3 Mass transport Flashcards
Haemoglobin
protein molecules with a quaternary structure
primary structure
seqeuence of amino acids in the four polypeptide chains
secondary structure
each polypeptide chain is COILED into a helix
tertiary structure
each polypeptide chain is FOLDED into a PRECISE SHAPE
quaternary structure
all 4 polypeptide chains linked together to form an almost spherical molecule
haem group
contains ferrous/ fe2+ ion, each of which can combine with a single O2 so therefore 4 O2 molecules can be carried by a single haemoglobin molecule
Loading
aka Associating- when heamoglobin bindes with oxygen.
occurs in the lungs.
unloading
aka dissociating- when haemoglobin releases its oxygen .
takes place in the tissue.
high affinity
hb with high affinity takes up oxygen more easily but releases it less easily.
low affinity
hb with low affinity for oxygen takes it up less easily but release it more easily.
role of haemoglobin
to transport oxygen
how is hb efficient at transporting o2?
- readily associates with oxygen at the surface where gas exchange takes place.
- readily dissociates from oxygen at the tissue requiring it
Can hb change its affinity?
Yes, because it changes its shape in the presence of certain substances eg CO2 where hb binds moreloosely to O2 so oxyugen is released.
Conditions at gas exchange surfaces
1) O2 concentration is high
2) CO2 concentration is low
3) affinity is high so oxygen is associated
conditions at respiring tissue
1) O2 concentration is low
2) CO2 concentration is high
3) affinity is low so oxygen is dissociated
why are there different types of hb affinity?
> each species have hb with diff amino acid sequence
therefore diff quaternary and tertiary structures
therefore diff oxygen binding properties
due to their structures, some have high affinity for O2 and some have low affinity for O2
Oxygen dissociation curve
- they show the affinity of haemoglobin for oxygen
the shape of one type of hb molecule can change under different conditions so there are many diff oxygen dissociation curves
what do oxygen dissociation curves show?
Oxygen dissociation curves show the relationship between oxygen levels (as partial pressure) and haemoglobin saturation
Cooperative binding
1st binding: Q structure changes so Hb changes shape.
- makes it easier for other subunits to bind to an O2.
- smaller increase of partial presuure needed to bind 2nd molecule.
- Binding of 4th is harderbevause maj or binding sites=full so it’s less likely for s single O2 to find am empty site to bind to.
OxD curve more to the left
greater affinity of hb
loading=easier
Bohr effect
the greater the conc of CO2, the more readily the Hb unloads the oxygen.
behaviour of hb at gas exchange surface (lungs)
>low co2 >affinity for O2 increased >high O2 in lungs >oxygen more readily loaded by hb curve more to the left ****opposite at respiring tissue/muscles
effect of CO2 on hb
dissolved carbon dioxide is acidic and the low pH causes hb to change shape
the more active a tissue, the more O2 is unloaded. why?
high rate of respiration more co2 lower ph shape change low affinithy O2 unloaded more readily more O2 available for respiration
