BIO MOLECULES Pt 2 (Carbohydrates)
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BIO MOLECULES Pt 2 (Carbohydrates)
biology unit bio molecules
Second part of the series - on carbohydrates mainly.
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
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 -
(tend to occur in nature as ring structures)
(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
reaction, forming a
A new covalent bond called a
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 ______.
because of the shape of the
molecules and the formation of
bonds. Makes amylose quite
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
molecules and branched
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
(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
can form between them.
About 60-70 cellulose molecules become cross-linked by hydrogen bonds to form bundles called
These, in tern, are held together by more hydrogen bonds to form larger bundles called
(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
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