chapter 6 energy and metabolism

metabolism

-totality of an organism’s chemical reactions

an organism’s metabolism

-transforms matter and energy

-is subjected to the laws of physics

-amino acids take up space and have mass (they are matter)

-energy is required to link AA to form proteins (they also have matter)

metabolic pathways

-consists of 1000s of biochemical reactions that all require energy transformations

-many and many steps required

-end result is a product

-there are two types of pathways required to maintain the cell’s energy balance

in each step:

1. Is a separate chemical reaction

2. catalyzed by a specific enyzme 

how does the end result of a metabolic pathway look like

what are the two types of pathways required to maintains the cell’s energy balance

1. catabolic 

2. anabolic

catabolic pathways- catabolism

1. break down complex molecules (food) into simpler ones

2. release energy

3. ex: cellular respiration→ the breakdown of glucose molecules

catabolic

large molecules are broken down into small ones and energy is released

cellular respiration equation

C₆H₁₂O₂ → CO₂ + H₂O

anabolic pathways

1. build more complex molecules

2. require more energy

3. ex: photosynthesis 

anabolic

small molecules are assembled into larger ones and enrgy is required

photosynthesis equation

CO₂ + H₂O → C₆H₁₂O₆ + O₂

energy

-the capacity to cause change

-exists in various forms 

-sustains most of earth’s life 

-bioenergetics 

what are the various forms of energy

-some can perform work

-fundamental to all metabolic processes

-rearrange matter from one form to another 

sustains most of earth’s life

comes from the sun

bioenergetics

study of energy flow through a living system

what are the types of energy

-potential energy

-kinetic energy

-thermal energy

potential energy

-stored energy, the energy matter has because of its structure

-membrane potential (Na⁺) moving in/out of cell

-chemical energy store in molecular structures 

→like glucose molecules 

-in a compressed spring 

kinetic energy

energy in motion, movement of objects

thermal energy

-associated with the random movement of atoms or molecules

-heat: when thermal energy is transferred from one molecule to another

energy

can be converted from one form to another

free energy (aka Gibb’s Free Energy “G”)

-describes the energy available to do work

-similar to potential energy

usable energy

-available energy that can do work under cellular conditions

-often interested in the change in free energy, referred to as change in G

change in G

-determines whether a reaction is spontaneous or nonspontaneous 

-affected by all chemical reactions/biological processes 

-change in H→change in total energy of the system (enthalpy change)

-T is temperature in Kelvins

-change in S→ change in entropy (energy lost due to disorder)

entropy increase

solid to gas 

enthalpy increases

gas to solid

free energy and spontaneous change

-addition of external energy is NOT required

-free energy decreases and the stability of a sytem increases

exergonic reactions

-energy is exiting the system 

-spontaneous 

-proceeds with a net release of free energy

-change in G is negative (change in G<0)→ this happends when energy is released in a chemical reaction 

-change in G=G_{final state}-G_{starting state}

free energy and nonspontaneous change 

-addition of external energy IS required

-free energy increase and the stability of a system decreases

endergonic reactions

-energy in entering the system

-nonspontaneous

-a reaction that absorbs free energy from its surroundings

-change in G is positive (change in G>0)→ this happens when energy is absorbed into a chemical reaction

--change in G=G_{final state}-G_{starting state}

activation energy(E_A)

-the initial energy required for a reaction to proceed/start

-heat energy is the main source in the cell

→usually obtained from the surroundings of the system 

→helps reactants reach their transition state 

-causes reactant(s) to becomes contorted and unstable

-allows bond(s) to be broken or made

-once in this state, the reaction occurs very quickly

→enyzmes function by lowering the E_A barrier; the change in G is unaffected

thermodynamics

-the study of energy transformations

→how heat, work, temp, and energy react 

→describes how energy in a system changes 

→determines whether a system can perform useful work on its surroundings

closed system

-isolated from its aurroundings

-reactions in a closed system eventually reach equilibrium (change in G = 0)

open system

-energy and matter can be transferred between the system and surroundings

-organisms are open systems

→constant flow of food in and waste out

→prevents equilibrium (change in G does not equal 0)

a multistep open hydroelectric system

-cellular respiration is analogous to this system

-glucose is broken down in a sereis of exergonic reactions that power the work of the cell 

- The product of each reaction becomes the reactant for the next, so no reaction reaches equilibrium

the laws of thermodynamics

-1st

-2nd