Unit 1.1 MoleculesUnit 1.1 Molecules

Biology Department

Watford Girls Grammar School

IntroductionFor each of the following you should be

able to: Describe the properties Know the general formulae & structure Understand the role in animals & plants

•Water

•Carbohydrates

•Lipids

•Proteins

•Nucleic acids

WaterWater is a polar molecule It forms weak hydrogen bonds It remains a liquid over a wide

temperature rangeWater molecules stick to one another =

cohesion (surface tension)Water molecules stick to other

substances = adhesion (capillarity)

O

H

H

+

+-

Water It has a high specific heat capacity – so

water can maintain a reasonably constant temperature (homeostasis)

It has a high latent heat of vaporisation – so animals use water to cool themselves

It is less dense as a solid (ice)…… and ice is a poor conductorWater is a good solvent

Carbohydrates Contain the elements Carbon

Hydrogen & Oxygen There are 3 types:

Monosaccharides Disaccharides Polysaccharides

Monosacharides

(CH2O)n

If n=3, triose (glyceraldehyde) If n=5, pentose (fructose, ribose) If n=6, hexose (glucose, galactose)Monosaccharides are used for

Energy Building blocks O

C C

C C

C

C

IsomerismThey can exist as isomers:

& glucose OH

OH

DisaccharidesFormed from two monosaccharidesJoined by a glycosidic bondA condensation reaction:

glucose + glucose maltose glucose + galactose lactose glucose + fructose sucrose

Condensation reaction

O

C C

C C

C

CO

C C

C C

C

C

OH OH

Condensation reaction

O

C C

C C

C

CO

C C

C C

C

C

OH OH

Condensation reaction

O

C C

C C

C

CO

C C

C C

C

C

O

H2O

Condensation reaction

O

C C

C C

C

CO

C C

C C

C

C

O

A disaccharide1,4 glycosidic bond

41

PolysaccharidesPolymers formed from many

monosaccharidesThree important examples:

Starch Glycogen Cellulose

Starch Insoluble store of glucose in plantsformed from two glucose polymers:

Amylose

-glucose

1,4 glycosidic bonds

Spiral structure

Amylopectin

-glucose

1,4 and some 1,6 glycosidic bonds

Branched structure

Glycogen

Insoluble compact store of glucose in animals

-glucose units1,4 and 1,6

glycosidic bondsBranched structure

CelluloseStructural polysaccharide

in plants-glucose1,4 glycosidic bondsH-bonds link adjacent

chains

O

O

O

O

O

LipidsMade up of C, H and OCan exist as fats, oils and waxesThey are insoluble in waterThey are a good source of energy

(38kJ/g)They are poor conductors of heatMost fats & oils are triglycerides

TriglyceridesFormed by esterification……a condensation reaction between 3

fatty acids and glycerol:

Glycerol

H

C

H C

C

H

H

H

H

O

O

O

Fatty acidsCarboxyl group (-COOH) attached to a long non-polar

hydrocarbon chain (hydrophobic):

H

H

C

HH

C

H

H

C

HC

O

O

H

C

HH

C

H

H

C

H

H

C

H

H

A saturated fatty acid (no double bonds)

HH

C

O

O

H

C

HH

C C

C C H

C

H

H

C

H

HA polyunsaturated fatty acid

C

O

O

H

C

HH

C

H

H

C

H

H

C

H

C

HH

C

H

H

C

H

H

A monounsaturated fatty acid

H H

Esterification

H

C

H C

C

H

H

H

H

O

O

OC

O

O

H

C

HH

C

H

H

C

H

H

C

H

H

Glycerol Fatty acid

Esterification

H

C

H C

C

H

H

H

H

O

O

OC

O

O

H

C

HH

C

H

H

C

H

H

C

H

H

Glycerol Fatty acid

Esterification

H

C

H C

C

H

H

H

H

O

O

OC

O

O

H

C

HH

C

H

H

C

H

H

C

H

HGlycerol Fatty acid

Esterification

H

C

H C

C

H

H

H

H

O

O

OC

O

O

H

C

HH

C

H

H

C

H

H

C

H

H

Ester bond

water

EsterificationThis happens three times to form a

triglyceride:

glycerol fatty acids

PhospholipidsOne fatty acid can be replaced

by a polar phosphate group:

glycerol Hydrophobic fatty acids

hydrophilicphosphate

Functions of lipidsProtection of vital organsTo prevent evaporation in plants &

animalsTo insulate the bodyThey form the myelin sheath around

some neuronesAs a water source (respiration of lipids)As a component of cell membranes

Proteins Made from C H O N & sometimes SLong chains of amino acidsProperties determined by the aa

sequence

Amino acids

H

CH

N C

HH

O

O

R

~20 aaGlycine R=HAlanine R=CH3

aminecarboxyl

Peptide bonding

HC

HN C

HH

O

O

R

HC

HN C

HH

O

O

R

Peptide bonding

HC

HN C

HH

O

O

R

HC

HN C

HH

O

O

R

Peptide bonding

H

CH

N C

HH

O

O

R

HC

HN C

HH

O

O

R

Peptide bonding

CH

N C

HH

OR

HC

HN C

H

HO

H

O

O

R

water

Peptide bond

A condensation reaction

Peptide bonding

CH

N C

HH

OR

HC

HN C

H

O

O

R

A dipeptide

Primary structureThe sequence of aa is know as the

primary structureThe aa chain is a polypeptide

Secondary structureH-bonding forms between the –COOH

and the -NH2 of adjacent aa

This results in the chains folding:

Secondary structure

-helix -pleated sheet

Tertiary structureBonding between R-groups

gives rise to a 3D shapeH-bonds =O HN-

Ionic bonds –NH3-COO-

Disulphide bridge

--CH2S-SCH2-

affected by temp & pH

affected by pH

affected by reducing agents

Quaternary structureSome proteins have

more than one polypeptide chain

Each chain is held together in a precise structure

eg Haemoglobin

Types of proteinsFibrous proteins

e.g. collagen Insoluble structural

Globular proteins e.g.enzymes Soluble 3D shape

Functions of proteins Enzymes – Transport – Movement – Cell recognition – Channels – Structure – Hormones – Protection –

Amylase

Haemoglobin

Actin & myosin

Antigens

Membrane proteins

Collagen & keratin

Insulin

Antibodies

Nucleic acidsDNA & RNAMade up of nucleotides:

phosphate

pentose sugar

base

Nucleotides2 types of base:

Pyrimidines - Cytosine C Thymine T

Purines Adenine A Guanine G

Complimentary base pairingAdenine will only bind with ThymineCytosine will only bind with Guanine

T C GA

DNA structure

nucleotide

Condensation polymerisation of the deoxyribose nucleotides

ReplicationDuring cell division the DNA must

replicateThe DNA double helix unwindsThe exposed bases bind to free floating

nucleotides in the nucleoplasmDNA polymerase binds the

complimentary nucleotidesReplication is

semiconservative

The genetic codeThe sequence of nucleotide bases

forms a codeEach ‘code word’ has three letter – a

triplet codeEach codon codes for a specific amino

acid e.g: GGG = proline CGG = glycine ATG = tyrosine ACT = stop (no amino acid)

Protein synthesisThe DNA codes for

proteinsA copy of DNA

(mRNA) is made in the nucleus (transcription)

The mRNA is used to make a protein (translation) in the cytoplasm

TranscriptionThe DNA polymerase

unwinds the DNAFree nucleotides join

onto complimentary bases

RNA polymerase links adjacent nucleotides

The completed mRNA moves out of the nucleus

Transcription

Amino acid activation transferRNA:

tRNA binds onto a specific amino acid

TranslationmRNA binds to a ribosome tRNA carries an amino acid to the

ribosome

TranslationA second tRNA brings another aaThe two aa’s bindThe process repeats

TranslationA polypeptide chain formsEventually a stop codon is reached

The Human Genome Project A multinational project aimed at sequencing

the entire human genome Visit the Human Genome Web site:

www.ornl.gov/hgmis/project/about.html www.sanger.ac.uk

Acknowledgements Animated cell models used by kind

permission of The Virtual Cell website:

Feel free to use this presentation for educational non-profit making purposes.

Quiz 1. Which of the following is not an

important property of water

a) Its polar nature

b) Its low specific heat capacity

c) Its high latent heat of vaporisation

d) Its low density in solid form

Quiz 2. The general formula for a

monosaccharide is:

a) (CH2O)n

b) (CHO)n

c) C(H2O)n

d) CnH2On

Quiz 3. Sucrose is made up of

a) glucose + fructose

b) glucose + galactose

c) glucose + glucose

d) galactose + fructose

Quiz 4. Amylopectin is made up of:

a) -1,4 glycosidic ondsb) -1,4 & -1,4 glycosidic bonds

c) -1,4 & 1,6 glycosidic ondsd) -1,4 & 1,6 glycosidic onds

Quiz 5. Formation of a triglyceride does

NOT involve:

a) A condensation reaction

b) Esterification

c) Polymerisation

d) A reaction between 3 fatty acids & glycerol

Quiz 6. The general formula of a saturated

fatty acid is:

a) CnH2nO2

b) Cn(H2O)n

c) (CH2O)n

d) (CH2)nO

Quiz 7. Which of the following is not

responsible for a proteins tertiary structure

a) ionic bonding

b) covalent bonding

c) hydrogen bonding

d) disulphide bonding

Quiz 8. Which of these is not an amino

acid:

a) alanine

b) cysteine

c) glycine

d) cytosine

Quiz 9. Which process involves tRNA:

a) transciption

b) translation

c) DNA replication

d) gene mutation

Quiz 10. The formation of RNA does not

involve:

a) ribose sugar

b) thymine

c) removal of water

d) phosphate