Energy in a Cell

The Need for Energy (9.1)

Photosynthesis (9.2)

Respiration and Fermentation (9.3)

The Need for Energy

Why does a cell need energy?

Active Transport (moving materials against the concentration gradient)

Cell Division

Movement (flagella or cilia)

Production, transport, and storage of proteins

Other Examples?

How does a cell store energy?

First, how does a cell get energy? Breaking bonds

So, how does a cell store energy? Forming bonds

Energy is stores in the bonds of adenosine triphosphate or ATP

How ATP stores energy Phosphate groups are negatively charged

Bonding them together requires a lot of energy Therefore, the bonds store a lot of energy

How is the energy in ATP used?

ATP binds to a cell at a specific site

The phosphate bond is broken ATP ADP

The energy from the bond is appropriated to the process that requires the energy

The ADP can be “recharged” by adding another phosphate

Obtaining Energy Autotroph vs. Heterotroph

Photosynthesis

Food synthesized

Energy from sun stored in glucose

Carbon dioxide taken in

Oxygen given off

Produces sugars

Requires light

Occurs only in the presence of chlorophyll

Respiration

Food broken down

Energy of glucose released

Carbon dioxide given off

Oxygen taken in

Produces carbon dioxide and water

Does not require light

Occurs in all living cells

vs.

Photosynthesis

The process by which organisms that contain the pigment chlorophyll convert light energy into chemical energy stored in the molecular bonds of organic molecules (e.g., sugars)

Chlorophyll absorbs most wavelengths of light (except what?)

Photosynthesis

The chlorophyll is found in the thylakoid discs of chloroplasts

Photosynthesis

6CO2 + 6H2O +light energy C6H12O6 + 6O2

Photosynthesis occurs in 2 phases Light-dependent – occurs in thylakoid discs Light-independent – occurs in stroma

Photosynthesis is not a very efficient process. Of the sunlight reaching the surface of a leaf, approximately: 75% is evaporated (heats up water in the leaf) 15% is reflected 5% is transmitted through the leaf 4% is converted to heat energy 1% is used in photosynthesis 

Photosynthesis

Light-dependent Reactions

Electron Transport Chain

Put in: Sunlight (energy)

Water (H2O)

NADP ADP

Get out:

Oxygen (O2)

NADPH ATP

Light-independent Reactions

Calvin Cycle

Put in: NADPH ATP

Carbon dioxide (CO2)

Get out: NADP ADP

Glucose (C6H12O6)

Light-dependent Reactions:The Electron Transport Chain

One molecule of chlorophyll absorbs one photon of light and looses one electron.

This electron is passed down through a chain of molecules ultimately leading to the reduction of NADP to NADPH

ATP is also formed in the process

The chlorophyll regains the lost electron from a water molecule H2O is split with photons (photolysis) O2 is released

2 H2O + 2 NADP+ + 3 ADP + 3 Pi + light → 2 NADPH + 2 H+ + 3 ATP + O2

Light-independent Reactions:The Calvin Cycle

CO2 is captured from the atmosphere, and with the energy from ATP and the hydrogen from NADPH, 3-carbon molecules are formed that will later be used to make sugars (e.g., glucose)

3 CO2 + 9 ATP + 6 NADPH + 6 H+ → C3H6O3-phosphate + 9 ADP + 8 Pi + 6 NADP+ + 3 H2O

Why make sugar for energy instead of just using ATP?

Respiration

The process by which mitochondria break down food molecules (like glucose) to produce ATP

There are several possible metabolic pathways by which cells can obtain the energy stored in chemical bonds:  Glycolysis Cellular respiration Fermentation

Glycolysis

No oxygen is required (anaerobic)

Glycolysis occurs in the cytoplasm of cells, not in organelles, and occurs in all kinds of living organisms.

Prokaryote cells use glycolysis and the first living cells most likely used glycolysis. 

Glucose Pyruvic acid + 2 ATP

Cellular Respiration:The Citric Acid Cycle (Krebs Cycle)The Electron Transport Chain

Oxygen is required (aerobic)

The products of glycolysis (pyruvic acid + 2 ATP) are transferred into the mitochondria…

…and are used in the citric acid cycle and electron transport chain to accomplish the reaction below:

C6H12O6 + 6O2 6CO2 + 6H2O + 36ATP

Fermentation

No oxygen required (anaerobic)

Lactic acid fermentation Glucose pyruvic acid (glycolysis) lactic acid + 2 ATP Occurs in muscles when oxygen deprived

Alcoholic fermentation Glucose pyruvic acid (glycolysis) carbon dioxide + alcohol

+ 2 ATP What is this used for?

Fermentation vs. Cellular Respiration