Cells Flashcards
What are eukaryotic cells?
-Cells that contain a nucleus and membrane-bound organelles
Describe the structure of the nucleus.
-Nucleus is enclose in a double membrane which is known as the nuclear envelope
-It has many pores known as nuclear pores which are important channels for allowing mRNA and ribosomes to exit and enzymes and molecules to enter
-In the centre is the nucleolus which is the centre of ribosome production
-Around the nucleolus is chromatin which is the genetic material of the cell and what chromosomes are made from
-The nucleus sort of has its own cytoplasm known as nucleoplasm
What is the function of the Nucleolus?
-Spherical structure found in the nucleus that produces and assembles ribosomes
What is the function of the Nuclear envelope?
-Separates the contents of the nucleus from the contents of the cytoplasm
-Furthermore, it has many nuclear pores which facilitate thing entering and exiting the nucleus
-for example, newly produced ribosomes can exit through these pores, and DNA polymerase can travel in during DNA replication
Describe the structure of Mitrochondria.
-The mitochondria is surrounded by two membranes (double membrane bound)
-The inner membrane forms folds called the Cristae
-A liquid is found in the middle called the matrix and it contains ribosomes and small loops of DNA to produce proteins used in respiration
-It also contains Enzymes for respiration
What is the function of the Mitochondria?
-It is the site of aerobic respiration
Describe the structure of the RER (rough endoplasmic reticulum).
-Membrane bound organelle
-Consists of series’ of flattened sacs called cisternae
-Ribosomes are on the outside, on the cisternae
What is the function of the Nucleus?
-Site of DNA replication and transcription
-Contains the genetic code for each cell
Describe the structure of SER (smooth endoplasmic reticulum).
-Membrane bound organelle
-Made of a series of folded membranes called cisternae
What is the function of the RER (rough endoplasmic reticulum)?
-RER is the site of protein synthesis
-Folds and processes proteins
What is the function of the SER (smooth endoplasmic reticulum)?
-Synthesises and stores lipids and carbohydrates
-also transports proteins via large surface area
Describe the structure of the Golgi apparatus.
-Made of series of flattened and curves sacs called the cisternae
-Secretary vesicles can pinch off of the cisternae
What are the functions of the Golgi apparatus?
-Modifies and transports proteins (in vesicles)
-produces glyoproteins (carbohydrates and proteins)
-transports, modifies and stores lipids
-Forms lysosomes (break off from the cisternae in secretary vesicles)
-can transport items around the cell is vesicles
What are lysosomes?
-Bags of digestive enzymes formed from the Golgi apparatus
-membrane bound organelle that releases hydrolytic enzymes
What is the function of lysosomes?
-Hydrolyse Phagocytic cells
-autolysis (break down dead cells)
-exocytosis, release enzymes to destroy material outside of the cell
-release hydrolytic enzymes
Describe the structure and types of ribosomes.
-Ribosomes are made of two sub-units, a larger one and a smaller one
-80s are large(r) ribosomes found in eukaryotic cells
-70s are smaller ribosomes found in prokaryotic cells, mitochondria and chloroplasts
What are the types of ribosomes?
-80s are large ribosomes found in eukaryotic cells
-70s are smaller ribosomes found in prokaryotic cells, mitochondria and chloroplasts
What is the function of ribosomes?
-the site of protein synthesis
What are centrioles?
-Hollow fibres made of rings of microtubules
-Two are at a right angle of each other
-Release spindle fibres during cell division
What is the function of centrioles?
-Release spindle fibres during cell division
What is a vacuole?
-found in plants
-membrane bound organelle filled with fluid
What is the function of a vacuole?
-Makes cells turgid
-Temporary store of sugars and amino acids
-pigments may colour petals to attract pollinators
Describe the structure of chloroplasts.
-double membrane bound
-contains folded membranes embedded with pigment called Thylakoids
-These stack on top of each other to form granum
-cell is filled with a fluid called stroma which contains enzymes for photosynthesis
-Small circular DNA and ribosomes used to synthesise essential proteins for chloroplast replication and photosynthesis
What are Thylakoids and Granum?
-Found in chloroplasts
-thylakoids are Folded membranes containing chlorophyll
-They stack on top of each other to form granum
-granum are held together by lamallae
What is the function of Chloroplasts?
-Site of photosynthesis
Describe the structure of the cell wall in plants.
-Made of Microfibrils consistent of the cellulose polymer
Describe the structure of the cell wall in fungi?
-Made of nitrogen containing polysaccharides, Chitin
What is the function of the cell wall?
-Provide structural support and strength to the cell
What organelles are found in plant cells but not animal cells?
-Chloroplasts, the Cell wall and the Cell vacuole
What are the key differences between prokaryotic cells and eukaryotic cells?
-The cells are much smaller
-no membrane-bound organelles
-smaller ribosomes (70s)
-no nucleus
-cell wall made of Murein
What are Prokaryotic cells?
-Small single celled organisms that do not have a nucleus or membrane bound organelles
What are Specialised cells?
-Cells designed to carry out a particular role in the body
How are specialised cells organised?
-Specialised cells are organised into tissues, tissues into organs, and organs into systems
What do prokaryotes have instead of a Nucleus?
-Prokaryotes have a Single-circular DNA molecule that is free in the cytoplasm
Describe the structure of a cell wall in a Prokaryote.
-The cell wall contains a Glycoprotein called Murein
What extra organelles may Prokaryotes have?
-One or more plasmids
-A Capsule surround the cell
-one or more flagella
What is a Capsule?
-Protective slimy layer that allows a Prokaryote to retain moisture and adhere to surfaces
What are flagellum?
-A tail like structure that rotates to move the cell
What are Plasmids?
-Circular pieces of DNA
What are Viruses?
-Acellular and non-living structures that infect a host cell to replicate themselves
Describe the structure of Viruses.
-Viruses are Acellular and non-living
-They consist of genetic material, either RNA or DNA
-They are enclosed in a Capsid
-They have attachment proteins on their envelope
What is Mitosis?
-Mitosis is the part of the cell cycle in which a eukaryotic cell divides to produce two daughter cells
-Each daughter cell has identical copies of DNA produce from the parent cell during DNA replication
- It has four key stages (PMAT); Prophase,Metaphase,Anaphase and Telophase
What stage of the cell cycle does DNA replication happen?
-DNA replication occurs during the interphase stage of the cell cycle
How do Eukaryotic cells replicate?
-Eukaryotic cells enter the cell cycle and divide by mitosis or meiosis
How do prokaryotic cells replicate?
-Prokaryotic cells replicate by binary fission
How do viruses replicate?
-Viruses replicate inside of the host cells they invade
-They inject their nucleic acid in to the cell to replicate the virus particles
-They do not undergo cell division as they are non-living
What are the stages of interphase?
-G1; growth
-S; DNA synthesis
-G2; growth and preparation for mitosis
What are the stages of the cell cycle?
-interphase; the longest stage, when organelles double, the cell grows and DNA replicates
-nuclear division; can be either Mitosis or Meiosis
-Cytokinesis; the division of the cytoplasm to create the new cells
What is interphase?
-Interphase is the longest stage of the cell cycle
-in interphase, Organelles double, the cell Grows and the DNA replicates
-It has three phases, G1, S and G2
-In G1, the cell grows in S, DNA synthesis occurs and in G2, the cell prepares for mitosis and more growth
What is Cytokinesis?
-The last and shortest stage of the cell cycle
-it is, the division of the cytoplasm to create the new cells
What is Nuclear division?
-The middle stage of the cell cycle
-Nuclear division is either mitosis, creating two identical cells with identical DNA for growth and repair
-Or nuclear division can be Meiosis, creating four genetically different haploid cells in order to create gametes
What does diploid mean?
-a cell that contains two copies of each chromosome
What does Haploid mean?
-A cell which contains only one set of each chromosome
What happens in Prophase?
-chromosomes condense and become visible
-In animal cells, Centrioles separate and move to opposite poles of the cell
-plants don’t have centrioles but have a spindle apparatus
-the nucleus breaks down followed by the nuclear envelope
What can we see in prophase?
-densely compacted DNA, chromosomes are now visible in the nucleus
-Can’t see nucleus and nuclear envelope for its broken down
What happens in Metaphase?
-The Chromosomes align along the equator of the cell
-spindle fibres release from the poles and attach to the centromere between the chromatids of the chromosome
What can we see in Metaphase?
-Chromosomes aligned along the equator
-spindle fibres from the centrioles attached to the centromere
What happens in anaphase?
-The spindle fibres retract pulling sister chromatids apart, dividing the centromere and pulling the chromatids to each pole
-These separated chromatids are now referred to as chromosomes
-This stage requires ATP provided by respiration in the mitochondria (Stored from interphase (G2))
What can we see in anaphase?
-We can see spindle fibres moving sister chromatids to each pole
What happens in Telophase?
-The spindle fibres disintegrate
-The nucleus starts to reform
-The chromosome become long and thin (de-condense) and are now back to chromatin
What can we see in Telophase?
-Chromosomes aren’t visible as they de-condense back to chromatin
-The spindle fibres are disintegrated
-the nucleus reforms
What is Mitotic index
- The number of cells in mitosis / Total number of cells
What is Chromatin?
-Chromatin is a mixture of DNA helixes and proteins in the nucleus (around the nucleolus) during
-Condenses to form chromosomes
What are chromosomes?
-A structure in a cell that contains genetic material known as as DNA
-Condensed Chromatin
-Replicate in the S phase (interphase) of the cell cycle
What are Chromatids and Centromeres?
-Chromatids are two sister (identical) structures that contain genetic code
-In Mitosis they are attached by a centromere and as a unit called chromosomes
-Simply, chromatids are structures that are a replicated chromosome
What is Binary fission?
-The process by which prokaryotic cells divide
-The circular DNA replicate and both copies attach to the cell membrane (plasmids also replicate)
-The **cell membrane grows between the two DNA molecules **
-it pinches inwards forming two daughter cells with one copy of circular DNA and multiple plasmid copies
Describe the process of Binary Fission.
-Circular DNA in Prokaryotic cells replicates into two and both attach to the cell membrane
-Plasmids also replicate
-The cell membrane Grows between the DNA molecules
-it pinches inwards and a new wall is formed creating two daughter cells containing one of each replicated DNA and multiple replicated plasmids
Explain what happens if Mitosis is not a controlled process.
-Uncontrolled cell division can lead to the formation of tumours and cancers
-Many cancers are directed at controlling the rate of cell division
What does each type of cell have that can be used to identify it?
-Each type of cell has specific molecules on its surface that identify it. These molecules are Antigens
-These molecules include proteins and enable to immune system to identify them
What are lymphocytes?
-Cells that are part of your immune system that can recognise and identify potentially harmful foreign substances in the body
-They then can destroy or neutralise these cells to prevent harm
How can Lymphocytes distinguish between pathogens and self-cells?
-Antigens; Specific molecules on the surface of cells can be used to identify themselves
-These are usually proteins and their unique ad identifiable tertiary structure is used to recognise them
What harmful substances are recognised by Lymphocytes?
-Pathogens (e.g. bacteria, fungi or viruses such as HIV)
-Cells from other organisms of the same species (harmful for those with organ transplants)
-Abnormal body cells (e.g. cancer cells)
-Toxins (possibly released from pathogens like Cholera)
What are Antigens?
-Antigens are molecules that generate an immune response by Lymphocytes cells when detected in the body
-They are usually proteins and are located on the surface of cells
What is Antigen variability?
-Pathogens DNA can mutate frequently, and if a mutation occurs in the gene which codes for the antigen, then the shape of the antigen will change
-Therefore, any previous immunity is no longer effective as the memory cells will have a memory for the old antigen shape
Why does Antigen variability happen?
-The DNA in pathogens can mutate frequently, and if the gene coding for the antigen mutates, the shape of the Antigen will change
-The memory cells in the blood will only have a memory for the old antigen shape
What are the physical and chemical barriers in humans?
-The Skin
-Stomach acid
-gut and skin flora (compete for space and food with pathogens)
What is a Phagocyte?
-A Macrophage (type of white blood cell) that carries out phagocytosis
-They are found in the blood and in tissues
What is Phagocytosis?
-Phagocytosis is a non-specific response
-Any non-self cell that is detected will trigger the same response to destroy it
What is a non-specific immune response?
-When any non-self cell triggers the same immune response to destroy it
What is the role of Opsonins in Phagocytosis?
-They are Antibodies that bind to Antigens to form antigen-antibody complexes
-They tag pathogens as foreign
-Phagocytes are attracted to molecules produced by Pathogens
-Receptors on the surface of Phagocytes Bind with The Opsonins on the pathogen
Describe the process of phagocytosis (neutrophils).
-Phagocytes are attracted to molecules produced by pathogens
-Receptors on the phagocyte bind to the opsonins on pathogens that tag them as foreign
-The phagocyte engulfs the pathogens
-The pathogens are held in a special vacuole/vesicle called a phagosome
-Lysosomes fuse with the phagosome forming a phagolysosome
-Lysosomal enzymes (lysozymes) hydrolyse the pathogen
What is the role of lysosomes in phagocytosis?
-They bind to the Phagosome (where pathogen is held in a vesicle/vacuole)
-Produces a phagolysosome
-The Lysosomal enzymes hydrolyse the pathogen
-These enzymes are called lysozymes
What is a Phagosome?
-When a phagocyte engulfs a pathogen, the pathogen is held in a vacuole/vesicle
-This is called a phagosome
-Binds with lysosomes to form a phagolysosome
What are the categories of white blood cells?
-There is the non-specific immune system which have the white blood cells called phagocytes
-This is subdivided into Macrophages and neutrophils
-And there is the specific immune system which use lymphocytes
-This is subdivided into B and T lymphocytes
How does Antigen presentation happen?
-In Macrophages, a glycoprotein called MHC in the cytoplasm moves to the phagolysosome
-They then bind to the antigens from the destroyed pathogen forming a MHC-Antigen complex
-These complexes move to the cell surface
-The Macrophage is now an Anitgen presenting cell
What is MHC?
-A glycoprotein found in the cytoplasm of macrophages
-Moves to the phagolysosome and binds with antigens from a destroyed pathogen to form a MHC-Antigen complex
-These complexes can move to the cell surface
What is antigen presentation?
-When MHC moves to the phagolysosome and binds with antigens of a destroyed pathogen it forms a MHC-antigen complex
-This moves to the cell surface of the Macrophage, presenting the antigens
-This presents the antigens to lymphocytes
Describe the process of Phagocytosis (Macrophages).
-Phagocytes are attracted to molecules produced by pathogens
-Receptors on the phagocyte bind to the opsonins on pathogens that tag them as foreign
-The phagocyte engulfs the pathogens
-The pathogens are held in a special vacuole/vesicle called a phagosome
-Lysosomes fuse with the phagosome forming a phagolysosome
-Lysosomal enzymes (Lysozymes) hydrolyse the pathogen
-Glycoproteins called MHC in the Cytoplasm move to the phagolysosome and bond with the antigens of the destroyed pathogen
-These MHC-Antigen complexes move to the cell membrane and the cell is now Antigen-presenting
What are T Cells
-They are white blood cells, lymphocytes and are part of the specific immune system
-They are made in the bone marrow like all lymphocytes, but mature in the thymus
-They are involved in Cell-mediated responses
-Each unique T cell has a unique T cell receptor on its surface, and since there are millions of unique T cells, there will be a T receptor for every antigen
-There are many types, mainly T helper and T killer cells
Describe the process of cell-mediated immunity.
-A T helper cell binds to the surface antigens on APC’s using there receptors
-The T helper cell is now activated and undergoes mitosis
-The T helper cells also release cytokines molecules called interleukins which can cause phagocytes to increase phagocytosis and B lymphocytes to undergo mitosis
-T helper cells also can activate T killer cells
-These T killer cells identify abnormal cells and attaches to them releasing a protein called perforin which destroys the abnormal cells by forming holes in the cell membrane
-The T helper cells also form T memory cells which are long lived and can rapidly differentiate into T killer cells if the pathogen is detected again
What is the Cell-mediated response?
-T cells response to antigens which are presented on antigen presenting cells, rather than deatached antigens
-Therefore, the antigens are cell-mediated as they are bound to a cell (via MHC)
Describe the role of Cytokines in the Immune system.
-Cytokines are signalling proteins released from cells, e.g phagocytes and T helper cells release interleukins
-In phagocytosis, phagocytes release interleukins signalling to phagocytes and other immune cells to move to the site of infection
-In Cell-mediated responses, T helper cells release interleukins which triggered many responses, **mainly mitosis of itself forming clones, mitosis of B lymphocytes and the increased rate of phagocytosis by phagocytes
Describe the roles of Cytotoxic T cells (Killer T cells) in the cell-mediated response.
-T killer cells destroy abnormal or infected cells
-T killer cells are activated by interleukins released from T Helper cells
-T killer cells attach to the MHC-antigen complex on APC’s stimulating the release of the protein Perforin
-The Perforin creates holes in the cell surface membrane of infected and abnormal cells creating holes
-The cell is now freely permeable and the cell dies
Describe the role of T helper cells in the cell-mediated response.
-Bind to MHC-antigen complex on APC’s
-Release cytokines called interleukins
-This stimulates mitosis of B lymphocytes, activates T killer cells and increased rate of phagocytosis in phagocytes
-The T helper cells also undergo mitosis forming clones
What is CD4 and CD8?
-Surface molecules attached to lymphocytes that locks onto the MHC in MHC-antigen complexes
-CD4 is on T helper cells and CD8 on T killer cells
What are B lymphocytes?
-White blood cells involved in the specific immune system
-Mature in the bone marrow
-Part of the Humoral response which involves B cells and antibodies in bodily fluids
Describe B cell activation.
-There are millions of different B cells all with different antibodies on their surface
-When antigens in the blood collide with a complementary antibody, the B cell takes it in via endocytosis and presents it on the surface
-This APC B cell then collides with a T helper cell which activates the B cell to go through clonal expansion and differentiation (Clonal selection)
-B cells undergo mitosis making large number of cells that differentiate into plasma cells or memory B cells
-These plasma cells make antibodies
-The memory cells rapidly differentiate into plasma cells if re-infected by the same pathogen
What is Clonal expansion?
-When an activated B cell rapidly undergoes mitosis and the cells differentiate into Plasma cells and B memory cells
Describe the structure of antibodies.
-A Quaternary structure protein consisting of 4 polypeptide chains
-Each antibody has two antigen binding sites, where the tertiary structure of the site complements the antigen that it binds to
-There is a heavy chain in the centre, and light chains to its sides; these chains are held together by disulfide bridges
-There is a variable region at the top where the antigen binding site is
-The rest is a constant region
-There is a hinge region in the middle so it can change the distance between antigens it binds to
What are the function of antibodies?
-They act as opsonin marking foreign bodies for phagocytosis
-They can bind to multiple antigens sticking them together
-This is called agglutination it makes it easier for phagocytes to locate and destroy pathogens and it prevents pathogens spread around the body
-Can Stick to viruses to stop them invading host cells
-Stick to bacterial toxins preventing them from harming body cells, these are called antitoxins
What are antibodies?
-proteins produced by plasma cells
-They have a specific variable antigen binding point which binds to antigens
What are memory B cells?
-Cells that live in your body for decades
-they will rapidly divide by mitosis if an antigen that was previously encounters bind to it
-These will differentiate to plasma cells produced a large number of antibodies very quickly
What are plasma cells?
-Cells that produce a large number of antibodies
-differentiate from B cells
What are B lymphocytes role in the Humoral response?
-When a complimentary antibody on the cell surface of the B lymphocyte binds with an complementary antigen it take it in via endocytosis
-Becomes an APC
-T helper cell will bind to it, activating the B cell
-Then B cells will rapidly undergo mitosis and differentiate into plasma cells and memory cells (clonal expansion)
What are primary and secondary immune responses?
-Primary response is the typical humoral response
-The secondary response is when there is now memory cells which means the differentiation into plasma cells from mitosis can happen much quicker producing antibodies to kill pathogens
What is active immunity?
-Active immunity is the production of antibodies by the immune system in response to antigens
-Can be natural by exposure to antigens
-Or artificial, such as vaccines where antigens are injected to produce antibodies
What is passive immunity?
-Passive immunity is the introduction of antibodies from another person on animal
-Can either be natural from the crossing of mothers antibodies through placenta and breast milk
-Or artificial where antibodies are injected into the body
What are vaccines?
-Antigens injected in the blood stream to trigger a primary immune response
-They normally contain a weakened version of the virus or an inactive version, so it is not a challenge for the immune system.
Why do we have vaccines?
-It is artificial active immunity, antigens are added so next time it triggers a secondary immune reponse
-This will produce lots more antibodies a lot quicker so it can be dealt with faster and whilst minimising symptoms
What is Herd immunity?
-When enough of the population is immune or vaccinated that they can’t spread the pathogen
-This means those who aren’t immune or vaccinated are significantly less likely to get it and the pathogen dies down
-This only works if enough of the population is vaccinated or immune
Why are Viruses so hard to treat?
-They replicate inside host cells, making it hard to destroy them without destroying self cells
-viruses have different structures and replicate in a different way than bacteria, for example viruses have a protein coating rather than a cell wall like bacteria
-Therefore they can’t be killed by antibiotics
Describe the structure of HIV.
-In the core; there are **two strands of RNA **(genetic material) and the enzyme reverse transcriptase surrounded by a capsid (protein coat)
-On the outside; there is a lipid envelope surrounded by attachment proteins that allow it to attach to its host cell
What cells does HIV attack?
-T helper cells
How does HIV replicate in host cells
-HIV attaches to protein CD4 on the surface of T helper cells
-the HIV lipid envelope then fuses with the membrane of the T helper cell
-The capsid passes into the cell and the reverse transcriptase copies the viral RNA into a DNA copy (double stranded)
-This DNA is transported across the nucleus and integrates into the host DNA
-Then, mRNA is transcribed and the T helper cells produce proteins to make new viral particles
-HIV is replicated
Why can’t antibiotics be used on Viruses?
-Many antibiotics work by preventing the bacteria from making cell walls
-Without this the bacteria can’t control the entry and exit of water and will therefore burst
-However, HIV and other viruses don’t have a cell wall and reproduce in host cells so are unaffected
Why is HIV dangerous?
-Once HIV is activated and replicates, the T helper cell dies
-without enough T helper cells, antibodies production from B lymphocytes and the cell mediated response becomes less effective
-Thus you can get infections and cancer easier
What is AIDS?
-acquired immunodeficiency syndrome occurs when the T helper cells being killed by HIV replication interfere with the normal functioning of the immune system
-For example, antibody production from B lymphocytes and the cell-mediated response becomes less effective
-Thus they get infections like tuberculosis and cancer
What is a monoclonal antibody?
-A mono-clonal antibody is a single type of antibody that can be isolated and cloned
-Antibodies are proteins which have binding sites which are complementary in shape to certain antigens and are produced by certain B lymphocytes
-Therefore its useful to have clones of one type of antibody for one type of antigen which may be present in abundance
What are the types of targeted medications used with monoclonal antibodies?
-Direct monoclonal antibody therapy
-Indirect monoclonal antibody therapy
What is Direct monoclonal antibody therapy?
-Some cancer can be treated using monoclonal antibodies which binds to the specific antigens of the cancer cells
-These are given to the patients which bind to the antigens and prevent chemical bindings to the cancer cell, leading to uncontrolled cell division
-Or they can be used to identify and destroy these cancer cells in an immune response
What is indirect monoclonal antibody therapy?
-This is when antibodies have drugs attached to them which then bind to the antigens of cancer cells
-This drug is often a cytotoxic drug and kills the cancer cells directly
-This reduces harmful side effects that chemotherapy and radiotherapy can cause
What can monoclonal antibodies be used for?
-Targeted medication, such as direct and indirect monoclonal antibody therapy
-Can be used for medical diagnosis, via an ELISA test
-Pregnancy testing
Describe the process of an ELISA test in a pregnancy test.
-A mobile antibody complementary to the shape of the antigen and has a coloured dye attached
-A second antibody complementary in shape to the antigen is immobilised in the test, and hence will bind with the antigen-antibody complex from the first step if the antigens are present, leading to a coloured dye area
-A third antibody is immobilised and is complementary to the first antibody
Describe the process of an ELISA test.
-Add a test sample and secure to the base of the apparatus being used
-Wash to remove unbound sample
-Antibody complementary to the tested antigen is added
-Wash to remove unbound antibodies
-A Second antibody with an enzyme is added complementary to the first antibody
-Wash to remove unbound second antibodies
-The substrate for the enzyme is added producing coloured products
-The presence of colour indicates the antigen is present and the intensity of the colour is the quantity
What are the Ethical considerations of monoclonal antibodies?
-Animals, often mice, are required to harvest these monoclonal antibodies and they die in the process
What are the ethical considerations of vaccines?
-Production and testing of vaccines may be done on animals
-The vaccine must be tested on humans to determine toxicity
-They are very expensive
-Should they be compulsory?
-What is the transparency of what’s in them?
What is the equation for magnification?
Magnification = Image size / actual size
What is the equation linking actual size, magnification and image size?
Magnification = Image size / actual size
What are plasma membranes?
-They are the membranes that can surround Organelles and cells
-Described as the fluid-mosaic model as it describes the movements of the molecules in it and its mosaic like structure
-It’s main function is to control what enters and exits the cell, but also has important receptors on it
-It is partially permeable
-made of proteins, phospholipids, glycoproteins and glycolipids
What is the phospholipid bilayer?
-The phospholipids in the phospholipid bilayer aligns themselves as a bilayer
-The hydrophilic heads are attracted to the water on the outside
-The hydrophobic tails are on the inside of the bilayer
What is cholesterols function in the plasma membrane (fluid-mosaic model)?
-Restricts the lateral (sideways) movement of other molecules in the membrane
-useful as to make the membrane less fluid at high Temperatures preventing water and dissolved ions from leaking out of the cell
-Makes the membrane rigid
-Also prevents water and dissolved ions leaking out as it is very hydrophobic
Describe the difference between peripheral and integral proteins in the plasma membrane.
-Peripheral proteins do not extend completely across the membrane and provide structure or are attached to other molecules
-Integral proteins span from side to side on the membrane that aid in the transport of molecules through the membrane
What is the function of peripheral proteins in the plasma membrane?
-Provide mechanical and structural support to the membrane
-can be connected to proteins or lipids (to form glycolipids) to form receptors
What is the role of integral proteins in the plasma membrane?
-They are protein carriers or channels that are involved in the transport of molecules across the membrane
Describe what molecules can pass across the phospholipid bilayer alone.
-Lipid-soluble molecules
-very Small molecules (typically non-polar)
What is the function of protein channels in the plasma membrane?
-Form tubes that fill with water enabling water-soluble ions to diffuse across (aquaporin)
-Or carrier proteins will to bind to other molecules and change shape to transport them across the membrane
What is the function of Glycolipids in the plasma membrane?
-Made up of a carbohydrate that is bound to a lipid
-Act as cell surface receptors
-Allows cells to adhere to each other forming tissues
What is the function of Glycoproteins?
-Carbohydrates bound to a peripheral protein
-Act as cell receptor
-Act as neurotransmitters
-Allow cells to recognise each other
-Allows cells to adhere to each other forming tissues
What molecules cannot pass through the phospholipid bilayer?
-Water soluble (polar) substances
-Sodium ions
-Large molecules
What are the components of the plasma membrane?
-Glycolipids
-Glycoproteins
-Proteins (peripheral and integral)
-Cholesterol
-Phospholipids
What is the definition of simple diffusion?
-The net movement of molecules from an area of high concentration to an area of low concentration until equilibrium is reached
-Does not require ATP
Describe the process of Simple diffusion.
-The net movement of molecules from an area of high concentration to an area of low concentration until equilibrium is reached without the use of ATP
-For the molecules to move they have kinetic energy that they possess to enable to constantly move in fluids
-For molecules to simply diffuse across the membrane, they must be lipid soluble or small non-polar molecules
What is Facilitated diffusion?
-A passive process (doesn’t require ATP) where molecules use proteins to be transported
-The movement of ions and polar molecules which can’t simply diffuse (small polar and water soluble ions) can be transported across the membrane with the facilitation of protein channels and carrier proteins
Describe the role of protein channels in facilitated diffusion.
-A protein channel is lined with hydrophilic amino acids and contains water
-Hydrophilic substances can pass through the pore
-However it can be partially selective depending on the size and charge of molecule passing through. This is due to their narrow pores
-They can be open or close depending on external factors e.g. change in voltage across the membrane or an interaction with neurotransmitters
Describe the structure of protein channels.
-Integral proteins with a central pore
-Contains water and is lined with hydrophilic molecules
-This attracts hydrophilic substances
-They can have narrow pores allowing only select molecules through (depending on size and charge)
Describe the role of carrier proteins in facilitated diffusion.
-The carrier protein has a binding site for a certain chemical/molcecule
-The tertiary structure changes when the chemical/molecule is bound to the binding site, allowing the chemical through
What is the definition of osmosis?
-The net movement of water from an area of high water potential to an areal of low water potential across a partially permeable membrane
What is water potential?
-The pressure created by water molecules measured in kPa
-This pressure is the pressure imposed on the membrane
-So water with more solute in it has less pressure, as there is less water applying pressure upon the membrane
-Pure water has the highest water potential of zero kPa as it is only water molecules
What is the definition of active transport?
-The net movement of a substance from a low concentration to a high concentration using** metabolic energy (ATP) and a carrier protein**
Describe the process of active transport
-The molecule being actively transported bind to a complementary receptor on the carrier protein
-ATP binds to the carrier protein from the inside of the cell and is hydrolysed into ADP and PI (inorganic phosphate)
-The ADP is released whilst the PI stays bound
-The tertiary structure of the protein then changes allowing the molecule to move out
-The Inorganic phosphate is released and the protein changes to its original shape
Describe the role of ATP in Active transport.
-Once the molecule being actively transported binds to the specific receptor on the carrier protein, ATP binds to a receptor on the carrier protein
-The ATP is hydrolysed into PI and ADP
-PI remains bound and the tertiary structure of the carrier protein is changed
-PI is then released and protein goes back to its original shape
-ADP and PI later reform into ATP during respiration
Describe the role of a carrier protein in active transport.
-The molecule being actively transported bind to a complementary receptor on the carrier protein
-ATP binds to the carrier protein from the inside of the cell and is hydrolysed into ADP and PI (inorganic phosphate)
-The ADP is released whilst the PI stays bound
-The tertiary structure of the protein then changes allowing the molecule to move out
-The Inorganic phosphate is released and the protein changes to its original shape
Describe the co-transport of glucose and sodium ions in the ileum.
-Sodium ions are actively transported from the epithelial cells into the blood, reducing the concentration of sodium ions in the epithelial cell
-Sodium ions then diffuse from the lumen into the epithelial cell
-However, the sodium ion diffuse through a co-transporter protein, so glucose or amino acids are also attached and transported into the epithelial cell against the gradient
-Glucose then diffuses into the blood by facilitated diffusion
Describe the adaptation of the Epithelial cell for the co-transport of glucose.
-Lots of Mitochondria for the ATP needed for the sodium-potassium pump
-High surface area for the sodium-glucose co-transporter protein (This is done by microvilli)
-Glucose is quickly diffused into the blood which is flowing maintaining a steep concentration gradient
What is co-transport?
-Occurs when one substance is coupled with the transport of another substance
How are cells adapted for rapid transport?
-High surface area
-lots of mitochondria to produce ATP used in active transport
-lots of protein channels and carrier proteins
What is cell fractionation?
-A method of studying cells so individual organelles be studied
-Allows us to look at the structures and functions of organelles to be studied
-It is a two step process of homogenisation and ultracentrifugation
Describe the process of cell homogenisation.
-Cells are broken open in a blender
-These cells are blended in a cold, isotonic and buffered solution
-The solution is filtered to remove large cell debris
-This produces the homogenate
What are the conditions the cells must be in in cell fractionation?
-Cold; to reduce enzyme activity which could damage organelles
-Isotonic; must be the same water potential to prevent osmosis causing organelles to shrivel or burst
-Buffered; The solution has a pH buffer to prevent damage to organelles
Why must the cell solution be cold in cell fractionation?
-To reduce enzyme activity which could damage the organelles
Why must the cell solution be isotonic in cell fractionation?
-Must be the same water potential as to prevent osmosis as this could burst or shrivel the organelles
Why must the cell solution be buffered in cell fractionation?
-The solution has a pH buffer as to prevent damage to organelles
What does Isotonic mean?
-When a substance has the same water potential as something else
-For example, in cell fractionation, the solution added to the cell solution has the same water potential as the water inside the cell
Why is the cell solution homogenised in cell fractionation?
-To break the cell membrane open and release the organelles
Describe the process of differential centrifugation in cell fractionation.
-A centrifuge spins a sample of homogenate at gradually increasing speeds to separate the organelles according to density
-The centrifuge is first spun slowly at low speeds and the most dense organelles form a pellet at the bottom
-Each time, The supernatant is removed, leaving a pellet of organelles
What is the Supernatant?
-The liquid remaining above the pellet after different centrifugation
Why is cell centrifugation used in cell fractionation?
-To separate the organelles
What is the order of organelle density from high to low?
-Nuclei
-Chloroplasts
-Mitochondria
-Lysosomes
-Endoplasmic reticulum
-Ribosomes
What is magnification?
-The increase in size of an object when viewed through a microscope
-Magnification = image size / actual size
What is resolution?
-The ability to distinguish between two separate objects that are close together
What are the Limitations of Scanning electron Microscopes (SEM’s)
-Has a low resolution that TEM’s
-Does not produce colour
-Cannot use live specimens as its in a vacuum and the beam reaches a high temperature
What are the pros of scanning electron microscopes?
-Can be used on thick or 3D specimens
-They can view 3D structures that produce three dimensional pictures
How do Scanning electron microscopes work?
-A beam of electrons scatter across the specimen in a vacuum
-The electrons bounce of the surface and the electrons are detected forming an image
-This produces a three dimensional image
What are electron microscopes?
-They use electrons to form an image
-Include TEM’s and SEM’s
-This greatly increases the resolution, as a beam of electrons has a much smaller wavelength than light
-They have a max resolution of roughly 0.2nm or 0.0002 µm
-They also have a max magnification of x 1.5 Million
How do transmission electron microscopes work?
-TEM’s use electromagnets to focus a beam of electrons on a specimen in a vacuum
-The denser areas absorb more electrons, appearing darker
What are the limitations of transmission electron microscopes (TEM’s)?
-They can only be used on very thin specimens
-Cannot be used on live specimens as the sample is in a vacuum and dehydrated
-The lengthy and complex staining process can cause artefacts to be introduced
-No colour
What are the pros of transmission electron microscopes?
-They give a high resolution image with more detail
-Allows the internal structures within cells or even organelles to be seen
How do optical (light) microscopes work?
-They use light to form an image
-They are limited to the wavelength of light which is 200nm or 0.2 µm
-Can be used to observe eukaryotic cells and nuclei and possibly chloroplasts and mitochondria but not anything smaller such as smaller organelles
-The max magnification is about x 1500
What are the limitations of light microscopes?
-Low magnification and resolution compared to electron microscopes
-limited to the wavelength of light for its resolution being limited to 0.2 µm
What are the Pros of optical (light) microscopes?
-no complex staining process
-doesn’t require strong conditions
-colour images
-Sample can be alive
Describe convert unites from mm down to nm.
- to go down in order from; m, mm, µm, nm, you must multiply by 1000
-To go up from; nm, µm, mm, m you must divide by 1000
What does µm stand for or mean?
-Micrometers
