Photosynthesis and Respiration

Energy and ATP• ATP

– Adenosine triphosphate

– Adenine, 5-carbon sugar, 3 phosphate groups

• ADP– Adenosine

diphosphate– Adenine, 5-carbon

sugar, 2 phosphate groups

ADP and ATP

• Storing energy– When a cell has energy available, it can store

small amounts by adding a phosphate group to ADP, producing ATP

• Releasing energy– Breaking bonds between the 2nd and 3rd

phosphate groups– Powers several cellular activities

• Active transport, protein synthesis, muscle contraction

Photosynthesis

• Method of converting sun energy into chemical energy usable by cells

• Autotrophs utilize this process– Photoautotrophs- light– Chemoautotrophs- chemicals

• Equation6CO2 + 6H2O + light → C6H12O6 + 6O2

Chloroplast

Electron Carriers

• Carrier molecule- a compound that can accept a pair of high-energy electrons and transfer them along with most of their energy to another molecule– Process: electron transport– Molecule: electron transport chain

• NADP+: NADP+ accepts and holds 2 high-energy electrons along with H+

• When this occurs it becomes NADPH

• NADPH can then carry high-energy electrons to chemical reactions elsewhere

Light-Dependent Reactions

• Require light

• Produce oxygen gas

• Convert ADP and NADP into ATP and NADPH

Light-Dependent Reactions

1. Pigments in photosystem II absorb light

2. Energy is absorbed by electrons which are passed on to electron transport chain

- Electrons come from breaking bonds between water molecules

- Create 2 electrons, H+ ions, and oxygen

Light-Dependent Reactions3. Electrons move through electron transport

chain– from photosystem II to photosystem I– Energy is used to transport H+ ions from

stroma to inner thylakoid

4. Pigments in photosystem I use energy from light to reenergize the electrons

– NADP+ picks up high energy electrons and H+ ions

– Becomes NADPH

Light-Dependent Reactions

5. H+ ions are continuously pumped into thylakoid membrane

– Inside= positively charged; outside= negatively charged

– Difference in charges provides the energy needed to make ATP

6. ATP synthase- protein in membrane– Spins like a turbine – Allows H+ to cross membrane– ATP synthase binds ADP and a phosphate group

together to produce ATP

Light-Independent Reaction

• Calvin Cycle

• Uses ATP and NADPH to produce high-energy sugars

• Does not require light

Calvin Cycle

1. 6 CO2 molecules enter cycle– Combine with 6 5-carbon molecules– Result = 12 3-carbon molecules

2. 3-carbon molecules are converted into higher-energy forms (energy from ATP and NADPH)

3. 2 3-carbon molecules are removed from cycle

– Used to produce sugars, lipids, amino acids, etc.. For metabolism and growth of plant

Calvin Cycle

4. Remaining 10 3-carbon molecules are converted back to 6 5-carbon molecules– Combine with 6 new carbon dioxide

molecules to begin the next cycle

Factors affecting Photosynthesis

• Water– Lack of water can slow or even stop

photosynthesis– Desert plants have waxy coating to reduce

water loss

• Temperature– Enzymes function at particular temp ranges

• Intensity of Light– Increasing light increases rate of

photosynthesis– There is a maximum rate of photosynthesis

Cellular Respiration• Breakdown of glucose to produce energy

– 1g of sugar releases 3811 calories of heat energy– Calorie- amount of energy needed to raise the temp of 1g

of water 1˚ Celsius

6O2 + C6H12O6 → 6CO2 + 6H2O + energy

• Steps:– Glycolysis– Krebs Cycle– Electron Transport Chain

Glycolysis

• Process in which one molecule of glucose is broken in half, producing 2 molecules of pyruvic acid (3-carbon compound)

• In cytoplasm

• 2 ATP → 4 ATP

• NAD+ = electron carrier– Accepts 4 high-energy electrons– Becomes NADH

Glycolysis

• Energy yield is small but happens very fast

• Does not require oxygen

• Problem: NAD+ molecules fill up with electrons; without NAD+ ATP production stops

Fermentation

• Releases energy from food molecules by producing ATP in the absence of oxygen– Anaerobic- not in air

• 2 main types– Alcoholic fermentation– Lactic acid fermentation

• Convert NADH to NAD+ – Allows glycolysis to continue producing a

steady supply of ATP

Alcoholic Fermentation

• Pyruvic acid + NADH → alcohol + CO2 + NAD+

• Causes bread dough to rise

• Yeast in dough runs out of oxygen, begins fermentation which produces CO2

Lactic Acid Fermentation

• Pyruvic acid + NADH → lactic acid + NAD+

• Produced in muscles during rapid exercise when the body cannot supply enough oxygen to the tissues

• Some unicellular organisms produce lactic acid as a waste product– Cheese, yogurt, buttermilk, sour cream– Pickles, sauerkraut

Krebs Cycle

• Pyruvic acid is broken down into carbon dioxide in a series of energy-extracting reactions

• Aerobic- requires oxygen

• AKA citric acid cycle – because citric acid is the first compound produced

• In mitochondrion

Krebs Cycle

Krebs Cycle

• Pyruvate Oxidation:– Pyruvic acid enters mitochondrion

– A carbon atom is removed to form CO2

– The other 2 carbon atoms are joined to coenzyme A to form acetyl-CoA

A. Acetyl-CoA adds to a 4-carbon molecule producing a 6-carbon molecule called citric acid

Krebs Cycle

B. -Citric acid is broken down to produce a 5-carbon chain

- CO2 is released- electrons transferred to energy carriers

C.- 5-carbon chain is broken down into a 4 carbon chain

- CO2 is released- ATP is produced

D. – 4 carbon chain is ready to accept acetyl CoA to start cycle all over

- FAD is converted to FADH2

- NAD+ is converted to NADH

Electron Transport Chain• Uses high-energy electrons from the

Krebs cycle to convert ADP to ATP

• In mitochondrion

Electron Transport Chain

A.-NADH and FADH2 are passed along ETC and transfer their electrons down ETC

• Eukaryotes: membrane of mitochondrion• Prokaryotes: cell membrane

– H+ ions are transferred to intermembrane space

B.-electrons from ETC combine with H+ ions and oxygen to produce H2O

Electron Transport Chain

C. Energy is used to transport of hydrogen ions by 2 high-energy electrons – H+ ions build up in the intermembrane space

making it positively charged– The other side of the membrane is negatively

charged

Electron Transport Chain

D.-Inner membranes of mitochondria contain ATP synthase

- ATP spins when H+ ion crosses membrane

- While rotating, the enzyme grabs a low-energy ADP and attaches a phosphate producing ATP

Totals

• Glucose = 2 ATP

• Krebs + ETC = 34 ATP

• Total = 36 ATP

• Final wastes: water and carbon dioxide