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Bcem 431 > Lecture 6 > Flashcards

Lecture 6 Flashcards

1
Q

What are the three classes of proteins that allow metal ions into the cell or the blood

A

Channels (facilitated diffusion of metals into the cell, don’t ever need NRG, passive)

Exchangers (taking na out and letting ca in)

Transporters (exclusively require energy, active transport )

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2
Q

What is iron required for in humans

A

The biosynthesis of:

Heme containing proteins

Iron sulfur cluster proteins

Iron in enzymes (ex. Ribonucleotide reductase)

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3
Q

What is myoglobin

A

An oxygen carrier in muscle tissues

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4
Q

What is a heme

A

It’s a prosthetic group (or cofactor) that carries O2

It’s an iron porphyrin (has iron in centre of some rings)

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5
Q

What is the oxidation state of fe in the heme

A

2+, if it bind to oxygen is becomes 3+ (because hard ligand)

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6
Q

Why does the heme sit so deep in the myoglobin?

A

Because it was put there post translationally

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7
Q

What happens if the heme fe binds to carbon monoxide instead of oxygen

A

C=O is toxic so when it bind in place of oxygen it poisons the heme and oxygen can’t bind anymore

You suffocate

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8
Q

What is hemoglobin

A

Oxygens carrier in the blood

Has four subunits (tetramer) so it binds four heme groups

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9
Q

What type of binding does hemoglobin show in contrast to myoglobin

What does the inflection point mean

What order reaction is myoglobin

A

Coorperative ( the affinity of oxygen changes if one heme group is bound to oxygen) shows sigmoidal kinetics

Because one inflection point, this means two site get preferentially occupied then the other two

Myoglobins is a 1st order reaction, has only one subunit so it doesn’t show cooperativity

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10
Q

Know how to draw the heme

A

Slide four

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11
Q

How is the heme/protoporphyrin made?

A

There are two steps, one in the cytosol and the other in the mitochondria

Starts with succinyl coa from TCA and glycine

The final step is the insertion of Fe2+ to form the final heme

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12
Q

What does electron transfer protein or redox proteins use for their function

A

Heme groups or iron sulfur clusters

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13
Q

What is the shape of the heme group and why

A

It’s very tightly packed and fe is very tightly bound

The heme group is flat and planar because of the tightness

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14
Q

What is cytochrome c and mitochondrial cytochrome oxidase

A

Mitochondrial Cytochrome oxidase is a heme copper oxidase which reduces O2 to H2O

Cytochrome c with a heme binds to the oxidase to deliver 4 electrons and hydrogen through the pump and allow this redox to happen

Copper is involved

When cytochrome c comes in, the oxygen in its heme gets replaced by copper

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15
Q

What are three different iron sulfur cluster proteins

A

Ferrodoxin and rubredoxin , aconitase

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16
Q

What always need to happen to iron

A

It always need to be very tightly bound , cannot be free in the blood

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17
Q

What are the irons surrounded by in iron sulfur cluster

A

By four Sulfurs which come from cys side chains or elemental sulfur

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18
Q

Ferredoxin has how many clusters

Aconitase

Diff form of ferrodoxin

Rubredoxin

A

4 fe (cube shape)
3 (broken cube)

2 (flat square)

1

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19
Q

If the heme sulfur clusters are not formed what happens

A

Many diseases since iron is now free in blood

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20
Q

How are clusters formed

A

By desulfuration of cys to make elemental sulfur

Then the cluster is made and sent to heme sulfur cluster proteins (HSC)

Then atp dependent insertion of those clusters into recipient proteins

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21
Q

What is ribonucleotide reductase

A

Converts rna to dna

Is an example of a diiron (3+) cluster

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22
Q

ribonucleotide reductase structure

A

Has fe surrounded by oxygen, bidentate binding so fe3+

23
Q

What is special about iron

A

Essential element for growth/survival of all living organisms

One of the most abundant elements in earths crust

Can be very toxic since it can make oxygen radicles through Fenton chemistry ( which is why only specific amounts of iron can be given to people and why fe is bound so tight)

If high oxygen conditions, iron is found in fe3+ form

In anaerobic conditions or low ph fe2+ (ferrous) is dominant

Fe2+ highly soluble (bound with low affinity 10^-14M, fe3+ is not (10^-18)

24
Q

What form is fe in in food then when it’s in our bodies

A

In food it’s fe3+ which then turns to fe2+ in our bodies since oxygen rich

25
Q

What happens to fe once it’s in our body

A

Then it’s secreted into the blood where is bound to transferrin as fe3+

This whole transferrin fe3+ complex can be taken up through transferrin receptors

26
Q

Where is the largest pool of iron found in the body

Why

A

In the hemoglobin proteins in red blood cells.

This is because iron need to always be in the bone marrow where red blood cells are being made

27
Q

What recycles red blood cells

A

Macrohpages. The iron is realeased back and cycle of iron transferrin starts again

28
Q

What recycles red blood cells

A

Macrohpages, the. The iron is realeased back and cycle of iron transferrin starts again

29
Q

Where is iron stored as in the cell, what about in liver

A

In cell it’s present as 2+

In liver it’s in the ferritin storage protein as fe3+

30
Q

What is a machine that can measure the exact amount of iron in the tissues

A

ICP-MS

31
Q

What are hepatocytes

A

Liver cells

32
Q

How many grams of iron in the blood

In hepatocytes

In transferrin iron complex

In gut

What happens to the amount as it goes to different part in the body

A

2.5g

1g

3mg

1-2mg

Amount gets smaller (more divided up)

33
Q

What is a gut cell called

Red blood cell

Liver cell

A

Enterocyte

Erythrocytes

Hepatocyte

34
Q

How is iron taken up by enterocytes (gut cells)

A

Fe3+ its first converted to fe2+ then it goes through the DMT (divalent metal ion Transporter) in the cell

It either forms ferritin complex or

Fe2+ is taken out of the cell via jak2, ferroportin and hephastin convert it to 3+

When out of the cell it’s back into fe3+ where it’s bound to transferrin

35
Q

What is the TfR1 in the enterocytes (or hepatocytes)

A

It’s a transferrin receptor

Converts the fe3+ to 2+ for it to go inside the cell

By Reducing

36
Q

How is iron taken up by macrophage (white blood cell)

A

Macrophage targets cancer cells by shooting iron at them, which causes oxidative damage through Fenton chemistry

So it’s taken in to the macrophage by rbc transferring it, goes from fe3+ to 2+ inside the macrophage

Can either from the insoluble ferritin storage thing

Or leave the macrophage via ceruloplasmin copper protein turning it into fe3+ to bind to transferrin

37
Q

How is iron taken up by hepatocytes

A

It’s already in the tresferrin fe complex

Goes into the cell via tfr1 binding to transferrin and converting its 3+ to Fe2+

Then it can either form ferritin storage or export the iron back out via ceruloplasmin and deliver it to other tissues

38
Q

What is ferritin

A

Insoluble iron 3+ clusters mostly found in helatocytes (in liver)

Made up of 24 identical subunits, has a tetrahedral arrangement

The iron sulfur clusters is placed in the middle

Can open up and close so that iron leaches out through the middle

39
Q

What is transferrin

A

It transports iron through the serum to the bone marrow where red blood cells are made

Also transports iron from the gut to the liver for storage

40
Q

How long do red blood cells circulate t

A

120 day (meaning they’re very stable proteins when bound to iron)

Then they are chewed up by macrophages which store the iron for recycling in our bodies

41
Q

What is holotransferrin

Apo transferrin

A

Iron is bound

Ligands not bound

42
Q

How is iron taken up by cells via the tf cycle

A

First the apotransferrin (no iron bound) is present.

Once fe3+ bind to give holotransferrin, TFR1 recognizes and binds it.

This TFR1 and holotransferrin are taken into the cell Clathrin coated pits forming an Endosome (still bound in the endosome so still fe3+)

A proton pump on the endosome lowers the pH, this makes the transferrin release iron (now unbound) turning fe3+ to 2+ still

DMT on the endosome transports the fe 2+ iron back out of the endosome

The fe2+ free in the cell cytosol turns into fe-s clusters in the mitochondria OR

Can go into ferritin as fe3+ as storage

43
Q

How does co2 change HCO3 concentration

If carbonate binds to holotransferrin what happens

A

Increased co2, lower HCO3

Lower co2, higher HCO3

The solution would turn to a lower pH

44
Q

What is ferritin

A
45
Q

How can we detect liver damage base on ferritin

A

Can look at how much iron in the blood

Blood turns dark.

46
Q

What is hepicidin structure

A

A sulfur rich protein (cysteine rich)

Made of two beta sheets

47
Q

What is hepicidin structure

A

A sulfur rich protein (cysteine rich)

Made of two beta sheets

48
Q

What is hepicidin used for

A

It’s an iron regulator

So it’s made in the liver in response to high iron, released in the bloodstream, then shuts down iron coming in from the gut and macrophages

Shuts it down by binding to ferroportin

49
Q

What diseases are caused by too much hepicidin (low iron)

What diseases are caused by too low hepicidin (high iron)

A

Anemia

Hereditary hemochromatosis

50
Q

What is the mechanism of hepicidin inhibition intake of iron from enterocytes and macrophages

A

After hepicidin binds to ferroportin, ferroportin becomes phosphorylated by JAK2 (kinase)

The phosphorylated ferroportin is internalized by the cell and degraded

This stops the efflux of iron into the blood from cells (like macrophage, hepatocytes and enerrocytes)

51
Q

In the presence of hepicidin jak2 acts as a

A

Negative regulator

52
Q

How is hepicidin made to help against bacteria

A

It’s made in the liver During inflammation in the host

This inflammation making the hepicidin decreases level of iron in the blood which invading pathogenic bacteria use

53
Q

What is lactoferrin when there is inflammation

A

It’s secreted by neutrophils and targets the inflammation

Looks like transferrin but binds iron even stronger (so take more iron out of blood during inflammation), which is why it again makes iron less available for bacteria

Bcem 431 (26 decks)

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