Carbohydrates

Question 1

What are carbohydrates

Answer 1

Organic compounds containing carbon, hydrogen and oxygen, made of basic units called monosaccharides

Question 2

What is a monosaccharide?

Answer 2

A small organic molecules that are the building blocks for larger carbohydrates
They have general formula of CnH2nOn

Question 3

What are the functions of monosaccharides?

Answer 3

1. Source of energy in respiration, C-H and C-C bonds broken to released energy, transferred to make ATP
2. Building blocks for larger molecules e.g. glucose makes starch, glycogen etc
3. Intermediates in reactions e.g. trioses intermediates in photosynthesis+respiration
4. Constituents of nucleotides e.g. deoxyribose dna, ribose in RNA ATP ADP

Question 4

How can monosaccharides with same formula have different structure?

Answer 4

Carbon atoms in monosaccharides make a ring when dissolved in water, and can alter binding to make straight chains. E.g. Glucose has alpha glucose and beta glucose isomers

Question 5

What are the structures of alpha glucose and beta glucose

Answer 5

See sticky note

Question 6

What are disaccharides?

Answer 6

2 monosaccharides bonded together, forming a glycosidic bonds with the removal of water in a condensation reaction.
Glycosidic bond named by which carbons between e.g. 1,4-glycosidic bond
If bond straight, it is alpha glucose, if alternates, it is beta

Question 7

What disaccharides are formed by what monosaccharides and what is their role?

Answer 7

Maltose - glucose + glucose - in germinating seeds
Sucrose - glucose + fructose - transport in phloem of flowering seeds
Lactose - glucose + galactose - in mammalian milk

Question 8

What are polysaccharides?

Answer 8

Large, complex polymers formed by monosaccharide units linked by glycosidic bonds.

Question 9

Why is glucose stored as polysaccharides?

Answer 9

Soluble in water so would increase concentration of cell contents, and draw water in by osmosis.
Polysaccharides are:
1. Insoluble so no osmotic effect
2. Cannot diffuse out of cell
3. Compact molecules so can be stored in small spaces
4. Carry lots of energy in C-C and C-H bonds

Question 10

What is starch?

Answer 10

Starch is the polysaccharide that stores glucose in plants, it is made of alpha glucose bonded in 2 ways forming amylose and amylopectin

Question 11

What is amylose and amylopectin (in starch)

Answer 11

• Amylose is a linear, unbranched molecule with alpha1,4-glycosidic bonds which is repeated, creating a chain that coils into a helix.
• amylopectin is chains of glucose joined by alpha1,4-glycosidic bonds cross linked with alpha1,6-glycosidic bonds. They fit in amylose and every 24-30 glucose molecules, the 1,6-glycosidic bond is formed, creating side branch

Question 12

What is glycogen?

Answer 12

Storage polysaccharide of glucose in animals. Very similar to amylopectin with alpha1,4-glycosidic bonds and alpha1,6-glycosidic bonds, but 1,6 occurs every 8-10 molecules, so more branched and compact

Question 13

What is cellulose

Answer 13

A structural polyscharride used in plant cell wall made of beta glucose
-Beta glucose monomers are held by B1,4-glycosidic bonds to make straight, unbranched chain, beta link rotates adjacent glucose by 180degrees. -Hydrogen bonds form between the OH group of adjacent parallel cellulose chains making microfibrils, held in bundles called fibres.
- cell wall has a layer of fibres, that run parallel within a a layer, but at angle to adjacent layers. Permeable due to spaces between fibres

Question 14

What is chitin?

Answer 14

A structural polysaccharide in exoskeleton of insects and in fungal cell walls. Long chains of B1,4 monomers but has groups derived from amino acids added to form a heteropolysaccharide.
Strong, waterproof and lightweight. Adjacent monomers rotated 180degresz from beta link, so parallel chains cross link with hydrogen bonds to form microfibrils