Download Introduction to: Cellular Respiration

CELLULAR RESPIRATION
Honors Biology
Chapter 9
Chemical Pathways
BASIC NEED FOR ENERGY
Energy in Food:
What is the difference between a:
calorie(lower case c) and Calorie (upper case C)?
-A calorie is the amount of energy needed
to raise the temperature of 1 gram of water
by 1 degree C.
-A Calorie is a kilocalorie, or 1000 calories
For example, 1 gram of glucose releases 3811
calories, on a food label 3.8 Calories
BASIC NEED FOR ENERGY
Energy in Food:
 The reason we eat is to get energy
 We get carbohydrates from our food which are
broken into Glucose
Organisms cannot use glucose directly, it must be
broken down into smaller units…… ATP
This process in living things begins with
glycolysis.
 If oxygen is present, glycolysis is followed by
the Krebs Cycle and electron transport chain
– This is called Cellular Respiration

AN OVERVIEW:
CELLULAR RESPIRATION
The equation for cellular respiration is exactly
the opposite of photosynthesis.
 Equation:

6O2 + C6H12O6  6CO2 + 6H2O and energy
BREAKING DOWN ENERGY SLOWLY:

Glucose needs to be broken down in small
steps so that energy is not wasted.
FIRST STEP: GLYCOLYSIS
Definition: The process of breaking the glucose
in half to form 2 molecules of pyruvate, a 3
carbon chain.
 Uses 2 ATP to start reaction
 Produces 4 ATP and 2 NADH
 Occurs in the Cytosol (not mitochondria)

GLYCOLYSIS






Does not require oxygen
Very Fast – thousands of ATP
produced in milliseconds
Stops when it runs out of NAD+
(electron carrier)
If oxygen is available: Cellular
respiration starts
If oxygen is NOT available, to
make more NAD+, your body
goes through fermentation.
This way ATP can be made even
without Oxygen.
WHY USE ATP IN GLYCOLYSIS IF YOU WANT ATP?
You have to use a
little energy to make
even more energy.
 Like a bank, you put
money in to earn
interest.
 Net ATP gained per
glucose molecule=2

Glucose
Animation
Pyruvate molecules
FERMENTATION
Fermentation is releasing energy in the absence
of oxygen. It is an ANAEROBIC process.
 Ultimately it allows NADH to be converted to
NAD+, allowing glycolysis to continue.
 There are two main types of fermentation

 Alcoholic
Fermentation
 Lactic Acid Fermentation
ALCOHLIC FERMENTATION
ALCOHOLIC FERMENTATION
Alcoholic fermentation is found in Yeasts, and a
few other microorganisms.
 The equation is:
Pyruvic acid + NADH  alcohol + CO2 + NAD+

Note: Carbon Dioxide is also produced, so when
yeast conducts fermentation, there is the
release of carbon dioxide as well as alcohol.
ALCOHOLIC FERMENTATION

Alcoholic fermentation diagram
LACTIC ACID FERMENTATION

Pyruvic acid from glycolysis can be converted to lactic acid.

This conversion regenerates NAD+ for glycolysis to
continue

The equation is:
Pyruvic acid + NADH  lactic acid + NAD+
Lactic acid fermentation is used by muscles when they run
out of oxygen, ultimately causing soreness.
Lactic acid is also created by unicellular organisms in the
production of cheese, pickles, kimchi and other foods.
LACTIC ACID FERMENTATION

Lactic Acid fermentation diagram
KREBS CYCLE

In the Krebs Cycle, pyruvic acid is broken down
into carbon dioxide.
KREBS CYCLE
Where does it occur: Mitochondria
 It requires oxygen – it is AEROBIC
 It is also known as the Citric Acid Cycle

KREBS CYCLE
1. Pyruvic acid enters the mitochondria
2. One carbon becomes part of carbon
dioxide and NAD+ becomes NADH
3. The other 2 carbons join coenzyme A to
form acetyl-CoA
4. Acetyl-CoA adds to a 4-carbon molecule
producing citric acid
Animation
KREBS CYCLE
5. The citric acid is broken down to a 5carbon molecule
6. Carbon dioxide is released and NAD+
becomes NADH
7. The 5-carbon compound is broken into
a 4-carbon compound
8. Carbon dioxide is released and NAD+
becomes NADH, ADP also becomes ATP
Animation
KREBS CYCLE
9. The 4-carbon compound is recycled, to
be used again in the cycle
10. FAD is converted into FADH2
11. NAD+ is converted into NADH
So far, from 1 glucose
Glycolysis produced: 2 NADH and 2 ATP
Krebs Cycle produced: 8 NADH and 2 FADH2 and 2 ATP
Animation
KREBS CYCLE
KREBS CYCLE
What happens to the Krebs cycle products?
Carbon Dioxide is released to the atmosphere
ATP is used for cellular activities
NADH and FADH2 are used in the electron
transport chain to produce large amounts of ATP
ELECTRON TRANSPORT CHAIN

Uses the high energy electrons from the Krebs
cycle to convert ADP into ATP
ELECTRON TRANSPORT CHAIN
Where does it occur: Inner membrane of the
Mitochondria
 It requires oxygen – it is AEROBIC

ELECTRON TRANSPORT CHAIN
1.
2.
3.
4.
Electrons from the NADH are transferred to
carrier proteins
These electrons transport H+ across the
membrane
Electrons move down the chain, allowing
additional H+ movement
At the end of the chain, oxygen accepts
electrons, and left over H+, creating water
Animation
ELECTRON TRANSPORT CHAIN
ELECTRON TRANSPORT CHAIN
5. The H+ buildup on the other side of the
membrane creates a gradient
6. The H+ moves through ATP synthase,
spinning the protein
7. Each rotation charges an ADP, attaches
a phosphate, and creates ATP
Animation
CELLULAR RESPIRATION TOTALS
So far, from 1 glucose
Glycolysis:
2 ATP
Krebs Cycle:
2 ATP
Electron Transport:
32 ATP
Totals:
36 ATP from 1 glucose molecule
This is 38% efficiency
The rest of the energy is released as heat
ENERGY USE BY HUMANS
Cells contains small amounts of ready ATP
-About 5 seconds worth
After that, your body uses lactic acid formation
-This lasts for about 90 seconds
-You breathe hard to get rid of the lactic acid buildup
For exercise longer than 90 seconds, cellular
respiration is used
-This is a slow method to generate ATP
-Glycogen (a form of carbohydrate) is used for the first 15-20
minutes of cellular respiration
-After that other molecules, such as fats, are broken down