UNIT 2; section 3 variation in biochemistry + cell structure

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the role of Hb

in red blood cells

carries o2 around the body

found in a variety of organisms = all vertebrates

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Hb and oxyhaemoglobin

large protein , = quarternary structure --- 4 polypeptide chains

each chain has a haem group = contains iron

each molecule of Hb can cary 4 o2 molecules

in the lungs the o2 joins to Hb to form oxyhaemoglobin = ASSOCIATION

near body cells o2 leaves oxyhaemoglobin =  returns to Hb =DISSOCIATION

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Affinity for o2 and po2

affinity = tendency a molecule has to bind to o2

Hb's affintity for o2 varies depending on the conditions its in

1 condition that affects it is the po2 = partial pressure of o2

po2 is a measure of o2 conc.

the greater the conc. of dissolved o2 in cells, the higher the po2

as po2 increases = Hb's affinity for o2 also increases
o2 loads onto Hb to form oxyhaemoglobin where theres a high po2= association
oxyhaemoglobin unloads its o2 where theres a lower po2 = dissociation

high po2 in the lungs (alveoli)
when cells repsire they use up o2 = lowers the po2

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affinity

Alveoli in lungs  -
high o2 conc.
high po2
high affinity
o2 loads
association

respiring tissue -
low o2 conc.
low po2
low affinity
o2 unloads
dissociation

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dissociation curves

show how saturated the Hb is with o2 at any given partial pressure

the affinity of Hb for o2 affects how saturated the Hb is ;
where po2 is high (in the lungs) , Hb has a high affinity for o2 ,so it has a high saturation of o2

where po2 is low (respring tissues), Hb has a low affinity for o2, so it has a low saturation of o2

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why is the curve s-shaped

saturation of Hb can also affect the affinity = this is why the graph is s-shaped

when Hb combines with the first o2 molecule ,its shape alters = easier for other moelcules to join too

as the Hb starts to become saturated = harder for o2 to join

as a result - the curve has a steep bit in the middle where its really easy for o2 moleules to join + shallow bits at each end where its harder

when the curve is steep , a small change in po2 causes a big change in the amount of o2 carried by the Hb

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carbon dioxide conc.

partial pressure of co2 = measure of the conc. of co2 in a cell

pco2 also affects o2 unloading

Hb gives up its o2 more readily at a higher pco2 = lower affinity

when cells respire they produce co2 = raises pco2
* increases the rate of o2 unloading so the dissociation curve shifts right

saturation of a blood with o2 is lower for a given po2 , meaning more o2 is being released

= the bohr effect

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different types of Hb

low o2 enviroments -
have Hb with a higher affinity for o2 than human Hb
dissociation curve is further left than ours

high activity levels -
Have Hb with a lower affinity for o2 than human Hb 
as they need their Hb to easily unload o2 
dissociation curve is to the right 

size
small mammals have a higher surface area to volume ratio than larger mammals
^lose heat quickly - high metabolic rate to keep them warm = high o2 demand 
mammals smaller than humans have Hb with with a lower affinity than human Hb - they need to be able to easily unload o2 to meet the demand 
dissociation curve is to the right of ours

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animal cells

nucleus = genetic materail

plasma membrane = holds cell together + controls entry and exit 

cytoplasm = gel like substance where most chemical reactions happen

ribosomes = where proteins are made 

mitochondria = aerobic respiration 

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plant cells

few extra cells 

palisade cell = leaf cell which absorbs light for photosynthesis

rigid cell wall = made of cellulose, it supports and strenthens the cell 

chloroplasts = where photosynthesis occurs

permanent vacuole = contains cell sap + a weak solution of sugar + salts . also pushes the chloroplasts closer to edge so they can absorb light

chloroplasts

double membrane 
thylakoid membranes - stacked to form grana 
grana are linked by lamellae 
stroma is the fluid filled space 

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polysacchrides

made of lots of monossachrides 
eg. 

cellulose starch glycogen

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cellulose

cell wall in plants 

long unbranched chains of B-glucose 

bonds between sugars are straight - so cellulose chains are straight 

cellulose chains linked by hydrogen bonds - from strong fibres - microfibrils

strong fibres mean cellulose provides structural support for cells

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beta-glucose

glucose is a monossarchride with 2 forms - alpha and beta

beta glucose is the same as alpha glucose  - EXCEPT the OH and H on the right are swapped around 

alpha glucose reads - HO OH 

beta glucose reads - HO H 

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condensation reactions

when monossachrides join , a molecule of h2o is released 

bond = glycosidic 

second beta glucose molecule is upside down 
^ this lines the 2 OH groups up so the glycosidic bond is straight 

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starch

main energy store in plants
doesnt effect osmosis as it is insoluble = good for storage 
mixture of 2 polyssacrhides of alpha glucose = amylose and amylopectin 

amylose
long unbranched chains of a-glucose
coiled structure due to bonds between the glucose molecules = good for storage 

amylopectin

long branched chain 
side branches allow enzymes that break down the molecule to get at the glycosidic bonds easily = so glucose can be quickly released quickly ie = large s.a.

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glycogen

main energy storage in animals 

polyssachrides of a-glucose

similar to amylopectin - more side branches coming off 
lots of branches means stored glucose can be released quickly 

very compact - so good for storage

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