OFFICIAL OCR A2 Biology - F214 Thread

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Chunkeymonkey62

I know that, but in my diagram, there are hydrogen ions in the stroma, that go through an electron carrier, and back our through an ATP synthase?

All I know is that hydrogen ions in the stroma are pumped into the thylakoid space using energy created from the movement of the electrons down the electron carriers. They then diffuse down their proton gradient through the ion channels w/ ATP synthase enzyme :smile:

Reply 1381

LearningMath

AnniG

NADH dehydrogenase is used to remove the hydrogens from the NADH at the beginning of oxidative phosphorylation...

I think he's refering to how the reduced NAD reaches the matrix from the cytoplasm, not that we need to know it :p:

Reply 1382

loveisjustasong

InvoluntarySlacker

The loop of Henle shiz, it just seems a bit bland and vague. Is this all we need to know:
High NaCl conc in medulla, high water pot. in descending limb
NaCl diffuses into descending limb, water diffuses out by osmosis down water pot. gradient and into capillaries
At the apex of the henle, theres a high solute conc (HIGHER THAN MEDULLA???)
At the thin ascending limb, Na and Cl diffuses out into medulla (AND INTO CAPILLARIES?!?!?!?)
Thick ascending limb impermeable to water, ions forced out by active transport
fluid in tuble now high in water pot
DCT and CD water reabsorption

To begin, as the fluid goes down the loop of henle, it has a relatively low water potential as most of the water was reabsorbed in the PCT.

Anyway, it all begins with the ascending limb. Na and Ca ions are actively pumped out of the ascending limb and into the medulla. This lowers the water potential of the medulla. The ascending limb is impermeable to water so there is no osmosis in this part of the henle. The descending limb on the other hand is permeable to water. Water diffuses out of the descending limb because there's a water gradient formed because of the ions being pumped into the limb. So now the water potential of the medulla becomes higher and at this point, the sodium ions and calcium ions diffuse back into the descending limb. This makes the water potential of the medulla even high and the water diffuses into the surrounding capillaries (vasa recta).

Something to remember. If there's a question saying why is there a high concentration of ions at the bottom of the henle compared to the rest, just simply say the counter current system causes a build up of ions at the bottom of the henle.

Ok, thanks! We were taught to write it in the way you've just written (reverse - beginning with the ascending limb) if they specify countercurrent.

thanks everyone else :biggrin:

Reply 1383

Remarqable M

AnniG

NADH dehydrogenase is used to remove the hydrogens from the NADH at the beginning of oxidative phosphorylation...

no i think they are re-oxidised back to NAD and the hydrogen ions take part in chemiomosis and the electrons are accepted by NADH - Coenzyme Q reductase(the first electron carrier in the transport chain)

Reply 1384

GoingInForTheKill

What do people think is the hardest module in this unit?

Reply 1385

conorf199

is negative feedback only found in endotherms?

Reply 1386

conorf199

GoingInForTheKill

What do people think is the hardest module in this unit?

Excretion

Reply 1387

Nimbus

LearningMath

I think it's one of those sketchy biology concepts like the hairpin countercurrent multiplier, they just breeze a lot of it.

I guess if you imagine the Sodium ions reach a loop state where the concentration is constant on either side... 3 diffuse in and 3 diffuse out. Whereas the potassium is being moved in and then not moved out at the same rate, 2 K in for 1 K out for example. They would eventually reach a loop state as well, but whilst repolarizing the above ratios apply.

Yeah I guess I#ll just learn the overview picture, but arrrrrrgh I must say: I hate these little "gloss overs". :sigh:

.
Just hoping when we go to uni, the lectures won't go "actually, what you've studied at A-level was all a lie again...". :p:

Thank for the help btw(sorry if I haven't say so earlier!xD).

GoingInForTheKill

What do people think is the hardest module in this unit?

Hmmm...probably excretion as well - too much to learn and they have some wacky stuff in the syllabus - pregnant testing anyone? :p:

But really, for me it's nerves - it contains the most overviews/breeze throughs and they're driving me nuts to learn what we should actually write in the exam and what not... :woo:

I seriously am going to find a physiology book ro something after exams and just read it and understand the real story behind it...

Reply 1388

Remarqable M

GoingInForTheKill

What do people think is the hardest module in this unit?

The hardest is the Excretion :mad:

Reply 1389

Tinkerbelle ♥

I just can't understand why everyone seems to know so much more than me and in so much more detail! I've been going to all my lessons!!! :woo:

Reply 1390

LearningMath

Remarqable M

She didnt dispute that, NADH dehydrogenase is an enzyme which catalyses the donation of electrons to complex I and the oxidation of NAD. The shuttle mechanism you refered to is in a strecch and challenge question at the base of page 91.

Reply 1391

AnniG

Remarqable M

That's the same as what I said I just didn't use any detail - the enzyme NADH dehydrogenase is definitely the enzyme that oxidises the NADH!

Reply 1392

GoingInForTheKill

Remarqable M

The hardest is the Excretion :mad:

Yeah i agree but its just the kidney stuff thats abit dodgy, the liver stuff is straight forward.

Reply 1393

InvoluntarySlacker

GoingInForTheKill

What do people think is the hardest module in this unit?

Respiration. :emo:

Reply 1394

Remarqable M

AnniG

That's the same as what I said I just didn't use any detail - the enzyme NADH dehydrogenase is definitely the enzyme that oxidises the NADH!

sorrry

but yea your correct!

Reply 1395

BHAM!

This thread is starting to confuse me lol good luck for the exam everyone!

Reply 1396

clad in armour

SPECIFICATON POINT - "Explain the importance of coenzymes with reference to Acetyl Coenzyme A and NAD"

Reply 1397

GoingInForTheKill

InvoluntarySlacker

Respiration. :emo:

Respiration is straight forward, what dont you understand? I may be able to help :smile:

Reply 1398

InvoluntarySlacker

clad in armour

SPECIFICATON POINT - "Explain the importance of coenzymes with reference to Acetyl Coenzyme A and NAD"

Coenzymes are needed to transport vital molecules to other parts of the cell in order for aerobic respiration to happen.

CoA transfers Pyruvate from the cytoplasm to the mitchondria for the next stage of respiration. If it this couldn't happen, only anaerobic respiration can occur and a low yield of ATP can be produced to be used by the cell.

NAD is needed to take hydrogen to the ECT. This is important as hydrogen spilts into a H+ ion and electron. The electron is used to create ATP as it provides the energy for hydrogen ions to be pumped through the membrane and diffuse back through the ATPase where ATP will be synthesised from ADP + Pi.