This document provides a comprehensive and extensive summary of the LIFE128 module for the whole semester and proves useful for exam revisions. In addition, several confusing concepts are explained in a simple manner.
LIFE 128
Patricia’s Lecture
The genetic material in almost all cells is the same but the Genes expressed in
different cells are distinct.
Developmental biology is largely about understanding which genes are turned
on, which are turned off and when.
By the fusion of the sperm and egg, primordial germ cells are generated.
Mammalian development: Most of our knowledge comes from the mouse
There are three types of mammals
Monotremes -lay eggs
Marsupials -short gestation, immature young
Placentals -placentas, are more mature when born than marsupials.
Mouse embryo also called egg cylinder has an elongated shape which isn’t
found in humans.
Primordial germ cells are formed by a signalling molecule called bone
morphogenetic protein 4 (BMP4). There is a receptor on the membrane of the
embryo which reacts to BMP4. High levels of BMP4 are needed for embryonic
cells to become PGCs. Therefore, only those that are near the membrane are
exposed to high levels of these and eventually become PGCs.
PGC Migration in the mouse embryo.
The sex chromosome of the PGCs determines whether an ovary/testis will
develop in the embryo.
Retinoic acid (a metabolite of vitamin A) is a lipophilic molecule that plays an
important role in various stages of embryonic development by regulating gene
expression.
Retinoic acid is required for primordial germ cells to become oocytes. As a
result, male PGCs express an enzyme, cytochrome P450 that degrades retinoic
acid.
Spermatogenesis: In males, PGCs give rise to spermatogonial stem cells (SSCs)
which generate more SSCs and then differentiate again to form primary
spermatocytes. Primary spermatocytes undergo meiosis to become secondary
spermatocytes giving rise to spermatids.
, The flagellum of the sperm is required for sperm propulsion. The motor protein
of the flagellum is the axoneme.
Primary oocytes are arrested in prophase I until puberty then complete the
meiotic division to form secondary oocytes and a polar body. During the second
meiotic division, the secondary oocyte stops at metaphase II. If the oocyte is
fertilised, triggers the completion of meiosis II and the formation of 2nd polar
body
The zona pellucida has specific areas to which the sperm can only bind. Mouse
oocyte secretes a specific glycoprotein, ZP3 to which only the mouse sperm can
bind to.
Polyspermy: Where more than one sperm binds to the ovary leading to embryo
failure. The cortical reaction prevents this. The egg releases enzymes that
harden the zona pellucida so that more sperm cannot penetrate. The enzymes
also modify ZP3 so the oocyte can no longer bind sperm.
•Absence of female chromosomes results in hydatiform mole, a mass of
placenta-like cells. The absence of male chromosomes results in
parthenogenetic embryos, which can sometimes have organs but development is
chaotic and the embryo becomes grossly disorganised.
Lesley’s lecture on Mutation
All proteins follow the central dogma: being transcribed from DNA to RNA to
proteins except prions proteins and retrovirus.
The mutation is either induced (either by physical agents or chemical agents) or
spontaneous (natural).
Frameshift mutations occur when there is a small deletion causing a shift in
transcription.
DF508 mutation • Most frequent mutation, • Deletion of three nucleotides
deleting phenylalanine at position 508 (DF508) • Occurs in the CFTR gene.
There are 6 classes of CFTR mutations.
Auxotrophy (Ancient Greek: αὐξάνω "to increase"; τροφή "nourishment") is the
inability of an organism to synthesize a particular organic compound required
for its growth.
Meiosis Lecture
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