BSCI 170 - Metabolism and Oxidation & Reduction

What is metabolism?

the collection of all biochemical reactions that occur in a cell

What are catabolic reactions often accompanied by?

the transfer of electrons between reactants

Energy Storage

• We talk about energy being stored in glycogen, starch, and lipids

• Where exactly is the energy stored?

• If electrons are rearranged or released, then potential energy can be ______.

  • the excess energy is _______.

• the energy is stored in chemical bonds (covalent > weak), mostly in electrons, as potential energy

• reduced

• released

Combustion of Organics

• What is combustion?

  • Organics + O₂ —> CO₂ + H₂O + Energy

• Example: Combustion of Glucose

  • C₆H₁₂O₆ + 6O₂ —> 6CO₂ + 6H₂O + 686,000 cal/mol

  • We know that the reaction is ________ because energy is released

combustion is rapid chemical combination with oxygen, exergonic

Oxidation

• A reaction with _______ is also a form of oxidation

  • Rust is a result of the oxidation (slow combustion) of iron

oxygen gas

Oxidation-Reduction Reactions

• Energy is stored in _______ bonds

  • ______ bonds result from electron sharing

• When covalent bonds are broken or rearranged, electrons can be transferred between _________.

• These electron-transfer reactions are called __________-_________ reactions

  • also called redox reactions

covalent, covalent, reactants, oxidation, reduction

Oxidation-Reduction Reactions

• What is the top compound A?

• What is the bottom compound A?

• What is the top compound B?

• What is the bottom compound B?

• the reducing agent

• the oxidized compound

• the oxidizing agent

• the reduced compound

What is oxidation?

an electron is lost

What is reduction?

an electron is gained, addition of a negatively charged electron reduces overall charge of the molecule

Mneumonic for Remembering

• OIL RIG

  • Oxidation is Loss

  • Reduction is Gain

• LEO the Lion says GER

  • Loss Equals Oxidation

  • Gain Equals Reduction
    

N/A

Practice:
Na + Cl —> Na⁺ + Cl^-

• Na loses an electron, so it is _______

• Cl gains an electron, so it is ________

oxidized, reduced

What is the generalized equation for redox reactions?

In this equation what are the reducing and oxidizing agents?

the reducing agent is CH₄ (methane) and the oxidizing agent is 2O₂

True or False: Oxidations and reductions occur in isolation

false, oxidations and reductions NEVER occur in isolation

• electrons are not floating freely in solution like H⁺

If one reactant is oxidized, then another reactant MUST be ________

reduced

Redox Reactions

• It is not always easy to determine which molecule is more reduced

• In biological reactions, electrons rarely move alone.

  • Electrons often combine with ______ as they move

• The molecule with more _________ is usually the more reduced one.

protons, hydrogens

What is reduced and what is oxidized?

lactate is reduced and pyruvate is oxidized

What is reduced and what is oxidized and why?

• Glucose is oxidized to CO₂

  • Glucose loses electrons and H+

• O2 is reduced to H2O

  • O2 gains electrons and H+

Oxidation of Cellular Fuel

• Important Points:

  • each electron transfer reaction is _________

    • electrons ____ energy with each transfer

    • electrons in H₂O have ____ (potential) energy than they did in glucose

  • released free energy drives ___ _________

exergonic, lose, less, ATP synthesis

Stepwise Energy Harvest

• Energy from glucose is not released at ____

• Glucose is combusted in a series of _____, _______-________

• Electrons (and protons) are stripped away and transferred to another molecule (_______ _______)

once, small, enzyme-catalyzed, electron carrier

Nicotinamide Adenine Dinucleotide

• Derivative of ______

  • B vitamin

• Oxidized form, NAD+, serves as an important ______ ________ during _______ __________.

niacin, electron acceptor, cellular respiration

What is the reduced form of NAD+?

NADH

Respiration is the cumulative effect of 4 separate events. What are they?

• Glycolysis (lysis of glucose)

• Pyruvate oxidation and citric acid cycle (oxidation of carbon and salvaging of high-energy electrons)

• Electron transport (stripping energy from the electrons)

• Oxidative phosphorylation (using the energy from the electrons to synthesize ATP)

For your reference

N/A

For your reference

N/A

What is the first step in the complex, multistep process of oxidizing glucose?

glycolysis

• Glycolysis means _____ ________

  • glyco = _________ __ ______

  • lysis = __ _______

  • occurs in the _______ of eukaryotes

  • What is glucose?

sugar splitting, relating to sugar, to unbind, cytosol, one six-carbon sugar

What occurs in glycolysis?

one six-carbon sugar (glucose) is oxidized to two, three-carbon molecules (pyruvate)

Glycolysis

• A complex, 10-step biochemical pathway

  • several ______-________ steps

  • several ___________ steps (to make ___)

• Conceptually, a very simple process

• We can do it the hard way or the easy way

oxidation reduction, phosphorylation, ATP

What is step 1 of glycolysis?

“Priming the Pump”

• In this phase, the starting molecule of glucose gets rearranged, and two phosphate groups are attached to it. The phosphate groups make the modified sugar—now called fructose-1,6-bisphosphate—unstable, allowing it to split in half and form two phosphate-bearing three-carbon sugars. Because the phosphates used in these steps come from ATP, two ATP molecules get used up.

What is step 2 of glycolysis?

Cleavage, Rearrangement & Energy Release

• In this phase, each three-carbon sugar is converted into another three-carbon molecule, pyruvate, through a series of reactions. In these reactions, two ATP molecules and one NADH molecule are made. Because this phase takes place twice, once for each of the two three-carbon sugars, it makes four ATP and two NADH overall.

Step 3: Summary

• What does one glucose produce?

• What is the net ATP produced?

• What does 2NAD+ + 4 e- + 4 H+ produce?

• 2 Pyruvate + 2 H₂O

• 2 ATP

• 2 NADH + 2H+

Substrate- Level Phosphorylation

• In glycolysis, ATP is generated by the transfer of a _______ _______ from a ___________ ________ to ADP to make ATP

phosphate group, phosphorylated substrate

Example of Substrate-Level Phosphorylation:

N/A

Glycolysis: What you need to know

• What are the starting reactants?

• What are the ending products?

• glucose, NAD+, ADP, P_i (inorganic phosphate)

• pyruvate, NADH and H+, ATP

Glycolysis: Final Accounting

• All _ carbons originally in _______ are now in the _ pyruvates

  • No carbons fully oxidized to ___

• No __ has been consumed

6, glucose, 2, CO2, O2

Glycolysis Is Fundamental

• Glycolysis is a fundamental pathway used by all living organisms

  • Evolved very early

    • Before ______ was available in the ___________

• Glycolysis is very ________

  • generates only small numbers of ___ but does it quickly

• Sufficient for many ____________

oxygen gas, atmosphere, efficient, ATP, microorganisms

Glycolysis Is Not Enough

• Problem: Glycolysis requires a continuous supply of ______ to keep operating, BUT ______ is limiting in cells

  • Without a mechanism for regenerating ______ from _______ or for obtaining new ____, glycolysis will ____

NAD+, NAD+, NAD+, NADH, NAD+, stop

What is one solution for this problem?

in the absence of oxygen: fermentation

Fermentation

• There are many different ferementation pathways

• All have two common purposes, what are they?

• oxidize

Reactants: C₆H₁₂O₆ + 6O₂

Products: 6CO₂ + 6 H₂O

• In this reaction, which reactant is being oxidized and which is being reduced?

• Which reactant is the oxidizing agent, and which is the reducing agent?

• What else is being produced by this reaction?

• Does this reaction happen all in one step? Why or why not?

• C₆H₁₂O₆, 6O₂

• 6O₂, C₆H₁₂O₆

• Energy

• Happens in one step because redox reactions are comprised of a reduced half and an oxidized half

Reactants: 4H₂ + CO₂

Products: CH4 + 2H2O

• In this reaction which reactant is being oxidized and which is being reduced?

• Which reactant is the oxidizing agent, and which is the reducing agent?

• What else do you think is being produced by this reaction?

• CO2, 4H2

• 4H2, CO2

• Energy

Reactants: CH4 + 2O2

Products: CO2 + 2H2O

• In this reaction, which reactant is being oxidized and which is being reduced? Why did you choose these?

• Which reactant is the oxidizing agent, and which is the reducing agent?

• What do you notice about the reactants of this product compared to last reaction?

• Why do you think this reaction happens closer to the surface?

• 2O2, CH4

• CH4, 2O2

• O2 is present

• Closer to the surface because there is more oxygen there

Reactants: COO- + Fe3+

Products: Fe2+ + CO2

• In this reaction, which reactant is being oxidized and which is being reduced?

• Which reactant is the oxidizing agent, and which is the reducing agent?

• What else do you think is being produced by this reaction?

• COO-, Fe3+

• Fe3+, COO-

• Energy

Other electron acceptors (oxidizing agents) do not release as much energy as _______.

oxygen

Cellular respiration is a _______ of reactions that are designed to capture the most ______ from the oxidation of glucose as possible.

series, energy

Oxidation of Glucose

• What are the reactants? products?

• Oxidation of glucose means elections are protons are removed from _______ and transferred to _______

• Complete reaction is highly _________

  • delta G = -686,000 cal/mol

• Reactants C6H12O6, 6O2; Products: 6CO2, 6H2O, Energy

• glucose, O2

• exergonic