Water
 Life on earth evolved in water,and all life
still depends on water.
 At least 80% of the mass of living
organisms is water and almost all
 chemical reactions of life take place in
aqueous solution.
1
.
Hydrogen bonds
Water molecules are charged, with the oxygen atom
being slightly negative and the hydrogen atoms
being slightly positive. These opposite attract each
other, forming hydrogen bonds. These are weak,
long distance bonds that are very common and very
important in biology.
H
Covalent
Bonds
H
O
H
H
H
H
Water Molecules
O
Hydrogen
bonds
O
O
H
H
2
Water has a number of Important
properties essential for life.



Solvent- It is a very good solvent. Molecules such as
salts, sugars, amino acids dissolve readily in water
(once dissolved they can be transported e.g. glucose in
the bloodstream).
Specific heat capacity- Water has a high specific heat
capacity (4.2 joules of energy to heat 1g water by 1oC).
This means that water does not change temperature
easily. This minimises fluctuations in temperature inside
cells and means that sea temperature is quite constant.
Latent heat of vaporisation- Water requires a lot of
energy to change state from a liquid to a gas, providing
a cooling mechanism in animals (sweating and panting)
and plants (transpiration). As water evaporates it
extracts heats from the surrounding area, cooling the
3
organism
Water has a number of Important
properties essential for life.
Density- Water is its solid state (ice) is less dense than
the liquid state.As the air temperature cools, bodies of
water freeze from the surface, forming a layer of ice with
the liquid beneath, This allows aquatic ecosystem to exist
in low temperatures.
Cohesion- Water molecules due to hydrogen bonds
stick together, so water has a high cohesion. This explains
why long columns of water can be suck up tall trees by
transpiration without breaking. It also explains surface
tension which allows small animals to walk on water,
4


Cells are very technical
and they need to
constantly import raw
materials to get rid of
waste. Some of the
exchanges of raw
materials occur as a
passive process but e.g.
diffusion and osmosis,
but not all substances
can move freely.
Cells must control the
passage of substances
through their
membranes.
5
Diffusion




All particles in liquids and gases are in
constant motion
The motion results in a net movement of
all the particles in a high concentration
into one of a lower concentration.
In a mixture of gases, diffusion causes
each gas to spread evenly throughout
the space that the gases take up.
The process above also happens when a
soluble substance moves through a
liquid until it is evenly dispersed.
6

If substances are to move up the concentration gradient
they require energy. Some protein molecules act as
molecular pumps. This allows active transport to take
place. Animal and plant cells that specialise in absorption
have plenty of mitochondria to provide the ATP for active
transport.
7
A greater surface area means
that there is more cell
membrane across which
diffusion, osmosis, facilitated
diffusion and active transport
can take place. Large insoluble
lipid molecules e.g. glucose and
amino acids need more help.
They get the help from intrinsic
proteins within the phospholipid
membrane. These protein
molecules provide
transmembrane ‘channels’
through which small, water
soluble molecules such as
glucose can pass. This is known
as facilitated diffusion.
8
ENZYMES
Biological processes are regulated by the action of
enzymes. Enzymes as proteins that act as catalysts. The
importance of enzymes is lowering activation energy so
that the chemical reactions necessary to support life can
proceed sufficiently quickly and within an acceptable
temperature range. The mode of action of enzymes in
terms of the formation of an enzyme - substrate
9
complex.
The way enzymes work can also be shown by considering
the energy changes that take place during a chemical
reaction. We shall consider a reaction where the product has
a lower energy than the substrate, so the substrate turns
into the product. Before it can change into the product, the
substrate must overcome an “energy barrier” called the
activation energy (EA).
10
In a chemical reaction the larger the activation
energy, the slower the reaction will be because
only a few substrate molecules will by chance
have sufficient energy to overcome the
activation energy barrier.
Most physiological
reactions have large
activation energies,
so they simply don’t
happen in a useful
11
time scale.
There are about 40,000 enzymes in a human cell each
controlling a different chemical reaction.
This is
how a
substrate
fits into
an
enzyme
in a
reaction.
12
Enzyme molecules have a complex tertiary structure.
The substrate molecules of the enzyme must be
precisely the right shape to fit it into part of the
molecule called the active site. The substrate
molecules are attracted to the active site and form an
enzyme - substrate complex. This complex only exists
for a fraction of a second, this is when the products of
the reaction form. The activation energy is low in this
reaction because it is controlled by enzymes and little
energy is needed to bring the two substrate
molecules together.
This is a diagram to
show an enzyme in
13
action.
ENZYME ACTIVITY
The properties of enzymes related to their
tertiary structure.The effects of change in
temperature,pH,substrate
concentration,and competitive and noncompetitive inhibition on the rate of
enzyme action
14
HOW ENZYMES WORK


Enzymes are ORGANIC
CATALYSTS. A CATALYST is
anything that speeds up a
chemical reaction that is
occurring slowly.
How does a catalyst work?
The explanation of what
happens lies in the fact that
most chemical reactions that
RELEASE ENERGY
(exothermic reactions) require
an INPUT of some energy to
get them going. The initial
input of energy is called the
ACTIVATION ENERGY
15
Enzymes





An enzyme is a biological
catalyst
The pockets formed by tertiary
and quaternary structure can
hold specific substances
(SUBSTRATES).
These pockets are called
ACTIVE SITES.
When all the proper substrates
are nestled in a particular
enzyme's active sites, the
enzyme can cause them to
react quickly
Once the reaction is complete,
the enzyme releases the
finished products and goes back
to work on more substrate. 16
Properties of Enzymes relating to
their tertiary structure.

The activity of enzymes is strongly
affected by changes in pH and
temperature. Each enzyme works best
at a certain pH and temperature,its
activity decreasing at values above
and below that point. This is because
of the importance of tertiary
structure (i.e. shape) in enzyme
function and forces, e.g., ionic
interactions and hydrogen bonds, in
determining that shape.
17
The effects of change in
temperature.
Temperature: enzymes work best at an optimum
temperature.
Below this, an increase in temperature provides more
kinetic energy to the molecules involved. The numbers of
collisions between enzyme and substrate will increase so
the rate will too.
Above the optimum temperature, and the enzymes are
denatured. Bonds holding the structure together will be
broken and the active site loses its shape and will no
longer work
18
The effect of change in pH.

pH: as with temperature, enzymes have an
optimum pH. If the pH changes much from the
optimum, the chemical nature of the amino acids
can change.
This may result in a change in the bonds and so the
tertiary structure may break down. The active site
will be disrupted and the enzyme will be
denatured.
19
The effect of change in concentration

Enzyme concentration: at low enzyme concentration there is great
competition for the active sites and the rate of reaction is low. As
the enzyme concentration increases, there are more active sites and
the reaction can proceed at a faster rate.
Eventually, increasing the enzyme concentration beyond a certain
point has no effect because the substrate concentration becomes
the limiting factor.

Substrate concentration: at a low substrate concentration there are
many active sites that are not occupied. This means that the
reaction rate is low.
When more substrate molecules are added, more enzyme-substrate
complexes can be formed. As there are more active sites, and the
rate of reaction increases.
Eventually, increasing the substrate concentration yet further will
have no effect. The active sites will be saturated so no more
enzyme-substrate complexes can be formed.
20
Competitive and non-competitive inhibition
Inhibitors slow down the rate of a reaction. Sometimes
this is a necessary way of making sure that the reaction
does not proceed too fast, at other times, it is
undesirable
Reversible inhibitors:
Competitive reversible inhibitors: these molecules have a
similar structure to the actual substrate and so will bind
temporarily with the active site. The rate of reaction
will be closer to the maximum when there is more ‘real’
substrate.
21
Competitive and non-competitive inhibition
Non-competitive reversible inhibitors:
these molecules are not necessarily
anything like the substrate in shape.
They bind with the enzyme, but not
at the active site. This binding
change the shape of the enzyme’s
active site though, so the reaction
rate decreases. When the inhibitor
leaves the enzyme return to it’s
normal shape
Irreversible inhibitors:
These molecules bind permanently with the enzyme molecule and so
effectively reduce the enzyme concentration.
22
Eukaryotic and
Prokaryotic Cells
Prokaryote = without a nucleus
Eukaryote = with a nucleus
23
Eukaryotic cells
24
Components









Cytoplasm
Nucleus
Mitochondria
Chloroplast
Ribosomes
RER
SER
Golgi body
Vacuoles
25
Components cont.







Lysosomes
Cytoskeleton
Centriole
Cilium and Flagellum
Microvilli
Cell membrane
Cell Wall
26
Prokaryotic cells
27
Components









Cytoplasm
Ribosomes
Circular chromosome (DNA)
Plasmid
Cell Membrane
Mesosome
Cell Wall
Capsule (or slime layer)
Flagellum
28
Summary of Differences!
Prokaryotic Cells
Eukaryotic cells
small cells (< 5 mm)
larger cells (> 10 mm)
always unicellular
often multicellular
no nucleus or any membrane-bound
organelles
always have nucleus and other
membrane-bound organelles
DNA is circular, without proteins
DNA is linear and associated with
proteins to form chromatin
ribosomes are small (70S)
ribosomes are large (80S)
no cytoskeleton
always has a cytoskeleton
cell division is by binary fission
cell division is by mitosis or meiosis
reproduction is always asexual
reproduction is asexual or sexual
29
The Ultrastructure Of A
Typical Bacterial Cell
30
The Bacterial Cell

This is a
diagram of
a typical
bacterial
cell
31
The Bacterial Cell

This is what a
bacterial cell
looks like under
an electron
microscope.
32
Next- The Organelle and their
functions
33
Bacterial Cell Wall



Made from the Glycoprotein murein.
Its purpose is to provide the cell with
strength and rigidity.
It is permeable to solutes.
34
Cell Membrane



This is made from phospholipids,
proteins and carbohydrates, forming a
fluid-mosaic.
It surrounds the bacteria and is its most
important organelle.
It is controls the movement of
substances in and out of the cell.
35
Genetic material


The prokaryotic Bacterial cell has no
nucleus.
Its genetic material (DNA) is in the form
of a circular chromosome which is in the
cytoplasm
36
Ribosomes





These are the smallest and most
numerous of cell organelle.
Bacteria have small (70s) ribosomes
Their purpose is protein synthesis for
the cells own use.
They consist of protein and RNA.
They are located free in the cytoplasm
37
Flagellum



This is a rigid rotating tail.
It’s purpose is to propel the cell.
Clockwise rotation is what propels the
cell forward, anticlockwise rotation
causes a chaotic spin.
38
Plasmid



A plasmid is a small circle of DNA.
Bacterial cells have a number of
plasmids.
Plasmids are used to exchange DNA
between bacterial cells.
39
Capsule




This is a kind of slime layer covering the
outside of the cell wall.
It is composed of a thick
polysaccharide.
It is used to stick cells together and as a
food reserve.
It is also there to protect the cell from
desiccation, and from chemicals.
40
OSMOSIS
41
Osmosis is the net
movement of water
molecules across a
Partially-permeable
membrane.
Water molecules move
randomly with a
certain amount of
kinetic energy…
42
Distilled water separated by a partiallypermeable membrane:
Water molecules are moving from
one side of the membrane to the
other but there is no net osmosis
43
If a substance is dissolved in water, the
kinetic energy of the water molecules is
lowered.
This is because some water molecules
aggregate on the surfaces of the other
molecules…
44
For osmosis we talk about the
potential water molecules have to
move – the OSMOTIC POTENTIAL.
Distilled water has the highest
potential (zero).
When water has another substance
dissolved in it, the water molecules have
less potential to move. The osmotic
potential is NEGATIVE.
45
Water molecules always move from
less negative to more negative water
potential.
Net osmosis
= LN MN
46
The osmotic potential of a cell
is known as its WATER
POTENTIAL. For animal cells,
the water potential is the
osmotic potential of the
cytoplasm.
47
An animal cell with water
potential –50kPa is
placed in a solution…
48
Water potential of
cytoplasm = -50kPa
Osmotic potential of
solution= -20kPa
If the osmotic
potential of the
solution is less
negative than the
water potential of the
cytoplasm(the
solution is
hypotonic), net
endosmosis will
occur, i.e. water will
move into the cell
from the solution.
The result will be
haemolysis (the cell
will burst)
49
Water potential of
cytoplasm= -50kPa
Osmotic potential of
solution = -80kPa
If the osmotic
potential of the
solution is more
negative than
the water
potential of the
cytoplasm (the
solution is
hypertonic), net
exosmosis will
occur. The result
will be crenation
(the cell will
shrivel up)
50
Water potential of
cytoplasm= -50kPa
Osmotic potential of
solution= -50kPa
If the
osmotic
potential of
the solution
is the same
as the water
potential of
the
cytoplasm
(the solution
is isotonic),
there will be
no net
osmosis.
51
In animal cells, the water potential is
equal to the osmotic potential of the
cytoplasm, but this is different in plant
cells…
Plant cells have a cell wall, which
exerts an inward pressure when the
cell is turgid. This is known as the
pressure potential.
The water potential of an animal cell is
equal to the osmotic potential of the
cytoplasm plus the cell wall pressure:
W.P.= O.P. + P.P.
52
A plant cell with water
potential –50kPa is
placed in a solution…
53
If the solution is
hypotonic, net
endosmosis
occurs and the
cell becomes
fully turgid.
Water potential of cell = 50kPa
Osmotic potential of
solution = -20kPa
54
Water potential of cell
= -50kPa
Osmotic potential of
solution = -80kPa
If the solution is
hypertonic, net
exosmosis
occurs and
causes
plasmolysis
(the cell
membrane pulls
away from the
cell wall. The cell
wall stays intact).
55
Water potential of cell
= -50kPa
If the solution is
isotonic, no
net osmosis
occurs. The cell
is not
plasmolysed, but
it is not fully
turgid either.
Osmotic potential of
solution = -50kPa
56
Your
body is made up of millions of cells.
Mammals and plants are multicellular which means
they have many cells.
Each type of cell carries out a different function.
57
Differentiation


This is the development of a young,
unspecialised cell into a mature specialised
cell.
This enables cells to carry out a particular
function.
58
 Cells
that are similar in shape and
have a common function are often
collected together and attached to
each other.
 They form a tissue.
 A tissue is a collection of
DIFFERENTIATED CELLS which
are specialised for a particular
function within the organism.
59
An example of a tissue.
We know that a tissue is a group of cells with
a similar structure.
 So, if we look at skeletal muscle, this is a
TISSUE made up from skeletal muscle cells.

60
What is an ORGAN?
Different tissues are grouped together to
make an ORGAN.
 An organ contains several different tissues,
all of which contribute to its overall function.
 An example of an organ is the pancreas.
 Organs work in groups called organ
systems, eg, respiratory system.

61
KEY WORDS!




MULTICELLULAR
DIFFERENTIATION
TISSUES
ORGANS
62
Biology
The development of internal gas exchange
surfaces in larger organisms to maintain
adequate rates of exchange. Mammals (alveoli,
bronchioles, bronchi, trachea, lungs), including
the ventilation system.
63
To enable efficient gas exchange organisms
have to be ‘adapted’. In this case the walls of
the alveoli are made up of a layer of epithelial
cells which are flattened. The capillaries are
also made up from this way. This allows gases
to diffuse through two cells only. To keep the
alveoli moist water constantly diffuses through
it.
64
The respiratory system is the
gas exchange organ in
mammals. It contains the
following:





Alveoli
bronchioles
bronchi
Trachea
lungs
This can be seen on the following diagram:
65
66


The concentration
gradient across the
respiratory system is
maintained by:
Blood flow on one
side
Air flow on the other
side
This allows oxygen to
diffuse down its own
gradient from air to
blood, while carbon
dioxide can diffuse
down its own
concentration gradient
from blood to air.
The flow of air into and out of the alveoli is known as
Ventilation, and has two stages:
67
Inspiration:
Expiration:
How it works-
How it works:




Diaphragm flattens and
contracts
Intercostal muscles contract
making the ribs come up and out
This increases the volume of the
the thorax which in turn
increases the lung and alveoli
volume
Pressure of air is decreased and
so air flows IN to equalise this.




Diaphragm relaxes and curves
upwards
Ribs fall as intercostal muscles
relax
This decreases volume of thorax
which in turn decreases lung and
alveoli volume.
This increases the pressure of
air and so air flows OUT to
equalise this.
68
The following
diagram helps explain
this:
69
Table to show what happens to the composition of air
when it reaches the alveoli
Component
Atmospheric
Air (%)
Expired
Air (%)
N2 (plus inert gases)
O2
CO2
H2O
78.62
20.85
0.03
0.5
100.0%
74.9
15.3
3.6
6.2
100.0%
70
The Gut Wall
Frehana Ali
71
The Gut Wall
The gut wall is divided into 3 main layers:
 An outer muscle layer, protected by a
thin coating of fibres
 A middle layer, called the submucosa
 An inner layer, called the mucosa
72
The structure of the gut wall is not the same all
along the gut.
The layers have special features in different regions
that allow that part of the gut to carry out specific
functions.
The different regions are:
•Oesophagus
•Stomach
•Duodenum
•Ileum
73
Oesophagus




Main function - To push food to the stomach.
Muscle layer – Two thick layers force solid
food along by peristalsis.
Submucosa – Elastic to allow expansion as
food passes. Glands secrete mucus to
lubricate passage of food.
Mucosa – Lining has several layers of
flattened cells; outer layers can be rubbed off
as food passes without causing damage to
cells underneath. Folds allow expansion as
food passes.
74
Stomach




Main function – Temporary food store.
Muscular churning mixes and breaks up food.
Hydrochloric acid produced kills micro
organisms in food. Some digestion.
Muscle layer – Three layers run in different
directions. As the layers contract and relax, this
creates an effective churning action
Submucosa – Separates muscular and
glandular layers.
Mucosa – Layer is thick with deep pits. These
contain many glands that secrete mucus,
enzyme and acid.
75
Doudenum (first 25cm of small intestine)




Main function – Neutralisation of stomach
acid. Point of entry for Pancreatic juice and
bile. Digestion and some absorption.
Muscle layer – Two layers for peristalsis.
Submucosa – Contains Brunner’s glands
that secrete alkaline mucus. This helps to
neutralise stomach acid.
Mucosa – Contains many glands that secrete
mucus and enzymes. Folded into numerous
projections called villi. These increase the
surface area for absorption of digested food.
76
Ileum (lower part of small intestine)




Main function – Completion of digestion.
Absorption of products of digestion.
Muscle layer – Two layers peristalsis.
Submucosa – Contains many blood and
lymph vessels that take up absorbed food
and transport them around the body.
Mucosa – Similar to Duodenum, but fewer
glands. Patches of cells called Paneth cells,
at base of glands, which help defend against
bacterial infection. Some enzyme production.
77
THE HUMAN
DIGESTIVE
SYSTEM.
•EPITHELIAL CELLS.
•ORGANS.
•TISSUES.
78
Epithelial cells are highly specialized cells that line the small intestine. They
help with the process of absorption of water, glucose molecules and mineral
ions. The cells surface if highly folded, since this greatly increases the surface
area of the cell. A greater surface area means that there is more cell
membrane across where diffusion, osmosis, facilitated diffusion and active
79
transport can take place.
AN INTESTINAL
EPITHELIAL CELL.
Maltase, for example, digests maltose into
glucose, which passes immediately into the
cytoplasm of the nearby epithelial cells.
The epithelial cells lining
the small intestine have
huge numbers of very
thin, finger-like
projections on their
surface, called microvilli
as seen on the picture
opposite. The membranes
of these microvilli contain
the enzymes that break
down disaccharides into
monosaccharides.
80
INTESTINAL EPITHELIAL CELLS.
The panels depicts the
bulk of this surface area
expansion, showing villi,
epithelial cells that cover
the villi and the microvilli
of the epithelial cells. Note
in the middle panel, a light
micrograph, that the
microvilli are visible and
look something like a
brush. For this reason, the
microvillus border of
intestinal epithelial cells is
referred to as the "brush
border".
81
INTESTINAL EPITHELIAL
CELLS.
If examined closely, the lumenal surface
of the small intestine appears similar to
velvet due to it being covered by millions
of small projections called villi which
extend about 1 mm into the lumen. Villi
are only the most obvious feature of the
mucosa which houses a dynamic, selfrenewing population of epithelial cells
that includes secretory cells, endocrine
cells and the mature absorptive
epithelial cells which take up nutrients
from the lumen and transport them
into blood, fulfilling the basic function
of the digestive system.
A light microscope view of
epithelial cells from the small
intestine. x 1000.
82
EPITHELIAL CELL DYNAMICS.
The mucosa of small intestinal mucosa is
arranged into two fundamental structures:
Villi are projections into the lumen covered
predominantly with mature, absorptive enterocytes,
along with occasional mucus-secreting goblet cells.
These cells live only for a few days, die and are shed
into the lumen to become part of the ingesta to be
digested and absorbed. That's right, we're all really
cannibals.
Crypts (of Lieberkuhn) are moat-like invaginations
of the epithelium around the villi, and are lined
largely with younger epithelial cells which are
involved primarily in secretion. Toward the base of
the crypts are stem cells, which continually divide
and provide the source of all the epithelial cells in the
crypts and on the villi.
83
EPITHELIAL CELL DYNAMICS.
Coordinated contractions of smooth muscle
participate in several ways to facilitate
digestion and absorption in the small intestine:
foodstuffs are mixed with
digestive enzymes from the pancreas
and bile salts from the biliary system
nutrient molecules in the lumen
are constantly dispersed, allowing
them to contact the epithelium where
enzymatic digestion is completed and
absorption occurs
chyme is moved down the
digestive tube, making way for the
next load and also eliminating
undigestable, perhaps toxic
substances
In most animals, the small intestine cycles
through two states:
Following a meal, when the lumen of the small
intestine contains chyme, two types of motility
predominate: segmentation contractions chop,
mix and roll the chyme and peristalsis slowly
propels it toward the large intestine.
The interdigestive state is seen
between meals, when the lumen
is largely devoid of contents.
During such times, so-called
housekeeping contractions
propagate from the stomach
through the entire small intestine,
sweeping it clear of debris. This
complex pattern of motility is the
cause of "growling".
84
EPITHELIAL CELL DYNAMICS.
The tight junctions between cells are impermeable to large
organic molecules from the diet (e.g. amino acids and
glucose). Those types of molecules are transported
exclusively by the transcellular route, and only because the
plasma membrane of the absorptive enterocytes is
equipped with transporter molecules that facilitate entry
into and out of the cells.
An electron microscope view of epithelial cells from the
small intestine.
Magnification x 2000.
85
EPITHELIAL CELL DYNAMICS.
It is important to recognize that the
epithelium of the gut is not a monotonous
sheet of functionally identical cells. As
ingesta travels through the intestine, it is
sequentially exposed to regions having
epithelia with very different characteristics.
This diversity in function results from
differences in phenotype of the enterocytes
- that is, the number and type of transporter
molecules they express in their plasma
membrane and the structure of the tight
junctions they form. Even within a given
segment there are major differences in the
type of transport that occurs - for example,
cells in the crypts transport very differently
than cells on the tips of villi.
Within the intestine, there is a proximal to distal
gradient in osmotic permiability. As you proceed
down the tube, the effective pore size through the
epithelium decreases. This means that the
duodenum is much more "leaky" to water than the
ileum and the ileum more leaky than the colon. Do
not interpret this to mean that as you go down the
tube, the ability to absorb water decreases! It means
that water flows across the epithelium more
"freely" in the proximal compared to distal gut
because the effective pore size is larger. The distal
intestine actually can absorb water better than the
proximal gut.
The observed differences in permiability to water
across the epithelium is due almost entirely to
differences in conductivity across the paracellular
path - the takehome message is that tight junctions
vary considerably in "tightness" along the length of
the gut.
86
ORGANS.
•An organ is a group of
physically-linked
different tissues
working together to
perform a specific
physiological function.
A picture of
the small
intestine.
87
TISSUES.
A tissue is a group of similar cells
performing a particular function.
•Simple tissues are composed of one type of
cell, while;
•Compound tissues are composed of more
than one type of cell.
88
The sites of production and action of
amylases; endopeptidases;
exopeptidases; lipase; maltase; and
bile. Mechanisms for the absorption
of food by the ileum, including roles
of diffusion, facilitated diffusion and
active transport.
89
Amylase production sites




The human body produces amylase twice
during the digestive process.
The first time food comes into contact with
it is in the mouth, where it is secreted by
the salivary glands in saliva.
Amylase is an enzyme, and so therefore a
protein, and is easily denatured by the
extreme pH of the stomach.
Therefore it is produced again by the
pancreas, and is added to the chyme in the
duodenum.
90
Endopeptidase production sites




Some endopeptidases with are secreted into
the stomach from gastric glands in the
mucosa layer e.g. pepsin, rennin.
These have an optimum pH of about 1 or 2
They are denatured in the neutral pH of the
chyme when it enters the duodenum.
More endopeptidases are produced in the
pancreas and join the chyme in the
duodenum.
91
Exopeptidase and maltase sites




Exopeptidases are found in the
membranes of epithelial cells in the
ileum.
They are linked to proteins which allow
protein entry into the cells.
Maltase is also found in epithelial cell
membranes
They are linked to proteins which allow
monosaccharide entry into the cell.
92
Bile and lipase production sites




Bile is produced in the liver
It is then stored in the gall bladder till it is
needed.
Lipase in produced
in the pancreas.
Both join the chyme
in the duodenum.
93
General enzyme actions.




Enzymes like amylase, endo- and
exopeptidases, lipase and maltase are all
catalysts in breakdown reactions.
The thing that is to be reacted is called the
substrate.
The substrate joins to the active site in the
enzyme
The active site is specific to the substrate
94
How an enzyme catalyses
reactions (1)



The substrate is then distorted by the
enzyme.
This shapes the substrate into a
transition state where the end product is
more likely to be achieved
E.g. the stretching of a bond that is
broken in the end products.
95
How an enzyme catalyses
reactions (2)



The enzyme also lowers the activation
energy of the reaction.
This is the energy required for the reaction
to take place
If this is lowered the reaction takes place a
lot faster
96
Specific reactions catalysed




Amylase catalyses the break down of
starch into maltose
Endopeptidases and exopeptidases
catalyse the break down of polypeptide
chains
Maltase catalyses the breakdown of
maltose into glucose
Lipase catalyses the breakdown of
triglycerides into fatty acids and
glycerol.
97
Endopeptidases and
Exopeptidases







Endopeptidases break down larger poly peptide
chains into smaller ones.
They do this by targeting particular amino acids.
E.g pepsin breaks bonds between tryosine and
phenylaline
Exopeptidases break off amino acids from the ends
of polypeptide chains.
Carboxypeptidases work from the carboxyl acid end
of an amino acid
Aminopeptidases work from the amino end
Dipeptidases break dipeptides in half.
98
Bile




Bile is a yellow alkaline fluid
It is used to neutralise the acidic chyme
when it leaves the stomach.
It is also used to emulsify fats into
droplets called micelles.
This can then be broken down using
lipase.
99
Absorption of sugars and amino
acids in the ileum




Monosaccharides and amino acids are
absorbed into the epithelial cells in the ileum.
This is done used active transport, which
involves the use of ATP.
This means they can be absorbed very
quickly even against a concentration gradient.
They are then allowed to diffuse into the
capillaries of the villi which flow into the
superior mesenteric artery and therefore
round the body.
100
The absorption of lipids in the
ileum






The fatty acids and glycerol are absorbed into the
epithelial cells.
Here they are re-synthesised into lipids and are
formed with proteins to form lipoproteins called
chylomicrons.
These diffuse into the lacteal.
This is the lymph vessel in the villi
They are carried through to join the vena cava artery
and are carried through the body
NB Lipids are not properly broken down until they are
needed for respiration, in the liver or muscle cells. 101
Extracellular Digestion In
Saprophytic Fungus
102

Fungi are not consumers unlike animals.

They are either saprophytes (decomposers)
or pathogens.

Therefore use saprophytic nutrition.

This means they do not ingest food but use
extra cellular digestion.
103
Extracellular Digestion



This means that the fungi secrete digestive enzymes.
These digestive enzymes are carbohydrases,
proteases and lipases.
These are secreted in to the material around them
which enables them to absorb the soluble products
such as amino acids and sugars. They are absorbed
by facilitated diffusion and active transport
104
Hyphae



Fungi is composed of thin threads called
hyphae.
These grow quickly penetrating dead
materials such as leaves.
When mould grows on bread it looks like
cotton wool but is in fact a mass of hyphae.
105
Hyphae

This mass of hyphae is also known as a fungi
mycelium.

The hyphae gives the fungi a large surface
area to volume ratio.
106
Biochemical Tests
107
Biochemical Tests
Biochemical tests identify the main biologically
important chemical compounds.
For each test take a small amount of the substance
to test, shake it in water in a test tube.(The
substance may need grinding with a pestle and
mortar, to break up the cells and release the cell
contents.)
Many of these compounds are insoluble, but the
tests work just as well in a fine suspension.
Benedict’s Test For Reducing
Sugars
All monosaccharide’s and most disaccharide's will reduce
copper (II) sulphate, producing a precipitate of copper (I)
oxide on heating, so they are called reducing sugars.
Benedict’s reagent is an aqueous solution of copper (II)
sulphate, sodium carbonate and sodium citrate.
 Grind up sample

To approx. 2cm3 of test solution add equal quantity of
Benedict’s reagent.

Shake, and heat for a few minutes at 95C in a water bath

A precipitate indicates reducing sugars

Original Pale Blue = no reducing sugar
Brown/Red = reducing sugar
109
Benedict’s Test For NonReducing Sugars
Non-Reducing sugars do not reduce copper sulphate.
However, if it is first hydrolysed to its constituent
monosaccharides, it will then give a positive Benedict’s
Test.
First test a sample for reducing sugars, to see if there are any
present before hydrolysis.
Then using a separate sample,
 Boil the test solution with dilute hydrochloric acid for a few
minutes to hydrolyse the glycosidic bond.
 Neutralise, by adding small amounts of solid sodium
hydrogen carbonate until it stops fizzing.
 Perform the Benedict’s test
 A positive result indicates the presence of simple nonreducing sugar.
110
Iodine Test For Starch



To approximately 2cm of the test solution add 2 drops of
iodine/potassium iodide solution.
A blue/black colour indicates the presence of starch.
Starch is only slightly soluble in water, but the test works
well in a suspension or as a solid.
111
Emulsion Test For Lipids
Lipids do not dissolve in water, but do dissolve in ethanol.
This characteristic is used in the emulsion test.
 Grind up sample
 Shake some test sample with about 4cm3 of ethanol.
 Decant the liquid into a test tube of water leaving any undissolved substances between.
If there are lipids dissolved in the ethanol, they will precipitate
in the water, forming a cloudy white emulsion.
112
Biuret Test For Protein



To about 2cm3 of test solution add an equal volume of
biuret solution, down the side of the test tube.
A blue ring forms at the surface of the solution, which
disappears on shaking, and the solution turns lilac-purple,
indicating protein.
The colour change is due to a complex between nitrogen
atoms in a peptide chain and copper (II) ions, so this is
really a test for peptide bonds.
113
Differential Centrifugation


This is the most common method of
fractionating cells
Fractionation is the separation of the
different organelles within the cell
114
Method:



1. Cut tissue in an icecold isotonic buffer.
It is cold to stop
enzyme reactions,
isotonic to stop
osmosis and a buffer
to stop pH changes.
2. Grind tissue in a
blender to break open
cells.
Filter to remove
insoluble tissue
115


4. Centrifuge
filtrate at low
speeds ( 1000 X g
for 10mins )
This pellets the
nuclei as this is the
densest organelle
116


5. Centrifuge at
medium speeds ( 10
000 x g for 30
mins )
This pellets
mitchondria which
are the second
densest organelle
117


6. Centrifuge at
high speeds ( 100
000 x g for 30
mins)
This pellets ER,
golgi apparatus and
other membrane
fragments
118


7 Centrifuge at
very high speeds (
300 000 x g for
3hrs)
This pellets
ribosomes
119
Investigating Cell Function
 Differential
Centrifugation allows
us to look at each organelle within
the cell
 We can look at the individual
organelles and study them in detail
 This helps to determine each
organelles function within the cell
120
The Electron Microscope




Microscopes allow us to see living organisms which
are too small to be seen by the naked eye
The electron microscope uses beams of electrons
rather than light to illuminate the specimen
A beam of electrons has an effective wavelength
of less than 1 nm so it can be used to resolve small
sub-cellular ultra-structure
The development of the electron microscope
allowed biologists to view the organelles within a
cell for the first time
121
There are two types of
electron microscope




The transmission
microscope. (TEM)
Works like a light
microscope, it transmits a
beam of electrons through
a thin specimen
Then focussing the
electrons to form an
image on a screen
This is the most common
form of electron
microscope and gives good
resolution.



The scanning electron
microscope (SEM)
This scans a fine
beam of electron onto
specimen and collects
electrons scattered
by surface
This has poor
resolution but gives
good 3-D images
122
Disadvantages of the
Electron Microscope


The specimens must be fixed in
plastic and viewed in a vacuum and so
they must be dead
Sometimes specimens can be damaged
by the electron beam and must be
stained with an electron-dense
chemical
123