9/3 What rules govern cellular energy flow?Chapter 5

• Quiz at end of this lecture covers all notes up to end of friday

• CH 4: please go back and look at the review questions! Questions 1a, 4-4, 4-5, 4-7 are best.

• What do cells use energy for?• What units are used to measure energy in an isolated systems

like cells?• How much energy is contained in proteins, lipids and

carbohydrates? ATP is ultimate energy currency!• 1st Law of Thermodynamics: energy is conserved!• 2nd Law of Thermodynamics: disorder of energy in a system

always increases!• How does standard free energy let us predict reactions? ΔGo’

• Don’t forget to read CH 5!!!!

Becker_6e_IRCD_Chapter_5 2

What six forms of “work” are present in biological systems? How is this relevant to what happens in a cell?

Energy is the capacity to do work or cause change!What are 6 ways cells use energy?

• 1) Synthetic Work is the Classic: Biosynthesis– Cells use energy to form chemical bonds and make more

ordered products– Why do cells need energy for maintenance?– Why do cellular needs change over time?

• Cellular time frame:• Time frame of organism life span• Inception>growth>reproduction>maintenance>repair

– Synthesis of large molecules:• DNA, Proteins, Lipids, Polysaccarides

– Synthesis of small molecules:• Glucose, amino acids, fatty acids, etc

– Degradation of biomolecules requires energy• Damaged collagen or tissues• Digestion

2 ) Homeothermy: energy generates HEAT (work) which vitally modifies enzyme function/activities in the cell or the

organism.

“Source”: broken chemical bonds“Heat”: a by-product of many other types of energy transfer

“Change”: is the temperature of the system

3) Concentration Gradients represent a very important type of stored energy in the cells of the body!

Gradient: more molecules stacked on one side of a PM than other!Cells establish gradients using energy from broken bonds!Gradients are expensive to maintain!

Release energy (dam analogy) when gradient is released,,,i.e. Mitochondrial H+ gradient/motion is used to make ATP!

Up to 2/3 of cellular energy expenditure is used to run pumps that maintain chemical gradients across the plasma membrane! Na+-outside and K+-inside the cell!

4) What kinds of motion require energy? 1)Flagellated cells (sperm) -cells move relative to environment when a dynein arm moves relative to a microtubule 2) Ciliated epithelium (bronchi)-move particles relative to cells when a dynein arm moves relative to a microtubule

3) Muscle cells-contraction/shortening in given dimension

4) Chromosomes -chromosomes move relative to spindle when kinetochore moves relative to microtubules

5) Cyclosis in plant cells -organelles etc move through cytoplasm when mysoin moves relative to microfilaments -6) mRNA moves relative to ribosome: during protein synthesis

7) Movement of plant parts (venus flytrap) -biological "hydraulic movement"-leaves snap shut as turgor pressure in key cells changes rapidly

8) Amoeboid movement-cytoplasmic flow and movement of actin within the cell

5) Electrical Work can also be performed, typically from an established concentration gradient!Membrane potentials (mV)!Current electric eels!Current ECG or EMG!Changes in electric fields and navigation!

• 6) Energy can also be used by cells to provide for bioluminescence!

• Fireflies and signaling• Deep sea fish (symbiotic bacteria)• Energy converted to released photons of light!

How are cells classified relative to energy source?• Autotrophic: energy generation is independent of

contributions from pre-existing life.– Photosynthetic: Only about 40% of the captured energy is

actually converted to sugars etc.– Chemosynthetic: bacteria

Heterotrophic: Obtain energy that was converted to storage chemicals by autotrophs!

Energy Released from storage via:Glycolysis-Fermentation-Respiration-Other pathways for energy use also exist!

How do we measure energy use, content and production in living things in an isolated system?

• Chemistry: 1 calorie (cal) – energy needed to heat 1 ml of water 1 degree (from 14.5 to

15.5 C)• Nutrition: 1 kilocalorie (kcal) or Calorie (Cal)

– energy needed to heat 1,000 ml or 1 liter of water – 1 degree (from 14.5 to 15.5 C)

• Joules are a unit of energy more commonly used by European scientists 1 J= 0.239 cal or 1 cal= 4.184 J

• We usually refer to energy content as:– cal/mole OR Cal/grams

Examples of Energy Content:

• Carbohydrates: 4 Cal/g….400 g= 1,600 Cal• Protein: 4 Cal/g….200g = 800 Cal• Lipids: 9 Cal/g…..200g = 1,800 Cal

• All cells of body require a total of about 2,000 Cal/day• All cells of body require a total of about 2,000,000 cal/day

Cells in your body need __grams glucose/day for 2,000 CalBasic calculations on test will not require a calculator.

Adenosine Triphosphate (ATP) is the energy currency that mediates most forms of cellular work!

Whys is ATP handy in this regard?

1st Law of Thermodynamics: energy is conserved in different forms in a cell!

• Energy can change forms (chemically or physically) in a cell but can’t be created from nothing or simply disappear!

• The total amount of energy in a cell is dependent on what enters and leaves!

• Heat Content (enthalpy or H) takes into account internal energy, pressure and volume

• ΔH = ΔE + ΔPV • ΔH = ΔH products - ΔHreactants • If heat content of products is less than reactants: heat was

released---Exothermic! • If heat content of products is greater than reactants: heat had to

be added to the system from and external source: Endothermic!

2nd Law of Thermodynamics: disorder of energy in a cellular system always increases!

• Systems and chemical reactions tend towards greater randomness!• This lets us predict if a reaction will spontaneously occur under a set of

conditions!• Entropy or S measures system randomness!• Change in or Delta (Δ) S measures changes in Randomness!

• Gibbs Free Energy measures system spontaneity!• ΔG measures changes in Free Energy• System Temperature: measured in absolute units called Kelvins• Gibbs Free Energy measures system spontaneity!• ΔG measures changes in Free Energy• System Temperature: measured in absolute units called Kelvins

• ΔG = ΔH -TΔS Change in G=(Change in Enthalpy)-(Temp)X(change in Entropy)• If ΔG is NEGATIVE: Spontaneous reaction occurs!

ATP ADP + Pi + Energy• If ΔG is POSITIVE: reaction requires ADDED energy from an external source

before it will occur! ADP + Pi + Energy ATP• A negative ΔG means it occurs, but RXN speed is not indicated!

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Negative ΔG means energy released by this “oxidation”Positive ΔG means energy required for this “reduction”

Standard Free Energy (ΔGo’ )lets us predict if a reaction will occur in a cell under a set of observed conditions.

• Assume reactants and products are present at molar concentrations of 1 M and pH=7.0

• ΔGo’=-2.303RT log keq• 2.303 is a mathematical constant • R is the gas constant: 1.987 cal/mole K• T is temperature in Kelvin (usually 298 K)• Keq: Equilibrium Constant-ratio of products

and reactants when the reaction comes to its normal equilibrium

• The larger the - ΔGo’ more energy is released in achieving Keq!

ATP hydrolysis releases energy so cells can run chemically unfavorable reactions.

ATP provides ΔGo’ that allows cells to perform unfavorable reactions under the condition inside a cell!

Classic ΔGo’ values for hydrolysis to lower energy state products:

• ΔGo’ Kcal/mole• ATP > ADP + Pi• ΔGo’ = -7.3 energy released!• Glucose + Pi>G-6-P +H2O• ΔGo’ = +3.3 energy required!• Net ΔG = (-7.3) + (+3.3)= -4• ATP+Glucose> G-6-P +ADP• ΔGo’= -4 kcal/mole• Negative so reaction occurs• The enzyme hexokinase

speeds the reaction up!

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