Ch 4 Food's Energy Value

kilocalorie

foods energy value

measure of heat

1kcal = quantity of heat to raise the temp of 1kg of water by 1 degree C

direct calorimetry

burning food in a bomb calorimeter

direct measurement of heat produced

indirect calorimetry

gas analysis

radioactive isotopes

HR monitor

accelerometer

combustion heat definition

heat liberated by oxidizing a specific food

avg gross energy value

combusiton heat of carbs

4.2 kcal/g

varies with arrangement of carb molecules

combustion heat of lipids

9.4 kcal/g

varies with composition of fatty acids

combustion heat of protein

5.65kcal/g

varies for each amino acid and relative N₂ content

Coefficient of digestibility

some portions can’t be digested

differences between gross and net energy

avg coefficient of digestibility for carbs

97%

avg coefficient of digestibility for lipids

95%

avg coefficient of digestibility for proteins

92%

____ lbs/wk is healthy fatloss

1-2 lbs/wk

mass balance model

food mass ←—> mass excretion

macronutrient composition is important (coefficient of digestibility)

energy

capacity for work

as exercise increases, there must be an increase in energy transferred

bioenergetics

flow and energy exchange within a living system

energy system focused view of metabolism

first law of thermodynamics

energy can neither be created nor destroyed

transforms

some lost as heat

potential energy relates to

structure or position

ATP—ADP—AMP

kinetic energy relates to

energy of motion and heat

enzymatic cascade

multiple enzymatic reactions combined together

altering its structure

free energy (G) — energy potential

energy investment and output phases

endergonic processes

energy conserving

chemical reactions that store or absorb energy

increase in free energy for biologic work

exergonic processes

physical or chemical process that releases energy

decrease in free energy

second law of thermodynamics

entropy

the total entropy (disorder) of an isolated system can never decrease over time

natural processes are irreversible and energy tends to disperse

potential energy degrades to kinetic energy

photosynthesis

endergonic process

traps radiant solar energy

synthesize glucose from CO2 and H2O

oxygen as by-product

cellular respiration

converts chemical energy stored in plants to ATP

exergonic process

used for mechanical work of contraction

used for chemical work of glycogen, triacylglycerol, and protein synthesis

mechanical work in humans

muscle contraction

chemical work in humans

biosynth of cellular molecules

transport work in humans

transfer of substances among cells

enzymes

protein catalysts

accelerate chemical rxns

reduces energy input req.

coenzymes

facilitates enzyme’s action

“cobinder” or temporary carrier of intermediary products in a reaction

turnover rate (of enzymes)

how quickly substrate becomes product

depends on pH and temp

enzyme action

active site joins with substrate through lock and key mechanism

specific!

releases and can be used again

some bind incompletely, interfering with function

substances inhibit enzymes

slow the rxn rate

bind to active sit to prevent activation

change structure/enzymatic ability to bind

non-competitive enzyme inhibitors

cancer drugs

anti-depression

acquired immunodeficiency syndrome meds

ACE inhibitor

shuts down renin

angiotensin converting enzyme inhibitor

SSRI

selective serotonin reuptake inhibitor

hydrolysis

catabolic—break down

digests carb, lipid, and protein into simpler forms

splits chemical bonds by adding water

H+ and OH+ to the reaction byproducts

sucrose —> glucose + fructose

condensation

anabolic

components bind together to form more complex molecules

removal of H2O

glucose + glucose —> maltose

redox reactions

transfer of electrons

seen in ETC

reduction = gain electron

oxidation = lose electron

exercise affects redox rate

enzymes can work in both directions

based on demands (ATP/ADP, Pⁱ, H⁺)

6 enzyme classifications

1. oxidoreductase

2. transferases

3. hydrolases

4. lyases

5. isomerases

6. ligases

ligases

join to molecules to synth new one

**gluconeogenesis

isomerases

small chemical conversation

changing shape slightly

Triose Phosphate Isomerase, Phosphoglucomutase

lyases

removal of a molecule

ex: deamination

hydrlases

ex: lipase

breakdown molecules using water

transferases

ex: hexokinase

transfers molecules

oxidoreductase

add or remove electrons

ex: lactate dehydrogenase