Biology 30 Energy in Cells (O3) Need for Energy

All living organisms need energy in order to survive. It is essential to life.

Living organisms are endergonic systems o Requires the absorption of energy

Energy is used in cells for a variety of purposes: o Active transport through a membrane o Cell division o Transport of materials in a cell o Synthesis (making proteins)

ATP

ATP is the universal way that energy is exchanged in all biological systems.

No matter what type of energy source (food) that an organism uses, eventually it gets converted to ATP.

ATP reaction is written as: ADP + Pi + energy ---> ATP

o ATP = adenosine triphosphate o ADP = adenosine diphosphate o Pi = inorganic phosphorus

The forming of ADP into ATP : o requires energy (endothermic) o Note: Forming ATP is like charging a re-chargeable battery. ADP is the battery in need

of charging (Pi and Energy) Photosynthesis

Recall: o Cells use energy during ACTIVE TRANSPORT

to move important molecules into the cell. Where does this energy come from?

o All animals are heterotrophs – meaning they require food to survive. There are a number trophic levels:

We do not make our own food for energy like plants, algae and some bacteria and archaea. This is summarized by the carbon-oxygen cycle below:

o This means that autotrophs take in carbon dioxide, water, and light energy to make organic compounds (sugars) and oxygen. These products (sugars and oxygen) are used by autotrophs and heterotrophs to produce energy in a process called cellular respiration.

Autotrophs under go PHOTOSYNTHESIS to produce sugars (starches made up of glucose molecules)—we say the sun’s energy is stored in a chemical bond.

The basic equation for photosynthesis is:

UV energy + CO2 + 6H2O C6H12O6 + 6 O2

This is the simple equation for photosynthesis, but MANY reactions occur inside the chloroplast.

The chlorophyll in chloroplasts is one pigment (a green one, there are others) that absorbs sun energy. This absorbed energy excites electrons and causes a phosphate to attach to ADP molecules (making ATP!)

Parts of Photosynthesis

In photosynthesis there is part of the reaction that requires sunlight, and there is part of the reaction that does not require sunlight.

The light dependent part (part that requires light) is called the photochemical portion of the reaction. This is where oxygen and ATP are produced.

The light independent part (part that does not require light) is called the thermochemical portion of the reaction. This portion is also known as The Calvin Cycle. This is where sugar is produced.

The whole point of these reactions is to make a safe, energy rich molecule, which is glucose. Chemosynthesis

In this process, we can still produce energy without sunlight.

In chemosynthesis, chemical energy from inorganic molecules, like sulfur, is used as food to make energy (ATP).

Ex. organisms which live in very hot water near hydrothermal vents. (usually archaebacteria)

https://www.youtube.com/watch?v=BLOUFrncG7E

https://www.youtube.com/watch?v=D69hGvCsWgA

Cellular Respiration

The purpose of cellular respiration is to get energy from sugars to produce ATP.

When we consume the sugars from plants, (producers) or animals that have eaten plants (primary consumers), energy from the sugar bonds is released.

The release of this energy is called respiration. o It is called respiration because it requires oxygen.

This process can be summarized as:

o When animals and plants consume energy molecules like

starch and glucose, many reactions occur. o Glycolysis (anaerobic) o Citric Acid Cycle (aerobic) o Electron Transport Chain

The Citric Acid Cycle and the Electron Transport Chain occur inside the mitochondrion.

Animation: o https://www.youtube.com/watch?v=4Eo7JtRA7lg

We will look at each of these processes in turn: Cellular Respiration: Glycolysis

Glycolysis is the only metabolic pathway shared by ALL organisms.

Is a 10-enzyme step process

Occurs in the cytoplasm. o i.e. not in an organelle

Glycolysis releases a 2 – ATP molecules per glucose molecule that are used to drive other reactions

This process does not require O2 (Anaerobic) NOTE: From here, pathways diverge in different organisms and in different situations—oxygen poor (anaerobic) and oxygen rich (aerobic). Cellular Respiration: Citric Acid Cycle (CAC)

This is also known as the Krebs Cycle.

The CAC occurs inside the mitochondrial matrix.

It is called a cycle, because one of its end-products is recycled in the cycle.

Forms several intermediate energy molecules: o GTP o NADH o FADH2.

Named because it forms citric acid – an important intermediate molecule.

Produces ATP (2) and CO2.

Cellular Respiration: Electron Transport Chain (ETC)

From the Krebs cycle (Citric Acid cycle) inside the mitochondrion, the ETC occurs inside the mitochondrial membrane.

This is where oxygen is consumed, and water formed.

It causes a cascade of energy release by using the other energy molecules of NADH, FADH2 to cash in and make more ATP (30).

Cellular Respiration: SUMMARY

When we break down 1 glucose molecule we get the following ATP produced:

2 glycolysis - 2 (Start CAC)+ 2 CAC + 30 ETC = 32 ATP

SO, back to our original reaction—the important component is the ENERGY:

C6H12O6 + 6O2 6CO2 + 6H2O + 32ATP

We now know: o where oxygen is consumed, (ETC) o how CO2 is generated, (CAC) o where the H2O comes from (ETC) o and how many energy molecules are made.

Anaerobic Respiration

The normal process of cellular respiration requires OXYGEN!

If no oxygen continues to be present or, in some organisms like yeast, where it is not used, fermentation occurs.

This is also known as anaerobic respiration.

Uses the 3-C (sugars) molecules (end product of glycolysis) and makes lactic acid in our muscles or in yogurt or ethanol (as in brewing).

Only another 2 ATP molecules (NOT the 32 in aerobic respiration) are made

This occurs with some fungi, and with Lactobacillus acidophilus in yogurt, and in yeasts.

This is the basis of cheese, yogurt, buttermilk, root beer (real root beer), breads, wines, spirits. Interesting Side Note:

In vigorous exercise, lactic acid builds up in our muscles when we’ve exhausted the oxygen supply in our haemoglobin

o i.e. We produce more lactic acid than our cells can remove and they begin to seize up creating pain.

Athletes can increase their tolerance for lactic acid.