quaestio: how do organisms obtain the energy stored in food? nunc agenda: list what foods you have...
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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.
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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?
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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
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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).
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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.”
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Examples of Energy Needs
• 1. Locomotion. (Muscle Contractions)
• 2. Building complex molecules from simple ones (Synthesis).
• 3. Digestion.
• 4. Breathing, Talking, Thinking, Existing!
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Chemicalenergy
Heat CO2
H2O
+
A Heterotroph’s nutrition must supply the organism with enough chemical energy to fuel its life’s activities.
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In fireflys, Energy in the form of ATP combines with an enzyme to run a chemical reaction to produce flashes of lights
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Ctenophores (Comb Jellies), like fireflies, have bioluminescence using the power of ATP.
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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
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Introducing the major players and processes:
ADP ATP
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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
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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.
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: Nitrogenous Base
: 5-carbon sugar
ATP: C10H16N5O13P3
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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
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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
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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.
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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
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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.
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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.
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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?
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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.
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More on ATP vs. Glucose• Glucose Chemical Formula– C6H12O6
– Smaller Molecule with More Energy.
• ATP Chemical Formula– C10H16N5O13P3
– Larger Molecule with Less Energy.
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Glucose
ATP
Glucose holds more energy than ATP
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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.
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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
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Ways to transfer energy in the cell
• Transfer phosphate groups• Transfer electrons• Transfer hydrogen
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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-).
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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.
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Remember Oil Rig!
Oxidation
Is
Loss (of electrons)
Reduction
Is
Gain (of electrons)
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Another way to remember:LEO goes GER
• Lose• Electrons• Oxidation
• Gain• Electrons• Reduction
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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.
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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.
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Hydrogen Ion = H+ =
Proton
Hydrogen was Oxidized
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Hydrogen
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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.
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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).
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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)
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Hydrogen Acceptors, Cont’d
• The extra energy (electrons) carried by NADH and FADH2 can be used to make ATP from ADP.