Carbohydrates Flashcards

1
Q

Functions of carbohydrates

A

1) Energy stores (glycogen, starch).
2) Components of structural material
(e.g. chitin for insect exoskeletons).
3) Parts of other important
macromolecules – DNA and RNA,
glycoproteins, and glycolipids.
4) Signalling function (recognition of cell surface molecules on other cells)

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2
Q

general formula for carbohydrates

A

C: H O:
1 : 2: 1
carbohydrates are hydrates of carbon with the
general formula Cx(H2O)x

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3
Q

Characteristics of monosaccharides

A
  1. Monosaccharides are colourless, crystalline solids that are
    soluble in water and other polar solutions – in other words
    monosaccharides are hydrophilic.
  2. Monosaccharides have names ending with “ose”.
    Glucose, Ribose, Deoxyribose….
  3. Most have a sweet taste
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4
Q

Continued

A
  1. The backbone of the monosaccharide is a carbon chain with
    all carbons joined by single covalent bonds.
    Glucose when solubilised, they form a ring structures
    5- Monosaccharide chains contain a single carbonyl group
    (C=O)
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5
Q

If it contains an aldehyde
carbonyl group.

A

aldose
D-Glyceraldehyde

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6
Q

If it contains a ketone
carbonyl group

A

ketose
Dihydroxyacetone

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7
Q

Common 6-carbon monosaccharides

A

Glucose
Most abundant sugar in nature; in many foods, e.g.
bread, pasta, fruit, cereals.
Most of the carbohydrates we eat are converted into
glucose for energy.

Fructose
Naturally occurring in foods such as honey & fruit.

Galactose
In nature primarily found as part of lactose (milk sugar).

Mannose A by-product of metabolism, also found in some fruitsand vegetables.

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8
Q

Monosaccharides have chirality

A

The chiral carbon which
determines whether a
carbohydrate is in the D
or L configuration is the
one furthest from the
carbonyl group

In glucose
Carbons 2-5 are chiral
C6 = Not a chiral carbon. Chiral
carbon should have 4
different atoms/groups
attached to it!

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9
Q

Which chiral carbon
determines D/L
configuration?

A

C5
D-glucose and L-glucose
are enantiomers.

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10
Q

Enantiomers

A

1- Do they have the same chemical formula? YES
2- Do they have chiral carbons? YES
3- Can they be superimposed? NO
4- Are they mirror images? NO

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11
Q

diastereomers.

A

1- Do they have the same chemical formula?
2- Do they have chiral carbons?
3- Can they be superimposed?
4- Are they mirror images?
YES
YES
NO
NO
These molecules are called diastereomers.

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12
Q

Hexoses…..

A

Same Chemical Forumula

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13
Q

How many diastereomers can a molecule have?

A

A molecule with n chiral carbons has (2n-2) diastereomers.
Example:
A molecule with 4 chiral carbons will have 24-2 = 14 diastereomers.

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14
Q

carbon derived from the carbonyl carbon is known as

A

the anomeric carbon

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15
Q

D-glucose

A

The ring has 6 members
Rings with 6 members are
called pyranose rings.

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16
Q

Fructose

A

Fructose is a ketose
The ring has 5 members
Rings with 5 members are
called furanose rings.

17
Q

Common furanose monosaccharides

A

Deoxyribose is part of the structure of DNA
Ribose is part of RNA.

18
Q

Forming carbohydrate polymers

A

Monosaccharides are joined together to form
disaccharides, oligosaccharides and polysaccharides by
condensation reactions.
 Covalent bonds that form between a carbohydrate and
another molecule are called glycosidic bonds (this
other molecule does not need to be another
carbohydrate).

19
Q

Maltose

A

Condensation reaction between α-D-glucose + either α or β-D-glucose
Covalent bond is α-1,4-glycosidic
Formula is: C12H22O11

20
Q

Sucrose

A

Condensation reaction between α-D-glucose + b-D-fructose
Covalent bond is α-1,2-glycosidic
Formula is: C12H22O11

21
Q

Lactose

A

Condensation reaction between b-D-galactose + a/b-D-glucose
Covalent bond is b-1,4-glycosidic
Formula is: C12H22O11

22
Q

Cellobiose

A

Condensation reaction between b-D-glucose + b-D-glucose
Covalent bond is b-1,4-glycosidic
Formula is: C12H22O11

23
Q

Why are some bonds named as a bonds and some b?

A

alpha glycosidic bonds are formed when the OH on the C1
(anomeric carbon) is below the ring
beta glycosidic bonds are formed when the OH on the C1
(anomeric carbon) is above the ring.

24
Q

Starch

A

 energy store of plants
 Very large polymer of a-D-glucose.
Amylopectin: Branched polymer (every 24-30 glucose
molecules there is a branch).
 Glucose monomers are linked through a-1,4-
glycosidic bonds.
 The bond linking branches to the main chain is an
a-1,6-glycosidic bond.
Amylose: Linear polymer. Glucose monomers are
linked through a-1,4-glycosidic bonds.

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Glycogen
 energy store of animals  Very large polymer of a-D-glucose with many branches Branched polymer (every 8-12 glucose molecules there is a branch).  Glucose monomers are linked through a-1,4- glycosidic bonds.  The bond linking branches to the main chain is an a-1,6-glycosidic bond.
26
Cellulose
 for structural support in plant cell walls  Very large, unbranched polymer of b-D-glucose.  Most abundant polysaccharide on earth.  Humans cannot digest cellulose. We do not have the correct enzymes (called cellulases) to break the b-1,4-glycosidic bonds.
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Chitin
 structural component of insects, molluscs and fungi cell walls Polymer of: N-acetylglucosamine (shortened to GlcNAc). This molecule contains: b-D-glucose Amino group Acetyl group
28
Continued
 Chitin is a polymer of N-acetylglucosamine  The covalent bond linking the GlcNAc monomers is b-1,4-glycosidic.
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GLYCOSYLATION
Cellular process that attaches an oligosaccharide to a protein. Can occur as the protein is being made or is added afterwards (post-translational modification). Estimated that more than half of proteins made in eukaryotic cells are glycosylated.
30
Continued
Creates a diversity of structures – vastly increases the number of functions proteins can perform.  Position the carbohydrate is attached.  Types of sugars attached.  Short or long chains.  Branched or unbranched. Glycoproteins Structure is mostly protein with short, linear, oligosaccharides added on. Proteoglycan Structure is mostly polysaccharides held together by a protein chain.
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Types of Glycoprotein
Glycoproteins are classified by the type of the glycosidic bond that connects the carbohydrate to the protein. There are 2 main types of glycoproteins: N-linked and O-linked ~90% of glycoproteins are N-linked.
32
Production of glycoproteins
N-linked glycoproteins are formed in the endoplasmic reticulum and then the golgi. O-linked glycoproteins are made in the golgi.
33
N-linked glycoproteins
Connects the sugar and protein through a nitrogen atom that is on either an asparagine or lysine amino acid. Functions include:  Cell-cell adhesion.  Cell signalling.  Host-pathogen recognition. Only found in eukaryotes and Archaea, not Bacteria
34
Cell surface glycoproteins are used by viruses
* Haemagglutinin and Neuraminidase are receptors on the flu virus protein coat. * Haemagglutinin binds to specific N-linked glycoproteins on the cell it wants to infect. * Neuraminidase cleaves an oligosaccharide in the cell membrane to disconnect the virus.
35
O- linked glycoprotein
Connects the sugar and protein through an oxygen atom that is on either a serine, threonine or hydroxy-lysine amino acid. Found in eukaryotes, Archaea and Bacteria. Functions include:  ABO blood groups.  Extracellular matrix component.  Shock absorption in joints.
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Proteoglycans
The polysaccharide chains within the proteoglycans change the properties of water to a slimy, gel-like texture. This texture is a useful function in cartilage, mucus and synovial fluid in joints. They provide shock absorption because they are surrounded by a lot of water and can release it when pressure is applied. Proteoglycans also provide structural support as part of the extracellular matrix in eukaryotic cells.
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