Topic 2-Cells Flashcards
What are general non-specific defence mechanisms?
stomach acid, mucus membranes, skin ph and phagocytosis
What are the 2 specific defence mechanisms?
Cell mediated response (T cells) and humoral response (B cells)
what do all cells contain on their surface?
antigens
What are antigens?
Foreign molecules (proteins, glycoproteins or glycolipids) that induce an immune response leading to the production of antibodies.
why is there such a variety of antigens?
Many of them are proteins which means they have different tertiary structures
what types of things can lymphocytes identify by their antigens?
pathogens, non self cells, toxins and abnormal body cells
are specific lymphocytes produced in response to a pathogen?
no, youre born with around 10 billion lymphocytes so it is likely that one will be complementary
how and why are self cells recognised?
basically so your immune system doesnt eat you alive, this would be auto immune where it attacks its own cells. in the foetus the lymphocytes are colliding with self cells and the ones that are complementary to self cells will die or be surpressed
where are lymphocytes produced in adult cells
bone marrow
what happen if lymphocytes produced in the bone marrow are found to be complementary to self cells?
They undergo apoptosis, programmed cell death
how to reduce risk of transplant rejection?
immunosupressents and using a transplant from a closely related donor
what produces symptoms of autoimmune disease?
if the process of eliminating lymphocytes complementary to self cells doesnt work and some get left
what is clonal selection?
- when a lymphocyte gets infected (finds a complementary antigen) it gets stimulated to divide and make copies of itself, this is a bit time consuming and causes a delay between exposure and defence to the pathogen
do pathogens or lymphocytes mutate and divide faster?
pathogens!
what are pathogens?
bacteria, viruses, or other micro-organisms that can cause disease
what are non-specific defence mechanisms?
-Skin
-Mucus membranes
-Phagocytosis
how do specific defences differ from non specific defences?
what are the two specific defence mechanisms and the type of white blood cells involved?
- Cell mediated response involves T lymphocytes (remember T in cell mediated)
-Humoral response, B lymphocytes
what type of white blood cells involved in the humoral response?
B lymphocytes
what type of white blood cells are involved in the cell mediated response?
T lymphocytes
what function do both types of lymphocytes need to have?
Need to distinguish between self cells and non-self cells
are specific lymphocytes produced in response to an infection?
-No, you are born with 10 million types of lymphocytes, each is complementary to a different shaped antigen
-High likelihood that if you’re infected you have at least 1 lymphocyte that has the complementary receptor to that pathogen
what do lymphocytes in the immune system identify?
- Pathogens
- Non-self cells
- Toxins (released from pathogens)
- Abnormal body cells
what happens to lymphocytes in the foetus that collide with self cells?(because in the foetus they wont meet pathogens)
they either die, or are supressed
where are b lymphocytes produced in adults?
Bone marrow
what happens to lymphocytes produced in the bone marrow that produce an immune response to self antigens?
they undergo programmed cell death, apoptosis, to stop them from maturing
what precautions are taken to prevent an immune response to transplants?
-Immunosupressants will be given
-transplant will need to be as genetically close to recipient as possible
what is autoimmune disease
when the process of destroying lymphocytes that attack self cells doesn’t work, they can attack own body cells
Describe clonal expansion in the cell mediated response
-Helper T cell receptor binds to complementary antigen
-Triggers clonal expansion, helper T cells divide by mitosis to create clones
what is clonal selection
-lymphocytes infected (receptor binds to complementary antigen) will divide and reproduce
what can be a problem in clonal selection?
-antigen variability
-because the pathogen reproduces so quickly, if there is a change in the gene that codes for the antigen, the antigen may change
-immunity of the old antigen shape is no longer effective
what is antigen variability?
-The gene that codes for antigen shape on the surface of the pathogen may change, causing immunity (either through clonal selection or vaccination) to be ineffective
What happens next if a pathogen gets through physical and chemical barriers (e.g. stomach acid, skin ph) and into the blood?
White blood cell response,
either:
phagocytes: non specific
lymphocytes: specific
what are phagocytes
a group of white blood cells that engulf and digest pathogens in phagocytosis
what are macrophages?
a type of phagocyte that specialise in the removal of pathogens and move around the blood looking for them
is phagocytosis specific or non specific
non specific
what will phagocytes respond to
any non self cells, they will trigger a response to destroy them, not specific about what they are
how do phagocytes find pathogens?
they are attracted to chemical debris left by pathogens in the blood, they will move toward the chemicals and recognise the foreign antigens on the pathogen
what do phagocytes do once they have identified a pathogen
phagocyte engulfs the pathogen, surrounding it with its cell membrane
What are the steps of phagocytosis?
- Phagocyte is attracted to chemical debris left in blood by pathogen, it recognises it as foreign from its antigen
- Phagocyte surrounds and engulfs the pathogen in its membrane
- Pathogen is contained in a vesicle inside the phagocyte: the phagosome
- There is little vesicles called lysosomes that contain enzymes, they fuse with the pathogen
- The lysosomes hydrolyse the pathogen
- After the pathogen has been destroyed, the antigen is leftover and is moved to the cell surface of the phagocyte, now the phagocyte is an antigen presenting cell, which triggers the specific immune response
give an example of a type of phagocyte
Macrophage
what enzyme hydrolyses the pathogen/abnormal material that has been engulfed in a phagocyte?
lysozyme
are lymphocytes part of non-specific or specific immune response?
Specific
where are B lymphocytes (B cells)
made?
Bone marrow
Where are T lymphocytes (T cells) made?
Thymus
where is the thymus gland located in humans
chest
is the cell mediaTed response specific?
yes because T cells respond to Antigen Presenting Cells (APC’s) where the cell presents an antigen that is not its own
what are Antigen presenting cells?
APC’s are cells that present antigens that are not their own
what (4) situations will create APC’s?
- Infected body cells (will present viral antigens on their surface)
- Macrophages (will present the antigen of the engulfed pathogen on their surface)
- Transplant cells (will present the antigens of another organism)
- Cancer cells (will have abnormal shaped self cell antigens)
what cells trigger a cell mediated response
antigen presenting cells
Do T cells respond to antigens in the blood that are detached from cells?
no, they will only respond if they are on cells, this is why it is the cell mediated response
Outline the cell mediated response
- Clonal selection. Specific helper T cell (type of T lymphocyte cell present from birth) with a complementary receptor will bind to the antigen of a pathogen
- This activates clonal expansion, the helper T cell will divide rapidly by mitosis to create a large number of clones
- Clonal differentiation. Some of the cloned helper T cells will divide into different types of T cells: Cytotoxic T cells, memory T cells
- The clones that remain as helper T cells will activate the B cells in the humoral response
what are cytoxic t cells
- a type of b lymphocyte produced during clonal differentiation of the cell mediated response
-attacks abnormal or infected cells
-release a substance called a protein called perforin, which embeds in the cell surface membrane and makes a hole
-this means anything can enter or exit the cell and the cell inevitably dies
when are cytotoxic t cells most active?
during viral infections because viruses infect body cells, and cytotoxic t cells kill abnormal cells
this is why you get a sore throat when you get a cold
what types of cells does the humoral response involve?
b cells
antibodies (which travel in bodily fluids hence name humoral)
what are antibodies made of?
antibodies are small, quaternary structure proteins
where are antibodies found?
bodily fluids
blood, breast milk, saliva, tears etc.
surface of B cells
what is the structure of antibody?
4 polypeptide chains that form a Y shape (because it is a quaternary protein it has 4 polypeptides)
2 heavy chains and 2 light, shorter chains
where are the binding sites and variable and constant region on an antigen?
the binding sites are tops of the Y at both sides, top of the polypeptide chains
the variable is the middle of the Y, varies between antibodies
constant region also in the middle of the Y, is consistent with all antibodies
what makes each antibody physically different?
the variable region, it is different on every single antibody
If an antibody collides with an antigen in the blood what happens?
the antibody will bind with the antigen and trigger the humoral response
Outline the humoral response
- The receptor (antibody) on a specific B cell binds to its complementary antigen and engulfs and digests it, so now the B cell becomes an antigen presenting cell
- The antigen presenting B cell collides with a T cell, which activates clonal expansion through mitosis, forming many clones of the B cell
- B lymphocyte goes through clonal differentiation, some become plasma cells which produce more of those antibodies, some become memory cells
what do plasma cells secrete?
plasma cells produced in clonal differentiation of the humoral response secrete antibodies of that b cell which in the blood then combine with all the complimentary antigens of that antibody
what do memory b cells do?
they live for decades in your body and contain the antibody to detect the antigen if it appears again, so plasma cells can be produced rapidly if that antigen is ever encountered again, this is immunity when your body knows how to respond to it and already has the antibodies
what are primary and secondary immune responses?
the first time that pathogen is encountered by the body and memory cells are made, all subsequent reocurrances are secondary immune responses
how are the heavy polypeptide chains combined in an antibody?
disulfide bonds
what is agglutination?
- Antibodies bind to the antigens on pathogens, forming antibody-antigen complexes, only if the tertiary structure of the variable region is complimentary to the antigen.
- The hinge region (between the light and heavy chains) allows the antibody to bind to 2 pathogens antigens at the same time, causing agglutination, (clumping of pathogens)
- The antibodies with the pathogens attract phagocytes (because of the toxins from the pathogens)
- phagocytes bind to the antigens and phagocytose all the pathogens together
what are monoclonal antibodies
Produced in-vitro (in test tube etc.)
scientists extract a B lymphocyte and clone it, then isolate the antibodies
because they are clones they all have the same tertiary structure of the variable region and are therefore monoclonal (cloned from one)
how are monoclonal antibodies produced through hybridomas?
- mouse is injected with specific antigen
2.mouse lymphocytes are stimulated to find the specific antibody for that antigen - these b lymphocytes are extracted and combined with tumour cells to create a hybridoma cell (tumor cell/lymphocyte), so it divides fast like a tumour but creates monoclonal antibodies
- the hybdridoma are cloned to produce many copies of the monoclonal antibodies
what is the resolution of light and electron miscroscopes?
light-can resolve images 2 um apart
electron- 2 nm apart
what is the defintion of resolution?
minimum distance apart that 2 objects can be distinguished as seperate
what is the calculation for magnification?
magnification=size of image/size of real object
what are the 2 main types of electron microscope?
scanning electron microscope (SEM)
transmission electron microscope (TEM)
how does an electron microscope work?
beam of electrons are focused through electromagnets in a vacuum environment (vacuum so particles in the air dont move the electrons out of the beam)
what are limitations of using an electron microscope?
-whole specimen must be in a vacuum, so living specimens cannot be observed
-specimens have to be very thin so that electrons can pass through
how can you tell if an image is from a light microscope
only microscope images that will have colour
what is it called when different parts inside a cell are separated
fractionation
what is a common method for cell fractionation?
centrifugation
what is the process of cell centrifugation?
- Cells are blended in a homogeniser, this forms a fluid called homogenate which is like blended cell juice, the purpose is to break apart and separate the organelles in the cell. homogenate is placed in a cold, buffered solution at the same water potential as the cells.
- The tube of homogenate is put in a centrifuge and spun at a low speed to seperate the organelles
- the heaviest organelles, nuclei, go to the bottom of the tube, forming a sediment
- the rest of the fluid is called the supernatant, this is removed and put in another tube. the nuclei are extracted from the sediment.
- the supernatant is respun to find the next heaviest organelle, the mitochondria
in cell homogenation, why is the homogenate put in a cold, buffered solution at the same water potential as the cell?
-prevent organelles bursting under osmotic pressure
-inactivate any enzymes so the ph isnt fluctuating
what type of cells are humans made up of?
eukaryotic cells
describe cell surface membrane
-controls exchange of materials in the internal and external environment of the cell
-the membrane is partially permeable
-formed from a phospholipid bilayer
what is chromatin?
-complex of dna and histone proteins, genetic material in the nucleus
describe structure and function of the nucleus
-Present in all eurkaryotic cells, is a large organelle seperated from the cytoplasm by a double membrane called the nucleur envelope
-Nucleur pores are important channels allowing rna and mrna out of the nucleus, and allowing enzymes in
-nucleus contains chromatin (what chromosomes are made from)
-chromosomes are in the nucleus as dna tightly wrapped around proteins called histones
what are histones
proteins that dna is wrapped around to form chromosomes
what is the structure of a mitochondrion?
-double membrane, inner membrane folded to form cristae
-matrix (its like a cytoplasm but for an organelle) where enzymes are and where reactions happen in aerobic respiration
-
where are ribosomes found in cells?
In the cytoplasm, or on the rough endoplasmic reticulum in eukaryotic cells
what are ribosomes the site of?
translation
what is the rough ER?
-rough endoplasmic reticulum has ribosomes on its surface
-folds of membranes, continues into
-the nucleur envelope
processes proteins made by ribosomes
what is the smooth ER
-smooth endoplasmic reticulum is distinguishable from rough because of the absence of ribosomes on its surface
-its more folded membranes, just outside of the rough ER
-Involved in production and processong of lipids
does mitosis cause variation?
no, all the daughter cells are genetically identical
what is the purpose of the cell cycle and mitosis?
to produce identical daughter cells for growth and asexual reproduction
what are the 3 stages of the cell cycle?
- Mitosis (PMAT)
- Interphase
- Cytokinesis
what is mitosis
form of cell division that produces identical cells through PMAT
what is interphase?
Cell grows and prepares to divide, chromosomes are replicated
what is cytokinesis
parent and replicated organelles move to each side of the cell, the cell divides, producing 2 daughter cells
what happens in prophase
spindle fibres appear, chromosomes condense
what happens in metaphase
chromosomes line up in the middle of the cell, attached to spindle fibres
what happens in anaphase
spindle fibres contract, pulling chromosomes to opposite poles (sides) of the cell
what happens in telephase
nucleur membrane reforms, chromosomes decondense
Does mitosis produce identical or unique daughter cells?
identical
what is the purpose of mitosis?
produces identical daughter cells for growth and repair as well as asexual reproduction (e.g. plants or microbes such as yeast)
does mitosis cause genetic variation?
no, because all the daughter cells produced are genetically identical
