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Topic 1: Cell Biology
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Giant Algae: can grow to a very long length but only contain a single nucleus and are
unicellular
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Microscopes and Magnification:

SI Units

1 m = 100 cm

1 cm = 1 cm

1 mm = 0
...
0001 cm

1 nm = 0
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Metabolism – chemical reactions inside the cell, made up of catabolism (breakdown of
molecules) and anabolism (build up of molecules)
Reproduction – producing offspring either sexually or asexually
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Growth – an irreversible increase in size
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Excretion – getting rid of the waste products of metabolism
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MNEMONIC: MR H GREN



Multicellular Organisms (eukaryotes):
Multicellular organisms show emergent properties
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When cells interact they can perform functions that they could not achieve if they were alone
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If a cell
becomes too large, its diffusion distance becomes too long to be efficient and its surface area
to volume ratio becomes too small to allow the necessary exchange
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However, since the uptake of resources and the removal of heat/waste goes
via the cell membrane, the rate of uptake/removal is proportional to surface area
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The more surface area, the more exchange of nutrients and gases into the cell and wastes out
of the cell
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The more volume, the more nutrients and gases that are needed inside the cell
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Stem Cells:
• Stem cells are unspecialised cells
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• They have the capacity to differentiate into several cell types when given a certain
chemical signal
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Totipotent – can become any type of cell
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Multipotent – can become a limited number of other particular types of cells
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Therapeutic Use of Stem Cells:
Leukaemia:
• Leukaemia is a cancer of white blood cells/leucocytes
• Leucocytes are made in the bone marrow from multipotent adult stem cells
• The leucocytes are released into the blood stream to fight off infection
• Leukaemia is when these cells grow abnormally
• Chemotherapy is used to kill all the bone marrow cells, the normal cells as well as the
abnormal cells
• Stem cells can be obtained from donor bone marrow or umbilical cord blood
• These are introduced into the patient’s blood and the stem cells migrate to the bone
marrow and start to produce healthy leucocytes



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This is an asexual method of reproduction in which
a parent cell divides into two smaller but equally sized cells
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Eukaryotes:
Eukaryotes have a compartmentalised cell structure
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Eukaryotes:







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Each phospholipid has two
regions; the glycerol-phosphate head (polar and hydrophilic) and the
fatty acid tail (non-polar and hydrophobic)
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The backbone of the membrane is a bilayer produced from huge numbers
of molecules called phospholipids
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Davson-Danielli Model:
In this model of membrane structure, there is a bilayer of phospholipids in the centre of the
membrane with layers of protein on either side
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• Red blood cells contained enough phospholipids to form an area twice as large as the
plasma membrane, suggesting a phospholipid bilayer
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Singer-Nicholson Model (current model):
Suggested that proteins occupy a variety of position within the membrane
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The proteins are
floating in the phospholipid bilayer
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They referred to the membrane as a fluid mosaic where the membrane is fluid and not rigid
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Membrane Proteins:
Functions of membrane proteins:
• Hormone binding sites – hormones transported by the blood will only act on cells that
have the appropriate protein receptor on the outside of their membrane
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Cell adhesion – this is provided by integral proteins that stick out and bind to specific
proteins on adjacent cells
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Channels for passive transport – when a hydrophilic substance passes through the
channel from an area of high to low concentration
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Cholesterol in Membranes:
The fluidity of animal cell membranes needs to be carefully controlled
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Cholesterol disrupts the regular packing of the hydrocarbon tails of phospholipid molecules,
so prevents them crystallising and behaving as a solid
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Functions:



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The molecules move down the concentration gradient and don’t require any
energy
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These substances move passively through the
membrane via channel proteins down the concentration gradient
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A solvent is a liquid in which particles dissolve
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The direction in which water moves is due to the concentration of solutes, rather
than the concentration of water molecules, so it is called osmosis, rather than diffusion
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Active Transport:
Active transport is the passage of materials against a concentration gradient
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The hydrolysis of ATP causes a change in shape in the protein pump resulting in the forced
movement of the substance
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The theory suggests that some organelles found inside eukaryotes were once free
living prokaryotes
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Evidence for this theory comes from the fact that the mitochondria and
chloroplasts share some characteristics with prokaryotic cells (contain ribosomes, small
pieces of DNA, have a double membrane, can replicate themselves by binary fission)
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6: Cell Division

The Cell Cycle:
The cell cycle is an ordered set of events that occur between the birth of a cell, growth and
its division into two daughter cells
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G1 phase:
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Cell grows
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DNA is transcribed
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Protein is synthesised
S phase:
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DNA is replicated
G2 phase:
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Cell prepares for division
Mitosis:
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Nucleus divides
Cytokinesis:
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Cytoplasm divides

Interphase:
Most of the time in the cell cycle the cell is in interphase (G1, S and G2)
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Many metabolic reactions need to occur before a cell can divide,
these include:
• Protein synthesis – the cell needs to synthesise proteins and enzymes to enable it to
grow, copy its contents and then divide
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• Increase number of organelles – the cell needs to ensure both daughter cells will have
the necessary numbers of organelles needed to survive
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Mitosis:







Prophase:
- Supercoiling makes the chromosomes shorter and thicker
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- Nuclear membrane is broken down
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- Sister chromatids line up separately along the equator of the cell
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Telophase:
- New nuclear membrane forms around each set of chromosomes
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Mitotic Index:
𝑚𝑖𝑡𝑜𝑡𝑖𝑐 𝑖𝑛𝑑𝑒𝑥 =

𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑐𝑒𝑙𝑙𝑠 𝑖𝑛 𝑚𝑖𝑡𝑜𝑠𝑖𝑠

𝑡𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑐𝑒𝑙𝑙𝑠


Cyclins:
Cyclins are compounds that control the cell cycle
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Cyclins control enzymes called
CDKs (cyclin dependent kinases) that direct cells through the cell cycle and control specific
events such as spindle fibre formation and chromatid alignment
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The cell cycle is usually under strict control by a complex chemical control system that
responds to signals both inside and outside of the cell
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However, sometimes cell division may continue
unchecked and produce an excess of cells which clump together forming a growth known as
a tumour
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Mutations to these genes result in uncontrolled cell division, resulting in the formation of a
tumour
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This is known as
metastasis
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