2 - CELLS Flashcards
What is an antigen?
A foreign body that stimulates the body’s immune response leading to the production of an antibody
Describe phagocytosis of pathogens (non-specific immune response)
- phagocyte is attracted to/detects foreign antigen on pathogen
- engulfs pathogen and forms a phagosome around it
- lysosomes fuse with phagosome and release lysozymes
- lysozymes hydrolyse and digest pathgoen
- phagocyte absorbs its products and presents its antigen on the outside of its membrane to stimulate the specific immune response
Describe the response of B lymphocytes to a foreign antigen (the humoral
response)
- antigen binds to specific B cell receptors
- specific B cell cloned rapidly by mitosis
- B cell differentiates into plasma and memory cells
- plasma cells secrete specific antibodies into the blood
- antibodies stimulate agglutination
- phagocytosis occurs
Describe the response of T lymphocytes to a foreign antigen (the cellular
response)
- After phagocytosis, phagocyte displays antigen on outside of its membrane
- Specific T cells bind to antigen, then clones rapidly by mitosis
- Produces specialised T cells:
Killer T cells - hydrolyse pathogen
Helper T cells - stimulate antibody response
Memory T cells - remember antigen for next exposure
What is clonal selection?
When a specific T cell becomes activated after binding to its antigen
What is clonal expansion?
When a T cell divides by mitosis to produce clones
What’s the difference between primary and secondary immune response?
- antibodies are released much quicker the second time around because the immune system recognises the antigen
- It so quick that the pathogen is suppressed before you are able to experience symptoms because you are immune to the pathogen
What is a vaccine?
- Injection of antigens from attenuated (dead or weakened) pathogens
- Stimulating formation of memory cells
Describe the replication of HIV in helper T cells
- HIV attachment proteins bind to receptors on helper T cell
- Lipid envelope fuses with cell-surface membrane of T cell and releases capsid into cell
- Capsid uncoats, releasing RNA and reverse transcriptase
- Reverse transcriptase (enzyme) converts the 2 single strands of RNA to DNA
- Viral DNA incorporated into helper T cell DNA
- DNA transcribed into HIV mRNA then the HIV mRNA is translated into new HIV proteins forming Viral proteins
- Virus particles assembled and released from cell (via budding)
How do you use/set up a light microscope?
- clip prepared slide onto stage
- select lowest powered objective lens
- use course adjustment knob to bring stage up to just under the objective lens
- look down the eyepiece and move the coarse knob down until the image becomes more in focus
- adjust the fine adjustment knob until you get a clear image
- ## if you need to see the slide with a higher magnification then change to a higher objective lens
What are the 2 types of electron microscope?
- transmission
- scanning
How does a transmission electron microscope work?
- they use electromagnets to transmit a beam of electrons through the specimen
- denser parts absorb more electrons making them appear darker on the image while less dense areas are lighter, forming an image
How does a scanning electron microscope work?
- they scan a beam of electrons across a specimen
- this knocks off electrons off the cells surface and these electrons come together to form an image
What are artefacts?
Visible details that aren’t part of the specimen being observed
- eg dust or fingerprints when looking through a microscope
State the advantages and disadvantages of the 2 types of electron microscope
Transmission:
✅ - high resolution so can be used to see small objects
❌ - 2D images
❌ - can only be used of non living specimens as they are placed in a vacuum
Scanning:
✅ - can be used on thick specimen that are 3D
❌ - gives lower resolution images than TEMs
❌ - can only be used on non living
Describe how viruses replicate
- The virus uses its attachment proteins to bind to specific receptor proteins on host cells.
- The virus injects its viral DNA or RNA into the host cell.
- The virus uses the host cell’s machinery and resources, such as enzymes and ribosomes, to replicate viral particles.
- New viral particles are released from the host cell.
Describe the process of mitosis
I:
- DNA replicates semi conservatively to form 2 identical chromatids
- Cell growth
P:
- chromosomes condense becoming shorter/thicker and appear as sister chromatids held by a centromere
- nuclear envelope breaks down
- centrioles move to opposite poles forming spindle network
M:
- spindle fibres attach to chromosomes by their centromeres and move chromosomes to equator
A:
- spindle fibres shorten and contract
- centromere divides pulling chromatids to opposite poles of cell
T:
- chromosomes uncoil becoming longer and thinner
- nuclear envelope reforms
C:
- two identical daughter cells formed
Describe how prokaryotic cells replicate
- Replication of circular DNA
2 replication of plasmids - division of cytoplasm to produce 2 daughter cells
Describe how cancer treatments control rate of cell division
- some disrupts spindle fibre activity/formation
-> spindle fibres pull chromatids to opposite poles, so prevents/slows mitosis - some prevent DNA replication in interphase
-> so canes make 2 copies of each chromosome
Explain the importance of mitosis in the life of an organism
- growth of multicellular organisms by increasing cell number
- replacing cells to repair damaged tissues
- asexual reproduction
Describe how tumours and cancers form
Mutations in DNA/genes controlling mitosis can lead to uncontrolled cell division
Mass of abnormal cells formed (tumour)
What are the 2 types of tumour?
Malignant - cancerous (can spread)
Benign - non cancerous
Describe the structure and function of the nucleus
- Stores DNA for polynucleotide production
- produces mRNA from DNA for protein synthesis
- DNA stored as chromosomes in the nucleus
How many daughter cells does binary fission produce?
2
Explain how you would use cell fractionation and ultracentrifugation to separate cell components
- homogenise tissue (blends cells gently to disrupt cell membrane, breaking open cell and releasing organelles)
- place in a cold, isotonic, buffered solution
- cold to slow down enzyme activity (so organelles not broken down)
- isotonic so water doesn’t move in or out of organelles by osmosis (so they don’t burst)
- buffered to keep pH constant (so enzymes don’t denature) - Filter homogenate (to remove unwanted debris eg. whole cells)
- Ultracentrifugation to separate organelles in order of density/mass
- centrifuge homogenate in a tube a high speed
- remove pellet containing heaviest organelle
- respin supernatant at a higher speed
- repeat at increasing speeds until all organelles separated out
Order of heaviest to lightest organelles:
Nuclei -> chloroplasts/mitochondria -> lysosomes -> ER -> ribosomes
Describe how to convert into different units (e.g meters to millimeters etc)
X1000⬇️ Metre ⬆️ /1000
X1000⬇️ Millimetre ⬆️ /1000
X1000⬇️ Micrometer ⬆️ /1000
X1000⬇️ Nanometre ⬆️ /1000
