Biological Molecules
and
… Digestion
Carbohydrates

All contain the elements carbon hydrogen
oxygen

Twice as many hydrogen atoms as oxygen
atoms in each molecule
Three main types

Monosaccharide

Disaccharide

Polysaccharide
Monosaccharides

Are the simple sugars
e.g. glucose, fructose, galactose

These are the monomers
Glucose

-glucose
Disaccharides

Contain two simple sugars joined together

Glycosidic bond is formed

e.g. maltose, sucrose, lactose
Disaccharides

Monomers join by a condensation reaction

Water is given out
Condensation
Glycosidic bond
Maltose

Two molecules of -glucose joined
together
Sucrose

One molecule of  -glucose joined to one
molecule of fructose
Polysaccharides

Contains many simple sugars
e.g. starch
Polysaccharide
Starch – for storage
Compact
 lots
of glucose can be stored in a small space
Easily broken down
 supply
glucose when needed for respiration
Lipids


One of the most important types is:
triglycerides
Usually known as:
fats and oils
Fat 
Solid at room temperature
Oil 
Liquid at room temperature
Triglycerides
Consists of :
three fatty acid molecules

one glycerol
Saturated and unsaturated
triglycerides

Depends on the form of the fatty acid
chains
Proteins

Polymer

Monomer is amino acid

Draw an amino acid
Amino group
Carboxylic group
Amino acids

20 different amino acids

Joined together by condensation

Peptide bond is formed

Polypeptide is many amino acids joined
together
Polypeptide – primary structure

Chain of amino acids

Held together by peptide bonds

Differences due to the type, number
and position of amino acid
Secondary structure
Folding of polypeptide chain
forming an alpha helix
Secondary structure
Held together by hydrogen
bonds
Tertiary structure
Further folding of secondary
structure, held together by
hydrogen, ionic, disulphide and
hydrophobic bonds
Quaternary structure
More than one polypeptide
joined together
The digestive system
Heterotrophic
Nutrition

Organisms that can not manufacture
the organic molecules they require
Must eat them
Must consume them –
CONSUMERS OR HETEROTROPHS


Most of the chemicals eaten are
storage molecules
Digestion
Definition:

Break down of large insoluble organic
molecules into small soluble organic
molecules
Classes of organic molecules
Starch
Lipid
Protein
How are the molecules joined
together?
Starch
Lipid
Protein
How are the molecules joined
together?
Starch
Glycosidic
bond
Lipid
Ester
bond
Protein
Peptide
bond
What enzymes break them
down?
Starch
Lipid
Protein
What enzymes break them
down?
Starch
Carbohydrase
Lipid
Lipase
Protein
Protease
What type of reaction is
involved?
Starch
Lipid
Protein
What type of reaction is
involved?
Starch
Hydrolysis
Lipid
Hydrolysis
Protein
Hydrolysis
Hydrolysis
The addition of water to break down a
large molecule into a smaller molecule
Condensation

Removal of water to join two molecules
together
Breakdown of starch
Starch
amylase
salivary
gland
pancreas
Maltose
maltase
ileum
Glucose
Membrane attached enzymes

Most enzymes are secreted into the gut
BUT

Some enzymes are attached to
membrane of the epithelial cells of the
ileum
Examples of ......
membrane attached enzymes
Maltase
 Sucrase
 Lactase

Why are the enzymes attached to
the membranes?


The reactions they control, produce
molecules which can be absorbed
through the membrane
If this happened in the centre of the
gut the molecules may never come in
contact with the membrane
What is the difference between
maltose, sucrose and lactose?
Glucose plus glucose - maltose
 Glucose plus fructose - sucrose
 Glucose plus galactose - lactose

Absorption

Passing the products of digestion into
the cells lining the gut
Assimilation

Making the absorbed molecules part of
the cells of the body