Transcript Carbohydrates L3 - RGA

Q1
Uptake of the products of
digestion (small intestine)
Absorption
Q2
Breaking down large
molecules into smaller
ones
Digestion
Q3
2 types of digestion
Chemical
Mechanical
Q4
Where does ingestion
occur
Mouth
Q5
Using the products of
digestion in cells?
assimilation
Biological Molecules
AS Biology
Biological Molecules
 80% of the mass of living
organisms is water.
 13% is composed of
organic (carbon-based)
MACROMOLECULES,
of which there are 4
groups
 CARBOHYDRATES
 PROTEINS
 LIPIDS (FATS)
 NUCLEIC ACID
Carbon
• Carbon-containing
molecules=organic
molecules
• Carbohydrates, proteins
and lipids all contain
carbon
• Carbon atoms can form
4 chemical bonds with
other carbons or
different atoms
Polymers & monomers
What are polymers?
Long chained molecules consisting of repeating units
What are monomers?
The repeating unit that join together to form polymers
Macromolecules
Carbon chains can be
straight
Carbon chains can be
branched
CARBOHYDRATES
• This type of molecule contains only the
elements:
»C
»H
»O
CARBOHYDRATES
Divided into 3 main types;
1. Monosaccharides
Single sugars
Monosaccharides – single
sugars
Examples
Alpha Glucose
6 carbons
Fructose
6 carbons
Galactose
6 carbons
Glucose – C6H12O6
• Glucose is the best
known
monosaccharide,
having the general
formula C6H12O6.
Alpha Glucose
CARBOHYDRATES
Divided into 3 main types;
1. Monosaccharides = single sugars
2. Disaccharides
sugars containing 2 monosaccharide
residues
Disaccharides– 2
monosaccharide residues
joined together
Examples
sucrose
Alpha
Glucose
Making Chains
• Disaccharides are
formed when two
monosaccharides join
together.
• The reaction involves the
formation of a water
molecule, & so is called a
condensation reaction.
• The type of bond formed
is called a glycosidic
bond.
Breaking Chains
The bonds between the individual monomers in
disaccharides and polysaccharides can be broken by
hydrolysis, which is the reversal of condensation
reactions.
A hydrolysis reaction does not occur by putting a
carbohydrate in water – an enzyme is required. In the
case of starch, this enzyme is amylase.
Disaccharides (to learn)
• There are 3 common disaccharides:
– Maltose: glucose + glucose
– Sucrose: glucose + fructose
– Lactose: glucose + galactose
Draw how the disaccharides:
maltose and lactose are formed
• For each identify the water molecule that is
produced
• Draw out the complete disaccharide &
identify the glycosidic bond
galactose
CARBOHYDRATES
Divided into 3 main types;
1. Monosaccharides = single sugars
2. Disaccharides = sugars containing 2
monosaccharide residues
3. Polysaccharides =
very large molecules that contain many
monosaccharide residues
Making Longer Chains
• Polysaccharides are long chains of many monosaccharides joined
together by glycosidic bonds.
• There are three important polysaccharides:
• Starch
• Glycogen
• Cellulose
Polysaccharides – many
monosaccharide residues
joined together
Examples
Carbohydrates
Sugars
Monosaccharides
(monomers)
Disaccharides
(dimers)
Polysaccharides
(polymers)
Glucose
Maltose
Starch
Fructose
Sucrose
Glycogen
Galactose
Lactose
Cellulose
Carbohydrate digestion
Polysaccharide
insoluble
disaccharide
monosaccharide
soluble
Carbohydrate digestion example
Starch
Polysaccharide
Starch
Disaccharide
Maltose
monosaccharide
Alpha glucose
Salivary amylase &
pancreatic amylase
Maltase in
intestinal
epithelium (cells
lining small
intestine)
Starch
• Starch is the plant storage polysaccharide. It is
insoluble and forms starch granules inside many plant
cells. It’s insolubility means it does not affect the water
potential of cells.
• It is not a pure substance, but a mixture of two
structures (both alpha glucose polymers though)
• Amylose
• Amylopectin
Amylopectin can be broken
down more easily because it
has “more ends”
Glycogen
Glycogen is similar in structure to
amylopectin. It is made by animals as
their storage polysaccharide, being
found mainly in muscle and the liver.
Its branched structure means it can
be mobilised (broken down to
glucose) very quickly.
Cellulose
Cellulose is only found in plants where it is the main
constituent of cell walls.
Cellulose is made from beta glucose arranged in long parallel
chains. The chains are held together in a bundle by hydrogen
bonds, forming microfibrils which are very strong.
The beta glycosidic bond cannot be broken down by amylase,
but requires a specific cellulase enzyme. Only bacteria
contain this enzyme, so herbivores like cows & termites have
bacteria in their guts. Humans cannot digest cellulose – it is
what we call fibre or roughage.
Proteins
Proteins are the most complex and diverse group of bioligical
compounds. They have an astonishing range of different
functions:
structure e.g. collagen (bone, cartilage, tendon), keratin
(hair), actin (muscle)
Enzymes e.g. amylase, catalase, pepsin (>10000)
Transport e.g. haemoglobin (oxygen), transferrin (iron)
Pumps e.g. sodium-potassium pumps in cell membranes
Hormones e.g. insulin, glucagon, adrenalin
Antibodies
Blood clotting
And many more
Proteins
Proteins are made of amino acids which have a central carbon
atom with three different chemical groups attached:
R-group
Carboxylic
acid group
Amino group
Alpha
carbon
Amino acids are so called because they have both amino groups
NH2) and acidic groups (-COOH).
Amino acids are made of the five elements C H O N S
There are 20 different R-groups and so 20 different amino acids.
This means that there are many, many different proteins with
differing numbers and combinations of amino acids
(-
Proteins- making and breaking
Joining amino acids involves, again, a
condensation reaction. The bond formed is
called a peptide bond
Two amino acids form a dipeptide, many
amino acids form a polypeptide. In a
polypeptide, one end is still the amino group
and the other end the acidic group.
The same type of reaction, hydrolysis, is
again involved in breaking down (or
hydrolysing) proteins. This can be
achieved in the presence of protease
enzyme or by boiling with dilute acid.
Protein structure
Polypeptides are just a string of amino acids, but they fold up to form
the complex structures of working proteins. To help understand protein
structure it is broken down into four levels – but be aware that these are
not real sequential stages in protein formation
PRIMARY STRUCTURE
SECONDARY STRUCTURE
TERTIARY STRUCTURE
QUARTERNARY STRUCTURE
Protein: primary structure
This is just the sequence of amino acids in the polypeptide chain, so is
not really a structure at all
This can also be shown using the three letter abbreviations for each
amino acid:
Gly – Pro – His – Leu – Tyr – Ser – Trp – Asp - Lys
Protein: secondary structure
This is the folding that then occurs, being held together by hydrogen
bonds between the amino and carboxyl groups.
The two main types of secondary structure are the alpha helix and the
beta pleat.
In the alpha helix the polypeptide chain is wound round to form a helix
that is held together by many hydrogen bonds. In the beta pleat, the
polypeptide chain zig-zags back and forward, once again held together by
hydrogen bonds
Protein: tertiary structure
This is the three dimensional structure formed by the folding up
of the whole chain, with every proteins properties and functions
being related to this. E.g. the unique shape of an enzymes active
site is due to its tertiary structure. Three kinds of bond hold
this structure together:
Hydrogen bonds,which are relatively weak
Ionic bonds between the R-groups, which are quite strong
Sulphur bridges between the sulphur containing amino acids,
which are strong
Protein: quarternary structure
This structure is found only in those proteins that contain more
than one polypeptide chain, and simply means how the different
chains are arranged together e.g. haemoglobin
Globular or Fibrous?
The final 3-D shape of a protein can be described as globular or
fibrous
GLOBULAR: most
proteins, soluble, have
biochemical roles e.g.
enzymes, receptors,
hormones
FIBROUS: look like
“ropes”, are insoluble
and have structural
functions e.g. Collagen,
keratin
Biochemical test for proteins,
carbohydrates (sugars, starch),
and lipids
Lipids
You can test for the
presence of lipids by using
the EMULSION TEST.
1.Add alcohol to the sample of
food.Shake to dissolve any lipid.
2. Two layers of liquid will form. Pour
the top layer of & add water.
3. A cloudy white EMULSION shows
the presence of a lipid
Starch
The presence of starch can be teated using the iodine test.
Starch + iodine
blue-black colour
With other polysaccharides, iodine remains yellow-brown
Sugars
Sugars can be identified with blue Benedict’s solution.
However there are two types of sugar:
Reducing Sugars – these carry
out reduction reactions and
include all monosaccharides and
most disaccharides.
When heated with Benedict’s,
the colour changes from blue to
green to orange/red
Non-reducng sugars
(mainly sucrose in fact) do
not react with Benedict’s
unless first hydrolysed by
heating with acid first. As
Before adding Benedict’s,
you must neutralise the
acid with an alkali
Proteins
Proteins can be identified with blue Biuret Reagent (copper
sulphate and sodium hydroxide).
Blue Biuret reagent turns lilac in
the presence of protein