Textbook Chapter 15: Metabolism-Basic Concepts and Design Flashcards
As discussed, digestion renders the macromolecules in our meals into biochemically more manageable fragments. Proteins are hydrolyzed to the 20 amino acids, polysaccharides are hydrolyzed to simple sugars such as glucose, and fats are hydrolyzed to fatty acids. This stage is strictly ……..
- a preparation stage; no useful energy is captured at this point
The generation of energy from the oxidation of food takes place in three stages (3):
- In the first stage (top panel), large molecules in food are broken down into smaller units
- In the second stage (middle panel), these numerous small molecules are degraded to a few simple units that play a central role in metabolism. In fact, most of them—sugars, fatty acids, glycerol, and several amino acids—are converted into acetyl CoA the activated two-carbon unit that is the fuel for the final stages of aerobic metabolism. Some adenosine triphosphate (ATP) is generated in the second stage, but the amount is small compared with that obtained in the third stage.
- In the third stage (bottom panel), ATP is produced from the complete oxidation of acetyl CoA. The third stage consists of the citric acid cycle and oxidative phosphorylation, which are the final common pathways in the oxidation of fuel molecules.
——– brings the breakdown products of proteins, sugars, and fats into the citric acid cycle [also called the tricarboxylic acid (TCA) cycle or Krebs cycle], where they are completely oxidized to ——
- Acetyl Co-A
- CO2
Living organisms require a continual input of free energy for three major purposes:
(1) the performance of mechanical work in muscle contraction and cellular movements
(2) the active transport of molecules and ions
(3) the synthesis of macromolecules and other biomolecules from simple precursors.
phototrophs
Photosynthetic organisms
chemotrophs
obtain energy through the oxidation of carbon fuels
Large molecules are constructed step by step in a series of ……
linked reactions called metabolic pathways
The enzymes involved in metabolism are organized into
large complexes. The formation of metabolic enzymes into complexes (2):
- This organization allows for faster transfer of substrates and products between the individual enzymes within the complex. Instead of diffusing freely in the cellular environment, substrates are channeled directly from one enzyme to another, reducing the chance of side reactions and increasing the overall speed of the metabolic process.
- Some metabolic pathways involve the production or consumption of unstable or toxic intermediates. By forming complexes, cells can compartmentalize these reactions and efficiently process these intermediates without causing harm to the cell. The close proximity of enzymes within the complex allows for rapid conversion of these intermediates into more stable or less toxic forms.
Metabolism
a linked series of chemical reactions that begins with a particular biomolecule and converts it into some other required biomolecule in a carefully defined fashion
intermediary metabolism
These pathways are interdependent—a biochemical ecosystem—and their activities are coordinated by exquisitely sensitive means of communication in which allosteric enzymes are predominant.
Glucose is metabolized to pyruvate in 10
linked reactions. Under anaerobic conditions, pyruvate is —– and, under aerobic conditions, to —. The glucose-derived carbon atoms of acetyl CoA are subsequently oxidized to —–
- metabolized to lactate
- acetyl CoA
- CO2
catabolism
Those reactions that transform fuels into cellular energy are called catabolic reactions
anabolism
Those reactions that require energy—such as the synthesis of glucose, fats, or DNA
amphibolic pathways
When pathways can be either anabolic or catabolic, depending on the energy conditions in the cell
A pathway must satisfy two criteria minimally:
(1) the individual reactions must be specific (the pathway functions as intended and doesn’t involve unwanted side reactions)
(2) the entire set of reactions that constitute the pathway must be thermodynamically favored
A reaction that is specific will yield only —— or —— from its reactants. For example, ——
- one particular product
- set of products
- glucose can undergo step-by-step conversion to yield carbon dioxide and water as well as useful energy.
A reaction can take place spontaneously only if the change in free energy, is —-
negative
The ΔG of a reaction depends on (2)
- the nature of the reactants and products (expressed by the term ΔG°’, the standard free-energy change)
- Their concentrations (expressed by the second term).
An important thermodynamic fact is that the overall free energy change for a chemically coupled series of reactions is equal to ——-
- the sum of the free-energy changes of the individual steps
- This principle is based on the fact that Gibbs free energy is a state function, meaning it depends only on the initial and final states of the system and not on the path taken to reach those states. Therefore, the overall change in Gibbs free energy for a series of coupled reactions can be calculated by summing the ΔG values for each individual reaction.
Metabolic pathways are formed by the —— such that the overall free energy of the pathway is negative
- coupling of enzyme-catalyzed reactions
Part of the free energy derived from the oxidation of carbon fuels and from light is transformed into this readily available molecule
adenosine triphosphate (ATP)
Most of catabolism consists of reactions that …
extract energy from fuels such as carbohydrates and fats and convert it into ATP
ATP is an energy-rich molecule because …
its triphosphate unit contains two phosphoanhydride linkages. Phosphoanhydride linkages are formed between two phosphoryl groups accompanied by the loss of a molecule of water. A large amount of free energy is liberated when ATP is hydrolyzed to adenosine diphosphate (ADP) and
orthophosphate (Pi) or when is hydrolyzed to
adenosine monophosphate (AMP) and pyrophosphate (PPi)
Explain why ATP has a central position in phosphoryl-transfer reactions.
Creatine phosphate
A high-phosphoryltransfer-potential molecule in vertebrate muscle, serves as a reservoir of high-potential phosphoryl groups that can be readily transferred to ADP. This reaction is catalyzed by creatine kinase.
The more reduced a carbon is to begin with, the ——- is released by its oxidation
more free energy
Nicotinamide adenine dinucleotide NAD+ (4):
what it is made of+ what it is known as+ reactive part?+ what happens in oxidation?
- a pyridine nucleotide
- a major electron carrier in the oxidation of fuel molecules
- The reactive part of NAD+ is its nicotinamide ring, a pyridine derivative synthesized from the vitamin niacin
- In the oxidation of a substrate, the nicotinamide ring of NAD+ accepts a hydrogen ion and two electrons
Flavin adenine dinucleotide (FADH2) (2)
Reactive part+accept
- The reactive part of is its isoalloxazine ring, a derivative of the vitamin riboflavin
- Can accept two electrons. In doing so takes up two protons
Coenzyme A reactive site
- ## The terminal sulfhydryl group in CoA is the reactive site, where other molecules attach themselves to
Acyl Group
Acyl groups are linked to the sulfhydryl group of CoA by
thioester bonds
The hydrolysis of a thioester is thermodynamically more favorable than that of an oxygen ester, such as those in fatty acids, because :
the electrons of the C=O bond form less
stable resonance structures with the C-S bond than with
the C-O bond.
