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Friday, 18 January 2019

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1 Structure of eukaryotic cells
The nucleus: Contains hereditary material and controls cell’s activities, produces RNA and
ribosomes
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Mitochondrion: Has a double membrane (controls what
enters/exits) that folds to form cristae
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The matrix
makes up the centre of the organelle - contains proteins,
lipids, ribosomes, DNA that allows mitochondria to control
their own production of proteins (enzymes needed for
respiration)
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Chloroplasts: Carry out photosynthesis in plants
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The grana made up of thylakoids (contains photosynthetic pigment called
chlorophyll)
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Smooth endoplasmic reticulum: synthesises, stores and transports lipids/carbs

Rough endoplasmic reticulum: double membrane embedded with ribosomes, synthesise
protein/glycoproteins and send to the Golgi apparatus
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The Golgi modifies proteins by adding nonprotein compartments (carbs), produces secretory enzymes, secretes carbs in cell walls of
plants
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Lysosomes: A type of Golgi vesicle that releases lysozyme
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Ribosomes: made up of a large and small unit
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Where
protein synthesis takes place
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Provides strength to prevent
cell bursting
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In fungi, the cell wall is made up of chitin
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They contain sugars/amino acids (food
store)
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Friday, 18 January 2019
Cell specialisation and organisation:

Specialised cells have evolved to have more/fewer organelles to suit their role
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2 Structure of prokaryotic cells and or viruses
Pro vs Euk:


- Euk has a distinct nucleus, have chlorophyll, membrane bound organelles, larger
ribosomes and no capsule/plasmids


- Pro has no true nucleus, no chlorophyll, no membrane bound organelles, smaller
ribosomes and a capsule/plasmids

Bacteria:

Cell wall - made up of murein
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They contain genetic material, a capsid and
an attachment protein
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3 Method of studying cells
Resolution: ability to distinguish between 2
separate points as distinct from each other
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of times greater an image is
than the object

1mm = 1000 micrometers


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Cell fractionation:

Solution needs to be: COLD (reduced enzyme activity), ISOTONIC (same H20 potential to
prevent shrinking/swelling due to osmosis), BUFFERED (so pH doesn’t fluctuate - a change
could affect structure of the organelle)

1) Homogenisation: cells placed in homogeniser to break down cell membranes; and then
filtered to remove debris

2) Ultracentrifugation: filtrate placed in centrifuge and spun at a low speed, the most
dense organelle (nuclei) forms a pellet at the bottom
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Electrons are negatively charged = can be focussed using electromagnet

Needs to be in a Vacuum as electrons are absorbed/deflected by molecules in the air

Transmission: directed beam of electrons at specimen, creates image based on electrons
absorbed
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AD: higher mag/res than light

DIS: expensive, samples have to be dead as they are in a vacuum, image may contain
artefacts, complex staining process
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1) Interphase: cell increases in size, DNA is replicated, cell develops more organelles
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3) Metaphase: chromosome line up along the equator, spindle fibres attach to centromeres

4) Anaphase; centromeres divide and pulls the arm of the chromatid to opposite poles and
the chromosomes form a ‘v’ shape

5) Telophase: chromosomes uncoil, nuclear envelope/2 nuclei form, then cytokinesis
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Cells that lose the ability to divide undergo apoptosis to
control cell numbers
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Many cancer treatments are directed
at controlling the rate of cell division/preventing DNA replication
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Viruses: Being non-living, viruses do not undergo cell division
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REQUIRED PRACTICAL 2:

- Stained, squashed root cell tip

- Under optical microscope to identify stages on mitosis

Mitotic index: ratio of cells undergoing mitosis to cells that are not
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of cells in mitosis / total no
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This allows lipid
soluble substances to enter/leave and prevents water entering and leaving
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Other proteins that are in the bilayer are Protein channels (allow water soluble
ions to diffuse across) and Carrier proteins that bind glucose/amino acids then change
shape in order to move them across the membrane
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Cholesterol occur within the bilayer - they add strength
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They also pull together fatty acid tails to
prevent too much movement
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The carb
extends the bilayer where it acts as a receptor for specific chemicals
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Glycoproteins act as a receptor for hormones/neurotransmitters
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E
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allows lymphocytes to recognise its own cells
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The cell surface membrane has a fluid-mosaic model
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Below 0: Bilayer has less kinetic energy/closely packed together = more rigid

0-45: Phospholipids and move around - membrane is partially permeable
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Only small non polar molecules and diffuse
across the bilayer - CO2 and 02

Facilitated diffusion: it Is a passive process - doesn’t need ATP energy
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Carrier proteins/Protein channels - proteins form water
filled hydrophilic channels
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The channels are
specific
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Osmosis - the passive movement of water from a region of high water potential to a lower
water potential across a partially permeable membrane
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Carrier protein acts as a pump and co-transports molecules/ions with K+ or Na+ (Na is
actively removed/K is actively taken in from the surroundings)
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On the inside of the cell, ATP binds to the protein causing to be
hydrolysed and forms ADP and a phosphate
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The phosphate molecule is released and causes the
carrier protein to revert back to its original shape
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Co-transport and the absorption of glucose in the ileum:

Epithelial cells that line the ileum have projections called microvilli (allow more room for
carrier proteins) which increases its surface area to increase the rate of absorption
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Glucose diffuses into blood via
facilitated diffusion, but the concentration gradient remains a constant as glucose is used
up in respiration
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This takes place in one type of protein carrier
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Na diffuses into
the epithelial cells through a co-transport protein
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Adaptations off membrane for rapid transport:


- external membranes

- More protein channels/protein carriers




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4 Cell recognition and the
immune system
Defence mechanisms: Two responses cell-mediated process involving T
lymphocytes and humeral response
involving B lymphocytes
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These proteins allow the immune system
to identify:


- Pathogens - release toxins/kill cells

- Non-self material

- Toxins

- Abnormal body cells - cancer cells

Phagocytosis: Two types of phagocytes - Neutrophils (made in bone marrow and travel in
blood) and Macrophages (made in bone marrow and travel in blood/settle in lymph nodes)

Neutrophils have a multi lobed nucleus and Macrophages have one
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2) Binds to pathogen

3) Pathogen engulfed and isolated in a vesicle
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T Lymphocytes and cell mediated immunity
Antigen: stimulates an immune response - triggers production of antibodies

Lymphocytes: produced by stem cells in the bone marrow
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Cell-mediated immunity: T cells only respond to antigens attached to a body cell
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1) Pathogens engulfed by phagocytes

2) Phagocytes places its antigens on its cells surface membrane

3) Receptors on a specific helper T cell bind to it
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Cytotoxic T cells search for infected cells, attach themselves and secretes a toxic
substance which creates holes in the membrane and causes it to die
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1) B cell processes the antigens on an invading pathogen and presents them on their
surface- -becomes an APC

2) The APC binds to complimentary receptors on a T helper cell and releases cytokines
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ALL PLASMA CELLS DIE BUT MEMORY CELLS REMAIN


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Primary Vs Secondary response
Primary: slight delay as T helper cell has to select specific effector B cell
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Immune system: makes its own antibodies after being stimulated by a foreign antigen


Active immunity: production of antibodies in response to the presence of an antigen

Natural immunity: become immune after catching disease

Artificial immunity: become immune after vaccination


Passive immunity: transferring AB from person to another
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It
has a specific variable region complementary to an
antigen
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Variable region - specific sequence of amino acids,
meaning the tertiary structure of the binding site fits a
specific antigen, so an antigen-antibody complex can
form
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Neutralisation: AB bind to all antigens on a pathogen and prevents its attaching to other
cells


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Monoclonal Antibodies: an antibody produced by a single clone of cells
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g
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mAB are produced that are
specific to the receptors on their cancer cells
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They attach to the surface and block chemical signals that stimulate their
uncontrolled growth
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g
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By using mAB that are complementary to the antigen, it is
possible to measure the level of PSA
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Direct: uses a single AB

Indirect: uses 2 different AB

1) Apply sample to surface, so antigens attach
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Wash to remove unattached AB

3) Add second AB (enzyme attached) that binds with the first AB
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Ethical issues:


- production of mAB involves mice

- Not enough research done into the side effects

Vaccination
1) The vaccine contains small no
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Important as it’s
hard to vaccinate the whole population
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Inside the envelope, is a
capsid which contains RNA/reverse
transcriptase enzyme
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Replication of the virus:

1) HIV enters bloodstream

2) Attachment proteins on HIV bind to the receptors on Helper T cells

3) RNA is rejected

4) Reverse transcriptase makes a complimentary strand of DNA from viral RNA template

5) Newly made DNA inserted into T helper cell’s nucleus and into the cell’s DNA

6) HIV DNA creates mRNA - contains instructions to make new viral proteins/RNA to go
into the new HIV

7) HIV particles break away from helper T cell with a piece of its cell surface membrane
which forms their lipid envelope

AIDS: HIV attack helper T cells
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As a result, the body can’t produce an adequate
immune response and become susceptible to infections/cancers
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But viruses rely on a host to carry out their metabolic activities
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ELISA test can be used in this situation to detect HIV


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