A-level Biology Edexcel - CARBOHYDRATES

Name 3 ways in which carbohydrates are useful

1. Energy store

2. Energy source

3. Cellulose (structure)

What are all carbohydrates made up of?

Carbon, hydrogen, oxygen

What are the three main groups of carbs?

Monosaccharides

Disaccharides

Polysaccharides

What is the general formula for monosaccharides?

(CH2O)n

What is the formula fo triose sugars?

C2H603

What is the importance of triose sugars?

Important in mitochondria, where glucose is broken down into triose sugars during respiration

What is the molecular formula for pentose sugars?

C5H10O5

Give an example of a pentose sugar

Ribose

Draw a ribose molecule

What is the molecular formula for hexose (monosaccharide) sugars?

C6H12O6

Give examples of hexose ((monosaccharide) sugars

Glucose, fructose, galactose

Name two isomers of glucose

Alpha glucose and beta glucose

Draw alpha glucose

Draw beta glucose

How is a disaccharide formed?

When two monosaccharides join together in a condensation reaction where water is removed

How are monosaccharides bonded?

they have bonds but not glycosidic as they are only one unit

Name the monosaccharides of sucrose

(Alpha ) glucose and fructose

What is the source of sucrose?

Stored in plants such as sugar cane

Name the monosaccharides of lactose

(Alpha) glucose and (beta) galactose

What is the source of lactose?

Main carb in milk

Name the monosaccharides of maltose

(Alpha) glucose and (alpha) glucose

What are polysaccharides?

many monosaccharides joined by a condensation reaction that forms glycosidic bonds

What are molecules with 3-10 sugars known as?

Oligosaccharides

What are true polysaccharides?

11 or more monosaccharides

What is different from oligosaccharides and polysaccharides?

Polysaccharides do not taste as sweet

Name 3 ways in which polysaccharides' structure makes them ideal as storage molecules

1. Compact so large numbers can be stored in cell

2. Glycosidic bonds are easily broken, allowing rapid release of monosaccharide units for cellular respiration

3. Insoluble in water so do not affect water balance

How are polysaccharides broken down?

Hydrolysis, where water is added to the glycosdic bond

When might hydrolysis take place?

- During digestion in the gut

- In muscle and liver cells when the carbs are broken down to release sugar for cellular respiration

What are the three main types of polysaccharide?

Starch, glycogen, cellulose

What is starch used for?

Energy storage in plants

What is starch made up of?

amylose and amylopectin which are made of alpha glucoses which are joined by 1-4 glycosidic bonds to make straight chains

What compounds of alpha glucose make up starch?

Amylose and amylopectin

Describe the structure of amylose

~ Long, unbranched chains of α-glucose

~ Angles of glyosidic bonds makes it a coiled structure - this makes it compact and good for storage

~ Amylose is insoluble so does not effect water potential

~ Contain 1-4 glycosidic bonds

Describe the structure of amylopectin

~ Long, unbranched chains of α-glucose

~ Has side branches which allows enzyme to hydrolyse bonds more easily - glucose is released quickly

~ Amylopectin is insoluble so does not effect water potential inside a cell

~ Contain 1-4 glyosidic bonds

~ Branches with 1-6 glycosidic bonds

What are the roles of amylose and amylopectin in starch?

Amylose releases glucose slowly over a longer period of time keeping you going longer.

Amylopectin releases glucose rapidly for cellular respiration

What is glycogen used for?

Only carbohydrate energy store in animals

Also important store in fungi

What is glycogen made up of?

Alpha glucoses 1-4 glycodic bonds to make straight chains and 1-six bonds to form branches

How does glycogen differ from starch?

Glycogen molecule has more 1,6 glycosidic bonds giving it many more side branches, meaning it can be broken down more rapidly
starch has 2 polysaachrides

Why is glycogen branched?

The branched structure means that it can be used as a source of glucose for active tissues with a constantly high rate of cellular respiration such as muscle and liver tissue

What is cellulose used for?

Structural support in plants

What is cellulose made of?

Long unbranched chains of beta glucose

What is special about the structure of cellulose?

Every other beta glucose has to be inverted so it can join by a 1,4 glycosidic bond, meaning that hydrogen bonds form between the chains

Why does cellulose not spiral?

It has strong hydrogen bonds between the chains formed between the positively charged -OH and the negatively charged oxygen atoms

Why can humans not digest cellulose?

We lack the necessary enzyme needed to break the 1,4 glycosidic bond between the monomers of beta glucose