The developing individual

First section of unit 2: growth, development and disease taken from the OCR textbook.

Includes, DNA, DNA replication, Mitosis, Cell cycle, Cancer, Stem cells, Lung and breast cancer, Clinical trials, 

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Human Biology
Unit 2:
Growth,
Development and
Disease

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Page 2

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DNA
DNA
= deoxyr
ibonucl
eic
aci
d.
DNA
stor
es
the
genet
ic
ma t
eri
al needed
for
t
he
cel
l,
pr
esent
i
n t
he
chr
omo somes
insi
de
the
nuclei
.
DNA is
made
up
of
a phosphat
e gr
oup,
a
fi
ve
car
bon
sugar
and
an
organi
c
base.
DNA is made up of 2 polynucleotide chains, which are linked by
hydrogen bonds between the organic bases.…read more

Page 3

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DNA carries the genetic information that all cells need in order to
function.
Every time a cell divides it needs to make sure that the DNA has been
copied accurately.
DNA replicates itself by semiconservative replication. This happens
during the S phase of the cycle.
1. The DNA molecule unwinds and `unzips' itself.
2. The enzyme helicase breaks the hydrogen bonds between the bases
3. New DNA nucleotides pair up with the now exposed bases, pairing up
with their correct partner (A&T, C&G)
4.…read more

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Each chromosome now has two chromatids held together by a
centromere
The chromosomes are now coiling up and condensing
They are becoming more visible
Human cells contain 23 pairs of chromosomes ­ one set from
the mother and one set from the father.
Cells containing pairs of chromosomes are called diploid cells.…read more

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G1 ­ First growth stage. Proteins are made and are used to build up cell
organelles.
S (synthesis phase) ­ DNA is replicated.
G2 ­ second growth stage. Cell organelles grow and divide and build up
its energy stores.
M (mitosis phase) ­ Nucleus undergoes mitosis and the cell divides
during cytokinesis.
CONTROL OF THE CELL CYCLE
The timing of the cell cycle is controlled by protein complexes made up
of activating proteins called cyclins and enzymes called cyclindependent
kinases (CDKs).…read more

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Phagocytic cells like macrophages are attracted to the
phospholipid and bind to it, the phagocytic cells then engulf the
fragments
WHY DO CELLS COMMIT `SUICIDE'?
Apoptosis occurs in cells that are infected with viruses or cells that have
DNA damage. It is used to destroy any cells that may cause harm to the
organism.
In a growing foetus, the fingers and toes are usually webbed apoptosis
causes the skin between the fingers and toes to disappear.…read more

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They will either carry the genetic code for the receptor protein in the cell
membrane, which binds to it and switches on the genes or it may carry
the code for a growth factor.
However if a change happens in the pronooncogens, this is called a
mutation. This can lead to uncontrolled cell division by causing excessive
amounts of growth factor or by producing a receptor protein which
triggers DNA replication.…read more

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Arsenic Lung cancer, skin cancer
Soot and mineral oil Skin cancer
Asbestos Lung cancer, mesothelioma
Alcohol Oesophageal cancer
AGEING
Cancer such as leukaemia are found mainly in younger people.
Cancer such as colon cancer is more common in people as they
age.
Older people have more contact with factors that cause cancers
like UV radiation.…read more

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Used to detect small tumours in the breast
Lowdose of xrays are passed through the breast
If a lump shows up on the xray then further tests are done
CT SCANS
The patient lies on a platform which slowly moves through a hole in the
CT machine
The machine is like a hollow tube and moves around the patient, taking
xrays from all different angles.…read more

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Most cases of breast cancer occur in women who have reached the age
of menopause, where their menstrual cycle has stopped.
Whilst a woman is menstruating, her body produces high levels of
oestrogen, after the menopause these oestrogen levels start to drop.…read more

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