Module 4 Respiration 1.4.3. Glycolysis

Learning Objectives Success Criteria To understand Glycolysis State that Glycolysis takes place in the cytoplasm (Grade D) State that during aerobi c respiration in animals pyruvate is actively pumped into mitochondria (Grade C) Outline the process of Glycolysis (Grade B/A)

Evolutionary perspective Prokaryotes first cells had no organelles Anaerobic atmosphere life on Earth first evolved without free oxygen (O2) in atmosphere energy had to be captured from organic molecules in absence of O2 Prokaryotes that evolved glycolysis are ancestors of all modern life ALL cells still utilize glycolysis The enzymes of glycolysis are very similar among all organisms. The genes that code for them are highly conserved. They are a good measure for evolutionary studies. Compare eukaryotes, bacteria & archaea using glycolysis enzymes. Bacteria = 3.5 billion years ago glycolysis in cytosol = doesn’t require a membrane-bound organelle O2 = 2.7 billion years ago photosynthetic bacteria / proto-blue-green algae Eukaryotes = 1.5 billion years ago membrane-bound organelles! Processes that all life/organisms share: Protein synthesis Glycolysis DNA replication

Glycolysis - occurs in cytoplasm Breaking down glucose “Glyco – lysis” (splitting sugar) Ancient pathway which harvests energy where energy transfer first evolved transfer energy from organic molecules to ATP still is starting point for ALL cellular respiration but it’s inefficient generate only 2 ATP for every 1 glucose glucose      pyruvate 2x 6C 3C Why does it make sense that this happens in the cytosol? Who evolved first? That’s not enough ATP for me!

GLYCOLYSIS (carbohydrate splitting) First stage of aerobic respiration & anaerobic respiration. Doesn’t need O2 – so this stage is anaerobic! Occurs in the cytoplasm of all living cells

Glycolysis - phosphorylation The first stage actually begins by phosphorylating glucose to hexose 1,6-bisphosphate. Each glucose uses 2 molecules of ATP

Glycolysis - phosphorylation Glucose ATP ADP Glucose 6 phosphate Fructose 6 phosphate Fructose 1,6-bisphospahte

Glycolysis - lysis This stage involves the breaking of the hexose bisphosphate into two triose phosphate molecules. The triose phosphate is an intermediate in many biochemical reactions. The phosphate group allows the sugar to form stronger interaction with the next enzyme in the pathway.

Glycolysis – oxidation/ATP formation Each Triose phosphate is oxidised to a 3 carbon molecule called Pyruvate Each Triose Phosphate has hydrogen removed (oxidation) to reduce one NAD+ to NADH + H+ Each Triose Phosphate adds a phosphate to ADP reducing this to ATP (substrate level phosphorylation) Note that each Triose phosphate releases enough energy for the formation of two ATP

Summary of glycolysis Glycolysis takes place in the cytoplasm of the cell. It does not require oxygen. The hexose sugar (glucose) is converted into two 3C atoms compounds called pyruvate. Two ATP are consumed but four are produced making a net gain of 2 ATP Two NADH + H+ are produced which will yield more ATP when they are transferred to the mitochondria and oxidative phosphorylation. Yield: 2 Pyruvate + 2 ATP + 2NADH + 2H+

The first stage of respiration: glycolysis Boardworks A2 Biology Respiration

Glycolysis Why is Glycolysis termed anaerobic? NAD+ + 2H  NADH + H+ (oxidised form ) (reduced form) NB Rather then write NADH, examiners often simply refer to it as reduced NAD or reduced coenzyme Glycogen You start with glycogen. 2 ATP 4 ADP + 4Pi 4 ATP Triose -phosphate (3C x 2) Pyruvate (3C x2) Glucose (6C) 2H x 2 NAD Reduced NAD 2 ADP Nicotinamide adenine dinucleotide = So it gains electrons You finish with Pyruvate Why is Glycolysis termed anaerobic? What is the NET production of ATP?

The sums The end products of glycolysis are pyruvate and reduced NAD Energy is released during this reaction. 4 molecules of ADP + Pi converted to 4 molecules of ATP. So net gain of 2 molecules of ATP 2 pairs of hydrogen atoms produced 2 Molecules of pyruvate.

Products of Glycolysis 2 reduced NAD (NADH + H+) 2 Pyruvate 2 ATP

THIS DEPENDS ON THE AVAILABILITY OF OXYGEN!!! The Fate of Pyruvate! THIS DEPENDS ON THE AVAILABILITY OF OXYGEN!!!

Task Complete exam questions (SA)

Plenary Make list of what is needed for glycolysis and what is produced Explain where oxidation occurs and substrate level phosphorylation

Learning Objectives Success Criteria To understand Glycolysis State that Glycolysis takes place in the cytoplasm (Grade D) State that during aerobi c respiration in animals pyruvate is actively pumped into mitochondria (Grade C) Outline the process of Glycolysis (Grade B/A)