Biological Molecules November 2022 RJS

carbohydrates and lipids

What three elements do carbohydrates contain? + general formula

Carbon, hydrogen and oxygen.
Cx(H2O)x

What are the functions of glucose, starch, glycogen and cellulose?

a source of energy (glucose), a store of energy (starch and glycogen) and as structural units (cellulose)

Where are monosaccharides soluble?

Monosaccharides are soluble in water, and are insoluble non-polar solvents.

Hexose sugars have…

6 carbon atoms and exist in rings

Pentose sugars have…

5 carbon atoms exist in rings

Triose sugars have…

3 carbon atoms and exist in straight chain

What is glucose?

Glucose is a monosaccharide hexose sugar, they are monomers that can bond to form disaccharides and polysaccharides.

What are disaccharides?

-They are when two monosaccharides join together. When they join a condensation reaction occurs to form a glycosidic bond.

• A glycosidic bond is when a water molecule is removed leaving an oxygen acting as a link between the two monosaccharides.

How are disaccharides broken?

They are broken by hydrolysis , the addition of water. The water provides the hydroxyl group and a hydrogen , which helps the glycosidic bond to break.

What is a-glucose + a-glucose

maltose

What is a-glucose + sucrose

sucrose

What is b-glucose + a-glucose

lactose

What are polysaccharides?

They are polymers of monosaccharides

How are polysaccharides made into energy stores?

-Joining lots of glucose molecules together into polysaccharides can create a store of energy.
-Examples of energy stores: starch in plants in chloroplast. Glycogen in cells of liver and muscle cells.

What is starch and chloroplast made up of?

Amylose and amylopectin

Why are polysaccharides less soluble in water than monosaccharides?

-They have a larger size,the amylose may form a double helix structure which is hydrophobic.
-Furthermore, if many water molecules did dissolve in cytoplasm , the water potential would decrease and excess water would diffuse in.

What are 3 examples of polysaccharides?

-Amylose (plants)- forms long chains of a-glucose and have glycosidic bonds between carbon 1-4.
-Amylopectin (plants) - forms a-glucose with glycosidic carbon bonds 1-4. But has branches between carbon 1-6.
-Glycogen (in animals) : like amylopectin , it has carbon 1-4 bonds and branches formed by glycosidic bo

What is cellulose ?

It's a homopolysaccharide made from long chains made from long chains of up to 15000 b-glucose molecules bonded together through a condensation reaction to form glycosidic bonds

How are glycosidic bonds formed?

It's formed by the removal of water , a condensation reaction.

What are cellulose beta glucose like?

-Cellulose chains are straight and lie side by side.
-The hydrogen and hydroxyl groups on carbon 1 are inverted compared to a-glucose
-The hydrogen bond is rotated - gives additional strength and stops spiralling
-Hydroxyl groups on carbon 2 sticks out , enabling hydrogen bonds to be formed between them

What is the arrangement of cellulose chains?

The microfibrils are embedded in pectins to form the wall
Macrofibrils run in all directions criss-crossing the wall for extra strength

What is the structure of plant cell walls?

-microfibrils and Macrofibrils have very high tensile strength due to glycosidic bonds and hydrogen bonds
-Microfibrils run in all directions cross-crossing the wall for extra strength
-It is difficult to digest cellulose - due to its glycosidic bonds

What is the function of plant cell walls?

-each cell provides strength as plants don't have a rigid skeleton
-There is a space between Macrofibrils for water and mineral ions to pass into and out of the cell. Making cell fully permeable
-Cell had high tensile strength , prevents cell from bursting when turgid
-Macrofibril reinforced with other substances , eg lignin, makes cell wall waterproof

What are bacterial cell walls like?

The cell wall is not made of cellulose but peptidoglycan, lie in parallel , cross linked by short peptide chains

What are lipids?

-lipids contain C,H,O
-They are insoluble in water as they aren't polar
-They dissolve in alcohol
-The three most important lipids are : triglycerides, steroids and phospholipids
-They are examples of macromolecules

What are triglycerides structure

1 glycerol backbone with 3 fatty acid tails.

What is glycerol

Glycerol has 3 carbon atoms. It is an alcohol so it has 3-OH , which are important to the structure of triglycerides

What are fatty acids?

They have a carboxyl group (-COOH) on one end, attached to a hydrocarbon tail.
The carbon chains can be up to 2-20 carbons long. The carboxyl group ionises into H+ and COO- groups. Therefore this is an acid due to free H+ ions.

What are saturated fatty acids like?

-no C=C Bonds in molecule
-Forms straight chains
-solid at room temperature , high melting point

What are unsaturated fatty acids like?

-Forms a kink in the chain where double bond is
-These kinks push the molecules apart slightly, making them more fluid.
-more unsaturated fatty acids , the lower the melting point

How are ester bonds formed?

-Condensation reaction happens between the -COOH group of fatty acids and the -OH group of the glycerol.
-Due to the 3 -OH group, three fatty acids will bond. A water molecule is produced and the covalent bond, the ester bond

What are the functions of triglycerides?

-Energy source - Triglycerides are broken down in respiration to release energy and generate ATP. -The ester bonds are hydrolysed and then glycerol and fatty acids can be broken down completely
-Triglycerides are insoluble in water- so can be stored without affecting the water potential
-Insulation - Adipose in whales (blubber), lipid in nerve cells act as an electrical insulator, animals prepare for hibernation
-Buoyancy - fat is less dense than water so used by aquatic molecules to help them float
Protection - protect vital organs .

What is the structure of phospholipid?

-glycerol, two fatty acids, and a phosphate group
-One of the three -OH groups on the glycerol forms an ester bond by a condensation reaction
-2 hydrophobic tails and hydrphilic head (due to the charged phosphate making it polar)

What are examples of steroid hormones and what are they made from?

-Testosterone, oestrogen, vitamin D are all made from cholesterol
-They are small and hydrophobic so they can pass through the cell membrane and any other membrane inside the cell.
-Steroid hormones are abundant in plants and in ingestion and absorption some can be converted into animal hormones.

Where is cholesterol made?

Liver

How are ester bonds broken?

hydrolysis reaction