Biology Chapter 8

Why do glucose metabolism require so many steps?

- This could be accomplished by setting glucose on fire (non-enzymatically), but all the released energy would be lost as heat. -Biology's trick: don't transfer all the energy at once. Generate some ATP at a time and capture electrons 2 at a time and transfer to an intermediate electron carrier (i.e. NADH) Later: transfer these electrons to O2 in a manner that efficiently captures the energy released to make ATP.

glucose functions

-all cells can metabolize (breakdown) glucose to make ATP when necessary - plants store glucose as starch ( long chains of glucose) - animals store glucose as glycogen (highly branched along chains of glucose) - glucose is picked off from glycogen (or starch in plants ) whenever we need energy

overview of two major phases of glycosis

1. Energy investment phase (or Preparatory Phase) Glucose "activation" (by attaching 2 high-energy phosphates) 2. Energy harvesting phase (or Payoff Phase) Fructose bisphosphate cleaved into 2 three-carbon molecules of G3P. Each G3P converted to pyruvate, generating ATP and NADH

step two of cellular respiration

Acetyl-CoA breakdown to CO2 in the Krebs Cycle Generates 3NADH, 2FADH, 1 ATP and 2CO2

key point in ETC and chemiosmosis

After ETC, the depleted electron carriers (NAD+ and FAD+) are ready to pick up new electrons in glycolysis and krebs cycle. ETC pumps protons (H+) from inside matrix to the inter-membrane space. The buildup of protons (H) in the intermembrane space (away from the matrix) generates a proton gradient - which will be used to make ATP by chemiosmosis. Oxygen is essential for this process. It accepts the electrons at the end of the ETC. If O2 is taken away, electron transport stops, NAD+ does NOT get remade (NADH accumulates) and hence Krebs Cycle also stops.

Importance of glycosis

Begins the oxidation and breakdown of simple sugars All cells can do it (glycolysis is done in cytoplasm) Anaerobic pathway (does not require O2) Generates two pyruvate molecules - which can be further broken down in further steps. Generates a net of two ATP molecules And two NADH (high-energy electron carriers) Glycolysis is heavily regulated - 10 different enzymes are required - several of which are regulated (turned ON/Off) Ensures proper use of nutrients Ensures production of ATP only when needed

Step 2: The Acetyl-CoA is now broken down in the Krebs cycle (aka Citric Acid Cycle

Breakdown of each Acetyl-Cogenerates: 2 CO2 3 NADH 1 FADH2 (another e- carrier) 1 ATP

gylocosis is used virtually by every organism on earth

Earlier forms of life appeared under the anaerobic (no oxygen) conditions existing before plants (and their photosynthesis). Therefore these primitive simple life forms probably used only glycolysis to generate ATP. Some modern microbes still lack enzymes for cellular respiration and rely solely on glycolysis and fermentation Examples: various microorganisms still thrive in places where oxygen is limited or absent ("where the sun don't shine") Stomach and intestines of animals Deep in soil Bogs and marshes

fementation continued

Fermentation allows NAD to be recycled when oxygen is absent Fermentation does not produce more ATP by itself, but regenerates NAD, which can be used to continue glycolysis. If the supply of NAD were to be exhausted, glycolysis would stop, energy production would cease, and the organism would rapidly die. Organisms use one of two types of fermentation to regenerate NAD Lactic acid fermentation Alcohol fermentation

Step 3 (Oxidative Phosphorylation):

From glycolysis, pyruvate oxidation and Krebs we've created 10 NADH and 2 FADH2 for every glucose molecule. Now these electron carriers each release two electrons into an electron transport chain (ETC), a chain of membrane proteins embedded in the inner mitochondrial membrane. O2 accepts the electrons at the end of the ETC. Electron movement in ETC causes H to be pumped from the matrix across the inner membrane and into the intermembrane space, producing a concentration gradient of H. Proton electrochemical gradient (high in inner membrane, low in mitochondrial matrix) is then used to generate ATP by chemiosmosis in the next step.

Energy harvesting phase

Fructose bisphosphate is split into two three-carbon molecules of glyceraldehyde 3-phosphate (G3P) Each G3P molecule is converted into a pyruvate, generating two ATPs per conversion, for a total of: 4ATPs and 2 NADH (electron carrier which will be used to generate tons more ATP later) Because two ATPs were used to activate the glucose molecule (during prep phase) there is a net gain of 2ATPs per glucose molecule

glycosis and cell respiration - connections to metabolism

Glycolysis and the Krebs cycle connect to many other metabolic pathways Glycolysis accepts a wide range of carbohydrates Proteins (broken down to amino-acids) and Fats (broken down to glycerol + fatty acids) can also feed glycolysis and/or Krebs Cycle.

gradients are essential for life

In higher animals, O2 is essential for life. Why? Disruption of O2 or ETC shuts down cellular respiration. Tissues such as heart and CNS that demant high levels of ATP will die if cellular respiration stops. Therefore, poisons that interfere with ETC causes DEATH.

some cells ferment pyruvate to form alcohol and carbon dioxide

Many microorganisms, such as yeast, engage in alcohol fermentation under anaerobic conditions Generates alcohol and CO2 from pyruvate As in lactic acid fermentation, the NAD is regenerated so that glycolysis can continue

mitochondrian membranes

Mitochondrion has two membranes: The inner membrane encloses a central compartment containing the fluid matrix The outer membrane surrounds the organelle, forming the intermembrane space between the two membranes.

electron transfer chain

NADH and FADH transfer their high-energy electrons into the electron transport chain on mitochondrial inner membrane and generate a proton gradient.

If oxygen is NOT present, fermentation then occurs:

Occurs in cytosol Works in the absence of O2. pyruvate is converted into either lactate (aka lactic acid) - in animal muscle, or into ethanol and CO2 (in yeast). Replenishes NAD+ so that glycolysis can continue

If oxygen IS present, Cellular Respiration occurs:

Occurs in mitochondria Requires oxygen. Breaks down pyruvate into carbon dioxide and water. Produces an additional 32-34 ATP molecules!

gyclosis breakdown (stage 1)

Occurs in the cytosol. Does NOT require oxygen. Breaks glucose into pyruvate. Yields 2 molecules of ATP and 2 molecules of NADH from every molecule of glucose 10 different reactions, each catalyzed by a different enzyme.

step three of cellular respiration

Production of 32 ATP by Oxidative Phosphorylation Transfer of electrons along the electron transport chain (ETC) generating a H+ gradient. Use of the H+ gradient to generate 32 ATP by chemiosmosis.

Step 1: pyruvate oxidation

Pyruvate is converted to Acetyl-CoA in the mitochondrial matrix After pyruvate is transported from the cytoplasm to the mitochondrial matrix: Pyruvate is broken down into Acetyl-CoA, releasing 1 CO2 and generating one NADH

step one of cellular respiration

Pyruvate oxidation to Acetyl-CoA Generatew Acetyl-CoA and 1 NADH.

2 main stages that cells convert glucose to ATP

Stage 1: Glycolysis: break down glucose to pyruvate while releasing some ATP (10 reactions) Stage 2: Cellular Respiration: if O2 is present, break down pyruvate into CO2 and H20 while generating LOTS of ATP. Alternative to Stage 2: if NO O2 is present: keep glycolysis going by Fermentation - breakdown or pyruvate into CO2 and lactic acid (muscles) or ethanol (yeast).

oxidative phosphorlytation

The ETC creates a H+ electrochemical gradient. The electrochemical gradient of H is then used to form ATP by chemiosmosis

ATP generation (chemiosmosis)

The H gradient generated by ETC  (high in intermembrane space, low in matrix) is a source of potential energy. This potential energy can be harnessed by allowing the H+ to flow back into the matrix through ATP synthase - which acts as a turbine and generates LOTS of ATP as it rotates.

glycosis goal

The overall goal of Glycolysis is to split 1 glucose molecule (a six-carbon sugar) into 2 molecules of pyruvate (a three-carbon sugar) and generate a small amount of ATP and NADH.

summary for glycosis

Used: 1 glucose; 2 ATP; 2 NAD+ Made: 2 pyruvate Various different fates pyruvate is incompletely oxidized = source of energy. If can completely oxidize pyruvate, get 18 times more ATP from glucose (aerobic) 4 ATP (net ATP production = 2) Used for energy-requiring processes within the cell 2 NADH Carry high energy electrons. Glycolysis is heavily regulated Ensures proper use of nutrients Ensures production of ATP only when need

glycosis and cellular respiration

breakdown (oxidise) sugar molecules (glucose) to make ATP (energy)

metabolism function

breakdown molecules that contains alot of energy (i.e. carbs, fats, proteins)

cellular respiration

breaks down the two pyruvate molecules into six carbon dioxide molecules and six water molecules. The chemical energy from the two pyruvate molecules aids in the production of 32 ATP

photosynthetic organisms

capture the energy of sunlight and store it in the form of glucose

Glucose activation phase

glucose is converted to highly reactive frustose biophosphate by two enzyme catalyzed reactions, using 2 ATPS

glucose

key energy storage molecule, used or stored as needed

how cells generate ATP

metabolism

cellular respiration occurs here

mitochondria (powerhouses of the cell), organelles specialized for the aerobic breakdown of pyruvate

glucose metabolism occurs

over many steps catalyzed by many enzymes

lactic acid fermentation

produces lactic acid from pyruvate Muscles that are working hard enough to use up all the available oxygen ferment pyruvate to lactate A variety of microorganisms use lactic acid fermentation, including the bacteria that convert milk into yogurt, sour cream, and cheese

fermentation

the 2nd Stage of Glucose breakdown. Occurs when O2 is NOT available. Allows NAD to be recycled so that we can continue to make some ATP even in the absence of O2(via glycolysis) In fermentation, pyruvate remains in the cytoplasm and is converted into lactate (or ethanol CO2)

ATP

the currency of cellular energy

Photosynethisis

the source of cellular energy to make fuel (glucose)