Carbohydrates Flashcards

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1
Q

Monomers, the polymers they form and the bonds within them

A

Alpha glucose- starch (amylose) and glycogen joined with (glycosidic C1-C4, + glycosidic C1-C4 chain and C1-C6 branches.) bonds.

Beta glucose- cellulose joined by glycosidic C1-C4 bonds.

Amino acids- polypeptides joined by peptide bonds.

Nucleotides- DNA, RNA joined by phosphodiester bonds.

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2
Q

What’s the empirical formula for carbohydrates?

A

Carbon: hydrogen: oxygen ratio CH2O(n) where n= the number of carbon atoms.

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3
Q

The role of carbohydrates

A

Monosaccharides: single unit sugars e.g. glucose, fructose, galactose.

  • source of energy/ aerobic respiration/ generates ATP
  • make up polysaccharides
  • building DNA and RNA nucleotides
  • chemical intermediates

Polysaccharides: large, insoluble polymers e.g.starch (amylose), glycogen, cellulose.

  • starch acts as energy stores in plants/ animals
  • cellulose makes plant cell walls and has a structural role.
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4
Q

Alpha and beta glucose

What’s an isomer?

A

a-glucose: the H on the right and left point above the plane of the ring.
b- glucose: the H on the right points below the plane of the ring while the H on the left points above.

Glucose is an isomer: both alpha and beta forms are the same molecule but different arrangement.

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5
Q

The food test for reducing sugars

A

Add 2cm3 Benedict’s solution to the sample.
Heat in water bath, 90 degrees for 5 minutes.
Colour change from light blue to red (copper II sulphate) if reducing sugars is present.

Scale. Blue, green, orange, red.

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6
Q

Name 3 common disaccharides and the monosaccharides that make them.

A

Maltose- 2 alpha glucose. A reducing sugar.

Sucrose- glucose and fructose. A non-reducing sugar.

Lactose- glucose and galactose. A reducing sugar.

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7
Q

Food test for non-reducing sugars

A

If the solution stays blue in the Benedict’s test, it’s a non-reducing sugar.
Boil with hydrochloric acid then neutralise with alkali.
Repeat Benedict’s test by heating at 90 degrees for 5 minutes.
Colour change from light blue to red.

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8
Q

Formation of starch

A

Condensation reaction between many alpha glucose monomers.
Water released.
Forms C1-C4 glycosidic bonds.
Tightly coiled/ compact, insoluble polysaccharide.

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9
Q

The role of starch in plants

A

Starch consists mainly of polysaccharide amylose.
It is a storage polysaccharide for energy.
Amylose is compact, so a plant cell can store a lot of energy in a small space.
Amylose is coiled by hydrogen bonding within the chain.
It is insoluble so cell water potential/ enzymes are not affected and it cannot diffuse out of cells.
Hydrolysis of starch releases glucose for use in respiration to make ATP.

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10
Q

What are the similarities and differences between starch (amylose) and glycogen (containing amylose and amylopectin)?

A
Similarities:
Both polymers made from alpha glucose.
Compact.
Insoluble.
Store of energy for respiration/ ATP.
Condensation reaction between monomers forming glycosidic bonds.

Differences:
Amylose has C1-C4 glycosidic bonds only whereas glycogen has C1-C4 chains and C1-C6 branches.
Amylose is in plants while glycogen is in animals.
Amylose is an unbranched, coiled chain while glycogen is heavily branched so has more ‘terminal ends’ which allows for rapid hydrolysis/ release of glucose for respiration.

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11
Q

Food test for starch

A

Add 2cm3 of iodine/ potassium iodide solution.

Colour change from orange to blue/black.

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12
Q

The formation of cellulose

A

Polymer of beta glucose (monomer).
Condensation reaction between monomers forming C1-C4 glycosidic bonds.
Every 2nd beta glucose rotates 180 degrees.
Forms a straight cellulose strand.

Multiple parallel strands, bonded by extensive hydrogen bonding.
Forming microfibrils.

Many microfibrils combine to form macro fibres.
Macro fibres combine to form cellulose.

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13
Q

Relate the structure of cellulose to its function with plant cells.

A

Fibrous polysaccharide.
Tensile.
Withstand osmotic forces when cells absorb water by osmosis and become turgid.
Spaces between cellulose strands allow material to pass through freely to cell surface membrane.

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