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Animal Physiology and Embryology
1.
What are enzymes ? Describe their properties and classification.
Enzymes ( /ˈɛnzaɪmz/) are proteins that catalyze (i.e., increase the rates of) chemical
reactions.[1][2] In enzymatic reactions, the moleculesat the beginning of the process,
called substrates, are converted into different molecules, called products. Almost all chemical
reactions in abiological cell need enzymes in order to occur at rates sufficient for life. Since
enzymes are selective for their substrates and speed up only a few reactions from among many
possibilities, the set of enzymes made in a cell determines which metabolic pathways occur in
that cell.
Like all catalysts, enzymes work by lowering the activation energy (Ea‡) for a reaction, thus
dramatically increasing the rate of the reaction. As a result, products are formed faster and
reactions reach their equilibrium state more rapidly. Most enzyme reaction rates are millions of
times faster than those of comparable un-catalyzed reactions. As with all catalysts, enzymes are
not consumed by the reactions they catalyze, nor do they alter the equilibrium of these reactions.
However, enzymes do differ from most other catalysts in that they are highly specific for their
substrates. Enzymes are known to catalyze about 4,000 biochemical reactions. [3] A
few RNA molecules called ribozymes also catalyze reactions, with an important example being
some parts of the ribosome.[4][5] Synthetic molecules called artificial enzymes also display
enzyme-like catalysis.[6]
Enzyme activity can be affected by other molecules. Inhibitors are molecules that decrease
enzyme activity; activators are molecules that increase activity. Many drugs and poisons are
enzyme inhibitors. Activity is also affected by temperature, chemical environment (e.g., pH), and
the concentration of substrate. Some enzymes are used commercially, for example, in the
synthesis of antibiotics. In addition, some household products use enzymes to speed up
biochemical reactions (e.g., enzymes in biological washing powders break down protein
or fat stains on clothes; enzymes in meat tenderizers break down proteins into smaller molecules,
making the meat easier to chew).
Control of activity
There are five main ways that enzyme activity is controlled in the cell.
1. Enzyme production (transcription and translation of enzyme genes) can be enhanced or
diminished by a cell in response to changes in the cell's environment. This form of gene
regulation is called enzyme induction and inhibition (see enzyme induction). For
example, bacteria may become resistant to antibiotics such as penicillin because
enzymes called beta-lactamases are induced that hydrolyze the crucial beta-lactam
ring within the penicillin molecule. Another example are enzymes in
the liver called cytochrome P450 oxidases, which are important in drug metabolism.
Induction or inhibition of these enzymes can cause drug interactions.
2. Enzymes can be compartmentalized, with different metabolic pathways occurring in
different cellular compartments. For example, fatty acids are synthesized by one set of
enzymes in thecytosol, endoplasmic reticulum and the Golgi apparatus and used by a
different set of enzymes as a source of energy in the mitochondrion, through βoxidation.[81]
3. Enzymes can be regulated by inhibitors and activators. For example, the end
product(s) of a metabolic pathway are often inhibitors for one of the first enzymes of the
pathway (usually the first irreversible step, called committed step), thus regulating the
amount of end product made by the pathways. Such a regulatory mechanism is called
a negative feedback mechanism, because the amount of the end product produced is
regulated by its own concentration. Negative feedback mechanism can effectively adjust
the rate of synthesis of intermediate metabolites according to the demands of the cells.
This helps allocate materials and energy economically, and prevents the manufacture of
excess end products. The control of enzymatic action helps to maintain a stable internal
environment in living organisms.
4. Enzymes can be regulated through post-translational modification. This can
include phosphorylation, myristoylation and glycosylation. For example, in the response
to insulin, thephosphorylation of multiple enzymes, including glycogen synthase, helps
control the synthesis or degradation of glycogen and allows the cell to respond to
changes in blood sugar.[82] Another example of post-translational modification is the
cleavage of the polypeptide chain. Chymotrypsin, a digestive protease, is produced in
inactive form as chymotrypsinogen in the pancreas and transported in this form to
the stomach where it is activated. This stops the enzyme from digesting the pancreas or
other tissues before it enters the gut. This type of inactive precursor to an enzyme is
known as a zymogen.
2.
Write notes on :
(i) Water soluble vitamins
(ii) Minerals.
3. Give a general account of circulatory system in animals.
The circulatory system is an organ system that passes nutrients (such as amino
acids, electrolytes and lymph), gases, hormones, blood cells, etc. to and from cells in the body to
help fight diseases, stabilize body temperature and pH, and to maintain homeostasis.
This system may be seen strictly as a blood distribution network, but some consider the
circulatory system as composed of the cardiovascular system, which distributes blood,[1] and
the lymphatic system,[2] which distributes lymph. While humans, as well as other vertebrates,
have a closed cardiovascular system (meaning that the blood never leaves the network
of arteries, veins and capillaries), some invertebrate groups have an open cardiovascular system.
The most primitive animal phyla lack circulatory systems. The lymphatic system, on the other
hand, is an open system.
Two types of fluids move through the circulatory system: blood and lymph. The blood, heart, and
blood vessels form the cardiovascular system. The lymph, lymph nodes, and lymph vessels form
the lymphatic system. The cardiovascular system and the lymphatic system collectively make up
the circulatory system.
Human cardiovascular system
Cross section of a human artery
The main components of the human cardiovascular system are the heart, blood, and blood
vessels.[3] It includes: the pulmonary circulation, a "loop" through the lungs where blood is
oxygenated; and the systemic circulation, a "loop" through the rest of the body to
provide oxygenated blood. An average adult contains five to six quarts (roughly 4.7 to 5.7 liters)
of blood, which consists of plasma, red blood cells, white blood cells, and platelets. Also,
the digestive system works with the circulatory system to provide the nutrients the system needs
to keep the heart pumping.
Pulmonary circulation
Main article: Pulmonary circulation
The pulmonary circulatory system is the portion of the cardiovascular system in which oxygendepleted blood is pumped away from the heart, via thepulmonary artery, to the lungs and
returned, oxygenated, to the heart via the pulmonary vein.
Oxygen deprived blood from the vena cava, enters the right atrium of the heart and flows through
the tricuspid valve (right atrioventricular valve) into the right ventricle, from which it is then
pumped through the pulmonary semilunar valve into the pulmonary artery to the lungs. Gas
exchange occurs in the lungs, whereby CO2 is released from the blood, and oxygen is absorbed.
The pulmonary vein returns the now oxygen-rich blood to the heart.
Systemic circulation
Main article: Systemic circulation
Systemic circulation is the portion of the cardiovascular system which transports oxygenated
blood away from the heart, to the rest of the body, and returns oxygen-depleted blood back to the
heart. Systemic circulation is, distance-wise, much longer than pulmonary circulation, transporting
blood to every part of the body.
4.
Write notes on :
(i) Diffusion of gases in lungs
(ii) Physiology of heart.
5. Write an essay on mechano reception of invertebrates.
A mechanoreceptor is a sensory receptor that responds to mechanical pressure or
distortion. There are four main types in the glabrous skin of humans: Pacinian
corpuscles, Meissner's corpuscles,Merkel's discs, and Ruffini corpuscles. There are also
mechanoreceptors in hairy skin, and the hair cells in the cochlea are the most sensitive
mechanoreceptors, transducing air pressure waves into nerve signals sent to the brain. In
the periodontal ligament, there are some mechanoreceptors, which allow the jaw to relax
when biting down on hard objects; the mesencephalic nucleus is responsible for this
reflex.
Mechanism of sensation
Mechanoreceptors are primary neurons that respond to mechanical stimuli by firing action
potentials. Peripheral transduction is believed to occur in the end-organs.
In somatosensory transduction, the afferent neurons transmit messages through synapses in
the dorsal column nuclei, where second-order neurons send the signal to the thalamus and
synapse with third-order neurons in the ventrobasal complex. The third-order neurons then send
the signal to the somatosensory cortex.
[edit]Feedback
More recent work has expanded the role of the cutaneous mechanoreceptors for feedback in fine
motor control.[1] Single action potentials from RAI and PC afferents are directly linked to activation
of related hand muscles,[2] whereas SAI activation does not trigger muscle activity.
[edit]History
Work on humans stemmed from Vallbo and Johansson's percutaneous recordings from human
volunteers in the late 1970s.[3] Work in rhesus monkeys has found virtually identical
mechanoreceptors with the exception of Ruffini corpuscles, which are not found in the monkey.
[edit]Types
[edit]Cutaneous
Cutaneous mechanoreceptors are located in the skin, like other cutaneous receptors. They are all
innervated by Aβ fibers, except the mechanorecepting free nerve endings, which are innervated
by Aδ fibers. They can be categorized by morphology, by what kind of sensation they perceive
and by the rate of adaptation. Furthermore, each has a different receptive field.
6.
Discuss how ionic and osmotic balance is maintained in animals.
Osmoregulation is the active regulation of the osmotic pressure of an organism's fluids to
maintain the homeostasis of the organism's water content; that is it keeps the organism's fluids
from becoming too diluted or too concentrated. Osmotic pressure is a measure of the tendency of
water to move into onesolution from another by osmosis. The higher the osmotic pressure of a
solution the more water wants to move into the solution. Pressure must be exerted on
the hypertonic side of a selectively permeable membrane to prevent diffusion of water by osmosis
from the side containing pure water.
Organisms in both aquatic and terrestrial environments must maintain the right concentration
of solutes and amount of water in their body fluids; this involves excretion (getting rid of metabolic
wastes and other substances such as hormones that would be toxic if allowed to accumulate in
the blood) via organs such as the skin and the kidneys; keeping the amount of water and
dissolved solutes in balance is referred to as osmoregulation.
Osmoregulation in plants
Whilst there are no specific osmoregulatory organs in higher plants the stomata are important in
regulating water loss through evapotranspiration and on the cellular level the vacuole is crucial in
regulating the concentration of solutes in the cytoplasm. Strong winds, low humidity and
high temperatures all increase evapotranspiration from leaves. Abscisic acid is an
important hormone in helping plants to conserve water - it causes stomata to close and
stimulates root growth so that more water can be absorbed.
Plants share with animals the problems of obtaining water but unlike in animals the loss of water
in plants is crucial to create a driving force to move nutrients from the soil to tissues. Certain
plants have evolved methods of water conservation. Xerophytes are plants that can survive in dry
habitats, such as deserts, and are able to withstand prolonged periods of water shortage.
Succulent plants such as the cacti store water in the vacuoles of large parenchyma tissues. Other
plants have leaf modifications to reduce water loss, such as needle-shaped leaves,
sunken stomata, and thick, waxycuticles as in the pine. The sand-dune marram grass has rolled
leaves with stomata on the inner surface. Hydrophytes are plants in water habitats. They mostly
grow in water or in wet or damp places. In these plants the water absorption occur through the
whole surface of the plant, e.g. the water lily.
7.
Explain the role of hormones in reproduction.
Hormones are organic chemical substances secreted by ductless glands (or
endocrine glands) and are released into the blood stream for onward transportation to
their target organs.
Hormones are organic chemical substances secreted by ductless glands (or
endocrine glands) and are released into the blood stream for onward transportation
to their target organs. Examples are: Pituitary, Thyroxin, Adrenalin, Insulin,
Estrogens, progesterone, Testosterone, Para hormone, etc.
The major endocrine glands include the two Adrenal glands, the Pituitary gland, the
four Parathyroid glands, the Sex glands, and the Thyroid gland. A few hormones are
produced by endocrine tissue present in organs that are not primarily endocrine
glands. Such organs include the Brain, Stomach and Pancreas.
Generally, hormones regulate a variety of body functions. They may be grouped
according to the functions that they control. These functions include:- the way the
body uses food; growth; sex and reproduction; the regulation of the composition of
the blood; the body’s reaction to emergencies and the control of hormones
themselves.
For the sake of this paper, the role of hormones will be viewed in respect of
mammalian production with regard to Sex hormones.