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Part 2:
Cellular Respiration
Cellular Respiration
The Energy Compound: ATP
The Energy Compound: ATP
Organisms use different chemical compounds to store and release energy.
One of the principal chemical compounds that cells use to store and release energy is ADENOSINE TRIPHOSPHATE, also known as ATP.
One of the principal chemical compounds that cells use to store and release energy is ADENOSINE TRIPHOSPHATE, also known as ATP.
ATP is made up of:
Adenine (a nucleotide),
Ribose (a 5-carbon sugar)
Three Phosphate Groups held together by high energy bonds. The three phosphate groups are the key to ATP's ability to store and release energy.
Adenosine Diphosphate (ADP) is a compound that looks a lot like ATP but with one very important exception. Instead of having three phosphate groups ADP only has TWO.
Adenosine Diphosphate (ADP) is a compound that looks a lot like ATP but with one very important exception. Instead of having three phosphate groups ADP only has TWO.
This difference is the key to way in which living things store energy.
STORING ENERGY
STORING ENERGY
When a cell has energy available, it can store small amounts of it by adding a phosphate group to ADP molecules, turning it into ATP.
RELEASING ENERGY
RELEASING ENERGY
When a cell needs to release energy to power a biological process it breaks a bond between one of the phosphate groups in ATP, turning it into ADP. The breaking of the bond releases energy!
So in a weird way ATP is like a fully charged battery ready to power the cell and the organism.
ATP has enough energy to power a variety of cellular activities, including:
ATP has enough energy to power a variety of cellular activities, including:
- active transport across cell membranes
- protein synthesis (making proteins)
- muscle contraction.
- initiating chemical reactions
- AND MORE!
The characteristics of ATP make it exceptionally useful as the basic energy source of all cells!
The characteristics of ATP make it exceptionally useful as the basic energy source of all cells!
ATP and Glucose
ATP and Glucose
Most cells have only a small amount of ATP, enough to last only a few seconds of activity. This is because ATP is only very good at transferring energy and not good for storing large amounts of energy for a long period of time.
Most cells have only a small amount of ATP, enough to last only a few seconds of activity. This is because ATP is only very good at transferring energy and not good for storing large amounts of energy for a long period of time.
So what's a better way for cells to store energy? GLUCOSE!!
So what's a better way for cells to store energy? GLUCOSE!!
A single molecule of the sugar glucose store more than 90 times the chemical energy of a molecule of ATP. Cells regenerate ATP and ADP only when needed by using the energy in carbohydrates (sugars) like glucose.
F O O D. We all love it, but why do we need it? Well, food provides living things with the chemical building blocks they need to grow and reproduce. Food serves as a source of raw materials for the cells of the body. Most of all, food serves as a source of energy.
F O O D. We all love it, but why do we need it? Well, food provides living things with the chemical building blocks they need to grow and reproduce. Food serves as a source of raw materials for the cells of the body. Most of all, food serves as a source of energy.
Cells gradually release the energy from glucose and other food compounds. Cells can do this with OXYGEN present; this is AEROBIC CELLULAR RESPIRATION. And without OXYGEN being present this is known as FERMENTATION or Anaerobic Cellular Respiration.
Cells gradually release the energy from glucose and other food compounds. Cells can do this with OXYGEN present; this is AEROBIC CELLULAR RESPIRATION. And without OXYGEN being present this is known as FERMENTATION or Anaerobic Cellular Respiration.
AEROBIC VS. ANAEROBIC
AEROBIC VS. ANAEROBIC
Aerobic means something does require oxygen.
Aerobic means something does require oxygen.
Anaerobic means something does NOT require oxygen.
Anaerobic means something does NOT require oxygen.
Much more ATP energy is able to be produced using Aerobic Cellular Respiration!
Much more ATP energy is able to be produced using Aerobic Cellular Respiration!
Typically when we refer to Cellular Respiration we are actually referring to Aerobic Cellular Respiration which is made up of the reactions Glycolysis, the Krebs Cycle, and the Electron Transport Chain.
Typically when we refer to Cellular Respiration we are actually referring to Aerobic Cellular Respiration which is made up of the reactions Glycolysis, the Krebs Cycle, and the Electron Transport Chain.
Cellular respiration is the process that releases energy by breaking down glucose and other food molecules in the presence of oxygen.
Cellular respiration is the process that releases energy by breaking down glucose and other food molecules in the presence of oxygen.
There are three main stages of (aerobic) cellular respiration:
There are three main stages of (aerobic) cellular respiration:
- Glycolysis - Cytoplasm/cytosol
- Krebs Cycle - mitochondrial matrix
- Electron Transport Chain - inner mitochodrial membrane
Where does it happen?
Where does it happen?
Aerobic Cellular Respiration Takes Place in the Cytoplasm & the Mitochondria of cells.
Aerobic Cellular Respiration Takes Place in the Cytoplasm & the Mitochondria of cells.
The Locations:
The Locations:
STEP ONE:
Glycolysis takes place in the cytoplasm.
STEP TWO:
The Krebs Cycle takes place inside the mitochondrial matrix.
STEP THREE:
The Electron Transport Chain takes place within the inner mitochondrial membrane.
What happens during (aerobic) Cellular Respiration?
What happens during (aerobic) Cellular Respiration?
Each of the three stages of aerobic cellular respiration captures some of the chemical energy available in glucose sugar and uses it to produce ATP energy!
Each of the three stages of aerobic cellular respiration captures some of the chemical energy available in glucose sugar and uses it to produce ATP energy!
Glycolysis
Glycolysis
The process in which one molecule of glucose, a 6-carbon molecule. is broken in half, producing two molecules of pyruvic acid (pyruvate), a 3-carbon compound.
2 ATP molecules are produced during glycolysis
2 ATP molecules are produced during glycolysis
Glyco = sugar, and lysis = break so glycolysis is the breaking of (glucose) sugar!
Location: Cytoplasm
The Krebs Cycle
The Krebs Cycle
The second stage of cellular respiration that occurs in the presence of oxygen. During the Krebs cycle, pyruvic acid is broken down into carbon dioxide (which is released) in a series of energy reactions that transfer high energy electrons to other molecules.
2 ATP molecules are produced during the Krebs Cycle
2 ATP molecules are produced during the Krebs Cycle
The Krebs Cycle is also known as the Citric Acid Cycle because citric acid is a molecule created during this cycle.
Location: Mitochondrial Matrix
The Electron Transport Chain
The Electron Transport Chain
The third stage of cellular respiration that uses high-energy electrons created during the Krebs cycle to convert ADP into ATP.
34 ATP molecules are produced during the Electron Transport Chain
34 ATP molecules are produced during the Electron Transport Chain
Location: Inner Mitochondrial Membrane
(Anaerobic) Fermentation
(Anaerobic) Fermentation
When oxygen is not present, glycolysis is followed by a different pathway. The combined process of this pathway and glycolysis is called FERMENTATION.
When oxygen is not present, glycolysis is followed by a different pathway. The combined process of this pathway and glycolysis is called FERMENTATION.
Fermentation: a process in which energy is released from food molecules by producing ATP in the absence of oxygen.
Fermentation: a process in which energy is released from food molecules by producing ATP in the absence of oxygen.
During fermentation, cells convert NADH to NAD+ by passing high-energy electrons back to pyruvic acid. This action converts NADH back into the electron carrier NAD+ allowing glycolysis to continue producing a steady supply of ATP.
The goal of fermentation is to create more of the reactants that glycolysis needs to continue so that glycolysis can keep making ATP. Though glycolysis doesn't make a lot of ATP energy (it only makes 2 ATP per molecule of glucose), some energy is still better than no energy at all!
Because fermentation does not require oxygen, it is said to be ANAEROBIC. Anaerobic means "not in air".
The two main types of fermentation are alcoholic fermentation & lactic acid fermentation.
The two main types of fermentation are alcoholic fermentation & lactic acid fermentation.
Alcoholic Fermentation
Alcoholic Fermentation
Yeasts and a few other microorganisms use alcoholic fermentation, forming ethyl alcohol and carbon dioxide as wastes.
The equation for alcoholic fermentation after glycolysis is:
The equation for alcoholic fermentation after glycolysis is:
pyruvic acid + NADH --> alcohol + CO2 + NAD+
Lactic Acid Fermentation
Lactic Acid Fermentation
In many cells the pyruvic acid that is made in glycolysis can be converted into lactic acid. Because this type of fermentation produces lactic acid, it is called lactic acid fermentation. This process regenerates NAD+ so that glycolysis can continue.
The equation for lactic acid fermentation after glycolysis is:
The equation for lactic acid fermentation after glycolysis is:
pyruvic acid + NADH --> lactic acid + NAD+
Fun Fact:
Fun Fact:
When you are being physically active (i.e. exercising) and using a lot of energy your muscle cells begin to produce ATP by lactic acid fermentation. The buildup of lactic acid causes a painful, burning sensation.
Can you feel the burn!!??
ATP Energy Totals
ATP Energy Totals
How many ATP molecules can be made from one glucose sugar molecule?
How many ATP molecules can be made from one glucose sugar molecule?
The Totals
The Totals
FERMENTATION (ANAEROBIC CELLULAR RESPIRATION)
FERMENTATION (ANAEROBIC CELLULAR RESPIRATION)
During GLYCOLYSIS (which can occur with or without oxygen present) cells produce just 2 ATP molecules per molecule of glucose. Lactic acid fermentation and alcoholic fermentation does not create ATP on their own.
AEROBIC CELLULAR RESPIRATION
AEROBIC CELLULAR RESPIRATION
But in the presence of oxygen (aerobic environment) everything changes! When oxygen is present glycolysis is followed by the Krebs Cycle and then the Electron Transport Chain!
2 ATP molecules are made during the KREBS CYCLE, and 34 ATP molecules can be made during the ELECTRON TRANSPORT CHAIN.
That means that AEROBIC CELLULAR RESPIRATION allows for a cell to produce around 36-38 ATP molecules per glucose molecule!
Fun Fact:
Fun Fact:
Our diets contain much more than just glucose! These other organic molecules can be turned into ATP energy using aerobic cellular respiration! Complex carbohydrates are broken down into simple sugars like glucose. Lipids and proteins can be broken down into molecules that enter the Krebs cycle or glycolysis at different points in the process. Thus, the cell can generate chemical energy in the form of ATP from just about any source!
The BIG Picture:
The BIG Picture:
The diagram on the left shows how many ATP molecules can be produced in each step of cellular respiration (which is aerobic) and fermentation (which is anaerobic).
The diagram on the left shows how many ATP molecules can be produced in each step of cellular respiration (which is aerobic) and fermentation (which is anaerobic).
Part 3:
Part 3:
Comparing the Reactions
Comparing the Reactions
The energy flows in photosynthesis and cellular respiration take place in opposite directions.
Photosynthesis is the process that "DEPOSITS" chemical energy.
Photosynthesis is the process that "DEPOSITS" chemical energy.
Cellular Respiration is the process that "WITHDRAWS" energy.
Cellular Respiration is the process that "WITHDRAWS" energy.
In Photosynthesis organisms STORE ENERGY in GLUCOSE.
In Cellular Respiration, organisms RELEASE the ENERGY stored in GLUCOSE.
The equations for photosynthesis and cellular respiration are the reverse of each other.
The equations for photosynthesis and cellular respiration are the reverse of each other.
Carbon Dioxide & Oxygen
Carbon Dioxide & Oxygen
Photosynthesis removes carbon dioxide from the atmosphere, and Cellular Respiration puts it back.
Photosynthesis releases oxygen into the atmosphere and Cellular Respiration uses that oxygen to release energy from food.
The release of energy by cellular respiration takes place in ALL Eukaryotes (plants, animals, fungi, and protists) and some prokaryotes (bacteria, archaea).
The release of energy by cellular respiration takes place in ALL Eukaryotes (plants, animals, fungi, and protists) and some prokaryotes (bacteria, archaea).
Energy capture by photosynthesis only occurs in plants, algae, some bacteria, and some protists.
Energy capture by photosynthesis only occurs in plants, algae, some bacteria, and some protists.
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