Structure carbohydrates and nucleic acids. Signals and receptors are

Structure and function work simultaneously, meaning that the
structure of something deciphers how efficient or appropriate the object is for
its specific function. Structure can be defined by, the way something is
formed, arranged or constituted. Whereas, the term function refers to
something’s role, job or responsibility.  Adaptations through evolution are how specific
biological structures of an organism have developed to carry out their
distinctive functions with the greatest efficiency. Individuals, who possess traits
with advantageous characteristics are in a better position to reproduce and
pass on genetic information to offspring; therefore, are favoured by natural
selection. These traits are produced by certain alleles and new alleles in a
species or population, which arise from mutation. If a mutation produces a
change in structure of a biological molecule, its function can be affected
dramatically. A change in the composition of a molecule has a knock-on effect
on the structure and therefore, function of a cell, tissue or even an organ. This
is because all biological functions are dependent on the mechanisms in the organism’s
body at a molecular level. In fact, these biological mechanisms are controlled
by other clusters of perfectly arranged molecules, which are complex biological
machines. These complexes are made up of macromolecules; such as, proteins,
lipids, carbohydrates and nucleic acids. Signals and receptors are additionally
made up of more of these macromolecules and control the rate and activation of
these biological machines. Implying, all these different molecules must have extremely
specific chemical formulae, controlling their unique structure, special function
and behaviour.

The function of an egg cell of any organism is to give rise
to a new individual. For this to occur the egg must be activated by spermatozoa
cells of similar species. Nevertheless, activation can be artificial by chemical
and physical treatments. Other organisms, such as, some species of lizards
reproduce parthenogenetically, meaning they can activate their own egg cells
without sperm cells. The nucleus of egg cells are haploid- meaning that the
nucleus only contains half the number of chromosomes as would be found in a
normal somatic cell of that specific species. An example is a human oocyte has
23 chromosomes in contrast to the normal 46 chromosomes in a human somatic
cell. This is very important as when a sperm cell of the same species
fertilises the egg the haploid nuclei fuse to create a new, unique diploid
nucleus. Meiotic non-disjunction can sometime occur when the gametes are formed
and can cause aneuploidy. Aneuploidy is most often fatal to the embryo, as the
genetic abnormality is so large; therefore, can go unnoticed. However, in some
cases the embryo develops, and the foetus is born. Examples of aneuploidy are
trisomy of chromosome 21, better know as Down’s syndrome and monosomy of the X
chromosome, which is commonly called Turner’s syndrome.

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Even though the egg will eventually give rise to every type
of cell in the body the egg cell itself is extremely specialised. Eggs are so
specialised that the cytoplasm can completely modify the somatic cell nucleus
by changing its conditions. The cytoplasm changes in terms of the IP3
glycophosphoprotein receptor increasing in sensitivity as well as, in number.
It is important that this molecule is correct in constitution because, it is
responsible for the release of Ca(++) ions from the endoplasmic reticulum. The
N-terminal of this protein is a binding suppressor region and is therefore in
control of specific IP3 binding affinity. IP3 additionally regulates the
release of IRBIT, a modulating pseudo ligand of Ca(++) release rate

Egg cells additionally have a large nutrient reserve used
for the initial and very early development of the embryo. In mammals this
nutrient reserve is supplied by the mother in her placenta, meaning depending
on the size of the species the nutrient reserve varies in size. For example,
organisms like a bird or a frog have a relevantly large egg cell, compared to a
mammal’s egg. However, even in mammals the egg cell is always the largest cell
in the body. An example in which this is apparent is the female human, where an
egg cell is approximately 0.1mm and an average somatic cell ranges between
20-30µm. The egg cell must be so big in size as it requires a large cytoplasmic
volume. The egg cytoplasm holds the micromolecules and macromolecules required
for development. These include lipids, proteins, polysaccharides and yolk
granules. Yolk granules can also sometimes be enclosed by a membrane and
organisms that develop separate from the mother tend to have more yolk granules
in their egg cells.

The cells additionally have a specific glycoprotein coat,
some of which are secreted by the egg; where as others are deposited by
surrounding cells. The egg can then have an immediate plasma membrane or a
protein coat- which protects the cell from damage and forms a species-specific
barrier. In nonmammalian species this is called the vitelline layer and in
mammals the layer is called a zona pellucida. After the sperm has penetrated
the zona pellucida, 3 specific glycoproteins mzp1, mzp2 and mzp3 are released.
Mzp1 and 2 do not have inhibit the sperm binding to the oocyte. However, mzp3
of an unfertilised egg restricts sperm cells binding and induce a cellular
exocytosis in sperm cells called the acrosome reaction. Implying mpz3 is a
receptor for sperm- making it’s shape and structure extremely important for
fertilisation. The binding site of mzp3 is close to the c-terminus and is
encoded by exon-7 of the mzp3 gene. Proving that biological mechanism are
controlled on a complex, precise molecular level. Supported by that when mzp3-
exon-7 complex fuses with other molecules in the oocyte a chimeric protein is
produced. This chimeric protein is vital for sperm to bind to the egg in
mammals. (Litscher, Willaims and Wassarman, 2009).

Secondary vesicles are also found in egg cells. They are
found in the cortex of the cytoplasm; which, is just underneath the plasma
membrane. Once the egg has been activated by the sperm, cortical granules
release their contents via exocytosis. The molecules released can additionally
alter the egg coat so that no other sperm can enter the cell. Egg cells entail
a very high number of ribosomes for the purpose of embryogenesis and protein
synthesis. rRNA (ribosomal RNA) is especially amplified in egg cells; for
example, in some amphibian egg cells. There could be between 1 and 2 million
copies of the rRNA. Synthetic activities are an extremely important part of egg
cells too. Yolk synthesis actually occurs in organs outside of the ovaries;
such as, the liver in birds and amphibians. The yolk in then transferred into
the cell by receptor-mediated endocytosis.

Egg also rely on the support of the surrounding cells; for
example, insects have nurse cells. These nurse cells are the progeny of oocytes
and create cytoplasmic bridges between themselves and the egg cells. Through
here vital macromolecules for embryogenesis are passed into the oocyte
cytoplasm. These include, mRNA, proteins and ribosomes, which are extremely
important for the development of the embryo. In vertebrates and invertebrates
egg cells also rely on follicle cells. These cells are surrounded by an
epithelial layer and gap junctions are the only connections between them and
the egg. Follicle cells provide the egg with smaller precursor molecule. Mammal
oocytes are surrounded by granulosa and cumulus cells. Granulosa cell
proliferate depending on the oocyte’s conditions and the hormones present.
These cells also have very specific cell markers; such as, Lhegr, which is a
LH-receptor. Additionally, the cells have complex signalling factors, for
example, FOXL2. FOXL2 is a transcription factor, which controls division of
hormone-producing granulosa cells (Caburet, 2011). Supporting the idea that the
body is regulated by clusters of molecules that control the production of
further molecules that change the condition of particular cells.

. To conclude by the examples the given, it is proven that
the structure of any biological molecule si extremely important for carrying
out it’s function. The molecules are extremely specific in terms of shape,
size, charge and hydrophobicity. Implying that one wrong unit; such as, an
amino acid, monosaccharide or fatty acid can change the whole configuration and
therefore, the properties of that individual molecule. In addition, the
function of this molecule may be to regulate the release or concentration of
another, meaning the structure of that molecule is critical for the control of
the condition of a cell. It is also imperative that a cell, as a whole unit,
has the correct structure. Beit that correct amount of particular organelles,
number of chromosome, its shape, size and it’s outer membrane or coating. All
these factors work together in order for the cell t function as its highest
capability. Allowing the tissue and organ to perform their appropriate function
at the correct rate and moment, due to complex biological mechanisms.



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