Unit 2 - Cells Flashcards
what is the structure of an animal cell?
see labelled diagram
what is the structure of a plant cell?
see labelled diagram
what is the structure of an algal cell?
similar to plant cells - same organelles including a cell wall & chloroplasts
what is the structure of a fungal cell?
similar to plant cells
cell wall of chitin
do not have chloroplasts as they do not photosynthesise
what is the function of the cell surface (plasma) membrane?
regulates the movement of substances into & out of the cell
separates cell contents from surroundings
allows different conditions to be maintained within the cell
allows cell interaction/attachment to form tissues
has receptor molecules, which allow it to respond to chemicals like hormones
selectively permeable
what is the structure of the cell surface (plasma) membrane?
made of phospholipid bilayer, embedded proteins &
lipids
intrinsic - span the bilayer, extrinsic - partially embedded
hydrophilic phosphate heads on the outside, hydrophobic lipid tails on the inside
on the surface of animal cells & on the inside of cell walls
what is the function of the nucleus?
to control the cell’s activities by coding for polypeptides
contains DNA as chromatin (DNA wound around histone proteins)
the nucleolus is the site of ribosomal RNA & synthesis of ribosomes
nuclear envelope & nuclear pores separate DNA from cytoplasm
nuclear pores control the movement of molecules between nucleus & cytoplasm
what is the structure of the nucleus?
the nuclear envelope is a double membrane that has nuclear pores
histone protein-bound linear DNA is arranged as chromosomes
1 or more nucleoli
what is transcription?
copying a section of DNA into RNA
what is translation?
synthesis of amino acids & so a polypeptide from an RNA template
what is the function of ribosomes?
the site of protein synthesis & translation
what is the structure of ribosomes?
very small
made from protein, RNA & rRNA subunits (rRNA is made in nucleolus)
made up of a large subunits & a small subunit
located in the cytoplasm and attached to RER
70s ribosomes are in prokaryotes & chloroplasts & mitochondria
80s ribosomes are in eukaryotes
what is the function of the rough endoplasmic reticulum (RER)?
site of protein synthesis
what is the structure of the RER?
a system of membrane-bound flattened sacs & fluid-filled cisternae (spaces)
the surface is covered with 80s ribosomes
what is the function of the smooth endoplasmic reticulum (SER)?
site of lipid/steroid hormone synthesis
processes lipids
fat storage & transport
triglycerides - storage of Ca2+ in muscle fibres
phospholipids - make new membrane
what is the structure of the smooth endoplasmic reticulum (SER)?
a system of random membrane-bound flattened sacs & fluid-filled cisternae (spaces)
the surface is not covered in ribosomes
what is the function of the golgi apparatus?
to covalently modify proteins (that have come from the RER)
processes & sorts proteins according to their destination
releases golgi vesicles (e.g. secretory for exocytosis or lysosomes)
how are proteins modified in the golgi apparatus?
add carbohydrates to protein to form glycoprotein
add lipids to protein to form lipoprotein
what is the structure of the golgi apparatus?
stacks of 4-8 membrane-bound flattened sacs with fluid-filled cisternae
vesicles from RER or SER arrive at golgi & fuse with it
contains enzymes that modify proteins
produces golgi vesicles at the edges of the sacs
what is the function & structure of golgi vesicles?
to store lipids & proteins made by the golgi apparatus & transports them out of the cell via the cell surface membrane
a small fluid-filled sac in the cytoplasm, surrounded by a membrane
produced by golgi apparatus
what is the function of lysosomes?
contains hydrolytic enzymes (lysozyme)
to fuse with vesicles/phagosomes containing bacteria during phagocytosis
to digest invading cells
to break down unwanted organelles & cellular debris/worn out components
what is the structure of lysosomes?
round organelle surrounded by a membrane with no clear internal structure
contain hydrolytic enzymes (lysozyme)
produced by & pinch off from golgi
describe the endomembrane transport system
- autoradiography can track the amino acids through the cell from time 0
- through the RER after 10 mins
- through the golgi after 30-60 mins
- being secreted after approximately 90 mins
what is the function of mitochondria?
site of aerobic respiration (energy transfer from organic molecules to ATP & energy release)
link reaction
has a role in Kreb’s cycle
oxidative phosphorylation (releasing energy to make ATP)
what is the structure of mitochondria?
oval-shaped
double membrane (outer & inner mitochondrial membrane)
outer membrane regulates entry & exit of substances
intermembrane space
inner membrane is folded into cristae & matrix that contains enzymes for link reaction & Kreb’s cycle (large sa to hold the electron transfer chain & the enzyme ATPsynthase)
large sa maintained by sausage-shape & short diffusion distance so quick diffusion in & out
70s ribosomes
DNA loops
what is the function of chloroplasts?
site of photosynthesis
light dependent reaction on thylakoid membrane
light independent reaction in stroma
what is the structure of chloroplasts?
small, flattened
smooth double membrane (chloroplast envelope)
stroma (fluid-filled) where the synthesis of sugars happens - light independent reaction (calvin cycle)
thylakoid: where light dependent reaction happens - (fluid-filled membrane sacs) in stacks called grana that contain chlorophyll (photosynthetic pigment) + intergranal/stromal lamellae that link grana
contains 70s ribosomes & loops of chloroplast DNA
contains ATPsynthase (makes ATP)
what is the function of the cell wall?
to provide mechanical strength to prevent cell lysis (bursting) due to osmotic entry of water
to allow plants to develop turgor pressure/become turgid
to allow water to pass along it (from cell wall to cell wall by apoplast pathway) so helps water move through plant
freely permeable
what is the structure of the cell wall in plant cells?
made of cellulose molecules - polymers of b-glucose
cellulose is bundled into microfibrils with multiple h-bonds
microfribrils form mesh lattice which is freely permeable
thin middle lamella that marks the boundary b/w2 cells & join adjacent cells together with Ca pectate
plasmodesmata channels for exchanging substances with adjacent cells
in fungi, the cell wall is made of chitin
what is the function of the vacuole?
to change volume to maintain turgidity, giving support
to store substances e.g. minerals, pigments, sugars
contains enzymes for breaking down molecules
isolates unwanted chemicals inside the cell
what is the structure of the vacuole?
large, fluid-filled (water) & membrane-bound (tonoplast)
the tonoplast is selectively permeable
contains hydrolytic enzymes to break down molecules
all mature plant cells have a vacuole
contains cell sap
in cytoplasm
what is a tissue?
a group of similar, specialised cells that work together to perform a particular function
what is an organ?
a group of tissues that work together to perform a particular function
what is an organ system?
a group of organs that work together to perform a particular function
make up an organism
what is the structure & function of the flagella?
hair-like structure
rotates to allow the cell to move
what is the structure & function of the nucleoid?
not attached to histone proteins
code for polypeptides & genetic information for replication
what is the structure & function of the cytoplasm in prokaryotes?
contains simple, non-membrane-bound organelles
aqueous stage where reactions occur
what is the structure & function of the ribosomes in prokaryotes?
70s
site of protein synthesis
what is the structure & function of the slime capsule?
protect bacterium from other cells e.g. from immune system
allow bacteria cells to stick to each other for protection
surrounds cell wall
what is the structure & function of the cell wall in bacteria?
made of murein/peptidoglycan (glycoprotein)
freely permeable
supports cell & prevents osmotic lysis
what is the structure & function of the cell surface membrane in bacteria?
phospholipid bilayer
selectively permeable
controls movement of substances into & out of the cell
what is the structure & function of the plasmids?
small rings of DNA in the cytoplasm
contain several genes e.g. antibiotic resistance that can be transferred to other bacteria cells via pili
eukaryotic cells vs prokaryotic cells structure
distinct nucleus w nuclear envelope vs no true nucleus (DNA as nucleoid in cytoplasm)
DNA associated with histone proteins, forming chromatin vs DNA not associated with histone proteins
there are no plasmids & DNA is linear vs some DNA might be in circular strands called plasmids
contain complex, membrane-bound organelles (RER, SER, mitochondria, GA) vs no membrane-bound organelles
chloroplasts might be present vs no chloroplasts, sometimes bacterial chlorophyll associated with CSM
10-100 micrometres vs 1-10 micrometres
80s & 70s ribosomes vs 70s ribosomes only
cell wall of cellulose vs cell wall of murein/glycoprotein
no outer capsule vs may have slime capsule
what are viruses?
acellular/non-living particles
they have no metabolism & cannot replicate outside of a host cell
what is the structure of a virus?
nucleic acids e.g. DNA & RNA (single-stranded) as genetic material but can only reproduce inside living host cells
nucleic acid is enclose in a protein coat (capsid), which protects nucleic acid from being digested by host enzymes
attachment proteins attach to host cell’s receptor protein e.g. gp120 on HIV
some viruses (e.g. HIV) have PL bilayer membrane
HIV has enzyme called reverse transcriptase
what is cell specialisation?
cells of multi-cellular organisms are specialised in different ways to perform a specific function
each specialised cell has evolved more or fewer specific organelles & structures to suit its function
give examples of specialised cells & their special features
muscle cells have many mitochondria to produce ATP needed for powerstroke b/w actin & myosin
phagocytes (neutrophils) have many lysosomes
root hair cells have many mitochondria for active uptake of minerals via protein pump & H+ co-transporters
describe cell specialisation
- all cells in an organism e.g. humans are produced by mitotic divisions from the fertilised egg (zygote) so they are genetically identical
- every cell contains all the genes needed for it to develop into any type of cell, but only some of the genes are expressed in a cell at one time
- different genes are switched on in each type of specialised cell & the rest of the genes are switched off
- the cells of a multi-cellular organism have therefore evolved to become more suited to their specific function & perform it more efficiently
so the organism functions more efficiently
define magnification
the number of times larger the image is compared to the actual object
define resolution
the ability to distinguish b/w 2 separate points that are close together
what is the formula linking magnification, image size & actual size?
m=i/a
how does a light/optical microscope work?
uses light to form an image
uses glass lenses to focus the image
the specimen can be alive & held in water/wax/oil
light passes through 10-50 micrometre specimen
coloured stains are used to give contrast
how does an electron microscope work?
uses a beam of electrons to form an image
uses electromagnets to focus the beam of electrons
the specimen is held in a vacuum (to allow e-s to flow)
heavy metals are used to stain specimen
specimen is dead or dehydrated
how does a transmission electron microscope work?
electrons pass through a very thin section (50nm)
heavy metals (e.g. lead) give contrast
denser parts of the specimen absorb more electrons so they appear darker
2d image produced
how does a scanning electron microscope work?
a beam of electrons is scattered off a gold-covered specimen surface & gathered in a detector to form an image
shows the surface of the specimen & 3d image
what are the advantages of a light microscope?
image can be in colour
can view living specimens
easier to prepare
easier to use
cheaper
quicker
more portable
what are the disadvantages of a light/optical microscope?
lower max. resolution of 0.2 micrometres
lower max. magnification of x1500
cannot see detail of organelles/ultrastructure
what are the advantages of an electron microscope?
higher max. resolution: TEM 1nm & SEM 20nm
higher max. magnification of x500,000
can see detail of organelles/ultrastructure
SEM forms 3d image
what are the disadvantages of an electron microscope?
more expensive
more complex & time-consuming preparation (e.g. dehydration)
more difficult to use
specimens must be dead
forms black & white image
may create artefacts
TEM: sections must be very thin - 50nm
only produces 2d image
SEM: lower resolution & magnification than TEM
how is an eyepiece graticule used?
- epg is placed in eyepiece lens
- epg calibrated against a known scale (e.g. micrometre slide) for each magnification
at low power 1 epg unit = 25 micrometres
at medium power 1 epg unit = 10 micrometres
at high power 1 epg unit = 2.5 micrometres
describe the process of cell fractionation
- make solution ice cold, ensure it is isotonic & add buffer solution
- homogenise the cells to break the CSM & release organelles
- filter the solution through gauze to remove large cell or tissue debris
- put solution in centrifuge for ultracentrifugation, starting at low speed
- heavier organelles are forced to the bottom of the test tube while lighter organelles stay at the top
- nuclei is separated first bc it is the heaviest organelle, forming a pellet. the supernatant is poured off for the next round of ultracentrifugation
- the process is repeated at higher speed and for longer until all organelles are separated
- the order of separation is: nucleus, chloroplasts, mitochondria & lysosomes, ER & ribosomes
why is the solution ice-cold, isotonic & buffered?
ice-cold: reduce enzyme activity/digestion
isotonic: no water potential gradient so no net osmosis so cell not damaged by bursting or shrinking
buffered: maintain pH so proteins are not denatured
define mitosis
the division of the nucleus into 2 genetically identical nuclei
then, the cytoplasm & csm divide to form 2 genetically identical daughter cells
what is the purpose of mitosis? (4)
growth - increase in cell number
repair & replacement of damaged/worn out cells e.g. skin cells
asexual reproduction e.g. cloning plants
producing genetically identical daughter cells to maintain the genome
what is the purpose of the cell cycle?
to ensure cell division happens when needed & to prevent it from happening when it is not needed
what are the 3 stages of the cell cycle?
- interphase
- mitosis
- cytokinesis
describe interphase
cell increases in size/biomass
DNA replicates, chromosomes are copied
cell actively synthesises proteins & organelles
ATP produced to release energy for cell division
describe mitosis
nucleus divides
sister chromatids separate
pmat: prophase, metaphase, anaphase, telophase
describe prophase
chromosomes condense & become visible
each chromosome is in the form of 2 identical sister chromatids joined at the centromere
nuclear envelope breaks down & nucleolus disappears so chromosomes are free in cytoplasm
centrioles move to opposite poles & form spindle fibres that extend to the equator of the cell
describe metaphase
chromosomes move to equator
spindle fibres attach to centromere of the chromosomes (the kinetochore)
describe anaphase
spindle fibres shorten & poles move apart
centromeres divide
sister chromatids separate & are pulled to opposite poles of the cell (v shape)
there is complete set of chromosomes at each pole
ATP required - mitochondria around spindle fibres
describe telophase
chromatids at the poles uncoil into chromatin & are not visible
each pole has identical copies of each chromosome
spindle fibres break down
nuclear envelope & nucleolus reform around chromosomes @ each pole so 2 nuclei formed
describe cytokinesis
contractile ring forms
cytoplasm divides
csm divides
in plant cells, new cell wall plates form
to form 2 genetically identical daughter cells
describe the appearance of chromosomes in each stage of mitosis
p: random arrangement
m: lined up on equator
a: v shape - pulled apart
t: at 2 poles
what is mitotic index & how is it calculated?
measure of how fast a tissue is dividing/growing
= ratio of cells undergoing mitosis
useful for cancer calculations
cells in mitosis/total number of cells
what is cancer?
group of diseases caused by uncontrolled division & growth of cells
bc of mutation of genes that regulate mitosis & cell cycle
so a group of abnormal cells forms a tumour that constantly expands in size
describe benign tumours
non-cancerous
localised in one area
grow slowly
cells resemble the tissue they originate from
often harmless unless *see other card
can be surgically removed
describe malignant tumours
cancerous
cells break off primary tumour & travel through bloodstream to form secondary tumours in other parts of the body = metastasis
difficult to treat/find& remove
cells do not resemble tissue they originate from
cells do not die
catabolic
why do tumours cause harm?
invade healthy tissue which causes:
pressure on surrounding cells (e.g. brain tumours) which affects normal function
pressure on blood vessels/nerves supplying healthy tissues
pressure on airways in lungs
what are the causes of cancer?
exposure to radiation - x-ray, gamma ray, uv
age - increased cell division w age so increased chance of mutation
lifestyle - smoking & alcohol
ingesting carcinogens e.g. tar & asbestos
viruses e.g. HPV, hep B & C
what is the rate of mitosis affected by?
environment of the cell
growth factors
controlled by 2 types of regulatory genes
checkpoints of the cell cycle are closely regulated - g1, s & g2 e.g. proto-oncogenes & tumour-suppressor genes
what does treating cancer involve?
killing dividing cells by blocking part of the cell cycle
chemotherapy - drugs used to treat cancer disrupt cell cycle by:
preventing DNA replication
inhibiting metaphase by interfering w spindle formation
targeting rapidly dividing cells so also kills healthy cells
describe the process by which bacterial (prokaryotic) cells divide
binary fission
- single loop of DNA replicates
both copies attach to csm
plasmids replicate - csm grows & elongates b/w the 2 DNA molecules
it pinches inwards, dividing cytoplasm into 2 - new murein cell wall forms b/w 2 DNA molecules
forming 2 nearly genetically identical daughter cells
each w single copy of DNA & variable # of plasmid copies
formula for calculating population of bacteria
bacterial population = # at start x 2^# of divisions
how do viruses replicate?
- attach to host cell using attachment proteins on their surface
- inject their nucleic acid (RNA or DNA) into host cell
- genetic information on injected viral nucleic acid provides gene instructions for host cell to make new viruses by producing viral components (proteins & nucleic acid)
what is an antigen?
a molecule recognised as foreign by the immune system, which stimulates a specific immune response - the production of antibodies
where are antigens found?
on the surface of:
pathogens e.g. bacteria csm, cell wall or virus’ capsid
viral infected cells - (apc) cell will present viral antigens on its csm to signify distress
transplant organs - tissue matching & immunosuppressant drugs needed
cancer cells - DNA mutations may create antigens
toxins produced by bacteria
what species can the immune system identify?
pathogens
cells from other organisms of the same species
abnormal body cells
toxins
what are the 2 types of defence system against infectious disease?
non-specific defence system:
gives immediate, initial response/barrier to infection
1. physical (skin, mucus) & chemical (acid, enzymes) barriers
2. phagocytosis
specific defence system
can distinguish b/w antigens
slower to act during the first infection by a pathogen/ag bc cell division takes time
faster responses to reinfection by the same pathogen/ag so host does not suffer symptoms - so immune
1. cell-mediated response by t lymphocytes (t helper cells & t cytotoxic cells)
2. humoral response by b lymphocytes (antibody production in bloodstream)
what are the 2 types of white blood cell?
lymphocytes
phagocytes
describe the process of phagocytosis
phagocyte attracted to pathogen by chemicals & recognise ag (stimulated by cytokines)
attachment to ag with receptors
endocytosis/engulfing pathogen
the pathogen is enclosed in a phagosome
lysosomes containing lysozyme
fuse with phagosome (to become a phagolysosome)
enzymes hydrolyse/digest pathogen
ag presented on phagocyte csm (apc)
describe the specific immune response (humoral)
the pathogen has antigens on its surface
the pathogen is engulfed by a phagocyte in phagocytosis
phagocytes present antigens to b cells
cytokines activate complementary b cells & stimulate phagocytosis
clonal selection of b lymphocytes with receptors complementary to antigens & b cells divide by mitosis to form clones (clonal expansion)
differentiate into plasma cells that produce monoclonal antibodies (stim. by cytokines)
the antibodies are specific & complementary to the antigen & bind to destroy the pathogen
many b cells become memory cells, remain in lymph nodes/blood & give immunity
describe the specific immune response (cell-mediated)
the pathogen has antigens on its surface
the pathogen is engulfed by a phagocyte in phagocytosis
phagocytes present antigens
th cells release cytokines that stimulate other parts of the specific immune response
clonal selection of specific th & tc cells with receptors complementary to antigens
th & tc cells divide by mitosis to form clones (clonal expansion)
tc cells activated
tc cells attach their complementary receptor to the antigen (in csm of ag presenting or infected cell)
tc cells produce a protein (perforin) that creates holes in csm so it becomes freely permeable - therefore the infected cell dies & viruses inside are destroyed
many th & tc cells become memory cells, remain in lymph nodes/blood & give immunity
what is the role of T helper cells?
stimulate & activate other parts of the immune response by releasing cytokines e.g. to stimulate phagocytosis & to activate B cells & killer T cells
what is the role of antigen-presenting cells in the cellular response?
present antigens of the pathogen on csm
tc cells bind to apc to kill them
what is an antibody?
proteins with specific binding sites to a particular antigen, which are synthesised by plasma b cells
what is the structure of an antibody?
antibody binding sites are complementary to a specific antigen
4 polypeptide chains (2 short, 2 long) - quaternary structure joined by disulfide bonds
each antibody has 2 variable regions, which are determined by a unique primary structure complementary to each antigen
2 specific ag binding sites that form antibody-antigen complexes
different primary structure on different antibodies
constant regions act as markers for phagocytosis
every antibody has constant regions with the same primary structure
how do antibodies prepare the antigen for destruction?
form ab-ag complex
agglutination - cluster apc together so easier to engulf in phagocytosis
constant regions act as markers that phagocyte receptor proteins bind to, which triggers endocytosis of the pathogen
antitoxin antibodies bind to bacterial toxins to neutralise them, making them harmless
what is the role of memory cells in primary & secondary immune response?
primary response is slow, weak & short-lasting
low conc. of abs in blood
host suffers symptoms
b, th & tc memory cells formed
secondary response to reinfection by the same pathogen is faster, stronger & longer-lasting
higher conc. of abs in blood
bc memory b cells & plasma cells produce more antibodies & faster
how do vaccines work?
dead or inactive form of the pathogen or antigens
stimulate specific immune response
production of b, th & tc memory cells
active immunity
upon reinfection by the same pathogen, the immune response is faster, stronger & longer-lasting
describe herd immunity
if a sufficient number of the people/proportion of the population are vaccinated against a disease, the pathogen will not be transmitted from one host to another
what are the ethical considerations of vaccines?
production & testing may be done with animals
risks/side effects vs benefits
must be tested on humans to test toxicity
vaccines are expensive - should they be made free on the NHS?
should vaccines be compulsory?
what are the differences b/w active & passive immunity?
active involves memory cells vs passive does not
active involves production of antibodies by plasma memory cells
passive involves antibody being introduced from another source
active is long term bc antibody is produced in response to antigen
passive is short term bc antibody is broken down
active can take time to develop vs passive is fast acting
what is the structure of HIV (human immunodeficiency virus)?
retrovirus - RNA & genes
non-living - does not metabolise, acellular
2 RNA strands - code for 13 proteins
capsid - protein coat
membrane derived from host th cell
reverse transcriptase converts RNA into viral DNA
attachment proteins of surface e.g. gp120
describe the cycle of HIV (RHJH notes)
- binding of attachment protein gp120 to receptor protein on Th cells
- triggers fusion of viral envelope to csm
- viral RNA enters cytoplasm
- reverse transcriptase converts RNA into viral DNA
- viral DNA is inserted into host DNA by integrase
- viral mRNA is made & exits nucleus
- host ribosomes translate viral mRNA into viral proteins
- new viral assembly & host cell lysis
describe the replication of HIV in th cells
reverse transcriptase
uses HIV RNA to make DNA copy
viral DNA is joined to host cell’s DNA
viral DNA is used to make HIV RNA copies
& HIV capsid proteins/enzymes
made at host ribosomes
assembly of new virus particles
budding off from host cell membrane
host cell is destroyed
how does HIV cause AIDS?
not enough T-cells to activate B-cells
so reduced antibody production & less effective immune response
memory cells destroyed
person more prone to opportunistic infections or cancer
e.g. pneumonia
why are antibiotics ineffective against viruses?
antibiotics stop metabolism but viruses do not have a metabolism
viruses are within host cells so antibiotics cannot access them
antibiotics work against cell components e.g. ribosomes which viruses do not have
what are the uses of monoclonal antibodies?
medical diagnosis
targeting medication to specific cell types by attaching a therapeutic drug to an antibody
describe how monoclonal antibodies are used in pregnancy tests
- urine passes through reaction zone
- HCG hormone binds to the mobile mAb that is specific to it
- (it passes up the stick) HCG binds to the immobilised HCG antibodies in the result window
- mobile HCG antibodies which DO NOT attach to HCG
- bind to immobilised antibodies in the control window
- blue dye appears in both the control & result windows, showing a +ve result
what are the ethical issues of monoclonal antibodies?
expensive
side effects
use of animals in production
how are antibodies used in indirect ELISA testing?
- HIV antigens are attached to a test well in a dish
- a sample of blood plasma is added to the well. if HIV antibodies are present, they bind to the HIV antigens
- the well is washed to remove unbound HIV Abs. a second antibody with an enzyme attached is then added (made by injecting mouse w HIV antibody) & enzyme-linked Ab binds to anti-HIV Abs
- the well is washed again to remove unbound enzyme-attached Abs. a yellow substrate solution is added, which changes to blue if the enzyme is present. a blue colour shows the person has HIV antibodies
why cannot ELISA testing be used to tell if a person has AIDS?
AIDS is the symptom so would need a different test
must look at Th cell count, which would be low in a person with AIDS
describe the process of direct ELISA testing
- known antibody is absorbed (stuck) to the test well in a dish
- the patient’s sample is added
detection of unknown antigen/pathogen due to ag-ab complex - sample washed to remove unbound antigens
- enzyme-linked ab is added (complementary to ab-ag complex so will bind) then washed to remove unbound enzyme-linked abs
- substrate added, which will bind to enzyme-linked ab & cause colour change to blue = antigen is present
how can the results of ELISA testing be quantified?
use calibration curve & colorimeter
what are the roles of membranes within cells?
controlling entry & exit of substances into/out of organelles
separating cell components from cytoplasm so specific reactions can take place in specific organelles - isolation & creating optimum conditions
holding components of some reaction in place e.g. ribosomes on RER, ETC
regulating the transport of materials into & out of cells - transport medium e.g. Golgi vesicles
provide an internal transport system e.g. RER, SER
isolate potentially damaging enzymes from other cellular content e.g. hydrolytic enzymes in lysosomes
describe the fluid mosaic model of CSM
fluid: components can move laterally & membrane is flexible/self-sealing
mosaic: pattern of proteins of varying size as seen on SEM
label parts of CSM
water
hydrophilic phosphate head
hydrophobic fatty acid tails
cholesterol
intrinsic channel protein (spans bilayer)
intrinsic carrier protein
extrinsic protein
glycocalyx - glycoprotein & glycolipids
what is the structure & function of each of the following CSM components?
cholesterol
intrinsic protein
extrinsic protein
glycolipid
glycoprotein
phospholipid
see booklet
why don’t most molecules freely diffuse across CSM?
not lipid-soluble/polar so cannot pass through phospholipid bilayer
too large to pass through channels in the membrane
same charge as the charge on protein channels so are repelled
charged ions so cannot pass through non-polar hydrophobic FA tails in PL bilayer
what affects the permeability of the membrane?
- ethanol - lipid-soluble
ethanol dissolves lipid so damages membrane
increases membrane permeability - temperature
increased temp.
= increased KE
= increased movement of phospholipids & other components
= increased fluidity & permeability of the membrane
–> affects membrane proteins’ position & sometimes function
- channel & carrier proteins - selectively permeable
how many of a certain type of molecule is let through
define simple diffusion
diffusion is the random movement of particles from a region of higher concentration to a region of lower concentration, down a conc. grad.
no carrier or channel protein
Fick’s law
rate of diffusion
α
SA x difference in conc. (conc. grad.)
—————————————————-
diffusion distance
fast = big/small
rate of diffusion is proportional to SA & diffusion gradient
rate of diffusion is inversely proportional to diffusion distance
describe facilitated diffusion
movement of particles down conc. grad. (passive), but requires intrinsic transport proteins
- channel proteins
form hydrophilic channels across the membrane that allow water-soluble/polar/charged ions & molecules e.g. glucose & AAs to pass through membrane
channels are selective & specific - each channel only opens in the presence of a specific molecule - carrier proteins
these change shape when a specific molecule binds to it, allowing molecules to move from higher to lower conc.
no external energy is needed (passive)
increased # transport proteins = increased permeability of membrane
do osmosis & redo transport across membranes FC
define active transport
the movement of molecules or ions into or out of a cell from a region of lower conc. to region of higher conc. using ATP hydrolysis & carrier proteins (conformational change in shape)
against conc. grad.
describe the process of active transport
- molecule or ion binds to receptor sites on the carrier protein
- on the inside of the cell/organelle, ATP binds to the protein & ATP is hydrolysed into ADP + Pi
- this causes the protein to change shape (3y structure) & opens to the opposite side of the membrane
- the molecule/ion is released to the other side of the membrane
- ADP + Pi is released (recombines –> ATP) from the protein so protein reverts to original shape & process is repeated
