Section 1: Development and Physiology Part 1 Flashcards
What can A single cell, a fertilised egg cell give rise to?
a complex multicellular organism.
How does Developmental Biology connect with other “disciplines” ?
it brings different aspects of biology together.
What disciplines doe developmental biology connect?
Cell Biology: how cells change
Genetics: how genes bring about changes
Gene transcription: how genes are turned on and off
Cell signaling: How cells communicate with each other
And much more….
What does cell biology impact the understanding of?
How defects in development cause disease
The basis of many cancers
How to repair when parts of the body are not functioning
What is a multicellular organism?
An organism that consists of more than one cell
Prokaryotes (bacteria and archaea):
all unicellular although can form co-operative communities
biofilms – a surface coating
colony of one or more species of uni-cellular
organisms that co-operate metabolically
Eukaryotes:
protists, plants, animals and fungi
What is Dictyostelium?
a cellular slime mold that serves as a model for the evolution of multicellularity. It presents a simple example of how cells can co-operate for the benefit to
survival of the population
How do we study development ? and why
we generally do not study this on humans, this is because observation is difficult, morally and ethically we can’t do experiments on human embryos, we wouldn’t want nor could we breed humans
How does Dictyostelium function mulicellularly?
The feeding stage of Dictyostelium consists of single cells that function individually but when
starved, cells can migrate and co-operate to form a motile aggregate with specialised cells
that form a stalk and fruiting body to release spores (asexual reproduction). This helps survival
of the organism providing an opportunity for spores to spread to a more favourable location
to germinate.
In Dictyostelium is it true multicellularity?
no its multicellular existence is achieved by aggregation of single cells
What are model organisms?
organisms that researches use to study and identify general principles in biology
How are most complex multicellular organisms formed?
most complex multicellular organisms are made up of very many cell types that form specialised tissues that build specialised organs.
The different cell types form tissues and the different tissues are organised into organs. The organs function together within the organism.
why were particular organisms chosen for the study of development?
different models have different advantages for certain questions, this might differ depending on the type reproduction (sexual, asexual etc.)
How many types of animal tissue are there?
there are 4 main types of animal tissues
What are the four types of animal tissues?
Epithelial , Connective , Muscle , Nervous
What is epithelial tissue?
-covers the body and lines the organs and cavities within
-contains cells that are closely joined
What is connective tissue?
-binds and supports other tissues
-sparsely packed cells within the extracellular matrix (ECM)
-6 types of connective tissue –loose
-fibrous (tendons/ligaments)
-Bone (mineralised)
-Adipose tissue (fat)
-Blood (cells and plasma)
–Cartilage
What is muscle tissue?
consists of filaments of proteins actin and myosin (for contraction)
Skeletal, smooth and cardiac muscle
What is nervous tissue?
- receipt, processing and transmission of information
Neurons (transmit impulses) and glial cells (support cells
What is the extracellular matrix (ECM)?
The Extracellular Matrix (ECM) is a
collection of molecules secreted by cells
that provides structural and biochemical
support to the surrounding cells.
What is the problem of reproducing a multicellular organism with specialised cells?
To reproduce, true multicellular organisms must solve the problem of regenerating a whole
organism from germ cells (i.e sperm and egg cells).
Bacteria and other single celled organisms can reproduce by simple binary fission- the cell
grows and simply splits.
Some multicellular organisms are capable of asexual reproduction where the offspring are
identical genetic copies of the parent – a “clone”.
What are the types of Asexual Reproduction?
Spore formation, Budding , Fragmentation, Parthenogenesis, Vegetative propagation.
What is Spore formation?
as seen in Dictyostelium; also in fungi
What is Budding?
e.g. “simple” invertebrate animals such as hydra can reproduce by budding. New individuals arise from outgrowths of existing ones
What is Fragmentation?
in this form of asexual reproduction the body can regrow from a fragment:
If the body is broken/divided into pieces, all or some of the fragments can develop into new
individuals by regeneration of lost body parts. This requires the presence of powerful “stem
cells” throughout the body. Upon injury these stem cells can form a blastema of
proliferating, undifferentiated cells that can be re-organised spatially to produce the correct
differentiated cells, in the right order, the reform the missing part. Annelid worms, flat
worms such as planaria, echinoderms such as the star fish and algae (e.g. Spyrogira) can
asexually reproduce in this way.
What is Parthenogenesis? (virgin birth)
– in this form of asexual reproduction the body can regrow from a fragment:
If the body is broken/divided into pieces, all or some of the fragments can develop into new
individuals by regeneration of lost body parts. This requires the presence of powerful “stem
cells” throughout the body. Upon injury these stem cells can form a blastema of
proliferating, undifferentiated cells that can be re-organised spatially to produce the correct
differentiated cells, in the right order, the reform the missing part. Annelid worms, flat
worms such as planaria, echinoderms such as the star fish and algae (e.g. Spyrogira) can
asexually reproduce in this way.
What is Vegetative propagation?
this type of asexual reproduction is widespread in plants where
the vegetative part of plant (leaves, stems and roots) can propagate without seeds. This
happens naturally (for example underground roots that give rise to new plants) and is used
widely in horticulture- e.g. “cuttings”
What is sexual reproduction?
The vast majority of new complex organisms arise from a fertilised egg cell- also called a
ZYGOTE. The fertilised egg cell has to give rise to many different cell types.
What are the advantages of sex?
It allows genetic variation between individuals → genetic variation in the population.
In asexual reproduction the offspring are genetically identical to the parent.
❖ Variation allows the population to adapt to changing conditions.
❖ Variation is the driving force for evolution
❖ And necessary for a healthy adaptive population
How widespread is sex?
Meiosis and sexual reproduction only occur in a small number of lineages on the tree of life.
e.g.
❖ Bacteria- only asexual reproduction
❖ Most algae, fungi and some land plants - asexual and sexual reproduction. Yeast- mostly
by binary fission- but can undergo sexual reproduction- especially if under stress.
❖ Animals- mostly sexual reproduction but some exceptions- hydra can reproduce by
budding. Even an exception among vertebrates- the guppy (fish).
Summarize the genetics of sexual reproduction.
- Germ cells contain a random distribution of half the chromosomes of the parent (n)
- Fusion of germ cells restores the full compliment of genes (2n).
- offspring share 50% of their genes with each of their parents- but which 50% is randomly
determined - so siblings will each have 50% of the genes of each parent- but a different 50%.
- siblings share on average 50% of their genes. But the shared genes between siblings
could be as low as 0% or as high as 100%- 50% on average
What is Spermatogenesis?
the production of mature sperm is a continuous process in the adult
male. It occurs in the seminiforous tubule of the testes.
In the embryonic testes the primordial germ cells- or the stem cells that will give rise to all
sperm, differentiate – these are called the spermatogonia. Mitotic divisions that make more
of these stem cells continue throughout the life of the male. To form sperm the
spermatogonia undergo two meiotic cell divisions –forming primary and secondary
spermatocytes respectively. Both are produced in the seminiferous tubule with the more
mature cells located closer to the lumen. Following meiosis the haploid spermatids then
differentiate into mature, motile sperm released into the lumen. This last step is not a
division but a differentiation- called spermiogenesis- distinct from spermatogenesis which is
the whole process.
What is oogenesis?
Oogenesis begins already in the developing ovary of the female embryo, with the
production of primordial germ cells or oogonia- these are produced by mitosis and are the
stem cells of the future eggs. The oogonia give rise to the primary oocytes by initiating the
first meiotic division but they arrest in prophase. These primary oocytes are present in the
ovary of the female at birth, each contained within a protective follicle- they remain
quiescent like this until puberty when hormonal release causes their maturation. In humans
generally only one ovum continues to mature in each cycle- so normally only one offspring
born- dizygotic twins would result from a double ovulation- animals with multiple births
would of course mature and release multiple eggs simultaneously.
At puberty then Follicle stimulating hormone periodically stimulates follicles to grow and
induces the primary oocyte to complete meiosis I- this is an unequal division- producing a
single secondary oocyte and extruding the extra genetic material in a polar body. the
secondary oocyte arrests in metaphase of meiosis II and is released as an ovum during
ovulation in this arrested state. In humans, meiosis II is not completed until a sperm
fertilises the ovum at which point a second polar body containing the excess genetic
material is extruded. In other animals the sperm may enter the ovum earlier, or later or at a
similar stage to humans.
The ruptured follicle is left behind after ovulation and degenerates.
Oogenesis differs from spermatogenesis in 3 major ways, what are they?
- Cytokenesis is unequal in meiosis- most cytoplasm going to a single daughter cell
(oocyte)- goes on to form the ovum. The polar bodies degenerate.
Why? -Cytoplasm is needed to support the future zygote. Eggs- largest cells in animal
kingdom, In oviparous animals- e.g. frog- takes time to build up yolk and cytoplasm for embryo- 3years to sexual maturity - The cells from which sperm develop continue to be generated by mitosis through life of
individual - not believed to happen in female. - Oogenesis marked by long resting periods whereas spermatogenesis is continuous.
What do the egg and sperm contain?
Egg: The egg is full of molecules needed for nutrition, metabolism and development of the
embryo
Sperm: The sperm cell is specialised to move to the egg and penetrate it. The head of the sperm is
tipped with a special body the acrosome- contains enzymes to help the sperm penetrate the
egg. The sperm cell contains a large number of mitochondria to provide the energy (ATP) needed to move the tail or flagellum for motility. The sperm cell contains little else
What happens in fertilization?
❖ Brings male and females gametes together – produces diploid zygote
❖ It also activates the egg, triggering the beginning of embryonic
development
What animal is used to describe the steps of fertilization?
a sea urchin. covered in lecture 2 notes.
What is polyspermy?
POLYSPERMY: fertilisation by
multiple sperm which would lead to an increased genetic compliment and in non-viable
zygote]
What are the steps of fertilization in mammals?
- Fertilisation is internal
- Egg cloaked in follicle cells released with egg
- Sperm undergoes capacitation in uterus- molecular changes that enable sperm to
enter the egg - Egg has tough extracellular matrix called the zona pellucida - presents receptors for
sperm binding. - Binding of the receptor leads to acrosomal reaction- entry through zona pellucida
- No known fast block to polyspermy but similar cortical reaction for slow block
- Whole sperm taken into the egg- base used to form centrioles for spindle
- Nuclei do not fuse but both nuclear envelopes disperse- chromosomes align on
spindle in cytoplasm. - First cell division slower- 12-36 hours
What are the Three broad interrelated processes are involved in building an embryo?
- Cell division
- Cell differentiation.
- Morphogenesis.
What is a simple definition for cell division?
Cell division and growth are both tightly regulated during development
What is a simple definition for cell differentiation?
A complex organism requires many hundreds of different cell types to form structures and
carry out specific functions. For example, red blood cells are required to carry oxygen,
muscle cells are required for movement, neurons are required to receive and transmit
signals. The cells that arise by cell division from the zygote have to become different to each
other over time.
What is a simple definition for morphogenesis?
Or “creation of form”. How the organism takes on a three dimensional shape with all the
cells types in the right place to form structures and carry out functions
What does organogenesis involve?
organogenesis involves more local
interactions between cells and morphogenetic changes in tissue and cell shape- and in cell
arrangement.
What are many of the changes in organogenesis are brought about by?
Induction:- the influence of
one group of cells on neighbouring cells, changing the way in which the responding cells
develop
What was the experiment that showed induction?
the Spemann and Mangold experiment in 1924 elegantly demonstrated the ability
of cells to influence each other / communicated with each other through Induction.
What did the the “organiser” experiment show?
This means that the organiser cells from the donor could change the fate of the recipient cells.
- Cells that form the secondary axis are not all derived from the graft (donor cells), a large
proportion of cells are recruited from the recipient. This means that the organiser cells from
the donor could change the fate of the recipient cells. - With time an almost complete second axis could be formed. This means that the organiser
cells can set in motion a whole chain of events leading eventually to the production of a
whole new body plan. This is why Spemann called the cells of the dorsal blastopore lip, the
primary organiser.
What is Neurulation?
- It sets aside the cells for and forms the rudiments of the entire nervous system.
- It is the first event in organogenesis.
GO TO LECTURE #4
What is the coelom?
this is a fluid-filled cavity which forms by splitting the
mesoderm- it is by definition surrounded by mesoderm on all sides. Many of the organs as they form will push into this space- although contained within the peritoneum
What are the the somites?
are mesoderm cells that form into blocks on either side of the neural tube (see figure below). These are transitory structures that later dissociate to form different cell types.
1. The muscle blocks of the body and muscles attached to the skeleton
2. The vertebrae of the back-bone. The cells from within the somite that will form the vertebrae (blue on lower diagram) leave the somite and migrate around the notochord and neural tube. The notochord later degenerates; the only remnants forming the “disks” between the vertebrae.
What cell layer does the entire embryo form from? (In a chick)
The entire embryo will form from one cell layer- the
epiblast
What is the primitive streak?
Gastrulation involves cells
from the epiblast moving underneath through a line at
the midline of the disk called the primitive streak.
The organogenesis of a chick
GO TO LECTURE # 4
What are AMNIOTES?
Reptiles, including birds, and mammals left an aquatic
life and must produce their young on dry land. Their eggs and embryos have special characteristics that reflect this- they are AMNIOTES
What are the two evolutionary events from Amniotes?
- Evolution of a protective egg shell on externally laid eggs (reptiles, birds and a few
mammals (monotremes)
or - Evolution of a uterus and placenta to facilitate internal development inside the mother’s
body in mammals.
Definition of Amnion?
- surrounds the embryo, forms
fluid filled sac that bathes the embryo.
Made from ectoderm and mesoderm
Definition of Chorion?
outer membrane- exchanges gasses between embryo and surrounding air. O2 and CO2 diffuse freely across the egg shell.
Definition of Yolk sac?
encloses the yolk- blood vessels develop in the yolk sac to bring nutrients to the embryo. The first site of blood production.
Definition of Allantois?
waste disposal sac- metabolic wastes. Also performs gas exchange.
