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Author Topic: VCE Biology Question Thread  (Read 3570651 times)  Share 

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Scooby

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Re: VCE Biology Question Thread
« Reply #1770 on: May 25, 2014, 04:43:09 pm »
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3 questions for you guys!  ;D
  • Why are clotting factors not normally present in plasma?
  • Name one inherited disease caused by the absence of a clotting factor
  • Name the clotting factor involved.

Thanks :)

Fibrin is insoluble in blood, and if it were present in plasma, it would cause thrombosis. Haemophilia A is a type of coagulation disorder and is caused by a deficiency of factor VII. When you get to Unit 4, you can use it as an example of an X-linked recessive disorder as well
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jessica666

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Re: VCE Biology Question Thread
« Reply #1771 on: May 25, 2014, 05:53:06 pm »
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Can anyone give me a simple explanation of humoral and cell-mediated response?

also, do antibodies, when they attach to antigens, inactivate the antigen themselves? Or do they act as a marker to attract other cells to engulf the antigen?
« Last Edit: May 25, 2014, 06:15:26 pm by jessica666 »

Reus

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Re: VCE Biology Question Thread
« Reply #1772 on: May 25, 2014, 06:21:35 pm »
+1
can anyone give me a simple explanation of humoral and cell-mediated response?
Simple? I don't think thats possible haha!

Well Humoral and Cell-Mediated responses fall under the 3rd line of defence also known as the specific/adaptive immunity.

Humoral:
  • B-lymphocytes are the major cells involved.
- Produced in the Bone Marrow (thus the name B-lymphocytes)
  • Each B-Cell has its individual antibody/antigen complex
  • Production of antibodies
  • B-Cells differentiate (clonal expansion) into
- B-Plasma cells (effector cells): secrete antibodies
- B-memory cells: remain in the body so when the antigen is encountered again, a response can rapidly be reenacted.

Cell-Mediated:
  • Carried out by T-Cells
  • T-Cells made in the Bone Marrow however matured in the Thymus (hence its name  T-Cells)
  • T-Cells include; Helper T cells (Th), Cytotoxic T cells (Tc) and Suppressor T cells.
  • Helper T cells active cytotoxic cells and present antigens to immature B cells.
  • Cytotoxic cells detect/recognise cells with infection, are able to destroy these foreign cells with contact
  • Lastly Suppressor T cells, literally suppress the immune responses once the antigen has been removed

Antibodies; are proteins that bind and neutralise antigens. Are quite specific (like an enzyme-substrate complex).

That's just on top of my head! Hope it helps :) It sure was great revision/practise just before my SAC haha.
« Last Edit: May 25, 2014, 06:36:10 pm by Marco Reus »
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howlingwisdom

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Re: VCE Biology Question Thread
« Reply #1773 on: May 25, 2014, 09:52:45 pm »
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Do all antigen-presenting cells have MHC class-2 markers?
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eagles

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Re: VCE Biology Question Thread
« Reply #1774 on: May 25, 2014, 10:05:17 pm »
+1
Yes. Antigen-presenting cells such as macrophages, certain B cells and dendritic cells express MHC class II. The fragment of the antigen is bound there for the T cell to recognise.

katiesaliba

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Re: VCE Biology Question Thread
« Reply #1775 on: May 26, 2014, 11:14:37 pm »
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'As B and T lymphocytes mature, those that carry receptors for molecules that already exist in the body are either inactivated or they self-destruct by programmed cell death. This process provides the capacity of the immune system to distinguish 'self' from 'non-self'. This results in self-tolerance, which means that there are no mature lymphocytes that will react against self-marker molecules.'


This passage is from my textbook and I don't really understand what it's saying. Why would B and T lymphocytes carry receptors for molecules already present in the body?
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lzxnl

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Re: VCE Biology Question Thread
« Reply #1776 on: May 26, 2014, 11:37:01 pm »
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To paraphrase:

"If B and T lymphocytes are created that target cells of the body, they are either inactivated or destroyed. This is important so that the immune system does not target itself"

You can never be sure that no genetic mutation will occur to make a B or T cell have dodgy receptors.
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Re: VCE Biology Question Thread
« Reply #1777 on: May 26, 2014, 11:52:30 pm »
+1
To paraphrase:

"If B and T lymphocytes are created that target cells of the body, they are either inactivated or destroyed. This is important so that the immune system does not target itself"

You can never be sure that no spontaneous genetic mutation will occur to make a B or T cell have dodgy receptors.

And even so, the risk factors behind spontaneous mutations such as random deamination, depurination and tautomerism can be addressed and mitigated to an extent.

It's actually quite straightforward nowadays to establish a risk of mutation by inducement (non-spontaneous, e.g. by some mutagenic substance), given the necessary biochemical and epidemiological data. For example, the mutagenic impact of benzene on DNA is well established from both clinical (in vivo) and in vitro biochemical knowledge, as well as long-term clinical epidemiological study.

While this doesn't contradict your statement that "you can never be sure", I'm just being a bit nit-picky and adding that it is only with spontaneous mutations can a wholly unpredictable mutation arise - and even then the definition of 'unpredictable' is ambiguous :)
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simpak

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Re: VCE Biology Question Thread
« Reply #1778 on: May 27, 2014, 12:07:41 am »
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It's not about genetic mutation though - there will always be self-reactive cells present in the body of someone without any dodgy mutations spontaneous or not.  The way the system works (normally) is to create an antigen receptor for every possible theoretical antigen by combining different parts of proteins together initially.  This includes cells specific to antigens in your body.

Then the system goes ahead and 'tests' the cells against the antigens naturally present in your body inside a specific organ (bone marrow or thymus) before letting them into the periphery - it can weed out the cells that happen to have expressed an antigen receptor that recognises something expressed by self cells.  98% of the T cells created initially will die (in a normal functioning immune system) - either because they don't recognise any antigen (they were created against something that can't be presented) or because they happened to recognise a self antigen.  Because everyone (bar identical twins) has a different genetic makeup they all express self proteins with different shapes and this means that what constitutes 'self' and what needs to be 'disallowed' during development differs for everyone - this is why the specificities of the final peripheral pool of immune cells isn't entirely genetically encoded in the outset and you're allowed to begin with more cells than what you end up with circulating through lymph nodes and the blood.  In fact, it would be impossible for you to genetically encode individual antigen receptors against all theoretical antigens in the human genome because there isn't enough DNA.  The lymphocytes use a special process during development to manipulate the actual genome in those cells (cut and snip the DNA) and give different combinations of protein segments to create fresh antigen receptors - the process is completely random and that's what leads to the development of self-recognising receptors on some of the cells initially.  But fortunately these cells will be killed later on.

(NB: Not all of these cells are killed and this is true for everyone, you and me both - this is how you can end up with an autoimmune disease, when one of these abhorrent cells becomes activated because the process of self-tolerance failed).

Basically, the answer to the original question is:
The B and T cells carry receptors to antigens present in the body because the specificity of these cells isn't encoded in the germ-line.  You make everything first, and then you reduce it to what you actually need later on in the process of lymphocyte development.

Lymphocyte development is very complex and you're not required to know about most any of it.  Just know that there are physiological processes, such as cell-death or peripheral inactivation, that serve to prevent the self-reactive cells present in every single normal person from entering the periphery and being able to cause autoimmune disease.
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katiesaliba

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Re: VCE Biology Question Thread
« Reply #1779 on: May 27, 2014, 06:37:22 pm »
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What are granulated cells and how does granulation assist in their functioning?
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Reus

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Re: VCE Biology Question Thread
« Reply #1780 on: May 27, 2014, 06:46:43 pm »
+1
What are granulated cells and how does granulation assist in their functioning?

Granules are small packets of enzymes and other substance for example inflammatory chemicals like histamine. --> that are made up by Leucocytes that assist them in performing their function. For those white blood cells that are phagocytic (macrophages, etc) the enzymes in the granules (vesicles) will be released onto the eaten foreign material and break down its component pieces; hence bacteria is killed. The enzymes have to be kept in these designated vesicles because if they were free inside the white blood cell, they would destroy it from the inside.

Hope this helps :)
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millie96

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Re: VCE Biology Question Thread
« Reply #1781 on: May 27, 2014, 07:26:24 pm »
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Can somebody please explain the cell mediated response?
also, where do MHC markers come into play

Reus

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Re: VCE Biology Question Thread
« Reply #1782 on: May 27, 2014, 07:42:16 pm »
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Can somebody please explain the cell mediated response?
also, where do MHC markers come into play
Well the cell meditated response is a subclass of the third line of defence (adaptive/specific).
Cell mediated response occurs when a pathogen is already in the cell. This level of immunity is carried out by T cells. There are several types of T cells which include
  • T Helper (Th): activate cytotoxic cells and present antigens to immature B cells.
  • T Cytotoxic (Tc): typically detect/recognise cells that have been infected and henceforth release a protein that 'punches' holes into the membrane of that cell. (destroys foreign cells)
  • T Supressor (Ts): come into effect when all antigens have been eliminated. they prevent immune responses from continuing in order to avoid 'over work' and damage to the immune system.

MHC (Major Histocompatibility Complex) markers; generally MHC #1 (found on all cells except red blood cels) and MHC #2 (on lymphocytes & macrophages, dendritic cells etc...)
These literally assist the body to distinguish between self and non-self cells. However more importantly, the MHC markers have antigen fragments on the surface (process of phagocytosis) of APC (antigen presenting cells). Which in turn allows the T helper cell to recognise the antigen and stimulate B cells (humoral) and T cytotoxic cells to initiate the immune response.

Hope this helps out :)
« Last Edit: May 27, 2014, 07:45:38 pm by Reus »
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howlingwisdom

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Re: VCE Biology Question Thread
« Reply #1783 on: May 27, 2014, 07:44:25 pm »
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Can somebody please explain the cell mediated response?
also, where do MHC markers come into play
The cell mediated response is basically when the cytotoxic T-cells directly acts upon the virus/cancerous/fungi affected cells. For example, when a phagocyte (or other antigen presenting cells such as dendritic cells) engulf the pathogen (which could be a virus) it presents the non-self antigen fragments of the pathogen on its MHC marker on the surface of the cell membrane. The MHC marker in this case basically acts like a 'stage', kind of like a 'trophy holder' and stimulates the T-helper cell. The type of the marker would be class-2 since it is an antigen presenting cell and the stimulation of the T-helper cell would occur by interleukin-1 or you can just say cytokines and also matching receptors. The T-helper cell will then stimulate inactive T-lymphocytes to undergo clonal expansion and to differentiate into cytotoxic-T cells, T-supressor cells and T-memory cells.
The cytotoxic-T cells destroy virus-infected cells by releasing perforins (a kind of protein) which punches holes and lyses the membrane of the infected cell.

I hope this helps you somewhat and please, anyone correct me if I am incorrect!

(EDIT: beaten :P)
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Reus

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Re: VCE Biology Question Thread
« Reply #1784 on: May 27, 2014, 08:47:08 pm »
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Are Mast Cells and Basophils the same thing? Other than promoting an inflammatory response and blood flow through the secretion of histamines, do they have different distinct functions?

Quite confused tbh :/ Our teacher hinted to say Mast Cells instead... however is there a difference? Or is it just a different name?
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