Chapter 9: Energy in a Cell

Energy - essential for all life

                needed to do "work"

                is produced, stored and used in living systems

ATP- adenosine triphosphate

         energy currency

         quick energy

PO₄^3- is a negatively charged ion, so it repels other phosphates

       thus, large amount of energy is req'd to bind them together

        stores large amount of energy once bound

                        AMP < ADP < ATP

Energy stored in ATP is available when it is broken down

Cycle is important b/c ATP is a renewable resource

        req's less storage space

ADP can be used for energy too

ATP does not just hydrolyze spontaneously.  Enzymes bind to

ATP to harness energy.  Phosphate is removed from ATP to

give ADP and enzyme-P_i

Uses for Cell Energy:

        making new molecules

        maintaining homeostasis

        build cell structures

        move ions against gradient (active transport)

Photosynthesis

To understand photosynthesis, you must understand the nature of light...

Visible light (sunlight) is actually a continuum of light of different wavelengths

The color of light is determined by its wavelength (as well as the energy it possesses)

R    O    Y    G    B    I    V

low energy                                                               high energy

long wavelength                                               short wavelength

The color of an object is the color of the light reflected

Plants use light energy to make chemical energy (ATP)

Chloroplasts and pigments

photosynthesis occurs in the membranes of the thylakoid discs in the chloroplasts.  Step 1 is the absorption of light by pigments.

Pigments of plants absorb specific wavelengths of light

Chlorophyll- 2 types- a and b

                absorb all light but green (so plants look green)

Photosynthesis occurs in 2 separate reactions:

        Light dependent:  light => ATP

        Light independent:  ATP => glucose

Light Dependent Reactions

sunlight ---> thylakoid membrane --> chlorophyll e^- excited -->-->----> electron transport chain ------> ATP

Second electron transport chain ------> NADP⁺ --> NADPH

NADP- nicotinamide dinucleotide phosphate, has a binding site

                for electrons

NADPH- stores energy

Electrons have to be replaced on chlorophyll before it can

absorb more light- PHOTOLYSIS- energy splits 2 waters

into oxygen and hydrogen and electrons

Light Independent Reactions

Dark reaction, carbon fixation, Calvin cycle

6 rounds of the cycle make 1 sugar

Uses carbon dioxide to make the carbon backbone of the sugar

Getting Energy to Make ATP

Cellular Respiration

Break down of food molecules to form ATP

3  steps:  glycolysis, citric acid cycle, e^- transport chain

anaerobic (no oxygen req'd)                           aerobic

1.  Glycolysis: breaks down glucose (6C) ------> pyruvic acid (3C)

                        2 ATP in ----------------------> 4 ATP out

2.  Citric Acid cycle:

 pyruvic acid => mitoch.---> acetic acid (2C) + CO₂---> acetyl coA

Net gain: 1 ATP, 2 NADH, 1 FADH₂

3. Electron Transport Chain

        on the cristae of the mitochondria

        similar to the chain found in the chloroplasts

        produces 32 net ATP-  VERY efficient

Fermentation: bacteria, yeast, sometimes our cells are w/o

                        oxygen:  electron transport chain backs up so,

glycolysis => fermentation

1. Lactic acid fermentation

                                       2NADH      2NAD⁺  -> glycolysis -> 2 ATP

glucose -------> pyruvic acid --------------> lactic acid

2.  Alcoholic fermentation (yeast make beer!)

       glucose -----> pyruvic acid ---------> carbon dioxide + alcohol