biochem exam 3 Flashcards
aldoses
ketoses
trioses
pentoses
hexoses
aldoses: aldehyde, sugar
ketoses: ketone, sugar
trioses: 3 carbon sugar
pentoses: 5 carbon sugar
hexoses: 6 carbon sugar
Where the chiral centers are in
aldoses
ketoses
trioses
pentoses
hexoses
aldoses
ketoses
trioses
pentoses
hexoses
need help
Number of possible stereoisomers as a function of number of chiral centers
2^n
if 4 chiral
2^4 = 16 stereoisomers
“D” and “L” are defined in reference to glyceraldehyde
D: OH on right
L: OH on left
In nature, almost all monosaccharides are “D” isomers (though there are some “L” sugars). Know what this means.
means that the OH furthest from the carbonyl is to the right
epimers
epimeric pairs
enantiomers
diastereomers
epimer: only 1 chiral center is different
epimeric pair: molecules with only 1 chiral carbon that is different
enantiomer: all chiral centers are different
diastereomer: all but 1chiral center is different
The standard abbreviations for:
fructose
galactose
glucose
mannose
ribose
fructose (Fru)
galactose (Gal)
glucose (Glc)
mannose (Man)
ribose (Rib)
D-Aldoses that you have to know
do you know the structures yet?
what are the number of carbons and which are ketoses and which are aldoses
D-ribose
D-glyceraldehyde
Dihydroxyacetone
D-fructose
D-glucose
D-Galactose
D-Mannose
D- Aldoses:
D-glyceraldehyde - 3
D-ribose - 5
D-glucose - 6
D-Mannose - 6
D-Galactose - 6
D-ketoses:
Dihydroxyacetone - 3
D-fructose - 6
YES, I KNOW THEM. GOD IS GOOD
NO, I DON’T AND GOD IS STILL GOOD
- there are only two D-ketoses and fructose is 6 and Dihydroxyacetone is 3, the rest of the molecules are D-aldoses*
- do linear sugars spontaneously cyclize in solution if so, what molecules can they form
how are the two molecules formed?
can anything else be done to the molecules so that they turn to another molecule
cyclized sugars with hemiacetals or hemiketals form from linear sugars
hemiacetal:
aldehyde + OH = hemiacetal
hemiacteal + OH = acetal
hemiketal:
ketone + OH = hemiketal
hemiketal + OH = ketal
- What pyranoses and furanoses are
pyranose: 6-membered oxygen-containing ring
furanose: 5-membered oxygen-containing ring
- What anomers (anomeric pairs) are (α and β), and what mutarotation is (did he talk about this?- he actually skipped it…)
anomer: The carbonyl carbon becomes a new chiral center called the anomeric carbon. Which is where we determine if there is a hemiacetal or not :)
forms if the OH attacks from the top or the bottom
- What Haworth perspectives are
the ring form of the sugar where the OH is either up (beta) or down (alpha)
- There are many derivatives of hexose. Remember N-acetyl-β-D-glucosamine, but don’t memorize structures.
N-acetyl-β-D-glucosamine has
- acetyl group
- OH & CH2OH up
- is a glucose
- amine group
it is the subunit of chitin!
- Most monosaccharides are reducing sugars, what does this mean
what makes a disaccharide a reducing sugar
what disaccharides are reducing sugars and which are not
reducing sugars: carbonyl group can be oxidized
When a disaccharide is formed, if the anomeric carbon of at least one of the monomers remains ‘free,’ and has a hemiacetal the disaccharide is a reducing sugar; but if both anomeric carbons are part of the O-glycosidic bond, the disaccharide is not a reducing sugar.
Maltose and lactose are reducing sugars, while sucrose and trehalose are not.
how are blood glucose levels measured
how can average blood glucose over time be measured
Blood glucose levels are measured using glucose oxidase (more specific than Fehling’s Reaction).
Average blood glucose level over a period of time (2-3 months) can be measured by measuring the concentration of glycated (glycolsylated) hemoglobin (GHB; a.k.a. hemoglobin A1c).
The shorthand for indicating the structures of disaccharides, such as lactose and sucrose
lactose = Gal(β1→4)Glc (a reducing sugar) or sucrose = Fru(β2↔1α)Glc (non-reducing)
- The disaccharides in Maltose & Trehalose
Sucrose
Lactose
Maltose & Trehalose (Glc, Glc), Sucrose (Fru, Glc), and Lactose (Gal, Glc)
which of the following is an aldopentose
D- glyceraldehyde
D-ribose
D-glucose
Dihydroxyacetone
D-fructose
D-ribose
Sugars form Rings: The Cyclization of Sugar
An aldehyde and an alcohol can react to form a _____.
If another alcohol is available, the reaction can happen again to form an _____.
This same theme can happen with _____.
This is important because ______ have ____ groups (aldoses), or _____ groups (ketoses), and alcohols!
These groups can react with themselves, in the same molecule, and _____!
An aldehyde and an alcohol can react to form a hemiacetal.
If another alcohol is available, the reaction can happen again to form an acetal.
This is important because monosaccharides have aldehyde groups (aldoses), or ketone groups (ketoses), and alcohols!
These groups can react with themselves, in the same molecule, and cyclize!
Cyclization takes place as a result of interaction between the functional groups of distant _____
Between ____ and ____ to form a cyclic hemiacetal in aldohexoses
Between ____ and _____ To form a cyclic hemiketal in ketohexoses
what is the structure of a hemiacetal
what is the structure of an acetal
Cyclization takes place as a result of interaction between the functional groups of distant carbons
Between C-1 and C-5To form a cyclic hemiacetal in aldohexoses
Between C-2 and C-5 To form a cyclic hemiketal in ketohexoses
hemiacetal: on carbon there is:
OR
OH
R
H
acetal:
OR
OR
R
H
For D-sugars: CH2OH is ___
alpha OH is ___
beta OH is ___
For L-sugars: CH2OH is ___
alpha OH is ___
beta OH is ___
For all:
alpha OH is ___ CH2OH
beta OH is ____ CH2OH
For D-sugars: CH2OH is up
alpha OH is down
beta OH is up
For L-sugars: CH2OH is down
alpha OH is up
beta OH is down
alpha OH is opposite CH2OH
beta OH is same side CH2OH
what is the hexose derivative that you are supposed to know
what is it used for
N-acetyl-β-D-glucosamine
(bacterial cell walls, and other things)
Many sugars (including glucose) are _____!
The carbonyl (aldehyde or ketone) can be ____
For example, the linear form of D-glucose can participate in ____ reactions.
An example of this is an older way of testing blood glucose. _____ Reaction
any sugar with a hemiacetal can ‘open up’ to form a _____
Many sugars (including glucose) are reducing agents!
The carbonyl (aldehyde or ketone) can be oxidized
For example, the linear form of D-glucose can participate in REDOX reactions.
any sugar with a hemiacetal can ‘open up’ to form a reducing sugar
as it is reducing, it is itself being oxidized
what happens to a reducing agent as it reduces another compound
what must a reducing sugar have an oxidizable aldehyde group. Ketoses are reducing sugar because they can be converted to aldoses
a reducing agent is oxidized as it reduces another compound
a reducing sugar must have an oxidizabe aldehyde group. Ketoses are reducing sugar because they can be converted to aldoses
A hemiacetal, when opened up, forms an ____, which can be ____
If hemiacetal: “____ _____”
If not, not ____
is it reducing?
A hemiacetal, when opened up, forms an aldehyde, which can be oxidized because it is a carbonyl!
If hemiacetal: “reducing end”
If not, not reducing
is it reducing? Look for hemiacetal
Measuring [Blood glucose]- old fashion way
what do you need to monitor for diabetes
what is the rxn that is involved
what does the brown color mean
diabetes need to monitor the concebtration of glucose in their blood, in order to adjust theur insulin dosage
the rxn used is
D-glucose + O2 + glucose oxidase (which oxidizes glucose) forms D-glucono-delta-lactone + H2O2
this turns blood “brown” and we meausre the color change
the more brown, the more glucose in blood
what is another way to measure glucose
what does hemoglobin react with and what does it form
what is this molecule also called
what does this molecule tell you about the person
measure A1C
Glucose reacts with Hemoglobin to form “glycated hemoglobin (GHB)”
GHB is A1C
gives broader picture of your “glucose habits” because
[GHB] is proportional to average G1C over the preceding 2-3 months
monosaccharides to disaccharides
how can monosaccharides form disaccharides
through what bond can two sugar molecules be joined and between what type of carbons
what atoms form the O-glycosidic bond:
is maltose a reducing sugar, why or why not
Monosaccharides can form di- and poly-saccharides through glycosidic bonds!
Two sugar molecules can be joined via a glycosidic bond between an anomeric carbon and a hydroxyl carbon
O-glycosidic bond:
between the anomeric (hemiacetal) carbon of one sugar and an -OH group of another sugar
maltose is a reducing sugar because it has an available hemiacetal
Disaccharides: Glycosidic Bonds
what is numbered
what do the numbers refer to
what is possible between the same monosaccharides
what are enzyme specific for
what type of bond can humans not digest and what polysaccharide is it in
for all Disaccharides,
α: OH ____. CH2OH
β: OH ____ CH2OH
These glycosidic bonds are numbered
The numbers (ex: 14) refer to the carbons involved in the bond. 1 is the anomeric carbon. 5/6 is the CH2OH carbon.
Multiple linkages are possible between the same monosaccharides.
Enzymes are specific for these linkages.
Humans cannot digest most β-glycosidic bonds which is in cellulose and lactose
For all:
α: OH opp. CH2OH
β: OH same side CH2OH
what you need to know about disaccharides
maltose
lactose
surcose
trehalose
what monosaccharides make it up and which are reducing and which are non-reducing
what do you have to be reducing and non-reducing
maltose: Glc (a 1 - 4) Glc - reducing
lactose: Gal (b 1 - 4) Glc - reducing
sucrose: Fru (b 2 - 1a) Glc or Glc (a 1 - 2b) Fru - non-reducing
trehalose: Glc ( a 1 - 1a)Glc - non-reducing
reducing has a hemiacetal (OR, OH, R, H) and non-reducing has an acetal (OR, OR, R, H)
Polysaccharides!
what does poly mean
what does saccharide mean
what are 3 major functions
what kind of molecules are storage and what are they stored for
what kind of molecules are structural
cell surface polysaccharides are what kind of molecule
what is the nomenclature
what are they also known as
“Poly” (many) “saccharide” (sugar)
Polysaccharides are carbohydrates made up of many sugars bound together
Major Functions: Storage, Structure, Recognition (cell-cell recognition)
Starch and Glycogen are storage (energy) molecules
Chitin and Cellulose are structural molecules
Cell surface polysaccharides are recognition molecules
Nomenclature:
Homopolysaccharide vs. Heteropolysaccharide
These are also known as “glycans”
Polysaccharides!
In nature, most carbohydrates exist as polysaccharides
Homo/Hetero
Linear/Branched
Glucose is usually tied up in a large polysaccharide
Homoepolysaccharide
unbranched: same monomers made into a polymer but not branched
branched: same monomers made into a polymer but branched
heteropolysaccharides
two monomer types. unbranched
- made of two different monomers into an unbranched polymer
multiple monomer types, branched
- - made of two different monomers into a branched polymer
Polysaccharides
why store carbohydrates as polysaccharides rather than as monosaccharides
Osmolarity
1 - storing glucose in glycogen = lower [free glucose]
2 - glycogen is largely insoluble and therefore does not contribute to osmotic pressure
3 - without glycogen, glc conc. would be ~0.4M leading to cell explosion because water would rush into cells (?)
Polysaccharides
why store carbohydrates as polysaccharides rather than as monosaccharides
concentration gradient and thermodynamics
[Glc] inside the cell is less than outside.
Glc tends to move into the cell.
If Glc was free…
[Glc] inside the cell is greater than outside.
Glc cannot move into the cell.
Storage Homopolysaccharides - Starch
Starch (in plants) is composed of two polysaccharides, what are they
amylose & amylopectin
Amylose: unbranched glucose polymer (α1 - 4 linkage)
Amylopectin (also glucose): linear parts (α1 - 4 linkage)
- Branches out every 24-30 residues (glucose) using α1 - 6 linkages
Starch granules are thought to be clusters of amylose and amylopectin
Double helical structures can form
Non-reducing end glucose sugars are removed sequentially.
amylose and amylopectin both have glucose monomers
Storage Homopolysaccharides – Glycogen
which organism is it the main storage for
why is it more compact
Main storage polysaccharide in animals
Greatest abundance in liver and muscle cells
Similar in structure to amylopectin, but with more branch points
Unbranched glucose polymer (α1 - 4 linkage)
Branches out every 8-12 residues (glucose) using α1 - 6 linkages - glycogen has more frequent branching than amylopectin which branches every 24-30 glucose
It is more compact. Why? - less surface area and also more space to chop off glucose
Why Branching?
to use polysaccharides as sources of energy, degradative enzymes must degrade polymers into monomers
these degradative enzymes act only on non-reducing ends (has acetal)
each branch ends with a non-reducing sugar
branching makes possible more rapid degradation
Structural Homopolysaccharides - Cellulose
Cellulose is the primary structural component of plant cells
Most abundant polysaccharide in nature
Unbranched: 10,000-15,000 glucose monomers
β-(1-4)-linked glucose (previous polymers were α glucoses); water-insoluble, tough
Starch was a tightly coiled helix, cellulose is a straight chain
Wood (50% cellulose), Paper (90%), Cotton (90%)
How is Cellulose so Strong?
what does the bond allow for
there are hydrogen bonds:
- between the sheets to strengthen the structure
- intrachain hydrogen bonds
- interchain hydrogen bonds
(also seen in the base pairing of DNA/RNA)
β-(1-4)-linked glucose allow for the formation of hydrogen bonds
most animals cannot use cellulose as a fuel source because they lack the enzyme to hydrolyze β-(1-4)-linkages
Most animals do have the α-amylase enzyme to digest amylose (starch)
so basically because it has the β-(1-4)-linked glucose which allows for hydrogen bonds
Structural Homopolysaccharides - Chitin
is it branched
what is the monomer
is it abundant
what is it the main part of
where is it also found
straight-chain (unbranched), like cellulose
monomer is N-acetylglycosamine
the second-most abundant polysaccharide
the main part of exoskeletons in lobsters and insects
chitin is also a component of the cell walls of some fungi to inhibit the synthesis of chitin
Structural Heteropolysaccharides - Peptidoglycan
where are they found and are the flexible or rigid
what is the pattern of their subunits
what are its subunits and how are they arranged
what drug blocks its synthesis
Peptidoglycans: rigid component of bacterial cell walls
Alternating monosaccharides (repeating disaccharides)
Peptide-cross-linked linear polysaccharides
Penicillin and related antibiotics block synthesis
Structural Heteropolysaccharides – Glycosaminoglycans (GAGs)
what is the pattern of its subunits
are there cross links
what is it a component of
are they polar, what do they do
what are examples
Repeating disaccharides (…ABABAB…) with an amino side-group
No cross-links
Components of the gel-like extracellular matrix (ground substance – connective)
Highly polar molecules attract water lubricant/shock absorbers
Examples: hyaluronan, chondroitin sulfate, keratan sulfate, heparin
Structural Heteropolysaccharides – Glycosaminoglycans (GAGs) examples
hyaluronan
chondroitin sulfate
keratan sulfate
heparin
Glycoconjugates
what are they
what are they made of
what are the 3 types
Information carriers,
“anchors” embedded in the cell membrane, plus oligo- or polysaccharides (floating outside of the cell membrane – into the ECM)
proteoglycans = proteinn + glycosamineglycans
glycoproteins. = protein + carbohydrate
glycospingolipids = membrane lipid + oligosaccharide and lipopolysaccharides
Glycoconjugates - Proteoglycans
what are they composed of
where is it found
what is the main site of biological activity
what is its function
Core protein + glycosaminoglycans
Found on the cell surface or in extracellular matrix
1 or more glycosaminoglycan chain(s) covalently bound to a core protein
The glycosaminoglycan is often the main site of biological activity
Proteoglycan Aggregates
ECM component
Absorbs/release large amounts of water (polarity)
Functions as “shock absorber”
Glycoconjugates - Glycoproteins
how are they linked
what are they composed of
where can you find this
what are examples
what is the O and N linkage
Glycoproteins: proteins covalently linked to carbohydrates through N- or O-linkages
Protein + 1 or more oligosaccharide(s)
Carb components are smaller/more structurally diverse than in proteoglycans
Cell surface/ECM
Hormones, Immunoglobulins (IGs)
O-Linkage:
Between hydroxyl groups of serine or threonine and N-acetylgalactosamine
N-Linkage:
Between asparagine and N-acetylglucosamine
Glycoconjugates - Glycolipids and Lipopolysaccharides
what is another name for this
what are the composed of
where does this happen
what are they binding sites for
LPS
where are they most dominant
is it a toxin and if so what kind
what are they targets for
Glyco(sphingo)lipids:
Oligosaccharides covalently bound to lipids via a glycosidic linkage
On the outer surface of plasma membranes
Often binding sites for proteins (antigens, blood group determinants)
Lipopolysaccharides:
Dominant surface feature of gram-negative bacteria (E. coli, Salmonella enterica)
Endotoxin (released when bacteria dies inflammatory/immune response)
Prime targets of antibiotics
what are the main groups of glycoconjugates?
(1) proteoglycans
(2) glycoproteins
(3a) glycolipids
(3b) lipopolysaccharides.
Some lectins
what is the function of each and where does it attach onto
human selectin: mediate inflammatory response
viral lectins (esp. influenza): attach onto oligosacahrides on human cell membrane
H. pylori lectin: attach onto the oligosaccharides of gastric cells
cholera & pertussis toxins: attach to host cell oligosaccahrides
- it may be possible to prevent disease by blocking the lectin
human selectins
Human selectins mediate the inflammatory response (RA, asthma, psoriasis, MS, transplant rejection) – and are therefore potential drug targets
Lectins
what are they
where are they found?
what do they serve
what do human selectins do
what are P-lectins on
Proteins that specifically and strongly bind carbohydrates (usually attached)
Found in all organisms.
these proteins in viruses and bateria attach onto the oligosaccharides/other carbohydrates of other proteins and can use NA to chop off and release viral contents from the cell
Serve a wide variety of cell-cell recognition, signaling, and adhesion processes (CAMs)
Human selectins mediate the inflammatory response (RA, asthma, psoriasis, MS, transplant rejection) – and are therefore potential drug targets
P-selectins on endothelial cells and oligosaccharides on leukocytes
Lectins and Viral Infections
what is the cell membrane covered with
what do some proteins have
what is influenza and what is it called
what does it bind
what is going on in simple terms
what does neuraminidase do
what drugs is used for the flu
what do neuraminidase inhibtors do
The cell membrane is covered in glycoproteins.
Some proteins are “decorated” with a carbohydrate called neuraminic acid (sialic acid). Neu5Ac is typical.
Influenza has a receptor-binding membrane fusion glycoprotein (lectin) called Hemagglutinin (HA)
it binds to sialic acid-attached glycoproteins
( so the flu virus has a glycoprotein or lectin called Hemagglutinin or HA that can bind onto the carbohydrate neuraminic acid or sialic acid)
AND a neuraminidase (NA) which clips sialic acid off of the glycoprotein
neuraminidase inhibitors - Oseltamivir (Tamiflu) - competitive inhibitor, so this drug binds onto the enzyme instead of the substrate
Neuraminidase inhibitors are drugs that block the function of the viral neuraminidase protein. By blocking this protein enzyme it stops the release of viruses from the infected host cell and prevents new host cells from being infected.
Lectins and Human Health
H.pylori
-where does it attach onto
what can block adhesion
cholera and pertussis
- where does it bind
- what can prevent disease
what diseases is it linked to
what are some Pharmacological tools
H.pylori attaches to gastric cells surface oligosacchariddes
- analogs of those oligos may block adhesion
cholera toxin and pertussis toxin are lectins that attach to host cell oligosaccharides
- it may be possible to prevent disease by blocking the lectin
Linked to all kinds of cancer, ulcers, inflammation, etc.
Pharmacological tools: PTx blocks Gi so can’t turn off AC (cAMP)
CTx leaves AC on (cAMP)
Sodium and water out diarrhea (death?)
Starch: Amylose
function
type of polysaccharide
core subunit/monomer
linkage
is it branched/unbranched/crosslinked
Storage
Homopolysaccharide
Glc
α1→4
unbranched
Starch: Amylopectin
function
type of polysaccharide
core subunit/monomer
linkage
is it branched/unbranched/crosslinked
Storage
Homopolysaccharide
Glc
α1→4 unbranched
branched (α1→6)
Glycogen
function
type of polysaccharide
core subunit/monomer
linkage
is it branched/unbranched/crosslinked
Storage
Homopolysaccharide
Glc
α1→4
branched (α1→6)
Cellulose
function
type of polysaccharide
core subunit/monomer
linkage
is it branched/unbranched/crosslinked
Structural
Homopolysaccharide
Glc
β1→4
unbranched
Chitin
function
type of polysaccharide
core subunit/monomer
linkage
is it branched/unbranched/crosslinked
Structural
Homopolysaccharide
GlcNAc
β1→4
unbranched
Peptidoglycans
function
type of polysaccharide
core subunit/monomer
linkage
is it branched/unbranched/crosslinked
Structural
Heteropolysaccharide
Repeating disaccharide
peptide cross-links
Glycosaminoglycan
function
type of polysaccharide
core subunit/monomer
linkage
is it branched/unbranched/crosslinked
Structural
Heteropolysaccharide
Repeating disaccharide
Proteoglycans
Composition
Location (example)
Protein + 1 or more glycosaminoglycan(s)
Cell surface
Glycoproteins
Composition
Location (example)
Protein + oligosacch. (smaller, more diverse)
Cell surface (e.g., glycophorin)
Glycolipids
Composition
Location (example)
Lipid + oligosacch.
Outer memb. surf. (e.g., blood group determinants)
Lipopolysaccharides
Composition
Location (example)
Lipid + oligosacch.
Outer memb. surf. of gram-neg. bact. (target of antibodies)
Human selectins (on human cell surfaces)
Bind to oligos on:
Function or examples
(Potential) drug action
Other human cells
Inflammatory response
May block interaction, response
Bacterial lectins (on cell surfaces)
Bind to oligos on:
Function or examples
(Potential) drug action
Human cell surfaces
H. pylori
Oligo analogs to block adhesion
