Carbohydrates Flashcards
What three elements are in carbohydrates
Carbon, hydrogen and oxygen
What are sugars with six carbon atoms called
Hexose sugars
Aqa simple glucose molecule
Could be asked to draw it
What are monosaccharides
Single sugar molecule
Three examples of monosaccharides
Glucose, galactose and fructose
Key feature of monosaccharides
Soluble in water- large number of OH groups- hydroxyls groups which can form hydrogen bonds with water molecules- another name for this is hydrophilic- dissolve in water.
Molecules with 5 carbon atoms
Pentose monosaccharides
Free science lessons structure of ribose
Go on video scroll to end
What are isomers
The two forms of glucose
What do the numbers represent
Carbon atoms
The difference between the glucose isomers
The position of the hydroxyl (OH) group on carbon 1
Difference between alpha and beta glucose
-If carbon 1 hydroxyl points below below the ring then we call this isomer alpha glucose.
- If the carbon 1 hydroxyl group points above the ring then we call this isomer beta glucose.
How are disaccharides formed
They are formed when two monosaccharides chemically react together
What is the disaccharide called when two alpha glucose molecules react
Maltose
When we make a disaccharide what do we also produce
A molecule of water- the water molecule is formed from a hydrogen atom from one of the monosaccharides and a hydroxyl group from the other - condensation reaction.
What is the bond between monosaccharide molecules when forming a disaccharide
Glycosidic bond - formed between carbon 1 on one alpha glucose and carbon 4 on another= 1,4 glycosidic bond.
Free science lessons maltose
Need to know structure
What happens if we add water to a disaccharide
Breaks the glycosidic bond- converts the disaccharide back into its monosaccharides- hydrolysis reaction -in cells this reaction is normally carried out by enzymes.
The three disaccharides you need to know
maltose= glucose+glucose
Sucrose=glucose+fructose
Lactose=glucose+galactose
Is glucose soluble or insoluble in water
Soluble- contains a large number of hydroxyl groups- hydroxyls groups are polar due to the small negative charge on the oxygen atom and the small positive charge on the hydrogen atom- can form hydrogen bonds with water molecules.
Problem with glucose being soluble
If a cell contains a large amount of dissolved glucose then this can cause water to move into the cell by osmosis - to solve this problem plant cells store glucose as starch
What is starch
A storage form of glucose- find it in starch grains
What are the two molecules starch consist of
Amylose and amylopectin
Structure of amylose
Polymer of alpha glucose molecules- also joined by 1,4 glycosidic bonds- each bond forms in a condensation reaction, producing a molecule of water. The amylose molecule then twists into a compact helix with hydrogen bonds forming between glucose molecules along the chain -holding it in place.
How do cells convert starch back to glucose
When the cell needs glucose, water is used to break the glycosidic bonds- hydrolysis reaction.
Why does starch have a helical shape
Makes starch a very compact molecule
Structure of amylopectin
Polymer of alpha glucose joined by 1,4 glycosidic bonds. The chains have a branch every 25-30 glucose molecules. The branch is simply another chain of alpha glucose molecules joined by 1,4 glycosidic bonds. Joining the branches is a glycosidic bond between carbon 6 and carbon 1- coil up compact.
Is starch soluble or insoluble in water
Insoluble- means starch doesn’t cause water to enter cell by osmosis
How is starch broken down
Enzymes used to break down the glycosidic bonds in starch- hydrolysis reaction- requires water- enzymes act at end of molecules- amylopectin has lots of branches- has lots of ends- rapid breakdown.
What is the animal glucose storage molecule
Glycogen- found in liver and muscle cells- polymer of alpha glucose- most alpha glucose molecules joined by 1,4 glycosidic bonds, glycogen also contains branches, at the branch points are 1,6 glycosidic bonds. The main difference is that glycogen is more branched than amylopectin- makes it more compact- lots of free ends- rapid breakdown.
Why does the breakdown of glycogen need to be quick
Animals have high rate of respiration- energy needs of animals can change rapidly- may have to move quickly to escape from predator.
Structure of cellulose
-polymer of BETA glucose, glucose molecules need to be flipped every other to bond between OH.
-Unbranched- also form water
- straight chain with no branches- cellulose molecules can get close to each other.- hydrogen bonds form between neighbouring chains - lots of hydrogen bonds form- makes cellulose extremely strong.
What is it called when cellulose chains join together
A microfibril- they then group together to form larger structures called macrofibrils- they then join together to form a cellulose fibre. These cellulose fibres form the plant cell wall-
Key feature of cellulose
It’s strength- allows cellulose cell wall to carry out its function
-The cellulose cell wall is also permeable to molecules like water
