Photosynthesis and...

Chapter 9

Quiz #11: You will be able to describe the structure and function of

ATP

You will be able to identify the inputs and outputs of each process of respiration and photosynthesis.

You will be able to identify the important steps of each process.

You will be able to locate when and where each process occurs in the cell.

The three main laws of thermodynamics are three of the most important statements in science.

They must be followed anytime you are dealing with energy transfers.

1) Energy cannot be created or destroyed. Energy can only change forms

2) Systems of energy tend to move towards randomness

3) Energy never stops flowing from one place to another

Every action by every organism on the planet is only possible thanks to different energy forms.

Fundamental energy (basic life tasks) Roots absorbing water, breathing

Immediate energy (sudden bursts) Flowers blooming; walking

Long term energy (savings account) Fruits, vegetables and nuts; Fat storage

Emergency energy (oh look! A tiger…) Flytraps; Epinephrine (Adrenaline)

We have lots of different forms of energy in our world. Coal, oil, solar, wind, water, ethanol

Our energy sources are the food we consume.

These are good energy sources, but we can’t use them as energy until we convert them into a useful source. I don’t power up my cell phone with water; I power it up

with electricity produced by the energy of water moving through a dam.

Before our bodies can use the energy from food, we have to turn food, liquids and gasses into a usable power source called an ATP molecule

ATP is a nucleic acid molecule holding together three molecules of phosphates.

ATP can be used in our body both as a unit of power (just like electricity) and as a unit of energy storage (just like a battery).

Phosphates do not easily bond to each other, like two positive ends of magnets trying to repel.

The only way to hold the phosphates together is with high amounts of energy

Therefore as long as the 3 phosphates are attached to each other, the ATP is holding large amounts of energy

It can carry this energy anywhere in the cell

ATP

ADP Phosphate

P P P

P P

P

How does the cell “plug in” ATP to use it’s energy?

ATP is highly unstable. It wants to break off one of the phosphate molecules.

All enzymes have a special site that is shaped to fit a phosphate molecule.

ATP will release its phosphate into an enzyme, effectively “plugging in the battery.”

Now, once the enzyme finds its substrate, it has enough power to perform it’s function

ATP, after having given up a phosphate, is now ADP (Adenosine Diphosphate)

ATP is so unstable, it only exists for microseconds.

Every cell in every organism needs to constantly be powering up new ATP molecules to replace the used ones.

In this chapter we will talk about respiration, fermentation, and photosynthesis.

Each of these are processes that plants, animals, fungi and bacteria use to recharge their ADP molecules into ATP

Essentially, these processes are the power plants of cells.

Cell respiration is the primary process of energy production for animals, and a secondary process for plants.

Respiration consists of three stages. Each stage requires different inputs and outputs and run under different circumstances.

The equation for cell respiration is

6O2 + C6H12O6 6CO2 + 6H2O + energy

*Note: Glucose is a 6-carbon molecule*

Notice that one of the inputs for cellular respiration is a glucose molecule.

One gram of glucose releases 3811 calories of heat energy Because a calorie is so small, food labels, workout

machines, etc, all measure calories as a kilocalorie (1000 calories) and label it with a capital “C”.

What we don’t want to do is burn all of those calories at once. We want to break the glucose into pieces and use only a little at a time.

Glycolysis is the first step of cell respiration. It occurs in the cytoplasm.

Glycolysis is ten steps long. It begins with a molecule of glucose. Here are the important steps: Step 1 and Step 3 require ATP to be used. (As is typical in

life, you have to spend some now in order to earn more later)

Step 4 and 5 split the glucose into two 3-carbon molecules called PGAL

From now on, each step of cell resp. will happen twice, one for each molecule of PGAL produced.

In step 6, a molecule of NAD+ becomes NADH. This will be used later.

In steps 7 and 10 each, one ADP becomes an ATP.

At the end of glycolysis, the cell has built two molecules of pyruvic acid. These two molecules can now enter one of three

different stages of energy production.

Inputs of glycolysis: 1 glucose, 2 ATP

Outputs of glycolysis: 2 pyruvic acids, 4 ATP, 2 NADH

Net Gain: 2 Pyruvic Acids, 2 ATP, 2 NADH

Glycolysis is constantly occurring in the cell.

Where the pyruvic acids go next depends on your situation and environment. 1st, is there any oxygen present?

2nd, why do you need the energy? Are you exercising? Fatigued? In danger?

If oxygen is present, your cell will go through aerobic respiration (Citric Acid Cycle and Electron Transport Chain)

If oxygen is not present, your cell will go through anaerobic respiration (Fermentation)

Before the pyruvic acids enter the Citric Acid cycle, they have to do what is called the “intermediate step”

The pyruvic acid enters the mitochondria

The 3-carbon pyruvic acids give off a CO2 molecule and become a 2-carbon molecule called “acetyl-CoA.”

Also, another molecule of NADH is formed

Now, the acetyl-CoA can enter the Citric Acid Cycle

The citric acid cycle takes place in the mitochondria.

The cycle is six steps long. It begins with one molecule of acetyl-CoA.

There is one complete cycle for every molecule of acetyl-CoA, but two for every molecule of glucose.

The first step of the cycle is when a molecule of acetyl-CoA (a 2-carbon molecule) bonds with a 4-carbon molecule to form a 6-carbon molecule (Citric Acid)

During one cycle, 2 carbons are removed to produce CO2 and the original molecule becomes a 4-carbon molecule again.

During one cycle, the cell also produces one molecule of ATP, 3 molecules of NADH, and one molecule of FADH2

Net gain for one molecule of acetyl-CoA (for every glucose): 1 (2) ATP

3 (6) NADH,

1 (2) FADH2,

2 (4) CO2

The electron transport chain follows glycolysis and the citric acid cycle.

The ETC takes place in the inner membrane of the mitochondria.

You have seen that during the first two stages we have produced many molecules of NADH and FADH2. They will be used here in the ETC.

The ETC is powered thanks to the concept of diffusion and equilibrium

The ETC is a series of carrier proteins embedded in the inner mitochondrial membrane.

NADH and FADH2 are like ATP because they are power sources (think, miniature batteries).

The NADH and FADH2 give off an electron which powers each protein channel in sequence.

The function of these proteins is to move hydrogen atoms from inside the membrane to outside the membrane.

This creates an unequal ratio of hydrogen atoms along the membrane. The membrane is NOT in equilibrium

The only way for the hydrogen atoms to get back across the membrane is through a special protein channel enzyme called ATP synthase.

ATP synthase looks like an upside-down light bulb.

As the hydrogen atoms pass through the ATP synthase, they provide power to the enzyme.

When the enzyme has power, it attaches phosphates to ADP molecules in the “bulb” part and produces an ATP molecule.

Each molecule of NADH powers the ETC enough to build 3 molecules of ATP FADH gives a little less power and can build only 2 ATP

This means the ETC can produce a total of 32 ATP per glucose molecule.

Add that to the four ATP already produced, you have a maximum-possible net gain of 36-38 ATP molecules from 1 molecule of glucose.

To remove the electron from the ETC, the cell bonds it with a molecule of oxygen. This is why you need to breathe. This is what the oxygen

is used for.

If no oxygen is present (holding your breath, underwater, asthma, etc) the pyruvic acid will not go through the citric acid cycle. You can only get energy through glycolysis.

For glycolysis to start again, you need the NADH to become NAD+ again. This happens in fermentation.

There are two types of fermentations Alcoholic fermentation: The NADH becomes NAD+,

with alcohol as a waste product

Only performed by yeasts and microorganisms (animals don’t do this)

Pyruvic acid + NADH Alcohol + CO2 + NAD+

Lactic Acid fermentation: muscles convert NADH back to NAD+ and produce Lactic Acid as waste.

Pyruvic acid + NADH Lactic Acid + NAD +

Muscles have enough ATP readily available for a few seconds of intense exercise.

After that, if the exercise is anaerobic (sprinting, swimming, lifting weights), ATP is produced via lactic acid fermentation.

The average human being can only handle this for approximately 90 seconds. Then they need oxygen.

Lactic acid is helpful for a few seconds, but harmful long term. Oxygen is required to remove the lactic acid and relieve the soreness felt in your muscles This is why you breath deep after intense exercise

For exercise longer than 90 seconds, the body forces the organism to take in oxygen. This allows the cells to enter aerobic respiration.

What is the main source of energy for all life? The sun!

Plants need to be able to capture light and transform it into a usable energy source.

The process of using energy from the sun to make sugars for energy storage or usable energy is called photosynthesis.

The equation for photosynthesis is

Energy + 6 CO2 + 6 H20 C6H12O6 + 6 O2

Note: this is the exact opposite of the cell respiration equation

Photosynthesis is two parts: Light-dependent and Light-Independent Reactions

Photosynthesis takes place in the chloroplast of plant cells.

Chloroplasts contain stacks of disks called thylakoids. Each thylakoid contains different types of pigments.

Pigments are the chemicals that run photosynthesis.

The most common type of pigment is chlorophyll.

Chlorophyll absorbs all wavelengths of sunlight except for the color green, which it reflects.

This is why plant leaves and stems are most often colored green.

When sunlight strikes the pigments in the plant cells, it energizes these pigments (think, solar panels)

The pigments are then able to take this energy and add an electron to an NADP+ molecule into an NADPH. The source of the electron is H2O

The pigments also use an electron transport chain to produce ATP.

**Not much ATP is produced. But it’s all from the sun’s energy so, for the plant, it’s all free**.

What do plants do with this energy? And how do they survive during winter, or when the sun isn’t shining, or when their leaves have fallen?

Plant cells go through a process called the Calvin cycle immediately after the light reactions.

The Calvin cycle uses energy from ATP built in the light reactions to produce sugars for respiration. Plant cells undergo both photosynthesis AND

respiration; animal cells only undergo respiration.

The Calvin cycle takes place in the stroma (the space inside the chloroplast in between the thylakoids)

The first step of the Calvin cycle is called carbon-fixation, because three molecules of CO2 are attached to three 5-carbon molecule called RuBP (Ribulose Bisphosphate)

Throughout the next series of steps, the three 6-carbon molecules are rearranged into six 3-carbon molecules.

One of these 3-carbon molecules leave the chloroplast and are used to build sugars.

The other five 3-carbon molecules are recombined to build new RuBP molecules so that the cycle can begin again.

The Calvin Cycle requires 18 ATP and 12 NADPH for power. But it gets this power from the sun.

In the Light Reactions H2O and Sunlight are required (free energy)

ATP and NADPH are produced

In the Calvin Cycle CO2 is required

The ATP and NADPH from the light reactions are needed

Glucose (and other sugars like starch, maltose, cellulose, etc) are produced

The inputs of energy come entirely from the sun. The benefits of that energy go entirely to the plant!

Cell Respiration Photosynthesis

Sugars are broken down Sugars are built

Glucose is main source of energy Sun is main source of energy

CO2 given off CO2 taken in

Oxygen taken in Oxygen given off

Produces water Requires water

Does not require light Requires light

Occurs in all living cells Occurs only in presence of pigments

QUIZ 11: The job of insulin is to tell the liver to absorb blood

glucose after a meal.

Diabetes 1 is the inability of the pancreas to produce insulin.

Explain how Diabetes 1 can eventually lead to death from lack of available ATP.