module 2; cells Flashcards
describe the structure & function of the nucleus
structure:
nuclear envelope - double membrane
nuclear pores
nucleoplasm - granular jelly-like material
chromosomes - protein bound, linear DNA
nucleolus
function:
site of DNA replication & transcription (makes mRNA)
carries genetic code for each cell
describe the structure & function of the endoplasmic reticulum
structure:
rough & smooth ER have folded membranes called cisternae
rough ER have ribosomes on cisternae
function:
RER - protein synthesis
SER - synthesis & store lipids & carbohydrates
describe the structure & function of the golgi apparatus & vesicles
structure:
folded membrane - making cisternae
secretary vesicles pinch off cisternae
function:
adds carbs to proteins to form glycoproteins
produces secretary enzymes
secretes carbs
transports, modify & stores lipids
forms lysosomes
molecules that are ‘labelled’ with destination
finished product is transported to the cell surface in golgi vesicles when they fuse with membranes then content released
describe the structure & function of lysosomes
structure:
bags of digestive enzymes - can contain 50 different enzymes
function:
hydrolyse phagocytic cells
breaks down dead cells fully (autolysis)
exocytosis - releases enzymes outside of cell to destroy material
digests worn out organelles for reuse
describe the structure & function of the mitochondria
structure:
double membrane
inner membrane - called cristae
fluid centre - called mitochondrial matrix
loop of mitochondrial DNA
function:
site of aerobic respiration
site of ATP production
DNA to code for enzymes needed in respiration
describe the structure & function of ribosomes
structure:
small - made up of 2 subunits of protein &. rRNA
80s - largest ribosome found in eukary cells
70s - smaller found in prokary cells, mitochondria & chloroplasts
function:
site of protein synthesis
describe the structure & function of the vacuole
structure:
filled with fluid
single membrane - tonoplast
function:
make cells turgid - provides support
temporary store of sugars & amino acids
pigments may colour petals to attract pollinators
describe the structure & function of chloroplasts
structure:
double membrane
has thylakoids (folded membranes with pigment)
fluid-filled stroma contains enzymes for photosynthesis
function:
site of photosynthesis
describe the structure & function of the cell wall
structure:
plant cells - made of microfibrils with cellulose polymers
fungi cells - made of chitin
function:
provides structural strength to the cell
describe the structure & function of the plasma membrane
structure:
phospholipid bilayer - molecules embed within & attached on outside
function:
controls entrance & exit of molecules
what are the differences between eukaryotic and prokaryotic cells?
prokary cells are smaller, don’t have membrane-bound organelles, have smaller ribosomes, don’t contain nucleus & have cell walls made of murein
some prokary cells could also have plasmids, capsule around cell &/or flagella
describe the structure & function of a virus
are acellular & non-living
structure:
genetic material
capsid
attachment protein
function:
replicates inside of cells - difficult to destroy without harming host cell
define magnification
refers to how many times larger the image is compared to the object
define resolution
the minimum distance between 2 objects in which they can still be viewed as separate
what are the 3 types of microscopes?
optical (light) microscope
transmission electron microscope
scanning electron microscope
explain how a optical (light) microscope works
a beam of light condensed to create the image
what are the advantages & disadvantages of using an optical (light) microscope?
advantages:
colour images
can view living samples
disadvantages:
poorer resolution - as light as a longer wavelength
lower magnification
small organelles inside cell are not visible
explain how an electron microscope works
a beam of electrons is condensed to create the image
electromagnets are used to condense the beam
what are the advantages & disadvantages of using an electron microscope (scanning or transmission)?
advantages:
higher resolving power as electrons have a short wavelength
higher magnification
disadvantages:
black & white images - samples need to be stained
sample must be in vacuum (has to be non-living) - as electrons are absorbed by air
explain the process of how a transmission electron microscope (TEM) creates an image
- very thin specimens & placed in vacuum
- electron gun produces beam of electrons that pass through specimens
- some parts absorb electrons & appear dark
- image produced is 2D & shows detailed images of internal structure of cell
explain the process of how a scanning electron microscope (SEM) creates an image
- specimens don’t need to be thin as electrons aren’t transmitting through
- electrons are beamed onto surface & electrons are scattered in different ways depending on contours
- 3D image produced
how can magnification be calculated?
by using the IAM formula
magnification = image size / actual size
what is an eye piece graticule & what is it used for?
its a scale on a glass disc
its used to measure the size of the object that is being viewed under the microscope
what is cell fractionation?
its where cells are broken open to release the contents of an organelle so it can be studied
how should cells be prepared for cell fractionation?
cells must be prepared in a cold, isotonic & buffered solution
cold - to reduce enzyme activity, when cells break open enzymes are released which could damage organelles
isotonic - must be same water potential to prevent osmosis, organelles could shrivel/burst
buffered - solution has pH buffer to prevent damage to organelles
describe the process of cell fractionation
- homogenisation:
cell broken open (homogenised) using a blender
cells blended in cold, isotonic & buffered solution
solution filtered to remove large debris - ultracentrifugation
filtered solution spun at different speeds in centrifuge
organelles separate according to their densities
what is differential centrifugation?
centrifuge spins & centrifugal forces cause pellets of the most dense organelles to form at the bottom.
centrifuge is spun at low speed & process is repeated at faster speeds.
each time supernatant is removed leaving behind a pellet of organelles.
supernatant spun again to remove next pellet of organelles.
what is the order of density for organelles (from most to least)?
nuclei - most dense
chloroplasts
mitochondria
lysosomes
endoplasmic reticulum
ribosomes - least dense
how do eukaryotic cells replicate?
eukary cells enter cell cycle and divide by mitosis/meiosis
how do prokaryotic cells replicate?
prokary cells replicate by binary fission
how do viruses replicate?
viruses don’t undergo cell division (they are non-living) so they replicate inside host cells by injecting their nucleic acid in cell
what are the stages in the cell cycle?
3 stages:
1. interphase (G1, S & G2)
2. nuclear division (mitosis / meiosis)
3. cytokinesis
name & describe the first stage of cell division
interphase (longest stage) is where organelles double, cell grows & then DNA replicates
name & describe the second stage of cell division
nuclear division can be either mitosis (creating 2 identical diploid cells) / meiosis (creating 4 genetically different haploid cells)
what is the difference between mitosis & meiosis?
mitosis creates cells with identical DNA for growth & repair
meiosis creates gametes
name & describe the last stage of cell division
cytokinesis is the division of the cytoplasm to create new cells
name the stages of mitosis
prophase, metaphase, anaphase & telophase
describe what occurs during prophase
chromosomes condense & become visible
nucleolus disappears
in animal cells - centrioles separate & move to opposite poles of cell
why are centrioles important in prophase?
responsible for creating spindle fibres which are released from both poles to create spindle apparatus - which attaches to centromere and chromatids on chromosome in later stages
do plants have centrioles?
no, they only have the spindle apparatus
describe what occurs during metaphase
chromosomes align along equator of the cell
spindle fibres released from poles now attach to centromere & chromatid
describe what occurs during anaphase
spindle fibres start to retract & pull centromere & chromatids towards opposite poles
separated chromatids are now chromosomes
this stage requires ATP - provided by by respiration in mitochondria
describe what occurs during telophase
chromosomes at each pole become longer & thinner
spindle fibres disintegrate & nucleus starts to reform
how is the mitotic index calculated?
mitotic index = (no.of cells in mitosis/ total no.of cells) x 100
name & describe the process of cell division in prokaryotic cells
binary fission:
1. replication of the circular DNA & of plasmids
2. division of cytoplasm to produce 2 daughter cells - each with copy of circular DNA & plasmids
describe the structure of the plasma membrane
membranes described as fluid-mosaic model as it has a mixture & movement of phospholipids, proteins, glycoproteins & glycolipids
these molecules arranged within bilayer forms partially permeable membrane
how is a phospholipid bilayer formed?
phospholipids align as a bilayer due to the hydrophilic heads being attracted to water & hydrophobic tails being repelled by water
how does cholesterol affect the plasma membrane & explain why its important
cholesterol restricts the lateral movement of molecules in the membrane. this is useful as it makes membrane less fluid at high temps & prevents water & dissolved ions from leaking out the cell
name the proteins that are embedded into the phospholipid bilayer & their function
- peripheral proteins - provide mechanical support or they are connected to proteins / lipids to make glycoproteins / glycolipids
- integral proteins - are protein carriers / channel proteins involved in the transport of molecules across the membrane
what is the difference in functions between protein channels & carrier proteins?
protein channels form tubes that fill with water to enable water-soluble ions to diffuse whereas carrier proteins will bind with other carriers & larger molecules (e.g. glucose & amino acids) & change shape to transport them to other side of membrane
give examples of molecules that are able to pass through the plasma membrane
lipid soluble molecules ( e.g. some hormones) & very small molecules ( e.g. CO2, O2 & H2O)
give examples of molecules that cannot pass through the plasma membrane
water soluble, polar substances (e.g. Na ions) & large molecules (e.g glucose)
name the types of transport
- simple diffusion
- facilitated diffusion
- active transport
- osmosis
define simple diffusion & describe its process
it’s the net movement of molecules from an area of high conc to an area of low conc until equilibrium is reached - doesn’t require ATP
KE provides energy for molecules as they move constantly in fluids
define facilitated diffusion & describe its process
its s passive process but differs from simple diffusion as proteins are used to transport molecules.
for movement of ions & polar molecules which cannot diffuse
how do protein channels & carrier proteins help with facilitated diffusion
protein channels from tubes filled with water & these allow water-soluble ions to pass through membrane - still selective as the channel only opens for certain ions when they bind to protein
carrier proteins will bind to molecule (e.g. glucose) which causes change in shape of protein - shape change allows molecule o be released to other side of membrane
define osmosis
osmosis is the movement of water from an area of high water potential to an area of lower water potential across a partially permeable membrane
what is water potential & give an example
it’s the pressure created by water molecules & is measured in kPa.
pure water has a water potential of 0 - when solutes dissolve the water becomes -ve & the more -ve the water potential is the more solute is needed to dissolve in it
explain the water potentials of different solutions
isotonic = water potential is same as solution & cell within solution
hypotonic = water potential is more +ve in solution (closer to 0) than the cell
hypertonic = water potential of solution more -ve than the cell
define active transport
it’s the movement of a substance from a low conc to a high conc using metabolic energy & a carrier protein
explain the process of active transport
- transport occurs through carrier proteins spanning the cell membrane
- molecules binds to receptor complementary in shape to the protein
- ATP binds to carrier protein from inside
the cell & is hydrolysed into ADP + Pi - causes carrier protein to change shape & release molecule onto other side
- phosphate ion is released & protein returns to its original shape
why is active transport needed for the co-transport of glucose & Na ions?
to absorb glucose from the lumen to the gut there must be a higher conc of glucose in the lumen compared to epithelial cell (for facilitated diffusion) but usually there is more glucose in the epithelial cells so active & co-transport is required
explain the process of the co-transport of glucose & Na ions in the ileum
- sodium ions are actively transported out of the epithelial cell into the blood
- this reduces the Na ion conc in epithelial cell
- Na ions can diffuse from lumen down their concentration gradient into epithelial cell
- the protein the Na ions diffuse through is a co-transported protein so either glucose / amino acids also attach & are transported into epithelial cell against their conc gradient
- glucose then moves by facilitated diffusion from the epithelial cell to the blood
how are cells adapted for rapid transport across their internal / external membranes?
an increase in their SA &/or an increase in no.of protein channels & carrier molecules in their membranes
how does our immune system identify pathogens?
our bodies have cells (e.g. lymphocytes) to identify pathogens & they destroy them so they don’t cause our body harm
how can lymphocytes distinguish between pathogens & self-cells?
each type of cell has specific molecules on its surface that identify it - these molecules are usually proteins (their 3D tertiary structures enable unique shapes to be made)
what type of non-self cells can surface molecules identify?
- pathogens (e.g. bacteria, fungi or viruses)
- cells from organisms of same species (harmful for those with organ transplants)
- abnormal body cells (e.g. cancer cells)
- toxins (some pathogens release toxins into blood e.g. cholera)
define antigen
antigens are molecules that generate an immune response by lymphocyte cells when detected in the body - they are usually proteins & they are located on the surface of cells
what is antigen variability & provide an example of it
as pathogen’s DNA can mutate frequently, the antigens that were previously used for it (naturally through prior infection / artificially through vaccine) are no longer effective as well as the memory cells in the blood. this is antigen variability.
e.g. the influenza virus mutates & changes its antigens very quickly - so new flu vaccine is created each year
what is the 1st line of defence in our immune system?
our chemical & physical barriers (e.g skin & stomach acid)
what is the 2nd line of defence in our immune system?
white blood cells - these have a specific (lymphocytes) & non-specific (phagocytes) responses
what is a phagocyte & where are they found?
it’s a macrophage (type of white blood cell) that carries out phagocytosis - they are found in the blood & tissues
what is phagocytosis?
it’s a non-specific response - any non-self cell that is detected will trigger the same response to destroy it
describe the process of phagocytosis
- phagocytes are in the blood & tissues & any chemicals / debris released by non-self cells attract phagocytes & they move towards these cells
- phagocytes have many receptor binding points on their surface - these attach to chemicals / antigens
- phagocyte changes shape to move around & engulf pathogen
- the engulfed pathogen is contained in a phagocyte vesicle
- a lysosome within the phagocyte will fuse with the phagosome & release its contents
- lysozyme enzyme is released into the phagosome - this is a lytic enzyme which hydrolyses the pathogen
- this destroys the pathogen
- the soluble products are absorbed & used by the phagocyte
what is the difference between lymphocytes & T lymphocytes (T cells)?
all lymphocytes are made in he hone marrow but T cells mature in the thymus
what is a cell-mediated response?
its a response involving T cells & body cells
is the cell-mediated response specific or non-specific & why ?
its specific as T cells respond to antigens on the surface of the cells
what are antigen-presenting cells (APC)?
it’s any cell that presents a non-self antigen on its surface
give examples of APC’s
infected body cells - present viral antigens on their surface
macrophage - engulfs & destroys pathogen & presents their antigens on its surface
cells of transplanted organs - have different shapes antigens on their surface compared to your self antigens
cancer cells - have abnormal shaped self-cell antigens
describe the process of the cell-mediated response
- once pathogen has been engulfed & destroyed by a phagocyte - antigens are positioned on the cell surface (now APC)
- helper T cells have receptors on their surface which can attach to the antigen on APC
- once attached this activates the helper T cells to divide by mitosis to replicate & make many clones
- cloned helper T cells differentiate into different cells:
remain as helper T cells & activate B lymphocytes
stimulate macrophages to perform more phagocytosis
become memory cells for that shaped antigen
what is the role of cytotoxic T cells?
they destroy abnormal or infected cells
how do cytotoxic T cells carry out their role?
they release a protein called perforin which embeds in the cell surface membrane & makes a pore so any substances can enter / leave the cell
what are cytotoxic T cells commonly used for & why?
commonly used for viral infections as viruses infect body cells & cytotoxic T cells cause cell death - prevents viral replication
where are B lymphocytes (B cells) made?
in the bone marrow
what is the humoral response?
it’s a response involving B cells & antibodies
why does the humoral response use antibodies?
antibodies are soluble & transport in bodily fluids
describe the process of B-cell activation
- antigens in the blood collide with their complementary antibody on a B cell
- when this B cell collides with helper T cell receptor it activates B cell to go through clonal expansion & differentiation (clonal selection)
- B cells undergo mitosis to make many cells - they differentiate into plasma cells (makes antibodies) / memory B cells
- B memory cells divide rapidly into plasma cells - so when reinfected with the same pathogen antibodies can be made quickly
how do memory B cells eliminate pathogens & how is it effective?
as memory B cells don’t make antibodies - they will divide by mitosis & make plasma cells rapidly if they collide with an antigen they have previously encountered.
it’s effective as it results in large no.of antibodies produced = pathogen destroyed before any symptoms occur
what type of immunity do memory B cells provide?
active immunity
what is a primary & secondary response?
refers to the number & speed of which antibodies are produced when you are first exposed to an antigen compared to your second exposure
describe the structure of antibodies
quaternary structure - protein (4 polypeptide chains)
heavy chain & light chain
what is agglutination?
it’s where antibodies can bind to multiple antigens to clump them together which makes it easier for phagocytes to locate & destroy pathogens
what is passive immunity?
this is where antibodies are introduced into the body but the pathogen doesn’t enter the body so plasma & memory cells aren’t made - no long term immunity
give an example of passive immunity
antibodies passed to a fetus through the placenta or through breast milk to a baby
what is an active immunity?
it’s immunity created by your immune system following exposure to a pathogen / antigen
name & describe the types of active immunity
- natural active immunity - following infection & creation of the body antibodies & memory cells
- artificial active immunity - following weakened version of pathogen / antigen through a vaccine
what is a vaccine?
it’s a small amount of weakened / dead pathogen / antigen that is introduced to. the body
how does an immune system respond to a vaccine?
- vaccine enters body by mouth / injection
- exposure to antigens activates B cell to go through clonal expansion & differentiation (clonal selection)
- B cells undergo mitosis to make large no.of cells - differentiate into plasma / memory B cells
- plasma cells make antibodies
- B memory cells can divide rapidly into plasma cells when reinfected with same pathogen
what is herd immunity?
it’s when enough of the population is vaccinated against the pathogen so it cannot spread easily amongst the population
why is herd immunity important?
it protects those who are not vaccinated (e.g. those who are already ill to have a vaccine / have lowered immunity / are too young)
describe the structure of HIV
core = genetic material (RNA) & enzyme reverse transcriptase - needed for viral replication
capsid = outer protein coat
envelope = extra outer layer made out of membrane taken from host cell membrane
protein attachment = on exterior of envelope to enable virus to attach to host T helper cell
where does HIV replicate?
in the T helper cells
how does HIV replicate?
- HIV transported around the blood until it attaches to CD4 protein on the T helper cell
- HIV protein capsule fuses with T helper’s membrane - allowing RNA & enzymes from HIV to enter
- HIV enzyme reverse transcriptase copies viral RNA into DNA copy & moves to T helper’s nucleus - called retrovirus
- mRNA is transcribed & T helper starts creating viral proteins to make new viral particles
what is the difference between HIV & AIDS?
HIV positive is where a person is infected with HIV whereas AIDS is when replicating viruses in T helpers interfere with the immune system
how does AIDS affect the immune system?
T helper cells are destroyed by the virus so the host cannot produce adequate immune response to other pathogens - left vulnerable to infections & cancer
what is a monoclonal antibody?
it’s a single type of antibody that can be isolated & cloned
what are antibodies?
they are proteins which have binding sites complementary in shape to certain antigens
what are monoclonal antibodies used for?
- medical treatment
- medical diagnosis
- pregnancy tests
what is direct & indirect monoclonal antibody therapy used for?
used to treat cancer
how does direct monoclonal antibody therapy affect cancer cells?
- monoclonal antibodies are designed with binding sites complementary in shape to cancer cell’s antigens
- antibodies given to cancer patients & attach to cancer cells - when antibodies are bound to cancer cells it prevents chemicals binding to cancer cells that enable uncontrolled cell division
- monoclonal antibodies prevent cancer cells from growing - only attaches to cancer cells so doesn’t harm other cells
how does indirect monoclonal antibody therapy affect cancer cells?
- monoclonal antibodies complementary in shape to the antigens on outside of cancer cells have drugs attached to them
- cancer drugs are delivered directly to cancer cells & kill them - reducing harmful side effects that chemo & radiotherapy produce (AKA bullet drugs)
what tests are monoclonal antibodies used for?
pregnancy
influenza
hepatitis
chlamydia
prostrate cancer
explain the types of antibodies used in the ELISA test
- 1st mobile antibody, complementary to the antigen being tested for & has coloured dye attached
- 2nd antibody complementary in shape to the antigen is immobilised in the test
- 3rd antibody is immobilised & is complementary in shape to the 1st antibody
explain how the ELISA test works
- add the test sample from patient to the base of beaker
- wash to remove any unbound test sample
- add an antibody complementary in shape to antigen that is being tested in the presence of the test sample
- wash to remove any unbound antibody
- add 2nd antibody that is complementary in shape to 1st antibody & binds to the 1st - 2nd antibody has enzyme attached to it
- rinse off any unbound antibodies
- the substrate for the enzyme (which is colourless) is added - substrate produces coloured products in presence of enzyme
- presence of colour = presence of antigen in test sample & the intensity of colour = quantity present
what are the ethical issues with creating monoclonal antibodies?
creating them requires mice to produce antibodies & tumour cells - ethical issues debate whether the use of animals is justified to enable the better treatment of cancer in humans & to detect disease
