Topic 4: Cellulose and plant cell wall Flashcards
What are the 2 isomers of glucose? (2 points)
- Alpha glucose / α glucose
2. Beta glucose / ß glucose
The _ glucose molecule has two hydroxyl groups ________ to one another.
α (alpha)
adjacent
Cellulose if made from _____ _-________ __________.
1,4 glycosidic bonds cannot be made because the two ________ groups are not next to each other.
One glucose molecule must be ________ (flipped) so bonding can take place.
Then a __________ ________ joins two β-glucose monomers together.
A _ , ________ bond forms
Cellulose if therefore an ___________ molecule.
many β-glucose molecules
(beta glucose)
hydroxyl
inverted
condensation reaction
β 1,4 glycosidic
unbranched
Describe the structure of starch (4 points)
- Many alpha glucoses
- Branched
- 1,4 and 1,6 glycosidic bonds
- Compact
What is the function of starch? (1 point)
- Energy storage molecule in plants as it is easily hydrolysed to release glucose.
What are the properties of starch? (1 point)
- Insoluble in water (no osmotic effect)
Describe the structure of cellulose (4 points)
- Made of many beta glucoses
- Every alternate beta glucose is inverted
- Unbranched
- 1,4 glycosidic bonds - form between 2 OH groups with removal of water
What is the function of cellulose? (2 points)
- Cellulose microfibrils are a component of the plant cell wall for strength and support to plant cells and allow turgor (for further support)
What are the properties of cellulose? (2 points)
- Insoluble in water
2. High tensile strength
Key Summary: What are the similarities between the structure of starch and cellulose?
(3 similarities)
- Both made of glucose molecules
- Both have 1,4 glycosidic bonds
- Both are polysaccharides
Key Summary: What are the differences between the structure of starch and cellulose?
(4 differences)
- starch is made of alpha glucose, cellulose of beta glucose
- starch is branched (amylopectin) with 1,6 glycosidic bonds, cellulose is unbranched/straight chain
- starch has alpha 1,4 glycosidic bonds, cellulose has beta 1,4 glycosidic bonds
- in starch all molecules are in the same orientation, but in cellulose every alternate glucose is inverted
Key Summary: Describe the structure/formation of a cellulose molecule. (4 points)
- many beta glucoses
- joined by beta 1,4 glycosidic bonds between 2 OH groups in condensation reactions with removal of water
- every alternate glucose molecule is inverted
- long unbranched/straight polysaccharide chain
How does cellulose form the cell wall? (5 steps - start from cellulose being formed)
- Beta glucose forms cellulose molecules
- Cellulose molecules form microfibrils
- Microfibrils are arranged at angles in layers
- Microfibrils are bonded together in a matrix of hemicelluloses and pectins
- Lignin (secondary thickening) added to form the secondary cell wall
What is a cellulose molecule? (3 points)
- Long chains of several thousand beta glucose molecules,
- every alternate one inverted,
- joined by 1,4 glycosidic bonds in condensation reactions.
Many (60-70) cellulose _________ (long chains of glucose) lie parallel to each other and are cross linked by _________ _______ to form a cellulose _________.
molecules
hydrogen bonds
microfibril
_________ ______ form between δ+ _______ atoms and δ– ______ atoms on ____ groups that stick out from the beta glucoses on adjacent cellulose molecules.
This is called ______-________
Hydrogen bonds
hydrogen
oxygen
OH
cross-linking
Key Summary: Describe the {structure/formation} of a cellulose microfibril (5 steps)
- beta glucoses joined by β 1,4 glycosidic bonds in condensation reactions,
- with every alternate glucose molecule inverted,
- forming an {unbranched chain/cellulose molecule}.
- 60-70 cellulose molecules lie parallel to each other
- and are cross-linked and held together by hydrogen bonds between polar groups on beta glucoses of adjacent cellulose molecules.
Key Summary: Describe the role of hydrogen bonds in the formation of a cellulose microfibril
(4 steps)
- There are weak intermolecular forces of attraction between δ+ and δ- dipoles.
- Hydrogen bonds form between beta glucoses on adjacent cellulose molecules (δ+ H on OH group of one and δ- O on CH2OH group of another).
- Hydrogen bonds cross link cellulose molecules in a microfibril to hold the parallel cellulose molecules together.
- Which contribute to the strength of the microfibril.
Microfibrils are laid down in ______ at different ______ for strength.
This arrangement allows ______, with some ________ and it also allows for exchange of materials through the _____.
layers
angles
rigidity
flexibility
wall
The layers of microfibrils are embedded in a matrix of ___________ and ______ (short, branched polysaccharides).
This forms the ______ cell wall (Present in growing plant cells).
What properties does this arrangement give the ________ cellulose cell walls? (2 properties)
hemicelluloses
pectins
primary
primary
- Strength
- Flexibility
The secondary cell wall is formed once the cell has stopped __________.
_______ (secondary thickening) is then added to further strengthen the cell wall and at this point the cell wall becomes less _________ to water.
The cell wall can now carry out its function – ________ and ________.
growing/elongating
Lignin
permeable
strength
support
Key Summary: Describe the structure of a plant cell wall (5 points)
- made of cellulose – molecules made of many beta glucoses, every alternate inverted, β 1,4 glycosidic bonds, unbranched
- bundles of many cellulose molecules form microfibrils held together by hydrogen bonds between adjacent molecules
- layers of microfibrils laid down at different angles to each other form a mesh in a matrix of hemicelluloses /pectins
- has primary and secondary cell walls.
- lignin present in secondary cell wall.
Which contains 1,6 glycosidic bonds, starch or cellulose? (or both or neither)
starch
Which is an unbranched molecule, starch or cellulose? (or both or neither)
cellulose
Which is a polymer of glucose, starch or cellulose? (or both or neither)
both
Which is found in plant cell walls, starch or cellulose? (or both or neither)
cellulose
Which is made of alpha glucose, starch or cellulose? (or both or neither)
Starch
Which contains 1,4 glycosidic bonds, starch or cellulose? (or both or neither)
both
Which can form hydrogen bonds with other similar molecules, starch or cellulose? (or both or neither)
cellulose
Which is a glucose store in animal cells, starch or cellulose? (or both or neither)
neither
Which provides support in a plant, starch or cellulose? (or both or neither)
cellulose
Which is formed by condensation reactions, starch or cellulose? (or both or neither)
both
Does cellulose contain alpha or beta glucose?
beta glucose
Is starch unbranched or branched?
branched
What is the function of cellulose in a plant cell? (1 point)
- (component of) Cell wall (for strength and support)
What is the function of cellulose in the diet? (2 points)
- Roughage/fibre
2. Keeps food moving through the digestive system
Which type of bond(s) are found in a cellulose molecule?
1,4 glycosidic bonds
Which type of bond(s) link cellulose molecules in a cellulose microfibril?
Hydrogen bonds
State 4 properties of starch that make it a good energy storage molecule (4 properties)
- Large
- Insoluble
- Compact
- Easily hydrolysed
Is a cellulose molecule branched or unbranched?
Unbranched
How many cellulose molecules make up a cellulose microfibril?
60-70
What does cellulose provide in the plant cell wall? (2 things)
- Strength
2. Mechanical support
What is the bond that holds together adjacent cellulose molecules in a cellulose microfibril?
Hydrogen bond
