Biology - Topic 1: molecules

Most abundant elements in living organisms?

carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur

Where do almost all chemical reactions of life take place?

Aqueous solutions

Four main groups of organic molecules?

> carbohydrates

> Proteins

> Lipids

> Nucleic acids

What percentage of cells are water?

80%

Main role of water in living things?

Solvent

Properties of water as a biological molecule?(4)

> one oxygen, one hydrogen

> covalent bonds between O and H

> Polar

> Oxygen slightly negative and hydrogen slightly positive

What is it meant by water being 'polar'?

Water is 'charged' because electrons are not shared equally - oxygen slightly negative and hydrogen slightly positive

Diagram of a water molecule?

What does the polar nature of the water molecule allow it to do?

for weak chemical bonds with other water molecules

How do water molecules stick together?

Positive hydrogen ends of a water molecule attract the negative ends of an oxygen molecule

What bonds form between water molecules?

Hydrogen bonds

Diagram of water molecules and bonds between them?

page 7

Purpose of water as a solvent?

> most cell's reactions take place in aqueous solution

> it can act as a transport medium in living organisms

> its different effects of hydrophilic and hydrophobic molecules like lipids

Why are ions soluble in water?

They are charged

List of inorganic ions?

> calcium

> iron

> magnesium

> potassium

> nitrate

> phosphate

> hydrogen carbonate

Role of calcium?

> Calcium pectate of the middle lamella of plant cell walls

> essential in bones, teeth, blood clotting and muscle contraction

Role of iron?

> Part of Haem group in haemoglobin

>important electron carrier in respiration

Role of magnesium?

Gives chlorophyll its light absorbing properties

Potassium role?

maintains electrical gradient across membrane of neurone

Role of nitrate?

important in amino acids, nucleic acids and chlorophyll

Role of phosphate?

> phospholipids in cell membrane

> part of adenosine triphosphate (ATP) and nucleic acids

Role of hydrogen carbonate?

natural buffer

What is a buffer?

chemicals which resist changes to pH and ensure the environment remains at a particular pH

What are organic molecules?

all carbon containing molecules?

How are organic molecules made?

Polymers made of monomers through polymerisation

What are carbohydrates?

A group of organic compounds whose molecules contain C, H, and O only

3 groups of carbohydrates?

> monosaccharides

> disaccharides

> polysaccharides

Sugars that are monosaccharides?

> glucose

> fructose

> ribose

Sugars that are disaccharides?

> maltose

> sucrose

> lactose

Sugars that are polysaccharides?

> starch

> cellulose

> glycogen

Features of monosaccharides? (3)

> same number of carbon and oxygen atoms

> white crystalline solids which dissolve in water to give a sweet taste

> reducing sugars

General formula for monosaccharides?

C(H2O)n

What is a reducing sugar?

it takes oxygen or electrons from other chemicals pr donates hydrogen to it, in doing so the sugar becomes oxidised

Name for sugars that contains 6 carbon atoms?

Hexose sugars

Diagram for alpha glucose?

see page 13

Diagram for beta-glucose?

page 13

Fructose diagram?

see page 13

How are alpha-glucose, beta-glucose, and fructose all related?

They are isomers

Iosmer?

same molecular formula but different structural formula

How is a disaccharide formed?

formed when 2 monosaccharides chemically bond together

What reaction creates a disaccharide?

Condensation - water is produced

Reaction when a disaccharide is reversed?

Hydrolysis

Name of bond between the two monosaccharides?

Glycosidic bond

General formula for disaccharides?

C12H22O11

Diagram for formation of disaccharide?

see page 15

Hydrolysis?

a reaction in which a larger molecule reacts with water and, in doing so, split into smaller ones

Condensation reaction?

when two smaller molecules join together to form a larger one an release a water molecule

Monomers of maltose?

alpha-glucose molecules

Monomers of sucrose?

alpha-glucose and fructose

Properties of maltose and sucrose?

> dissolve in water to give sweet taste

How is maltose formed?

formed when starch is digested but further digestion is needed to form glucose monomer

Where is maltose found?

Small intestine

Role of sucrose?

sucrose is the form in which carbohydrate is transported through the phloem

Where is sucrose found?

Phloem

Is maltose a reducing sugar?

Yes

Is sucrose a reducing sugar?

No

Examples of polysaccharides?

> starch

> glycogen

> cellulose

General formula of polysaccharides?

(C6H10O5)n

Are polysaccharides sweet?

No

Where is starch found?

Chloroplasts

Properties of starch? (4)

> Compact

> No osmatic effect

> Easily hydrolysed

> Large molecule

Why is starch readily broken down?

branching in amylopectin creates terminal ends which are easily hydrolysed

What does starch being a large molecule prevent it from doing?

Passing through a cell membrane

What compounds are starch composed from?

> amylose

> amylopectin

What monomers is starch made from?

Alpha glucose

Why does starch have a different shape?

Amylose and amylopectin have different bonds between the molecules

What is amylose made up of?

alpha glucose

Bonds in amylose?

1-4 glycosidic bonds

Shape of amylose?

Spiral

How are amylose spirals held in place?

Hydrogen bonds

How much of starch is made up of amylose?

20%

amylose diagram?

page 21

What is amylopectin made up of?

alpha glucose

Bonds in amylopectin?

1-4 glycosidic bonds and 1-6 glycosidic bonds

Shape of amylopectin?

Branched

Why is amylopectin more easily hydrolysed?

Large number of terminal ends due to branching

amylopectin diagram?

page 22

How much of starch is made up of amylopectin?

80%

Where is glycogen found?

fungal and animal cells

Where in mammals is glycogen found?

Liver and muscle cells since a lot of respiration occurs there

form in which glycogen is found in liver and muscle?

Small granules

Structure of glycogen?

Similar to amylopectin but more highly branched

What monomer is glycogen made up of?

alpha glucose

Bonds in glycogen?

1-4 and 1-6 glycosidic bonds

Why is it important for glycogen to be easily hydrolysed?

It is more important for animals to be able to gain access to glucose quickly than for plants

Main difference between cellulose and starch/glycogen?

Cellulose is not for storage but is a structural polysaccharide

glycogen diagram?

page 23

Role of cellulose?

providing strength and rigidity to plant cell walls

What monomer is cellulose made up of?

beta-glucose

Bonds in cellulose?

1-4 glycosidic bonds

Shape of cellulose chains?

Straight chains

How is cellulose formed/structure?

> every other beta-glucose has to rotate 180°

> this allows hydrogen bonds between chains for cross linkage

> chains group together to form microfibrils

> microfibrils arrange into lattice for more tensile strength

diagram of cellulose structure?

page 24

What are lipids called instead of polymers?

Macromolecules

Why aren't lipids molecules?

it is not made up of monomers - it has two different sub units

How to lipids react with water?

They are insoluble

Why are lipids insoluble?

They are non-polar and so are hydrophobic

What are lipids soluble in?

organic solvents

Examples of lipids?(4)

> triglycerides

> phospholipids

> steroids

> waxes

Most common type of lipids?

Fats and oils