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The functions of carbohydrates in organisms include: (3)
- Energy source - released from glucose during respiration
- Energy store - eg. starch
- Structure - eg. cellulose
- (Some carbohydrates also form part of larger molecules like nucleic acids and glycolipids.)
Carbohydrates contain the elements:
Carbon, hydrogen and oxygen.
Why are carbohydrates called carbohydrates?
How many percent of organic matter in the cell does it make up?
- Essentially means "hydrated carbon" - because the elements are found in proportions Cn(H2O)n - for every carbon present, the equivalent of a water molecule is also present.
- Makes up 10% of organic matter of a cell.
There are a number of different monosaccharides, all containing between 3 and 6 carbon atoms. All have similar properties, what are they? (properties common to all mono & disaccharides)
- Are soluble in water
- Are sweet tasting
- Form crystals
Monosaccharides are grouped according to the number of carbon atoms present. Name the groups with 3, 5 & 6 carbon atoms. Which is the most common and give example for that one.
- 3-carbon monosaccharides - triose sugars5 - pentose sugars (tend to occur in nature as ring structures)
- 6 - hexose sugars (Most common, eg. glucose and fructose. Tend to occur in nature as ring structures.)
Different shaped forms of the same molecule are called?
- eg. alpha-glucose & beta-glucose
What is the difference between alpha and beta glucose?
- In the alpha-glucose ring, the OH at C1 is below the plane of the ring. (H is above)
- In beta-glucose, the OH at C1 is above the plane of the ring. (H is below)
- (The difference in structure leads to some very different properties)
Two monosaccharide molecules can be joined together in a ________ reaction, forming a _________ molecule. What is the new covalent bond that is formed called? What is eliminated/released?
- Two monosaccharide molecules can be joined together in a condensation reaction, forming a disaccharide molecule.
- A new covalent bond called a glycosidic bond forms, and water is eliminated.
Name some polysaccharides
- Starch, glycogen, cellulose
- Forming and breaking these involves forming and breaking of glycosidic bonds.
The breaking down of glucose in living organisms takes place in a series of _____. Each ____ is driven by a specific _____.
Steps, step, enzyme
Animals and plants have enzymes that break ____-glucose only. They cannot break down ____-glucose because of its different arrangement of the __ and ___ at ___.
- break alpha-glucose only
- cannot break down beta-glucose
- arrangement of the H and OH at C1.
- (Because enzyme function is based on shape)
Two alpha-glucose bonded together form a disaccharide called?
Many glucose molecules joined together (from condensation reactions repeated many times) can form a molecule called?
The glycosidic bond between all the glucose subunits in amylose occurs between carbon number what and what? So it is often called what?
- Occurs between C1 of one and C4 of the next.
- Often called a 1,4-glycosidic bond
Long chains of amylose ____ into a _____ because of the shape of the ______ molecules and the formation of _______ bonds. This makes amylose quite ______.
coil into a spring because of the shape of the glucose molecules and the formation of glycosidic bonds. Makes amylose quite compact.
Explain why iodine is used as a starch test.
Because iodine molecules become trapped in the "coils" of the spring of the polysaccharide, and this causes iodine (in potassium iodide solution) to change colour from yellow/brown to blue/black.
What is one feature that is different from a polysaccharide and a mono/disaccharide?
These large molecues are insoluble in water.
What is contained in starch? Where is starch stored in? What can it be broken down into?
- Consists of a mixture of long, straight-chain amylose molecules and branched amylopectin.
- Stored in chloroplasts and elsewhere in plant cell in membrane-bound starch grains. Cells of plant storage organs (eg. potato tubers) contain a lot of starch grains.
- Starch can be broken down to glucose molecules, which may then be respired to release energy.
What is the difference between starch and glycogen?
- Starch is the energy-storage polysaccharide in plants, whereas glycogen is in animals.
- Glycogen have shorter 1-4 linked glucose chains and have many more branches extending from chain. (More chains means glucose can be released more quickly)
- Means is is more compact than starch, and forms glycogen granules in animal cells (esp. liver and muscle cells)
Features of energy-storage molecules starch and glycogen?
- They do not dissolve - stored glucose does not affect water potential (vital in both plant and animal cells because glucose can be stored in cells without dramatically reducing its water potential).
- They hold glucose molecules in chains so that they can easily be "broken off" from the ends to provide glucose for respiration when required (by enzymes).
When beta-glucose form polymers through numerous condensation reactions, what shapes are produced?
- Long and straight (can contain 10,000 beta-glucose molecules)
- Stronger than the chains in amylose
- Called cellulose chains
- Only found in plants, but most abundant structural polysaccharide in nature.
Why is cellulose strong?
- Because the glucose monomers contain so many OH groups, many hydrogen bonds can form between them.
- About 60-70 cellulose molecules become cross-linked by hydrogen bonds to form bundles called microfibrils.
- These, in tern, are held together by more hydrogen bonds to form larger bundles called macrofibrils.
- (So in summery, the numerous hydrogen bonds between the cellulose chains add to strength of the structure. )
Macrofibrils are embedded in a polysaccharide glue of substances called what to form cell walls?
Structure and function of plant cell wall?
- Strong - provide great strength to each cell, supporting the whole plant.
- Arrangement of macrofibrils allows water to move through and along cell walls, and water can pass in & out of cells easily.
- Wall prevents cell from bursting and makes them turgid
- Arrangement of macrofibrils in cell walls determines how cells can grow & change shape - eg. guard cells and stomata
- Cell walls can be reinforced with other substances to provide extra support or to make it waterproof.
Give examples of other structural carbohydrates.
- Chitin forms exoskeleton of insects
- Peptidoglican is basis for cell wall found around most bacterial cells