Class Notes (806,680)
Canada (492,403)
Biology (6,676)
Biology 1002B (1,340)
Tom Haffie (863)

Supplementary Biology Notes.doc

4 Pages
Unlock Document

Western University
Biology 1002B
Tom Haffie

BIOL 1020 – CHAPTER 8 LECTURE NOTES Chapter 8: An introduction to metabolism Why do organisms need energy? How do organisms manage their energy needs? I. Energy and thermodynamics A. Living organisms require energy to do work, any change in state or motion of matter 1. energy can be expressed in units of work (kJ) or heat energy (kcal); 1 kcal = 4.184 kJ 2. energy can change forms (energy conversion) 3. organisms carry out transformation in energy forms between potential energy (capacity to do work) and kinetic energy (energy of motion, actively performing work) 4. organisms commonly use chemical bonds for storage and transfer of (potential) energy 5. work is required for the processes of life B. Two laws of thermodynamics describe the constraints on energy usage 1. First law: the total amount of energy (+ matter) in a closed system remains constant (principle of conservation of energy) • The universe is a closed system • Living things are open systems 2. Second law: in every energy conversion, some energy is converted to heat energy that is lost to the surroundings, and thus cannot be used for work • Every energy conversion increased the entropy of the universe. • Energy converted to heat in the surroundings increases entropy (spreading of energy) • no energy conversion is 100% efficient • organisms must get a constant influx of energy because of energy is lost in conversions II. Metabolic reactions include anabolism and catabolism, and involve energy transfers A. Recall that metabolism is the sum of chemical activities in a organism B. Metabolism can be divided into anabolism (anabolic reactions) and catabolism (catabolic reactions) 1. anabolic reactions are processes that build complex molecules from simpler ones 2. catabolic reactions are processes the break down complex molecules into simpler ones C. Chemical reactions involve changes in chemical bonds and substance concentrations, along with changes in free energy 1. free energy = energy available to do work in a chemical reaction (such as: create a chemical bond) • free energy changes depend on bond energies and concentrations of reactants and products • bond energy = energy required to break a bond; value depends on the bond • left undisturbed, reactions will reach dynamic equilibrium when the relative concentrations of reactants and products is correct  forward and reverse reaction rates are equal; concentrations remain constant  cells manipulate relative concentrations in many ways, so that equilibrium is rare for key reactions 2. exergonic reactions – the products have less free energy than reactants • the difference in energy is released and is available to do work • exergonic reactions are thermodynamically favored; thus, they are spontaneous, but not necessarily fast (more on activation energy later) • catabolic reactions are usually exergonic • ATP + H O2à ADP + P is hiihly exergonic in cellular conditions 3. endergonic reactions – the products have more free energy than the reactants • the difference in free energy must be supplied (stored in chemical bonds) • endergonic reactions are not thermodynamically favored, so they are not spontaneous • an endergonic reaction is coupled with an exergonic reaction to provide the needed energy to drive an endergonic reaction  together, the coupled reactions must have a net exergonic nature  reaction coupling requires that the reactions share a common intermediate(s) EXAMPLE: A à B (exergonic) C à D (endergonic) Coupled: A + C à B + D (overall exergonic) Actually: A + C à I à B + D  typically, the exergonic reaction in the couple is ATP + H2O à ADP + P i • anabolic reactions are usually endergonic One way that organisms manage their energy needs is to use ATP as a ready energy source for many reactions. 1 of 4 BIOL 1020 – CHAPTER 8 LECTURE NOTES III. ATP is the main energy currency in cells A. Recall ATP (adenosine triphosphate) is a nucleotide with adenine base, ribose sugar, and a chain of 3 phosphate groups B. The last two phosphate groups are joined to the phosphate group chain by unstable bonds; breaking these bonds is relatively easy, and releases energy; thus: 1. hydrolysis of ATP to ADP and inorganic phosphate (P ) releasis energy ATP + H O 2 ADP + P i 2. the amount of energy released depends in part on concentrations of reactants and products, but is generally ~30 kJ/mol C. Intermediates are involved when ATP hydrolysis is coupled to a reaction to provide energy; often these involve phosphorylated compounds, with the inorganic phosphate removed from ATP transferred onto another compound rather than being immediately released EXAMPLE: glucose + fructose à sucrose + H O (e2dergonic; requires ~27 kJ/mol) ATP + H O 2 ADP + P (providis ~30 kJ/mol) coupled: glucose + fructose + ATP + H O à2sucrose + H O + ADP2+ P i intermediates: glucose + fructose + ATP + H O à2glucose-P + fructose + ADP à sucrose + H O + ADP + P 2 simplified: glucose + fructose + ATP à sucrose +ADP + P i D. Thus, energy transfer in cellular reactions is often accomplished through transfer of a phosphate group from ATP E. Making ATP involves an endergonic condensation reaction 1. reverse of an exergonic reaction is always endergonic ADP + P à iTP + H O (ende2gonic, usually requires more than ~30 kJ/mol) 2. must be coupled with an exergonic reaction; typically from a catabolic pathway F. ATP is typically created in catabolic reactions and used in anabolic reactions, linking those aspects of metabolism G. Cells maintain high levels of ATP relative to ADP 1. maximizes energy available from hydrolysis of ATP 2. ratio typically greater than 10 ATP: 1 ADP H. Overall concentration of ATP still very low 1. supply typically only enough for a few seconds at best 2. instability prevents stockpiling 3. must be constantly produced 4. in a typical cell, the rate of use and production of ATP is about 10 million molecules per second 5. resting human has less than 1 g of ATP at any given time but uses about 45 kg per day Redox reactions are used to harvest energy from some chemicals; the acceptors of that energy typically cannot be used directly as energy currency. IV. Redox reactions are also used for energy transfer A. Electrons can also be used for energy transfer 1. Redox reactions: recall reduction, gain electrons; oxidation, lose electrons; both occur simultaneously in cells (generally no free electrons in cells) 2. Typically, the oxidized substance gives up energy with the electron, the reduced substance gains energy with the electron 3. Commonly occur as a chain of redox reactions or electron transfers (more on electron transport chains later) 4. As the electron is transferred to an acceptor molecule, it releases free en
More Less

Related notes for Biology 1002B

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.