• Chapter 9

• Energy in a Cell

• Why ATP?

• Adenosine triphosphate

• ATP stores energy in the bonds between adenosine and three phosphates (which are charged).

• Bonds are easily broken because phosphates don’t like being near each other and energy is released.

• Energy in ATP

• Each time you add a phosphate group to adenosine, energy is required (and stored)

• AMP (adenosine monophosphate)

• ADP (adenosine diphosphate)

• Most energy released when ATP breaks down to ADP

• The ADP and phosphates can be recycled

• Capturing & Using Energy

• Many proteins have a special site for ATP to bond

• When ATP is broken into ADP, the protein can easily capture the energy

• Energy used to maintain homeostasis, eliminate waste, keep things going the right direction, and everything else that requires energy

• Photosynthesis

• The process that uses the sun’s energy to make simple sugars

– These sugars are then converted into complex carbohydrates

• There are two phases to photosynthesis:

– The light-dependent reactions (convert light energy into chemical energy, ATP)

– The light-independent reactions (produce simple sugars)

_•6CO₂ + 6H₂0 à C₆H₁₂O₆ + 6O₂

• The Chloroplast & Pigments

• What is the chloroplast?

• Membranes in chloroplast (thylakoid membrane) contain pigments – molecules that absorb specific wavelengths of sunlight

– The pigments are arranged in clusters known as photosystems for efficiency

• Chlorophyll is the most common pigment

– Absorbs most wavelengths of light except green

• Light-Dependent Reactions

• Light excites (energizes) electrons in the photosystems

• Electrons are passed to a series of proteins in the thylakoid called the electron transport chain (ETC).

• At each step, energy is “lost” from the electron.

• This energy is used to pump hydrogen ions into the center of the thylakoid disc.

• Light-Dependent Reactions

• After the electrons have traveled down the ETC, they are re-energized at a second photosystem and passed down another ETC.

• At the end, electrons still have energy

• Are taken to another part of the chloroplast (stroma) by an electron carrier molecule called NADP+ (nicotinamide adenine dinucleotide phosphate)

• NADP+ combines with two electrons and a hydrogen ion to become NADPH, which is used in the light-independent reactions

• Restoring Electrons

• Photosystems constantly need new electrons

• Plants split water to get molecules in a process known as photolysis (2 electrons per water molecule)

– Oxygen is released into the air

– Hydrogen is pumped into the thylakoid

• Chemiosmosis

• H+ ions build up in the thylakoid

• H+ ions diffuse out with a lot of energy and create ATP

– Like popping a hole in a water balloon

• Light-Independent Reactions

• The Calvin cycle (Melvin Calvin) is a series of reactions that use carbon dioxide to form sugars

• Takes place in the stroma of the chloroplasts

• Cellular Respiration

• The process by which mitochondria break down food molecules to produce ATP.

• Three stages:

– Glycolysis

– Citric acid cycle (Krebs cycle)

– Electron transport chain

• Glycolysis is anaerobic (no oxygen required)

• The other two stages are aerobic

• Glycolysis

• Glycolysis is a series of chemical reactions in the cytoplasm of a cell that break down glucose (6 carbons) into two molecules of pyruvic acid (3 carbons)

– 2 ATP are required

– 4 ATP are made

– 2 NADH are made

• Inbetween

• After glycolysis, pyruvic acid undergoes a series of reactions

• It changes from a 3-carbon molecule into what is called Acetyl-CoA

_•This process produces 1 NADH and 1 molecule of CO₂

• Citric Acid Cycle

• Also called the Krebs cycle

• A series of chemical reactions similar to the Calvin cycle in that the molecule used is the first reaction is also the one of the end products (4-carbon molecule)

• Products per turn of cycle (2 turns per glucose)

– 3 NADH

_–2 CO₂

_–1 FADH₂

– 1 ATP

• Electron Transport Chain

• Similar to one in chloroplasts during photosynthesis

• Energy from electrons pull protons across membrane

• Build up of protons utilized by ATP synthase to make ATP

• Final electron acceptor is oxygen

• ATP Totals from Aerobic Respiration

• 10 NADH molecules = 30 ATP

– 2 from glycolysis

– 1 when pyruvic acid changes to Acetyl-CoA

• Happens twice per glucose for a total of 2

– 3 during the citric acid cycle

• Happens twice per glucose for a total of 6

• 2 FADH₂ molecules = 4 ATP

– 1 during the citric acid cycle

• Happens twice per glucose for a total of 2

• 2 ATP during glycolysis

– 4 ATP are made, but 2 are used

• 2 ATP during citric acid cycle

– 1 per pyruvic acid

• GRAND TOTAL = 38 ATP per glucose

• Fermentation

• Anaerobic process

• Follows glycolysis and provides a means to continue producing ATP until oxygen is available again

• 2 major types:

– Lactic acid fermentation

– Alcoholic fermentation

• Lactic Acid Fermentation

• When NADH and FADH₂arrive at the electron transport chain, they cannot release their energized electrons to oxygen

• Nothing can be done with the FADH₂ – it builds up

• NADH can be converted back to NAD+ and ran back through glycolysis

• 2 molecules of pyruvic acid use two NADH to make two molecules of lactic acid

– Causes muscle cells to fatigue

• Only 2 molecules of ATP produced each time

• Alcoholic Fermentation

• Similar to lactic acid fermentation in that NADH is “recycled.”

• Instead of lactic acid being produced, alcohol and carbon dioxide are produced

– Helps bread rise

– Helps form beer and wine

– Comparing Photosynthesis & Respiration

^{Photosynthesis}	^{Cellular Respiration}
^{Food synthesized}	^{Food broken down}
^{Energy from sun stored in glucose}	^{Energy of glucose released}
^{O2 given off}	^{O2 taken in}
^{Produces sugars from PGAL}	^{Produces CO2 and H2O}
^{Requires light}	^{Doesn’t require light}
^{Occurs only in the presence of chlorophyll}	^{Occurs in ALL living cells}