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Topic 2 - ID - Coggle Diagram
Topic 2 - ID
Cell structure
NucleusSTRUCTURE:
- Nuclear Envelope - double membrane.
- Nucleoplasm - granular, jelly-like material.
- Chromosomes - Protein-bound, linear DNA.
- Nucleolus - smaller sphere inside which is the site of rRNA production and makes ribosomes.
- Nuclear Pores.
FUNCTION:
- Site of DNA replication and transcription.
- Contains the genetic code for each cell.
Endoplasmic reticulumSTRUCTURE:
- Rough and Smooth ER both have folded membranes called cisternae.
- Rough ribosomes on the cisternae.
FUNCTION:
- RER - protein synthesis
- SER - Synthesis and store lipids and carbohydrates.
Golgi Apparatus and VesiclesSTRUCTURE:
- Folded membranes making cisternae
- Secretary vesicles pinch off from the cisternae
FUNCTION:
- Glycoprotein formation - add carbohydrates to proteins.
- Produce secretary enzymes
- Secrete carbohydrates
- Transport, modify & store lipids
- Label molecules with their destination
- Transport finished molecules to surface cell membrane in Golgi vesicles where they are released via exocytosis.
LysosomesSTRUCTURE:
- Bags of digestive enzymes - can contain 50 different enzymes.
FUNCTION:
- Hydrolyses phagocytic cells.
- Autolysis - break down dead cells.
- Exocytosis - releases enzymes to outside of cell to destroy material.
- Digest worn out organelles.
MitochondriaSTRUCTURE
- Double membrane
- Inner membrane called the cristae
- Matrix - fluid-filled centre
- Loop of Mitochondrial DNA
FUNCTION:
- Site of aerobic respiration
- Site of ATP production
- DNA to code for enzymes needed in respiration.
RibosomesSTRUCTURE:
- Small, made up of two sub-units of protein and rRNA
- 80s - large ribosome found in Eukaryotic cells.
- 70s - smaller ribosomes found in prokaryotic cells, mitochondria and chloroplasts.
FUNCTION:
- The site of Protein synthesis.
VacuoleSTRUCTURE:
- Filled with fluid surrounded by a single membrane called a tonoplast.
FUNCTION:
- Make cells turgid and therefore provide support
- Temporary stored of glucose and amino acids
- Pigments may colour petals to attract pollinators.
ChloroplastsSTRUCTURE
- Surrounded by double membrane
- Thylakoids - folded membrane embedded with pigment
- Stroma - fluid which contains enzymes for photosynthesis
- Found in plants.
FUNCTION:
Cell WallSTRUCTURE:
- In plant and fungi cells.
- Plants- made of microfibrils of the cellulose polymer.
- Fungi - made of chitin, a nitrogen-containing polysaccharide.
FUNCTION:
- Provides structural strength to the cell.
Plasma MembraneSTRUCTURE:
- Found in all cells.
- Phospholipid bilayer - molecules embed within and attach on outside (proteins, carbohydrates, cholesterol).
FUNCTION:
- Controls entrance and exit of molecules from the cell.
Key differences between Prokaryotic and Eukaryotic cells
- Cells are Much smaller.
- No membrane bound organelles
- Smaller ribosomes
- No nucleus
- Cell wall made of Murein
MAY ALSO CONTAIN:
- Plasmids
- Capsule around the cell
Flagella
Viruses
Virsuses are acellular and non-living
The structure of virus particules consists of Viral genome, Envelope, viral matrix & attachment proteins.
Viruses replicate inside of cells, making it difficul to destroy them without harming the host cell.
Methods to study cells
Microscopes
Electron Microscopes
Electrons are absorbed by air, which is why samples must be in a vaccum. For this reason only non-living specimens can be examined. The image is also black & white as the sample must be stained.
Transmission Electron Microscopes (TEM)
- Extremely thin specimens are stained and placed in a vaccum.
- Electron gun produces a beam of electrons that pass through the specimen.
- Some parts absorb electrons and appear dark.
- The image is 2D and shows images on the internal structure of the cell.
Scanning Electron Microscope (SEM)
- Do not need to be thin as electrons aren't passing through the specimen.
- Electrons are beamed across the surface of the cell and are scattered depending on the shape.
- This produces a 3D image.
Magnification
Structures under an optical microscope can be measured using:
IMAGE SIZE = ACTUAL x MAGNIFICATION
Eye Piece GraticuleInside of optical Microscopes there is a scale on a glass disc which is called the eyepiece GraticuleThis can be used to measure the size of objects you are viewing under the Microscope.
- Each time you change the objective lens, you need to calibrate to find the distance between each division.
Cell Fractionation
Used to isolate different organells so they can be studied.
This enables individual structures and functions to be studied.
Preliminary stepsThe cells must be prepared in a **cold, isotonic & buffered solution.
- Cold = to reduce enzyme activity. When the cell breaks open enzymes are released which could damage the organelles.
- Isotonic = must be the same water potential to prevent osmosis as this could cause the organelles to shrivel or burst.
- Buffered = the solution has a pH buffer to prevent damage to organelles.
Step 1: Homgoenisation
After Filtering, the solution is broken up (homogenised) using a blender. The cells are blended in the cold, isotonic & buffered solution.
The solution is filtered to remove any large cell debris.
Step 2: UltracentrifugationThe filtered solution is spun at different speeds in a centrifuge.Organelles seperate according to densities.
- The centrifuge spins and the centrifugal forces causes pellets of the most dense organelles to form at the bottom.
- The centrifuge is first spun at a low speed and the process is repeated at increasingly faster speeds.
- Each time the supernatant (liquid) is removed, leaving behind a pellet of organelles.
- The supernatant is then spun again to remove the next pellet of organelles.
Differential Centrifugation order
- Nuclei
- Chloroplasts
- Mitochondria
- Lysosomes
- Endoplasmic reticulum
- Ribosomes
Cell division
The cell cycleThe cell cycle comprises three key stages: interphase (G1, S, G2), nuclear division (mitosis or meiosis) & cytokenesis.
- Interphase is the longest stage in the celll cycle. Interphase is when the organelles double, the celll grows and then DNA replicates.
- G1 - Growth
- S - DNA synthesis
- G2 - Growth & preparation for mitosis
- Nuclear Division can be either mitosis, creating two identical diploid cells, or Meiosis, creating 4 genetically different haploid cells.
- Cytokenesis is the final stage. It is the division of cytoplasm.
Mitosis
- One round of division.
- Genetically identical cells are made.
- Diploid cells are made.
- Growth and repair.
Stages of Mitosis
Prophase
Chromosomes condense and become visible
In animal cells, the centrioles separate (responsible for making spindle fibres) and move to opposite poles of cells. Plant cells have spindle fibres but no centromere.
Metaphase
Chromosomes line up along the metaphase plate.
Chromosomes align along the equator of the cell. The spindle fibres released from the poles now attach to the centromere and chromatid.
Anaphase
Chromosomes break at centromeres, and sister chromatids move to opposite poles.
The spindle fibres retract and pull the centromere and chromatids to opposite poles. This causes the centromere to divide in two and the individual chromatids pulled to opposite poles**.
This stage requires energy in the form of ATP.
Telophase
Nuclear membrane reforms, nucleoli reappear, chromosomes unwind into chromatin
The chromosomes become longer & thinner. The spindle fibre disintegrate and the nucleus starts to reform.
Mitotic Index
The mitotic index can be calculated by counting how many cells are visible in the field of view and how many are undergoing mitosis.
MITOTIC INDEX = CELLS IN MITOSIS / TOTAL x100
Binary Fission in Prokaryotic cells
Step 1: Replication of the circular DNA and of plasmids
Step 2: Division of the cytoplasm to produce two daughter cells, each with a single copy of the circular DNA and a variable number of Plasmids.
Viruses
Inject their nucleic acid into the host cell.
The host cell then replicates the virus particles.
Cell membranes
Plasma Membranes
All cells and organelle membranes have the same structure.
The membranes are described as a fluid-mosaic model due to the mixture and movement of the phospholipids, proteins, glycoproteins & glycolipids.
All of these molecules arrange within the phospholipid bilayer to create the partially permeable membrane.
Components of MembranePHOSPHOLIPIDS
The Phospholipids align as a bilayer due to the hydrophillic heads being attracted to water and the hydrophobic tails being repelled by water.CHOLESTEROL
Cholesterol is present in some membranes - restricts the lateral movement of other molecules in the membrane. This is useful as it makes the membrane less fluid at high temperature and prevents water and dissolved ions leaking.PROTEINS
- Peripheral proteins provide mechanical support, or they are connected to carbohydrates to make glycoproteins (function as receptors)
- Integral proteins are protein carriers or channel proteins involved in the transport of molecules across the membrane.
Partially PermeableMolecules that can pass through the plasma membrane:
- Lipid Soluble substances - (E.g some Hormones)
- Very small molecules - (E.g CO2, O2)
Molecules that cannot pass through the membrane:
- Polar substances - Water soluble (E.g sodium Ions)
- Large Molecules - (E.g Glucose)
-
Immune System & Response
Identifying Self and Non-self CellsYour body's immune system has cells to identify the presence of pathogens and potentially harmful foreign substances in the body and to then destroy or neutralise them to prevent harm.Each cell has specific molecules usually proteins which allow them to be identified. The unique tertiary structure enables lots of unique and identifiable shapes to be made.ANTIGENS - molecules that generate an immune response by lymphocyte cells when detected in the body.Non-self cells:
- Pathogens (E.g bacteria, fungi or viruses)
- Cells from other organisms (cells from organ transplants.
- Abnormal body cells (Cancer cells)
- Toxins (some pathogens release toxins).
Antigen Variability
Pathogens DNA can mutate frequently. If a mutation occurs in the gene which codes for the antigen, then the shape of the antigen will change.
Any previous immunity to this pathogen is no longer effective, as all memory cells will be for the old antigen shape.
This is known as antigen variability. The influenza virus mutates and changes its antigens very quickly.
Immune response
If a pathogen gets past the chemical & physical barriers (E.g skin + stomach acid) and enters the bood then the white blood cells are the second line of defence.
Phagocytes - non-specific response
Lymphocytes - specific response
T Lymphocytes
Lymphocytes are white blood cells involved in the specific immune response.
All lymphocytes are made in the bone marrow, but t cells mature in the thymus.
The cell-mediated response is the response involving t celll and body cells.
Phagocytosis - non-specific responseA phagocyte is a macrophage (type of white blood cell)PROCESS:
- Phagocytes are in the blood and tissues abd any chemicals or debris released by the pathogen attract the phagocytes.
- There are many receptor binding points on the surface of phagocytes. They will attach to chemicals or antigens on the pathogen via these receptors.
- The phagocyte engullfs the pathogen.
- The pathogen is contained within a phagosome vesicle.
- A lysosome within the phagocyte will fuse with the phagosome and release its contents.
- The lysozyme is released into the phagosome - which hydrolyses the pathogen.
- This destroys the pathogen.
- The soluble products are absorbed and used by the phagocyte.
Antigen Presenting Cells (APC)The cell-mediated response is specific because T cellls respond to antigens on the surface of cells.ANTIGEN PRESENTING CELLS - Any cell that presents a non-self antigen on their surface:
- Infected body cells will present the viral antigens on their surface.
- Macrophage when it has destroyed a pathogen will present the antigens on their surface.
- Transplant Organs will have different shaped anitgens to self-cell antigens.
- Cancer cells will have abnormal shaped antigens.
The Cell-mediated Response
- Once a pathogen has been engulfed and destroyed by a phagocyte, the antigens are positioned on the cell surface. This is now a APC.
- Helper T cells have receptors on their surface which can attach to the antigens on APC.
- Once attached this activates the helper T cells to divide by mitosis to replicate and make large numbers of clones.
- Cloned helper T cells differentiate into different cells.
- Some remain & activate B cells.
- Some stimulate macrophages.
- Some become memory cells.
- Some become cytotoxic T cells.
Cytotoxic T cellsCytotoxic T cells destroy abonrmal or infected cells.They release a protein, perforin, which embeds in the cell surface membrane and makes a pore so that any substance can enter or leave the cell.This causes cell death.
- Most common in viral infections because viruses infect body cells.
- Body cells sacrificed to prevent viral infection.
B Lymphocytes
All lymphocytes are made in the bone marrow and B cells mature there too.
The humoral response is the response involving B cells and antibodies. Antibodies are soluble and transport bodily fluids.
B cell activationThere are approximately 10 million different B cells which have antibodies on their surface complementary to different antigens.PROCESS:
- Antigens in the blood collide with their complementary antibody on a B cell - The B cell takes in the antigen by endocytosis and then presents it on its cell surface.
- B cell collides with T helper cell activating it to go through clonal expansion and diffrentiation.
- B cell undergoes mitosis - to make large numbers of cells which diffrentiate into plasma or memory cells.
- Plasma cells make antibodies.
- B memory cells can divide rapidly for secondary response - if body is reinfected with the same pathogen.
B Memory Cells
Memory B cells ca live for decades in your body, whereas plasma cells are short-lived.
Memory B cells do not make antibodies, rather they will divide by mitosis and make plasma cells rapidly if they collide with an antigen they have previously encountered.
This results in large numbers of antibodies being produced so rapidly that the pathogen is destroyed before any symptoms occur.
AntibodiesQuaternary structure protein (4 polypeptide chains).STRUCTURE:
- Y-shaped structure which consists of four polypeptides — two heavy chains and two light chains.
- Heavy & Light bound by disulphide bridge.
- Variable region at top, constant at bottom.
AGGLUTIONATION
- Antibodies are flexible and can binf multiple antigens together to clump them together.
- Makes it easier for phagocytes to locate and destroy.
Types of Immunity
Passive Immunity
Antibodies are introduced into the body.
The pathogen doesn't enter the body, so no plasma or memory cells are made.
No long term immunity
E.g - antibodies passed through the placenta or breast milk
Active immunity
Immunity created by your own immune system following exposure to the pathogen or its antigen.
NATURAL ACTIVE
Infection and the creation of the bodies own antibodies & memory cells.
ARTIFICIAL ACTIVE:
Introduction of a weakened version of pathogen or antigens via a Vaccine.
VaccinesSmall amounts of weakened or dead pathogen or antigens are introduced to the body.
- Exposure to the antigens activates B cells to go through clonal expansion and differentiation (Clonal selection).
- B cells undergo mitosis - to make large numbers of cells, these differentiate into plasma cells or memory cells.
- Plasma cells make antibodies.
- B memory cells are made - can divide rapidly into plasma cells when re-infected with the same pathogen (immunity).
Herd Immunity
If enough of the population are vaccinated the pathogen cannot spread easily amongst the population.
This provides protection for those who are not vaccinated or those who have lower immunity.
HIV
Structure
Core = genetic material (RNA) + reverse transciptase & integrase.
Capsid = outer protein coat
Envelope = extra outer layer, made of out of membrane taken from the hosts cell membrane.
Protein attachment = On the exterior of the envelope to enable the virus to attach to the host's helper T cell.
Replication of HIV in helper T cells
- HIV attaches to the a CD4 protein on the helper T cells whilst being transported around in the blood.
- HIV protein capsule then fuses with the helper T cell membrane, enabling the RNA and Enzymes from HIV to enter.
- Reverse trasncriptase converts the viral RNA into a DNA copy.
- Integrase moves the copy into the T helper cell nucleus.
- mRNA is transcribed and the T helper celll starts to create viral proteins to make new viral particles.
RETROVIRUS
AIDS
AIDS - when the replicating viruses in the helper T cells interfere with their normal functioning of the immune system.
With the helper T cells being destroyed by the virus, the host is unable to produce adequate immune response to other pathogens and is left vunerable to infections.
It is the destruction of the immune system that leads to death, rather than HIV directly.
Monoclonal antibodies
Functions
Targeted Medication
Direct Monoclonal antibody therapySome cancer can be treated using monoclonal antibodies which are designed with binding site complementary to the antigens outside of cancer cells:
- The antiboies are given to patients and bind to cancer cells.
- The binding of the antibodies, prevents chemicals binding which enable uncontrollable division.
- The monoclonal antibodies prevent cancerous growth as they only attach to cancer cells.
Indirect monoclonal antibody therapyCancer can also be treated with monoclonal antibodies complementary in shape to the antigens on the outside of cancer cells which have drugs attached:
- Cancer drugs are delivered directly to cancer cells and kill them.
- This reduces the harmful side effects that traditional chemo & radiotherapy produce.
- Often referred to as 'bullet drugs'
Medical diagnosisMonoclonal antibodies can be used to test for:
- Pregnancy
- Influenza
- Hepatitis
- Chlamydia
- Prostate cancer
Works via ELISA TEST
ELISA test
- Add the test sample from a patient to the base of the beaker.
- Wash to remove any unbound sample.
- Add an antibody complementary in shape to the antigen you are testing for in the sample.
- Wash to remove any unbound antibody.
- Add another antibody complementary in shape to the first with an enzyme attached.
- Wash to remove any unbound antibody.
- Add the substrate for the enzyme - which is initially colourless but produces coloured products.
- Review results - presence of colour indicates the antigen is present.
INTENSITY INDICATES QUANTITY PRESENT
Pregnancy test - Altered ELISA TEST**
- Mobile antibody complimentary in shape to hCG antigen, with coloured dye attached - at top.
- Immobilised antibody - complimentary in shape to the antigen as well binds to antigen with mobile attached (releasing enzyme) - producing blue strip in first box.
- Second immobilised antibody - complimentary in shaped to mobile antibody - binds to any antibodies which didn't bind to antigens releasing dye in second box.
POSITIVE - both boxesNEGATIVE - 2nd box only (E.g antigen never bound to mobile antibody)hCG - hormone in pregnant women urine
Ethical issuesCreating monoclonal antibodies required mice to produce the antibodies and tumour cells.
- Debate on whether this use of animals is justified for human benefit?