BioenergeticsBioenergeticsHow Do Organisms Acquire and

Use Energy?How Do Organisms Acquire and

Use Energy?

Metabolism

• All of the chemical reactions that occur in cells.– Organic substances are converted to other

organic molecules and energy is transformed.

• Energy– Anything that can do work.

• Example: move a muscle, make a protein

Laws of Thermodynamics

• First Law:– Energy may change forms, but it is neither

created nor destroyed.

• Second Law:– Energy changes always occur in the direction

in which the energy of the universe becomes more disordered.

Entropy

• The amount of disorder or randomness in the universe.– Without the input of energy from outside the system,

all systems are spontaneously moving closer to equilibrium at all times.

Uphill Struggle For Living Things

• Living things must do biological work to keep the forces of the universe from dismantling their highly ordered bodies.

• To do this, organisms need a constant supply of energy.

• Autotrophs and heterotrophs either produce or obtain energy to overcome this struggle.

Animal Respiration, Like Fire, Is Oxidation

• Joseph Priestly

– Championed the idea of “phlogistron”

• Phlogistron is the substance that flowed into the air when substances were burned.

Animal Respiration, Like Fire, Is Oxidation

• Antoine Laurent Lavoisier– Disproved theory of phlogistron.

• Hypothesized if burning substance releases phlogistron, then as the substance burns, its weight should decrease.

• Found the total weight had increased.

– He reasoned burning doesn’t add something to the air, it takes something out of the air.

– First to recognize fire and breathing both require oxygen.

Animal Respiration, Like Fire, Is Oxidation

• Types of energy:

– Kinetic • Energy that is doing

work

– Potential• Stored or inactive

energy

Metabolism is Efficient and Highly Specific

• Can’t burn glucose as you would wood.

• Need the process to be controlled to minimize the energy loss (entropy).

• Also need it to be specific.

• Need enzymes.

Metabolism is Efficient and Highly Specific

• Enzymes

– A class of proteins that catalyze, or speed up, the steps of metabolism

– Cannot force a reaction to go in a direction that is not consistent with the laws of thermodynamics

How Do Enzymes Work?

• They overcome the activation energy.

– Barrier that prevents molecules from undergoing otherwise favorable reactions

Hallmarks of Enzyme-Catalyzed Reactions

• Metabolic efficiency:

– Cellular metabolism is characterized by metabolic pathways.

• Sequences of enzyme-catalyzed reactions in which the product of one reaction serves as the reactant for the next.

Hallmarks of Enzyme-Catalyzed Reactions

• Metabolic specificity

– A given enzyme only binds to a specific kind of molecule, called its substrate

Metabolic Specificity

ATP: Energy Currency of Life

• Adenosine Triphosphate:– Assembled by energy-

yielding metabolic pathways.

– “Used” to drive energy-consuming pathways.

– A nucleotide.

Central Role of

ATP

Other Nucleotide-Based Compounds Shuttle Hydrogen

• These molecules shuttle hydrogen atoms from one place to another and from one compound to another.– NAD+/NADH,– NAD+/FADH2, – NADP+/ NADPH

• Play central role in metabolism.

How Do Organisms Use Energy?

• Cellular Respiration– Metabolic pathways in

which cells harvest the energy from the metabolism of food molecules

– Occurs in three stages• Glycolysis• Krebs Cycle• Electron Transport Chain

Glycolysis

• Occurs in the cytoplasm

• Net reaction:

C6H12O6

Glucose

2 C3H16O3

Pyruvic Acid

2 ADP 2 ATP

2 NADH2 NAD+

When Oxygen is Limited

• Two problems with anaerobic cellular respiration:– 2 ATPs / glucose molecule will not sustain

activity for long periods.– In the absence of oxygen, glycolysis converts

all of the limited NAD+ to NADH.• With no more available NAD+, glycolysis ceases.

Lactic Acid Fermentation

• H atoms are removed from NADH and added to pyruvic acid forming lactic acid.– Regenerates NAD+ in

order for glycolysis to continue

With Oxygen Present

• Transitional step before Krebs Cycle:– Accomplishes 3 things

• 1. Hydrogen atoms removed from pyruvic acid and added to NAD+ making NADH

• 2. Carbon atom is removed from pyruvic acid and lost as CO2

• 3. Resulting two-carbon molecule is attached to carrier molecule (coenzyme A) forming acetyl-CoA

– Performed by large enzyme in the in mitochondria

Krebs Cycle

• Occurs in mitochondria:

• Entering cycle: – 1 acetyl-CoA, 3 NAD+,

1 FAD, 1ADP + Pi

• Exiting the cycle:– 3 NADH, 1 FADH2, 1

ATP, 2 CO2

Electron Transport Chain

• Occurs in mitochondria:– Have cristae

• Folds of inner mitochondrial membrane

• Contains energy transforming machinery needed to convert the energy stored in NADH and FADH2 to ATP

Electron Transport Chain

• Components of the chain are enzymes – Grouped into 4 large

complexes • On inner mitochondrial

membrane

• End products of the chain– Gradient of protons across

the inner mitochondrial membrane

– water

ATP is Made Using Energy From Proton Gradient

• Proton gradient similar to dam– Hold water back until

you need it to do work– As water rushes down

its gradient toward equilibrium,

• Use a coupling mechanism –a waterwheel or turbine-to put that energy to work for you.

ATP is Made Using Energy From Proton Gradient

• The basic components of a dam are:– 1. Potential energy in

the form of a water gradient

– 2. An opening that directs the water flow in a specific path

– 3. A coupling mechanism to do the work

ATP is Made Using Energy From Proton Gradient

• Synthesis of mitochondria uses same basic components.– Protons moving down their

gradient fuels the synthesis of ATP by

• Mitochondrial ATP synthase

• This mechanism of ATP synthesis is called chemiosmosis.

Net Overall Yield of Cellular Respiration

• Net yield of ATP production from one glucose molecule– Glycolysis: 2 ATP– Krebs Cycle: 2 ATP– Electron Transport Chain

• Converting the energy stored in NADH and FADH2 to ATP: 32 ATP

– Total: 36 ATP

How Do Organisms Acquire Energy?

• Only photosynthetic organisms can make organic molecules from sunlight, CO2 and H2O.

– Heterotrophic organisms obtain organic molecules by consuming photosynthetic organisms.

Pigments absorb the Energy of Light

• Light is a form of energy called electromagnetic radiation.– Occurs in a vast spectrum of size and energy

• Shorter wavelength radiation has more energy than long wavelength radiation.

Pigments absorb the Energy of Light

• Photosynthetic tissues appear green because they contain pigments.– Molecules that absorb some wavelength of

light and reflect others.

• Green plants have the pigment chlorophyll– Absorbs red and blue parts of the spectrum

and reflects the green wavelength.

Pigments absorb the Energy of Light

• If a beam of blue light is aimed at a test tube containing chlorophyll, the solution fluoresces.– Light is briefly absorbed and emitted at a different

wavelength.

Photosynthesis

• Consists of two types of reactions:– Light-dependent reactions

• Produce ATP and NADPH

– Light-independent reactions• Also known as the Calvin-Benson Cycle.• Use ATP and NADPH to produce carbohydrates.

Light Reactions Make ATP and NADPH

• Chloroplasts– Large, green,

membrane-bound organelles.

– Site of photosynthesis– Thylakoids

• Contain the light-harvesting pigments.

– Stroma• Internal space of

chloroplast.

Steps of Light-dependent Reactions

Noncyclic vs. Cyclic Phosphorylation

• Noncyclic:– Flow of electrons follow a linear noncyclic

pathway:

– Produce more NADPH than ATP.– Problem: Calvin–Benson cycle requires 3

ATP for every 2 NADPH to make carbohydrate.

2 H2O + 2 NADP+ + ADP + Phosphate O2 + 2 NADPH + ATPLight energy

Noncyclic vs. Cyclic Phosphorylation

• Cyclic:– Depending on the

need for ATP, electrons can bypass the NADP+ and be passed back to the chlorophyll molecule from which they originally came.

– Still creates proton gradient.

Calvin-Benson Cycle

• Discovered in late 1940s-1950s– Used paper

chromatography and radioactive carbon.

• Depicted carbon-fixation in green algae

• Sugar-producing process of photosynthesis.

What Do Humans Need to Eat?

• Macronutrients supply energy for our metabolism.– Macronutrients: dietary components that are

needed in relatively large quantities for proper body function.

– Three kinds:• Protein• Fats• Carbohydrates

Proteins

• Make up the main structural components of our bodies.

• Made of 20 amino acids.– Our body can produce 12 from fats and

carbohydrates– The other 8, essential amino acids, have to be

obtained from our diet– Dietary proteins that provide all of the essential amino

acids in the proper proportions are called complete proteins or high-quality proteins.

Fats

• Main structural component of cell membranes

• Two groups of essential fats:– Omega-3 and omega-6 fatty acids must be

obtained from diet.

• Healthiest way to to obtain fat is to avoid foods rich in saturated fat (butter, lard) and cholesterol and concentrate on foods with unsaturated fats (vegetable oils).

Carbohydrates

• Main source of calories is most diets.– Not all are equally healthy.

• Healthy carbohydrates are those not heavily processed.– Examples: fruits, vegetable, whole grains

• Highly processed carbohydrates cause drastic spikes in insulin levels.– Followed by unstable blood glucose levels

and sensations of false hunger.

Micronutrients

• Include vitamins and minerals.

• Needed as cofactors for many enzymes.– In order for enzymes to catalyze cellular

reactions.

• Serve as building materials for bone and blood.

• Required in small amounts.

• Crucial for health and well-being.