Glucose Metabolism- Glycolysis, Kreb's Cycle, Electron Transport Chain

What are the overall/general steps to glucose metabolism resulting in ATP synthesis?

• glycolysis: occurs in cytosol where glucose is oxidized and ends in the production of 2 pyruvates

• matrix/link reactions: pyruvate travels into the mitochondrion matrix where it's converted to Acetyl-CoA, and the Krebs cycle happens,

• the NAD+ reduced to NADH released from the conversion of pyruvate to acetyl-CoA travels to the ETC chain. The 2e- it carried is released to protein e-carriers in ETC

• release of energy from the transfer of e- in ETC is used to pump H+ into the intermembrane compartment, creating a gradient.

• ATP synthase uses the potential energy in the gradient as a power source to make ATP from ADP and inorganic phosphate.

What is Glycolysis?

• a complex sequence of reactions (that occur in the cytosol of a cell) where a molecule of glucose is broken down into 2 molecules of pyruvate

• the oxidation of glucose to release energy gradually to make ATP (e- and H+ are stripped from glucose)

• anaerobic energy source

• each reaction step is catalyzed by its own enzyme

What are the steps to glycolysis?

1. 6C glucose is phosphorylated (2 ATP are hydrolyzed/transported to one glucose into 2 ADP-exergonic) and converted into 6C fructose

2. 6C fructose is very reactive/unstable, so it breaks down/splits into two sugars: 3C dihydroxyacetone phosphate and 3C PGAL/G3P

3. 3C dihydroxyacetone phosphate is converted into 3C PGAL.

4. The two 3C PGAL/G3P molecules are then converted into 3C Pyruvate (in this conversion, e- and H+ ions from the sugar are transferred to NAD+—>NADH, and 2 ADP—> 2ATP)

What is the energy investment phase in glycolysis?

• ATP is needed to make 6C glucose unstable to convert into 6C fructose, so ATP is hydrolyzed into ADP + Pi.

• Pi phosphorylates glucose also needed at the start of glycolysis to split glucose into 2 pyruvate molecules

What are the end products of glycolysis?

What does 1 cell gain at the end of glycolysis?

• 2 net ATP

• 2 NADH (e- carrier)

What is the purpose of the link reaction a.k.a. matrix reaction?

• each pyruvate produced from glycolysis is further oxidized and broken down so all energy available in glucose molecule is eventually released

• links/connects glycolysis to the Kreb’s cycle, allowing respiration to continue

What happens in the link reactions/matrix reactions?

• each pyruvate produced from glycolysis travels into the mitochondrial matrix

• 1 pyruvate is oxidized into (2C) acetyl CoA(2 e-stripped, NAD+—>NADH, go to ETC)

  2CO2 stripped and released (waste product, breathed out)

what kind of protein does pyruvate travel through to the matrix after glycolysis?

a transport protein/enzyme

what are the 3 products of only the link reactions frome one pyruvate, and where does each product go?

• one acetyl CoA (used in Kreb’s to get further broken down)

• NADH (carries e- to ETC)

• CO2 (breathed out, waste)

(if 2 pyruvates, there’s 2 acetyl CoA, 2 NADH, and 2 CO2)

Why are acetyl CoA 2 carbons?

Because when 1 pyruvate is oxidized to acetyl CoA one CO2 is released, so one carbons were stripped from 1 pyruvate

*remember that there are 2 pyruvates are produced from 1 glucose

What are the steps to the Kreb’s Cycle? (from one acetyl CoA)

1. (2C) acetyl CoA reacts with (4C) oxaloacetate, making (6C) Citric Acid

2. (6C) Citric Acid is oxidized (NAD+—> NADH) and releases one CO2, resulting in (5C) ox-ketoglutarate

3. similar process occurs when 5C) ox-ketoglutarate converts into 4C) oxaloacetate :

   • (5C) ox-ketoglutarate is oxidized (2NAD+—> 2NADH)

   • one CO2 released (resulting in 4C molecule)

   • one FAD—> FADH2

   • 1 ADP—>1 ATP

What are the 4 products of the all the Matrix reactions from one (3C) pyruvate? (link reactions + Kreb’s)

• 3 CO2 (one from pyruvate->acetyl, two from Kreb’s)

• 4 NADH (one from link, 3 from Kreb’s)

• 1 FADH2 (for ETC)

• 1 ATP (can be used as energy)

6 CO2 molecules are released from the Kreb’s Cycle (3 from one pyruvate, 6 from two pyruvate); why does this make sense?

Glucose is a 6C molecule, and so therefore has been completely broken down in the Kreb’s cycle as 6C are released in the form of CO2

What is the ETC?

A series of proteins, enzymes, and other molecules embedded in the inner membrane of the mitochondria (cristae) that transport e-

What are the steps of the ETC?

• 2 electrons are deposited from NADH or FADH2 (e- carrier) to the ETC

• e- are carried molecule to molecule spontaneously along the chain due to increasing affinity for e- of the electron carriers

• each carrier is reduced and then oxidized as e- comes and leaves

• coupled with these transfers is the pumping of 1 H+ for each e-

where does the O2 at the end of the ETC from from?

oxygen is breathed in

What happens at the end of the ETC when e- reach O2?

• 4 electrons, O2, and 8 H+ from the (aq) solution interact:

  • 4 electrons, O2, and 4 H+are used to form two H2O molecules. (H+ neutralizes the -2 charge of electrons from ETC)

  • other 4 H+ are pumped across the membrane

What are the end products of the ETC?

What are the end products of the ETC from 1 glucose?

• 4 net ATP

  (Glycolysis: 2 net)

  (Kreb’s: 1 ATP / pyruvate=2 ATP)

• 10 NADH

  (Glycolysis: 2 net)

  (matrix-Kreb’s:

  4 NADH / pyruvate= 8 ATP)

• 2 FADH2

  (Kreb’s: 1 FADH2/ pyruvate= 2)

Chemiosis

Chemiosis: the series of H+ pumping steps creates a gradient. the potential energy in the gradient is used by ATP synthase to make ATP from ADP and inorganic phosphate.

What happens with the ATP synthase?

• H+ flow through ATP synthase from intermembrane compartment back to matrix along its gradient from H→L (diffuses back=passive transport)

• H+ passing through causes synthase to spin, producing ATP

• action of ATP synthase phosphorylates ADP, producing ATP

• ADP + Pi —> ATP

Which region is the only region freely permeable to H+ ions?

ATP synthase

About how many ATP are produced through oxidative phosphorylation (through the actin of electron carriers?)

26-28 ATP

What kind of protein is ATP synthase?

an enzyme

What does PGAL/G3P stand for?

glyceraldehyde-3-phosphate

What happens when glycolysis occurs in an aerobic state?

pyruvate will enter the kreb’s cycle and undergo oxidative phosphorylation leading to a net production of 26-28 ATP molecules

hy

pyruvate is used to go through fermentation

What is the difference between substrate-level phosphorylation and oxidative phosphorylation?

The type of phosphorylation depends on the source of energy/where the energy comes from.

What is substrate-level phosphorylation?

When a phosphate group is transferred from a substrate (molecule) to ADP to form ATP.

When phosphate group is transferred ADP to form ATP, what is coupled with it?

a release of free energy (release to form)

what is the purpose of NADH made?

it carries electrons and hydrogens to the ETC

what is the equation of cellular respiration?

C6O12H6 + 6O2—> 6CO2 + 6H2O