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Cells
MCD YEAR 1
Anil Chopra
Contents
MCD – Cells 1 – Cells and Organelles ....................................................................... 1
MCD – Cells 2 – Pathogenic Microbes ....................................................................... 3
MCD - Cells 3 – Cell Membranes ............................................................................... 4
MCD- Cells 4 – Blood .................................................................................................. 7
MCD – Cells 1 – Cells and Organelles
Anil Chopra
1. Understand what constitutes a cell, and the scale of cells and molecules
What Constitutes a Cell?
- make up tissues and organs
- separated my membranes
- if they live independently: protozoa
- they can come together to form colonies  specialise.
- Many cells have polarity.
Scale if Cells
Size of cell: 50μm
Weight of a cell: (density = 1.06ng)
Size of virus: 0.1 μm/100nm
2. Demonstrate the following on a suitable transmission electron micrograph:
nucleus; nucleolus; nuclear envelope; mitochondrion; rough endoplasmic
reticulum; smooth endoplasmic reticulum; ribosomes; Golgi apparatus; secretory
granule; plasma membrane; cytoskeletal components.
1 Nucleus
1a Euchromatin
1b Heterochromatin
2 Nucleolus
3 Nuclear membrane
4 Nucleopore
5 Ribosomes
6 Rough endoplasmic reticulum
(with ribosomes) 7 Smooth
endoplasmic reticulum
8a Longitudinal- and crosssections of a mitochondrion
showing aristae8b Longitudinaland cross-sections of a
mitochondrion showing tubules
8c Longitudinal- and crosssections of a mitochondrion of
the prismatic type
8d Longitudinal- and crosssections of a mitochondrion
showing saccules
9 Longitudinal- and crosssections of a centriole10 Golgi
Apparatusus
11 Golgi vesicles
12 Endopinosomes,
endopinocytotic vesicles
13 primary lysosomes
14 secondary lysosomes,
phagocytosomes
15 tertiary lysosomes
16, 17 Multivesicular bodies
18 peroxisomes, microbodies
19 Secretory granules
20 Microtubules
21 Actin filaments
22 Intermediate filaments
linking to desmosomes
24 Glycogen granules
25 Fat droplets
26 Synapse
27 Synaptic body28 Cell
membrane with
glycocalyx(polysaccharides
and glycoproteins)
29 Intercellular space
30
31 Tight junction
32 Adherens junction
33 Fascia Adherens with actin
filaments (cardiac)
34 Punctum Adherens
35 Macula Adherens
(desmosome)
36 Hemidesmosome (joins cell
to basal lamina)
37 Gap junction38 Microvilli
with glycocalyx
39 Cilia
40 Basal bodies of microcilia
41 Stereocilia
42 Basal lamina
3. Identify the essential characteristics of prokaryotic and eukaryotic cells.
Prokaryotes
Eukaryotes
 Kingdoms of Monera and Archea
 Kingdoms of Animals, plants and
protocists.
 Do not contain organelles
 Contain organelles inc. nucleus
 May have flagella for locomotion
 Have 0.001 times DNA as eukaryote.  Have a high degree of organisation
 Have 1000 times DNA as prokaryote.
 High degrees of mutation
 Relatively rare mutations
 DNA is circular
 DNA chromosomal in nucleus
 Smaller Ribosomes
 Larger Ribosomes
 Contins a single copy of
chromosomes.
 Diploid containing 2 different
chromosomes
 Contains peptidoglycan.
 Contains NO peptidoglycan.
 Less defined cytoskeleton.
 Well-defined cytoskeleton.
4. Explain the relationship of individual cells to the organisation of the whole body.
5. Understand that cancer is a disorder of cell division
Relationships between cells and the whole body:
Cells ---make up tissues ---which make uporgans---which make up systems
 Many diseases/conditions are caused by problems at a cellular level.
 Cancer is caused by irregular cell division. Mutations include:
o Cells signalled to divide but then not to stop
o DNA copying correction mechanism is halted
o Telomeres are lengthened
o Calls not limited to tissue boundaries
o Tumours spread to tother tissues
o Cells die due to lack of O2.
6. Describe the predominant types of molecules in a cell
solutes include:
amino acids
soluble proteins
mRNA
tRNA
ions (K+, Na+, Mg2+, Ca2+, PO42-,
Lipids, cholesterol
Peptides
Cl )
sugars
Nucleotides: e.g. ATP, cAMP, GTP
MCD – Cells 2 – Pathogenic Microbes
Anil Chopra
1.
2.
3.
4.
Name the main types of infectious agent causing disease in humans
List the key differences between prokaryotes and eukaryotes
Give examples of each type of infectious agent and the disease it causes
Name the distinguishing features of the different types of infectious agent and
explain how they replicate
Example
Features
Type
Mycobacterium
Prokaryotes that replicated by binary fission, they
Bacteria
tuberculosis, E. coli,
contain chromosomes, but no nucleus. Their DNA
Neisseria meningitides is circular. They inhabit the gut, skin, they stimulate
the immune system and aid with metabolism and
provision of nutrients. Some are pathogenic and can
in the immuno-compromised, cause infections
(opportunistic infections).
HIV, common cold,
Not cells in their own right (obligate parasites),
Viruses
influenza
inhibit host cell from replicating. Contain DNA or
RNA and use reverse transcriptase to divide. Make
use of a host cell nuclear synthetic machinery to
replicate and divide by budding out of the host cell.
Show host specificity but infect almost all other life
forms including bacteria.
Candida albicans
Single celled eukaryotes that exist as yeasts or
Fungi
(thrush), aspergillus
filaments. Yeasts bud or divide; filaments (hyphae)
fumigatus
which have cross walls or septa.Usually affect
immuno-compromised people. Causes mycoses
(infection).
Protozoa
Malaria, leishmaniasis
Single celled eukaryotes, include intestinal, blood
and tissue parasites. Replicate in host by binary
fission or by forming trophozoites in a cell. Many
have complicated life cycle involving 2 hosts.
Infection acquired by ingestion or via a vector.
Helminths
Tapeworm, fluke,
roundworms
Multicellular organisms. Have life cycles outside
human host, visible to the naked eye. Complex life
cycle including embronation to generations in
different hosts.
MCD - Cells 3 – Cell Membranes
Anil Chopra
1) Explain the function of phospholipids
bilayers in aqueous environment.
Constitutes – phospholipid bilayer
C=C unsaturated bond causes kink in chain.
Causes them not to pack as tightly as the kinks
take up room.
Lipids have a hydrophilic head (polar) and
hydrophobic tail. To avoid water, the tails pack together.
They suspended in water and form micelles or droplets. They can also arrange
themselves into bilayers (a layer two molecules thick). Droplets in cells are called
liposomes.
 Cholesterol is also found in membranes – acts to increase membrane stiffness.
 Glycolipids are found on the extracellular side of the membrane with negative
charges inside the cell
The bilayers need to:
- Have selective permeability
- Be impermeable to macromolecules, biochemical intermediates
- Be permeable to nutrients, waste products
- Allow transfer of information (= signal transduction)
The Bilayer is Dynamic
Flip-flop: lipids switch sides in the bilayer - occurs less than once a month for any
individual molecule.
Diffusion: lipid molecules readily exchange places with their neighbours within a
monolayer (~107 times a second). This gives rise to a rapid lateral diffusion, with a
diffusion coefficient (D) of about 10-8cm2/sec, which means that an average lipid
molecule diffuses the length of a large bacterial cell (~2 µm) in about 1 second.
2) Draw the structure of phosphotidylcholine and identify the component parts.
3) Describe the permeability properties of the phospholipid bilayer.
Bilayer Permeable to:
Not permeable to:
Cations (K+, Na+, Ca+) & Anions (Cl-, HCO3-)
By osmosis/diffusion
Small hydrophilic molecules
down diffusion gradient
Macromolecules
H2O
O2
CO2
Some can
move by
facilitated diff.
or active trans.
4) Distinguish between simple diffusion, facilitated diffusion and active transport.
Lipids can exchange places with neighbours – Lateral diffusion, but can rarely “flip
flop” i.e. switch sides of the bilayer.
This can occur by:
- Facilitated diffusion: charged pores, vary in size, shape and other characteristics.
- Co-transport: coupled transporters, symporters, e.g. sugars and amino acids with
Na+ or antiporters e.g. Na+/K+ exchange.
5) Functions of membrane proteins
Proteins in the membrane increase the cell fluidity. They are also used for transport,
receptors, recognition and adhesion of cells, electron carriers.
Membrane Potential and Potassium Gradients
The Na+-K+ pump exchanges 3 Na+ ions from inside the cell for two K+ ions on the
outside. There are two consequences:
o Ionic gradients are created: less Na+ and more K+ inside the cell than outside.
o A charge gradient is created, as more positive charges are pushed out than are
coming in. This results in the inside of the cell being at a more negative potential
than the outside.
-
-
-
[K+]i is high inside the cell
There is a therefore a tendency for K+ to move out of the cell
This is counterbalanced by the electric potential which opposes the movement of
positive charges out of the cell, as this would accentuate the voltage difference
across the cell.
An equilibrium will be reached when the rate of inward movement of K+ ions
down the electrochemical gradient equals the rate of outward movement down the
concentration gradient
Thus the electrical imbalance caused by the sodium pump will not quite be
compensated by K+ movement
The end result is a membrane potential, with a voltage difference across the
membrane (inside negative).
This is important for signaling in nerves, muscles, etc
6) Explain the movements of ions across a cell membrane against a
concentration gradient.
Movement of ions:
- Cl- ions move into the cell down the concentration gradient.
- As proteins usually have a negative (-) charge, there is a high conc. of K+ ions
to balance out; and usually low Cl- ion concentration.
- Na+ ions are low in conc. in the cell.
- The Na+/K+ exchange pump, pumps 2K+ ions in for every 3Na+ ions pumped
out.
- This requires ATP  ADP + Pi
7) Explain the entry of glucose and amino acids against a conc. Gradient.
The Na/K exchange pump aids glucose transport. Glucose moves down its
concentration gradient into the cell, binds to glucose transporter and flip-flops along
with the Na ion moving down the concentration gradient.
8) Explain how external Chemical signals can be sensed at the interior of the cell
Signalling:
 Secretion of hormones – exocytosis: substances packed into intracellular vesicles toward
extracellular space by fusion with cell membrane.
 External messengers cause entry: e.g. messenger like neurotransmitter binds to
membrane-bound Ca2+ ion channel protein causing it to open.
 External messenger brings about other change e.g. endocytosis: engulfment of
extracellular substance by intracellular, membrane-bound vesicles or hormone
binds to receptor on membrane causing substrate within the cell to send off
second messenger to other parts of the cell e.g. nucleus.
The Neuromuscular Junction
 Depolarisation of the muscular post-synaptic membrane results in a propagated
action potential.
 The wave of depolarization extends into the t-tubules (invaginations of the cell
membrane) to transmit the activation signal into the core of each muscle cell in
the motor unit.
 Close contact with the sarcoplasmic
membrane via triadic junctions involving
the dihydropyridine (t-tubule membrane)
and ryanodine receptors (sarcoplasmic
reticulum membrane) results in calcium
release from the sarcoplasmic reticulum.
 Calcium diffusion into the myofilaments
lattice and calcium binding the troponin
on the thin filaments (actin) in skeletal
and cardiac muscle result in activation of
the contractile machinery and contraction.
MCD- Cells 4 – Blood
Anil Chopra
1) List the main functions of the blood.
 Respiratory function, ie transport of O2 and CO2
 pH buffering, ie stabilisation of acidity/alkalinity status
 Nutritional, ie transport of glucose, fats etc.
 Excretory, ie transport of waste products eg urea
 Hormone transport
 Haemostasis ie clotting to stop blood loss
 Defence against infection
 Temperature control
 Maintenance of fluid balance
2) List the major components of the blood.
 Plasma and the formed elements: erythrocytes (RBCs), leukocytes (WBCs),
thrombocytes (platelets)
 There is approximately 5-6l of blood in males and 4-5l of blood in females
3) Explain the difference between plasma and serum.
 When plasma is allowed to clot and the clot removed, the liquid that remains is
called serum. Serum is plasma minus fibrinogen.
4) Describe the essential features of the erythrocyte and list its major functions.
 Constitute almost half the volume of blood. Anucleate, biconcave discs – diameter
8.5μm, thickness 2.4μm filled with a concentrated haemoglobin solution
surrounded by a membrane. Functions are O2 transport in combination with
haemoglobin; CO2 transport – greatly facilitated by carbonic anhydrase which
speeds up CO2 + H2O H2CO3
5) Explain the erythrocytic difference between men and women.
 Females have a lower haematocrit (H) (% of blood which is the RBC), whole
blood Hb (Hb) (conc. of Hb) and red cell count (n). This is because increased
testosterone boost the bone marrow into producing more erythrocytes. Females
lose RBCs in menstruation.
 Also women tend to be small on the whole, and therefore carry less blood and
therefore fewer red blood cells.
 Red Blood cell parameters:
 N (or RBC) = number of red blood cells (about 5.1x1012 in males and 4.5x1012 in
females)
 H (or Hct) = haematocrit – this is the percentage of the volume of a sample of
blood occupied by the red blood cells (46% in males and 41% in females)
 Hb = concentration of haemoglobin in the blood (15.5g/dl in males and 13.7g/dl in
females)
 MCV = mean cell volume = Hct/(RBC x 100) (normally around 90fl)
 MCH = mean cellular haemoglobin (Hb x 10)/RBC (around 30pg)
 MCHC = mean cell haemoglobin concentration (Hb x 100)/Hct (around 34g/dl)
 Note that the final three do not depend on gender
6) Define anaemia and list the major causes.
 Anaemia is a condition in which the Hb falls below the
normal range for the subject.
 Disturbed production (Fe, B12 or folic acid deficiencies
and kidney disease).
 Increased destruction eg sickle cell disease.
 Haemorrhage – loss of red cells and iron.
7) List the major erythrocyctic differences between iron
deficiency and vitamin B12 deficiency anaemias.
 Iron deficiency anaemia – low values for haematocrit,
whole blood Hb, red cell count, mean cell volume, mean
cell Hb, mean cell Hb concentration ie all parameters.
Essential for haemoglobin production – it occurs due to the
lack of intake but more likely due to excessive loss
(microcytic- small cells)
 Vitamin B12 anaemia – low values of haematocrit, whole blood Hb and red cell
count but high values for mean cell volume and mean cell Hb. This is essential for
normal DNA synthesis during maturation of primitive erythroid cells (macrocyticlarge cells anaemia)
8) List the major differences between the leukocyte and platelet populations of normal
blood and the erythrocyte population.
 Leukocytes have a nucleus and are fewer in number than the RBCs but of a
similar or slightly larger size. Platelets are anucleate and very much smaller than
the RBCs.
 RBC : WBC = 500 : 1; RBC : Platelet = 12 : 1
9) Explain simply the major functions of the leukocytes and platelets.
 Leukocytes defend against infection; platelets are important in haemostasis,
stemming the loss of blood after a haemorrhage ie clotting.
10) Explain simply the meaning of phagocytosis, immune reaction, chemotaxis,
diapedesis.
 Phagocytosis – ingestion of foreign material by engulfing into the cytoplasm.
 Immune reaction – the role of lymphocytes. Antibodies bind specifically to the
antigen that induced its formation.
 Chemotaxis – movement of cells up a concentration gradient towards the site of
infection where the infected agent releases a chemical that is detected by the cells.
 Diapedesis – migration of cells through the walls of blood capillaries into the
tissue spaces.
11) Describe the major requirements, nutritional and otherwise, of normal
erythropoiesis.
 Iron is essential for haemoglobin production.
 Vitamin B12 and folic acid are essential for normal DNA synthesis during the
maturation of prmitive erythroid cells.


Erythropoiesis = takes place in red marrow (skull, ribs, sternum), there is a close
balance between production and destruction, which keeps RBC count within a
small range in health.
RBC production is under the control of erythropoietin (EPO)- which is produced
in the kidney and production is increased when renal tissue becomes hypoxic.