Cells Flashcards
Eukaryotic cells
plants, algae, animals and fungi
this means that all cells have a nucleus and membrane bound organelles
The nucleus
contains DNA arranged in chromosomes
within chromosomes there are genes that code for the primary structure of polypeptide
the nuclear envelope-double membrane that surrounds the nucleus, controls exit and entry of substance in nucleus and compartmentalises reactions
nuclear pores- allow passage of large molecules out of nucleus e.g. mRNA
Chromatin- linear DNA protein bound that condenses into visible chromosomes in division
the nucleolus- small but inside nuclearplasm, manufactures rRNA and ribsomes may be more than 1
function of the nucleus
1.stores genetic info codes for primary structure
2.protein synthesis requires mRNA production via transcription
3.also requires rRNA production to make ribsomes
4.where semi Conservative dna rep occurs
The mitochondrion
Where ATP is synthesised by aerobic respiration
double membrane- control entry and exit of molecules in and out of mitochondria
cristae- extentions form fold of inner membrane, provide Large SA for enzymes in aerobic respiration
The intermembrane space-space between inner and outer
The matrix- contains proteins,lipids, Mitochondrial DNA and 70s ribsomes
endoplasmic reticulum
RER- has ribsomes on its outer surface membrane
provide Large SA for protein synthesis
packages proteins into vesicles + transports them to golgi apparatus to be modified
SER- lacks ribsomes
synthesis, store and transport lipids
synthesis, store and transport carbs
packages triglycerides and carbs into vesicles and transport to the golgi
The golgi apparatus
sorts and modifies proteins by adding carbs or lipids on to them
modified proteins are packaged into vesicles, pinched off from the ends of the cisternae
exocytosis- vesicle moves to and fuses with cell surface membrane releasing contents to the outside
also forms lysosomes
Lysosomes
contain and release hydrolytic enzymes also contain lysozymes, enzymes that hydrolyse walls of certain bacteria
single membrane forms a sphere , isolate hydrolytic enzymes from rest of cell , prevents any unwanted breakdown of cells ultrastructure
functions-
fuse with foreign material ingested by phagocytic cells and release enzymes
release enzymes to outside of cell in order to hydrolyse and breakdown molecules outside of cell
the breakdown damaged and worn out organelles so molecules can be reused
completely breakdown cells after they have died- autolysis
ribsomes
made up of rRNA and proteins needed to synthesis proteins.May be found in cytoplasm or attached to membrane of RER
80s- larger and eukaryotic
70s- smaller and prokaryotic
cell surface membrane
controls the passage of molecules in and out of the cell
made of phosolipid bilayer and fluid mosaic model
differences between animal and plant cells
plant cells have
cell wall
chloroplast
vacuole
carbs stored as starch
don’t have-
glycogen
chloroplast
carry out photosynthesis
chloroplast envelope- double membrane that surrounds organelle controls what enters and exits
grana- stack of up to 100 discs called thylakoids which are also made from membranes, within membrane is the photosynthetic pigment called chlorophyll
stroma- fluid filled matrix, synthesisnof sugar
large SA for more chlorophyll
contain circular DNA and own 70s ribsomes
cellulose cell wall
consist of microfibrils, adds strength and overall rigidity
prevents cell from bursting under pressure
vacuoles
fluid filled sack bound by a single membrane
support cells
sugar and A acid storage
pigments stored here
cell specialisation
specialised cells form tissues
different tissues grouped into organs
different organs grouped into organ systems .
cells become specialised by gene expression
prokaryotic cell
don’t have nuclei or other membrane bound organelles
pro vs eukaryotic cell
pro have circular DNA not linear
pro DNA isn’t associated with histone and contains no intorns
pro don’t contain membrane bound organelles
pro has no true nucleus
pro has smaller ribsomes
pro can have capsules, one or more flagella and plasmids
pro have cell wall made of murine
viruses
acellular
very small and require living cells to replicate inside
contain DNA or RNA
genome surrounded by a protein coat called a capsid
envelope contains attachment proteins- bind to host cells
had an enzymes that replicates genetic info and inserts it into host DNA
viruses have no organelles so can’t replicated independently
light microscopes
specimens are illuminated by light and focused with a glass lense
can be living or dead
often have to be stained
limited to 1500x as at higher mags it loses resolution max res of 200nm
only see large organelles
eye peice graticule and stage micrometer
graticule- fits onto eyepiece like a ruler with numbers but no units
stage micrometer is a microscops slide with an accurate scale
use stage micrometer to calibrate eye peice graticule at certain mags
line them up
each division of stage is 10 micrometer is 24 is 240ųm in total
so if 90 divisons sit in this space
240/90= 2.67 ųm per eyepiece graticule divisions
then u can measure stuff
electron microscope
use a beam of electrons to illuminate specimens
has a very short wavelenght and so has a high resolving power 0f 1 NM and a mag of 500000×
can observe small organelles
have to be dead
TEM- go through specimen and enable veiw of internal structures
fixed in resin and sliced thin, thicker areas absorb more so it is darker
in a vacuum
stained using heavy metal
can create artifacts
SEM-
electrons bounce of surface
produce 3d image
light vs electrons
light-
illumination-light rays
focused by- lens
mag-x1500
res-200nn
can see large organelles
specimens- living
staining process- easy
electron-
beam of electrons
electromagnets
500000×
1nm
smaller organelles
dead
complex
magnification equation
actual size= image size/ mag
cell fractionation and ultracentrifugation
step 1) homogenised tissue in blender in a ice cold, isotonic and buffer solution
step2) filter to remove large peices producing a supernatant
3) differential centrifugation carried out, on a low speed the densest organelles are removed first and form pellets at the bottom which are remiver
4) then at a higher speed and less dense form pellet
5) repeat many times
nucleus is densest then chloroplast and mito then ribsomes
cell cycle
interphase (growth and semi Conservative replication)
nuclear division (mitosis)
cell division (cytokinesis)
movement from one phase to another is triggered by group of chem signals called cyclins
interphase
when cell increases in mass and size preps cell for division by synthesising proteins and replicating its DNA
G1 phase- cells make RNA enzymes and proteins required for growth, in this phase a signal is received telling cell to divide again
S phase- Repicated DNA semi Conservatively resulting In 2 sister chromatids
G2 phase- continues to grow I’m prep for mitosis e.g. form mitotic spindles and DNA is checked for errors
prophase
prophase-
chromosomes condense and are visible
these consist of 2 identical sister chromatids that are joined at centrometer
2 centrioles moved towards opp poles of cell
nuclear membrane breaks down into small vesicles
spindle fibres begin to emerge from centrioles
metaphase
chromosomes line up at the equator of the cell
chrosomes attach to spindal fibres by their centeomeres
anaphase
spindle fibres shorten and centromere splits
this pulls the sister chromatids to the opp poles of the cell
telephase
chromosomes arrive at opp poles and begin to uncoil
the spindle fibres break down
nuclear envelope begin to reform around each set of chromosomes
cytokinesis
final step in cell cycle
cytoplasm divides forming 2 genetically identical daughter cells
After mitosis( propahse metaphase anaphase and telophase)
importance of mitosis
growth of multicellular organisms- enables unicellular zygote to grow to multicellular organisms
growth can be across whole body or confined to certain areas
Replacement of cells and repair of tissues- damaged tissues can be repair as cells are constantly dieing and need to be replaced by genetically identical ones
happens rapidly on skin and gut lining
some animals can even regenerate whole body parts
asexual reproduction-
single parent organisms creates genetically identical offspring
in unicellular cell division results in reproduction of geneticaly identical offspring
in multicellular organisms new grow from parent organism and then detach from parent in diff ways
recognising the stages of mitosis
prophase- chromosomes condense and are visible but are all over the place
nuclear envelope is breaking down
metaphse- chromosomes limed up along the middle of the cell
anaphase- moving away from the middle towards opp poles
V formation
telophase- arrive at opp poles
begin to uncoil and nuclear envelope is reforming looks like an 8
cytokenisis-cleavage furrow forms and seperate 2 cells
mitotic index
proportion of cells undergoing mitosis
mitotic index = no of cell with visible chromosomes ÷ total no of cells
×100 to get percentage
cancer
arise due to uncontrolled mitosis
cancer cells divide rapidly and uncontrollably, forming a tumour (abnormal mass of cells)
start when these is a mutation in genes that controlled cell division, these 2 genes are called Oncogene (proto-oncogene) and tumor supresser gene
mutation common most dont cause cancer
either result in early cell death or cell being killed by immune system
most cells can be replaced so this rarely effects the body
mutations that result in gens of cancerous cells don’t result in death allowing mutationbto pass on to cell decendants by the time tumour are detected the containbmillions of these cells
carcinogenesis are any agents that may cause cancer
benign tumours don’t spread so don’t cause cancer
some spread these are called malignent and cause cancer
cancer treatments
almost 50% of people with cancer have a mutated p53 gene that helps control cell growth
but other reasons cause it so there is no single treatment
most work by controlling rate of mitosis
methotrexate- inhibits synthesis of DNA nucleotides in cell
Vincristine and taxol- prevent formation of mitotic spindles
binary fission
process of cell division in prokaryotic cells and is much simpler
due to them not having nucleus, chromosomes, membrane bound organelles or spindle fibres
1.single circular DNA molecule undergoes DNA replication
2.Any plasmids undergo DNA rep
3.Parent cell divides in 2 with cytoplasm roughly halfed between 2 daughter cells
4.The 2 daughter cells each contain a single copy of the circular DNA molecules and a variable no of plasmids
cell surface membrane
controls what enters and exits the cell
it is semi permeable
consists of proteins, glycoproteins, phosolipids, carbohydrates and cholesterol
phosolipids form a bilayer
fluid-bilayer constantly moving relavtive to everything in it
mosaic- proteins are unevenly distributed throughout membrane, diff shapes and sized
selectively permeable- determined by type and distribution of transport proteins and phosolipid molecules present
parts of cell surface membrane
phosolipid bilayer
channel protein
carrier proteins
glycoproteins
glycolipids
enzymes
cholesterol
what can and can’t cross cell surface membrane
Can-
small
non polar
lipid soluble
can’t-
large
polar
water soluble
channel proteins
have specific tertiary structure that span membrane and make hydrophilic tunnel across it
selective will one accept on or a few close types of molecules for transport
facilitated diffusion- small charge molecules e.g. ions and polar molecules
aquaporins- specifically water via osmosis
some are open all the time and some are gated so can open and close in response to signal
carrier proteins
specific tertiary structure and allow transport of ions and polar molecules by facilitated diffusion or A transport
change shape to move target molecules from one side of membrane to the other
typically selective for 1/ a few substances
often change shape in response to binding of their target molecules with the shape change moving it to opp side
enzymes
shape of A site is comp and specific to its substrate
e.g. Maltase enzyme is found in the cell membrane of small intestine
receptor
other protein molecules act as specific receptors for hormones with comp shape
attach to binding sites and allow a cell to respond
e.g. insulin
glycolipids and glycoproteins
glycolipids- composed of carbohydrates
attached to phospholipids within the membrane
they are important for cell recognition
glycoproteins- composed of carbs and protein
these are on the outer surface of the membrane and are important in cell rec, sometimes act as antigens
cholesterol
decreases permeability and increases the stability of the membrane by restricting movement of other molecules
diff types of cells have diff amount of cholesterol
causes fatty acid chains to pack close together, reducing permeability and increases stability of membrane
factor effecting permeability
ph- denatured enzymes creating holes in the membrane which makes it more permeable
temp- denatured proteins creating holes in the membrane making it more permeable
fatty acid tails become less rigid and more moment which increases permeability
ethanol- breaks down lipids ad they are soluble in it (dish soap is same)
diffusion rate (fricks law)
diffusion rate= (SA× conc gradient)/ diffusion distance or pathway
simple diffusion
passive process
when there are an equal no of molecules on either side (equilibrium) there is no more net movement
only allowance non polar small and lipid soluble molecules
Diffusion is the net movement of particals from a higher to lower concentration until evenly distributed
factors affecting rate of diffusion
temp- increase k energy faster movement of molecules causing faster rate of diffusion
SA- more cell surface membrane to pass through so faster diffusion e.g. Alveoli
Conc gradient- and conc gradient increases rate of diffusion is faster
diffusion Distance- thinner surface/Distance the faster the rate of diffusion (cause it need less energy?)
facilitated diffusion
proteins help molecules pass through membrane down comc gradient
polar molecules can’t pass between tails of bilayer as they are non polar and repel polar
so they move in through channel or carrier proteins
these have specific tertiary structures and only transport molecules with comp shapes to their binding sites
it is passive
still from higher to lower conc
Osmosis
Net movement of water molecules from a higher Water potential to a lower water potential across a partially permeable membrane
water is polar so uses aquaporin to move down water potential gradient
Water potential
pressure exerted by water molecules colliding with things
measure in KPa
more free moving water molecules higher wa p
pure water every molecule is free moving so it has the highest wa P possible so it has a value of 0
adding solute makes it more negative as water is a dipole and attract charges on molecules causing no of free loving water molecules to decrease
water moves down conc form high to low Wa P so from more to less free water molecules
hypotonic- solution has higher Wa P than cell so water moves into cell causing it to swell
Hypertonic- solution has a lower Wa P so water moves out of cell into solution causing it to shrink
Isotonic- same Wa P inside and outside of cell so no net movement of water
Active transport
transport of membranes against their conc gradient, from a low to high conc
only uses carrier proteins with specific tertiary structures and comp binding sites
requires ATP
energy produces from its hydrolysis cause carrier proteins to change shape and push the molecule through the membrane into an area of higher conc
co transport
co transporters are a type of carrier protein, bind to 2 molecules at a time
conc gradient of 1 molecule is used to move the other against its own conc gradient
e.g. glucose plus A acid absorption
Identifying self vs non self
each type of cell has a specific molecule on its cell surface membranevthat help to identify it
allows immune system to identify self and non self molecules- antigens
these come from pathogens, cells from other organism of the same species, abnormal body cells and toxins
antigen
An antigen is a foreign molecule- usually a protein- that stimulates an immune response that results in the production of a specific antibody
they have a specific shape and tertiary structure that is complimentary to an antibody or receptor of an immune cell
if not recognized bu immune system then it will be treated as non self and immune response will initiate
glycolipids and glycoproteins act as antigens
non specific immune response
phagocytes-
A group of white blood cells which can distinguish via receptors on their cell surface between cells that display self antigens and which don’t
e.g Neutrophils (most common type)
they will destroy any cell with non self antigen in phagocytosis
phagocytosis-
1) early in infection phagocytes move to site and engulf pathogen, forming a vesicles called a phagosome
2) phagocytes contain many lysosomes which fuse to phagosome
3)hydrolytic enzymes called lysozymes destroy pathogen, debris realised by exocytosis
antigen presentation
phagocytes also play key role as antigen presenting cells
after phagocytosis the display part of pathogen (antigen) on cell membrane
allows for the activation of other immune cells e.g T and B cells which can mount a specific immune response to help remove pathogen more efficiently.these have specific receptors complimentary shape to antigen presented
Specific immune response
involves immune cells becoming activated in response to presence of specific antigen, large amounts of specific immune cells are produced to provide Large response, typically removing entire pathogen and creating immunity as memory cells are produced so large and faster response when reinfected
split into
Cellular response- involves cells
humorless response- produces antibodies
these can be activated either by antigen directly via receptors on surface or indirectly via antigen presentation
The cellular response
antigen presentation initiates the cellular response
1)T helper cells have a receptor which is comp in shape to a specific antigen
2)upon binding T helper cell becomes activated and divide by mitosis to create many clones
3) also release cytokines-chem messengers- affects
stim B cells to divide my mitosis
stim phagocytes- phagocytosis
stim cytotoxic T cell- contain receptors which bind to antigens on surface of virally infected or cancer cells, upon binding release performing which makes holes in cell membrane leads to apologise and being destroyed
4)once activated some helper T cells become memory cells and stay in blood helping for faster immune response on re infection
The humoral response
involves antibodies
B cells can be stimed directly by antigen binding to receptors on their surface or indirectly by release of cytokines from T helper cells
upon stim they divide by mitosis to produce clones
some differentiate into plasma cells which produce and release large quantities of monoclonal antibodies secrete into the blood
this is primary response
some B cells became memory cells, which persist in blood (years) and help mount a father immune response on reinfection
antibody structure and function
monoclonal antibodies have some Tertiary structure produced by intentional or cloned plasma cells
they are an example of quaternary protein 4 polypeptide chains( 2 heavy 2 light) are joined by disulphate bridges. Form a Y shape
each antibody will have specific tertiary structure with 2 antigen binding sites that are comp to only 1 antigen
function- binds to antigen via binding site form antigen antibody complex, due to the 2 antigen binding sites allowing antibodies to bind to antigens and clump them together-agglutination. This marks the antigen and helps attract phagocytes to infection, leads to destruction via phagocytosis
HIV structure
human immunodeficiency virus
Causes acquired immune deficiency symdrome
like all viruses it is A cellular-no cell surface membrane and can’t rep independently. key features:
RNA genome
Reverse transcriptase allows production of a copy of DNA from viral RNA called Reverse transcription
Genome surrounded by protein coat called Capsid
lipid envelope contains attachment proteins enable virus to specifically bind to and infect T helper cells
HIV replication
Attachment proteins on HIV bind to specific receptors on T helper cells
viral RNA and reverse transcriptase enter cell
reverse transcrpitase converts RNA to DNA using host nucleotides, reverse transaction
Viral DNA into nucleus and is inserted into host cell genome (DNA)person is now infected
transcription of HIV DNA into HIV mRNA which translated to produce HIV proteins
Infected T helper cells starts to assemble new virus particals
virus paritcald are released from the T helper cells
over time this leads to a reduction in the no of T helper cells and is the driving force behind AIDS
AIDS
by replicating using body’s T helper cells HIV reduces an individuals ability to respond to pathogens as cell mediated response and humoral response is compromised as overtime no of T cells decrease as the are destroyed by infection
HIV doesn’t kill directly but by reducing no of T cells it leave people vulnerable to secondary diseases, this is why HIV leads to AIDS
Many AIDS suffers develop infections of lungs intestines or brains and eyes also experience weight loss and diarrhea.Also develop rare cancers that would normally be destroyed
uninfected have 800- 1200 T cells per mm³ of blood but someone with AIDS has as few as 200
AIDs can be screened for by checking no of T helper cells or by using ELISAs to measure conc of HIV antibodies
How do antibiotics work
work by preventing bacteria for synthesising murein cell walls or by directly damaging the cell wall, leads to bacteria being destroyed as they are susceptible to osmotic damage
some also inhibit binary fission by preventing DNA rep and protein synthesis
as viruses have capsids rather than a marine cell wall they don’t work for them also because viruses spend most of the time within host cell they are also out of reach of antibiotics
Vaccines
Dead or weakened or specfic antigen (attenuated) form of the pathogen that stimulates an immune response
typically infected intramuscularly contains antigen but never live form of pathogen
Covid 19 vaccine contained mRNA used by ribsomes to make spike protein( antigen) used by SARS-COV-2 to attach and infect lung cells
vaccines- secondary and primary response
both cellular and humoral response start after taking it.Focus on humoral, stim of B cells lead to differentiation into plasma cells + production of small no of antibodies
Memory cells also produced and upon actual infection memory cells will coordinate secondary response producing higher conc of antibodies and faster
can also replicate sec response by 2 or 3rd vaccine/ booster
Herd immunity
High rate of immunization
unvaccinated individual are also protected
as vaccinated recover from infection quickly and so are less likely to spread the pathogen to unvaccinated
Antigen variability
natural selection selects for pathogens that can vary their antigens and evade detection due to this
these random mutations mean T cells and antibodies aren’t complimentary to antigen anymore
viruses are experts at this on reason flu vaccine updates every year
vaccine ethics and evaluation
side effects
new vaccines developed and tested using animals and cell cultures, may show positive effects here but doesn’t mean they will have same + effect in humans- Common limitation
Harm may occur to animals during vaccine research, can be argue that it’s okay as it stops human suffering and allows drug development
If it causes lots of harm to animals the Vet would stop the experiment to minimize suffering, could be repeated at lower conc to reduce side effects
Active immunity
ones body producing antibodies and memory cells upon antigen exposure.
primary response is slower and it can take days to build up high enough conc to destroy pathogen,
due to memory cells u get long term immunity
natural- infection
artificial- vaccine
Passive immunity
pre-made antibodies are recieved from elsewhere
rapid acting and quickly destroys the antigen being targeted
your body doesn’t produce antibodies so no memory cells
only short term protection
natural- maternal antibodies from breast milk
artificial- monoclonal antibodies (antivenom/antiserum)
uses of monoclonal antibodies
have same tertiary structure produced by identical or cloned plasma cells
can also be made in lab
artificial antibodies can be used target therapeutic drugs as the antibody is specific to 1 antigen
drug is attached to antibody
can also be used as medical diagnosis in ELISA tests
ethics of monoclonal antibodies
side effects
cost
animal welfare
potential limited effectiveness in humans
often produced by introducing tumour to mice which are genetically engineered to produce large quantities of monoclonal antibodies
ELISA tests
Enzyme-linked immune system assay
These tests use monoclonal antibodies to detect a specific antigen in a sample
M antibodies are fixed to bottom of test well
A sample potentially containg antigen is added to well and will Bind to antigen binding site on antibody due to comp shape
well is washed to remove unbound
second monoclonal antibody is now added which is attached to enzyme will bring to another part of the antigen if it is present
well washed again so unbound washed away
last substrate is added and the enzyme on 2nd m antibody will convert this to coloured product
colour change= + result and confirms antigen presence
