Flashcards in chapter 11 Deck (104):
what are carbohydrates?
aldehyde or ketone compounds with multiple hydroxyl groups
what are the 4 roles of carbs?
1. energy stores, fuels, and metabolic intermediates
2. ribose and deoxyribose sugars form part of the structural framework of RNAand dna
3. polysaccharides are structural elements of cell walls of bacteria and plants
4. linked to many proteins and lipds: help mediate interactions among cells and among other elements in the cellular environment
what are monosaccharides
the simplest carbohydrates: adehydes or ketones that have 2 or more hydroxyl groups
empiricle formula of monsacharides
C-(H2O)n (carbon hydrate)
what are the smallest monosaccharides called?
what are the 2 trioses?
hihydroxy acetone, and glyceraldehyde
how many steroismoers of dehydroxyacetone and glyceraldehyde are there?
no stereoisomer for dihydroxyacetone, 2 stereoisomers for glyceraldehyde due to 1 symmetric carbon
in fischer projections, which bonds come out of the page and which go into the page?
horizontal bonds (in front of the plane)
vertical bonds (behind the plane)
what are monosaccharides called with 4, 5, 6, 7 carbon atoms?
tetroses, pentoses, hexoses, and heptoses
what do "L" and "D" designate in monosaccharides?
designate the absolution configuration of the asymmetric carbon farthest from the adehyde or keto group (D means OH on the right of the fischer projection)
are the D form and L form of the same sugar enantiomers?
yes they are mirror images
what are diastereomers?
not mirror immages of each other
what is it called if sugars differ in configuration at only 1 asymetric carbon?
how do you number a ketose?
start at end closest to carbonyl
why do sugars for rings?
aldehyde can react with an alcohol to form a hemiacetal
ketones can react with alcohol to form hemiketals
what do you call a 5 and 6 memvbered ring?
substituents drawn to the right on a fisher projection are draw ________ on a haworth projection?
drawn down (down right rule)
for D sugars the higest number carbon is drawn _______ on a hawarth projection, how about for an L sugar?
drawn up for D
drawn down for L
how does OH group at anomeric position drawn for L and D
for D, alpha is down, and beta is up.
for L, alpha is up, and B is down
how does the prevalence of different forms of fructose change in different situations?
fructose free in solution
•! furanose form
predominates in many
what are the 2 non-planar conformations pyranose rings can adopt? which is more common for glucose?
chair and boat, chair
what non planar conformation are furanoses in?
puckered - 4 atoms nearly coplanar and 5th is .5 angstroms above the plane
what are the 2 conformations of ribose?
c2-endo (c2 is out of the plane on the same side as c5)
c3-endo (c3 is out of the plane on the same side as c5)
monosaccharides may react with alcohols and amines to form?
what is a glycosidic bonds, specifically an oglycosidic bond and an nglycosidic bond
a glycosidic bond is the bond formed between the anomeric carbon of glucose and the hydroxyl oxygen atom of an alcohol (O-glycosidic bond) or an anomeric carbon atom of a sugar and a nitrogen atom of an amine (N-glycosidic bond)
what are reducing sugars?
sugars that can react with oxidizing agensts such as cupric ion (cu2+) because the open chain form has a free aldehyde group that can be oxidized
what is significant about reducing sugars
they can react with other moleculse to from mdified monosacharides (for example they can form glycosylated hemogolobin)
where are modified monosacharides usually found?
surface of cells (ie sialic acid)
what are examples of modified monosaccharides?
why are sugars phosphorylated?
1. phosphorylation makes sugars negatively charged, negative charge prevents these sugars from spontaneously leaving the cell by crossing the hydrophobic cell membranes
2. phosphorylation creates reactive intermediates what will more readily form linkages to other molecules
what are oligosaccharides
built by the linkage of 2 or more onosaccharides by o-glycosidic bonds
what is maltose
disaccharides containing 2 d-glucose residues joined by alpha-1,4-glycosidic bond
what is sucrose/table sugar
1 glucose and 1 fructose, 1,4 linkage, alpha for glucose and beta linkage for fructose
what is lactose
it is found in milk. consists of galactose joined to glucose by beta 1,4, glycosidic linkage
what is sucrose and lactose hydrolyzed by?
sucrase and lactase
where are sugar digestive enzymes found in the small intestine?
present on microvilli that project from the outer face of the plasma membrane of intestinal epitheilial cells
what are polysaccharides called if all the monosaccharides are the same?
what is the most common homopolymer in animal cells is?
glycogen (storage form of glucose)
what is a common homopolymer in plant cells?
cellulose (structural rather than nutritional)
what is the glucose reservoir in plants called?
what are 2 types of starch
1. amylose (unbranched type of starch, glucose residues in an alpha 1, 4 linkage.
2. amylopectin (branched form, ahs 1 alpha 1,6 linkage per 30 alpha 1,4 linkages)
what effects does glucose storage as starch minimize?
what does branching in strach provide?
more compact structure
how is starch injested by human beings hydrolyzed?
both hydolyzed by alpha-amylase, secreted by salivary glands and pancreas
very large branched polymer of gluose linked by alpha 1,4 glycosidic bonds (branches are alpha 1,6 glycosidic bonds present every 10 units)
what does the highly branched structur of glycogen permit?
rapid glucose release from glycogen stores (in muscle during exercise) this function is not really needed in plants
structure of cellulose
unbranced glucose polymer with beta 1,4 linkages
how does using beta 1,4 linkages instead of alpha 1,4 linkages change the structure of cellulose compared to glcogen?
beta 1, 4 linkages allow cellulose to form very long straight chains. optimal for construction of fiber with high tensile strength
how are fibrils formed
fibrils are formed by parallel chains that interact through hydrogen bonds
what advantages does using an alpha 1,4 linkage provide?
good for forming accessible store of sugar
why is fiber in our diet important? why can't we digest it
we lack cellulase (can't digest fiber)
important because soluble fiber such as pectin slows movement of food through gastrointestinal tract allowing for better absorption of food and nutrients, insoluble fibers such as cellulose increase rate at which digestion products move through large intestine
what are re proteoglycans?
proteins attached to a particular type of polysaccharide called glycosaminoglycans
composition of glycosaminoglycans
disaccharide repeating units containing a derivative of an amino sugar, either glucosamine or galatosamine; have negatively charged carboxylate and/or sulfate groups
major glycosaminoglycans in animals. in each case, what is one of the monomers?
in each case one of the monomers is a glucosamine derivative
what is the colletion of diseases that result from inability to degrade glycosaminoglycans? results?
mucopolysaccharidoses, results in skeletal deformaties and low life expectancy
what are the roles of proteoglycans?
1. function as lubricants and structural components in connective tissue
2. mediate adhesion ofcells to the extracellular matrix
3. bind factors that stimulate cell proliferation
2 key components of cartilage?
the proteoglycan aggrecan and the protein collagen
what does the triple helix of collagen functinally provide for cartilage?
structure and tensie strength
what does aggrecan functionally provide to cartilage?
acts as a shock absorber, cant absorb water (absorbed water allows it to spring back after being deformed) for example, when your foot hits the ground, water is squeezed from aggrecan cushioning the impact, and when the pressure is released, water rebinds to aggrecan
what enzyme is needed for oligosaccharide assembly? what are they specific to?
glycosyltransferases catalyze the formation of glycosidic bond, each type must be specific to the sugars being linked
general form of reaction catalyzed by glycosyltransferase?
sugar to be added comes in the form of an activated sugar nucleotide. acceptor X can be a simple monosaccharide, complex saccharide, or a serine or a threonine residue from a protein. such reactions can proceed with either retention or inversion of configuratation at the glycosidic carbon atom at which the new bond is formed. a given enzyme proceeds by one sterochemical path or the other
how does human ABO blood groups differ?
A and B antigens have an extra monosaccharide, N-acetylgalactosamine (A) or galactose (B). O antigen is the oligosaccharide foundation.
specific glycosyltransferases add extra monosacharide to o antigen foundation
what does a person inherit that leads to a certain blood type?
each person inherits from each parent a glycosyltransferase. O phenotype results from a mutation that leads to premature termination of translation and no active glycosyltransferase
why are different blood types present in humans?
selective pressure on human beings to vary blood type to prevent parasitetic mimicry by disease causing organisms
what are glycoproteins
carbohydrate groups covalenetly attached to proteins
difference between proteoglycans vs glycoproteins
proteoglycans have much higher carbohydrate than protein, while glycoproteins have higher protein compared to carbohydrate
where are glycoproteins found?
what are functions of glyco proteins
cell adhesion and binding of sperm to eggs
how are carbohydrates linked to proteins?
through asparagine (N-linked) or through serine or threonine (o-linked)
when can an asparagine residue accept an oligosaccharide?
an asparagine residue can accept an oligosaccharide only if the residue is part of an Asn-x-ser or asn-x-thr sequence
n-linked oligosaccharides have in common?
a pentasaccharide core consiting of 3 mannose and 2 n-acetylglucosamine residues.
what contributes to the variety of oligosaccharide patterns?
additional sugars are attached to this core to form the great variety of olligosaccharide patterns
what are most proteins present in serum component of blood?
what is erythropoietin? EPO
stimulates production of red blood cells
what is erythropoietin used as a treatment for?
how does glycosylation affect EPO in blood? how does unglycosylation affect EPO?
glycosylation enhances stability of EPO in blood, unglycosylated protein is rapidly removed from the blood stream by kidneys
How much is EPO is carbohydrate?
40% by weight
structure of EPO
165 residues and is n-glycosylated at 3 asparagine residues and O-glycosylated on a serine residue
where does glycosylation take place?
in the lumen of the endoplasmic reticulum (ER) and golgi complex
what type of glycosylation does the ER do? Golgi?
ER- n-linked glycosylation
Golgi- n-linked and o-linked glycoslylation
whatis the major sorting center of the cell?
what advantage does ER have in glycosylating proteins?
it has bound ribosomes that synthesize proteins in close proiximity to glycosylation machinery
what chain of events occurs as a protein is syntehsized by a ribosome attached to the ER?
peptide is inserted to lumen of ER as it grows guided by a signal seuqnce that directs prtoein throug ha channel in the ER lumen. signal sequence is cleaved from the protein in the transport process into ER. after protein has entered ER, glycosylation begins. N-linked glycosylation begins in ER and continues in golgi complex.
structure of golgi
stack of flattened membranous sacs
2 principle roles of golgi
1. carbohydrate units of glycoproteins are laltered and elaborated. o-linked sugar units added and n-linked sugars further modified
2. sorting: proteins proceed from golgi to lysozomes, secretory granules, plasma membrane etc. according to signals encoded for by their amino acid sequence
how can we determine the glycosylation pattern of a glycoprotein?
mass spectrometry: most approaches based on the use of enzymes that cleave oligosaccharides at specific types of linkages combined with the use of mass spec. for example n-linked oligosacchirdes can be released from proteins using peptide N-glycosidase F which cleaves n-glycosidic bonds. oligosaccharides are then analyzed using MALDI-TOF or other mass spec techniques
many oligosaccharide structures are consistent with the same mass why? and how do you gain more info?
many potential monosaccharide combinations. thus must cleave oligosaccharide with enzymes of varying specificities
where does beta 1,4, glactosidease cleave b-glycosidic bonds?
at galactose residues
what is a glycoform
a protein with several different glycosidation sites and thus ahve different glycosylated forms. greatly increase complexity of proteome
what determines what glycoform is produced?
each glycoform only generated in a specific cell type of developmental stage
enormous number of diverse sugars resulting in glycoproteins with diverse binding and biochemical properties is possible because?
1. different monosaccharides can be joined to one anotehr thorugh any of several oh groups
2. c-1 linkage can be alpha or beta
3. extensive branching is possible and can occur in many ways
what are lectins?
lectins are partners that bind specific carbohydrate structures
where are lectins found?
animals, plants, microorganisms
main function of lectin in animals? how does it provide this function?
facilitate cell-cell contact. lectin usually contains 2 or more binding sites for carbohydrate units. binding sites of lectins on surface of one cell interacts with arrays of carbohydrates displayed on surface of another cell
what interactions link lectins and carbohydrates
relatively weak interactions that ensure specificity yet permit unlinking (like velcro, each link os weak, but composit is strong)
functions of lectins in plants?
functions of lectins in e. coli
allow e. coli to adhere to epithelia cells of gastrointestinal tract because lectins on the e.coli surface recognize oligosaccharide units on the surface of target cells
what difference are the different classes of lectins based on?
based on their amino acid sequences and biochemical properties
what is a large class called C type?
one large class is the C type for calcium requiring, found in animals. calcium ion form bridges between protein and sugar through direct interactions with sugar and hydroxyl groups. 2 glutamate residues bind to both clacium ion and sugar, other protein sie chains form hydrogen bonds with other hydroxyl groups on carbohydrate
what are selectins
type of c type lectin. bind immune system cells to the sites of injury in the inflammatory response
what do L, E, and P forms of selectins bind to?
bind to carbohydrates on lymph-node vessels, endothelium, or activated blood platelets
how does influenza virus enter via cell surface carbohydrates
recognizes sialic acid on cell surface. viral protein hemagglutinin binds to cell surface carbohydrates, virus is taken into the cell, and viral protein neuramidase cleaves glycosidic bonds to the sialic acid residues.
inhibiting what protein may be a good anti influenza agent?
inhibitors of neuramidase