Why do cells need energy?
Energy to do the work of the cell which includes:
- Movement, growth, pump ions, and perform reactions needed for cellular function, etc.
Phototrophs vs Chemotrophs
- Organisms can harvest energy from their environment in one of two ways:
a. Obtain energy from the sun → phototroph - Plants are the most common → obtain energy from the sun to convert CO, & water into sugar and O2
b. Obtain energy from chemical compounds → chemotroph - Animals are the most common chemotrophs → obtain energy by ingesting other organism and breaking them down into CO2 & water
Autotroph vs Heterotroph
- Organisms can further be classified in two ways based on their source of carbon:
- If the organism can convert CO2 into glucose since they make their own organic source of carbon → autotroph
- If the organism is unable to convert CO2, they must ingest other organisms/molecules for a source of carbon → heterotroph
What is metabolism?
Metabolism → chemical processes that occur in a living organism to maintain life
- Includes the building up and breakdown of chemical compounds → allows energy to be harnessed or released
- These reactions are continuously happening in cells
- Many of these reactions are linked in such a way that the products of one reaction are the reactants of the next reaction → forming pathways
- There are two branches of metabolism → anabolism & catabolism
Types of energy:
- Two types of energy:
- Energy that is not associated with movement but rather is stored → potential energy
- Energy of motion → Kinetic energy
- Chemical bonds between pairs of atoms in a molecule hold onto a form of potential energy → Chemical Energy
- Bond strength & potential energy are linked
- Strong bonds = less potential energy
- Weak bonds = more potential energy
What is the most common chemical form of energy the body uses?
- Cells do not use all the energy they have at once best to keep it stored in a chemical form that is readily accessible to the cell
- Most common chemical form used by the cell is ATP →
the energy currency of the cell - The ATP molecule contains energy in its chemical bonds
- ATP (adenosine triphosphate) is composed of:
- Adenine
- A five-carbon sugar → ribose
- Three phosphate groups
- Note: if less than 3 phosphates:
- Only two phosphate groups → ADP (Adenosina diphosphate)
- Only one phosphate group → AMP (Adenosine monoprosphate)
How does ATP provide energy?
- ATP provides energy in a form that all cells can readily use → to perform the work of the cell
- ATP has a high amount of energy → the bonds between phosphate groups are weak
- Has high potential energy
- When the bonds between the phosphate groups are broken → the potential energy is released for the cell to do work
- Important: the chemical energy of ATP is held in the bonds connecting the phosphate groups
Examples of cellular work
- DNA, RNA, and protein synthesis
- Vesicle movement in a cell
- Pumping substances across membranes
- Breaking down fats to release energy
- Breaking down proteins into amino acids
- Oxidizing sugars to produce ATP
Laws of Thermodynamic: First Law
- Thermodynamics is the study of changes in energy that accompany events in the universe
- Concepts allow us to predict the direction that events will take and whether input of energy is required
- First Law → energy can be neither created nor destroyed
- Energy can be converted from one form to another → e.g. conversion of sunlight to chemical energy
Laws of Thermodynamic: Second Law
- Events in the universe have direction → proceed from a higher energy state to a lower energy state
- These events are thermodynamically favourable and are said to be spontaneous → no input of external energy
- Results in a reduction in the amount of useable energy → energy transformations are not 100% efficient
How are chemical reactions conducted?
- Atoms keep their identity but the bonds linking them change during a chemical reaction
- The concentrations of products and reactants can influence whether a reaction proceeds forward or backward
Free Energy (G)
- The amount of energy in a system available to do work → Gibbs free energy
- ΔG is the symbol for the difference in Gibbs free energy between the reactants and products of a chemical process
- If the products of a reaction have more free energy than the reactants → ΔG is positive
- Thermodynamically unfavourable → endergonic
- Needs an input of energy
- If the reactants have more free energy than the products → ΔG is negative
- Thermodynamically favourable → exergonic
- Energy is available for use in other processes
Gibbs Free equation
- Total energy (H) = energy available to do work (G) + energy lost to entropy (S)
- This can be rearranged to illustrate the state of Gibbs free energy:
ΔG = ΔH - TΔS - Where:
- H = total energy (enthalpy)
- G = energy available to do work
- S = energy lost to entropy or disorder
- T = absolute temperature in Kelvin
Remember: Δ = Change = Final state - initial state
What happens when ATP is hydrolyzed?
Answer: The reaction of ATP with water is exergonic (spontaneous) → releases energy
- At physiological pH → the phosphate groups in ATP are negatively charged & resist one another
- Compared to ATP, which has three phosphate groups, ADP contains two → meaning that it has a lower potential energy
What is activation energy?
- Chemical transformations require the breakage of certain covalent bonds within the reactant
- Reactants must contain sufficient kinetic energy to overcome the activation energy barrier → Eₐ
- Enzymes catalyze reactions by decreasing magnitude of Eₐ barrier → reaction can proceed
- Cells can carry out many reactions with a + ΔG (unfavorable)
Why do unfavorable reactions proceed in a cell?
- Relative concentrations of reactants to products are maintained above that defined by equilibrium constant (The cell keeps the ratio of [Reactants] to [Products] very high, which effectively makes the reaction favorable in the local environment.)
- Coupling endergonic and exergonic reactions - e.g. hydrolysis of ATP → drives endergonic reactions (The cell directly powers an “uphill” (unfavorable) reaction by linking it to a “downhill” (favorable) reaction. The most common energy source for this is ATP.)
How are chemical reactions catalyzed?
Chemical reactions are catalyzed by proteins called → enzyme
- The active site of an enzyme is formed by the assembly of certain amino acids in a three-dimensional structure
- The enzyme active site binds the substrate(s) and converts it to the products)
- The active site binds the substrate(s) and helps to stabilize the transition state → lowers the activation energy
- Anabolic and catabolic reactions are catalyzed by enzymes
How are enzyme activities affected?
- Enzyme activity can be reduced by two different kinds of inhibitors reversible & irreversible
- Enzyme activity can be increased by activators
- Because energy is needed for chemical reactions → many metabolic pathways are regulated
- An example of regulation is where the final product in a pathway inhibits the first step of the reaction known as → negatue feedback
- Important for maintaining balance in the cell and in helping the cell to conserve energy
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Introduction To Cell Biology And The Cell Theory28
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Molecules Of Life41
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Cells And Membrane40
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Nucleic Acids And Information Flow29
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Protein Structure, Function, And Synthesis32
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Making Life Work18
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Cellular Respiration32
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Photosynthesis25
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Cell Signalling29
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Cell And Tissue Form34
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DNA Replication And Cell Division49
