Unit 1A.3 _ CARBOHYDRATES 2_ POLYSACCHARIDES.pptx

lesson 1.3 carbohydrates As level biology edexcel

1. Lesson 1A. 3 CARBOHYDRATES 2: POLYSACCHARIDES

2. Which one of them need more time to be finished or to be created?

3. Which one of them you think it will need more time to unbind?

4. Learning Objectives Know the difference between monosaccharides, disaccharides, and polysaccharides, including glycogen and starch. Explain how monosaccharides join to form polysaccharides through condensation reactions, forming glycosidic bonds, and how these can be split through hydrolysis reactions. Relate the structures of monosaccharides, disaccharides, and polysaccharides to their roles in providing and storing energy.

5. Our focus Let’s zoom into the bread – it’s rich in carbohydrates . But what are carbs actually made of?” Today, we’ll focus on the carbohydrates — especially the more complex ones: Polysaccharide

6. 3. POLYSACCHARIDES Polysaccharides are carbohydrate polymers; repeated chains of many monosaccharides joined by glycosidic bonds in a condensation reaction. Molecules with between 3 and 10 sugar units are known as oligosaccharides, while molecules containing 11 or more monosaccharides are known as true polysaccharides. The glycosidic bond between two glucose units is split by a process known as hydrolysis. The hydrolysis reaction is the opposite of the condensation reaction that created the molecule, so water is added to the bond. Disaccharides break down to form two monosaccharides . Hydrolysis takes place during digestion. In muscle and liver cells, the carbohydrate stores are broken down to release sugars for use in cellular respiration.

7. 3. POLYSACCHARIDES

8. PROPERTIES OF POLYSACCHARIDES The structure of polysaccharides makes them ideal as energy storage molecules within a cell. They can form very compact molecules , which take up little space. They are physically and chemically inactive , so they do not interfere with the other functions of the cell. They are not very soluble in water , so they have almost no effect on water potential within a cell and cause no osmotic water movements.

9. CARBOHYDRATES AND ENERGY MONOSACCHARIDES AND DISACCHARIDES Every chemical reaction taking place in a cell needs energy. This energy is supplied by a substance called adenosine triphosphate, ATP. This ATP comes from the breakdown of the monosaccharide glucose, using oxygen, in the process of cellular respiration . Foods containing monosaccharides and disaccharides are a good source of relatively instant energy. However, these cannot be used to store energy because they are chemically active, and they are very soluble in water, so they affect the water balance of the cells.

10. POLYSACCHARIDES 1. Starch Starch is the storage polysaccharide of plants It is stored as granules inside plant cells Plants make glucose during photosynthesis and the molecules of glucose are joined to make the polysaccharide starch Starch is constructed from two different polysaccharides Amylose and amylopectin.

11. Starch Structure: Starch is constructed from two different polysaccharides 1. Amylose Unbranched helix-shaped chain with 1,4 glycosidic bonds between α-glucose molecules. A helix is a spiral shape The helix shape enables it to be more compact and thus more can be stored . 2. Amylopectin A branched molecule containing 1,4 glycosidic bonds between α-glucose molecules and 1,6 glycosidic bonds. The branches result in many terminal glucose molecules that can be easily hydrolysed for use during cellular respiration or added to for storage Both forms of starch are insoluble, so they do not dissolve and won't alter the water potential of cells.

12. Amylose and Amylopectin

13. Starch Function: Starch is the storage polysaccharide of plants ; it is stored as granules in plastids. Plastids are membrane-bound organelles that can be found in plant cells. They have a specialised functio n, e.g., amyloplasts store starch grains and chloroplasts carry out photosynthesis. The amylose in starch has a helical structure, which makes it very compac t, meaning that much can be stored in a small space. The amylopectin in starch has branches that provide many terminal glucose molecules that can be easily hydrolysed for use during cellular respiration or added for storage.

14. 2. Glycogen: Glycogen is the storage polysaccharide of animals and fungi It is highly branched and not coiled Glycogen is compact, which means that much can be stored in a small space. Liver and muscle cells have a high concentration of glycogen, present as visible granules ; this enables a high cellular respiration rate.

15. Glycogen Structure & Function: Glycogen contains both 1,4 and 1,6 glycosidic bonds. Glycogen is more branched than amylopectin The branching provides more terminal glucose molecules, which can either be added to or removed by hydrolysis ; this allows the quick storage or release of glucose to suit the demands of the cell This is essential in animal cells as animals are very metabolically active. Glycogen is compact , which means that much can be stored in a small space. Liver and muscle cells have a high concentration of glycogen , present as visible granules ; this enables a high cellular respiration rate. Glycogen is insoluble

16. Glycogen Structure & Amylopectin :

17. Glycogen Structure & Amylose :

18. Quick Q&A: “Which polysaccharide is best for quick energy release, and why?” What is the main structural difference between glycogen and amylose? Why is glycogen a better storage carbohydrate than amylose for animals? Both glycogen and amylose are made of glucose units. Why does amylose suit plants while glycogen suits animals?

19. Quick Q&A: