cellular energy. the first law of thermodynamics first law of thermodynamics – energy can be...

Cellular Energy

The First Law of Thermodynamics

• first law of thermodynamics– Energy can be transferred and

transformed, but it cannot be created or destroyed

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

The Second Law of Thermodynamics

• second law of thermodynamics: – Every energy transfer or transformation

increases the entropy (disorder) of the universe

During every energy transfer or transformation, some energy is unusable, and is often lost as heat


Fig. 8-3

(a) First law of thermodynamics (b) Second law of thermodynamics

Chemicalenergy

Heat CO2

H2O

+

Cell Energy

• Energy is essential to life• All living organisms must be able to

produce energy, store energy and use energy

• Cells need a a quick source of energy

• Cellular energy is stored in chemical bonds of the ATP molecule

ATP

• ATP = Adenosine triphosphate• Adenosine molecule with 3

phosphate groups attached

Adenosine P P P

Fig. 8-8

Phosphate groupsRibose

Adenine

ATP

• The charged phosphate groups act like the positive poles of two magnets, they repel each other

• Energy is contained in the bond that holds the phosphate molecules to the adenosine

• When a bond breaks, energy is released resulting in ADP (adenosine diphosphate)

• Refer to pg 229 fig 9.2

An organism’s metabolism transforms matter and energy, subject to the laws

of thermodynamics

• Metabolism is the totality of an organism’s chemical reactions


Enzyme 1 Enzyme 2 Enzyme 3

DCBAReaction 1 Reaction 3Reaction 2

Startingmolecule

Product

A metabolic pathway begins with a specific molecule and ends with a product. Each step is catalyzed by a specific enzyme

Organization of the Chemistry of Life into Metabolic Pathways

• Catabolic pathways release energy by breaking down complex molecules into simpler compounds– Cellular respiration, the breakdown of

glucose in the presence of oxygen, is an example of a pathway of catabolism


• Anabolic pathways consume energy to build complex molecules from simpler ones– The synthesis of protein from amino acids

is an example of anabolism


Photosynthesis

• Absorbing light energy and converting it into stored chemical energy (plants & algae)

• Principal product = glucose (O2 – major by-product)

• Takes place in chloroplast

Photosynthesis cont.

• Sun – ultimate source of energy

• Because photosynthesis is the essential step between solar energy and life – it is one of the most important biological processes.

Photosynthesis

• To use the energy solar energy, plant cells must trap light energy and store it in a form that is readily usable by the cell (ATP)

• Because light is not available 24 hours a day, the plant must have some way to store energy for later use photosynthesis

Photosynthesis

• Photosynthesis happens in two phases– Light dependent reaction

• Conversion of light energy into chemical energy

• Produces ATP – ATP immediate use by the plant

– Light independent reaction• Uses ATP to produce glucose

– Glucose - stored energy for later use

Chemical equation for photosynthesis

chlorophyll

CO2 + H2O + light energy glucose + H2O + O2

Chlorophyll a

6CO2 + 12H2O + light energy C6H12O6 + 6O2 + 6H2OMost of us don't speak chemicalese, so the above chemical equation

translates as:six molecules of water plus six molecules of carbon dioxide produce

one molecule of sugar plus six molecules of oxygen

Chloroplast• Chloroplast – cell organelle where

photosynthesis occurs• Composed of Thylakoids in stacks

(Grana), with space around (Stroma)• Chlorophyll is found in the membranes of

the thylakoids

Chlorophyll

• A green-colored pigment• Primary catalyst of photosynthesis• There are at least 4 different types

of chlorophyll (a, b, c, d)• Found in Chloroplasts

Structure of Chloroplast

• Thylakoid is the structural unit of photosynthesis. Thylakoids are stacked like pancakes in stacks known collectively as grana. The areas between grana are referred to as stroma.

• Chlorophyll is found in the grana

Light Dependent Reaction AKA:Photo Phase

• Step 1: Light energy is absorbed and energizes a chlorophyll molecule

• Step 2: Water molecules are split– Photolysis: breaking apart of a water molecule

by energized chlorophyll

• Step 3: Oxygen is released• Step 4: Hydrogen is bonded to hydrogen

acceptor (NADP)• Step 5: ATP molecule is made (energy

is stored in ATP)

Biology, Sixth Edition

Chapter 8, Photosynthesis: Capturing Energy

The Electron Transport Chain and Chemiosmosis

Light Independent Reaction AKA: Dark Phase

• Step 1: CO2 is bonded to RuBP– RuBP (ribulose biphosphate) – 5 carbon sugar with 2 phosphates– Resulting 6-carbon sugar is unstable and breaks to form 2

molecules of PGA (phosphoglyceric acid)– PGA is a 3-carbon sugar with a phosphate attached to it

• Step 2: PGA is converted to PGAL– PGA receives hydrogen and is energized by energy and

phosphate from and ATP molecule

• Step 3: Water is given off• Step 4: PGAL is converted to

glucose



The Calvin Cycle:Phases 1 & 21. Carbon uptake

– Adds carbon dioxide to 5C ribulose bisphosphate (RuBP)

– Catalyzed by RUBISCO; ribulose bisphosphate carboxylase

2. Carbon reduction phase– Citrate is made and broken

to form phosphoglycerate (PGA)

– PGA is rearranged and phosphorylated by ATP

– NADPH reduces the backbone further to form glyceraldehyde-3-phosphate (G3P)



The Calvin Cycle: Phase 3

3. Reformation of RuBP:– G3P is rearranged,– & phosphorylated – With further

investment of ATP… – To make RuBP, a

bisphosphorylated compound

• Alternatively, – G3P is shuttled out of

the cycle to produce glucose and other carbohydrates elsewhere



Partition of Function in the Chloroplast

• The light-dependent reactions (the harvesting of light) occur on thylakoid membranes

• The carbon fixation reactions (formation of carbohydrate) occur in the stroma

Conditions for photosynthesis

• Adequate supply of light• Temperature affects the rate of

photosynthesis– Proper temperature for photosynthesis

varies from plant to plant

• Lack of water will cause a plant to stop photosynthesis

• Cell’s ability to absorb sufficient CO2

Classification of organisms according to how they obtain

energy• Autotrophs

– “self-feeders” (producers) – organisms that make their own food (photosynthesis)

– All green plants, certain bacterial and protozoa

• Heterotrophs– “other-feeders” (consumers) – organisms

that must obtain their nutrition from source outside themselves

– Animals, humans, fungi, most bacteria



Engelmann’s Experiment: 1883

• Engemann sought to determine the wavelengths of light most important for production of oxygen

• He illuminated a strand of Spyrogyra (a green alga) with the spectrum of light from a prism while observing through a microscope

• Aerobic bacteria were attracted to the regions of high oxygen production: i.e. regions of photosynthesis

Aerobic bacteria



Absorption vs. Action Spectra• Chlorophyll appears green because it absorbs most

strongly in the red and blue.• The action spectrum is the result of the interaction of

accessory pigments with chlorophyll.

Absorption curves: chlorophylls a & b The action spectrum of photosynthesis

Cellular Respiration


• Glucose is produced during photosynthesis and is used in cellular respiration

• Cells need energy– Cells obtain the needed energy by

subjecting glucose to a chemical process that is very similar to burning

A Comparison of burning and Cellular Respiration of

sugar• Both give off water and CO2

• Both require oxygen• Both require activation energy• As the glucose is “burned” the energy

that it contains is released for the use by the cell, just as the burning of wood releases heat energy

• This process of burning food to release energy from it is called cellular respiration


• The breaking down of a food substance into usable cellular energy in the form of ATP

Aerobic Cellular Respiration

• Basically, cellular respiration is the opposite of photosynthesis (they are not the reverse of each other)

• Aerobic Cellular respiration breaks down glucose to form water, carbon dioxide and energy

Cellular Respiration Equation

C6H12O6 + 6 O2 6 CO2 + 6 H2O and

energy

As a result of respiration, energy is released from the chemical bonds

found in complex organic molecules (food).

Aerobic Cellular Respiration

enzymes• Glucose + oxygen ATP (energy) + water + carbon

dioxide

enzymes

• C6H12O6 + 6O2 38ATP + 6H2O + 6CO2

• Respiration takes stored chemical energy and converts it to a ready-to-use chemical energy (ATP)

Three phases of aerobic cellular respiration

• Glycolysis– Requires an input of glucose and ATP– Breaks glucose into 2 smaller molecules– Takes place in the cytoplasm– Doesn’t require oxygen– Net gain of 2 ATP

• Citric Acid Cycle (Krebs Cycle)– Produces 3CO2, and hydrogen– Occurs in the mitochondria– Net gain of 2 ATP

• Electron Transport Chain– Requires an input of hydrogen and oxygen– Occurs in the mitochondria– Forms water– Forms 34 ATP

Efficiency of cellular respiration

• Aerobic cellular respiration of glucose traps approximately 50-60% of the energy in the glucose molecule– This breakdown of sugar is one of the most

efficient energy processes know

• Cars – only 20% of energy available in the fuel is used, most of the rest radiates as heat

Two types of cellular respiration

•Aerobic Requires oxygen

Most cells carry on aerobic cellular

respiration

All three Respiration steps

•AnaerobicDoes not require

oxygen

Some bacteria and fungi

Glycolysis only

Anaerobic Cellular Respiration

• Some cells exist in environments that do not have oxygen available

• Many bacteria in the lower layers of swamps, lakes, or the ocean do not have oxygen

• Cellular fermentation: the breakdown of food (usually glucose) without oxygen– Produces only 2 ATP

Fermentation

• Uses only Glycolysis. • An incomplete oxidation - energy

is still left in the products (alcohol or lactic

acid).

• Does NOT require O2

• Produces ATP when O2 is not available.

Two Types of Cellular Fermentation

• Lactic acid fermentation– Formation of lactic acid from glucose– Bacteria that form yogurt and cottage cheese

• Alcoholic fermentation– The formation of alcohol and CO2 from glucose

– Preformed by yeast cells (baking evaporates the alcohol of bread dough and CO2 causes dough to rise)

Lactic Acid Fermentation

• Done by human muscle cells under oxygen debt.

• Lactic Acid is a toxin and causes soreness and stiffness in muscles.

Strict vs. Facultative Respiration

• Strict - can only carry out Respiration one way… aerobic or

anaerobic.• Facultative - can switch respiration

types depending on O2 availability. Ex - yeast

Importance of Respiration• Alcohol Industry - almost every society has a fermented beverage.

• Baking Industry - many breads use yeast to provide bubbles to raise the

dough.

Matching

Sugar Cane GinBarley SakiGrapes TequilaJuniper Cones VodkaAgave Leaves BeerRice WinePotatoes Rum

Comparing Photosynthesis and Cellular respiration

• Photosynthesis– Food accumulated– Energy form sun

stored in glucose– CO2 taken in– O2 given off– Goes on only in light

– Occurs only in presence of chlorophyll

• Cellular Respiration– Food broken down– Energy of glucose

released

– CO2 given off

– O2 taken in

– Goes on day and night

– Occurs in all living cells

cellular energy. the first law of thermodynamics first law of thermodynamics – energy can be...

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