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Biochemistry > Exam 3 > Flashcards

Exam 3 Flashcards

1
Q

Dihydroxyacetone

A
  • is a ketose

- has the same atomic composition as glyceraldehyde and they are tautomers which can interconvert

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2
Q

Isoprenoids

A
  • Biomolecules found in membranes that consist of terpenes (found in essential oils) and steroids
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3
Q

GM2, or Tay-Sachs ganglioside

A
  • disease results from incomplete enzyme processing of the glycan portion of glycosphingolipids
  • neural diseases
  • Tay-Sachs lysomes cannot digest ganglioside GM2 due to mutation in HEXA gene
  • HEXA responsible for breakdown of fatty acid substance GM2
  • Accumulation of GM2 causes the lysosomes in the neuronal cells and the neuronal cells themselves to bulge and die causing the disease
  • constituents of the ABO blood group antigens
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4
Q

Examples of Fatty Acids

A
  • When the hydrophilic head is in ionic form, then the acid is just referred to as stearate or oleate
    1. Stearic acid
  • saturated(all carbons have H’s, no double bonds) fatty acid
    2. Oleic acid
  • unsaturated(double bonds) fatty acid
  • one CIS double bond
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5
Q

How are fatty acids synthesized?

A
  • by the sequential addition of 2-carbon precursors.
  • fatty acids are synthesized stepwise from acetyl (2 C) building blocks
  • this is why most fatty acids have an even number of carbon atoms
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6
Q

Glyscosides

A
  • monosaccharide derivative
  • elimination of water between the anomeric hydroxyl of a cyclic monosaccharide and the hydroxyl group of another compound yields O-glycoside
  • O signifies the hydroxyl attachment
  • newly formed bond is a glycosidic bond (ether like)
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7
Q

Tetroses

A
  • monosaccharides where n=4

- The keto form of a tetrose is erythrulose, which only has one asymmetric carbon

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8
Q

Cyclization

A
  • creates a new asymmetric center
  • The new center is called an anomeric center and is designated as α (Oh group down) or β (Oh group is up/on the same side of CH2OH group)
  • Anomers interconvert by mutarotation (center figure)
  • These rings are shown in Haworth projection
  • C1 is the anomeric carbon in ring structures
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9
Q

Ceramides

A
  • sphingolipid derivatives
  • consist of sphingosine and a fatty acid
  • if a fatty acid is linked via an amide bond to the NH2 group that is on the C-2, it is called a ceramide
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10
Q

Compounds with >1 asymmetric carbon (chiral carbons)

A
  • may be enantiomers (mirror images) or diastereomers
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11
Q

Anomers

A
  • stereoisomers that differ in conformation at the anomeric carbon
  • The carbon in a cyclic sugar that is the carbonyl carbon in the open-chain (acyclic) form
  • start counting here
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12
Q

Cholesterol

A
  • Bulky, rigid structure disrupts regular fatty acid chain packing in membranes
  • weakly amphipathic because of –OH (hydroxyl group)
  • Fatty acid esters of cholesterol are extremely apolar
  • precursor to all steroids
  • major sterol in animal tissues
  • really no such thing as “good” or “bad”
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13
Q

What do the numeric abbreviations for fatty acids tell you about their composition? 18:3cΔ9,12,15

A
  1. 18 = Number of carbons
  2. 3 = number of unsaturated double bonds
  3. c = cis orientation
  4. Δ#= carbons at which double bonds occur
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14
Q

Alditol

A
  • monosaccharide derivative
  • reduction of the sugar carbonyl yields alditol
  • The reduction of glucose yields D-glucitol, also called sorbitol
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15
Q

Example of a Triaglycerol

A
  • Tristearin

- the triglyceride form of stearic acid

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16
Q

Oligosaccharide

A
  • Compound formed by linking several monosaccharides together (example, disaccharide, with 2)
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17
Q

Galactosylceramide

A
  • is found on brain cell membranes
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18
Q

Furanose

A
  • A five-member closed chain form of a monosaccharide
  • one of the ribose carbons cannot fit in the ring
  • heterocyclic compound is furan
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19
Q

Reducing and nonreducing sugars

A
  • Free anomeric carbon = reducing end (OH group on anomeric carbon)
  • Sucrose has no free anomeric carbons(no OH group on anomeric carbon), thus no reducing ends. It is a nonreducing sugar.
  • lactose is a reducing sugar
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20
Q

Niemann-Pick disease

A
  • Sphingomyelin accumulation
  • an individuals deficient in acid sphingomyelinase
  • Niemann-Pick is similar in pathology to Gaucher’s.
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21
Q

Lactones and Acids

A
  • monosaccharide derivative
  • oxidation of monosaccharides forms these, proceeds in several diff ways depending on oxidizing agent
    ex: D-gluconic acid.
  • Oxidation at C1 forms an aldonic acid
  • The aldonic acid is in equilibrium with the lactone (cyclic ester) form
    ex: β-D-glucuronic acid
  • Oxidation at C6 forms a uronic acid
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22
Q

Enantiomers

A
  • optical isomers that are non-superimposable mirror images of eachother
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23
Q

Glyceraldehyde

A
  • is an aldose
  • has the same atomic composition as dihydroxyacetone and they are tautomers which can interconvert
  • contains a chiral carbon thus it has two stereoisomers otherwise known as enantiomers. (R=D, L=S)
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24
Q

Diastereomers

A
  • are optical isomers that are not mirror images

- with 2 enantiomers each

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25
Q

Soaps

A
  • Soaps are formed by the treatment of fatty acids with strong bases(NaOH or KOH), saponification
  • water soluble
  • Soaps form micelles around oils, emulsifying the oil
  • the hydrophobic heads of soap molecules on the outside allow the micelle to be suspended in water
  • In hard water, soap reacts with calcium and magnesium ions to form a precipitate (scum)
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26
Q

Sphingolipids

A
  • unique because they are built on the amino alcohol sphingosine, rather than glycerol
  • major component of membranes
  • includes a long-chain hydrophobic tail, so it only requires only the addition of one fatty acid to make it a suitable membrane protein.
  • If a fatty acid is linked to the sphingosine via a AMIDE bond to the NH2 group on C-2, it is called a ceramide
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27
Q

How is cholesterol beneficial

A
  • Cholesterol cannot be metabolically degraded and as such is returned to the liver for excretion
  • High Density Lipoprotein is considered “good” because high levels of HDL counteract atherogenesis.
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28
Q

Monosaccharide

A
  • Simple sugars and derivatives with 3 to 9 carbon atoms
  • A single sugar
  • A carbohydrate that cannot be broken down into a simpler carbohydrate
  • presence of a carbonyl group (aldehyde or ketone) and one or more hydroxyl group, and a sugar
  • two major classes: aldoses and ketones
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29
Q

Major classes of membrane forming lipids/Structural

A
  • they differ in the nature of the head group
    1. Glycerophospholipids
    2. Sphingolipids
    3. Glycosphingolipids
    4. Glycoglycerolipids
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30
Q

Anomeric carbon

A
  • The carbon in a cyclic sugar that is the carbonyl carbon in the open-chain (acyclic) form
  • start counting here
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31
Q

Sphingolipids

A
  • Another type of membrane forming lipid bearing an amine group on the polar ”head”
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32
Q

Cerebrosides

A
  • are monoglycosyl ceramides
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33
Q

saturated fatty acids

A
  • contain no C-C double bonds
  • Fats that are rich in saturated fatty acids are solid at room temperature more solid (butter)
  • most stable arrangement of saturated fatty acids is the very close packing of the side chains of the lipid
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34
Q

Eicosanoids

A
  • diverse class of signaling molecules derived from lipids
  • derived from arachidonic acid
  • potent activators of wide range of physiological function, including inflammation, blood clotting, blood pressure regulation and reproduction
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35
Q

R/S in relation to D/L

- what do D and L refer to

A
  • R=D, clockwise
  • S=L, counterclockwise
  • D and L refer to configuration about the asymmetric carbon farthest from the carbonyl carbon (C=O)
  • forms of a monosaccharide that are nonsuperimposable mirror images (enantiomers)
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36
Q

Glycans

A
  • are metastable and their formation is unfavorable
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37
Q

Adipocytes

A
  • fat storage cells
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38
Q

Nonreducing sugar

A
  • do not have an OH group attached to the anomeric carbon, so they cannot reduce other compounds
  • without a hemiacetal
    ex: sucrose
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39
Q

Hexoses

A
  • prefer the pyranose ring structure when in aqueous solutions, but this depends on the structure of the sugar and its environment
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40
Q

Reducing sugar

A
  • any sugar that is capable of acting as a reducing agent because it has a free aldehyde group or a free ketone group
  • any sugar containing a hemiacetal
    ex: maltose and lactose
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41
Q

Phosphate esters

A
  • monosaccharide derivative
  • Sugar phosphates are important intermediates in metabolism
  • functioning as activated compounds in syntheses
  • very acidic
  • under physiological conditions exist as a mix of dianions and monoanions
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42
Q

Beta-anomer

A
  • when OH and C2OH groups are present on the same side of haworth projection
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43
Q

D-sugars vs L-sugars

A
  • D-sugars are preferred in nature

- L-sugars have certain specialized roles in nature

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44
Q

The four most common hexoses

A
  1. Fructose (Furanose form)
  2. Glucose
  3. Mannose
  4. Galactose
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45
Q

Properties of lipids

A
  • limited solubility in aqueous media
  • unlike macromolecules, they do not form covalently linked polymers, instead, they associate via noncovalent interactions
  • most are amphipathic (contain both hydrophobic and hydrophilic regions)
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46
Q

Glycosphingolipids

A
  • have glycans attached to sphingosine
  • head group contains saccharides
  • Constituents of ABO blood antigens
  • Includes cerebrosides and gangliosides, common in the membranes of brain and nerve cells
  • Several human diseases (including Tay-Sachs, Gauchers disease) result from incomplete enzymatic processing of the glycan portion of glycosphingolipids.
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47
Q

Wax Esters

A
  • Complex mixtures of nonpolar lipids
  • Form the protective coatings of leaves/stems/fruits
  • long chain fatty acid esterified to a long chain alcohol
  • firmness of waxes increase with chain length and degree of hydrocarbon saturation
  • Because of the extremely small polar region, waxes are completely water insoluble
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48
Q

Aldotetroses and ketotroses are _______

A
  • tautomers
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49
Q

Functions of fat storage

A
  1. Energy Production
  2. Heat Production
  3. Insulation
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50
Q

Simple fats

A
  • Triacylglycerols with the same fatty acid esterified at each position
  • most are mixed fats with a mixture of different fatty acids
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51
Q

Formula: (CH2O)n

A
  • When n = 1: formaldehyde
  • When n = 2: acetaldehyde
  • n = 3-9 gives compounds with properties of sugars
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52
Q

Glycerophospholipid

A
  • the major class of naturally occurring phospholipids
  • glycerol is prochiral
  • have an ester bond
  • plays major role in metabolis, minor membrane constituent
  • only has 2 fatty acid chains, the third chain contains a phosphate group unlike triaglycerol
  • Names of glycerophospholipids are derived from phosphatidic acid
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53
Q

Writing the structure of Disaccharides

A
  1. The sequence is written starting with the nonreducing end at the left, using the abbreviations in table 9.1
  2. Anomeric and enantiomeric forms are designated by prefixes (e.g. α- D-)
  3. The ring conformation is indicated by a suffix (p for pyranose, f for furanose)
  4. The atoms between which the glycosidic bonds are formed are indicated by numbers in parentheses between residue designations
    ex: 1->4 means a bond from carbon 1 of the residue on the left to the carbon 4 of the residue on the right

Complete abbreviation for sucrose: α-D-Glcp(1->2)-β-D-Fruf

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54
Q

Ketopentoses

A
  • have two chiral centers, so they have 2^2=4 stereoisomers in 2 pairs of enantiomers
  • the same logic can be used to describe ketohexoses
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55
Q

Phospholipids

A
  • One type of membrane forming lipid bearing a phosphate group in the hydrophilic “head” group.
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56
Q

Linolenic acid

A
  • a polyunsaturated fatty acid or PUFA

- indicates multiple double bonds

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57
Q

Chiral carbons

A
  • has two stereoisomers, otherwise known as enantiomers
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58
Q

4-carbon ketoses (ketotroses)

A
  • only have one pair of enantiomers because there is only one chiral carbon, C3.
  • Usually the names of ketoses are derived from the corresponding aldose name with the addition of ”ul”
    ex: Erythrose (aldose)->Erythrulose(ketose)
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59
Q

Ketose

A
  • A polyhydroxy ketone(C=O, two R groups)

ex: a carbohydrate containing a ketone functional group

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60
Q

Aldose

A
  • A polyhydroxy aldehyde (C=O, connected an H and R gp)

ex: a carbohydrate containing an aldehyde functional group.

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61
Q

Uncommon Fatty Acid characteristics

A
  • some have odd numbers of C atoms

- Some (unnatural) fatty acids have trans double bonds

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62
Q

Four major features of disaccharides

A
  1. The sugar monomers involved and their stereochemistry
  2. The carbons involved in the linkage
  3. The order of sugars (note whether the sugar is reducing; the free anomeric carbon can undergo oxidation)
  4. The configuration of the anomeric carbon (α or β)
  • vary in anomeric configuration among other features
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63
Q

Epimers

A
  • isomers differing only in configuration about one carbon, other than the anomeric carbon
    ex: mannose and glucose or glucose and galactose
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64
Q

Hemiacetal formation

A
  • results from reaction of an aldehyde with an alcohol
  • any carbon with an OH and OR group attached
  • with pentoses and hexoses(5/6 C)
  • monosaccharides with 5 or 6 carbons exist in this structure
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65
Q

Fischer Projection

A
  • A way of representing an acyclic (open chain) carbohydrate structure
  • Vertical lines point away from the viewer(dash) and horizontal lines point toward the viewer(wedge)
  • the most compact way to represent stereochemistry
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66
Q

Polysaccharide

A

Polymer formed from multiple saccharide units

- may be homopolysaccharide or heteropolysaccharide

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67
Q

Chair Conformation

A
  • the most stable conformation of cyclohexane that resembles a chair
  • lowest energy form, most stable bc sub on axial bonds in boat form tend to be crowded
  • axial (up and down/parallel to axis)
  • equatorial (side to side/perpendicular to axis)
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68
Q

The fluidity of fatty acids

A
  • decreases as the chain length increases and the number of cis double bonds decreases
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69
Q

Glycan

A
  • Generic term for oligosaccharides and polysaccharides
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70
Q

Chair Form

A
  • the lowest energy, or most stable, form

- The chair form is more stable because the substituents on axial bonds tend to be more crowded in boat form

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71
Q

6 Classes of Lipids

A
  1. Fatty Acids
  2. Triaglycerols
  3. Wax esters
  4. Phospholipids
  5. Sphingolipids
  6. Isoprenoids
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72
Q

Fat storage

A
  • The process of esterification of fatty acids into fats causes partial loss of the hydrophilicity of the polar head
  • as a result triacylglycerols are not water-soluble
  • This insolubility leads to oily droplets that are stored in “fat cells” or adipocytes.
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73
Q

Unsaturated fatty acids

A
  • contain one or more cis C-C double bonds
  • fats that are rich in unsaturated fatty acids are liquid at room temperature (olive oil)
  • the kink caused by the double bond does not allow for the tightly packing of fatty acid chains
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74
Q

Bonds to substituents on ring carbons can be defined as:

A
  • axial or equatorial depending on whether or not they are parallel or perpendicular to the axis
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75
Q

Gaucher’s diease

A
  • Glucocerobroside accumulation
  • an individuals deficient in glucocerebrosidase
  • Gaucher’s disease causes enlarged livers and spleens in the affected.
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76
Q

How is cholesterol bad

A
  • Low Density Lipoprotein (LDL) is considered ”bad” because its oxidation leads to atherosclerosis.
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77
Q

Glycoglycerolipids

A
  • Mostly found in plant(chloroplasts) and archaea membranes
  • most abundant of all polar lipids
  • major membrane components
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78
Q

Glycan biosynthesis

A
  • activated monomers are required
  • These monomers are usually nucleotide linked sugars
  • Glycans are never copied from template molecules, a different enzyme is employed to catalyze the addition of each monomer (unlike polynucs. and polypeps.)
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79
Q

Amphiphathic nature of lipids

A
  • form monolayers, micelles, or bilayers
  • the structure formed when a lipid is in contact with water depends on the structure of the hydrophobic and hydrophilic groups
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80
Q

Fatty acids

A
  • basic structure: hydrophilic group attached to a hydrophobic tail, has hydrocarbon chains
  • Carry a negative charge
  • the simplest lipids
  • WEAK acids
  • mostly cis in nature
  • Most common fatty acids have an “even-numbered tail”
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81
Q

Why are Glycerophospholipids prochiral?

A
  • Glycerol alone does not contain any stereocenters but the glycero-derivatives will generate an asymmetric center at C2
  • causes them to be prochiral
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82
Q

Aldopentoses

A
  • have three chiral centers, so they have 2^3=8 stereoisomers in 4 pairs of enantiomers
  • same logic can be used to describe aldohexoses
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83
Q

Lipids that form bilayers

A
  • tend to contain 2 hydrocarbon tails per polar head group

- The cylindrical shape promotes packing into a parallel array

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84
Q

Lipids

A
  • the major constituents of all biological membranes

- membrane lipids are ampiphatic

85
Q

Functions of carbohydrates

A
  1. Metabolism, storage and generation of energy (glucose, glycogen, starch)
  2. Molecular recognition (immune system)
  3. Cellular protection (bacterial and plant cell walls)
  4. Cell adhesion (glycoproteins)
  5. Biological lubrication (glycosaminoglycans)
  6. Maintenance of biological structure (cellulose, chitin)
86
Q

Major functions of lipids

A
  1. Energy storage
  2. Membrane structure
  3. Cell Signaling
87
Q

Gangliosides

A
  • are anionic glycosphingolipids containing one or more sialic acid residues
88
Q

Oligo/Polysaccharides

A
  • monosaccharides form these via glycosidic bonds
  • Just as monosaccharides can form glycosidic bonds with other hydroxyl containing groups, they can do so with one another to form oligo and polysaccharides
  • Glycosidic bonds between monosaccharides give rise to glycans
89
Q

Hydrogenation

- commercial use

A
  • unsaturated fat oils to a saturated fat
  • partial hydrogenation of unsaturated fat oils (like corn oil) is used commercially to convert them to firmer fats, which can be used as butter substitutes such as margarine or to stabilize them against spoilage.
90
Q

Trioses

A
  • monosaccharides where n=3
  • C2 is chiral center
  • glyceraldehyde and dihydroxyacetone
91
Q

Lipids that form micelles

A
  • tend to contain 1 hydrocarbon tail per polar head group

- The wedge shape promotes spherical molecules.

92
Q

Triaglycerols

A
  • FATS
  • Esters of glycerol with three fatty acid molecules
  • Contain no net charge
  • Glycerol esterified with three fatty acids (triester of glycerol and fatty acids)
  • They are the major long-term energy storage molecules in many organisms
93
Q

Pyranose

A
  • A six-member cyclic form of a monosaccharide
  • all of the ribose carbons can fit in the ring
  • heterocyclic compound is pyran
94
Q

conformational isomers

A
  • molecules with the same stereochemical configuration, but differing in the three-dimensional conformation (bond rotation).
95
Q

Lactose biosynthesis

A
  • the activated sugar is UDP-galactose
  • UDP-Gal is formed which activates the anomeric carbon for transfer to a carbohydrate acceptor
  • catalyzes the reaction between UDP-galactose to the OH group at C4
96
Q

Haworth Projection

A
  • A way of representing a cyclic (closed chain) carbohydrate
  • in fischer projection groups on left side face up, groups on right side face down
  • Substituents can either point up or down on this ring
97
Q

A molecule with n chiral centers will have how many stereoisomers?

A
  • will have 2^n stereoisomers, 1 for each chiral center
98
Q

Fluid Mosaic Model

A
  • a model describing cellular membrane structure, according to which proteins are embedded in a phospholipid bilayer and are free to move in the plane of the membrane
  • according to the model, a membrane is a fluid mixture of lipids and proteins
  • the asymmetric lipid bilayer is fluid and carries a host of proteins within it
  • The membrane is a mosaic of lipids and proteins (with oligosacchs often attached to both)
  • transition temp is kept below body temp of the organism to maintain fluid membrane
99
Q

Cellular membrane features

A
  • An important feature of cellular membranes is the wide variety of specific proteins contained within the lipid bilayer
  • many of these proteins carry oligosaccharide groups that project into the surrounding aqueous medium
  • other oligosaccharides are carried by glycolipids, with lipid portions inserted in the membrane
  • the two sides of the bilayer are usually different, both in lipid composition and in the placement and orientation of proteins and oligosaccharides
  • the protein content varies greatly among different kinds of membranes and appears to be directly related to functions a particular membrane must carry out
  • 60% protein and 40% lipid
  • The hydrophobic interior is typically twice as thick as the polar, hydrophilic head groups.
100
Q

Peripheral membrane proteins

A
  • asymmetric lipid bilayer is fluid and carries within it a host of proteins
  • these are exposed at only one membrane face or the other
  • can be separated from the membrane without disrupting the bilayer
  • they are held to the membrane by noncovalent interaction with lipid heads or with integral membrane proteins
101
Q

Integral membrane proteins

A
  • frequently involved in diffusion
  • are largely buried within the membrane, but are usually exposed on both faces
  • can only be extracted under conditions that disrupt membrane structure
  • frequently involved in transporting specific substances, or transducing chemical signals through the membrane
102
Q

Evidence for the fluidity of membranes

A
  • biological membranes are not rigid structures (lipids and proteins in constant motion)
  • if human and mouse cells are marked in its plasma membrane and fused together, eventually they will become intermixed
  • demonstrates LATERAL DIFFUSION (parallel to the membrane surface) can occur in the membrane
  • rate depends on membrane fluidity which depends on temperature and lipid composition
103
Q

Synthetic membranes

A
  • used in computational studies to learn about the dynamics of membrane LIPIDS (NO PROTEINS)
104
Q

Melting point of fatty acids affected by:

A
  • determined by length and degree of saturation of the hydrocarbon chain
    1. longer chain fatty acids and increased saturation correlate with higher values of temperature at gel state
    2. shorter chain fatty acids and unsaturated tails, correlate with lower values of temperature at gel state
    3. Cholesterol broadens transition temp (larger range)
105
Q

Which state do membranes need to be in fluid or gel?

A
  • need to exist in a semi-fluid liquid crystalline state to allow their associated proteins to move within the bilayer, interact with binding partners or substrates and change conformations
  • because it is essential to be fluid, the membrane composition is regulated as to keep the transition temperature below the body temperature of the organism
106
Q

Biological membranes are dynamic and assymetric

A
  • Every biological membrane has 2 distinct faces that encounter 2 different environments.
  • Because each side faces a different environment, the composition of lipids on either side will be different.
  • the two individual layers of a bilayer are called leaflets
  • the compositions of the two leaflets in the plasma membranes are very different in composition and structure because they deal with different surroundings
  • the lipid and protein content of a given membrane is tailored to the specific function of that membrane
107
Q

Membrane proteins are different than other globular proteins

A
  • they often have high proportions of hydrophobic amino acids in the part of the protein molecules that are embedded in the membrane
  • the segments of proteins that span membranes are often a-helical (dominant form), but can also be B-barrels
  • a helicals can pass back and forth through the membrane
  • B barrels are hydrophobic and most of their residues are buried in the membrane
108
Q

Lipids

A
  • are amphipathic and form various structures in water
  • they form monolayers. bilayers, micelles and vesicles
  • micelles are formed in water when shaken
  • structure formed depends on the hydrophilic and hydrophobic groups
  • the polar head group of the lipid is oriented toward solvent and the lipophilic tails are pointed inward toward the interior of the membrane.
109
Q

Triglycerols

A
  • helps with storage of fatty acids in organisms*
  • esters of glycerol with 3 fatty acid molecules
  • contain no net charge, bc carboxylates are esterified
  • causes it to be insoluble
  • simple fats
  • lipids found in foods (cholesterol and phosphate)
110
Q

A 18-carbon fatty acid with one double bond between C-9 and C-10 is designated?

A
  • 18:1c(delta)9
111
Q

fatty acid containing lipids

A
  1. triacylglycerolds (triglycerides)
  2. Glycerophospholipids
  3. Sphingolipids
112
Q

Melting point changes of membrane fluidity

A
  • at low temperatures the hydrocarbon tails pack closely together to form a nearly solid gel state
  • at higher temps a phase change occurs to liquid and the hydrocarbon tails become free to move about/disordered (melting temperature/transition temp, Tm)
  • transition temperature becomes broadened when cholesterol is added to the pure phospholipid bilayer (blurs distinction between gel and fluid state)
113
Q

Storage vs Structural Lipids

A
  1. Storage
    - used for energy production, heat production and insulation
  2. Structural
    - provide structure to membrane and tissues
114
Q

Glycolipid/glycoconjugates means?

A
  • glyco means a sugar/carbohydrate group attached to the lipid group
  • molecules of carbohydrate bonded to other compounds, such as protein and lipid.
115
Q

Sterol contains:

A
  • class of lipids containing a steroid nucleus and hydroxyl group
    ex: cholesterol
116
Q

Fatty acids vs Fats

A
  1. Fatty acids
    - consist of just the tails
  2. Fats, or triaglycerols
    - are the triesters of fatty acids and glycerol
117
Q

Functions of membrane proteins

A
  1. Mediate movement of ions and polar molecules across membranes (Cl- channel)
  2. Generate proton gradients for ATP production (ATP synthase in inner mitochondrial membranes)
  3. Respond to extracellular signals and communicate them to the cell interior (insulin receptor)
118
Q

Cell membranes are impermeable to?

A
  1. Ions

2. Large Polar (water soluble) molecules

119
Q

Bacteriorhodopsin

A
  • an integral membrane protein
  • a light-driven proton pump in some photosynthetic bacteria
  • It spans the membrane with 7 α-helices that pass back and forth through the membrane
  • A hydrophobicity plot can show that the membrane spanning helical regions are highly hydrophobic
  • this pattern of side chain hydrophobicity is typical of membrane-spanning proteins
120
Q

Post translational modifications

A
  • anchor proteins to membranes
    1. proteins involved in signaling are covalently modified via reactions that form acyl group transfers, or alkylation
  • modifications at the C and N terminus
    2. GPI-linked proteins are generally targeted to the outer leaflet of membranes that rich in cholesterol and sphingolipids
  • association of a lipid linked protein with membrane may be mediated by protein-lipid binding sites
121
Q

Membrane/Lipid Rafts

A
  • are dynamic structures rich in cholesterol, sphingolipids, and GPI
  • Cholesterol, sphingolipids and GPI can coalesce to form separate membrane domains that are small, short lived structures but in the presence of certain stimuli that form larger raft platforms
  • Possible roles in cell signaling and sorting proteins into specific organelles within a cell
  • clustering GPI proteins in raft platforms may accelerate signal transduction across the membrane
  • bilayer is thicker in the raft domains than in the surrounding membrane
  • Sterol-to-lipid ratio may be critical in determining raft formation
122
Q

Membrane Bilayer Thickness

A
  • bilayer thickness is a function of the lipid and protein composition in membrane domains
    1. at certain sterol-lipid ratios, membrane lipids form more ordered and elongated structures
    2. lipids change structure to accommodate proteins (more common)
    3. Hydrophobic mismatch will occur when the thickness of the bilayer core and SA of embedded protein don’t match (either the protein will undergo conformational change or bilayer will adjust until match)
123
Q

2 Ways Proteins are inserted into membranes

A
  1. The several integral membrane proteins are inserted into the bilayer cotranslationally (during ribosome protein synthesis) where they fold
    - translocon facilitates the insertion of hydrophobic regions of protein sequence into the bilayer
  2. Process for proteins that are not cotranslationally inserted into the membrane
    - A sequence of events happens in the synthesis of proteins on the rough endoplasmic reticulum (RER)
    - export from the RER to the golgi, the golgi modifies the protein if needed and sends the vesicles to the membrane
124
Q

Translocon Complex

A
  • facilitates the insertion of hydrophobic regions of protein sequence into the membrane bilayer.
  • The translocon complex is called SecY in prokaryotes and Sec61 in eukaryotes, sec=secretion
125
Q

Inside Positive Rule

A
  • ensures that proteins are inserted into the membrane with the correct topology
  • a matter of survival
  • inside of cell more negative, so amino acid side chains will orient so that more positive side will be toward inside of the cell
126
Q

delta G

A
  • free energy change
  • describes the equilibrium state for a process
  • equilibrium state is reached when concentrations of the substance are the same on both sides of the membrane
127
Q

Three circumstances when equilibrium state can be circumvented(doesn’t occur)

A
  1. The solute is bound by a macromolecule on one side of the membrane
    - this reduces the concentration of free solute on that side of the membrane
  2. The solute is an ion and its diffusion is influenced by the electrical potential maintained across the membrane
  3. by coupling transport to an exergonic process
    - A thermodynamically favorable process, like ATP hydrolysis, is coupled to transport against a concentration gradient
    - in the case of an active transport process
128
Q

Nonmediated transport

A
  • molecular diffusion (random wandering of molecules through membranes)
  • rate is dependent on the concentration difference across the membrane and the polarity of the material
  • rate of nonmediated transport across lipid membranes is faster for nonpolar substances
  • diffusion increases as the hydrophobic character increases
  • for ions and hydrophilic substances, diffusion through membranes is extremely SLOW
  • P in the equation is the permeability coefficient units of distance/time
129
Q

Facilitated Transport/Diffusion

A
  • accelerated diffusion
  • accomplished by pores/channels, carriers, and permeases
  • many need this type bc the slow nonmediated transport is insufficient for their functional and metabolic needs
  • can be active or passive
    1. Transport through pores/channels by transmembrane proteins
    2. Transport by carrier molecules
    3. Transport by permeases
130
Q

3 Types of Facilitated Transporters

A
  1. Ionophores (carrier molecule)
  2. Permeases
  3. Pores/Channels
131
Q

Ionophores

A
  • a carrier molecule
  • no directed flow, but increases the permeability of the cell membrane to ions
  • are produced by bacteria to kill competing bacteria by destroying the electrochemical gradients that store free energy and are needed to drive vital processes
  • several are useful antibiotics
  • The exterior of the ionophore contains hydrophobic amino acids
  • the interior, polar environment that is specific for binding ions the size of K+.
  • PASSIVE TRANSPORT, net transport goes in the direction that equalizes the concentration of ions on both sides (ALONG the concentration gradient)
    Ex: Valinomycin, an antibiotic produced by Streptomyces, acts as a potassium ionophore
  • acts as an ion carrier
132
Q

Permeases

A
  • membrane spanning proteins that recognize specific molecules for transport (transporters)
    1. ex: glucose transporter in erythrocytes (GLUT1)
  • operate in passive fashion (high to low conc)
  • does not form a pore which allows unrestricted flow, but rather the permease conformation is either only open to outside or only open to the inside
  • transport requires both binding of substrate and conformational change in permease
    2. some permeases couple the transport of more than one substrate or ion
  • symport or antiport
  • this cotransport strategy allows the thermodynamically unfavorable transport of some substrate AGAINST the conc gradient, when coupled to the favorable transport of the cosubstrate
133
Q

Symport

A
  • facilitated diffusion using permeases

- transports two solutes across the membrane in the same direction

134
Q

Antiport

A
  • facilitated diffusion using permeases

- transports two solutes across the membrane in the opposite direction

135
Q

Pore Facilitated Transport

A
  • pathogenic bacteria synthesize and secrete protein toxins that act as ionophores by creating pores in the plasma membranes of cells of the receiving organisms
  • many channels facilitate transport processes essential to cell survival
    ex 1: a-hemolysin (S. aureus)
  • is a pore forming ionophore, B sheet
  • 7 subunits produce a membrane spanning ion channel
  • Na+(sodium) into the cell
    ex 2: Gramicidin A toxin (B. brevis)
  • antibiotic that acts as an ion pore
  • forms an open helical structure
  • The alternating pattern of L- and D-amino acids forms a structure that resembles a β-sheet
  • K+ into the cell mostly
  • distinct from the α-helix which cannot act as a pore
136
Q

Aquaporins

A
  • facilitate rapid transport of water and thereby maintain osmotic balance within a cell while preserving critical ion gradients.
  • are water channels that increase water transport in some tissues: erythrocytes, salivary glands, kidney.
  • Plasma osmolarity varies considerably as the erythrocyte moves through lungs, capillaries, and kidneys
  • so rapid transport of water is critical to prevent rupture of the erythrocyte membrane.
  • use size exclusion, electrostatic repulsion, dynamic hydrogen bonding, and prevention of ion gradient formation as mechanisms of selectivity to allow water molecules to enter the cell
137
Q

Ion Selectivity for transport

A
  • Ion channels have a very high specificity for the ions which pass through them
  • Ion channels tightly control the flux of ion transport
  • Ion channels contain selectivity filters within them that chelate around the ions and completely desolvate(remove solvent component) them
  • ion selectivity is achieved by optimal geometry of chelating groups in ion channels
  • The ”filter” is generally made up of backbone or side chain oxygen atoms that interact with the ions as they pass through.
138
Q

Gating

A
  • is the switching between the conductive (open) and nonconductive (closed) channel conformations
  • voltage gated ion channel
  • when the potential across the membrane changes, the cytosolic side which was closed becomes less neg charged and moves S4 toward the other side pulling S5 and S6 with it, allows S6 to bend and open the channel
  • returns to closed conformation when resting state membrane potential is triggered by active ion transporters
  • The K+ pore is formed by the S5 and S6 helices
  • Gating is the result of repositioning of the S4 helix in response to changes in membrane potential
139
Q

Active Transport

A
  • transport AGAINST the concentration gradient
  • This means that the concentrations of certain substances must be maintained in a polarized fashion (one side of membrane will have higher concentration)
  • free energy is required, nonzero membrane potential
  • In most cases this free energy comes from the hydrolysis of ATP.
  • such direct coupling is seen in ion pumps, such as the Na+-K+ATPase
140
Q

Sodium-Pottasium Pump/ Na+ K+ ATPase

A
  • a member of the P-Type ATPase family that function i active transport across the plasma membrane
  • During each pumping cycle the y-phosphoryl group of ATP is transferred to the phosphorylation domain
  • 2 K+ ions are pumped into the cell and 3 Na+ions are pumped out of the cell for every ATP hydrolyzed
  • maintains higher concentrations of K+ inside and Na+ outside the cell
  • direct coupling
  • Na+-K+ ATPase works to restore resting potential
141
Q

How is sodium pottassium pump structurally able to function?

A
  1. A large alpha subunit that is involved with ATP hydrolysis and the coupled ion transport
  2. Slightly smaller beta subunit that acts as a chaperone and is required to target alpha subunit to plasma membrane
  3. A very small gamma(Y) subunit that helps with regulatin
142
Q

How is sodium pottassium pump Physically able to function?

A
  • Alpha subunit moves through the membrane 10 times which forms a multihelix channel which has 3 negative cytoplasmic domains
    1. ATP binding domain
    2. Phosphorylation domain
    3. Actuator domain
143
Q

How is Sod Pott Pump thermodynamically able to carry out its functin?

A
  • Requires free energy from ATP hydrolysis and transport to be coupled in order to carry out the function
  • no more than 2 K+ pumped in and 3 Na+ pumped out at a time (per hydrolyzed ATP)
  • E1 to E2 state, E1 is open only to cytosol, E2 open to surroundings
144
Q

Na+ K+ ATPase E2 state

A
  1. has a high affinity for cardiotonic steroids
    - Digitalis(Digitoxin) and ouabain act as inhibitors of the pump by locking it in the E2 conformation
    - In heart tissue this leads to activation of other means to reduce intracellular Na+, which cause Ca2+ influx, strengthening heart muscle contractions
    - Mutations can impair the function of the Na+-K+ ATPase resulting in neurological disease (Parkinsons)
  2. Sometimes it is ideal inhibit ion transporters
    - Proton pump inhibitors(PPIs) inhibit the H+-K+ ATPase (helps reduce the acidity of the stomach by limiting H+ ions being transported into the stomach)
    - in small doses digitoxin improves cardiac function
145
Q

The ABC transporters

A
  • ATP binding cassette transporters
  • responsible for multiple drug resistance in bacteria and the cystic fibrosis transmembrane regulator (chloride ion channel)
  • ATP-binding cassette transporters include the P-glycoprotein and the cystic fibrosis transmembrane regulator(CTFR)
  • Mutations in CFTR disrupt Cl- transport primarily in the lungs leading to cystic fibrosis.
  • The P-glycoprotein reduced the effectiveness of many anti-cancer drugs because it removes the drugs from malignant cells.
  • Many neurotoxins block ion channels necessary for the development of the action potential in neurons
146
Q

Sodium-glucose cotransport system

A
  • Glucose must be transported from a low concentration in the intestinal lumen to a higher concentration in epithelial cells of the cell wall
  • the favorable sodium gradient across the membrane provides the driving force for the unfavorable transport of glucose bc the Na-K pump is already ATP driven to pump cells so glucose is continuously transported as well
  • This is because Na+ gradient is maintained by the ATP driven Na+-K+ ATPase
  • Thus the sodium glucose transport system uses ATP indirectly to drive the transport of glucose.
  • many cotransport systems use Na conc grad as driving force, but H+ gradient can be used as well
147
Q

Neurons

A
  • Neurons are responsible for the conduction of electrical impulses and nervous system communication
  • The conduction of neural impulses is not accomplished by the flow of electrons, but by waves in membrane electrical potential on the surface of the membrane
  • As a response to some stimuli at the dendrites, ion channels will open up where the axon and cell body meet
  • This initiates a wave of depolarization/hyperpolarization that travels along the axon toward the terminal bulbs which form the synapses.
148
Q

The resting potential

A
  • the imbalance of ionic concentration across membranes gives rise to resting potential across a nerve axon
  • potential existing across axon membrane is primarily determined by K+ bc its more permeable due to K+ channel leaks
  • voltage gated channels are CLOSED
  • the outside of the neuron maintains a positive charge while the inside the inside maintains a negative charge at rest
149
Q

Action Potential

A
  • Membrane depolarization caused by the influx of Na+ via voltage-gated sodium channels generates the action potential
  • is a controlled and rapidly propagated change in membrane potential that is transmitted DOWN the length of the axon
  • This process involves voltage-gated potassium and sodium channels
  • the dendrites detect an excitatory stimulus which will OPEN the ion channels where the cell body meets the axon
  • this initiates a wave of depolarization/hyperpolarization
  • as Na+ channels open, Na+ rushes in and triggers a depolarizing event
  • at the same time K+ channels open to counteract this event, doing so ensures that the wave of depolarization only travels in one direction
    1. Depolarization
    2. Repolarization
    3. Hyperpolarization
    4. Na+-K+ ATPase works to restore resting potential
150
Q

Depolarization

A
  • caused by the influx of Na+ into the cell
151
Q

Repolarization

A
  • closure of Na+ channels
  • Opening of K+ channels to counteract
  • voltage gated channel
152
Q

Hyperpolarization

A
  • voltage gated K+ channels remain open after the potential reaches resting level
153
Q

Which storage and structural polysaccharide(s) can form “secondary” structures?

A
  1. amylose

2. cellulose

154
Q

Amino sugar

A
  • monosaccharide derivative
  • found in many polysaccharides and glycoproteins
  • modified sugars (especially amino sugars) are most often found as monomer residues in complex with oligosaccharides and polysaccharides
    ex 1: glucosamine
  • derived from glucose
    ex 2: galactosamine
  • derived from galactose
155
Q

Anomeric glycosides

A
  • do not interconvert by mutarotation in the absence of acid catalyst, makes them useful in determining sugar configurations
156
Q

Toxic Glycosides

A
  • toxic bc inhibit enzymes involved in ATP utilization
  • Ouabain inhibits the action of enzymes that pump Na-K ions across cell membranes to maintain necessary electrolyte balance
  • Amygdalin is toxic bc found in seeds of bitter almonds, the glycosides yields HCN upon hydrolysis
157
Q

Metastable compound

A
  • one that spontaneously breaks down slowly, unless catalyzed
  • saccharide polymers are sufficiently metastable to persist for long periods of time
    ex: glycan (unfavorable)
158
Q

Formation of disaccharides

A
  • not a simple process and requires activation
  • formation of glycosidic bond between two monomers in an oligosaccharide is a condensation reaction
  • involves the removal of a water molecule
159
Q

Homopolysaccharides

A
  • the polymer is made up from only one kind of monomer residue of the class of glucans
  • starch and glycogen contain repeating units of glucose so they are homopolysaccharides of the class glucans
    ex: cellulose, starch, glycogen
160
Q

Heteropolysaccharide

A
  • If two or more different monomers are involved in a polymer
    ex: Hyaluronic acid
161
Q

Polysaccharides/glycans fall in two major classes:

A
  1. Storage
    - starch(plants) and glycogen(animals) serve mainly to store sugars for energy
  2. Structural
    - cellulose, chitin and the polysacs of bacterial walls are structural materials
162
Q

Glycogen linkage and use

A
  • energy storage in bacteria and animals

- cant form helical structure due to branched nature, neither can glycans amylopectin

163
Q

amylose (starch) linkage and use

A
  • alpha-1,4 (linear chains), regular helical conformation
  • can form alpha helix secondary structure since it can not branch
  • energy storage in plants
164
Q

Polysaccharide degradation (breakdown of storage polymers)

A
  • is carried out by special enzymes which attach storage chains from the nonreducing ends
  • amylopectin and glycogen (starches) have many non reducing ends, so can be attacked simultaneously due to their branched nature
165
Q

Cellulose

A
  • beta-1,4 a linear chain bc sugar residues connected here

- structural functions in plants

166
Q

Why can’t humans make use of glucose molecules in cellulose?

A
  • Most animals are not able to digest cellulose due to the difference in linkage at the anomeric carbon
  • do not have the enzyme cellulase to cleave the B1-4 bonds in cellulose
  • indigestible, but cellulose help move food products through the alimentary tract and satisfy hunger
  • The exceptions are cows, termites and some fungi which all contain specialized enzymes (cellulases), bacteria, or protozoans to help
167
Q

Where is cellulose found?

A
  • Cellulose is not only found in plants but in marine invertebrates and human connective tissue
    1. Xylans
  • contain a β(1-4) linkage
  • Xylans have branched substituents called glucomannans
  • These types of polysacchas are called hemicelluloses
    2. Chitin
  • Homopolymer of N-acetyl-β-D-glucosamine
  • has the structure of cellulose, but hydroxyl on C2 of each residue replaced with a acetylated amino group
  • major structural component of the exoskeleton of many arthropods and mollusks
  • comparable to collagen in providing a matrix for mineralization
168
Q

Why isn’t chitin found on annelid species?

A
  • major structural component of the exoskeleton of many arthropods and mollusks, but not of this closely related species
  • this is due to annelid such as earth worms use collagen (a protein), but in a SEGMENTED exoskeleton
  • the ancestors of these invertebrates developed a mineral skeleton on a collagen matrix
169
Q

Glycosaminoglycans

A
  • serve structural and non structural purposes in vertebrate animals
170
Q

Heparin

A
  • is an anticoagulant that binds to antiprothrombin 2 and inhibits blood clotting
171
Q

Hyaluronic acid

A
  • abundant in synovial fluid and vitreous humor of the eye
  • used as a biological lubricant
  • helps prevent wrinkles
  • heteropoysaccharide
172
Q

Peptidoglycans

A
  • the gram-positive cell wall has a cross-linked, multilayered polysaccharide-peptide complex called peptidoglycan at the surface
  • The long polysacch. chains which consist of alternating (NAM) and (NAG) are crosslinked through short peptide
  • The reaction that generates the crosslinking in the peptidoglycan cell wall of bacteria is a key target for antibiotics
173
Q

Penicillin

A
  • inhibition of the cross linking region in peptidoglycan synthesis by penicillin
  • Penicillin resembles the 2 D-Ala residues linked to chain I
  • Penicillin contains a thermodynamically unstable lactam ring, which ruptures and causes it to link to chain I and inhibit peptidoglycan crosslinking
  • causes bacterial cell lysis due to turgor pressure
174
Q

Glycosylation

A
  • the attachment of saccharides to other biomolecules can occur in proteins or lipids
  • For this reason glycolipids or glycoproteins are commonly referred to as glycoconjugates
175
Q

Glycans can be linked to proteins in 2 ways

A
  1. N-linked glycosylation occurs via an Asn (asparagine amide groups)
  2. O-linked glycosylation occurs via a Thr or Ser residues in proteins (and sometimes Tyr)
    - threonine or serine hydroxyls
176
Q

O-linked glycoproteins

A
  • The blood group antigens are attached as O-linked glycans to membrane proteins or lipids
  • O-linked glycans are important in mollecular and cellular identification.
  • Rh factor determine +/- blood type
  • Type O blood=universal
177
Q

The Glycocalyx

A
  • is made up of carbohydrate groups attached to the glycoprotein, proteoglycan, and glycolipid components on the external surface of eukaryotic cells.
178
Q

Erythropoetin

A
  • A glycoprotein with both O- and N-linked oligosaccharides
  • a hormone synthesized within the kidney, stimulates production of red blood cells
  • EPO administered during cancer chemotherapy to counteract anemia
  • Recombinant EPO misused by some athletes to improve performance; presumably nonglycosylated
179
Q

Influenza virus

A
  • an RNA virus, carries on its surface a virus coded enzyme, neuraminidase
  • a target for antiviral drugs
  • neuraminidase is the enxyme that cleaves the sialic acid from the rest of oligosaccharide chain
  • Tamiflu inhibits neuramindase and blocks the release if newly formed virus particles from the cells
180
Q

Influenza Hemmagglutinin

A
  • is a spike on a virus made up of proteins
  • binds to sialic acid
  • attaches to host cells throught binding of hemmagglutinin to sialic residues on surface glycoproteins and lipids
181
Q

Glycome

A
  • describes the total set of sugars and glycans that a cell or organism produces
182
Q

Glycomics

A
  • the field of study that has been facilitated by the characterization of enzymes that digest specific links in polysaccharides
  • Of all the types of post-translational modifications, glycosylation is the most important in terms of coding capacity
  • Carbs have structural properties that provide them with significant coding capacity
  • Giving them the ability to transfer information
183
Q

Lectins

A
  • are carbohydrate binding proteins that possess recognition domains that bind to specific carb groups
  • Thus lectins deciper ”the sugar code” encapsulated by glycoproteins
184
Q

glycolytic pathway

A
  • breakdown of sugars to generate ATP
185
Q

gluconeogenesis pathway

A
  • the synthesis of polysaccharides such as glycogen
186
Q

pentose phosphate pathway

A
  • nucleotide synthesis
187
Q

Activated monomer for glycogen in synthesis

A
  • UDP-glucose is an activated form of glucose for glycogen synthesis (synthesized from blood glucose)
    1. Glucose is phosphorylated by hexokinase into glucose-6-phosphate
    2. that is isomerized to glucose-1-phosphate by phosphoglucomutase
    3. UDP-glucose pyrophosphorylase then catalyzes the synthesis of UDP-glucose
    4. UDP-glucose is the activated metabolically activated form of glucose for glycogen synthesis
188
Q

new monomers into a glycogen polymer

A
  • Glycogen synthase continually adds glucose residues to the 4-OH groups at the nonreducing ends of the glycogen polymer
  • After glycogenin transfers glucose from UDP-glu to a tyrosine residue on a protein it then transfers additional glycosyl units form UDP-glu to give alpha(1→ 4) linked primers up to 8 residues long
  • these primers are extended by glycogen synthase and glycogenin forms the core of the mature glycogen molecule
189
Q

2 major enzymes in glycogen synthesis

A
  1. Glycogen synthase

2. branching enzyme

190
Q

Glycogen synthase reaction

A
  1. Glycogen synthase is bound to starch granules in cells
  2. It is a glycosyltransferase that transfers an activated sugar to the sugar hydroxyl on a nonreducing end(NRE)
  3. Transfers Glc from UDP-Glc to NRE of a glycogen branch
  4. The branch has to be at least 4-residues in length
  5. The primer for glycogen synthase is a short chain of glucose residues assembled by a protein called glycogenin which transfers glucose from UDP-Glc to a Tyr residue within itself
  6. Glycogenin primers are extended by glycogen synthase
191
Q

Branching Enzyme Function

A
  • Glycogen synthesis requires polymerization of glucose units and branching via α(1-6) linkages
  • Branching is necessary to increase the solubility of the polymer and increase the number of NRE’s that can be utilized for glycogen mobilization
  • Glycogen synthase cannot carryout branching
  • Branching enzyme aka amylo-(1,4 -> 1,6)-transglycosylase has to carry out the branching reactions
  • It transfers a terminal fragment from a branch terminus to an OH group that is positioned on the interior of the glucose polymer → carbon 6 attacks carbon 1 in exampl
192
Q

Where does glycogen breakdown begin?

A
  • In animals, the digestion of starch and glycogen begins in the mouth
  • A-amylase in saliva cleaves a(1-4) linkages from the non-reducing ends, but cannot cleave the a (1-6) linkage at a branch point
  • For digestion to continue, a (1-6) - glucosidase (a debranching enzyme) is required to remove the limit dextrin, exposing additional a(1-4) linked saccharides
193
Q

Whee is glycogen stored and what enzyme breaks down the main polymer?

A
  • The principal glycogen stores in animals are the muscle and liver
  • glycogen is the major energy source for the contraction of skeletal muscle
  • Glycogen phosphorylase cleaves the alpha 1→ 4 bonds by phosphorolytic cleavages which yields glucose-1-phosphate
  • Importance of using the debranching enzyme scheme is due to animals need to generate energy very quickly following appropriate stimuli
  • Glycogen phosphorylase cleaves nonreducing ends of glycogen bc the more of these ends that exist in a polymer the faster the polymer can be mobilized
194
Q

2 major enzymes involved in glycogen debranching

A
  • Glycogen debranching enzyme = bifunctional glucantransferase catalyzes two reactions
    1. Transferase activity transfers three of the remaining four glucose residues from the limit branch to another nonreducing end via a new α(1-4) linkage
    2. α(1-6)-glucosidase activity removes the remaining glucose molecule
195
Q

Regulation of glycogen metabolism

A
  1. Hormone binds a cell surface receptor, releasing a G-protein which activates adenylate cyclase
  2. Adenylate cyclase synthesizes cAMP, which binds the regulatory subunit of PKA, releasing the active C subunit of PKA
  3. Active PKA phosphorylates phosphorylase B kinase, activating it
    4 .Active kinase converts inactive phosphorylase B to the active phosphorylase A
  4. Active phosphorylase A catalyzes glycogen breakdown
  • activates Protein kinase A by cAMP
196
Q

Glycogen storage Diseases

A
  1. Von Gierke Disease
    - liver, kidney and intestine
    - enzyme deficiency of glucose-6-phosphate (ER)
197
Q

Gluconeogenesis

A
  • Biosynthesis of glucose from non-carbohydrate precursors
  • pyruvate to glucose
  • Like glycolysis in reverse, but three “irreversible” reactions must be bypassed
  • energy expensive, but physiologically necessary
  • occurs when blood sugar is low in animals
  • gluconeogenesis is compartmentalized (cytosol, mitochondria, and ER)
  • exergonic reactions
  • primary organ is the liver then kidney cortex
198
Q

Irreversible reaction in glycolysis

A
  1. Hexokinase
  2. Phosphofructokinase
  3. Pyruvate kinase
199
Q

Bypass in gluconeogenesis

A
  1. Glucose-6-phosphatase
  2. Fructose-1,6-bisphosphatase
  3. Pyruvate carboxylase and phosphoenolpyruvate carboxykinase
  • 3 enzymes in glycolysis need to be bypassed by 4 enzymes in glucogeonesis
  • all the amino acids except those that start with a letter L can be converted into glucose
200
Q

Glycolysis

A
  • Glucose to Pyruvate.
  • catabolic pathway that converts a molecule of glucose into 2 molecules of pyruvate and produces metabolic energy in the form of ATP and NADH
  • Entirely in the cytosol.
  • Regulatory rxns (HK, PFK1, PK) are irreversible
201
Q

Bypass 1

A
  • Pyruvate carboxylase(mitochondria) and phosphoenolpyruvate carboxykinase(cytosol, PEPCK)
  • Uses biotin in the reaction
  • any precursors to pyruvate (lactate in the cori cycle) will have to go through these steps
202
Q

Bypass 2

A
  • Fructose-1,6-bisphosphatase
  • Enzyme: phosphofructokinase
  • Simple hydrolysis reaction
203
Q

Bypass 3

A
  • Glucose-6-phosphatase
  • enzyme: Glucose-6-phosphatase
  • Simple hydrolysis reaction
204
Q

Energy Costs of gluconeogenesis and reversal of glycolysis

A
  1. -42.7kJ/mol

2. +79.9 kJ/mol

205
Q

Cori Cycle

A
  • Some of the lactate produced in muscles enters the liver and is reoxidized to pyruvate by liver LDH
  • This pyruvate can then undergo gluconeogenesis to give glucose, which is returned to the bloodstream and taken up by muscle to regenerate the glycogen stores
  • called Cori cycle.
206
Q

glucose-alanine cycle

A
  • Pyruvate in peripheral tissues undergoes transamination to alanine, which is returned to the liver and is used for gluconeogenesis
  • key reaction*
  • Mechanism of alanine transaminase
  • Convert L-glutamate and pyruvate into a-ketoglutamate and L-alanine
  • The resulting L-alanine is shuttled to the liver where the nitrogen enters the urea cycle and the pyruvate is used to make glucose
207
Q

allosteric vs. hormonal control or regulation of Gluconeogenesis

A
  1. Allosteric control- activation or inhibition of enzymes
  2. Hormonal control
    - Two main hormones are insulin and glucagon
    - Both work to maintain optimum blood glucose levels
    - Both modulate glycogen synthesis or degradation.
    - Adrenalin promotes massive release of glucose
208
Q

gluconeogenesis in plants vs in animals

A
  • Involved in the conversion of stored fats into sugars (we cannot convert fats into sugars)
  • Sucrose (not glucose) is the final product
  • Occurs in chloroplasts during photosynthesis
  • Requires the interactions between lipid bodies, glyoxysomes, mitochondria, and cytosol
  • The two amino acids that cannot serve as precursors for gluconeogenesis are lysine and leucine

Biochemistry (15 decks)

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