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Carbohydrates! Flashcards

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1
Q

What is the empirical formula for carbohydrates?

A

(CH2O)n
Carbohydrates are hydrated carbon.
Need to have at least three carbons in the chain n=3 (simplest sugars are triose)

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2
Q

What is the name for a 1 sugar unit, a 2-20 sugar units and hundreds and thousands of sugar units?

A

Monosaccharide
Oligosaccharide
Polysaccharide

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3
Q

Give some characteristics of monosaccharides

A

Sweet tasting
Water soluble
Crystalline solid
Aldoses or ketoses
Open chain or ring structure

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4
Q

What is the simplest ketose sugar?

A

Dihydroxyacetone

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5
Q

What is the simplest aldose sugar?

A

Glyceraldehyde

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6
Q

How can you calculate the number of stereoisomers of a carbohydrate?

A

2 to the power of the number of chiral carbons

(every time a CH2O is added another chiral carbon is added and the more stereoisomers are formed)

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7
Q

How do you distinguish between L-aldoses and D-aldoses? And L-ketoses and D-ketoses?

A

Find the chiral carbon furthest away from the carbonyl group
If the -OH it is bonded to is on the left it is an L-aldose/L-ketose and if the -OH is on the right then it is a D-aldose/D-ketose

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8
Q

What is a reducing sugar? Are aldose sugars and ketose sugars reducing sugars?

A

A reducing sugar is a sugar that is itself able to be oxidised.
Aldose sugars are reducing sugars because they contain an aldehyde group (CHO) that can be oxidised to form a carboxyl group (COOH).
Ketose sugars contain ketone groups (R-CO-R) which cannot be oxidised but the hydroxyl group (-OH) closest to the carbonyl in the ketone is weaker and can be oxidised by removing the hydrogen (forming C=O) so can give a positive result for a reducing sugar.

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9
Q

How many isomers do aldoses and ketoses have?

A

Aldoses - 16
Ketoses - 8

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10
Q

What test can be used to identify a reducing sugar and how does it work?

A

Benedicts reagent.
The reducing sugars reduce copper 2+ ions to copper 1+ - this changes the colour of the solution from blue to brick red.
The reducing sugars are themselves oxidised (redox)

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11
Q

What are epimers?

A

When two carbohydrates have exactly the same structure apart from at one CH2O where the OH and the H are flipped.
H-C-OH and OH-C-H.

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12
Q

How are epimers named?

A

Use one of the carbohydrates as a reference and then state the carbon at which there is a difference
E.g. the C2 epimer of glucose is the sugar which has the same structure as glucose except the H and OH bound to the second carbon are flipped

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13
Q

What are the epimers of glucose?

A

mannose - at C2
galactose - at c4

but mannose and galactose are not epimers bc they differ at more than one C

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14
Q

What is the minimum chain length required for aldoses and ketoses to form a ring structure?

A

Aldoses - 4 carbons
Ketoses - 5carbons

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15
Q

What is an anomer?

A

In an open chain structure, the carbon of the carbonyl group is not a chiral carbon as it is only bonded to three groups (R-CHO). When it forms a ring structure it is bonded to four different groups so it becomes a chiral carbon.
This new chiral centre is called an anomeric carbon and the structure is called an anomer.

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16
Q

What are alpha and beta anomers?

A

The oxygen from the hydroxyl group can attack the carbon of the carbonyl from above or below the plane which forms two different structures.
One with the OH pointing upwards - Beta. One with the OH pointing downwards - Alpha.

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17
Q

In a ring structure which carbon is the first carbon?

A

The anomeric carbon

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18
Q

What are the most abundant molecules on earth?

A

Carbohydrates

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19
Q

What are the 3 alleles of the ABO gene?

A

IA
IB
i

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20
Q

How does the amount of chiral centres a molecule has relate to the amount of stereoisomers it can have?

A

In general, a molecule with n chiral centres
can have 2n stereoisomers

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21
Q

Six carbon aldose sugars (aldohexoses)
have 4 chiral centres. How many
stereoisomers are possible?

A

2^4 = 16

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22
Q

What 2 basic structures together make an aldose?

A

Carbon Sugar
Carbonyl group at end of chain – Aldehyde.
Basically a simple sugar containing an aldehyde group

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23
Q

Where are the chiral centres of aldose located?

A

C2, C3, C4 and C5

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24
Q

What kind of isomers are epimers?

A

Stereoisomer (specifically diastereomers)

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25
What are diastereomers?
Stereoisomers of a compound that are not mirror images of each other and are not superimposable. Have different configurations at one or more of the equivalent stereocenters and are not mirror images Basically some change but not all RRR -> RSR = diastereomer
26
What 2 basic structures make up a ketose?
Carbon Sugar Carbonyl group at a middle C position – Ketone
27
What is aldotetrose?
A specific type of aldose with 4 carbon atoms
28
How would monosaccharides present in aqueous solutions?
Monosaccharides with ≥5 carbons (e.g. glucose, fructose) and aldotetroses usually form rings (cyclic structures) in water. This happens because ring forms are more stable than linear forms in solution
29
How does an aldose/ketose open chain structure form a ring structure?
A hydroxyl group (-OH) on one carbon reacts with the carbonyl group (aldehyde or ketone). This forms a hemiacetal (from an aldehyde, as in aldoses) or hemiketal (from a ketone, as in ketoses)
30
You have an anomeric carbon, and the OH it has bonded with is up. Does that make this anomeric carbon beta or alpha?
Beta Beta is up down up down up Alpha is down down up down up
31
Give the basic information needed to draw B-D-Galactose, then draw it
It’s a hexose (6-carbon sugar) and an aldose. In water, D-galactose forms a six-membered ring called a pyranose. β-anomer means: the –OH on the anomeric carbon (C1) is up.
32
What are pyranose and furanose rings?
Pyranose and furanose refer to the cyclic forms of carbohydrates (sugars). Pyranose is a six-membered ring (5 carbons and 1 oxygen), while furanose is a five-membered ring (4 carbons and 1 oxygen)
33
Define steric hindrance
The slowing or prevention of a chemical reaction due to the spatial arrangement and bulkiness of molecules or groups
34
Why are pyranose rings not flat?
The tetrahedral (109.5°) geometry of carbon atoms causes the ring to pucker to reduce angle strain and steric hindrance
35
What form do pyranose rings usually take? Why?
Chair form. Axial substituents sterically hinder each other. Chair form of -D glucopyranose predominates as all axial positions are occupied by H atoms
36
What conformation do furanose rings make?
Envelope form - not planar
37
What's monosaccharide where the hydroxyl group is replaced by sulphate group?
Heparin - used in blood clotting
38
What is derivatisation of monosaccharides?
It means chemically modifying a monosaccharide by replacing one or more –OH (hydroxyl) groups with other functional groups
39
When are O-glycosidic bonds formed?
When a hydroxyl group reacts with the anomeric carbon This determines the structure of oligo and polysaccharides Look for OCH3
40
When are N-glycosidic bonds formed?
When the anomeric carbon reacts with a Nitrogen atom e.g. Nucleotides and glycoproteins Can also see it in adenosine triphosphate
41
What are disaccharides made of?
2 monosaccharides covalently linked by an O-glycosidic bond
42
Give 4 examples of disaccharides
Lactose (Gal1-4Glu) – found in milk. Trehalose (Glu1-1Glu) – found in insects. Maltose (Glu1-4Glu)- hydrolysis of starch. Sucrose (Glu1-2Fru)– found in plants.
43
Why are polysaccharides used to store energy?
compact granule, less osmotic pull due to bonding, less water associated with it
44
What is the blue arrow pointing to?
A hemiacetal The C is bonded to an O, used to be a double bond The C is chiral Must be an old straight chain aldose
45
What reactions form and break glycosidic bonds?
Condensation forms, leaving O linking them Hydrolysis breaks them Given is an example using maltose
46
How can you tell if a sugar is a reducing sugar?
A sugar is reducing if it has a free anomeric carbon that can convert to an open-chain form and expose an aldehyde or ketone group
47
What are polysaccharides also known as?
Glycans
48
Define homopolymer
Identical monosaccharides make up a polysaccharide
49
Define heteropolymer
Variable monosaccharides make up a polysaccharide
50
What are 3 biological functions of sugars?
Energy Structure Information
51
Why are mono and disaccharides better for energy use?
Monosaccharides and Disaccharides e.g. Glucose and Sucrose are easily metabolised to provide energy for cell
52
What are the 2 types of starch used as storage molecules? Describe their structures
Unbranched -Amylose Branched – Amylopectin 1-6 linkage every 30 residues.
53
Describe the structure of glycogen
Branched –1-6 linkage every 10 residues
54
Give 2 examples of homopolymers
Cellulose and Chitin Starch and glycogen
55
Where might you find a heteropolymer?
Bacterial cell wall NAG and NAM
56
What are glycoconjugates?
Glycoconjugates are molecules formed by the covalent attachment of carbohydrates to other biomolecules like proteins and lipids Various monosaccharides linked by BETA glycosidic bonds
57
Where might you find glycoconjugates?
Connective tissue
58
Describe the structure of cellulose
Unbranched polymer of glucose residues joined by b1-4 linkages. The beta configuration allows formation of very long straight chains. Parallel chains can interact by hydrogen bonding forming Fibrils.
59
Describe the structure of chitin
Linear homopolymer composed of N- acetylglucosamine linked by b1-4 glycosidic bonds Differs form cellulose by replacement of the C2 hydroxyl group with an acetylated amino group Parallel chains interact by H bonding leading to high tensile strength - 2nd most abundant carb on earth
60
What is the ground substance of connective tissues?
Proteoglycans
61
What are proteoglycans?
95% glycans with some protein associated The protein is associated with GAG chains
62
What is aggrecan?
Glycosaminoglycan attached to core proteins
63
What is a glycosaminoglycan?
A long, unbranched polysaccharide made of repeating disaccharide units, often sulfated and negatively charged (e.g. heparin, chondroitin sulfate, hyaluronic acid)
64
How can proteoglycans assemble with hyaluronic acid?
Proteoglycans (core proteins with GAG chains) can non-covalently attach to a long molecule of hyaluronan (hyaluronic acid). This forms huge molecular aggregates called proteoglycan aggregates Key example: Aggrecan (a cartilage proteoglycan) binds to hyaluronan with the help of link proteins, forming massive structures.
65
How can proteoglycan aggregates give strength?
These units can attach to long filament of Hyaluronan to form enormous assemblies These can interact with fibrous matrix protein e.g. collagen Forms cross-linked meshwork giving strength and resilience
66
What allows more structural variety, proteins or sugars?
Sugars
67
What are oligosaccharides synthesised by?
Glycosyltransferases These a specific to each sugar being linked
68
What is the structural difference between A and B blood group antigens?
They differ by one monosaccharide: A antigen has N-acetylgalactosamine (GalNAc), B antigen has Galactose, both linked α1,3 to the common O antigen backbone.
69
What enzymes are responsible for adding sugars to the O antigen in blood groups A and B?
Glycosyltransferases specific to A or B blood types: Type A adds N-acetylgalactosamine Type B adds Galactose ## Footnote They differ by only 4 amino acids out of 354.
70
How do type A and B glycosyltransferases differ?
Differ by 4amino acids out of 354 amino acids O phenotype is result of mutation resulting in no active glycosyltransferases
71
Why do people with blood type O not express A or B antigens?
The O phenotype results from a mutation that produces a non-functional glycosyltransferase, so no sugar is added to the O antigen.
72
What is the universal donor?
O
73
What is the universal recipient?
AB
74
How many monosaccharides do A and B blood groups differ by?
One
75
What are lectins?
Lectins are proteins that recognise and bind specific carbohydrate (sugar) structures on cells. They are ubiquitous – found in plants, animals, and microbes Binding is highly specific (like a lock and key) - recognition and adhesion processes
76
What are selectins?
A family of lectins involved in cell- cell recognition and adhesion e.g. the movement of T-lymphocytes to a site of infection or inflammation
77
How does the influenza virus use lectin?
Hemagglutinin (lectin) recognises sialic acid residues on host surface glycoproteins. After penetrating the membrane neuramidase (sialidase) breaks the glycosidic bond to release the virus Without neuramidase, virus non invasive. Tamiflu and Relenza inhibit the enzyme
78
Uses of lectins
Lectins recognise ‘old’ erythrocytes and remove them. Microbial/Viral pathogens utilise lectins for adhesion or toxin entry (recognise specific oligosaccharides of host cells)

Biochemistry (14 decks)

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