pyruvate to be converted into waste products (lactic acid in humans)

Functions of Mitochondrial Structure Outer mitochondrial membrane – separates the contents of the rest of the cell creating a compartment with ideal conditions for aerobic respiration Inner mitochondrial membrane – contains electron transport chains and ATP synthase which carry out oxidative phosphorylation Matrix – fluid inside the mitochondrion containing enzymes for the Kreb’s cycle and the link reaction 70s ribosomes Loop of DNA

Functions of Mitochondrial Structure Cristae – Tubular shelf-like projections that increase the surface area of the inner membrane making more space for oxidative phosphorylation Space between inner and outer membrane – Protons are pumped into this space by the electron transport chain Small space allows for a high proton gradient for chemiosmosis

Oxidative Phosphorylation ADP is phosphorylated into ATP using energy released by the oxidation of NADH into NAD⁺ Phosphorylation – a fancy pants science word for adding a phosphate to ADP Oxidative – basically oxidation (removing Hydrogen) powers something

Chemiosmosis Occurs in the inner mitochondrial membrane H⁺ protons form a gradient in the intermembrane space of the mitochondria Protons escape back to the matrix via the ATP pump