Exam 2 Flashcards
Types of Regulation
Allosteric, Covalent, Induction, Directional shift.
Allosteric
Affects how well the enzyme works. Effectors bind the enzyme (not covalent / not at active site) and either helps or inhibits reaction by:
Helping or hurting substrate binding to enzyme or enzyme activity. NADH/+ ratio affects several allosteric enzymes. Catalyze undirectional, non-reversible reactions
Induction
More enzyme protein is made when inducer is present (alcohol example). Allows for more product to be made and allows body to react to changing circumstances. Sometimes hormones use this mechanism.
Covalent Modification
Binds enzymes covalently (usually phosphate) which affects activity +/-. Occasionally used by hormones and mediated by cAMP
Directional Shift
Direction of a reversible enzyme is often affected by the concentration of r/p; consider glucose-1-phosphate or glucose-6-phosphate.
Phosphorylation of Glucose
Glucose + ATP -> glucose-6-phosphate + ADP
If in Liver Tissue, rxn is catalyzed by Glucokinase (Hexokinase type 4) - high Km and inducible by insulin
If in Muscle Tissue, rxn catalyzed by hexokinase (type 1 and 2) - low Km and inhibited by glucose-6-phosphate
When a cell needs to generate energy or deposit glucose
glucose first needs to be inside of the cell
Km
= [substrate] at half maximum velocity
Glycolysis
Process that oxidizes glucose into 2 units of pyruvate. 2 units of ATP are initially invested, but four are generated along with 2 NADH as byproducts. Aerobic -> pyruvate, anaerobic -> lactate
What happens to NADH generated in the cytosol during glycolysis (Anaerobic)
Used to regenerate NAD+ and maintain glycolysis
What happens to NADH generated in the cytosol during glycolysis (Aerobic)
NADH travels to mitochondria through one of two shuttles (because NADH cannot travel through mitochondrial inner membrane). Malate - Apartate, and Glycerol 3-phosphate shuttle
Malate - Aspartate Shuttle
Cytosol:
Apartate > (a-ketoglutarate > > glutamate) > Oxaloacetate > ( NADH + H+»_space; NAD+) > Malate then crosses over.
The reverse occurs in the matrix then crosses back to cytosol.
Regenerates NADH so more energy than the other shuttle
Glycerol 3-phosphate Shuttle
Glycerol-3-phosphate gets converted back to dihydroxyacetone phosphate by a membrane-bound mitochondrial glycerol-3-phosphate dehydrogenase 2, reducing one molecule of enzyme-bound FAD to FADH2. FADH2 then reduces ubiquinone to ubiquinol, which enters into oxidative phosphorylation.
Regenerates FADH so ultimately less energy that it’s counterpart.
Glycogenesis
Synthesis of glycogen, occurs in cytoplasm. Requires 1 unit of ATP, UTP/molecule of glucose.
Glycogenolysis
Breakdown of glycogen to form glucose-1-phosphate in cytoplasm
glycogen n + Pi glucose-1-phosphate + glycogen (n-1)
(glycogen phosphorylase, which hydrolyzes alpha 1,4 links, repeated until branch is only four glucose units in length)
Which hormone(s) favor glycogenesis
insulin
Which hormone(s) favor glycogenolysis
glucagon (affects liver) or
epinephrine (affects muscle)
Allosteric Modulation examples
phosphorylase A and B, phosphofructokinase, hexokinase, pyruvate kinase, pyruvate dehydrogenase
Covalent Modification examples
One of two ways that hormones work (regulate). Use Protein kinases and use ATP as a phosphate donor. Phosphatase is used to remove the P group from enzyme by phosphotase.
Glucocorticoids
induce gluconeogenic enzymes
Inducible Enzyme
Concentrations rise and fall in response to molecular signals.
Noninducible Enzyme
Basal rate, constitutive
Required all the time at relatively constant levels of activity (housekeeping genes)
Dietary fiber
carbohydrates and lignin from plants that are not digestible by human enzymes.
Cellulose, hemicellulose, pectin, lignin, gums, beta-glucans, fructans, resistant starches
Functional fiber
non-digestible carbohydrates that have been isolated, extracted, or manufactures and have been shown to have beneficial physiological effects in humans.
Cellulose, pectins, gums, beta-glucans
The only dietary fiber that is not also a functional fiber
Hemicellulose
Cellulose
Beta 1,4 linkage in glucose polymer
water insoluble
poorly fermented
Present in bran, legumes, nuts, peas, root vegetables, cabbages, apples
Hemicellulose
Heterogeneous group of polysaccharides substances containing different sugars
solubility depends on side chain
fermentability depends on sugar position
Present in bran, whole grains, nuts, legumes
Pectin
First degree galacturonic acid water soluble gel forming high ion bonding potential completely digested by colonic M.O. Present in apples, strawberries, citrus, legumes, nuts.
Lignin
Not a carbohydrate, but is a 3d polymer composed of three different phenol forms (trans-coniferyl, trans-sinapyl, trans-p-courmaryl
Gums
Hydrocolloids composed of sugars and sugar derivatives highly soluble gel-forming highly fermentable by colonic bacteria
Soluble fibers
fructans, some hemicelluloses, psyllium, beta-glucans, pectins, and gums (these last four are viscous
Insolube
Lignin, Cellulose, and some hemicellulose. All conssidered non-viscuous.
Chitosan, chitin, and some pectins and resistant starches are also considered insoluble or less soluble.
Soluble fibers are
- The water soluble components or fiber (Pectin, gums, some hemicelluloses, beta-glucans)
- Fermented by intestinal bacteria
- Delay gastric emptying time and decrease nutrition absorption
- Present in fruits, barley, oats, and beans
Insoluble fibers are
- Not water soluble
- Not fermented by intestinal bacteria
- Decrease intestinal transit time, reduce fecal bulk
- Present in wheat bran, vegetables, and grains
Characteristics of water-holding fibers
decreased transit time, increase fecal volume, softer stool
Characteristics of viscous fibers
delayed gastric emptying, decreased nutrient absorption, and decreased digestive function
Characteristics of absorbent fibers
decrease serum cholesterol, dimish lipid absorption, alter mineral balance, and increase fecal bile acid excretion.
Other plant sugars that are not absorbed in small intestine
Raffinose, stachyose, verbascose
Byproducts of fermentation of fibers in the Colon
Gasses (H2, CO2, and CH4), Short chain fatty acids: acetic, butyric, and propionic
Increased Na+ and water absorption
Nonfermentable fibers lead to microbial proliferation and contribute to fecal bulk and detoxification.
Diseases prevented by fiber
Colectoral cancer, GI diseases, atherosclerosis (disease serum cholesterol), NIDDM, controlling body weight.
Bifunctional enzymes
Non-inducible: phosphoglucoisomerase, aldolase, glyceraldehyde-3-P-dehydrogenase, phosphoglycerate kinase, phosphoglyceromutase, enolase, lactate dehydrogenase.
Glycolytic
Inducible: glucokinase, phosphofructokinase, pyruvate kinase
Gluconeogenic:
Inducible: glucose 6-phophatase, fructose-1,6-bisphosphatase, PEP carboxykinase, pyruvate carboxylase
