Cell Cycle and Structure 2 Flashcards
Differences between electron microscopes and light microscopes
- LM produce colour images, EM produces black and white images
- LM the specimen can be alive but in EM the specimen must be unalive
- EM has a higher resolution and magnification than LM
How do you efficiently mount a temporary slip
- gather cells by peeling a layer or scraping a sample of the specimen
- stain (e.g., iodine in potassium iodide)
- place cover slip on and lightly press down to avoid artefacts
What is prophase
- longest phase of mitosis
- chromatin condenses and chromosomes become visible
- nuclear envelope disintegrates and nucleolus disappears
-Centrioles move to opposite poles and extend the spindle fibres.
How may tumours and cancer develop?
Tumours (cancer) develops when cells lose control over the cell cycle and divide in an uncontrollable manner.
Results in a mass of rapidly dividing, abnormal cells.
Cancers result from mutations of key genes that control the cell cycle.
What are the key features of viruses?
Acellular, non-living (parasitic)
Contain DNA or RNA nucleic acids (genome)
Enclosed within a protein coat - capsid
Surface attachment proteins
Sometimes enveloped (e.g. HIV)
Require a specific host cell to enter and replicate
Detail the eukaryotic cell cycle.
DNA replication occurs in interphase when the chromosome are diffuse.
Mitosis is nuclear division
Cytokinesis is the division of the ‘cell body’.
Describe a prokaryote
- genetic material is circular loop
flagellum
ribosomes, smaller than those in eukaryotes
murein cell wall
cell surface membrane
plasmids
capsule
cytoplasm
What additional features may some prokaryotic cells have?
Cell wall made from muerin - protecting against osmotic lysis
External capsule - protection and helps bacteria to stick together
Plasmids - small circular pieces of DNA which have additional genes e.g. antibiotic resistance
Flagella - motile “tail(s)”
Pili - microscopic tube extensions to allow transfer of plasmid DNA between individual bacteria (transjugation)
How could you calculate the mitotic index for eukaryotic cells going through the cell cycle?
cells in mitosis / total number of cells
What are the steps to HIV replication?
- attachment proteins attach to receptors on CSM on T helper cells
- capsid is released into T cells where it uncoats and releases the genetic material (RNA)
- reverse transcriptase is used to make a complementry strand of DNA from the RNA template, so double stranded DNA molecule is made
- this is inserted into the human DNA
- the host cells enzymes are used to make viral proteins from the viral DNA found in the human DNA.
- viral proteins are assembled into viruses (which bud off/destroy the host cell and infect new cells)
What is the structure of HIV?
- capsid
- RNA strands held in capsid
- reverse transcriptase (enzyme) held in capsid
- attachemnt proteins
- envelope (membrane stolen from cell membrane of previous cell host)
Why do we use a sterile pipette/flame the loop, bottle neck and spreader in aseptic techniques?
To maintain a pure culture of bacteria
Why do we soak contaminated pipette tips in disinfectant in aseptic techniques?
To kill bacteria and prevent spreading outside of the lab
Why do we open the petri dish as little as possible in aseptic techniques?
To prevent bacteria in the dish getting out and bacteria in the air getting in and contaminating the plate
Why do we wash hands with soap in aseptic techniques?
To prevent contamination from bacteria on hands
Why do we disinfect the surfaces in aseptic techniques?
To kill bacteria on surfaces so contamination doesn’t occur
Describe and explain osmosis.
Movement of water particles from an area of high water potential to low water potential. This is a passive process
Describe and explain simple diffusion.
Movement of small, soluble particles from an area of high concentration to an area of low concentration. This is a passive process.
Describe and explain facilitated diffusion
The net movement of particles from an area of high concentration to an area of low concentration. This uses carrier and channel proteins to aid the diffusion of large/charged particles across a membrane. This is a passive process.
Describe and explain active transport.
Movement of molecules from an area of low concentration to high concentration. This uses carrier proteins and co transporters. This is an active process (requires energy)
Describe and explain co transport
Sodium ions are being actively pumped out of the cuboidal cells by active, ATP driven Na / K exchange pumps.
This sets up a sodium ion concentration gradient., with a higher concentration of sodium ions on the outside.
The co-transporter then facilitates the sodium ions diffusing in down their gradient to “pull in” glucose molecules into the cytoplasm against its gradient (maximum absorption).
The glucose can then passively diffuse out through other carrier proteins onto the other side / passing into the blood capillaries.
Outline the Na+/K+ pump model.
- Three sodium ions bind to the pump
- ATP attaches to the pump and transfers a inorganic phosphate to the pump (phosphorylation) causing it to change shape
- This results in the pump opening to the outside of the axon
- The three sodium ions are released
- Two potassium ions from outside the cell enter and bind to their sites
- The attached phosphate is released altering the shape of the pump again
- The change in shape causes the potassium ions to be released inside the cell
What are co-transporters?
- a type of carrier protein
- they bind with 2 molecules at a time
- where 1 of the molecules is going against the concentration gradient.
What is the structure of an antibody?
- 4 disulfide bridges
- 2 heavy strands
- 2 light strands
- variable regions near the tips on the ‘Y’ shape
- constant regions at the bottom of ‘Y’ shape
- 2 hinge regions
- antigen-antibody binding sites
How is the immune response split?
Into 2 sections:
- cellular
- humoral
Outline the CELLULAR section of the immune response
- receptor proteins on T-cells (type of lymphocyte) bind to complementary antigens on APCs
- T-cell is now activated
- T-cells either become helper T-cells or remain as memory cells
- Helper T-cells release chemical signals that activate and stimulate phagocytes and cytotoxic T-cells
- Cytotoxic cells kill abnormal and foreign cells (cancer cells eg)
Outline the HUMORAL section of the immune response
- B-cells become activated by helper t-cells and divide by mitosis
- They can become memory cells or become plasma cells
- plasma cells will secrete antibodies complementary to the antigen on ADC
Outline phagocytosis
- phagocyte is attracted to chemicals/substances secreted from pathogen
- phagocyte engulfs pathogen into a phagosome
- lysosomes in phagocyte fuse with phagosome and release hydrolysis enzymes called lysozymes
- lysozymes break down pathogen
- pathogen then displays the pathogens antigen on CSM and acts as an ADC
What is an ADC
- an antigen displaying cell
Outline an ELISA test
- antigen is bound to bottom of wells in a well plate
- a sample of blood plasma is added to the wells
- if there is the antigen-specific antibodies present then they will bind to the antigen
- the well is then washed out
- a secondary antibody (that has an enzyme attached to it) is added to the well plate
- this secondary antibody solution will bind to the antigen specific antibody
- the well plate is washed again
- a solution that contains a substrate which will react with the enzyme attached to the secondary antibody is added
- this will produce a coloured product
- this indicates that the blood plasma contains antigen-specific antibodies in their immune system.
What are some ethical issues surrounding the use of monoclonal antibodies?
- animals are needed in order to make them (suffering)
- they are expensive to make
- as successful as they have been, there has been multiple failures
Define eukaryotes
- cells with membrane-bound organelles
what is the function of ribosomes?
- used to make proteins
- mostly attached to rough endoplasmic reticulum
- ribosomes are larger in eukaryotes (80S) than in prokaryotes (70S)
What is clonal selection
where a specific kind of cell is stimulated to make genetically identical copies of itself by dividing by mitosis
what are monoclonal antibodies
Antibodies with the same tertiary structure produced by identical plasma cells
Why is it sensible to wait a while after recovery of an infectious disease before receiving a vaccine against it?
You will be producing antibodies against the antigen
The antibodies in your blood will bind to the antigen in the vaccine, marking it for destruction
So the vaccine won’t work
Describe how B lymphocytes would respond to a vaccination against a virus
B cell binds to specific antigen
B cell clones and divides by mitosis
These b cell clones turn into plasma cells that release the antibodies
B cells develop into memory cells
The bacteria in the intestine are prokaryotic cells. The epithelial cells which line the small intestine are eukaryotic cells. Describe the ways in which prokaryotic cells and eukaryotic cells differ. (6)
- prokaryotes do not have membrane bound organelles, eukaryotes do
- prokaryotes contain plasmids, eukaryotes do not
- prokaryotes DNA is not associated with histone proteins, eukaryotic DNA is
- prokaryotes have smaller ribosomes than eukaryotes do
- prokaryotes are generally smaller than eukaryotes
- prokaryotes have no nucleus, eukaryotes do have a nucleus
Scientists have investigated the effects of competitive and non-competitive inhibitors of the enzyme maltase.
Describe competitive and non-competitive inhibition of an enzyme. (5)
competitive inhibition is where an inhibitor has a complementary shape to the active site of an enzyme
it temporarily binds to the active site, forming an enzyme-substrate complex
THIS CAN BE UNDO WITH INCREASED CONCENTRATIONS OF SUBSTRATE
noncompetitive inhibition is where an inhibitor binds to the alosteric active site of an enzyme
when it forms an enzyme substrate complex, the tertiary structure of the enzyme is permanently changed and therefore it is no longer complementary to the substrate, so no enzyme-substrate complexes form
THIS CANNOT BE UNDONE BY INCREASED CONCENTRATIONS OF SUBSTRATE
Why can bacteria be described as acellular and non living
acellular - no cell surface membrane, not made up of cells
non-living - no metabolic processes
what are some functions of the golgi apparatus
packages and modifies proteins by adding carbohydrates
adding carbos to proteins to form glycoproteins or carbs to lipids to form glycolipids
forms lysosomes
what are some functions of the nucleus
makes ribsomal RNA
site of transcription
site of DNA replication
holds the genetic material
what are some functions of ribosomes
used for protein synthesis
what is the functional of the rough endoplasmic reticulum
transports proteins made by the ribosomes
what is the functional of the smooth endoplasmic reticulum
concerned with the synthesis and transport of lipids
what is the function of a lysosome
contains lysozymes that are used to digest broken fragments of cells or digest pathogens
what is the functions of mitochondria
produces ATP for aerobic respiration
functions of chloroplasts
site of photosynthesis (LDR)
function of a cell wall
to protect the cell from osmotic lysis
provides mechanical strength to the cell
permeable to water to provides a route for water to travel through the plant (xylem)
function of a cell vacuole
inflates with water to make cells turgid
stores sugars and amino acids as a food store
contains pigments to colour petals of flowers -> attracts insects for pollination
draw out a plant cell fully
compare to notes
draw out an animal cell fully
compare to notes
what is the purpose of the disulphide bridges in the structure of a monoclonal antibody
to hold the 2 polypeptide chains together
outline what agglutination is
antibodies bind to the antigen on two separate bacteria, causing the bacteria to clump together via a network of antigen-antibody complexes
this ‘clump’ makes it easy for phagocytes to locate as the antibodies serve as a marker
what are the differences between active and passive immunity
active is where antibodies are secreted by plasma cells, but passive has the antibodies directly introduced into the body from the outside
active is longer term lasting because memory cells are created, but passive is short term due to no memory cells are created, and the antibodies introduced get broken down over time
active takes longer to develop, passive is faster acting
example of natural active immunity
normal immune response after being infected
example of artificial active immunity
vaccination
example of natural passive immunity
antibodies across the placenta to the fetus, or in breast milk
example of artificial passive immunity
quick introduction of antibodies, such as antivenom for snake bites
How does a vaccine make someone immune to a pathogen? 5 marks
(Vaccine contains) antigen / attenuated/dead/inactive pathogen;
(Specific) helper T cell stimulates B cell specific to antigen;
B cell clones/divides by mitosis;
Plasma cells release antibodies;
Memory cells produced meaning higher concentration of antibodies/antibodies produced faster in secondary response/on infection with the actual pathogen;
