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  • Created on: 11-01-17 17:42

Defence mechanisms

Non - specific immune response - physical and phagocytosis

Specific immune response - cell mediated response (T lympocytes) and Humoral response (B lymphocytes.

Each cell has a specific protein molecule on its surface - complex tertiary structure. This allows the body to tell the difference between self and non-self.

In the fetus, lymphocytes are colliding with other cells and will have receptors that fit these cells. These will die. The remaining lymphocytes will be for foreign material. Lymphocytes in adults are produced in the bone marrow and if they show an immune response to self- antigens then they undergo apoptosis.

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When the pathogen enters the body, the body's first line of defence is to form a physical or chemical barrier. The next line of defence is the white blood cells. There are two types of white blood cell - phagocytes and lymphocytes.

Phagocytes will ingest and destroy the pathogen by a process called phagocytois.

Large particles like bacteria can be engulfed by cells in the vesicles formed from the cell-surface membrane.

The chemical products of pathogens act as attractants for the phagocyte.

Phagocytes have several receptors on their cell-surface membrane that recognise and attach to the chemicals on the surface of the pathogen,

They then engulf the pathogen to form a vesicle and a lysosome will move towards it and fuse with it and destroy the pathogen by hydrolysis of their cell walls.

The products of hydrolysis are absorbed into the cytoplasm of the phagocyte.

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Cell mediated response and T lymphocytes (1)

Immunity - the ability of organisms to resist infection.

An antigen is any part of the organism that is recognised as non-self and stimulates an immune response. Antigens are usually proteins that are part of the cell-surface membrane.

The specific immune response depends on the type of lymphocyte. They are produced by stem cells in the bone marrow. T lymphocytes mature in the thymus gland and are associated with cell mediated response which is immunity involving body cells.

Respond to self infected bidy cells due to the different antigens on their cell surface membrane.T T lymphocytes can distinguish between:

Phagocytes which have undergone phagocytosis and presented the foreign antigen in their cell surface membrane.

Body cells invaded by a virus and presented the antigens on the cell surface membrane

Transplanted cells from individuals with different antigens on the cell surface membrane.

Cancer cells (which present different antigens on the cell surface membrane)

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Cell mediated response and T lymphocytes (2)

T lymphocytes will only respond to antigens that are presented on a body cell rather than antigens within body fluids. (antigen presenting cells)

How T cells work(T cells are not effective against viruses becuase they need a host to replicate.):

Pathogen invades body/ taken in by phagocytes

The phagocyte places antigens from the pathogen on its own cell-surface membrane

Receptors on a specific helper T cells fit exactly onto these antigens,

This attachement activates the T cells to divide rapidly by mitosis and form a clone of genetically identical cells.

The cloned T cells - develop into memory cells, stimulate phagocytes to engulf pathogens by phagocytosis, stimulate B cells to divide and secrete the antibody, Activate cytotoxin T cells.

Cytotoxin cells kill cells by producing perforin(protein) that makes holes in the CS membrane. This then become permable to all substances and kills it.

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Humoral immunity and B lymphocytes

They mature in bone marrow and are involved in humoral immunity - involves antibodies that are present in body fluids or humour (like blood plasma).

The antibody form a B cell attached to the surface antigens from a pathogen

The antigen enters the B cell (endocytosis) and presents them on the CS membrane

T helper cells help bind to attach the antigens on the CS membrane

The B cell is now activated to carry out mitosis to form a clone (clonal selection). Each clone develops into plasma cells which secrete antibodies into blood plasma which destroy the antigen and are the primary immune response Or the develop into memory cells.

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Antibodies (1)

Antibodies are proteins with specific binding sites that are synthesised by B cells. They are made of 4 polypeptide chains help by disulfide bonds ensures the tertiary structure holds the polypeptide chains together maintaining a quaternary structure.

They have a constant region that allows the antibody to attach to a phagocyte or pathogen and assits in the process of phagocytosis.

They also have a variable region that has a specific shape and AA sequence that is complementary to the antigen and ensures it can attach to that one antigen only. When the antigen is bound to the region it is called an antigen-antibody complex.

Hinge region allows flexibility and he branches of the Y shaped molecule to move further apart to attach more than 1 antigen at a time.

The actions of an antibody is to attach to the antigens on a pathogen then prevent the pathogen binding to host cells. If the antibody has a number of binding sites, it may be able to attach multiple pathogens at the same time ( called aggutination). When the antigen is from a bacterial cell, antibodies cause aggulutination so they clump. This makes it easier for phagocytes to destroy.

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Antibodies : monoclonal antibodies (2)

Monoclonal antibodies - each antigen on a pathogen will induce a B cell to multiply and form a clone of itself. Each of these clones will produce a different antibody. It is medical value to be abe to produce antibodies outside the body and is even better if a single type of antibody can be isolated and cloned.

Because an antibody is very specific to an antigen(protein), monoclonal antibodies can be used to target specific substances, One type is cancer cells. The most successful way is monoclonal antibody therapy. MC antibodies are produced that are specific to antigens on cancer cells. These antibodies are given to a patient and attatch themselves to the recpetors on their cancer cells. They then attach to the surface of their cancer cells and block the chemical signals that stimulate their uncontrollable growth.

An advantage in this situation is antibodies are not toxic and are highly specific so leads to former side effects. Another method called indirect monoclonal antibody therapy involves attaching a radioactive or cytotoxic drug and killing the cells. They are used in small doses and this makes it cheaper and limits any side effects.

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Antibodies : monoclonal antibodies (3)

Monoclonal antibodies can be used for diagnosis of influenza, hepatitis and chlamydia as they provide a quicker result than traditional methods. Prostate cancer can be found as men produce more of the protein prostate specific antigen (PSA). By using a monoclonal antibody that reacts with the antigen, it can be possible to measure the level of PSA in the blood.

Pregnancy tests can be used at home as they rely on the fact the placenta produces a hormone called human chorionic gonnadatrophin (hCG) and that is found in the mum urine. If hCG is found, it binfd to the monoclonal antibodies in the pregnancy ***** and is trapped by a different antibody creating a coloured line.

Ethical issues involving monoclonal antibodies - production of it involves mice and these mice are used to produce both antibodies and tumour cells. They have been known to treat diseases but also have had some death associated with their use in treatment of multiple sclerosis. In 2006, healthy volunteers took part and within minutes of having the antibodies, they had multiple organ faliure.

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Vaccination - a deliberate exposure to antigenic material which activates the immune system to make an immune response and provide immunity,

Passive immunity - produced by the introduction of antibodies from an outside source. Immunity is required immedietly. As the antibodies are not being produced by the individual themselves, the antibodues are not replaced when they are broken down so no memory cells are formed. Examples include anti-venom from snake bites.

Active immunity- Produced by stimulating the production of antibodies by the individuals own immune system. Direct contact with the pathogen is necessary. These two types - natural active immunity which results frm an individual becoming infected with a disease under normal circumstances so the body provides its own antibodies. The 2nd type is artificial active immunity which is the basis of a vaccination.

A suitable vaccine must be economically avaliable in sufficent quantities to immunise most of the vunerable population. There must be few side effects. Must be able to be transported and made. It must be possible to vaccinate the population for herd immunity.

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Herd immunity - when a large proportion of the population is vaccinated so the pathogen has a hard time spreading. Once enough people have been vaccinised, it cannot spread.

Ring vaccination - vaccination of all people in the immediate vicinity of the new case - often used to control spread of livestock disease (usually animals).

Vaccinations sometimes wont eliminate a disease as it fails to give immunity to those with defective immune systems. Individuals may develop the disease straight after having the vaccine but there immunity levels are high enough to prevent it. The pathogen could murate and then this means the vaccines become useless.

Ethics of vaccines - Usually involves animals, could have side effects that could cause long time harm. People need to have the vaccine tested on them and it could become dangerous.

MMr- people thought it caused autism so there was a rise in the amount of people not getting the vaccine but getting MMR.

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The human immunodeficiency virus (HIV)

Acquired Immune Deficiency Syndrome (AIDS)

Structure of Hiv - On outside is a lipid envelope. Embedded in it are attachment proteins. Inside the envelope is a protein layer called a capsid that closes two strands of RNA and some enzymes. One of the enzymes is reverse transcriptase which catalyses the production of DNA from RNA. HIV belongs to a group of viruses called retroviruses.

Replication of HIV - uses its own RNA to produce new HIV particles. After infection, HIV enters the bloos stream. A protein on HIV binds to the CD4 protein present on many body cells particualry T helper cells. HIV protein fuses with the cell surface membrane of the body cell while RNA and enzymes enter the T helper cell. Reverse transciptase happens and converts virus RNA to DNA. Newly made DNA moves into the nucleus of the T helper cell and is inserted into the cells DNA. HIV's DNA in the nucleus creates RNA and provides instructions to produce viral proteins and RNA for a new HIV. mRNA takes part in protein synthesis to make new HIV particles. New HIV particles break away from the T helper cell using its CS membrane to serve as a lipid envelope.

HIV causes AIDS by killing the T helper cells. HIV victims have less than 800 T helper cells per mm3. AIDS victims have less than 200 T helper cells per mm3

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HIV and AIDS (2)

Without enough T helper cells, the immune system is compromised as it cannot stimulate enough B cells to produce antibodies of Tc cells to kill cells infected by pathogens.

The ELISA test (Enzyme Linked Immunosorbent Assay) Uses antibodies to detect the presence and type of protein (antigen) present in a sample - antigen - antibody reaction. It is a very sensitive test and can be used to detect HIV, tuberculosis, hepatitius and other diseases. Track the transmision of disease, detect presence and quantity of certain drugs. Detect presence of allegerns in food samples.

Antibiotics is useless against viral diseases like AIDS because the antibiotic is used to prevent bacteria making normal cell walls. In bacteria, as in plant cells, water constantly enters by osmosis. This entry of water would be fine due to the cell wall made of murein. Antibiotics inhibit certain enzymes required to make the peptide cross-linkages in bacterial cell walls. Viruses rely on host cells to carry out their metabolic activites and therfore lack their own metabolic pathways and cell structures. As a result, antibiotics are ineffective because there are no metabolic mechanisms or cell structures for them to disrupt.

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Structure of Cell surface membrane (CSM)

Membranes can use signals to communicate with others, allow impulses to travel the body, allow places for molecules to attach and take part in reactions.

Functions of phospholipids - Allow lipid soluble substances in/out, prevent water soluble substance in/out, make membrane flexible and self-sealing.

Proteins - some only go partial across - mechanical strength, with glycolipids act as cell receptors. Others go across the whole bilayer. Some are protein channels which allow water soluble ions across. Carrier proteins bind to ions or molecules (AA or glucose) then chnge its shape. Functions are - support, transporting, active transport via carrier proteins, cell surface receptors to identify cells, cells adhere together and acts as receptors for stuff like hormones.

Cholesterol - very hydrophobic so prevent loss of water. Pull togeter fatty acid tails to limit there movement. Functionsare - reduced movements, less fluid at high temp, prevent water loss.

Glycolipids - Carb covalently bonded with a lipid. Carb bit extends from bilayer into watery enviroment outside where it acts as a CS receptor.Function - recognition sites, stability, tissues. Glycoproteins- Carb chains attached to proteins. CS receptors, recognition, Tissues

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Passive transport

Passive - simple diffusion, facillitated diffusion, osmosis

Simple diffusion - something going from a high conc to a low conc down a conc gradient

Facilitated diffusion - movement of larger/charged molecules across a semi-permable membrane down a conc gradient. INVOLVES CARRIER PROTEINS AND PROTEIN CHANNELS

Osmosis - The passage of water from a region where it has a higher water potential to a region where it has a lower water potential through a selecively permable membrane.

Hypertonic - Leaving the cell

Hypotonic - entering the cell

Isotonic - entering/leaving - PERFECT.

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Active transport

Active - Active transport and co-transport.

Active transport - movement of molecules or ions into/out a cell from a region of lower conc to a region of higher concentration using ATP and carrier proteins.

AT - Some carrier proteins act as pumps and carry stuff against its concentration gradient. ATP Changes the shape of the carrier protein so the molecule can leave. The Rate of transport is faster.

CT - Tranports stuff like glucos and AA in the lleum.

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Immunity, white blood cells, B and T versions.

B - Humoral, found in body fluids,

Each B cell produces a specific antibody, Specific antibody attaches to an antigen. The antigen will enter the B cell and get presented on the surface (APC). T helper cells bind to the antigen and form a clone of B cells. This forms plasma cells that secrete antibodies and memory cells.

T - Cell mediated, inside cells,

Respond to APC's.  Different T cells respond to antigen (like T helpers) T Helpers fit onto antigen and are selected. The cloned T helper cells activate Cytotxic cells, memory, stimulate phagocytosis and stimulate B cells.

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Piff Ting indeed it's brill fam

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