Topic #7

Cellular Respiration

Cellular Respiration and Energy

How much energy is in food?

How is it measured?

A calorie is the amount of energy needed to raise 1 gram of water 1 degree celcius.

The calorie on food packages is actually a kilocalorie so 1,000 calories.

Cellular Respiration and Energy

Cells don’t just burn food…

They gradually break down the molecules to slowly release the energy in their chemical bonds to create ATP.

ATP as we know powers cell activities.

Cellular Respiration and Energy

The complex process in which cells make ATP by breaking down organic compounds is known as cellular respiration.

Cellular Respiration and Energy

The equation for cell respiration is:

O2 + Glucose CO2 + H2O + Energy

*Seem familiar!!!

Cellular Respiration and Energy

Cellular respiration begins with a biochemical pathway called glycolysis.

If there is no oxygen present in the cell the products of glycolysis will undergo the fermentation pathway

Cellular Respiration and Energy

This pathway that occurs in the absence of oxygen is known as anaerobic pathways, NO additional ATP is produced by this pathway.

In the presence of oxygen aerobic pathways produce a much larger amount of ATP then glycolysis does alone.

Cellular Respiration and Energy

What is the relationship between photosynthesis and cell respiration?

Photosynthesis removes CO2 from the atmosphere and cell respiration puts it back.

Cell Respiration removes O2 from the atmosphere and photosynthesis puts it back.

Glycolysis

In the glycolysis pathway one six carbon glucose molecule is oxidized to produce two three carbon pyruvic acid molecules.

Glycolysis

Glycolysis takes place in the cytosol of the cell.

Glycolysis needs 2 ATP molecules to start the chemical reactions.

It results in 4 ATP molecules so there is a net gain of 2 ATP’s from glycolosis.

Glycolysis

In glycolysis 4 electrons are removed from glucose and used to make NADH from NAD+…(NOT NADPH BUT SIMILAR)

Glycolysis

Glycolysis makes a relatively small amount of energy so why do it?

SPEED…it can make large amounts of energy in a few milliseconds!!!

It also produces pyruvic acid which is an essential reactant for the Krebs Cycle!!!

Krebs Cycle

The Krebs Cycle (aka Citric Acid Cycle) breaks down pyruvic acid into CO2 in a set of energy extracting reactions.

It occurs within the mitochondria!!!

Krebs Cycle

The three carbon pyruvic acid has a carbon removed and released as CO2

The two carbons which are left are converted to acetyl-CoA.

The acetyl-CoA is added to a four carbon molecule which is already present.

Krebs Cycle

This six carbon molecule called citric acid has the two carbons systematically broken off….the carbon is released as CO2.

This breakdown gives energy to produce NADH, ATP and FADH2…ALL ARE HIGH ENERGY MOLECULES!!!

Krebs Cycle

NADH and FADH2 are electron carriers which take electrons to the electron transport chain (ETC) so they can be used to produce ATP from ADP and a Phosphate.

Krebs Cycle

While these electrons are transported by the ETC they help pump H+ ions out of the mitochondrial matrix.

This causes a charge difference within the mitochondria.

ATP is produced by ATP synthase when the H+ ions are pumped back into the matrix.

Krebs Cycle

H+ ions and low energy electrons (Low energy because they have been used by the ETC) must be removed as water by being added to Oxygen.

Krebs Cycle

So for every glucose molecule 38 ATP molecules are produced and 36 are gained…REMEMBER the 2 used in glycolysis!!!

The rest of the energy held in glucose is released as heat…that is why you feel hot after exercise!!!

Fermentation

When there is no oxygen available to drive the krebs cycle fermentation will be used to release energy from food to make ATP.

Fermentation

There are two common fermentation pathways, they differ in enzymes used and products from pyruvic acid.

Fermentation

The first is lactic acid fermentation, an enzyme converts pyruvic acid into another three carbon compound called lactic acid.

Fermentation

After the same four steps of glycolysis occur an enzyme splits 2 H+ from 2 NADH+ and they are added to the pyruvic acid resulting in 2 lactic acid molecules.

Fermentation

Lactic acid fermentation plays an important role in manufacturing process of cheese and yogurt.

Fermentation

Lactic acid fermentation occurs in the muscles when strenuous work is being done the pain and cramping that results from working out is a result of a build up of lactic acid.

Fermentation

Some plant cells and yeast use a process of anaerobic respiration called alcoholic fermentation.

Fermentation

In this pathway pyruvic acid is produced through glycolysis in the same process but from pyruvic acid ethyl alcohol is produced.

Fermentation

Alcoholic fermentation is used by humans to produce alcohols such as wine, beer and liquor. It is also used to make bread, but the alcohol evaporates off in the cooking process.

Fermentation

The energy yielded from anaerobic respiration depends on how much energy glucose contains at the start and how much energy the ATP at the end is worth.

How Much Was Put In vs. How Much is Taken Out