Energy and metabolism

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Life can be viewed as constant flow of energy , channeled by organism to do the work of living. Each of the significant

property by which we define life --- order, growth, responsiveness, reproduction and internal regulation ---

requires constant supply of energy. Animals need to eat for a wide variety of cellular functions. Deprived of a source of energy, LIFE STOPS. Therefore a comprehensive study of

life would be impossible without discussing bioenergetics, the analysis of how energy powers the activities of living

systems.

Energy and

Metabolism

Charilyn D. Dela Cruz

The Flow of Energy in living Systems

* Cells are governed by the laws of physics and chemistry , so we must understand these laws in order to understand how cells function.

–The study of science that deals with heat changes.

It is the capacity to do work.

Energy* much of the work that living organisms carry out involves transforming potential to kinetic energy. • Energy can take many forms:

mechanical energy, heat , sound, electric current, light or radioactivity.* Heat is the most convenient way of measuring energy because all other forms of energy can be converted into heat.

–The unit of heat most commonly employed in biology is the kilocalorie (kcal).

–One kilocalorie is equal to 1000 calories (cal).

* One calorie is the heat required to raised the temperature of one gram of water one degree Celsius (0C )

The sun provides energy for living systems

• It is estimated that the sun provides the Earth with more than 13 x 1023 calories per year or 40 billion calories per second.

• Plants , algae and certain kinds of bacteria capture this energy in the form of photosynthesis.

• In the process of photosynthesis, energy from the sun is stored as potential energy in the covalent bonds between atoms in the sugar molecules.

• The strength of a covalent bond is measured by the amount of energy required to break it.

• For example: it takes 98.8 kcal to break one mole (6.023 x 1023 ) of the carbon – hydrogen (C-H) bond found in organic molecules.

Oxidation – Reduction Reaction Transfer

– Oxidation – reduction ( redox) always takes place together because every electron that is lost by one atom through oxidation is gained by another atom through reduction.

– Oxidation is the process by which molecule loses electron.– Reduction , a process by which molecule gains electron.– Oxygen is the most common electron acceptor in the

biological systems.– Redox play a key role in the flow of energy through

biological systems.

Energy (E) Transfer Overview

The Laws of Thermodynamics and Free Energy

– First Law states that energy cannot be created or destroyed.

– Second Law states that some energy is lost as disorder increases.

– Some of the energy dissipates into the environment as heat.

– Energy continuously flows to the biological world in one direction with new energy from the sun constantly entering the system to replace the energy dissipated as heat.

Chemical reactions can be predicted based on changes in Free Energy

The amount of energy actually available to break and subsequently form other chemical bonds is called the FREE ENERGY of that molecule. • Free energy is the energy available to do work in a

system.

Endergonic – reaction that requires an input of energy- energy must be supplied

Exergonic – “ outward energy”, - release the excess free energy as heat.

Energy and Chemical Reactions

Activation energy- Extra energy needed to destabilize existing chemical bonds and initiate a chemical rxn.

ATP: The Energy Currency of Cells

KEY CONCEPT * All cells need chemical energy.• The chief currency all cells used for their energy

transactions is the nucleotide Adenosine Triphosphate

* ATP powers almost every energy requiring process in the cell from making sugars to supplying activation energy for chemical reactions, to actively transporting substances across membranes, to moving to the environment and growing.

–Adenosine triphosphate (ATP) is a nucleotide triphosphate used in cells as a coenzyme often called the "molecular unit of currency" of intracellular energy transfer.

- ATP transports chemical energy within cells for metabolism.

- It is one of the end products of photophosphorylation, aerobic respiration and fermentation.

- It is used by enzymes and structural proteins in many cellular processes, including biosynthetic reactions, motility, and cell division.

Structure of ATP

O

OH OH

N

N

N

N

NH2

CH2OPOPOPO-O O O

O- O- O-

adenine

ribose

adenosine triphosphate ATP

ADP

adenosine diphosphate

How ATP stores energy

–The key to how ATP stores energy lies in its triphosphate group

ATP was discovered in 1929 by Karl Lohmann, and independently by Cyrus Fiske and Yellapragada Subbarow of Harvard Medical School. It was proposed to be the intermediary molecule between energy-yielding and energy-requiring reactions in cells by Fritz Albert Lipmann in 1941.It was first artificially synthesized by Alexander Todd in 1948.

Energy is released as food is oxidizedUsed to form ATP from ADP and Pi

ADP + Pi + Energy ATP In cells, energy is provided by the hydrolysis of ATP ATP ADP + Pi + Energy

ATP CYCLES CONTINUOUSLY

Biochemical pathways may have evolved in step wise fashion

In the primordial soup of early oceans, many reactions were probably single step reactions combining two molecules. As one of the substrates molecules was depleted, organism having an enzyme that could synthesize the substrate would have a selective advantage. In this manner biochemical pathways are thought to have evolved “backward” with new reactions producing limiting substrates for existing reactions.

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Feedback inhibition regulates some biochemical pathways

• Biosynthetic pathways are often regulated by the end product of the pathway• Feedback inhibition occurs when the end product of a reaction• combines with an allosteric site to shut down the enzymes activity.

Inhibition

Substrate1

Substrate2

Enzyme B Substrate3

Enzyme C Substrate4

Enzyme DProduct

Rate-limitingEnzyme A

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THERMODYNAMICS

ENERGY