Biology - AS Level - 10.1 - Biological Molecules - .1 - Carbohydrates
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- Define Monosaccharide:
- Basic molecular unit (monomer) of which other carbohydrates are composed. They include the reducing sugars glucose and fructose.
- The condensation of glucose:
- to form the disaccharide, maltose.
- The condensation of glucose and fructose:
- to form the disaccharide, sucrose (a non-reducing sugar).
- Carbohydrates contain:
- Carbon, hydrogen and oxygen (must write in full) H and O are present in the ration 2H:1O.
- Glucose formula:
- C>6H>12O>6
- Recognise fructose, formula:
-
CH>2OH O CH>2OH
| /\ |
C H OH C
|\\| | /|
H C--C OH
| |
OH H
C>6H>12O>6 - Isomers of Glucose:
- fructose and galactose
- Disaccharides form when:
- 2 monos are joined together.
- Condensation:
- joining small monomers together involves removing water. This is termed condensation.
- Maltose is formed by:
- the condensation of two glucose units.
- Define GLYCOSIDIC BOND
- O left which joins the 2 units together.
-
Glucose + fructose >
formula? - sucrose + water. C>12H>22O>11 (water removed, remember!)
- Glucose + galactose >
- lactose + water
- Breaking down disacchs...
- To form monos by addition of water (hydrolysis.)
- Polysaccharides define
-
These are large polymers made of many monosaccharide monomers. These are joined by condensation reactions.
Three needed to know - Starch (2 kinds)
-
Formed by the condensation of many glucose molecules.
Amylose (helix)
Amylopectin ( branched form)
Both forms are storage molecules. They store the glucose in PLANT cells. - Glycogen
-
formed from the condensation of many glucose molecules.
More branches than amylopectin - animals more likely to need large amounts of glucose faster. - Relate starch and glycogen structures to function:
-
1. Insoluble - does not cause osmosis to take place in the starch-containing cells.
2. Mols coiled and so a large quantity can be stored in a small space.
3. The branches have many terminal glucose units which can be released for respiration
4. They are large molecules that cannot pass across the outer cell membranes and so are not "washed" out of the cells. - Cellulose:
- Made of different type of glucose called beta-glucose (like b radiation, as opposed to a (fish) glucose) - right side H and OH stick is inverted.
- Caused by condensation:
- Every other molecule inverts
- Cellulose - function and why
- Structural molecule: Instead of curling like other polys, forms long straight chains. OH groups can then form h bonds with other chains. Chains join together to give microfibrils - these are strong and used to form cell walls of plant cells.
- Saccharide derivatives:
- eg esters, alcohols, amines.
- Heterosacchs -
- eg pectins, mucilages (components of mucus, eg slug and snail trails), tree gums, chitin (found in insect exoskeletons, eg scarabs)
- Monosacchs
- gluc, fruct, galact, 100s others
- disacchs
- sucr,malt,lact
- polysacch
- starch, glycogen, cellulose.
- CONDENSATION REACTION:
- when two monosaccharides are joined together to form a disaccharide or polysaccharide. Involves the removal of water.
- GLYCOSIDIC BOND:
- The O left which joins the two units together.
- Maltose =
-
glucose + glucose. (glycosidic bond, alpha,1-4)
(1 = clock of left mol, 4 = clock of right mol) - Sucrose =
- glucose + fructose. Formula = C12H22O11 (remember water removed) Same formula for other disacchs, other monos in as level.
- Lactose =
- glucose + galactose
- POLYSACCHARIDE:
- large polymer made of many monosacch monomers. Joined by condensation reactions.
- two forms of starch
-
amylose (helix, compact)
amylopectin (branched- lots of glucose ends - can break off each end so better for getting large amounts quickly)
Amylose gets tangled in amylopectin - slinky in tree!
STORAGE MOLECULE IN PLANTS - Test for starch
-
Iodine goes brown-blue-black if starch is present.
Iodine inside helix - can't see, no longer reflected light from iodine - blue-black - To lyse
- for an animal cell to burst.
- Glycogen - what?
- storage carb of animal cells. Large amounts in liver and muscles - lots of metabolic processes (chemical reactions) in liver means needs a lot of energy.
- Function of polysacchs:
- cellulose STRUCTURAL, others storage.
- 4 reasons why are good for storage:
-
1. Insoluble - no osmosis
2. Coiled mols - large quantity can be stored in small space
3. Branches have many terminal glucose units which can be used for respiration.
4. They are large mols which cannot pass across the outer cell membranes and so are not washed out of the cells (last resort answer) - What is beta-glucose?
-
Right OH-C-H bond is upside down.
When condense every other molecule inverts
COndenses to cellulose - Structure of glucose - why good for structure of cell membranes
- Doesn't curl - long straight chains. OH groups form H bonds with other chains. Chains join to give microfibrils (strong, used to form the cell walls of plant cells)
- starch, lactose, sucrose, fructose, glucose and maltose sweetest - least
- fructose, glucose, sucrose, maltose, lactose, starch.
- What mono and dis don't turn yellow in Benedict's?
- sucrose - non-reducing sugar.
- Benedict's test - 6 steps:
-
1. Set up water bath using standard lab equipment.
2. Place small amount of substance to be tested into test tube.
3. Add enough distilled water to dissolve, unless already in liquid form.
4. 10 drops of B Sol to test tube and place in bath.
5. Record colour change
6. If none in 10 mins class as negative result and fresh sample tested for a non-reducing sugar. - Starch test
- Put smallng tray and add a couple of drops of nto a spottting tray and add a couple of drops of iodine solution. Recorch is present.change. If it goes black then starch is present.
- Testing for a non-reducing sugar:
-
ONLY TO BE CARRIED OUT IF NEGATIVE RESULT HAS BEEN RECORDED FROM BENEDICT'S TEST [must be said for full marks]
1. Add no more than 3 drops of dil HCl to the solution to be tested in a tt. 2. Boil in water bath for 5mins. 3. Remove tt from bath and add NaHCO>2 little at time until fizzing stops (neutralises acid). 4. Add 10 drops Bs to tt and return to bath. 5 . If change from blue to brick red/orange, it can be concluded that a non-reducing sugar is present. - Saccharides made up of:
-
-
S_/ \_R
\_/
S = sweet group, R = reducing group - Sucrose properties:
- SRRS - sweet, doesn't reduce
- Lactose properties:
-
RSSR - not very sweet
Good because baby animals can be weaned off their mother's milk. - Maltose properties:
- RSRS - sweeter than lactose, not as sweet as sucrose, reduces more slowly than lactose but faster than sucrose.