Metabolism
- Cells constantly convert energy and matter from one form to another to stay alive.
- Metabolism refers to all chemical reactions of cells.
Metabolism is divided into two:
Catabolism
- This involves all reactions that break complex molecules into simpler ones.
- Catabolic reactions promote energy transfer from food to a unique form that can be used by cells to work.
Anabolism
- This involves reactions that generate large molecules from smaller molecules.
- For example, steroids promote anabolism facilitating the body to build up proteins in muscles from amino acids.
Cellular work and laws of thermodynamics
- Work is anything that is done that requires effort.
- Energy is the force needed to do work.
- Thermodynamics is the branch of science that studies the relationship between energy and work.
- The laws of thermodynamics include:
- The first thermodynamics law states that energy can’t be created nor destroyed.
- The second thermodynamics law states that chemical reactions that happen spontaneously increase the entropy, or disorder of an isolated system.
The first law of thermodynamics
- This law means that you cannot create new energy nor destroy it.
- Energy to be used has to come from somewhere and be used elsewhere.
- Energy transfer is moving energy from one place to another.
- Different types of energy can be grouped into two categories:
- Potential energy is the energy a molecule or an object possesses due to its position.
- Kinetic energy is the energy of molecules and objects in motion.
Potential energy
- It is also called stored energy.
- It includes several types of energy:
- Chemical potential energy, such as that found in the oil.
- Elastic potential energy
- Gravitational potential energy
The second law of thermodynamics
The law indicates that:
- In every energy system, the system’s potential energy decreases.
- It is not possible to convert heat to work
- In an enclosed system, the reaction proceeds if the total entropy increases.
Going to work in cellular factory
- Synthesis: cells have to build complex molecules such as DNA and proteins from simple molecules.
- Organization: intracellular membranes create cell compartments for the organization of materials.
- Transport and movement: cells transport materials from one cell part to another.
ATP (Adenosine Triphosphate)
- This is the form of energy used by cells.
- ATP has three parts:
- A ribose sugar
- A nitrogenous base.
- Three phosphate groups.
Metabolic pathways
- Metabolic pathways have many characteristics:
- Metabolic pathways are broken into small steps of single chemical reactions.
- Enzymes are important in metabolic processes by lowering activation energies.
- There is energy transfer during metabolism.
Helping hands from enzymes
- Activation energy is the minimum amount of energy required to trigger a reaction.
- Without activation energy, the reaction cannot proceed spontaneously.
- The breakdown of sugars is an exergonic reaction that proceeds spontaneously.
- Cellular enzymes provide differences between anabolism and catabolism.
Importance of enzymes
- Enzymes lower activation energy for reactions.
- Enzymes speed up rates of reactions.
- Enzymes bind substrates on their active sites bringing them together in the proper orientation.
- For a productive collision to occur to speed up a reaction, the following must occur:
- The reaction reactants must collide with each other.
- The reactants must be directed to each other in the correct way for chemical groups to interact.
- The reactants should possess sufficient kinetic energy.
Giving and taking electrons in redox reactions
- During metabolism, an electron can be transferred from one molecule to another.
- When a molecule donates an electron, it is oxidized.
- When a molecule receives an electron, it is reduced.
- Redox reaction occurs when one molecule accepts an electron while another one loses an electron in a reaction.
Getting what you need at the cellular level
- The things needed to keep cell functioning include the following:
- Building blocks for repair and growth. Human cells require building blocks like amino acids which are important in generating cells.
- Energy for cellular work. Animal cells need a constant energy supply for various activities like movement.
- Reducing power. Cells require a constant electron supply to promote anabolic pathways.
Revision
Which statement defines a coenzyme
An organic molecule required for the functioning of an enzyme
An aerobic reaction is one that requires __
Oxygen
The series of reactions involving the conversion of glucose to pyruvate is known as __
Glycolysis
When energy-yielding nutrients are consumed in excess, which one(s) can lead to storage of fat
fat, carbs and protein
Glycolysis is the conversion of __
glucose to pyruvate
Storing excess energy from dietary carbohydrate as body fat requires __ percent of the ingested energy intake
25%
What is a feature of the metabolism of surplus dietary fat
Excess fat is almost all stored
Fatty acid oxidation results in the direct production of __
Acetyl CoA
How many acetyl CoA molecules may be obtained from oxidation of a 16-carbon fatty acid
8
Which of the following can be synthesized from all three energy-yielding nutrients
Acetyl CoA
What is acetaldehyde
An intermediate in alcohol metabolism
What is the major energy carrier molecule in most cells
ATP
Which of the following is a feature of the electron transport chain
It captures energy in the high energy bonds of ATP
Production of excessive amounts of acetyl CoA molecules leads to the synthesis of __
Fatty acids only
Which process leads to the production of urea
oxidation of amino acids
In the average healthy person, about how much time is required by the liver to process the alcohol in a typical drink
1 hour
After digestion and absorption, an amino acid not used to build protein will first be subjected to __
Removal of its amino group
A typical cell contains “powerhouses,” which is another name for __
Mitochondria
In addition to energy, what are the principal end products of cellular oxidation of carbohydrates
Water and carbon dioxide
What organ is the major site for gluconeogenesis
Liver
If the carbohydrate content of the diet is insufficient to meet the body’s needs for glucose, what can be converted to glucose
Amino Acids
When a person is performing intense physical exercise and begins to feel fatigue and a burning pain in the muscles, the response of the muscles is to synthesize more __
lactate
What is one explanation for the generally lower tolerance for alcohol in women in comparison to men
Women have lower amounts of stomach alcohol dehydrogenase
The metabolism of alcohol begins in the __
Stomach
An immediate consequence of a cellular deficiency of oxaloacetate is a slowing of __
The Krebs cycle/ TCA cycle
The Cori cycle involves the interconversion of __
Lactate and glucose
What are the products of the complete oxidation of fatty acids
Water, carbon dioxide and energy
Which of the following is a feature of aerobic metabolism
Energy is produced more slowly than in anaerobic metabolism
What term is specific to reactions in which simple compounds are combined into more complex
Anabolic
