mass transport Flashcards
what is haemglobin
haemoglobin are a group of chemically similar molecules found in a wide variety of organisms
haemoglobin are protein molecules with a quaternary structure that has evolved to make them efficient at loading oxygen under one set of conditions and unloads oxygen under a different set of conditions
what is the structure of haemoglobin
like most proteins, haemoglobins have:
- primary structure
- secondary structure
- tertiary structure
- quaternary structure
what is the primary structure of haemoglobin
sequence of amino acids in the four polypeptide chains
what is the secondary structure of haemoglobin
in which each of these polypeptide chains coiled into a helix
what is the tertiary structure of haemoglobin
in which each of these polypeptide chains is folded into a precise shape - an important factor in its ability to carry oxygen
what is the quaternary structure of haemoglobin
in which ll four polypeptides are linked together to form an almost spherical molecule
Each polypeptide is associated with a haem group - which contains Fe2+ ion
Each a total of four o2 molecules that can be carried by a single haemoglobin molecule in humans
what is loading
the process by which haemoglobin binds with oxygen is called loading/ associating
In humans, this takes place in the lungs
what is unloading
the process by which haemoglobin releases its oxygen is called unloading or dissociating
what happens when haemoglobin has a high affinity for O2
takes up O2 easily and release it less easily
what happens when O2 has a low affinity for O2
haemoglobin with a low affinity for oxygen take oxygen less easily, but release it more easily
what is the role of haemoglobin
the role of haemoglobin is to transport oxygen
what is the most efficient way that haemoglobin can transport oxygen
to be efficient at transporting oxygen, haemoglobin must:
- readily associate with oxygen at the surface where gas exchange takes place
- readily dissociate from oxygen at the tissues requiring it
how does haemoglobin associate and dissociate at the same time
it changes its affinity (chemical attraction) for oxygen under different conditions
It achieves this because its shape changes in presence of certain substances, such as CO2
In the presence of CO2, the new shape of hemoglobin binds more loosely to oxygen
- as a result the hemoglobin releases its oxygen
different organisms have different haemoglobin - what does this mean
it means that they take up oxygen differently
why do different haemoglobins have different affinities fr oxygen
each species produces a haemoglobin with a slightly different amino acid sequence
the haemoglobin of each species therefore has a slightly different tertiary binding properties
depending on its structure haemoglobin molecules range from those that have a high affinity for to those that have a low affinity for oxygen
under what conditions causes haemoglobin to bind unevenly with oxygen
when haemoglobin is exposed to different partial pressures of oxygen it does not bind the oxygen evenly
what is the graph showing the relationship between the saturation of haemoglobin with oxygen ad the partial pressure called
the oxygen dissociation curve
explain the shape of the oxygen dissociation curve i
1) the shape of the haemoglobin molecule makes it difficult for the 1st oxygen molecule to bind to one of the sites on its four polypeptide subunits because they are closely united
Therefore at low oxygen concentrations, little oxygen binds to haemoglobin
-the gradient of the curve is shallow initially
2) however, the binding of this first oxygen molecule changes the quaternary structure of the haemoglobin molecule causing it to change
This change makes it easier for the other subunits to bind to an oxygen molecule
3) It, therefore takes a smaller increase in the partial pressure of oxygen to bind the second oxygen than it did to bind the first one
- know n as positive cooperativity because binding of the first molecule makes binding of the first molecule make the binding of the 2nd easier and so on - the gradient STEEPENS
4) Even though in theory, binding to the fourth oxygen molecule should be easier, in practice it is harder
This is simply due to probability with the majority the binding sites occupied, it is less likely that a single oxygen molecule will find an empty site to bind to
- the gradient of the curve reduces and the graph FLATTENS off
each species has a different haemoglobin shape what does this mean
each has different shapes and therefore different affinity for oxygen
when does the shape of haemoglobin change
the shape of any haemoglobin molecule can change under different conditions
this means that there are a large number of different oxygen dissociation curves
- they all have a roughly similar shape but differ in their position on the axes
what must be kept in mind when we are reading a dissociation curve
- the further to the LEFT the curve, the greater is the affinity of haemoglobin for oxygen (so it loads readily but unloads it less easily)
- the further to the RIGHT the curve, the lower is the affinity of haemoglobin for oxygen (so it loads less readily but unloads it more easily)
if the graph is to the left then…
increases in pH in tissue (low CO2)
Large animals with low metabolic rate e.g. elephant
myoglobin (pigment in muscles)
foetal HB
if the graph is to the right then…
decreases in CO2 (high CO2)
what does haemoglobin do in the presence of CO2
haemoglobin has a reduced affinity for O2 in the presence of CO2
the greater the concentration of CO2, the more readily the haemoglobin releases its oxygen - this is known as the Bohr effect and explains why the behaviour of haemoglobin changes in different regions of the body
how does the behaviour of haemoglobin changes at the gas - exchange surface (e.g. lungs)
the concentration of CO2 is low because it diffuse across the exchange surface and excreted from the organisms
the affinity of haemoglobin for O2 is increased, which couples with the high concentration of O2 in lungs, means that O2 is readily loaded by haemoglobin
The reduced CO2 concentration has shifted the O2 dissociation to the left
how does haemoglobin’s behaviour change at rapidly respiring tissue
in rapidly respiring tissues (e.g. muscles), the concentration of CO2 is high
The affinity of haemoglobin for O2 is reduced, which coupled with the law concentration of O2 in the muscles, means that O2 is readily unloaded from the haemoglobin into the muscle cells
The increased CO2 concentration has shifted the O2 dissociation curve to the right
what does the greater the concentration of CO2 do to haemoglobin
the greater the concentration of CO2 the more readily haemoglobin releases its oxygen
This is because dissolved CO2 is acidic and the low pH causes haemoglobin to change shape
how does haemoglobin load oxygen at exchange surfaces
- at the gas - exchange surface CO2 is constantly being removed
- pH is slightly raised due to the low concentration of CO2
- the higher pH changes the shape of haemoglobin into one that enables it to load oxygen readily
- his shape also increases the affinity of haemoglobin for oxygen, so it is not released while being transported in the blood to the tissues
how does haemoglobin unload oxygen at respiring cells
- in the tissues, CO2 is produced by respiring cells
- CO2 is acidic in solution, so the pH of the blood with is the tissue is lowered
- the lower the pH changes the shape of haemoglobin into one with a lower affinity for O2
- Haemoglobin releases the oxygen into the respiring tissue
what would the process of loading and unloading oxygen from haemoglobin described as
- it can be described as a flexible way of ensuing that there is always sufficient oxygen for respiring tissue
the more active a tissue…
the more active a tissue, the more oxygen is unloaded
This works as follows:
1. higher rate of respiration - more CO2 the tissues produce and therefore the lower the pH.
This leads to oxygen being readily unloaded leading to more O2 is available for respiration
how much of the haemoglobin saturated with oxygen
in humans,haemoglobin normally becomes saturated with oxygen as it passes through the lungs
in practice, not all haemoglobin molecules are loaded with ttheirr maximum FOUR oxygen molecules
As a consequence, the overall saturation of haemoglobin at atmospheric pressure is normally 97%
what happens when haemoglobin reaches a tissue with a low respiratory rate
only one of the oxygen molecules are normally released
blood returning to the lungs will therefore contain haemoglobin that is still 75% saturated with O2
what happens when haemoglobin reaches a tissue with a high respiring rate
if the tissue is very active, e.g. exercising muscle, then three O2 molecules will usually be uploaded from each haemoglobin molecule
how has species haemoglobin evolved to suit their needs
e.g. species that live in an environment with a lower partial pressure of O2 gas evolved haemoglobin that has a higher affinity for O2 than haemoglobin of animals that live where the partial pressure of O2 is higher
give an example of a species that lives in an environment where the partial pressure of O2 is low
LUNGWORM is an animal that lives on the seashore lungworm are not very active, spending almost all their life in a U - shaped burrow
oxygen diffuses into the lungworms’ blood from the water and it uses haemoglobin to transport oxygen to its tissue
when the tide goes out, the lungworm can no longer circulate a fresh supply of oxygenated water through its burrow
as a result, the water in the burrow contains progressively less oxygen as the lungworm uses it up
The lungworm has to extract as much oxygen as possible from the water in the burrow if it is to survive until the tide covers it again
how does the dissociation curve of the lungworm look like
the dissociation curve is shifted fat to the left of that of a human
This means that the haemoglobin of the lungworm is fully padded with oxygen even though it is little available in its environment
what is another example of an organism that lives in an environment with a low affinity
another example is the llama - an animal that lives at high altitude
at these altitudes, the atmospheric pressure is lowered and so the partial pressure is also lower
It is therefore difficult to load haemoglobin with O2
- LLamas also have a type of haemoglobin that has a higher affinity for O2 than human haemoglobin
how does the dissociation graph of llamas look like
it is shifted to the left
what happens to the exchange of material as organisms get bigger
all organisms exchange materials between themselves and the environment
small organisms this exchange takes place over the surface of the body
HOWEVER, with increasing size, the surface area to volume ratio decreases to a point where the needs of the organism cannot be met by the body surface alone
what do specialist exchange do
they absorb required nutrients and respiratory gases and remove excretory products
where are exchange surfaces located
specific regions of the organism
why do we need a transport system
a transport system is required to take materials to exchange surfaces and from exchange surfaces to cells
materials have to be transported between exchange surfaces and the environment
They also need to be transported between different parts of organisms
whether or not there is a specialised medium and a circulated pump depends on…
- the surface to area to volume ratio
- how active the organism is
the lower the surface area to volume ratio is, and the more active the organisms is, the greater is the need for a specialised system with a pump
what are the features of a transport system
- a suitable medium in which to carry materials e.g. blood
- a form of mass transport in which the transport medium is moved around in bulk over large distances - more rapid diffusion
- a closed system of tubular vessels that contains the transport medium and forms at branching network to distribute it to all parts of the organism
- a mechanism for moving the transport medium within vessels
This requires a pressure difference between one part an the other
what is usually the transport medium
it is normally a liquid based on water because water readily dissolves substances and can be moved around easily, but can be a gas such as an air breather in and out of the lungs
how are the features of a transport system achieved
in two main ways:
a) animals use muscular contraction either of the body muscles or of a specialised pumping organ, such as the heart
b) Plants rely on natural, passive processes such as the evaporation of water
e. g.
- a mechanism to maintain the mass flow movement in one direction, e.g. valves
- a means of controlling the flow of transport medium to suit the changing needs of different parts of the organisms
- a mechanism for the mass flow of water or gases, e.g. intercostal muscles and diagram during breathing in mammals
what is the circulatory system in mammals
mammals have a CLOSED CIRCULATORY SYSTEM in which blood is confined to vessels and passes twice through the heart
for each complete circuit of the body, its low pressure would make circulation very slow - blood is thereof returned to the heart to boost its pressure before being circulated t the rest of the tissue
what does the double pump system mean for the speed of substances being delivered to the body
As a result, substances are delivered to the rest of the body quickly, which is necessary as mammals have a high body temp and hence a high rate of metabolism
what is the heart
a muscular organ that lies in the thoracic cavity behind the sternum (breast bone)
It operates continuously and tireless throughout the life of a organism
what is the structure of the human heart
is really TWO SEPARATES PUMPS lying side by side
the pump on the left deals with OXYGENATED BLOOD
the pump on the right deals with DEOXYGENATED BLOOD
each pump has two chambers:
the ATRIUM
the VENTRICLE
what is the atrium
the atria RECIEVES blood from the VEINS
the atrium is thin-walled and elastic and stretches as it collects blood
what are the ventricles
the ventricles pump blodd AWAY form the heart
the ventricle has a much thicker muscular wall as it has to contract strongly to pump blood some distance, either to the lungs or the rest of the body
why not just pump the blood through the lungs to collect oxygen and then straight to the rest of the body before returning to the heart
if that was the case, the blood has to pass through tiny capillaries in the lungs in order to present a large surface area for the exchange of gases
in doing so, there is a very large drop in pressure and so the blood flow to the rest of the body would be very slow
how does the body maintain a high blood pressure
to increase the pressure of the blood, mammals have a system where blood is returns to the heart to increase pressure before it is distributed to the rest of the body
it is essential to keep the oxygenated blood in the pump on the left side separate from the deoxygenated blood in the pump on the right
where does the right ventricle pump to
the right ventricle pumps blood to the lungs and it has a thinner wall than the left ventricle
why does the left ventricle have a thick muscular was
it enables it to contract to create pressure to pump blood to the rest of the body
how much blood do the atria and ventricles pump
both atria contract together and both ventricles contract together
pumping the SAME VOLUME OF BLOOD
what are between each atrium and ventricle
valves
what do valves do
valves prevent the backflow of blood into the atria when the ventricles contract
