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The _____ are the primary sites of oxygen use in the cell and are responsible for most of the metabolic energy (adenosine triphosphate, or ATP) produced in cells.
Cells of all multicellular organisms are called _____.
Eukaryotic cells evolved from simpler, more primitive cells called _____.
The _____ is the membrane encapsulating the cell.
The _____, which is a gel-like, aqueous, transparent substance that fills the cell, connects the various membranes of the cell.
In plasma membranes, the sugar residues are all exposed to the outside of the cell, forming what is called the _____, the layer of carbohydrate on the cell's outer surface.
The electron transport (respiratory) chain is central to the process of _____, the mechanism by which most cellular ATP is produced.
The function of the _____ is to couple the energy released by nutrient oxidation to the formation of ATP.
electron transport chain
The _____ is a network of membranous channels pervading the cytoplasm and providing continuity between the nuclear envelope, the Golgi apparatus, and the plasma membrane. This structure, therefore, is a mechanism for communication from the innermost part of the cell to its exterior.
endoplasmic reticulum (ER)
_____ are cell organelles that contain digestive enzymes.
_____ are cell organelles containing enzymes that perform oxidative catabolic reactions.
_____ refers to the digestion of intracellular components (including organelles) by lysosomes.
Proteins that modify the cell's response to its environment
Proteins that regulate the flow of nutrients into and out of the cell
The catalysts for the hundreds of biochemical reactions taking place in the cell.
_____ are enzymes that phosphorylate (add phosphate groups to) other enzymes and, in doing so, convert the enzymes from inactive forms into active forms.
If an enzyme has a high Km value, then the enzyme has a (low/high) affinity for its substrate.
The regulation of metabolic pathways occurs through what three major mechanisms?
1. covaent modification of enzymes through hormone stimulation
2. modulation of allosteric enzymes
3. increase in enzyme concentration by induction
Enzymes that catalyze all reactions in which one compound is oxidized and another is reduced.
Types of oxidoreductases include: dehydrogenases, reductases, oxidases, peroxidases, hydroxylases, and oxygenases
Examples of oxidoreductases are the enzymes found in the electron transport chain located on the inner membrane of the mitochondria. Other exampes are the cytochrome P450 enzymes located on the ER of liver cells
Enzymes that catalyze reactions not involving oxidation and reduction, in which a functional group is transferred from one substrate to another.
Included in this group of enzymes are transketolase, transaldolase, transmethylase, and the transaminases.
The transaminases (alpha-amino transferases), which figure so prominently in protein metabolism, fall under this classification and are located primarily in the mitochondrial matrix.
Enzymes that catalyze cleavage of bonds between carbon atoms and some other kind of atom by adding water.
Digestive enzymes fall within this classification, as do those enzymes contained within the lysosome of the cell.
Types include; esterases, amidases, peptidases, phosphatases, and glycosidases
Enzymes that catalyze cleavage of carbon-carbon, carbon-sulfur, and certain carbon-nitrogen bonds (peptide bonds excluded) without hydrolysis or oxidation-reduction.
Citrate lyase, which frees acetyl CoA for fatty acid synthesis in the cytoplast, is a good example of an enzyme belonging to this cassification.
Types include; decarboxylases, aldolases, synthetases, cleavage enzymes, deaminases, nucleotide cyclases, hydrases or hydratases, and dehydratases
Enzymes that catalyze the interconversion of optical or geometric isomers.
Phosphohexose isomerase, which converts glucose 6-phosphate to fructose 6-phosphate in glycolysis (occurring in the cytoplast), exemplifies this particular class of enzyme.
Types include; isomerases, racemases, epimerases, and mutases
Enzymes that catalyze the formation of bonds between carbon and a variety of other atoms, including oxygen, sulfur, and nitrogen.
Forming bonds catalyzed by ligases requires energy that usually is provided by hydrolysis of ATP.
A good example of a ligase is acetyl CoA carboxylase, which is necessary to initiate fatty acid synthesis in the cytoplast. Through the action of acetyl CoA carboxylase, a bicarbonate ion (HCO-3) is attached to acetyl CoA to form malonyl CoA, the initial compound in starting fatty acid synthesis.
Secreted enzymes that function in the bloodstream.
Examples include the enzymes involved in the bloodclotting mechanism.
Focuses on intracellular enzymes, which, because of a problem within the cell structure, escape from the cell and ultimately express their activity in the serum.
Factors contributing to cellular damage and resulting in abnormal egress of cellular enzymes include:
- tissue ischemia, (ischemia refers to an impairment of blood flow to a tissue or part of a tissue; it deprives affected cells of oxygen and oxidizable nutrients)
- tissue necrosis
- viral attack on specific cells
- damage from organic chemicas such as alcohol and organophosphorus pesticides
- hypoxia (inadequate intake of oxygen)
Conditions for enzymes to be suitable for diagnostic purposes include:
- The enzyme must have a sufficiently high degree of organ or tissue specificity
- A steep concentration gradient of enzyme activity must exist betwwen the interior and exterior of the cells under normal conditions
- The enzyme must function in the cytoplasmic compartment of the cell
- The enzyme must be stable for a reasonable period of time in the vascular compartment
Mutated genes that encode abnormal, mitosis-signaling proteins that cause unchecked cell division.
The most common cause of increased production of an enzyme, resulting in a spike in its serum concentration, is
Substances that occur in body fluids as a result of malignant disease are called tumor markers.
An organized series of events that, once triggered, leads to cell death. (normally occurring cell death as opposed to pathological cell death)
A prelethal pathway leading to cell death accompanied by cellular swelling.
Energy used in the body is ultimately derived from the energy contained in the _____.
macronutrients -- carbohydrate, fat, and protein (and alcohol)
Comparison of simple combustion and metabolic oxidation
The energy liberated from simple combustion assumes the form of heat only.
- Burning glucose outside the body liberates heat.
- C6H12O6 + 6O2 --> 6CO2 + 6H2O + heat
Approximately 40% of the energy (heat) released by metabolic oxidation (inside the body) is savaged as ATP, with the remainder released in the form of heat.
1 kcal = _____ calories
1 kcal = 1,000 cal.
1 cal = _____ J
1 calorie = 4.18 joules
4.18 J = _____ cal.
4.18 joules = 1 calorie
1 kcal = _____ kJ
1 kilocalorie = 4.18 kilojoule
The potential energy inherent in the chemical bonds of nutrients is released if the molecules undergo oxidation either through combustion or through oxidation within the cell.
This energy is defined as free energy (G) if, on its release, it is capable of doing work at constant temperature and pressure--a condition that is met within the cell.
Gproducts – Greactants = ΔG of the reaction
Where G is free energy and Δ (delta) is a symbol signifying change
A reaction in which the reactants have more free energy than the products; it therefore gives off energy as heat (downhill).
Gproducts – Greactants = ΔG of the reaction is negative
Where G is free energy and Δ is a symbol signifying change
A reaction in which the products have more free energy than the reactants; it therefore requires energy (uphill).
Gproducts – Greactants = ΔG of the reaction is positive
Where G is free energy and Δ is a symbol signifying change
Energy level at which reactant molecules have been activated and can undergo an exothermic reaction.
The energy that must be imposed on the system to raise the reactants to their transition state (activated state).
If a boulder is to roll downhill, it needs to first be nudged out of its resting place at the top of the hill. This nudge is the required activation energy.
The ratio of the equilibrium concentration of product B to that of reactant A:
Keq = [B] / [A]
A Temperature of 25o C (298 K) and a Pressure of 1.0 atm and the presence of both the reactants and the products at their standard concentrations, namely 1.0 mol/L.
ΔG0 where the superscript zero designates the standard conditions.
Standard pH for biochemical reactions.
For most compartments in the body, the pH is near neutral (7.3); for biochemical reactions, a standard pH value of 7 is adopted by convention.
For human nutrition, the free energy change of reactions is designated by ΔG0.
The cell obtains chemical free energy through _____.
the catabolism of nutrient molecules.
An understanding of how chemical energy is transformed from macronutrients (the carbohydrate, protein, fat, and alcohol in food) to storage forms (such as ATP), and how the stored energy is used to synthesize needed compounds for the body, is fundamental to the study of human nutrition.
The addition of phosphate to a molecule.
Phosphorylation can be viewed as occurring in two reaction steps:
1. hydrolysis of ATP to ADP and phosphate
2. addition of the phosphate to the substrate (glucose) molecule
This reaction promotes gucose to a higher energy level, from which it may be indirectly incorporated into gycogen as stored carbohydrate or systematically oxidized for energy.
ATP is formed in the _____ after the macronutrients are _____.
ATP is formed in the electron transport chain after the macronutrients are oxidized.
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