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**

\

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