Biology a level biological molecules

==water dipole nature==

• a weak negatively charged region on the oxygen atom (δ-) and a weak positively charged region on the hydrogen atoms (δ+)

• This separation of charge due to the electrons in the covalent bonds being unevenly shared is called a dipole

what is a polar molecule

When a molecule has **one** end that is negatively charged and **one** end that is positively charged

why is water good at transporting substances

its dipole nature

cohesion

Hydrogen bonds between water molecules allow for strong **cohesion between water molecules**

adhesion

Water is also able to form hydrogen bonds with **other molecules**

==why is water a good solvent==

* Water molecules **surround charged particles**; the positive parts of water are attracted to negatively charged particles and the negative parts of water are attracted to positively charged particles

==what are monosaccharides==

the **monomers** of carbohydrate

are simple carbohydrates

are **sugars**

==what are **Disaccharides**==

**Two monosaccharides** can join together via **condensation reactions** to form **disaccharides**

glycosidic bond is formed

==what are polysaccharides==

* Polysaccharides are carbohydrate polymers; repeated chains of many monosaccharides **joined by glycosidic bonds** in a **condensation reaction**

==starch (polysaccharide)==

the **storage** polysaccharide of **plants**

* Starch is constructed from **two** **different** **polysaccharides**
* **Amylose** and **amylopectin** 

==glycogen (polysaccharide)==

he storage polysaccharide of animals and fungi

• It is highly branched and not coiled

• compact so can be stored in a small space

==function of monosaccharides==

to store energy within their bonds

structure:

• It is soluble so can be transported easily

• It has many covalent bonds which store energy

formation of disaccharides ( condensation)

glucose + glucose → maltose + water

glucose + fructose → sucrose + water

glucose + galactose → lactose + water

structure of disaccharides

maltose - 1,4 glycosidic bond

sucrose - 1.2 glycosidic bond

lactose - 1,4 glycosidic

disaccharides are easily soluble in water and sweet in taste

function of disaccharides

to **provide the body with a quick-release source of energy**

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structure of polysaccharides

• Branched or unbranched

  • Being branched increases the rate at which a polysaccharide can be broken down

• Straight or coiled

  • Being straight makes the molecules suitable for constructing cellular structures e

  • Being coiled makes a molecule more compact and suitable for storage

why are starch and glycogen useful as storage polysaccharides?

• Compact; large quantities can be stored

• Insoluble; they will have no osmotic effect

structure of starch

Amylose

• Unbranched helix-shaped chain with 1,4 glycosidic bonds

• Amylopectin

  • A branched molecule containing 1,4 and 1,6 glycosidic bonds

  • The branches result in many terminal glucose molecules that can be easily hydrolysed

structure of glycogen

• highly branched and not coiled

• It contains both 1,4 and 1,6 glycosidic bonds

• Glycogen is more branched than amylopectin

• compact

how are disaccharides and polysaccharides formed?

**two hydroxyl (OH) groups** on different monosaccharides interact to form a **strong glycosidic covalent bond** **(condensation)**

how a triglyceride is synthesised

the formation of ester bonds during condensation reactions between glycerol and three fatty acids

Forming an ester bond

An **ester bond** forms when the hydroxyl (-OH) group of the glycerol bonds with the carboxyl group (-COOH) of the fatty acid

**Saturated** fatty acids

contain **no carbon-carbon double bonds**

**Unsaturated** fatty acids 

contain carbon-carbon double bonds