Glycolysis - BIO 183

Cellular Respiration Overview (locations of things)

Glycolysis - cytoplasm

Oxidation of Pyruvate and Citric Acid Cycle - the mitochondrial matrix

ETC and Oxidative Phosphorylation - Components of the ETC and ATP synthase are embedded in the inner mitochondrial membrane

aerobic cellular respiration

C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + ~36 ATP

Glycolysis: whats happening

• 2 ATP input to prep glucose molecule

• Glucose is phosphorylated by hexokinase using ATP, forming glucose-6-phosphate.

• An isomerase then converts glucose-6-phosphate to fructose-6-phosphate.

• Phosphofructokinase (PFK-1) adds a second phosphate using another ATP, creating fructose-1,6- bisphosphate.

• This phase splits the 6-carbon sugar into two 3- carbon molecules, which are each processed further.

Electron Carrier

• they transfer electrons to electron transport chains where ATP is produced

• Common electron carriers: NAD, FAD, NADP

• NAD = oxidized

• NADH = reduced

Glycolysis: Phase 1

• 2 phosphorylations occur, which both require ATP

• Another enzyme splits fructose-1,6- bisphosphate into two 3- carbon molecules, Glyceraldehyde 3 Phosphate, or G3P

• These two molecules of G3P are processed in tandem through phase 2 of glycolysis

Glycolysis: Phase 2

• generates ATP and NADH

• the two 3GP are converted into 2 molecules of pyruvate

• for each glucose molecule, 4 ATPs are produced, while 2 NADH molecules are also generated through reduction of NAD+ to NADH

• final net result is 2 ATP (4 produced, 2 used) and 2 NADH per molecule of glucose

• 2 molecules of pyruvate

Summary of molecules used and produced in glycolysis

• ATP Use: 2 ATP are consumed in the 1st/investment phase to initiate the breakdown of glucose

• ATP Production: 4 ATP molecules are generated during 2nd/payoff phase

• Nat ATP Production: 2 ATP molecules (4 produced 2 consumed)

• Other Products: 2 molecules of NADH & 2 pyruvate produced

• SUMMARY: glycolysis begins with 1 molecule of glucose & ends with 2 molecules of pyruvat

Important Details About Glycolysis

• it does not require oxygen directly, can be referred to as anaerobic

• takes place in cytoplasm of both prokaryotic and eukaryotic organisms

• glucose enters cells either through active transport or integral proteins called GLUT proteins

• GLUT transports glucose through facilitated diffusion

• regulated by hormones

What influences the rate of glycolysis?

• ATP demand & levels: high cellular ATP levels can inhibit enzymes like PFK, decreasing the rate of glycolysis

• is oxygen present?

• Aerobic conditions: Pyruvate will be moved to mitochondria for CAC, ETC + chemiosmosis, which produces more ATP than glycolysis. Glycolysis rate decreases

• Anaerobic conditions: glycolysis is the only source of ATP for the cell so the rate dramatically increases

More stuff that influences the rate of glycolysis: cell type!

• active muscle cells perform glycolysis 100x faster than oxidative phosphorylation for high energy needs, even in presence of oxygen

• cancer cells: prefer utilize glycolysis even in the presence of oxygen. supports cell proliferation by producing lactate.

• lactate inhibits genes that regulate the cell cycle

• Red blood cells: don’t have mitochondria. Therefore rely on only glycolysis for ATP

Phosphorylation of ADP

energy + ADP + Pi → ATP (endergonic)

ATP in living systems

• loss of a phosphate group from a molecule is called dephosphorylation

• phosphorylation is process of adding a phosphate group to molecule

• phosphorylated molecules tend to be less stable and more reactive

• ATP IS GENERATED BY ENDERGONIC REACTION, where ADP undergoes phosphorylation

• Energy required for this reaction come from:

• → a coupled exergonic reaction (substrate-level phosphorylation

• or chemiosmosis

Cellular Respiration

The process by which cells extract energy from food (glucose) in the presence of oxygen to produce ATP, water, and carbon dioxide.

Redox (Reduction-Oxidation) Reactions:

Chemical reactions involving the transfer of electrons from one molecule to another.

•Oxidation

The loss of electrons from a substance. (Mnemonic: OIL – Oxidation Is Loss).

•Reduction

The gain of electrons by a substance. (Mnemonic: RIG – Reduction Is Gain).

Reducing Agent:

The molecule that donates electrons (and becomes oxidized) in a redox reaction.

Oxidizing Agent

The molecule that accepts electrons (and becomes reduced) in a redox reaction.

•Dehydrogenase

An enzyme that removes hydrogen atoms (protons and electrons) from a substrate and transfers them to an electron carrier like NAD+

NAD+ / NADH:

Nicotinamide adenine dinucleotide; an electron carrier that cycles between an oxidized state (NAD+) and a reduced, high-energy state (NADH).

Substrate-Level Phosphorylation

A method of forming ATP by the direct transfer of a phosphate group from a reactant molecule to ADP.

•Chemiosmosis

A process for making ATP using the enzyme ATP synthase and the energy of a proton gradient; accounts for 90% of ATP generated during respiration.

•Glycolysis

The first step of cellular respiration; a metabolic pathway that breaks down one glucose molecule into two molecules of pyruvate.

•Kinase

A type of enzyme that transfers a phosphate group from a high-energy molecule (like ATP) to a substrate.

•Isomerase

An enzyme that converts a molecule into its isomer (rearranging the atoms without changing the formula).

Phosphofructokinase (PFK)

The enzyme that catalyzes the third step of glycolysis; it is the "rate-limiting" step that regulates the speed of the entire pathway

Reduction-Oxidation (redox) reactions

• chemical reactions where electrons are transferred from one molecule to another

• molecules that can donate electrons in a redox reaction are reducing agents, and those that accept are oxidizing agents

• molecules that gain = reduced, those that lose = oxidized

• OILRIG