Biological Molecules

What is a condensation reaction

Loss of a water molecule between two monomers to form a covalent bond

What is a hydrolysis reaction

Breaking of covalent bond between monomers by adding a water molecule

What kinds of bonds occur in carbohydrates

Glycosidic bonds

What is an isomer

A compound with the same chemical formula but a different arrangement of atoms

What are glucose's isomers - add a structural difference

• Alpha-glucose: OH at C1 is below the plane of the ring

• Beta-glucose: OH at C1 is above the plane of the ring

Whats the difference between a hexose, triose and pentose monosaccharide

• Hexose - contains 6 carbon atoms

• Pentose - contains 5 carbon atoms

• Triose - contains 3 carbon atoms

How is a disaccharide formed?

• two monosaccharides join together

• condensation reaction takes place

• glycosidic bond is formed

• water is released

How is glucose adapted for its role

• small and soluble so can dissolve and be transported easily

• low reactivity

How is a polysaccharide formed?

• two monosaccharides join where a condensation reaction takes place

• A glycosidic bond is formed

• A molecule of water is released each time

• Many more condensation reactions take place until a long chain is produced

Describe the structure of amylose (starch)

• long chain of a-glucose

• has 1,4-alpha glycosidic bonds

• coiled shape - compact, allows large amount packed in small space

• unbranched

Describe the structure of amylopectin (starch)

• long chains of a-glucose

• 1,4-alpha glycosidic bonds

• branches formed by 1,6-alpha glycosidic bond

• coiled shape - more compact, allows large amount packed in small space

What is the advantage of having branches? (2)

• many accessible ends

• allows rapid release of glucose

Describe the structure of glycogen

• long chains of a-glucose

• 1,4-alpha glycosidic bonds

• HIGHLY branched - VERY compact

• branches formed by 1,6-alpha glycosidic bonds

• accessible ends

• smaller chains than amylopectin → less coiled

Describe the structure of cellulose

• long, straight chains of beta-glucose molecules

• b-glucose joined by 1,4 glycosidic links

• unbranched

• molecules invert alternatively by 180° (prevent coiling)

What are cellulose microfibrils?

• parallel cellulose chains that become cross linked by

• hydrogen bonds in between chains which provides strength (cross links)

Why are polysaccharides good sources of energy? (a-glucose for last)

• compact - more energy stored in small space

• can hold glucose in large chains - doesnt diffuse out of cell

• can be (un)branched

• insoluble in water - no impact on water potential of a cell

• easily hydrolysed to a-glucose when energy is needed

What are the properties of water?

• Polar

• High SHC

• High latent heat of evaporation

• Cohesive

• Ice has low density

• Good solvent

Explain waters polarity

• shared negative H electrons are pulled towards O atom

• so other ends of H atoms have slight positive charge

• unshared E-s on O atom give a slight negative charge

How are water molecules held together

• slight negative O atoms attract the slight positive H atoms of other water molecules

• this attraction = hydrogen bonding

Why is a high SHC good for water?

• water doesn’t experience rapid temperature changes

• living organisms have a stable temperature - for optimal enzyme reactions

Why is a high LH of evaporation good for water

• good cooling property for mammals

• eg when sweat evaporates, it cools surface of skin

Why is cohesion good for water

• water molecules stick together as they’re polar so there’s a great attraction

• helps water flow → useful to transport substances

• provides surface tension

How is the structure of ice different to liquid water?

• water molecules held further apart as each molecule forms 4 hydrogen bonds

• this forms a lattice shape

Why is low density good for ice

• useful for aquatic organisms as ice forms an insulating layer in cooler temperatures

• layer is on top of water so water beneath doesn’t freeze

What is the benefit of water being a good solvent

• ions can dissolve in water

• this can be transported around blood / plants which is useful for living organisms

What is the structure of an amino acid

• has amine group

• has carboxyl group

• has variable ‘R’ group

• contains C, O, H, N ; S

What bonds occur in proteins

Peptide bonds