Carbohydrates Flashcards
What are the 3 structure tiers of carbohydrates?
Monosaccharides, disaccharides and polysaccharides
How many units are there in a monosaccharide?
single (one)
what are the 2 classes of monosaccharide?
aldoses or ketoses
How many carbons are there in monosaccharides?
3-7
Name 5 common monosaccharides
ribose, glucose, mannose, galactose and fructose
How many monosaccharides are there in a disaccaride?
2
What are the monosaccharides joined by to produce disaccharides?
glycosidic bond
Name 3 common disaccharides
lactose, maltose and sucrose
What are polysaccharides?
polymers of 20 or more monosaccharides
Name 3 common polysaccharides
cellulose, starch and glycogen
What makes up an aldehyde group?
carbon bonded to hydrogen and double bonded to oxygen
What is the name of the monosaccharides that have an aldehyde group?
aldoses
What makes up a ketone group?
carbon double bonded to oxygen
What is the name of the monosaccharides that have a ketone group?
ketoses
What further way can monosaccharides be classified?
by the number of carbon atoms they contain
How many carbon atoms are there in a triose, pentose and hexose sugar?
3, 5 and 6
What are stereoisomers?
molecules made of the same atoms, connected in the same sequence but the atoms are positioned differently in space
Why do almost all monosaccharides exist as 2 stereoisomers?
all contain one or more asymmetric (chiral) carbon atom
What are enantiomers?
two stereoisomers that are mirror images of each other
What is an example of a molecule that exists as two enantiomers?
glyceraldehyde - two stereoisomers that are mirror images of each other
What are the two forms of sugar stereoisomers?
D- or L-
What type of sugar stereoisomers are most common in animals?
D- isomers
What are epimers?
sugars which differ in the configuration around one carbon atom
What structure do the common monosaccarides have?
cyclical
What happens to monosaccharides with 5 or more carbons?
they exist as ring structures
In the ring structure of a monosaccharide what groups is the covalent bond formed between?
carbonyl and hydroxyl
What does the bonding of carbonyl and hydroxyl groups on monosaccharides produce?
one of 2 stereoisomers
What are the 2 stereoisomers of glucose that can be produced by the cyclical structure of monosaccharides?
alpha and beta anomers
What creates different anomers of monosaccharides of over 5 carbons?
the orientation of the HCOH molecules at the end of the monosaccharide
What molecules in animals are derived from simple hexoses?
glucose, galactose and mannose
What happens when molecules are derived from hexose?
hydroxyl (OH) group is replaced by another group, for example amino (NH2)
What does OIL RIG stand for?
oxidation is loss (of electrons) and reduction is gain (of electrons)
What can monosaccharides be oxidised by?
relatively mild oxidising agents (e.g. cupric ions)
What are sugars capapble of reducing cupric ions known as?
reducing sugars
What is the semi qualitative test for the presence of reducing sugar known as?
Fehling’s reaction
What was Fehling’s reaction used for?
detect and measure elevated glucose levels in diabetics
When do disaccharides form?
when two monosaccharides are covalently linked with the elimination of water to form a glycosidic bond
What molecule is eliminated during the formation of a glycosidic bond?
water
What is a homopolysaccharide?
polymer of a single type of sugar
What is a heteropolysaccharide?
polymer of different types of sugar
What are the 2 forms of homopolysaccharides and heteropolysaccharides?
branched and unbranched
What does gluconeogenesis convert to glucose?
pyruvate and related three and four carbon compounds (eg lactate and glycerol)
Where does glycogenesis take place mostly in animals?
the liver
Where does glycogenesis occur less often in mammals?
the renal cortex and the epithelial cells which line the small intestine
What does the path from pyruvate to phosphoenolpyruvate lead through?
oxaloacetate
What is oxaloacetate an intermediate of?
the citric acid cycle
What can be a starting material for gluconeogenesis?
any compound that can be converted to either pyruvate or oxaloacetate
What proteins can be converted to pyruvate and oxaloacetate?
alanine and aspartate respectively
What are glycogenic amino acids?
amino acids that can yield three or four carbon fragments
Where does the glucose produced by gluconeogenesis pass to?
the blood to supply other tissues
Why must gluconeogenesis be regulated?
as it is expensive
Where in the cell do glycolysis and glyconeogenesis occur?
cytosol/cytoplasm of the cell
What does the formation of one molecule of glucose from pyruvate require in order for it to happen?
4 ATP, 2 GTP and 2 NADH
What would happen if glycolysis and glycogenesis were allowed to proceed simultaneously at high rates?
the result would be high consumption of ATP and production of heat
How are the glycolysis and glyconeogenesis pathways regulated?
when the loss of glucose through glycolysis goes up the movement of pyruvate towards glucose goes down and vice versa
What are the 4 functions of carbohydrates?
energy, stored fuel, structural, information carriers
What is glycolysis the process of?
glucose is broken down into pyruvate
In what cells does glycolysis occur?
all cells
Under what conditions, aerobic or anaerobic, can glycolysis occur?
both
How many enzyme catalysed steps are there involved in glycolysis?
10
What 2 phases can the enzyme catalysed steps of glycolysis be split into?
preparatory and payoff
What net gain of ATP is there at the end of glycolysis?
2 ATP molecules
What is produced from pyruvate when glycolysis occurs under aerobic conditions?
Acetyl Co-A (acetyl co enzyme A)
What is the production of Acetyl Co-A catalysed by?
pyruvate dehydrogenase
What cycle does the newly formed Acetyl Co-A enter?
citric acid cycle
What conditions does the production of Acetyl Co-A and the citric acid cycle occur under?
aerobic
What is produced by the citric acid cycle?
NAD and GTP
What is GTP later converted into?
ATP
What occurs after glycolysis in anaerobic conditions?
lactate dehydrogenase cataylyses the formation of lactate from pyruvate
What else is formed during the formation of lactate from pyruvate?
NAD+
How many ATP molecules are produced from the complete oxidation of glucose?
32
What is the name of the storage polysaccharide in plant cells?
starch
What type of polysaccharide is starch?
homopolysaccharide
What is found in the branched and unbranched chains of glucose within starch?
unbranched: amylose
branched: amylopectin
What is the main storage polysaccharide of animals?
glycogen
what parts of the glucose monomer are the bonds formed between in glycogen?
bonds between carbon 1 of one molecule and carbon 4 of another
Where are the branch points on glucose molecules in glycogen?
at carbons 1 to 6
How does branching in glucose compare to branching in starch?
glycogen is more extensively branched
What do multiple branch points of glycogen mean?
it can be broken down quickly when glucose is needed
What areas of the body is glycogen found?
abundant in the liver but also present in skeletal muscle
How are branch points introduced and removed?
introduced by branching enzyme and removed by debranching enzyme
What enzyme allows liver to be net exporter of glucose.?
glucose 6-phosphatase
What type of poly saccharide is cellulose?
linear, unbranched, homopolysaccharide
What are glucose residues linked by in cellulose?
beta 1 to 4 glycosydic bonds
Where is cellulose found?
plant cell walls
What are glycogen and starch ingested in the diet broken down by?
alpha amylases and glycosidases
What bonds do alpha amylases and glycosidases break?
alpha 1 to 4 glycosidic bonds between glucose subunits
What is lacking in vertebrates that means that they cannot break beta 1 to 4 glycosidic bonds and therefore not digest cellulose?
enzyme that can break these bonds
What is the name of the protist (bacteria) that produces the enzyme cellulase which breaks down beta 1 to 4 glycosidic bonds?
Trichonympha
What do ruminants have in their rumen/ hind gut that can breakdown cellulose?
symbiotic organisms
What type of polymer is chitin?
linear homopolysaccharide
What type of sugars is chitin composed of?
N-acetylglucosamine residues in beta 1 to 4 linkage
Can chitin be digested by vertebrates?
no
What is chitin an important component of?
the exoskeleton in insects
What is peptidoglycan?
heteropolymer of alternating beta 1-4 linked N-acetylglucosamine and N-acetylmuramic acid residues found on the outer layer of of bacterial cell walls
Where is peptidoglycan found?
bacterial and agal cell walls
How does a lysosome kill bacteria that contain peptidoglycan in cell walls?
hydrolyses beta 1-4 glycosidic bonds
What are glycosaminoglycans (GAGs)?
heteropolysaccharides in the extracellular matrix
What do glycosaminoglycans do?
provide viscosity, adhesiveness, tensile strength and elasticity
Give 4 examples of glycosaminoglycans
hyaluronic acid (found in synovial fluid of joints) chondroitin sulphate (in cartilage and aorta, adds tensile strength) keratin sulphate (in the cornea and dead cells (e.g. hair)) heparan sulphate (interacts with a large number of proteins e.g. growth factors)
What length of carbohydrate can be information carriers?
poly and oligosaccharides
What are oligosaccharides?
have between 3 and 10 units
What do information carriers provide between cells and extracellular surroundings?
communication
What are proteins labelled for?
transport to specific organelles or for distruction
What may be used to label proteins?
information carriers
What can recognition sites be used for?
extracellular signalling molecules such as growth factors or bacteria
What do most eukaryotic cells have attached to components of the plasma membrane?
specific oligosaccharide chains
What is the name of the carbohydrate layer that is formed on the plasma membrane?
glycocalyx
What are oligosaccharide chains attached to the plasma membrane used for?
cell to cell recognition and adhesion, blood clotting, the immune response and wound healing
what is the covalent bond formed between in order to create an information carrying poly/oligosaccharide?
a protein or lipid to form a glycoconjugate
Where are proteoglycans found?
cell surface of ECM
what are proteoglycans?
highly glycosylated proteins attached by serine residues to cell walls
Where are glycoproteins found?
cell surface or extra cellular matrix
What do glycoproteins contain?
oligosaccharides covalently linked to 3 different amino acid residues
Where are glycolipids found?
extracellular surface
What are glycolipids covalently linked to?
oilgosaccharides
What are glycolipids?
lipids found within the plasma membrane
What are lectins?
proteins that bind carbohydrates
What do lectins have a role in?
cell to cell recognition, signalling and adhesion
Where are lectins commonly found?
extracellular surface of cells
What are selectins?
a family of plasma membrane lectins that mediate cell to cell recognition and adhesion in a wie range of processes
What immune processes are selectins involved with?
movement of leukocytes through the capillary wall from blood to tissues at the sites of infection or inflammation
What is phosphofructokinase (PFK)?
the enzyme that is crucial to the formation of fructose 1 6 biphosphate in the preparatory stage of glycolysis
What happens without PFK in glycolysis?
glycolysis cannot be completed
What happens if there is a deficiency in PFK?
energy is not able to be obtained from glucose
How does PFK deficiency present?
muscle fatigue, weakness, pain and stiffness during exercise
What causes lack of PFK?
a genetic defect
What population is the PFK genetic defect present in?
spaniel
Is the PFK defect dominant or recessive?
recessive
How is PFK deficiency treated?
incurable and can only be managed through dietry changes and reducing or avoiding exercise
What dietary changes can be made in order to manage PFK deficiency?
high protein and low fat diet with low carbs
What is an example of a pathological lectin?
haemagglutinin (HA) in the influenza virus
What does HA do to host cells?
attatches to cell surface carbohydrates and allows of the viral membrane to fuse with the cell surface membrane
What does fusion of the HA glycoprotein to cell surface membrane mean?
genome of the virus can enter the cell where it can then replicate inside the cell
What can HA be used for?
treatments
How can HA be used safely for treatment?
inhibited to prevent it from attaching to cells and therefore stop it from binding to cell surface receptors in the first place. The stem of the HA molecule can also be targeted to block changes in the molecule that occur during fusion to the cell surface membrane
What do bacteria use as a storage polysaccharide?
dextrans
What are dextrans polymers of?
alpha 1-6 linked glucose subunits
Where are the branches located in dextrans?
alpha 1-3 and alpha 1-4
whereabouts in the body are bacteria that produce and secrete dextrans extracellularly found?
the mouth
What makes dextrans adhesive?
branching structure
What do these adhesive dextrans released by bacteria in the mouth form part of?
dental plaque that grows on teeth
What do the dextran bacteria cause when they become stuck to to the teeth and each other because of their adhesiveness and then proliferate?
teeth and gum damage leading to gingivitis and tooth decay
What is polysaccharide storage myopathy?
genetic condition in horses where they store glucose incorrectly
Why is glucose stored with multiple alpha 1-6 branches?
to make it easy to be broken down and release glucose
What sort of bonds are formed between glucose molecules within polysaccharide storage?
alpha 1-4
What enzyme makes alpha 1-4 bonds in glycogen formation?
glycogen synthase
what enzyme breaks alpha 1-4 bonds?
amylase
What enzyme makes the alpha 1-6 branching bonds during the formation of glycogen?
glycogen branching enzyme
What is over produced during polysaccharide storage myopathy?
glycogen synthase
What does the over production of glycogen synthase during polysaccaride storage myopathy mean?
more glycogen synthase than glycogen branching enzyme, creating long chains of glycogen with minimal branching. This means that the glycogen is relatively amylase resistant
What are the signs of polysaccaride storage myopathy?
lack of energy and muscle stiffness due to lack of available glucose
What may be broken down as an alternative source of fuel in a horse with polysaccharide storage myopathy?
muscle tissue
In polysaccharide storage myopathy, what does an overproduction of glycogen synthase mean for glycogen production?
glycogen synthase works resulting in overproduction of glycogen relative to how much is broken down
How can polysaccaride storage myopathy be managed?
incurable but switching to a low-starch, high fat diet can provide an alternative source of fuel
