Quaestio: How do organisms obtain the energy stored in food?

Nunc Agenda: List what foods you have eaten today and

the types of molecules that compose them.

Energy

• Energy: the ability to do work.

• Can you think of examples?– In what forms does energy exist?

– How do we use energy on earth?

A cell does 3 main kinds of work:

• Mechanical work: beating cilia, contraction of muscle cells, movement of chromosomes during reproduction

• Transport work: moving substances across membranes

• Chemical work: running chemical reactions, synthesis of polymers from monomers

The Law of Conservation of Energy

• The Law of Conservation of Energy: Energy can neither be created nor destroyed; it can only change forms. – Remember, the sum of energy in the universe is constant.

• Examples of energy conversions: – Photosynthesis

• (Light E Electrical E Chemical E)– Respiration

• (Chemical E Kinetic E Thermal E)– Internal Combustion Engine

• (Chemical E Thermal E Kinetic E).

Energy for Living Things

• All living things need energy to carry out their life processes.

• Nutrition: the life process in which organisms obtain energy in food for metabolic processes.

• Energy must exist to run “cellular machinery.”

Examples of Energy Needs

• 1. Locomotion. (Muscle Contractions)

• 2. Building complex molecules from simple ones (Synthesis).

• 3. Digestion.

• 4. Breathing, Talking, Thinking, Existing!

Chemicalenergy

Heat CO2

H2O

+

A Heterotroph’s nutrition must supply the organism with enough chemical energy to fuel its life’s activities.

In fireflys, Energy in the form of ATP combines with an enzyme to run a chemical reaction to produce flashes of lights

Ctenophores (Comb Jellies), like fireflies, have bioluminescence using the power of ATP.

Energy from Food• Living things rely on the chemical energy stored in

their food to survive.

• Carbohydrates, lipids, and proteins all have chemical energy and all can be broken down to yield energy– known as cellular respiration

• Carbohydrates are the foods most commonly broken down. – Created during photosynthesis

Introducing the major players and processes:

ADP ATP

ATP and ADP

• Cells use chemical energy in the form of ATP– The energy released during cellular respiration is

“stored” in the form of ADP and ATP.

• ADP: Adenosine diphosphate– Has two phosphate groups.

• ATP: Adenosine triphosphate– Has three phosphate groups

Behind the Names• Adenosine is the combination of a molecule of

the nitrogenous base adenine with a molecule of the sugar ribose.

– Adenine + Ribose = Adenosine

• Diphosphate = 2 phosphate groups attached to adenosine.

• Triphosphate = 3 phosphate groups attached to adenosine.

: Nitrogenous Base

: 5-carbon sugar

ATP: C10H16N5O13P3

Molecular Similarities

• ATP and ADP use the same subunits as the nucleic acids:

– A nitrogenous base (adenine is present in DNA and RNA).

– A 5-carbon sugar (ribose is present in RNA only).• Can you remember what DNA has?

– Phosphate groups

What makes ADP and ATP so important?

• ATP has more energy than ADP:– due to a high-energy bond between the 2nd and 3rd

phosphate group

• When the third phosphate group is removed from ATP, it forms ADP, and chemical energy is released. – ATP + H2O ADP + P + Energy

Phosphorylation

• Phosphorylation: the transfer of energy when a phosphate group is transferred among molecules.

• Phosphorylation is a common way for chemical energy to be transferred in living cells.– ATP loses a phosphate to the molecule that

becomes phosphyorylated.

ATP is recycled

• ATP is used continuously by a cell, but it can be regenerated by adding a phosphate to ADP.– It’s a renewable resource!

• If ATP could not be regenerated by the phosphorylation of ADP, humans would consume nearly their body weight in ATP each day

AMP

• AMP stands for adenosine monophosphate. It has only one phosphate group attached.

• AMP has lower energy than ADP (and ATP).

• ADP is rarely broken down into AMP for energy.

The Role of Glucose.

• Glucose (a simple sugar) is broken down to supply the energy needed to add a phosphate group to ADP to form ATP.

• One C6H12O6 molecule can be used to form 36 molecules of ATP.

More on Carbohydrates• Glucose is not usually present in its simple form in

the foods we eat.

• We need to break complex carbohydrates into glucose first.

• Review: Our digestive system breaks down complex carbohydrates:– Starch Maltose Glucose

• Can you remember what enzymes are involved and where?

Question• If ATP is directly used for energy, why do we

need glucose at all?

Answer: Glucose contains a lot more energy than ATP, but is actually a smaller molecule. Glucose is a good way to store chemical energy, while ATP is more appropriate for directly supplying immediate energy for cellular reactions.

More on ATP vs. Glucose• Glucose Chemical Formula– C6H12O6

– Smaller Molecule with More Energy.

• ATP Chemical Formula– C10H16N5O13P3

– Larger Molecule with Less Energy.

Glucose

ATP

Glucose holds more energy than ATP

Glucose vs. ATP

• Like a gold bar • Cash!

Can you explain the analogy?

Glucose is smaller but holds more energy, and needs to be broken down or exchanged before you can purchase with it. A suitcase full of money may be larger, like ATP, but can be used immediately.

Questions

• If ATP is used as the main source of energy in a cell, then why does a cell only keep a small amount of ATP present at any time?– ATP is constantly being recycled from ADP

Ways to transfer energy in the cell

• Transfer phosphate groups• Transfer electrons• Transfer hydrogen

Oxidation-Reduction Reactions: the transfer of electrons

• Oxidation: A chemical change in which an atom or a molecule loses electrons.– Example: When sodium combines with chlorine to

form sodium chloride (NaCl), sodium loses an electron to become a sodium ion (Na+).

• Reduction: A chemical change in which an atom or a molecule gains electrons.– Example: Chlorine gains the electron from sodium,

becoming a chloride ion (Cl-).

Questions

• Why did sodium (Na) become Na+? • Why did chlorine (Cl) become Cl-?

Answer: Sodium lost an electron and became a positive ion. It now has more protons than electrons. Sodium was oxidized.

Answer: Chlorine gained an electron and became a negative ion. It now has more electrons than protons. Chlorine was reduced.

Remember Oil Rig!

Oxidation

Is

Loss (of electrons)

Reduction

Is

Gain (of electrons)

Another way to remember:LEO goes GER

• Lose• Electrons• Oxidation

• Gain• Electrons• Reduction

Oxidation-Reduction Reactions

• When one substance is oxidized, another must be reduced.

• Redox Reaction: (short for Reduction-Oxidation Reaction): A reaction that involves both oxidation and reduction.

Gaining and Losing Hydrogen

• Occasionally, rather than exchanging electrons, molecules will exchange hydrogen atoms. – Recall: a hydrogen atom consists of one proton and one

electron. It is the simplest element.

• The molecule that loses the hydrogen is oxidized– called the oxidant.

• The molecule that gains the hydrogen is reduced– called the reductant.

Hydrogen Ion = H+ =

Proton

Hydrogen was Oxidized

Hydrogen

Redox Reactions, Cont’d

• Redox reactions involve a transfer of energy.

• The oxidant (the electron or hydrogen donor) normally loses energy and the reductant (the electron or hydrogen acceptor) gains energy.

Biochemical Pathway

• Cellular Respiration follows a biochemical pathway: a sequence of chemical reactions that leads to a result.

• This pathway is fueled by redox reactions. • *Remember – if a molecule loses a hydrogen

(oxidation), another molecule must accept that hydrogen (reduction).

Hydrogen Acceptors

• NAD and FAD are two coenzymes that serve as hydrogen and electron acceptors.

• NAD = nicotinamide adenine dinucleotide.• FAD = flavin adenine dinucleotide.

• To be reduced:• NAD + H NADH (higher energy)

• FAD + 2H FADH2 (higher energy)

Hydrogen Acceptors, Cont’d

• The extra energy (electrons) carried by NADH and FADH2 can be used to make ATP from ADP.