Carbohydrates

Question 1

Carbohydrate functions
[SISTER acronym]

Answer 1

Substrate for respiration (glucose is essential for cardiac tissues)
•Intermediate in respiration (glyceraldehydes)
•Structural (cellulose in plants, chitin in fungi, peptidoglycan/murein in bacteria)
•Transport (sucrose is transported in the phloem of a plant)
•Energy stores (starch, glycogen)
•Recognition of molecules outside a cell (attached to proteins or lipids on cell surface membrane)

Question 2

Starch is formed when […] monomers join together

Answer 2

Alpha glucose

Question 3

What is starch made up of

Answer 3

Amylose & amylopectin

Question 4

How are glucose molecules bonded in amylose

Answer 4

Using 1-4 glycosidic bonds

Question 5

What shape does amylose form

Answer 5

A helix shape
-> this stabilises the structure as it allows H bonds to form throughout
—> therefore making the molecule more compact + less soluble

Question 6

what bonds is amylopectin made of

Answer 6

1-4 glycosidic between a-glucose molecules but also 1-6 glycosidic bonds (every 25 glucose subunits)

Question 7

What structure does amylopectin have

Answer 7

A branching one

Question 8

What is cellulose

Answer 8

The main structural constituent of plant cell walls

Question 9

Cellulose has strong [………] which keeps the plant cell walls strong, which is important as plants don’t have a skeleton

Answer 9

Microfibrils

Question 10

Unlike glycogen and starch, cellulose is made up of […]

Answer 10

Beta glucose

Question 11

Every molecule in cellulose is rotated by […]

Answer 11

180°

Question 12

What bonds do cellulose have

Answer 12

• 1-4 glycosidic bonds that form between adjacent beta glucose molecules
• bonds between the rotated beta glucose molecules on the same cellulose chain and between the rotated B glucose on cellulose chains that lie alongside each other

Question 13

What is glycogen

Answer 13

The main storage polysaccharide in animals & fungi

Question 14

Why is glycogen so compact

Answer 14

Due to it forming more branches (than amylopectin)

Question 15

Why is it important that glycogen is a branched polysaccharide

Answer 15

It being branded makes it easier to remove glucose molecules when they are needed
-> hydrolysis can happen quicker when urgent need for glucose

Question 16

What bonds does glycogen have

Answer 16

1-4 and 1-6 (every ~10 subunits) glycosidic bonds

Question 17

Basic structure + functions of glycogen

Answer 17

STRUCTURE:
shorter chains than starch and is more highly branched

FUNCTIONS:
carbohydrate storage in animals, structurally suited for because:

• insoluble so does not tend to draw water into cells by osmosis
• insoluble so does not diffuse out of cells
  compact so a lot can be stored in a small space
• more highly branched than starch so has more ends that can be acted on simultaneously by enzymes so is therefore more rapidly broken down to form glucose monomers, which are used in respiration - important because animals have a higher metabolic rate and therefore respiratory rate than plants because they are more active.

Question 18

Basic structure + functions starch

Answer 18

STRUCTURE:
made up of chains of alpha-glucose linked by glycosidic bonds formed by condensation reactions.
chains may be branched or unbranched - unbranched chain wound into a tight coil that makes the molecule very compact

FUNCTION:
main role is energy storage for plants, structurally suited for because:

• insoluble and so doesnt affect water potential, so water isnt drawn into cells by osmosis
• large and insoluble so does not diffuse out of cells
• compact so a lot of it can stored in a small space
• when hydrolysed it forms alpha-glucose, which is easily transported and readily used in respiration
• branched form has many ends, each of which can be acted on by enzymes simultaneously meaning that glucose monomers are released very rapidly

Question 19

Basic structure + functions of cellulose

Answer 19

STRUCTURE:
made of monomers of beta-glucose rather than alpha glucose, unlike starch and glycogen.
unlike a coiled chain in starch, cellulose has straight unbranched chains that run parallel to one another, allowing hydrogen bonds to form cross-links between adjacent chains. this strengthens the molecule and makes it a suitable structural material.

FUNCTIONS:
provides rigidity to the plant cell and prevents the wall from bursting as water enters it by osmosis.
structurally suited to its function because:

• made up of beta-glucose and so form long, unbranched chains
• chains run parallel to each other and are crosslinked by hydrogen bonds that add collective strength
• molecules grouped to form microfibrils which are grouped to form fibres that provide more strength