Glycolysis

Four Main Stages of Cellular Respiration

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1. GlycolysisAnaerobic In cytosolbreaks glucose (6C) into 2 pyruvate molecules (3C)releases ATP

2. Pyruvate Oxidation(oxidative decarboxylationPyruvate converted to acetyl CoA releasing CO2

3. Kreb’s CycleWithin mitochondrial matrix Oxidize each acetyl CoA to CO2Releases ATP and co-enzymes (NADH, FADH2)4. Electron Transport Chain

1. Along the inner mitochondrial membrane2. Uses high energy electrons from NADH and

FADH2 to create an electrochemical proton (H+) gradient which powers ATP synthesis

Glycolysis

o glyco- “sugar”, and –lysis to break apart• First step of both anaerobic and aerobic cellular

respiration• No oxygen required for this step (anaerobic)• Occurs in the cytosol of the cell• Each step catalyzed by a specific enzyme• Energy (2 ATP) is required to start this process and 4

ATP is eventually produced

• Net: 2 ATP• Glucose is broken down into 2 pyruvates

The set of metabolic reactions that take place in the cells of an organism to convert biochemical energy from nutrients into ATP, and then release waste products.

catabolic exergonic series of reactions to

allow for slow, useable release

Cellular Respiration

Glycolysis (glyco - glucose, lysis - dissolving) is a pathway that occurs (with variation) in nearly every living organism on earth. It is a sequence of 10 enzyme catalyzed reactions that ultimately converts glucose to pyruvate. The intermediates provide entry and exit points for metabolism of other organic molecules.

Glycolysis: A Central Pathway

Each black arrow on the diagram represents a different enzyme catalyzed reaction. Major intermediates are shown, along with connected pathways.

An anaerobic reaction is one that takes place without oxygen. Glycolysis is anaerobic, and takes place in the cytoplasm.

Anaerobic vs. Aerobic

One of the major products of glycolysis, pyruvate, is a three carbon molecule.

Depending on the organism, the cell type, and the situation, this can be metabolized further in either the presence (aerobic) or absence of oxygen (anaerobic).

Pyruvate

Most eukaryotes and many prokaryotes will continue to break down pyruvate using oxygen a final oxidizing agent

Other organisms (or in different conditions), pyruvate can be metabolised without oxygen, using anaerobic pathways.

Aerobic Respiration

Pyruvate is not the only product of glycolysis, and to see what else is produced (and ultimately how energy is produced) we need to look in more detail.

Note the net reaction in the bottom of the diagram.

Glycolysis Overview

Glucose is insufficiently reactive and must be phosphorylated and isomerized to become more reactive. Like in all steps of glycolysis, enzymes are used to facilitate these reactions.

The phosphates come from ATP.

In the last step shown here, DHAP is converted to G3P, and the result is two molecules of G3P.

Energy Investment

The next five reactions occur twice, once for each G3P produced previously. These reactions release energy from the G3P molecules and convert it to Pyruvate.

Energy is captured in the form of ATP (4 produced here) and the reduction of two NAD+ into NADH. As two ATP are used in the energy investment phase, this results in a net of 2 ATP.

Net energy molecules per glucose: 2 ATP, 2 NADH

Energy Return

In photosynthesis we learned about how ATP could be generated through the process of photophosphorylation – this isn’t the only way that ATP can be created, as you’re now seeing.

Some enzymes, called kinases, can transfer phosphates from high energy donor molecules to recipient substrates (like ADP!)

This is given the name substrate level phosphorylation.

Substrate Level Phosphorylation

by no means do you need to memorize or learn all the names and steps.

follow the carbons and the energy (know where energy is captured and where waste is produced).

read page 98 of textbook for a detailed description

learn and love the finger dance!

What Do I Need to Know?

Why is glycolysis considered an anaerobic pathway?

Write out the net reaction of glycolysis including all reactants and products.

Some organisms can survive through glycolysis alone, what conclusions can you make about them?

How are molecules like amino acids and triglycerides related to the process of glycolysis?

What makes glucose so special as a starting point for this pathway?

Review