A2 Biology: Respiration - The Krebs Cycle

The Krebs cycle takes place in the mitochondrial matrix. This stage takes place in aerobic respiration.

1. Acetate (carried from the Link reaction by coenzyme A) joins with Oxaloacetate (4C) to form Citrate (6C). CoA is the released to collect more acetate.
2. Citrate is decarboxylated (CO2 is removed) and dehydrogenated (2H is removed) to form a 5C compound. 2H is accepted by a molecule NAD which becomes reduced NAD.
3. 5C compound is also decarboxylated and dehydrogenated to form a 4C compound and a molecule of reduced NAD.
4. 4C compound is changed to another 4C compound and during this change a molecule of ADP is phosphorylated to produce a molecule of ATP. (Substrate-level phosphorylation).
5. The 4C compound then changes into another 4C compound and 2H is removed and accepted by coenzyme FAD which becomes reduced.
6. The other 4C compound go through dehydrogenation  and oxaloacetate is regenerated and another molecule of NAD is reduced. 

There needs to be two turns round the cycle for each molecule of ATP

To conclude: 

• 6 Reduced NAD are produced
• 2 Reduced FAD are produced
• 4 molecules of CO2 are produced
• and 2 ATP are produced

A2 Biology: Homeostasis: Control of blood glucose concentration

If blood glucose concentration is too high it is detected by beta cells 

• Beta cells (in islets of Langerhans) then secretes insulin into the blood
• They target hepatocytes, muscles cells and other cells such as brain that have membrane bound receptors for insulin. Insulin binds to these receptors
• Adenyl cyclase is activated in each cell and converts ATP to cAMP
• this activates a series of enzyme reactions 
• Glucose is converted into glycogen for storage/lipids
• or used in respiration
• glucose leave cells through specific channels

If blood glucose concentration is too low

• This change is detected by alpha cells (in islets of Langerhans)
• Alpha cells secrete the hormone glucagon
• Targets cells are heptocytes which posses specific receptors for glucagon
• glycogen is converted to glucose - glycogenolysis
• glucose is made from amino acids and lipids - gluconeogenesis 

A2 Biology: Kidney Failure

If the kidney fails - unable to remove urea - not going through osmoregulation

3 main causes:

• Diabetes mellitus
• hypertension
• infections

Use of dialysis

Dialysis removes waste, salts and excess fluids from the blood by passing over a dialysis membrane. Dialysis membrane is partially permeable and contains the perfect plasma, so it has right amount of glucose, water and other substances but not urea. Urea is passed through into the dialysis membrane by diffusion.

Methods of control:

• Haemodialysis - blood from vein is passed through a machine which contains  artificial dialysis membrane and returns back into the blood. Heparin is added to act as an anticoagulant.

• Peritoneal dialysis - filters the body's abdominal membrane. A permanent tube is implant into the abdomen and dialysis solution is poured in to fill up the space between abdomen wall and organs. Several hours later this solution is drained from the abdomen.

• Kidney transplant - is a major surgery where a kidney from a healthy willing relative donor or a healthy kidney from a deceased person is implanted in and is attached to the blood supply and bladder. The old kidney remains in the body unless it is cancerous or likely to cause an infection. The patient would have to take immunosuppressants for life as the new organ would be treated as a foreign object and this would prevent it from being rejected.

A2 Biology: Respiration - Oxidative phosphorylation

-On inner mitochondrial membrane known as the cristae

• Has a series of electron carriers = electron transport chain
• Each one has a haem group (co factor) which contains iron, Fe.
  (If it's Fe2+ it is reduced ~ gained e- | If it's Fe3+ it's oxidised ~ loss e-)

1. NADH releases H to the first carrier
2. First carrier passed H to the second carrier
3. H now splits into H+ and e- and only the e- is passed on to the net carrier
4. H+ is pumped into the inter membrane space 
5. There is now a high concentration of H+ in intermediate slate = protein motive force/electrochemical gradient
6. H+ diffuses through the stalked particle which acts as a channel protein of hydrogen ions back into the matrix
7. H+ are back in matrix they recombine with their e- to form an Hydrogen atom.
8. H combines with O2 (which we breathe in) to form H2O hich is a waste product of respiration

• Enzyme involved - cytochrome oxidase
• Oxidose phosphorylation is making ATP using oxygen therefore involves electron transport chain
• Chemiosmosis - making ATP as H+ diffuse through stalked particle

A2 Biology: Respiration - Glycolysis

Glycolysis

• Happens in the cytoplasm of all cells
• It can take place in anaerobic or aerobic conditions.
• Glucose (6C sugar) is broken down to 2 molecules of pryuvate (3C compound)

Stage 1. Phosphorylation

• Glucose (6C sugar) - very stable - needs to be activated to be split
• An ATP molecule is hydrolysed - phosphate group attached to glucose at carbon 6
• Glucose > Fructose 6 phosphate
• Another ATP is hydrolysed - phosphate group attached to fructose 6 phosphate at carbon 1
• Activated - fructose 1,6 bisphosphate aka hexose, 1,6-bisphosphate
• Energy from hydrolysed ATP activates the sugar and prevents it from going out of the cell

2. Splitting hexose 1,6 bisphosphate

• each molecules of hexose 1,6 bisphosphate is splt into 2 x triose phosphate 

3. Oxidation of triose phosphate

• 2H atoms are removed from triose phosphate (involves dehydrogenase enzymes)
• These are helped by NAD which is a H acceptor - combines with H and becomes 'reduced NAD'
• 2 ATP formed - substrate level phosphorylation

4. Conversion triose phosphate > pryuvate

• 4 enzyme-catalysed reactions convert each phosphate to a pryuvate
• during this, 2 molecule of ADP are phosphorylysed to 2 ATP

So overall, 2 molecules of ATP (=net amount - 4 have been made but 2 are used again)

There are also 2 molecules of reduced NAD and 2 pryuvate which ill be used in next stage of respiration

A2 Biology: Osmoregulation in collecting duct

• The Loop of Henle is where most water is reabsorbed.
• The longer the loop of Henle the more water is reabsorbed from the filtrate - back in the blood.

E.g. A desert rat would have a longer loop of Henle than a horse or a beaver as it requires more water to be reabsorbed and conserve to help it survive in the heat. A beaver would have a smaller loop of Henle in comparison to the horse as it lives in water.

When you are THIRSTY 

• it is detected by osmoreceptors in the hypothalamus
• the osmoreceptors shrink due to a decrease in water potential in the blood
• it then synapses with neurosecretory cell - terminal bulb (which is equivalent to synaptic knobs) and fires off an action potential
• it releases vesicles that contains the hormones Antidiuretic Hormones (ADH) into the blood in the posterior pituitary gland
• ADH in blood targets cells forming walls of collecting duct
• causing a series of enzyme reactions including cyclic AMP
• vesicles with water channels aka aquaporins fuse with the cell membrane makin collecting duct more permeable to water
• the collecting duct passes through medulla (salty tissue fluid) so water pulls out of the filtrae by osmosis to be reabsorbed in blood.
• this produces a small quantity of concentrated urine
• water back in the blood  blood water potential is restored back to normal
• this process switches off = negative feedback

My revision notes: A2 Biology: Urea + Ornithine cycle + detoxification of alcohol

Deamination is the process where ammonia (NH3) is produced. Ammonia is very soluble and highly toxic. It also produces an organic keto acid which is then used in respiration. Ammonia is converted into Urea which is less soluble and less toxic. Urea travels in the blood and is transported to the kidneys where it is filtered out of the blood and stored into the bladder until released from the body.

The ornithine cycle

2NH + CO2 > CO(NH2)2 + H2O

ammonia + carbon dioxide > urea + water

Detoxification of alcohol

Alcohol can be bad for us but it also contains chemical potential energy which could be used in respiration.

• Alcohol is broken down b hepatocytes by the action of enzyme ehtanol dehydrogenase
• In result of this ETHANAL is made
• it is then dehydrogenated again by ethanal dehydrogenase
• Which produces ethanoate (acetate)
• combined with coenzyme A to form acetyl coenzyme A which enters respiration.
• Ethanol > Ethanal > Ethanoic acid > Acetyl coenzyme A

My revision notes: A2 Biology: EXCRETION + Kidney functions

Excretion - Removal of toxic waste products formed by metabolic reactions.

CO2 - from respirations

• Dissolves in H2O to form Carbonic acid >  lowers pH of blood and denatures enzymes
• Detected - by chemoreceptors/aorta > sends and impulse to the medulla bongata > increase rate and depth of breathing. If thi falls below the pH of 7.35 > find it difficult to breathe = respiratory acidosis. 
• Carbonic acid: CO2 + H2O > H2CO3
• H2CO3  >(dissolves in)> H+  +  HCO3- (hydrogen carbomate)
• H+  +  Hb (haemoglobin) > HHb (Haemoglobinic acid) 
• Which leads to Hb not being able to load enough O2 ad therefore reduce amount of O2 that Hb can load

Removal of urea by the kidney

KIDNEY FUNCTIONS

• Removes urea from blood to urine
• maintin water  potential of blood
• remove exceess ions etc

Different sections of the nephtons have different functions.

Ultrafiltration - takes place in the Bowman;s capsule

Blood contains - Red blood cells (RBC), white blood cells (WBC)

                        -Plasma, which contains - amino acids, glucose, H2O, CO2, O2, hormones, urea

Ultrafiltration filters the blood (plasma) but the RBC and WBC are too big to be filtered out. 

The capillary is made of endothermic cells which is very thing and flat an have tessellated margins. 

In the nephron, the afferent arteriole has a wider diameter than the efferent arteriole which means the blood pressure in the glomerulus (knot of capilleries in the nephron) increaser - so all the small molecule sin the blood (amino acids, urea, co2, h2o, o2 etc) gets forced out of the blood capillaries BUT blood cells and large plasma proteins are too large to be forced out.

The filtrate (plasma without plasma proteins) is forced out into the bowman's capsule. 

There is only a basement membrane is the only true separation between endothelial cells of the glomerulus ad the bowman's capsule

The kidney 

•Blood enters a kidney through the renal artery and leaves through the renal vein.

•Excretory products are removed from the blood and are collected in the form of urine.

•Urine collects in the central part of the kidney called the pelvis.

•Urine passes from each kidney to the bladder along a tube called the ureter.

•The outer darker region of the kidney is the cortex and the inner, lighter region is called the medulla.

My revision notes: A2 Biology: Control of Heart Rate

All cells, e. muscle cells have different requirements, depending on the activity e.g. exercising - muscle cells require an increase in oxygen, glucose and removal of carbon dioxide.

The average heart rate is 70 beats / min
SAN controls this with no need of neurone impulses

If you exercise you need to increase:

• Heart rate
• strength of contraction
• stroke of volume  volume of blood pumped / beat

When you exercise you produce more CO2 - which dissolves to form carbonic acid - lowers pH

> This is detected by chemoreceptors in carotid arteries (going to head and aorta)

> They send an impulse to the cardiovascular centre which in turn sends an impulse down an accelerator nerve to SAN 

> So heart beats faster and stronger

Why are the chemoreceptors in the head and aorta?

Carotid artery is going to the brain ensures that the blood is not acidic

Going for aorta as its the biggest artery as it has the most amount of blood passing through

If you eercise you got receptors in muscles > gets stretched > impulse sends to cardiovascular neurone > SAN  > Increase in heart rate

Stop eercising > decrease in CO2/muscle receptors not stretched > impulse vagus nerves > SAN > slows heart rate back to normal