Carbs and Lipid Structure Flashcards
aldoses
carb with an aldehyde group (a carbonyl group attached to an H and R group). aldose sugars have suffix “-ose” ie. glucose
ketoses
carb with a ketone group (a carbonyl group bonded to two other carbon atoms). ketoses have the suffix “-ulose” (fructose is an exception since it is actually a ketose)
example of a pentose (5 carbon) sugar
ribose
Stereoisomers
Have the same chemical formula (ie C6H12O6) but differ in position of the hydroxyl group on one or more of their asymmetric carbons. (different in every other perspective ie different chemical characteristics and recognized by different enzymes). (ie fructose, glucose, mannose and galactose are stereoisomers)
Epimers
stereoisomers that differ in the position of the hydroxyl group at only one specific C (ie glucose and galactose are C-4 epimers)
What is a significance in epimers?
C4-epimerase is able to change glucose into galactose and back forth. if you have a person with a genetic disorder that does not permit this person to ingest galactose, you don’t have to worry about galactose deficiency, because this person has that enzyme.
Which sugars are C4 epimers?
Glucose and galactose
Which sugars are C2 epimers?
glucose and mannose
enantiomers
mirror images of each other. most sugars in human tissues are in D form.
anomeric carbon
is term C1, which is counting down for the non-ring carbon. this is where cyclic sugars mutarotate.
glycation
the addition of a single glucose (linear form) to protein via a non-enzymatic reaction in a non-specific manner, which mainly occurs in plasma and interstitial fluids. (clinical note: in chronic hyperglycemia seen in poorly controlled diabietes results in increased levels of glycation on vascular tissues.)
Glycosylation
defined as the addition of a polysaccharide or an oligosaccharide (2-10 component sugars), to proteins, lipids, or other organic molecules in an enzymatic related manner. (ie glycolipids and glycoproteins. Glycosylation is a form of co-translational and post-translational modification which occurs in ER and golgi. glycosylations very important in cell-cell recognition.
glycation v. glycosylation
gycosylation:
chemical reaction: enzymatic, regulated
sugar unit: glycan (oligo or polysachharides)
location of reaction: ER & Golgi (part of co/post-translational modification.)
Impact on molecule: resulting in functionality.
glacation: non-specific & non-enzymatic, SINGLE LINEAR GLUCOSE, various places where glucose is present, typically reduces the physiological fn
oxidation is a loss or gain of elections?
“OIL RIG” oxidation is loss of electrons, reduction is gain of electrons. oxidation is gain O2 and loss H2, and reduction is loss O2 and gain H2
oxidize forms of glucose
D-gluconate (anomeric carbon is oxidized)
beta-D-glucoronate (C6 carbon oxidized)
what is the significance of oxidized sugars?
Glucuronic acid/glucuronate is commonly conjugated/added onto hydrophobic molecules
in the liver in order to make the molecule more hydrophilic/polar, thus more soluble and
excretable from the body. This conjugation step is called the second phase of drug
metabolism.
what are two important biological sugars?
Important biologic acidic sugars include glucuronic
acid (from glucose) and iduronic acid (from galactose). They are negatively charged in physiological pH.
reduced sugars
If the aldehyde of a sugar is reduced, all of the carbon atoms contain alcohol (hydroxyl) groups, and the sugar is a polyol (e.g. sorbitol from glucose or galactitol from galactose). If one of the hydroxyl groups is reduced so that the carbon contains only hydrogen, the sugar is a deoxysugar, such as the deoxyribose in DNA.
alcohol -> aldehyde = oxidation or reduction?
alcohol -> aldehyde -> acid = oxidation
reverse is reduction
Amino and N-acetylated amino sugars
Amino and N-Acetylated amino sugars contain an
amino group substitutes for one of the hydroxyls; an example is glucosamine. The amino group may also be acetylated; an example is N-acetylglucosamine.
• Biological Significance: these amino sugars are
essential components of glycosaminoglycans,
glycolipids and glycoproteins.
glucosaminoglycans
linear polymers of repeating disaccharides (50-150 repeats) that form ground substance of extracellular matrix. They are negatively charged at physiologic pH, and give glycosaminoglycans their strongly negative nature and water adsorption. Chondroitin sulfate is an example of glycosaminoglycan. disaccharide unit = [acidic sugar + N-acylated amino sugar]n (n=50-150 units)
glycans (and “gly” v. “glu”)
glycans: immediately think oligo or polysaccharides
gly means sugar but not glucose, glu means glucose
Disaccharides v. oligosaccharides v. polysaccharides
Disaccharides (2), oligosaccharides (3-12) and polysaccharides (>12)
glycosides
glycoside is a molecule in which a sugar is bound to another functional group via a glycosidic bond.
O-linked v. N-linked glycosidic bonds
O-linked: Mostly found in sugar-sugar or sugar-protein attachment e.g. di-, oligo- and polysaccharides, etc.
N-linked: Mostly found in nucleosides and nucleotides e.g. Adenosine triphosphate (ATP)
disaccharides
sucrose (glucose - fructose)
lactose (galactose - glucose)
maltose (glucose - glucose)
monosaccharides (& disaccharides)
glucose, fructose and galactose
maltose, sucrose and lactose
reducing sugar
concept that is related to anomeric carbon. If the –OH group on the anomeric carbon of a sugar
is not attached to any other structure, that sugar is a reducing sugar. Both lactose and maltose are reducing sugars, but sucrose is not. All monosaccharide hexoses are reducing sugars.
polysaccharides
common polysaccharides include glycogen (animal origin), starch (plant origin) and cellulose (plant origin). All of which are made of D-glucose only.
starch
glucose monomers are linked with each other in two forms: amylose (linear polymer) and amylopectin (branched polymer).
amylose
Amylose is an unbranched, single-chain polymer of 500-2000 glucose subunits with
only a-1,4-glycosidic bonds.
amylopectin
Amylopectin consists of the linear a-1,4-glucose polymers, as well as branched
a-1,6- ones. In starch, branches occur about every 25 linear residues.
cellulose
Cellulose is the most abundant carbohydrate on earth and provides structural integrity for
plants. It is also made of glucose with b(1->4) polymers of glucose. Humans cannot
digest cellulose.
glycogen
(an amylopectin only) is more densely branched (every 10-12 residues) compared to a starch amylopectin. One gram of glycogen adsorbs 3 grams of water.
physiological functions of carbohydrates
Storage: examples include starch in plants and glycogen in animals
Structure: examples include cellulose and exoskeleton of many insects
Cell recognition: examples include glycocalyx/cell coat, glycoprotiens and glycolipids.
non-membrane lipids
fatty acids, triacylglycerols, steroids and cholesterol
nomenclature of fatty acids
This naming system consists of the number of carbon atoms followed (after a colon) by the
number of double bonds and the position of the double bond(s). The carboxyl carbon is
number 1. For example, oleic acid has 18 carbons and one double bond, which is located
between positions 9 and 10. Oleic acid is denoted as 18:1(delta)9 or 18:1(9) without the .
Omega numbering system of fatty acids
The omega (w) numbering system: fatty acids are also classified by the distance of the double bond closest to the (omega) end (the methyl group end). For example, oleic acid is an omega-9 fatty acid, linolenic acid is an omega-3 fatty acid, and arachidonic acid is an omega-6 fatty acid
dietary essential fatty acids
gamma-linoleic (omega-6) and alpha-linolenic acids (omega-3). We must ingest them because humans can’t synthesize double bonds on fatty acids past
C9 position.
gamma-linoleic omega-6 fatty acids
Linoleic (omega-6) is a precursor for
arachidonic acid (C20:4), which is a
major precursor for eicosanoids
synthesis.
alpha-linolenic omega-3 fatty acids
Linolenic acid (omega-3) is a precursor of other omega-3 fatty acids that are important for growth and development.
arachidonic acid
arachidonic acid (C20:4) is a major precursor for eicosanoids (linoleic [omega-6] fatty acid [a dietary essential fatty acid] is the precursor to arachidonic acid)
branched fatty acids
example: pytanic acid, contains methyl group on the third carbon (b). Due to the methyl group,
it has to go through alpha-oxidation by a-
hydroxylase.
Refsum disease
Refsum disease is caused
by a deficiency in alpha-hydroxylase. This
results in the accumulation of phytanic acid
in the plasma and tissues, causing neuronal damage. (a toe looks like its been moved up)
trans fatty acids
Trans fatty acids are formed during the
partial hydrogenation of vegetable oils used in
margarine, Crisco, peanut butter, etc.
-Trans fatty acids are structurally similar to
saturated fatty acids, i.e. they are straight
even though they have a double bond.
-Epidemiological studies (e.g., Nurse’s Health
Study) show a correlation between trans
fatty acids and heart diseases.
Triacylglycerols
Triacylglycerols (TAGs), the storage form of fatty acids, are formed by attaching three
fatty acids (as fatty acyl CoA, activated form of fatty acids) to a glycerol backbone. They
are hydrophobic and non-polar.
steroids and cholesterol esters
Steroids and Cholesterol esters:
-Steroids (animal and plant origins) have a tetracyclic ring structure. Animal steroids are
derived from cholesterol.
-When the polar group of cholesterol is esterified to a fatty acid, it is referred to as a
cholesterol ester. Cholesterol ester is a nonpolar molecule.
cholesterol esters
-When the polar group of cholesterol is esterified to a fatty acid, it is referred to as a
cholesterol ester. Cholesterol ester is an extremely nonpolar molecule. This is a storage form of cholesterol.
