Where we left off…What are the products created by photosynthesis?• Oxygen gas (released through stomata)• * GLUCOSE * (C6H12O6)These are created by autotrophs (producers) from energy in sunlight • GLUCOSE = a form of energy that is storable and transportable

• But NOT readily usable by cells• Another cellular process is required in order

to transform energy stored in glucose into the energy currency that is usable by the cell…

ATP

Intro to: Respiration• What does the word “respiration” mean to you?• What about “cellular respiration”?

• Cellular Respiration – the process by which cells make ATP by breaking down organic compounds (glucose molecules)

Photosynthesis: 6 CO2 + 6 H2O + energy (sunlight) → C6H12O6 + 6 O2

Respiration: C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + energy (ATP)

• Cellular Respiration is essentially the reverse of photosynthesis! … Just look at the formulas!

• What types of organisms perform cellular respiration?Animals?Plants?Both?

The Mitochondrion• We referred to it as the “powerhouse” of the cell• The site of cellular respiration• One of three eukaryotic organelles surrounded

by a double-membrane… what are the other two?

• Internal Organization:• Cristae – Infoldings of the inner membrane• Matrix – Space within the inner membrane

Respiration OverviewThere are two phases to the overall process of cellular respiration

• GLYCOLYSIS (try to reason what this word means)

- Glyco = Sugar

- Lysis = Breakdown • RESPIRATION

- Anaerobic Respiration (Fermentation)

▪ Air (oxygen) is not needed/absent

- Aerobic Respiration

▪ Air (oxygen) is needed/available

The Cell’s Decision

• Start with glucose

• Cleave (break up) glucose into two smaller molecules

• Decide whether or not oxygen is present

• Carry out aerobic or anaerobic respiration

…to ferment, or not to ferment?

Glycolysis• Glycolysis occurs in the cytoplasm• Another example of a biochemical

pathway, catalyzed by enzymes

• Start with glucose • 2 ATP’s are spent in the first step• *** 2 molecules of NAD+ are consumed ***• 4 ATP’s are made in the fourth step• The end result of glycolysis is:

2 molecules of pyruvic acid (3-carbon)

Efficiency of glycolysis = 3.5 %

Glycolysis isn’t getting us as much “bang for our buck” as we could be getting out of one molecule of glucose

Anaerobic RespirationRemember: after glycolysis, the cell must make a decision about what to do next• When oxygen is NOT present in the cell, it chooses to carry out:

anaerobic respiration (fermentation)

LACTIC ACID FERMENTATION• An enzyme converts pyruvic acid into lactic acid (3-carbon)• NO ATP IS MADE• *** NAD+ is created ***

ALCOHOLIC FERMENTATION

- Performed by a special set of enzymes in yeast- CO2 is given off- End product is ethyl alcohol (2-carbon)

Fermentation and You

Lactic Acid Fermentation• Think about how your body is responding when you exercise • Muscles are working hard (using ATP)• You are breathing heavy (not getting enough O2)THESE ARE PERFECT CONDITIONS FOR FERMENTATION• After a hard workout, why are your muscles sore?ANSWER: Lactic acid has built up in the cytosol

Alcoholic Fermentation• This process is the basis of the beer and wine industry • Yeast cells are added to a fermentation

mixture, and ethyl alcohol accumulates • Baking bread also depends

on this type of fermentation

Aerobic Respiration• Anaerobic respiration is sufficient for

most small, unicellular organisms• However, for organisms with higher energy requirements

(like us), the low efficiency of glycolysis is not sufficientRemember: after glycolysis, the cell must make a decision about what to do next

• When oxygen is present in the cell, it chooses to carry out aerobic respiration

2 Main Steps• The Krebs (Citric Acid) Cycle

* Occurs in the matrix of the mitochondrion• Electron Transport Chain

* Occurs on the inner membrane of the mitochondrion

The Krebs Cycle• Pyruvic acid diffuses from the cytosol

into the matrix of the mitochondria

• It is then converted into a

2-carbon molecule called

Acetyl CoA in a simple reaction that creates and releases CO2

The History of the Krebs Cycle • Discovered by Hans Krebs,

German biochemist (1900-1981)• Sometimes called the citric acid cycle

The Krebs CycleOUTPUT:• 1 molecule of Acetyl CoA is broken

down by each turn of the cycle

• Therefore, one glucose molecule causes two cyclesTherefore, one molecule of glucose yields…

• 6 molecules of NADH• 2 molecules of FADH2

• 2 molecules of ATP• 4 molecules of CO2

These molecules will be

utilized in the next (and final) step of respiration: THE ELECTRON TRANSPORT CHAIN

The Electron Transport Chain• Occurs on the inner mitochondrial membrane

• NADH and FADH2 contain high energy electrons that are passed along a transport chain (similar to the chain in the light reactions of photosynthesis)

• The energy they release is used to pump protons out of the matrix• Chemiosmosis: protons diffuse back into the matrix

through the enzyme ATP synthase • Oxygen’s role = final electron acceptor• As electrons leave the transport chain, they are combined

with oxygen and protons in order to form water…O2 + 4e- + 4H+ → 2H2O

Energy ScorekeepingGlycolysis and Anaerobic Respiration

• Yields 2 ATP per

1 glucose molecule

• 3.5% efficiency

Glycolysis and Aerobic respiration

• Yields a total of 38 ATP per 1 glucose molecule

• 66% efficiency