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Biochemistry > Module 3 > Flashcards

Module 3 Flashcards

1
Q

– is the term used to describe the interconversion of
chemical compounds in the body, the pathways taken by individual molecules, their interrelationships, and the mechanisms that regulate the flow of metabolites through the pathways

A

Metabolism

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2
Q

Metabolic pathways fall into three categories.

A
  1. Anabolic pathways
  2. Catabolic pathways
  3. Amphibolic pathways
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3
Q
    • are those involved in the synthesis of larger and more complex compounds from smaller precursor
  • -for example, the synthesis of protein from amino acids and the synthesis of reserves of triacylglycerol and glycogen
A

Anabolic pathways

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4
Q
    • are involved in the breakdown of larger molecules, commonly involving oxidative reactions
    • they are exothermic, producing reducing equivalents, and, mainly via the respiratory chain
A

Catabolic pathways

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5
Q

– occur at the “crossroads” of metabolism, acting as links between the anabolic and catabolic pathways, for example, the citric acid cycle

A

Amphibolic pathways

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6
Q

energy requirement for human being is met from ____

A

carbohydrates (40%-60%)
lipids (mainly triacylglycerol, 30%-40%)
protein (10%-15%)

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7
Q

If the intake of metabolic fuels is consistently greater than
energy expenditure, the surplus is stored, largely as triacylglycerol in adipose tissue, leading to the development of ____

A

obesity

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8
Q

if the intake of metabolic fuels is consistently lower than energy expenditure, there are negligible reserves of fat and carbohydrate, and amino acids arising from protein turnover are used for energy-yielding metabolism rather than replacement protein synthesis, leading to _____

A

emaciation, wasting, and, eventually, death

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9
Q

– ample supply of carbohydrate, and the metabolic fuel for most tissues is glucose

A

Fed State

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10
Q

In the ___, glucose must be spared for use by the central nervous system (which is largely dependent on glucose) and the red blood cells (which are wholly reliant on glucose)

A

fasting state

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11
Q

As glycogen reserves become depleted (in fasting state), amino acids arising from protein turnover are used for __

A

gluconeogenesis

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12
Q

The formation and utilization of reserves of triacylglycerol

and glycogen, and the extent to which tissues take up and oxidize glucose, are largely controlled by the hormones ___

A

insulin and glucagon

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13
Q

– there is either impaired synthesis and secretion of insulin or impaired sensitivity of tissues to insulin action

A

diabetes mellitus

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14
Q

All the products of digestion are metabolized to a
common product,___, which is then oxidized by the
citric acid cycle

A

acetyl-CoA

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15
Q

– is the major fuel of most tissues
– most important carbohydrate
– formed by hydrolysis of dietary starch and disaccharides
converted to glucose in the liver
– universal fuel of the fetus
– precursor for synthesis of all the other carbohydrates in the body: Glycogen, ribose and deoxyribose, galactose

A

Glucose

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16
Q

is metabolized to pyruvate by the pathway of glycolysis

A

Glucose

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17
Q

Aerobic tissues metabolize pyruvate to acetyl-CoA, which can enter the citric acid cycle for complete oxidation to
CO2 and H2O, linked to the formation of ATP in the process of ____

A

oxidative phosphorylation

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18
Q

– can also occur anaerobically (in the absence of oxygen) when the end product is lactate.

A

Glycolysis

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19
Q

an alternative to part of the pathway of glycolysis

A

pentose phosphate pathway

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20
Q

Triose phosphate intermediates in glycolysis give rise to the ___

A

glycerol moiety of triacylglycerols

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21
Q

Pyruvate and intermediates of the citric acid cycle provide the carbon skeletons for the synthesis of ____

A

nonessential or dispensable amino acids

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22
Q

– is the process of synthesizing glucose from noncarbohydrate precursors such as, lactate, amino acids, and glycerol

A

Gluconeogenesis

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23
Q

Fatty acids may be oxidized to acetyl-CoA (B-oxidation) or esterified with glycerol, forming ___ as the body’s main fuel reserve.

A

triacylglycerol

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24
Q

Acetyl-CoA formed by β-oxidation of fatty acids may

undergo three fates

A
  1. As with acetyl-CoA arising from glycolysis, it is oxidized
    to CO2 + H2O via the citric acid cycle.
  2. It is the precursor for synthesis of cholesterol and other
    steroids.
  3. In the liver, it is used to form the ketone bodies, acetoacetate and 3-hydroxybutyrate, which are important fuels in prolonged fasting and starvation.
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25
Q

– are required for protein synthesis
– Some must be supplied in the diet since they cannot
be synthesized in the body (essential or indispensable)

A

amino acids

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26
Q

– remainder of the amino acids; can also be formed from metabolic intermediates by transamination using the amino group from other amino acids

A

nonessential or dispensable amino acids

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27
Q

After ___, amino nitrogen is excreted as urea, and the carbon skeletons that remain after transamination may

(1) be oxidized to CO2 via the citric acid cycle,
(2) be used to synthesize glucose (gluconeogenesis), or
(3) form ketone bodies or acetyl CoA, which may be oxidized or used for synthesis of fatty acids

A

deamination

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28
Q

– the nature of the substrates entering and metabolites leaving tissues and organs can be measured

A

tissue and organ level

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29
Q

– each cell organelle (eg, the mitochondrion) or compartment (eg, the cytosol) has specific roles that form part of a subcellular pattern of metabolic pathways

A

subcellular level

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30
Q 
Amino acids (resulting from the digestion of dietary protein) and glucose (resulting from the digestion of carbohydrates)
are absorbed via the \_\_\_\_
A

hepatic portal vein

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31
Q

– has the role of regulating the blood concentration of these (amino acids and glucose) water soluble metabolites
– also synthesizes the major plasma proteins (eg, albumin)
and deaminates amino acids that are in excess of requirements, synthesizing urea, which is transported to the kidney and excreted

A

Liver

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32
Q

– glycogen synthesis

A

Glycogenesis

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33
Q

– fatty acid synthesis

A

Lipogenesis

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34
Q
    • utilizes glucose as a fuel, both aerobically, forming CO2, and anaerobically, forming lactate
    • stores glycogen as a fuel for use in muscle contraction and synthesizes muscle protein from plasma amino acids
A

Skeletal muscle

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35
Q

– are mainly triacylglycerol, and are hydrolyzed to monoacylglycerols and fatty acids in the gut, then reesterified in the intestinal mucosa

A

Lipids

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36
Q
    • the largest of the plasma lipoproteins
  • -also contain lipid-soluble nutrients, including vitamins A, D, E, and K
    • is not taken up directly by the liver
    • It is first metabolized by tissues that have lipoprotein lipase
A

chylomicrons

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37
Q
    • hydrolyzes the triacylglycerol (chylomicrons)

- - releasing fatty acids that are incorporated into tissue lipids or oxidized as fuel

A

lipoprotein lipase

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38
Q
    • is the main fuel reserve of the body
    • It is hydrolyzed (lipolysis) and glycerol and nonesterified
      (free) fatty acids are released into the circulation
A

Adipose tissue triacylglycerol

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39
Q

In the liver, newly synthesized triacylglycerol and triacylglycerol from chylomicron remnants is secreted into the circulation in __

A

very low density lipoprotein (VLDL)

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40
Q

Partial oxidation of fatty acids in the liver leads to __

A

ketone body production (ketogenesis)

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41
Q
    • acts as the focus of carbohydrate, lipid, and amino acid metabolism
    • contains the enzymes of the citric acid cycle, β-oxidation of fatty acids and ketogenesis, as well as the respiratory chain and ATP synthase
A

mitochondrion

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42
Q

a precursor for the synthesis of glucose in the cytosol

A

oxaloacetate

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43
Q

– contain the enzyme system for triacylglycerol synthesis

A

membranes of the endoplasmic reticulum

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44
Q

Regulation of the overall flux through a pathway is achieved by control of one or more key reactions in the pathway, catalyzed by ___

A

regulatory enzymes

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45
Q
    • first reaction in a pathway that is saturated with the substrate
    • can be identified as a nonequilibrium reaction in which the Km of the enzyme is considerably lower than the normal concentration of substrate
A

flux-generating reaction

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46
Q

Enzymes catalyzing nonequilibrium reactions are
often ____ subject to the rapid actions of “feedback” or “feed-forward” control by allosteric modifiers, in immediate response to the needs of the cell.

A

allosteric proteins

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47
Q

True or False

Fatty acids (and ketone bodies formed from them) cannot
be used for the synthesis of glucose
A

True

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48
Q

True or False

Acetyl-CoA (and any substrates that yield acetyl-CoA) can be used for gluconeogenesis.

A

False

It can never be used for gluconeogenesis.

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49
Q 
Most of the amino acids in excess of requirements for
protein synthesis (arising from the diet or from tissue protein turnover) yield pyruvate, or four- and five-carbon intermediates of the citric acid cycle. These amino acids are
classified as \_\_\_
A

glucogenic

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50
Q

– two amino acids that yield only acetyl-CoA on oxidation, and hence cannot be used for gluconeogenesis

A

lysine and leucine

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51
Q

– amino acids that give rise to both acetyl-CoA and intermediates that can be used for gluconeogenesis

A

phenylalanine, tyrosine, tryptophan, and isoleucine

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52
Q

Those amino acids that give rise to acetyl-CoA are referred to as ___, because in prolonged fasting and starvation much of the acetyl-CoA is used for synthesis of ketone bodies in the liver.

A

ketogenic

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53
Q

Glucose uptake into muscle and adipose tissue is controlled by __, which is secreted by the β-islet cells of the pancreas in response to an increased concentration of glucose in the portal blood.

A

insulin

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54
Q

In the fasting state, the glucose transporter of muscle

and adipose tissue ___ is in intracellular vesicles.

A

GLUT-4

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55
Q

The increase in secretion of ___ by α cells of

the pancreas inhibits glycogen synthetase, and activates glycogen phosphorylase in the liver

A

glucagon

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56
Q
    • cannot contribute directly to plasma glucose, since muscle lacks glucose-6-phosphatase, and the
  • -primary use is to provide a source of glucose-6-phosphate for energy-yielding metabolism in the muscle itself.
A

Muscle glycogen

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57
Q

___ with a high Km, so that as the concentration of glucose
entering the liver increases, so does the rate of synthesis of
glucose-6-phosphate

A

isoenzyme of hexokinase (glucokinase)

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58
Q

as fasting is prolonged, the plasma concentration of ___ increases markedly

A

ketone bodies (acetoacetate and 3-hydroxybutyrate)

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59
Q

acetyl-CoA formed by oxidation of fatty acids in muscle inhibits pyruvate dehydrogenase, leading to an ___

A

accumulation of pyruvate

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60
Q

substrate for gluconeogenesis in the liver

A

glycerol

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61
Q

In patients with ___ as a result of release of cytokines in response to tumors and disease, there is an increase in the rate of tissue protein catabolism, as well as a considerably increased metabolic rate, so they are in a state of advanced starvation.

A

cachexia

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62
Q

is the study of the roles of sugars in health and disease.

A

Glycobiology

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63
Q

is the entire complement of sugars of an organism, whether free or present in more complex molecules

A

glycome

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64
Q

– the comprehensive study of glycomes, including genetic, physiological, pathological, and other aspects

A

Glycomics

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65
Q

Classification of Carbohydrates

A
  1. Monosaccharides
  2. Disaccharides
  3. Oligosaccharides
  4. Polusaccharides
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66
Q
    • metabolic intermediates in glycolysis and the pentose phosphate pathway (hexose monophosphate shunt)
    • Pentoses - important in nucleotides, nucleic acids, and several coenzymes
    • Glucose, galactose, fructose, and mannose - physiologically the most important hexoses
A

Monosaccharides

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67
Q
    • a molecule in which a sugar is bound to another functional group via a glycosidic bond
    • O-glycosidic bond
    • N-glycosidic bond
    • Exmples: salicin, cardiac glycosides, Ouabain, streptomycin
A

Glycosides

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68
Q

– sugars in which one hydroxyl group has been replaced by hydrogen
– Examples
Deoxyribose - derived from the sugar ribose by loss of an oxygen atom
l-fucose - Cosmetics, pharmaceuticals, dietary supplements
2-deoxyglucose - Competitively inhibits G6 PO4

A

Deoxy Sugars

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69
Q

– Components of Glycoproteins, Gangliosides and Glycosaminoglycans
– Examples
d-glucosamine - constituent of hyaluronic acid (water holding/filler)
d-galactosamine - Chondrosamine (cartilage)
d-mannosamine
– Clinical Importance: antibiotics (eg, erythromycin)

A

Amino Sugars (Hexosamines)

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70
Q

– sugars composed of two monosaccharide residues linked by a glycoside bond
Maltose - Glucose and glucose
Sucrose - glucose and fructose
Lactose - Glucose and galactose

A

Disaccharides

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71
Q
    • are condensation products of three to ten monosaccharides
    • Most are not digested by human enzymes.
A

Oligosaccharides

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72
Q

– are condensation products of more than ten monosaccharide units
– examples are the starches and dextrins, which may be linear or branched polymers
– are sometimes classified as hexosans or pentosans, depending on the constituent monosaccharides
(hexoses and pentoses, respectively)

A

Polysaccharides

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73
Q
    • foods contain a wide variety of other polysaccharides that are collectively known as ___;
    • they are not digested by human enzymes, and are the major component of dietary fiber.
  • -Examples are cellulose from plant cell walls (a glucose polymer; and inulin, the storage carbohydrate in some plants (a fructose polymer).
A

nonstarch polysaccharides

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74
Q

– a homopolymer of glucose forming an α-glucosidic chain, called a glucosan or glucan
– the most important dietary carbohydrate in cereals, potatoes, legumes, and other vegetables
– two main constituents:
Amylose (13%-20%)
Amylopectin (80%-87%)

A

Starch

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75
Q
    • 24 to 30 glucose residues
    • α1 → 4 linkages in the chains
    • α1 → 6 linkages at the branch points
A

Amylopectin (80%-87%)

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76
Q

– measure of its digestibility
– based on the extent to which it raises the blood concentration of glucose
– ranges from 1 (or 100) to 0 for those that are not hydrolysed at all
55 or less = Low (good)
56- 69 = Medium
70 or higher = High (bad)

A

glycemic index

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77
Q
    • animal starch
    • storage polysaccharide
    • more highly branched structure than amylopectin
    • Muscle glycogen
    • contain up to 60,000 glucose residues
A

Glycogen

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78
Q
    • polysaccharide of fructose found in tubers and roots of dahlias, artichokes, and dandelions
    • readily soluble in water
    • used to determine the glomerular filtration rate no nutritional value
A

Inulin

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79
Q
    • chief constituent of plant cell walls
    • Insoluble
    • Consists of β-d-glucopyranose units linked by β1 → 4 bonds
    • an important source of “bulk” in the diet
    • major component of dietary fiber
A

Cellulose

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80
Q
    • structural polysaccharide in the exoskeleton of crustaceans and insects
    • N-acetyl-d-glucosamine units joined by β1 → 4 glycosidic bonds
A

Chitin

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81
Q
    • occurs in fruits

- - a polymer of galacturonic acid linked α-1→ 4

A

Pectin

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82
Q
    • Aka mucopolysaccharides
    • Contains amino sugars and uronic acids
    • Proteoglycan - attached to a protein molecule; substance of connective tissue (Hold water occupy space)
    • Examples: hyaluronic acid, chondroitin sulfate, and heparin
A

Glycosaminoglycans

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83
Q
    • Aka Mucoproteins
    • Proteins containing branched or unbranched oligosaccharide chains
    • occur in cell membranes
    • Glycosylation
    • 5% of the weight of cell membranes
A

Glycoproteins

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84
Q

Biomedical Importance of Lipids

A

– fats, oils, steroids, waxes
– Common Physical proprties - Relatively insoluble in water: soluble in nonpolar solvents
– important dietary constituents: fat-soluble vitamins; Micronutrients; long chain omega-3 fatty acids
– stored in adipose tissue
– thermal insulator
– Myelin sheaths
– Lipoprotein
Clinical Diseases
obesity, diabetes mellitus, and atherosclerosis

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85
Q

– are a heterogeneous group of compounds, including
fats, oils, steroids, waxes, and related compounds, that are
related more by their physical than by their chemical properties

A

lipids

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86
Q

Fat is stored in ___, where it also serves as a thermal insulator in the subcutaneous tissues and around certain organs.

A

adipose tissue

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87
Q

Nonpolar lipids act as ___, allowing rapid propagation of depolarization waves along myelinated nerves

A

electrical insulators

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88
Q

Classification of Lipids

A
  1. Simple Lipids
  2. Complex Lipids
  3. Precursor or Derived Lipids
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89
Q

___ include fats and waxes which are esters of fatty acids with various alcohols

A

Simple lipids

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90
Q

Groups of Simple Lipids

A
  1. Fats – Esters of fatty acids with glycerol. Oils are fats in the liquid state.
  2. Waxes – Do not have triglyceride ester of three fatty acids; Fatty acid and alcohol esters
    - - Esters of fatty acids with higher molecular weight monohydric alcohols.
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91
Q

Groups of Complex Lipids

A
  1. Phospholipids
  2. Glycolipids (glycosphingolipids)
  3. Other complex lipids
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92
Q

– Lipids containing, in addition to fatty acids and an alcohol, a phosphoric acid residue
– frequently have nitrogen-containing bases (eg, choline)
and other substituents

A

Phospholipids

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93
Q

– Lipids containing a fatty acid, sphingosine, and carbohydrate

A

Glycolipids (glycosphingolipids)

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94
Q
    • Lipids such as sulfolipids and amino lipids

- - Lipoproteins may also be placed in this category.

A

Other complex lipids:

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95
Q

– group of glycolipids which include fatty acids, glycerol, steroids, other alcohols, fatty aldehydes, ketone bodies, hydrocarbons, lipid-soluble vitamins and micronutrients, and hormones

A

Precursor and derived lipids

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96
Q

– acylglycerols (glycerides), cholesterol, and cholesteryl esters are termed ___ because they are uncharged

A

neutral lipids

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97
Q

Fatty Acids Are Aliphatic Carboxylic Acids

A

free fatty acids – transport form in the plasma
Saturated – containing no double bonds
Unsaturated – containing one or more double bonds

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98
Q

Nomenclature

A

– systematic nomenclature names the fatty acid after the hydrocarbon with the same number and arrangement
of carbon atoms, with -oic being substituted for the final -e
– saturated acids end in -anoic
– unsaturated acids with double bonds end in -enoic

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99
Q

Nomenclature (Powerpoint)

A
  1. Palmitic – C16:0 or 16:0
    - - #C : # double bonds
  2. Linoleic – C18:2 (9,12)
    - - 18 Ϫ9,12
    - - ώ-carbon (methyl carbon)
    - - Ώ-6 family (18-12)
  3. Linolenic Acid – C18:3 (9,12,15) or 18 Ϫ9,12,15
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100
Q

Are there essential lipids?

A

Linoleic and linolenic acid (ADEK)

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101
Q

Are there essential amino acids?

A
    • Adults: 9

- - Infants: 10 (arginine)

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102
Q

Are there essential carbohydrates?

A

NO

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103
Q
    • Contain No Double Bonds

- - based on acetic acid (CH3—COOH)

A

Saturated Fatty Acids

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104
Q

Unsaturated fatty acids may be further subdivided as follows:

A
  1. Monounsaturated (monoethenoid, monoenoic) – acids,
    containing one double bond.
  2. Polyunsaturated (polyethenoid, polyenoic) – acids, containing two or more double bonds.
  3. Eicosanoids – These compounds, derived from eicosa
    (20-carbon) polyenoic fatty acids, comprise
    the prostanoids, leukotrienes (LTs), and lipoxins (LXs).
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105
Q

– exist in virtually every mammalian tissue, acting as local hormones; they have important physiologic
and pharmacologic activities.
– They are synthesized in vivo by cyclization of the center of the carbon chain of 20-carbon (eicosanoic) polyunsaturated fatty acids (eg, arachidonic acid) to form a cyclopentane ring

A

Prostaglandins

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106
Q

– have the cyclopentane ring interrupted with an oxygen atom (oxane ring)

A

thromboxanes

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107
Q
    • are a third group of eicosanoid derivatives formed via the lipoxygenase pathway
    • are characterized by the presence of three or four conjugated double bonds
A

leukotrienes and lipoxins

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108
Q

Geometric Isomerism

A

cis-

    • If the acyl chains are on the same side of the bond
    • i.e oleic acid

Trans-

    • If the acyl chains are on opposite sides
    • i.e. elaidic acid
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109
Q

Most Naturally occurring Unsaturated Fatty Acids

A

– Double bonds in fatty acids are in the cis-configuration
– Trans-double bonds are unnatural
Margarine, etc
Decrease liquid fluidity
– Trans fatty acids and saturated fatty acids are associated with an increased risk of atherosclerosis

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110
Q

– are present in certain foods, arising as a by-product of the saturation of fatty acids during hydrogenation, or “hardening,” of natural oils in the manufacture of margarine.

A

Trans fatty acids

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111
Q

True or False

Most Naturally Occurring Unsaturated Fatty Acids Have cis Double Bonds

A

True

112
Q

Physical and Physiologic Properties of Fatty Acids

A
    • Reflect Chain Length and Degree of Unsaturation
    • More saturated - More solid at body temperature
    • Polyunsaturated - Liquid to below zero dec celsius; membrane lipids; Hibernators
113
Q

Omega 3 Fatty Acids

A

α-linolenic (ALA) - Found in plant oils
eicosapentaenoic (EPA) - found in fish oil
docosahexaenoic (DHA) - found in fish and algal oils

114
Q
    • anti-inflammatory effects perhaps due to promoting the synthesis of less inflammatory prostaglandins and leukotrienes compared to omega 6
    • are beneficial, particularly for cardiovascular disease, but also for other chronic degenerative diseases such as cancer, rheumatoid arthritis, and Alzheimer disease.
A

Omega 3 Fatty Acids

115
Q
    • Main storage forms of fatty acids

- - carbons 1 and 3 of glycerol are not identical when viewed in three dimensions

A

Triacylglycerols (Triglycerides)

116
Q

– Many phospholipids are derivatives of ___, in which the phosphate is esterified with one OH group of glycerol and the other two OH groups are esterified to two long chain fatty acids (glycerophospholipids).

A

phosphatidic acid

117
Q

__ containing choline, (phosphatidylcholines, commonly called lecithins) are the most abundant phospholipids of the cell membrane and represent a large proportion of the body’s store of choline.

A

Glycerophospholipids

118
Q

has two long chain hydrocarbon tails

A

Phospholipids

119
Q

is important in nervous transmission, as acetylcholine, and

as a store of labile methyl groups

A

Choline

120
Q

– is a very effective surface-active agent and a major constituent of the surfactant preventing adherence, due to surface tension, of the inner surfaces of the lungs

A

Dipalmitoyl lecithin

121
Q

absence of Dipalmitoyl lecithin from the lungs of premature infants causes __

A

respiratory distress syndrome

122
Q
    • Ethanolamine or serine, respectively, replaces choline

- - plays a role in apoptosis (programmed cell death)

A

Phosphatidylethanolamine (cephalin) and phosphatidylserine

123
Q

– are found in the outer leaflet of the cell membrane lipid bilayer and are particularly abundant in specialized
areas of the plasma membrane known as lipid rafts
– are also found in large quantities in the myelin sheath that surrounds nerve fibers
– are believed to play a role in cell signaling and in apoptosis
– contain no glycerol, and on hydrolysis they yield a fatty acid, phosphoric acid, choline, and sphingosine

A

Sphingomyelins

124
Q

The combination of sphingosine plus fatty acid is known as

__, a structure also found in the glycosphingolipids

A

ceramide

125
Q
    • Give rise to cardiolipin
    • Found only in mitochondria
    • Alterations in function or decreased levels associated in heart failure and hypothyroidism and aging
A

Phosphatidylglycerol

126
Q
    • important in the metabolism and interconversion of phospholipids
    • found in oxidized lipoproteins and has been implicated in some of their effects in promoting
A

lysophosphatidylcholine (Lysolecithin)

127
Q

– are lipids with an attached carbohydrate or carbohydrate
chain
– are widely distributed in every tissue of the body, particularly in nervous tissue such as brain
– occur particularly in the outer leaflet of the plasma membrane, where they contribute to cell surface carbohydrates which form the glycocalyx

A

Glycolipids (Glycosphingolipids)

128
Q
    • major glycosphingolipid of brain and other nervous tissue
    • Converted to sulfatide (present in high amounts in myelin)
A

Galactosylceramide

129
Q
    • resembles galactosylceramide
    • head group is glucose rather than galactose
    • predominant simple glycosphingolipid of extraneural tissues
A

Glucosylceramide

130
Q

– complex glycosphingolipids derived from glucosylceramide
– Function in cell-cell recognition and communication and as receptors for hormones and bacterial toxins (cholera)
GM1

A

Gangliosides

131
Q
    • Precursor is cholesterol
    • Bile Acids
    • Adrenocortical hormones
    • Sex hormones
    • Vitamin D
    • Cardiac glycosides
A

Steroids

132
Q

– is a Precursor of Vitamin D

A

Ergosterol

133
Q
    • not steroids
    • related because they are synthesized, like cholesterol from fivecarbon isoprene units
    • rubber, camphor, the fat-soluble vitamins A, D, E, and K, and β-carotene (provitamin A)
    • Ubiquinone - Respiratory chain in mitochondria
    • Dolichol - takes part in glycoprotein synthesis
A

Polyprenoids

134
Q

auto-oxidation of lipids

  • -responsible for rancidity of foods
    • damage to tissues in vivo
  • -cancer, inflammatory diseases, atherosclerosis, and aging

free radicals

    • molecules that have unpaired valence electrons
    • reactive oxygen species (ROS)
  • -Chain reaction providing continuous supply of ROS: Initiation; Propagation and Termination
A

Lipid Peroxidation

135
Q

To control and reduce lipid peroxidation, both humans in

their activities and nature invoke the use of ___

A

antioxidants

136
Q

2 classes of antioxidant

A
  1. preventive antioxidants – reduce the rate of chain initiation
    - - eg Catalase; EDTA; DTPA; Glutathione peroxidase
  2. chain-breaking antioxidants – interfere with chain propagation
    - - eg Superoxide dismutase; vitamin E
137
Q
    • a part of the molecule is hydrophobic, or water insoluble; and a part is hydrophilic, or water soluble
    • Basic structure in biologic membranes
    • Micelles
    • liposomes
A

Amphipathic

138
Q

– Aka Tricarboxylic Acid Cycle (TCA) or Krebs Cycle
– Final common pathway for the aerobic oxidation of
Carbohydrates, Fatty Acids, and Proteins
– Occurs in most tissues but most significantly happens in
the Liver
– Reactions and Enzymes are found in the mitochondrial
matrix, except succinate dehydrogenase (inner
membrane)

A

Citric Acid Cycle

139
Q

Functions of Citric Acid Cycle

A
  1. Provides majority of ATP for energy
  2. Interconverts amino acids (transaminationdeamination)»creates amino acids or destroys amino acids (producing glucose)
  3. Has a crucial role in fatty acid synthesis
140
Q

Substrates and Product of Krebs Cycle (Citric Acid Cycle)

A 
Substrates: Acetyl CoA and Oxaloacetate
Products: 12 ATP(from 3 NADH, 1 FADH, 1 GTP), 2CO2,
H2O, heat
-- It’s a cycle!
-- Oxaloacetate will be regenerated
141
Q

Steps of Citric Acid Cycle

A 
“Cindy Is Kind So She Forgives More Often”
C itrate
I socitrate
alpha K etoglutarate
S uccinyl CoA
S uccinate
F umarate
M alate
O xaloacetate
142
Q

Mnemonic: (Krebs Cycle)

A 
F – 6 (FADH - Fumarate)
A – 5 (ATP - Succinate)
N – 3, 4, 8 (NADH - Alpha Ketoglutarate, Succinyl Coa and Malate)
All the rest, water
CO2 – 3,4
143
Q

Take Note (Krebs Cycle)

A
  • A-ketoglutarate dehydrogenase complex->requires 5 B
    vitamins
  • Steps produce ATP uses oxidative phosphorylation
    mainly except for the synthesis of Succinate
  • Gluconeogenic sites (liver, kidney) produce GTP, nongluconeogenic
    sites produce ATP
  • GTP is used in the gluconeogenic step
    oxaloacetate->PEP
144
Q

ATP Yield from TCA: Acetyl-CoA

A

ATPs from substrate level phosphorylation: 1
ATPs from NADH: 9
ATPs from FADH2: 2
TOTAL ATP YIELD: 12

145
Q

ATP Yield from TCA: Pyruvate

A

ATPs from substrate level phosphorylation: 1
ATPs from NADH: 12
ATPs from FADH2: 2
TOTAL ATP YIELD: 15

146
Q

Role in Transamination-Deamination Amino Acids

A
  • Amino acids may be used to create TCA intermediates
    (and ultimately glucose) or TCA cycles maybe used to
    create amino acids
  • Transamination Reactions: TCA intermediates->amino acids
  • Deamination Reactions: amino acids->TCA intermediates
147
Q

Role in Fatty Acid Synthesis

A
  • TCA Intermediate Citrate transports Acetyl CoA from
    the mitochondrial matrix and into the cytoplasm to
    initiate fatty acid synthesis (Citrate Shuttle)
148
Q

Other Functions (Kreb’s Cycle)

A
  • Succinyl CoA can be used for heme synthesis and to
    activate ketone bodies in extrahepatic tissues
  • Malate can be used for gluconeogenesis
149
Q

Regulatory Mechanisms

A
  • Krebs Cycle is active in both the well-fed state and
    fasting state
  • No hormonal control
  • No new synthesis of oxaloacetate
  • Regulatory mechanisms are not fully known
150
Q

Regulatory Mechanisms- Suspected Mechanisms:

A
  1. Pyruvate Dehydrogenase
  2. Allosteric Inhibition of Citrate Synthase by ATP and long-chain fatty Acyl CoA
  3. Allosteric Activation of mitochondrial NADdependent
    IDH
  4. Inhibition of Succinate dehydrogenase by oxaloacetate
  5. Concentration of oxaloacetate
151
Q

Inhibitors of the Citric Acid Cycle

A
  1. Fluoroacetate - inhibit conversion of citrate to cis-aconitate
  2. Arsenite - inhibit alpha ketoglutarate to succinyl coa
  3. Malonate - inhibit conversion of succinate to fumarate
152
Q
  • Major pathway for glucose metabolism (but also for
    galactose and fructose)
  • Made up of 10 Steps
  • Can work with or without oxygen
A

Glycolysis

153
Q

Glycolysis

A
  • Substrate: mainly Glucose
  • Product: Pyruvate or Lactate
  • Overall Reaction: Glucose + 2 ADP + 2Pi  2 Lactate or
    Pyruvate + 2 ATP + 2 H2O
  • Occurs in the cytoplasm of all cells
154
Q

Glucose Transporters (GLUTs)

A

GLUT – 1 -Erythrocytes, BBB, kidney, colon, placenta
Function: Uptake of glucose

GLUT – 2 - Liver, pancreatic B cell, small intestine, kidney
Function: Rapid uptake and release of glucose

GLUT – 3 - Brain(Neurons), kidney, placenta
Function: Uptake of glucose

GLUT – 4 - Heart and skeletal muscle, adipose tissue
Function: Insulin stimulated uptake of glucose

GLUT – 5 - Small intestine
Function: Absorption of Fructose at the luminal side of the SI

155
Q

Types of Glycolysis

A
  1. Anerobic Glycolysis
    In cells without a mitochondria (e.g. RBCs) or anoxic cells
    (e.g. white muscle)
    Final product: Lactate
  2. Aerobic Glycolysis
    In cells with a mitochondria and adequate supply of oxygen
    Final Product: Pyruvate
156
Q

2 Stages of Glycolysis

A
  1. Energy Investment Phase - uses ATP
    - Phosphorylated forms of intermediates are synthesized at
    the expense of ATP
  2. Energy Generation Phase - produce ATP
    - 2 molecules of ATP are formed by substrate level
    phosphorylation
157
Q

Irreversible Steps in Glycolysis

A
  1. Phosphorylation of glucose
  2. Phosphorylation of fructose 6-phosphate – Rate-limiting
    step of Glycolysis
  3. Formation of pyruvate
158
Q
  • Present in most tissues
  • Can phosphorylate glucose, fructose, galactose
  • Inhibited allosterically by Glucose 6P
  • Low Km
  • High affinity for glucose
  • Low Vmax
A

Hexokinase

159
Q
  • Present in liver parenchymal cells (to initiate FA synthesis, glyconesis), islet cells of the pancreas (to initiate insulin secretion)
  • Phosphorylate glucose alone
  • Inhibited by Fructose 6P
  • High Km
  • Low affinity for glucose
  • High Vmax
  • Liver activity stimulated by insulin
A

Glucokinase

160
Q

Fructose 6P->Fructose 1,6BP

A
  • Enzyme: phosphofructokinase-1 (PFK-1)
  • Irreversible and rate-limiting step of glycolysis
  • PFK-1 is different from PFK-2!
161
Q

Phosphofructokinases

A 
1. PFK-1
Converts Fructose 6P to Fructose 1,6BP
Inhibited by ATP and citrate
Activated by Fructose 2,6 Bisphosphate (most potent; via
allosteric activation) and AMP
  1. PFK-2
    Converts Fructose 6P to Fructose 2,6BP
    Inhibited by ↓insulin, ↑glucagon (starvation)
    Activated by ↑insulin, ↓glucagon (well fed)
162
Q

PEP->Pyruvate

A
  • Substrate-level phosphorylation to yield 1 ATP per
    molecule of phosphoenolpyruvate
  • Enzyme: Pyruvate Kinase
    Activated by Fructose 1,6BP
    Inhibited by phosphorylation, which occurs when ↑glucagon,
    ↑cAMP
163
Q

Steps involved in the Production of ATP

Glycolysis

A
  1. 1,3-bisphosphoglycerate->3-phosphoglycerate
    Enzyme: phosphoglycerate kinase
  2. PEP->pyruvate
    Enzyme: pyruvate kinase
164
Q
  • The most common enzyme defect in glycolysis
  • Manifests as chronic hemolytic anemia
  • Aldolase A deficiency may also cause hemolytic anemia
A

Pyruvate Kinase Deficiency

165
Q

Patients have low exercise capacity, particularly on high

carbohydrate diets

A

Muscle Phosphofructokinase Deficiency

166
Q

Role of NADH in Glycolysis

A
  • Oxidation of glyceraldehyde 3 phosphate->1,3
    bisphosphoglycerate
    Enzyme: glyceraldehyde 3 phosphate dehydrogenase
  • 2 Possible Fates
    1. Can enter the malate-aspartate or G3P shuttle and be
    converted to ATP
    2. Can be used to convert pyruvate to lactateAerobic
167
Q

Glycolysis: NADH converted to ATP;

transported using shuttles:

A
  1. Malate Aspartate Shuttle
    yields 3 ATPs each
    liver, kidney and heart
  2. Glycerol Phosphate Shuttle
    yields 2 ATPs each
    skeletal muscle and brain
168
Q

Anaerobic Glycolysis:

A

Pyruvate is converted to lactate by the action of Lactate Dehydrogenase

169
Q

Synthesis of 2,3 BPG

A
  • In RBCs, the reaction catalyzed by phosphoglycerate
    kinase is bypassed
  • 1,3-bisphosphoglycerate is converted to 2,3-
    bisphosphoglycerate or 2,3 BPG
  • Enzyme: Bisphosphoglycerate Mutase
  • Function: binds to HgB and causes a shift to the R of the
    Hemoglobin-O2 dissociation curve
  • Chronic hypoxia->reactive polycythemia->inc BPG
    mutase->inc 2,3 BPG->shift to the R
170
Q

Pyruvate to Acetyl Coa

A
  • This step is NOT strictly part of Glycolysis
  • Happens in the mitochondria
  • Enzyme: Pyruvate Dehydrogenase (PDH) complex
  • Also produces NADH and CO2
  • Regulation is of 2 Forms:
    1. End-Product Inhibition
    2. Regulation by interconversion of active and
    inactive forms
  • Activated by: NAD+, CoA and pyruvate
  • Inhibited by: ATP, Acetyl-CoA and NADH
171
Q

Pyruvate to Acetyl Coa - Co-enzymes:

A
  1. Thiamine pyrophosphate
  2. FAD
  3. NAD+
  4. Coenzyme A (contains pantothenic acid)
  5. Lipoic acid
172
Q
  • most common biochemical cause of congenital lactic acidosis
  • X-linked dominant
  • Brain is deprived of Acetyl-CoA: psychomotor retardation
    and death
  • Treatment: ketogenic diet
A

Pyruvate Dehydrogenase Deficiency

173
Q
  • inactivates pyruvate dehydrogenase by binding to lipoic acid
  • Aside from inhibiting pyruvate dehydrogenase, pentavalent aresenic (arsenate) also competes with inorganic phosphate as a substrate for glyceraldehyde 3P dehydrogenase
A

Arsenic Poisoning

174
Q

Chronic alcoholics are prone to thiamine-deficiency and may develop potentially fatal pyruvic and lactic acidosis

A

Chronic alcoholism

175
Q

Fates of Pyruvate

A
  1. Lactate (Lactate dehydrogenase) - Anaerobic
  2. Ethanol (Pyruvate decarboxylase) - Yeast and certain microorganisms
  3. Acetyl Coa (Pyruvate dehydrogenase) - Aerobic
  4. Oxaloacetate (Pyruvate carboxylase) - final step in gluconeogenesis
176
Q

ATP Yield of Glycolysis

A

Anaerobic: 4
Aerobic: 4

177
Q
  • Aka“Hexose Monophosphate Shunt”
  • Happens in the well-fed state
  • An alternative pathway for the metabolism of glucose
  • No ATP is used or produced
A

Pentose Phosphate Pathway

178
Q

Pentose Phosphate Pathway: What is it for?

A

Produces NADPH (NOT NADH!) which is required for: fatty acid and steroid biosynthesis, glutathione reduction inside RBCs, cytochrome P450, respiratory burst of WBCs, and synthesis of nitric oxide

Produces Ribose 5-phosphate required for biosynthesis of nucleotides

179
Q

Function of NADPH

A
  1. Lipid Synthesis
  2. Create antioxidant form of glutathione
  3. Create Oxygen Free radicals to kill bacteria
180
Q

Pentose Phosphate Pathway: Where does it occur?

A

In the cytoplasm

181
Q

it is required for synthesis of DNA and RNA (which is made up of nucleotides)

A

Ribose 5-phosphate

182
Q

Pentose Phosphate Pathway: What are the substrates?

A

Glucose-6-P

No consumption or production of ATP

183
Q

Pentose Phosphate Pathway: What are the products?

A

ribose-5-P, fructose-6-P, and glyceraldehyde-3-P

NADPH

184
Q

Pentose Phosphate Pathway: Which step is rate-limiting?

A

Reaction: glucose-6-P –> 6-phosphogluconate
Enzyme: glucose-6-P dehydrogenase

185
Q

Pentose Phosphate Pathway: ACTIVE in the ff sites

A 
Liver
Adipose tissue
Adrenals, thyroid and testes
RBC
LACTATING mammaries
186
Q

Pentose Phosphate Pathway: LOW in the ff sites

A

Skeletal muscle

NON-LACTATING mammaries

187
Q

Pentose Phosphate Pathway: Two Phases in Pathway

A

Phase 1: Oxidative (Irreversible)
Enzyme: Glucose-6-Phosphate dehydrogenase
Products: NADPH; Ribulose-5-P

Phase 2: Non-Oxidative (Reversible)
Enzyme: Transketolase - refers to several enzymes
Product: Ribose-5-Phosphate

188
Q

cofactor of transketolase for it to work

A

Thiamine

189
Q

Pentose Phosphate Pathway

A
  • Complete PPP (Oxidative and Non-Oxidative)
    for those organs that need both NADPH and ribose 5-P
  • Incomplete PPP (Non-oxidative phase Only)
    for all organs requiring ribose-5-P only
190
Q

Pentose Phosphate Pathway: Important Points:

A

At the start of the reaction – Glucose 6-phosphate
At the end of the reaction – Glucose 6-phosphate
Rate-Limiting Enzyme: G6PD (NOT G6P!)

191
Q
  • transfers two carbon unit of a ketose onto the aldehyde carbon of an aldose sugar
  • Co-factors: Mg2+ and Vitamin B1 (Thiamine)
A

Transketolase enzyme

192
Q
  • reduced glutathione (G-SH) removes H2O2 in a reaction catalyzed by glutathione peroxidase
  • reacting with H2O2 oxidizes glutathione (G-S-S-G) but only ONLY REDUCED glutathione can remove H2O2
  • very important in RBCs
A

Glutathione

193
Q
  • Most common disease producing enzyme abnormality in humans
  • Involves in NADPH in RBCs and activity of glutathione reductase causing free radicals and peroxides accumulate
  • Hemolytic anemia due to poor RBC defense against oxidizing agents
  • Precipitating factors: anything that causes oxidative stress
    most common: infection
    drugs (sulfonamides, primaquine, chloramphenicol)
    fava beans
  • Neonatal jaundice: 1 to 4 days after birth
A

Glucose-6-Phosphate Dehydrogenase (G6PD) Deficiency

194
Q

altered hemoglobin that precipitates within RBCs; irregular precipitates of denatured Hgb

A

Heinz bodies

195
Q

altered RBCs due to phagocytic removal of Heinz bodies in spleen

A

Bite Cells

196
Q
  • Deficiency in NADPH oxidase
  • converts molecular oxygen into superoxide in leukocytes (especially neutrophils and macrophages) and used in the respiratory burst that kills bacteria
  • Severe, persistent and chronic pyogenic infections caused by catalase-positive bacteria
A

Chronic Granulomatous Disease

197
Q
  • Another alternative pathway for glucose
  • Zero ATP is used or produced
  • Cellular site: cytoplasm
  • Organ site: Liver
A

Uronic Acid Pathway

198
Q
  • At the start of the reaction: glucose 6-phosphate
  • At the end of the reaction: glucoronic acid, ascorbic acid (EXCEPT humans and other species) and pentoses
  • Uses of Glucoronic acid
  • Product: Glucoronic Acid
A

Uronic Acid Pathway

199
Q
  • Deficiency of reductase enzyme needed to convert L-xylulose to xylitol
  • Accumulation of L-xylulose will lead to increase levels in the urine
A

Essential Pentosuria

200
Q

cofactor of Glutathione Peroxidase

A

Selenium

201
Q

Fructose Metabolism

A
  • Fructose is an Isomer of glucose
  • Fructose and Galactose: converted into Glycolytic Intermediates
  • Fructokinase is unaffected by fasting or insulin
  • Cellular site: Cytoplasm
  • Organ site: mainly in the Liver
    but also in kidney, intestines, adipose tissue, muscle, semen
202
Q
  • As part of synthesis of proteoglycans
  • For reactions of substrates such as steroid hormones, bilirubin, drugs excreted in the urine or bile as glucoronid conjugate
A

Glucoronic Acid

203
Q
  • Rapid glycolysis in the liver - NOT limited by PFK
  • More efficient and higher energy yield - Bypasses the energy investment phase of glycolysis
  • Flood the pathways in the liver leading to an increase in the following: Fatty acid synthesis; Esterification of fatty acids and Increased VLDL secretion
A

Fructose Metabolism

204
Q

2 ALDOLASES

A

aldolase A and aldolase B
1. Aldolase A: for glycolysis
fructose-1,6-BP -> DHAP + glycerol-3-P

  1. Aldolase B: for fructose metab
    fructose-1-P -> DHAP + glyceraldehyde
205
Q

Fructose Metabolism

A
  • Phosphorylation of fructose
    fructose -> fructose-1-P
    Enzyme: fructokinase or hexokinase
  • Formation of DHAP and Glyceraldehyde
    fructose-1-P -> dihydroxyacetone phosphate (DHAP) + glyceraldehyde
    Enzyme: aldolase B
206
Q
  • defect in fructokinase

- benign and asymptomatic whose only symptom is the appearance of fructose in blood and urine

A

Essential Fructosuria or fructokinase deficiency

207
Q
  • autosomal recessive deficiency of aldolase B
  • fructose 1-P, fructose 1,6 BP accumulates leading to increase phosphate and allosterically inhibiting liver glycogen phosphorylase resulting in decrease glycogenolysis and decrease gluconeogenesis
  • Symptoms: hypoglycemia, jaundice, cirrhosis, vomiting
  • Treatment: avoid intake of fructose and sucrose
A

Fructose Intolerance or Aldolase B Deficiency

208
Q
  • Mannose is an important component of glycoproteins
  • Very little contribution from diet
  • Isomerization between mannose and fructose

mannose-6-P -> fructose-6-P
Enzyme: phosphomannose isomerase

A

Mannose Metabolism

209
Q
  • Enzyme: aldose reductase

- Found in lens, retina, Schwann cells, liver, kidney, placenta, RBC, ovaries, seminal vesicles

A

Glucose -> Sorbitol

210
Q
  • Enzyme: sorbitol dehydrogenase

- Found in the seminal vesicles since fructose is the fuel of sperm

A

Sorbitol -> Fructose

211
Q
  • In DM, since there is SO MUCH GLUCOSE, equilibrium favors the formation of MORE SORBITOL.
  • But, the lens and nerves lack sorbitol dehydrogenase. Sorbitol accumulates in these tissues and attract water by osmosis.
    lens: formation of cataracts
    nerves: peripheral neuropathy
A

Sorbitol Metabolism

212
Q
  • also an isomer of glucose
  • Cellular site: cytoplasm
  • Organ sites: mainly in the liver, but also in many extrahepatic tissues such as the mammary gland
  • Needed to create the following:
    1. Lactose (for milk production)
    2. As a constituent of glycolipids (cerebrosides, proteoglycans, glycoproteins)
A

Galactose Metabolism

213
Q

Galactose Metabolism

A
  • Phosphorylation of galactose
    galactose -> galactose-1-P
    Enzyme: galactokinase or hexokinase
  • Formation of UDP-galactose
    galactose-1-P + UDP-glucose ->UDP-galactose + glucose-1-P
    (UDP-galactose is the activated form of galactose)
    Enzyme: galactose-1-P uridyl transferase

-Use of galactose as carbon source
UDP-galactose -> UDP-glucose
Enzyme: UPD-hexose-4-epimerase

214
Q
  • causes galactosemia and galactosuria
  • cataracts in early childhood
  • treatment: eliminate sources of galactose from the diet
A

Galactokinase Deficiency

215
Q
  • autosomal recessive condition of absence of galactose-1-P uridyltransferase
  • cataracts within a few days of birth
  • galactitol accumulates in the presence of galactose and lactose in the diet causing cataracts + hepatosplenomegaly + mental retardation
A

Classic Galactosemia or Galactose-1-P Uridyltransferase Deficiency

216
Q

are a group of inherited disorders characterized by deficient mobilization of glycogen or deposition of abnormal forms of glycogen, leading to liver damage and muscle weakness; some glycogen storage diseases result in early death

A

Glycogen storage diseases

217
Q

The initial steps in glycogen synthesis involve the protein ___, a 37-kDa protein that is glucosylated on a specific
tyrosine residue by UDPGlc

– catalyzes the transfer of a further seven glucose residues from UDPGlc, in 1 → 4 linkage, to form a glycogen primer that is the substrate for glycogen synthase.

A

glycogenin

218
Q

– catalyzes the formation of a glycoside bond between C-1 of the glucose of UDPGlc and C-4 of a terminal glucose residue of glycogen, liberating uridine diphosphate (UDP).

A

Glycogen synthase

219
Q

When a growing chain is at least 11 glucose residues long,
branching enzyme transfers a part of the 1 → 4-chain (at
least six glucose residues) to a neighboring chain to form a
1 → 6 linkage, establishing a ___.

A

branch point

220
Q

Production of glucose from the following intermediates

  1. intermediates of glycolysis and the TCA
  2. glycerol from triacylglycerols
  3. lactate through the Cori Cycle
  4. carbon skeletons (alpa-ketoacids) of glycogenic amino acids
A

Gluconeogenesis

221
Q

Gluconeogenesis: Where does it occur?

A
  • Occurs in the liver (90%) and the kidney (10%)
  • During prolonged fasting, the kidneys contribute as much as 40%
  • Occurs in both mitochondria and cytoplasm
222
Q

Gluconeogenesis: What is the substrate and product?

A

Substrate: Pyruvate
Product: Glucose

223
Q

Which step is rate-limiting?

A

Reaction: Fructose 1,6-biphosphate -> Fructose 6-Phosphate
Enzyme: Fructose 1,6-biphosphatase

224
Q
  • another substrate of gluconeogenesis
A

Glycerol

225
Q
  • enters main gluconeogenic pathway via citric acid cycle after conversion of succinyl Coa
  • a major precursor of glucose in ruminants
A

Propionate

226
Q

Gluconeogenesis

Step 10: Pyruvate -> OAA -> PEP

A

Enzymes: Pyruvate Carboxylase

KEEP IN MIND
CARBOXYLASES attach a carbon atom using CO2 as a substrate. ALL carboxylases require BIOTIN as a co-factor.

227
Q

Gluconeogenesis

Step 3: Fructose-1,6-BP -> Fructose-6-P

A

This is the rate-limiting step of gluconeogenesis

Enzyme: fructose-1,6-bisphosphatase
Activator: ATP
Inhibitor: Fructose-2,6-BP and AMP

Fructose-2,6-BP - promotes glycolysis and inhibits gluconeogenesis

228
Q

Gluconeogenesis

Step 1: Glucose-6-P -> Glucose

A
  • Final step, which is shared with glycogen degradation
  • End goal: releases free glucose into the circulation
  • Enzyme: glucose 6-phosphatase

Where does it occur?
Liver and kidneys only
Muscle lacks glucose-6-phosphatase
Muscle glycogen can only be used by muscle itself

229
Q

Gluconeogenesis: Energy Expenditure

A 
- Requires six phosphoanhydride bonds for the  synthesis of one glucose molecule from two  molecules of pyruvate or lactate
Pyruvate carboxylase : 2 ATP
PEP-carboxykinase: 2 GTP
Phosphoglycerate kinase : 2 ATP
- Oxidizes 2 NADH back to NAD+
230
Q
  • is the process of synthesizing glucose or
    glycogen from noncarbohydrate precursors
  • The major substrates are the glucogenic amino acids, lactate, glycerol, and propionate.
A

Gluconeogenesis

231
Q

Mitochondrial ___ catalyzes the carboxylation of pyruvate to oxaloacetate, an ATP-requiring reaction in which the vitamin biotin is the coenzyme

A

pyruvate carboxylase

232
Q

A second enzyme, ___, catalyzes the decarboxylation and phosphorylation of oxaloacetate to phosphoenolpyruvate using GTP as the phosphate donor

A

phosphoenolpyruvate carboxykinase

233
Q

– hormones that are responsive to a decrease in blood glucose, inhibit glycolysis and stimulate gluconeogenesis in the liver by increasing the concentration of cAMP.

A

Glucagon and epinephrine

234
Q

In gluconeogenesis, pyruvate carboxylase, which catalyzes the synthesis of oxaloacetate from pyruvate, requires acetyl-CoA as an ___

A

allosteric activator

235
Q

– Conversion of lactate to glucose
lactate generated during anaerobic metabolism
lactate brought to the liver where it is converted
to glucose via gluconeogenesis
glucose brought back to muscles and RBC

–Energy expense: 4 ATP molecules

A

Cori Cycle

236
Q

Gluconeogenesis: Metabolic Cost

A

►Gluconeogenesis is energetically expensive
►The sum of the biosynthetic reactions from pyruvate to free blood glucose:

2 Pyruvate + 4ATP + 2GTP + 2NADH + H+ + H2O
-> Glucose + 4ADP + 2GDP + 6Pi + 2NAD+

►ATP requirement of gluconeogenesis is supplied by the oxidation of fatty acids
►A defect in fatty acid oxidation will manifest as hypoglycemia

237
Q

Regulation of Gluconeogenesis

A

Regulated primarily by:
1. circulating levels of glucagon
Phosphorylates pyruvate kinase
Increases the transcription of the PEP carboxykinase
gene
2. availability of glucogenic substrates
3. allosteric activation by acetyl CoA- inhibits pyruvate dehydrogenase and diverts pyruvate towards gluconeogenesis
4. allosteric inhibition by AMP - inhibits fructose-1,6-bisphosphatase

238
Q
  • high amount of cytoplasmic NADH is formed by alcohol dehydrogenase and acetaldehyde dehydrogenase
  • high amount of NADH favors the following reactions:
    pyruvate&raquo_space; lactate
    OAA&raquo_space; malate
    DHAP&raquo_space; glycerol-3-phosphate
A

Alcoholism and hypoglycemia

239
Q
  • High fetal glucose consumption
  • Risk of maternal and fetal hypoglycemia especially
    during fasting
  • Hyperinsulinemia: due to ↑estrogen leading to fasting hypoglycemia
  • Insulin resistance: due to ↑HPL leading to post-
    prandial hyperglycemia
A

Hypoglycemia during pregnancy

240
Q
  • Premature and LBW babies have little adipose tissue

- Enzymes of gluconeogenesis are not yet completely functional

A

Hypoglycemia in the neonate

241
Q
  • is the process of synthesizing glucose or glycogen from noncarbohydrate precursors
  • Major substrates
    Glucogenic amino acids
    Lactate
    Glycerol
    Propionate (in ruminants)
A

Gluconeogenesis

242
Q
  • Liver and kidney -> major gluconeogenic tissues
    – Small intestine may also be a source of glucose in the fasting state
  • The only source of glucose during prolonged fasting
A

Gluconeogenesis

243
Q
  • Major storage carbohydrate in animals
  • Branched polymer of α-D-glucose
    α(1->4) glycosidic bonds: for elongation - primary bond, about 8-10 glucose residues
    α(1->6) glycosidic bonds: for branching

Where is it stored?
liver 100 g = 6% of liver
muscle 400 g =

A

Glycogen

244
Q

If monosaccharides are connected by glycosidic

bonds, what do you call the bonds that connect amino acids?

A

Peptide

245
Q
  • Synthesis of new glycogen molecules from α-D- glucose

Where does it occur?

  • Occurs in the liver and the muscle
  • Occurs in the cytosol
A

Glycogenesis

246
Q

Glycogenesis: What are the substrates and product?

A

Substrates: UDP-glucose
ATP and UTP
glycogenin: a core, primer protein

Product: Glycogen

247
Q

Glycogenesis: Which step is rate-limiting?

A

Reaction: elongation of glycogen, i.e., addition of α(1->4) bonds
Enzyme: glycogen synthase

248
Q

Glycogenesis

A

Glucose-6-P -> Glucose-1-P
Enzyme: phosphoglucomutase
This is a reversible process and is not rate-limiting

Synthesis of UDP-Glucose
Enzyme: UDP-glucose phosphorylase
Substrates: glucose-1-P and UTP

249
Q
  • The rate-limiting step of glycogenesis
  • Enzyme: glycogen synthase
  • Forms α(1->4) bonds between glucose residues
  • Bonds formed at the non-reducing end (i.e., carbon 4)
A

Glycogenesis

250
Q
  • Enzyme: branching enzyme composed of amylo α(1->4) -> α(1->6) transglucosidase
  • Forms new α(1->6) bonds by transferring 5 to 8
    glucosyl residues
A

Formation of branches in glycogen

251
Q
  • Shortening of glycogen chains to produce molecules of α-D-glucose

Location:
Occurs in the liver and the muscle
Occurs in the cytosol

A

Glycogenolysis

252
Q

Glycogenolysis

A

Substrate: Glycogen
- Leaves about 4 glucose residues before a branch point
called a limit dextrin

Products: Glucose-1-P and Free glucose

  • Liver: can release free glucose to circulation
  • Muscle: limited to glucose-6-P within muscle only
  • Free glucose is a product of the debranching process
253
Q

Glycogenolysis: Rate Limiting Step

A

Reaction: removal of glucose (breaks a(14) bonds)
Enzyme: glycogen phoshporylase

254
Q 
Enzymes: debranching enzyme composed of
α(1->4) -> α(1->4) glucantransferase
amylo-α(1->6) glucosidase
Bonds cleaved: α(1->4) and α(1->6)
Products: free glucose from the breakage of the
α(1->6) bond
A

Removal of branches

255
Q

Glycogenolysis

A

Conversion of glucose-1-P to glucose-6-P
Enzyme: phosphoglucomutase
Liver: glucose-6-P further converted to glucose
Muscle: glucose-6-P is the final product

Lysosomal degradation of glycogen
Enzyme: α(1->4) glucosidase
Also known as acid maltase, an enzyme that is different from glycogen phosphorylase

256
Q
  • Group of inherited disorders characterized by deposition of an abnormal type or quantity of glycogen in the tissues
  • 12 types total, all of which are due to enzyme deficiencies
    Abnormal glycogen metabolism
    Accumulation of glycogen within cells
A

Glycogen Storage Diseases

257
Q
  • Type I
  • deficiency in glucose 6- phosphatase
  • causes glycogen in liver and renal cells hypoglycemia + lactic acidosis/ketosis
A

Von Gierke’s

258
Q
  • Type II
  • deficiency in acid maltase
  • glycogen in lysosomes cardiomegaly and heart failure
A

Pompe’s

259
Q
  • Type III
  • debranching enzyme deficiency
  • milder form of Type I
A

Cori’s

260
Q
  • Type IV
  • branching enzyme deficiency
  • severe form of Type I (early death from heart and liver failure)
A

Andersen’s

261
Q
  • Type V
  • skeletal muscle glycogen phosphorylase deficiency
  • glycogen in muscle
  • muscle cramps + myoglobinuria but
  • NO lactic acidosis
A

McArdle’s

262
Q
  • Type VI
  • hepatic glycogen phosphorylase
  • glycogen in liver cells hypoglycemia
A

Hers’

263
Q

Blood Glucose Level

A

►After a carbohydrate meal = 6.5 – 7.2 mmol/L
►Post-absorptive state = 4.5 – 5.5 mmol/L
►Fasting = 3.3 – 3.9 mmol/L

264
Q

Sources of Blood Glucose

A
  1. From carbohydrates in diet
    Glucose
    Galactose and fructose are readily converted to glucose in liver
    2.From glucogenic compounds that undergo gluconeogenesis
  2. From liver glycogen by glycogenolysis
265
Q

Glucogenic Compounds that Undergo Gluconeogenesis

A
  1. Those involved in direct net conversion to glucose without significant recycling - Amino acids, propionate
  2. Those which are products of partial metabolism of glucose
    Lactate – reforms glucose through Cori Cycle
    Alanine – through Glucose – Alanine Cycle
    Glycerol
266
Q
  • Regulate blood glucose after a meal through glucokinase activity
  • Freely permeable to glucose which is then phosphorylated by glucokinase (in direct contrast to extrahepatic cells which are relatively impermeable to glucose but on entry is phosphorylated by hexokinase)
A

Liver

267
Q

GLUCOKINASE vs HEXOKINASE

A

►Hexokinase
Lower Km (higher affinity) for glucose
Inhibited by glucose 6-phosphate

►Glucokinase
Higher Km (lower affinity) for glucose
Not inhibited by glucose 6-phosphate

268
Q
  • Glucose filtered by glomeruli but reabsorbed by renal tubule
    ► Renal threshold for glucose = 9.5 – 10 mmol/L
    ► Reabsorption rate = 350 mg/min
  • When glomerular filtrate contains more glucose than can be reabsorbed -> GLYCOSURIA -> may indicate Diabetes Mellitus
A

Kidneys

269
Q
  • Produced by -> cells of islet of Langerhans in pancreas
  • Secreted as direct response to hyperglycemia
  • Enhance glucose transport by recruitment of glucose transporter in muscles and adipose tissue
  • Increases hepatic glycolysis
A

Insulin

270
Q
  • Produced by A cells of islet of Langerhans
  • Stimulated by hypoglycemia
  • Increases glycogenolysis and gluconeogenesis
A

Glucagon

271
Q
  • Elevates blood glucose
  • Antagonize action of insulin
  • Decreases glucose uptake in certain tissues, e.g.
    muscles
  • Mobilizes free fatty acid from adipose tissues
A

Anterior Pituitary Hormones (GH, ACTH)

272
Q
  • Secreted by adrenal cortex
  • Increases gluconeogenesis
  • Decreases utilization of glucose in extrahepatic tissues
A

Glucocorticoid

273
Q

Secreted by adrenal medulla

Increases glycogenolysis in liver and muscles

A

Epinephrine

274
Q

Diabetogenic action -> FBS elevated in hyperthyroidism

A

Thyroid hormone

275
Q

DM Type I vs Type II

A

►Type I
Insulin is absent or deficient because the pancreas lacks or has defective B-cells

►Type II
Deficiency of insulin receptors; insulin level is
normal or may be elevated

Biochemistry (9 decks)

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