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Test questions-Homework
October 5, 2012, 9:19 am
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2f. How does the structute of glycogen make it more suitable for its function than starch?
answer: It has more branches of amylopectin extending from the chain, the 1-4 chains are shorter and so are more compact and form granules in animal cells.

New questions: Why is glcyogen’s structure more suited to animals than starch’s? (2)
Why are glycogen and starch called ‘storage’ molecules, whereas alpha glucose is termed ‘energy soruce’? (1)

Comment by stefansoyombo

To answer Stefan’s 2nd question:
Starch and glycogen are considered ‘storage’ molecules because they are both ways of storing glucose (the energy source for most cells). Starch and glycogen are both polymers formed from alpha glucose, produced by repeated condensation reactions between glucose molecules (making amylose and amylopectin). When the glucose is needed, starch and glycogen can be broken down by hydrolysis reactions to glucose molecules, which can then be respired to release energy. It is beneficial for us to store energy for later use as otherwise the glucose is used up all at once.

Comment by charlieshah

Q1) The general strucure of glycogen has many side branches. This structural difference allows more glucose to be released quickly which is important for quick energy release in animals. Starch is good for storage, but glycogen is more effiicient as an energy source in animals.

Comment by Deelan Vadher

New Questions:
Which α-glucose polymer is found in plant cells? (1)
What kind of reaction occurs to break the bonds in a disaccharide? (1)
Name the specific bond formed to make a dissacharide? (1)

Comment by danielwatt

a) Starch (mixture of two polysaccharides- amylose and amylopectin)

b) A hydrolysis reaction involves adding a molecule of water (H2O) to a glycosidic bond which break it apart.

c) Glycosidic bonds

Comment by Deelan Vadher

Some new questions…
1. What is the name of the reaction that breaks a disaccharide into two alpha monosaccharides?
2. Why is cellulose the suitable molecule for plant cell walls?

Comment by charlieshah

1) A hydrolysis reaction involves adding a molecule of water (H2O) to a glycosidic bond which break it apart.

2) Cellulose is made up of long unbranched chains of Beta-Glucose. The bonds between the sugars are straight, so the cellulose chains are straight. The cellulose chains are linkes together by hydrogen bonds to from strong microfibrils. These strong fibres mean that cellulose provides structural support for cells (e.g in plant cell walls)

Comment by Deelan Vadher

2) The person above has covered most of the bases, but it’s also suitable because it’s insoluble and because the microfibrils form a sort of mesh; it’s not a solid impermeable layer, so it allows molecules to freely diffuse between the strands.

Comment by charlieprudence

New Questions:
1. Why do the long chains of amylose coil into a spring?
2. Why is it important that starch and glycogen do not dissolve?
3. Which type of glucose cannot be respired, and why?

Comment by sarahroche12

1) The angles formed by the glycosidic bonds give it a coiled structure (almost cylinderical)

2) Their insolubility prevents water to enter via osmosis (and swell). They are therefore more effiecient for storage.

3) Beta-glucose. Humans are unable to digest cellulose because the enzymes to breakdown the beta bonds are not found in vertebrates. Some bacteria contain these enzymes and thus are able to breakdown cellulose.

Comment by Deelan Vadher

To add to deelan’s point about structure, I’d say its just spring/helix like. However in cellulose, about 60-70 cellulose molecules become cross linked by hydrogen bonds to form microfibrils which make macrofibrils which criss cross to strengthen the wall even more.

Comment by stefansoyombo

New Questions:

1 What is the name of the chemical process by which 2 molecules join to form a disaccharide by loosing H20?

2 Give an example of the disaccharide formed after two a-glucose molecules react?

3 What does removing water from two monosaccharies cause?

4 Give an example of a polymer formed from a-glucose?

5 Where do you find starch and amylose in plants?

6 What polymer is only found in plants?

7 Why are polymers important?

8 How is the structure of cellose important?

9 Why is glycogen structure more suited to animals?

Comment by meganbpotter

*the arrangement of macrofibrils blows water to move through and along cell walls and pass in and out easily. It also determines how cells can grow or change shape.
9. Has more branches of amylopectin and is more compact than starch’s structure as tim 1-4 glucose chains are shorter.

Comment by stefansoyombo

Answers are :
1- A condensation reaction
2- Maltose
3- The formation of a disaccharide molecule resulting from a condensation reaction
4- Starch
5- You find them in chloroplasts or amyloplasts in the plant cells
6- Cellulose
7- Cellulose is important as it forms the cell wall of plant cells, giving the cells a strong structure. Starch is an important polymer, as it provides cells in plants with energy needed for specific processes, e.g active transport. Other polymers are also important as they form plastics, but that’s not relevant for AS biology
8- Cellulose has a rigid structure which reduces flexibility and increases strength. It is insoluble, which is useful as it prevents plant cells from becoming saturated and bursting, however the cellulose cell walls do let certain useful substances into the cell
9- Glycogen is highly branched (more so than starch) making it more compact and easy for animals to digest and use as an energy source.

Comment by benpessell

Amylose is an unbranched form of starch. When iodine solution as added to starch, iodine fits into the helix of the amylose molecule, producing a colour change.

State the colour of iodine solution in the prescence of starch. [1]

Hydrogen bonds hold the amylose molecule in its helical shape
Describe how a hydrogen bond is formed. [2]

Comment by Deelan Vadher

Well iodine, when used in the context of experiments is actually called iodine in potassium iodide solution and the iodine molecules get trapped in the coils of the spring in amylose producing a colour change from yellow/brown to blue/black.

Comment by stefansoyombo

Also, hydrogen bonds form when a slightly negatively charged part of a molecule comes close to a slightly positively charged hydrogen atom in tim same/another molecule. Usually seen in water (H2O)
Many thousands of hydrogen bonds form in polymers and this helps Ty stabilise the structure of the molecule

Comment by stefansoyombo

When hydrogen is bonded to a highly electronegative atom (in biology, it’s generally nitrogen or oxygen – here it’s oxygen), the bond becomes highly polarised. The hydrogen has a partial positive charge and the oxygen has a partial negative charge. A positive hydrogen molecule in an amylose molecule is attracted to a negative oxygen molecule in another monomer unit and forms a hydrogen bond.

Comment by charlieprudence

Describe how glycosidic bonds are formed and broken in living organisms. [7]

Comment by Deelan Vadher

How glycosidic bonds are formed:
Two monosaccharide molecules form a glycosidic bond in a condensation reaction, in which a molecule of water is lost. Two -OH groups react together and an oxygen bridge is formed.
In living organisms, an enzyme catalyses this reaction, generally for the formation of storage molecules. For example, glycogen synthase is involved in glycogenesis.
How glycosidic bonds are broken:
Glycosidic bonds are broken in a hydrolysis reaction, where a molecule of water is added. The oxygen bridge is broken.
In living organisms, this can either be by acid hydrolysis in the stomach, or by enzyme catalysed reactions.

Comment by charlieprudence

Describe how the structure of starch makes it suited to its function. [6]

Comment by Deelan Vadher

starch is insoluble in water so it doesn’t cause water to enter the cells by osmosis, which could make them swell. This makes it good for storage.

Comment by roobennithi

1e) what molecule is formed in the bond between two alpha glucose molecules?
1g) how does the structure of an alpha glucose monsaccharide differ to that of an alpha glucose disaccharide?

Comment by georgiawinfield

1e) Maltose
1g) The monosaccharide contains H20 where as when two a-glucose monosaccharides join it removes H20 so the disaccharide doesn’t contain H20.

Comment by meganbpotter

some new questions:

1) what are the properties that are common to all monosaccharides and disaccharides?
2) for the protein’s secondary structure, a chain of amino acids coils to form an alpha helix.
i) what are the coils held by?
ii) how else can a secondary structure be formed apart from forming into an alpha helix?
3) what two beta glucose join together, what has to happen to form the bond and how do you break the bond?

Comment by harveervirk6196

1. They are both sugars/ carbohydrates and contain carbon, hydrogen and oxygen

2.
(i) They are held by hydrogen bonds
(ii) It can be formed as a beta pleated sheet

3. Many beta glucose joined together forms a polysacchharide known as ‘cellulose’. The chain of cellulose molecules are joined together by hydrogen bonds which from strong microfibrils. Cellulose can be broken down into glucose molecules by ‘cellulase’.

Comment by roobennithi

What differs between alpha and beta glucose?
How is cellulose suited to making up the cell walls of plants?
How is the structure of starch and glycogen suited to being used as storage molecules?

Comment by zeemitha

– The OH on alpha glucose faces upwards and downwards on the beta glucose.

-Cellulose is very long, unbranched and has microfibrils which makes it strong. This makes it perfectly suited for its function.

-Starch is a large molecule which makes it good for its function of being a ‘energy storage’ in a plant. Glycogen is very compact, it has loads of branches meaning that stored glucose can be released quickly.

Comment by roobennithi

alpha glucose forms two polymers, what are they?
Where are these polymers found in general?
What are they used for?
Give a short description of the structure of cellulose

Comment by roobennithi

1. Alpha glucose forms starch and glycogen.
2. Starch is generally found in plants and glycogen is generally found in animals.
3. They are storage molecules.
4. Cellulose is a polymer of beta-glucose. It forms long, straight strands. Hydrogen bonds form between these strands to form microfibrils.

Comment by charlieprudence

List two examples of monosaccharides, disaccharides, and polysaccharides (6)

Comment by roobennithi

monosaccharides: glucose, fructose
disaccharides: maltose, sucrose
polysaccharides: cellulose, glycogen

Comment by charlieprudence

you could also have galactose as a monosaccharide, lactose as a disaccharide and starch as a polysaccharide

Comment by charlieprudence

Which disaccharide is composed of two glucose molecules connected through an a-1,4 glycosidic bond?
List the features of cellulose that make it a good structural molecule for plant cell walls?
What’s the equation for the condensation reaction to produce maltose?

Comment by charlieprudence

1. Maltose
2. Straight strands, that form hydrogen bonds between each other to form strong microfibrils
The microfibrils form a mesh with gaps between them, so molecules can diffuse freely through; it’s not a barrier to diffusion or osmosis.
Cellulose is insoluble.
3. 2 x C6H12O6 => C12H22O11 + H20

Comment by charlieprudence

1. What type of sugar is maltose?
2. Which glucose polymer is used for making cell walls?
3. What type of glucose forms starch?
4. What is the function of glycogen?
5. What is the main difference between glycogen and starch?

Comment by milliepaine

1)Maltose is a disaccheride made of two alpha-glucose
2)Cellulose
3)Beta-glucose forms starch
4)Glycogen’s function is as an energy store that is used up in respiration among other things in the body.
5)The main difference between glycogen and starch is that glycogen is a smaller molecule because it is more branched.

Comment by elliswhyte

2. I) Glycogen is better suited to it’s function than starch mainly because it is a smaller molecule. The reason it is a smaller molecule is that it is more branched than starch, and therefore more compact, making it preferable as an energy store in animals as it takes up less room.

New question: What is it about it’s structure, in particular it’s branches, that makes glycogen a good fuel for respiration?

Comment by elliswhyte

How do the branches in amylopectin and glycogen form?

Comment by charlieprudence

1)What makes up the microfibris of cellulose and what effect does this have?

2)What is the usage of glycogen?

Comment by graciemarlow

What reaction results in a glycosidic bond between glucose molecules?

What is the name of the disaccharide formed when two alpha glucose molecules bond?

Comment by alexmolyneux




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