Chapter 25 Flashcards
Metabolism
Refers to all of the chemical reactions that occur in the body.
What are the two types of metabolism? Describe them:
- Catabolism: chemical reactions that break down complex organic molecules into simpler ones. Are exergonic (produce more energy than they consume).
- Anabolism: chemical reactions that combine simple molecules and monomers to form the body’s complex structural and functional components. Are endergonic (consume more energy than they produce)
ATP (adenosine triphosphate)
The molecule that participates most often in energy exchanges in living cells. Couples energy-releasing catabolic reactions to energy-requiring anabolic reactions. “Energy currency” of a living cell. A typical cell has about a billion molecules of ATP, each of which typically last less than a minute before being used.
What is the energy released in catabolism used for?
About 40% of the energy released in catabolism is used for cellular functions; the rest is converted to heat, some of which helps maintain normal body temperature.
Oxidation
The removal of electrons from an atom or molecule; the result is a decrease in the potential energy of the atom or molecule. Because most biological oxidation reactions involve the loss of hydrogen atoms, they are called dehydrogenation reactions.
Reduction
The opposite of oxidation; it is the addition of electrons to a molecule. Reduction results in an increase in the potential energy of the molecule.
What two coenzymes are commonly used by animal cells to carry hydrogen atoms to another compound after a substance is oxidized?
- Nicotinamide adenine dinucleotide (NAD) (a derivative of the B vitamin niacin)
- Flavin adenine dinucleotide (FAD) (a derivative of vitamin B2 (riboflavin))
Oxidation–reduction (redox reactions)
Oxidation and reduction reactions are always coupled; each time one substance is oxidized, another is simultaneously reduced. In these reactions, oxidation is usually exergonic.
Phosphorylation
The addition of a phosphate group to a molecule. Increases its potential energy.
What three mechanisms of phosphorylation do organisms use to generate ATP?
- Substrate-level phosphorylation
- Oxidative phosphorylation
- Photophosphorylation
Electron transport chain
A series of electron acceptors. Oxidative phosphorylation removes electrons from inorganic compounds and passes them through the electron transport chain to molecules of O2.
What are the four ways that glucose can be used?
- ATP production
- Amino acid synthesis
- Glycogen synthesis
- Triglyceride synthesis
Glycogenesis
Synthesis of glycogen from glucose.
Lipogenesis
Synthesis of triglycerides.
How does glucose get moved into cells?
Get moved by gluT molecules, which are a family of transporters that bring glucose into cells via facilitated diffusion. A high level of insulin increases the insertion of one type of GluT, called GluT4, into the plasma membranes of most body cells, thereby increasing the rate of facilitated diffusion of glucose into cells. In neurons and hepatocytes, however, another type of GluT is always present in the plasma membrane, so glucose entry is always “turned on.” On entering a cell, glucose becomes phosphorylated. Because GluT cannot transport phosphorylated glucose, this reaction traps glucose within the cell.
Glucose catabolism
Complete oxidation of glucose (cellular respiration) is chief source of ATP in cells; consists of glycolysis, Krebs cycle,
and electron transport chain. Complete oxidation of 1 molecule of glucose yields maximum of 30 or 32 molecules
of ATP.
Cellular respiration
The oxidation of glucose to produce ATP.
What four sets of reactions does cellular respiration involve?
- Glycolysis
- Formation of acetyl coenzyme A
- Krebs cycle reactions
- Electron transport chain reactions
What is the difference between aerobic and anaerobic?
- Aerobic: with oxygen.
- Anaerobic: without oxygen.
Does glycolysis occur under aerobic or anaerobic conditions?
Glycolysis does not require oxygen, so it can occur under either aerobic or anaerobic conditions.
Aerobic respiration
What the reactions of the Krebs cycle and electron transport chain are referred to as since they require oxygen.
Anaerobic glycolysis
When glycolysis occurs by itself under anaerobic conditions.
Glycolysis (step one in cellular respiration)
Occurs in cytosol. Conversion of glucose into pyruvic acid results in production of some ATP. Reactions do not require oxygen.
What happens to pyruvic acid when oxygen is plentiful versus when oxygen scarce?
When oxygen is plentiful, pyruvic acid enters mitochondria, is converted to acetyl coenzyme A, and enters the Krebs cycle (aerobic pathway). When oxygen is scarce, most pyruvic acid is converted to lactic acid via an anaerobic pathway.
Formation of acetyl coenzyme A (step two in cellular respiration)
Occurs in mitochondria. A transition step that prepares pyruvic acid for entrance into the Krebs cycle. This step also produces energy-containing NADH + H+ plus carbon dioxide (CO2).
Coenzyme A (CoA)
Used in the transition step between glycolysis and the Krebs cycle in cellular respiration.
Acetyl group
A 2-carbon fragment that pyruvic acid get converted into when a molecule of CO2 is removed from it.
Decarboxylation
A substance that removes CO2 from pyruvic acid, which converts it into an acetyl group.
Acetyl coenzyme A
A molecule produced by an acetyl group attaching to coenzyme A.
Krebs cycle reactions (citric acid cycle) (step three in cellular respiration)
Occurs in mitochondria. Cycle includes series of oxidation–reduction reactions in which coenzymes (NAD+ and FAD) pick up hydrogen ions and hydride ions from oxidized organic acids; some ATP produced. CO2 and H2O are by-products. Reactions are aerobic.
Electron transport chain reactions (step four in cellular respiration)
Occurs in mitochondria. Third set of reactions in glucose catabolism: another series of oxidation–reduction reactions, in which electrons are passed from one carrier to next; most ATP produced. Reactions require oxygen (aerobic cellular respiration).
Chemiosmosis
In chemiosmosis, ATP is produced when hydrogen ions diffuse back into the mitochondrial matrix.
What five types of molecules and atoms serve as electron carriers?
- Flavin mononucleotide (FMN)
- Cytochromes
- Iron-sulfur (Fe-S) centers
- Copper (Cu) atoms
- Coenzyme Q (Q)
What is the summary of cellular respiration
23-25 ATP molecules from the ten molecules of NADH + H+, 3 ATP molecules from the two molecules of FADH2, 2 ATP molecules from glycolysis, and 2 ATP molecules from the Krebs cycle. A total of 30-32 ATP molecules are generated for each molecule of glucose catabolized during cellular respiration.
Glucose anabolism
Some glucose is converted into glycogen (glycogenesis) for storage if not needed immediately for ATP production. Glycogen can be reconverted to glucose (glycogenolysis). Conversion of amino acids, glycerol, and lactic acid into glucose is called gluconeogenesis.
Glycogen
A polysaccharide that is the only stored form of carbohydrate in the body. If glucose is not needed immediately for ATP production, it combines with many other molecules of glucose to form glycogen.
Glycogenesis
The synthesis of glycogen. Carried out by hepatocytes and skeletal muscles cells, which are stimulated by insulin from pancreatic beta cells.
Glycogenolysis
The process of splitting glycogen into its glucose subunits. Stimulated by glucagon and epinephrine.
Gluconeogenesis
The process by which glucose is formed from noncarbohydrate sources, such as triglycerides, lactic acid, and certain amino acids (think neo = “new”ly formed). Stimulated by cortisol and glucagon
Lipids
Are nonpolar and therefore very hydrophobic molecules. Don’t dissolve easily in water (Eg. Triglycerides).
Lipoproteins
“Transport vehicles”. Lipid and protein combinations - spherical particles with an outer shell of proteins, phospholipids, and cholesterol molecules surrounding an inner core of triglycerides and other lipids. Since lipids aren’t water soluble on their own, they get combined with proteins so that they can be transported in the blood.
Apoproteins (apo)
Proteins in the outer shell of lipoproteins. Designated by the letters A, B, C, D, and E, plus a number. In addition to helping solubilize the lipoprotein in body fluids, each apoprotein has a specific function.
What are the four major classes of lipoproteins? Describe them:
- Chylomicrons: transport dietary (ingested) lipids to adipose tissue for storage.
- Very-low-density lipoproteins (VLDLs): contain mainly endogenous (made in body) lipids.
- Low-density lipoproteins (LDLs): carry 75% of the total cholesterol in blood and deliver it to cells throughout the body. Contains the “bad” cholesterol.
- High-density lipoproteins (HDLs): remove excess cholesterol from body cells and the blood and transport it to the liver for elimination. Contains the “good” cholesterol.
What are the two sources of cholesterol in the body?
- Foods (some)
- Hepatocytes (most)