CELLS Flashcards
What are all of the eukaryotic cells you need to know?
animals plant fungal algal
what are the three parts of the nucleus?
nucleus: nucleolus, nuclear envelope, nuclear pores
What is found in a plant cell’s wall? What does it allow?
Plasmodesmata, channels for exchanging substances between adjacent cells
what can algal cells be that plant cells can’t be?
Algal cells can be unicellular (chlorella) or multicellular (seaweed)
What don’t all plant cells contain?
they don’t all contain chloroplasts
How can chloroplasts sometimes appear in algal cells?
As one large chloroplast instead of several smaller ones
How are fungal and algal cells similar?
fungal cells can also be multicellular (mushrooms) or unicellular (yeast)
What is the cell wall made up of in algal cells?
cellulose
What is the cell wall made up of in fungal cells?
chitin cell wall
What is the cell wall made up of in plant cells?
cellulose cell wall
What surrounds animal cells?
Cell-surface plasma membrane
function of cell-surface membrane
regulates movement of substances in and out of cell, has receptor
molecules on it allowing it to respond to chemicals like hormones
function of nucleus
control’s cell’s activities by controlling the transcription of DNA, pores allow substances to move between the cytoplasm and the nucleus, THE NUCLEOLUS MAKES RIBOSOMES
what is the nuclear envelope
double membrane which contains pores
function of mitochondria
site of aerobic respiration provide ATP, thus provides a source of energy, they are found in high numbers in cells that are very active and require a lot of energy e.g. muscle cells
structure of mitochondria
oval-shaped, double membrane, inner is folded to form structures called cristae, inside is the matrix which contains enzymes involved in respiration
function of chloroplasts
site of photosynthesis, found in algal and plant cells, LDR occurs in the thylakoid membranes, LIR occurs in the stroma
function of golgi apparatus
modifies and packages new lipids and proteins, also makes lysosomes
vesicles often seen at edges of the fluid filled, membrane bound sacs
structure of chloroplasts
double membrane, also contains thylakoid membranes which can be stacked to form grana in some parts of the chloroplast, the grana can be linked together by lamellae, which are thin flat pieces of thylakoid membrane
function of golgi vesicle
proteins/lipids packaged into golgi vesicles and they then transport them by moving towards the membranes and fusing with them releasing contents to target area/ exocytosis
stores lipids/proteins, transports them out of the cell via the cell-surface membrane
function of lysosomes
contains digestive enzymes, lysozymes, they are kept separate from the cytoplasm by the surrounding membrane and can be used to digest invading cells (phagocytosis) or can be used to breakdown worn out components of the cell
function of ribosomes
protein synthesis, found floating free in cytoplasm, prokaryotic ribosomes are smaller than eukaryotic
RIBOSOMES ARE MADE UP OF PROTEINS AND RNA (rRNA)
function of RER
The RER’s surface is covered witg ribosomes
folds and processes proteins that have been made at the ribosomes
functions of SER
no ribosomes,
synthesises and processes lipids
function of cell wall
provides structural support for the cell, prevents cell from changing shape, it is a rigid structure that surrounds plant/algal/fungal cells
function of cell vacuole
helps to maintain pressure inside the cell and keep the cell rigid, stops the plant wilting, involved in the isolation of unwanted chemicals inside the cell
structure of the cell vacuole
membrane that surrounds vacuole is called the tonoplast, it’s a membrane-bound organelle, it contains cell sap which is a weak solution of sugar + salts
what do prokaryotic cells not contain that eukaryotes do?
membrane-bound organelles
what is a cell wall made of in a prokaryotic cell?
murein cell walls
what is murein?
A glycoprotein, found in prokaryotic cell walls, a glycoprotein is a protein with a carb attached
NOT ALL PROKARYOTES HAVE A…
flagellum
feature of all porkaryotic cells that are not features of eukaryotic cells
DNA is not associated w/ histones, whereas eukaryotic they are
circular loop of DNA
DNA free in cytoplasm
No membrane-bound organelles
Murein/peptidoglycan in cell wall
what is the slime capsule’s function?
to protect the bacteria from attack by cells of the immune system
Binary fission:
circular DNA and plasmids replicate
cell gets bigger and DNA moves to opposite poles of the cell
cytoplasm begins to divide
new cell walls begin to form
cytoplasm divides and two new daughter cells produced, each have a copy of the circular DNA and varied numbers of copies of the plasmids
What are viruses?
ACELLULAR
just nucleic acids surrounded by protein
No cell-surface membrane, no cytoplasm, no ribosomes.
Strucutre of virus
Capsid - protein coat which protects genetic material
Attachment proteins which bind to receptors on a cell
They contain nucleic acids/genetic material which codes for viral proteins
Why are virsuses classed as acellular/non-living?
No cell-surface membrane
Not made of cells
Have no metabolism/no metabolic reactions
Cannot independently move/respire/replicate/excrete
Have no nutrition
How does a virus replicate once already inside the cell?
RNA converted into DNA using reverse transcriptase
DNA inserted into helper T cell’s/or other cell’s nucleus/DNA
DNA transcribed into viral/HIV mRNA
HIV mRNA translated into new HIV/viral proteins
How do viruses bind to host cells?
They use their attachment proteins to bind to the complementary receptor proteins on the cell-surface membrane of a host cell
Why can some viruses only infect one type of cell?
Their attachment proteins are only specific to the receptor proteins found on the cell-surface membrane of one type of cell
How does HIV replicate that is slightly different to other viruses?
HIV releases its capsid into the host cell as well as its genetic material
Conversion used in magnification calculations:
x 1000 x 1000
Mm –> Um –> Nm
/ 1000 /1000
What is resolution?
The ability of a microscope to be able to distinguish between two objects that are close together
If a microscope cannot distinguish between two objects then increasing the mag won’t help
A microscope cannot distinguish between objects that are smaller than its max. resolution
Tell me about optical microscopes:
Use light to form an image
Max resolution of about 0.2um
Can’t use opticals to view organelles smaller than that e.g. ribosomes, endoplasmic reticulum, lysosomes.
Possibly make out mitochondria
max mag = x1500
Electron microscopes:
Use electrons to form an image
Higher reso than optical
more detailed images
max reso. 0.0002um
max useful mag. x1 500 000
Produce black and white images, often coloured by a computer
TEMS
use electromagnets to focus beams of electrons, which is then transmitted through the specimen
Denser parts absorb more electrons - look darker on image
TEMS give high resolution images
can see internal structures of organelles
Need to view specimen in a vacuum - so cannot look at living organisms
Only used on thin specimens
SEMS
Scan a beam of electrons across the specimen
Knocks off electrons from the specimen which are gathered in the cathode ray tube to form an image
Images show the surface of the specimen and can be 3D
Can be used on thick specimens
Give lower resolution images than TEMS
Can only be used on non-living specimens
Differences between optical microscope and TEM
TEM CANNOT produce coloured images (optical CAN), highER/greatER resolution, however only on non-living/dehydrated organisms and specimen has to be thinNER (contrast)
TEM focuses a beam of electrons onto the specimen using electromagnets whereas optical uses light and uses lenses to focus to form an image
Denser parts absorb more elctrons, appear darker on image
How do you prepare a microscope slide?
Done using a temporary/wet mount where the specimen is suspended in a drop of liquid e.g. water/oil
Pipette a small drop of water onto the centre of the slide
Use tweezers to place thin section of your specimen on top of water droplet
Add a drop of stain
Add cover slip, stand slip upright on the slide next to the droplet, carefully tilt and lower it so it covers the specimen, avoid air bubbles as they’ll obstruct view of specimen.
artefacts
not part of the specimen
usually created during the preparation of a specimen, dust air bubbles fingerprints, obstruct view of specimen, innacucuracies caused by squashing/staining sample
How to make a temporary mount of plant tissue to identify position of starch grains:
Add a drop of water oj the glass slide
Obtain a thin section and place onto a glass slid, float on a drop of water
Stain with iodine dissolved in potassium iodide solution in order to identify the starch
Lower the cover slip slowly onto the specimen using a mounted needle and squash
What stains can you use in the preparation of a microscope slide?
Iodine in potassium iodide to stian starch
Eosin used to make cytoplasms show up
Why do you need to squash the sample on a microscope slide?
In order to spread out the cells, evenly distributed on the slide, in order to allow light to pass through to the specimen can be seen properly/clearly
Order of organelle separation during ultracentrifugation:
Nucleus (chloroplasts) mitochondria, lysosomes, endoplasmic reticulum, ribosomes
Isotonic, buffer, ice cold
no osmotic effect/prevent lysis/bursting of organelle
keeps pH constant so it doesn’t denature any enzymes
prevent any enzyme activity so the organelles are not broken down
why do we filter during cell fractionation?
remove cell debris or tissue debris such as connective tissue from the organelles
What does the cell cycle consist of?
A period of cell growth and DNA replication called interphase
And a period of cell division called mitosis
three stages of interphase
gap phase 1 - cell grows + new organelles and proteins made
Synthesis - DNA replication, ready to divide by mitosis
gap phase 2 - cell keeps growing and proteins needed for cell division made
then mitosis
What happens during interphase
DNA unravels and replicated as well as organelles being replicated and ATP CONTENT IS INCREASED
Mitsosis - INPROMEANTE
I - DNA (unravelled)/organelle replication
N - ATP content increased
P - DNA condenses
R - Centrioles move to opposite poles of the cell
O - Nuclear envelope breaks down, chromosomes free in cytoplasm
M - Chromosomes line up at equator of cell
E - Spindle attaches to the centromere
A - Centromeres divide
N - Spindles contract, get shorter pulling sister chromatids to opposite poles - V shaped
T - Cytokinesis finishes off in telophase (started in anaphase)
E - Chromatids uncoil/unwind once at pole, become long and thin and called chromosomes again
TWO GENETICALLY IDENTICAL DAUGHTER CELLS
What change to environmental conditions can increase the growth rate of the cells?
Increase temp –> increased enzyme activity
Increase glucose/O2 –> increased respiration
Increased conc of phosphate –> Increased ATP/DNA/RNA
Increased conc of nucleotides –> Increased DNA synthesis
If you’re using ethano-orcein as stain when preparing a root tip cell squash, what do you need to do before cutting 1cm from the tip?
Fix the tip in ethanoic acid
What do the objective and ocular lenses do?
Magnify the specimen
what is mitotic index?
number of cells with visible chromosomes / total number of cells observed
If using Feulgen stain, what will you need?
An extra rinse, rinse thoroughly
Why don’t you smear the cover slip sideways?
You’ll damage/break the chromosomes
what two pieces of the microscope help you to calculate the actual size of a cell?
eyepiece graticule
stage micrometer
Membrane structure - fluid mosaic model
Consists of lipids (mainly phospholipids) proteins and carbs
Fluid mosaic - phospholipid bilayer, cholesterol, glycoproteins, channel/carrier proteins/ proteins layer outside the bilayer, fluid mosaic is ‘dotted’
Glycolipids
Why is it called fluid mosaic model?
Fluid bilayer as the phospholipids are constantly moving
Proteins are scattered through the bilayer like tiles in a mosaic, e.g. channel, carrier, receptor proteins that detect chemicals released from other cells e.g. insulin binds to receptor proteins on liver cells –> absorb more glucose
glycoproteins?
proteins with a carbohydrate attached
glycolipids
lipid with a carb attached
what does the phospholipid bilayer not allow
water soluble substances (e.g. ions and polar molecules) to diffuse through, acts as barrier as it has a hydrophobic centre (of hydrophobic tails)
Why can water diffuse through the phospholipid bilayer even through it is polar?
Because it is so small so it can easily diffuse by osmosis
what is the purpose of cholesterol
gives the membrane stability
what is cholesterol
a lipid
where is cholesterol not present?
bacterial cell membrane
Describe what cholesterol does?
fits between phospohlipids, it binds to the hydrophobic tails causing them to pack much more closely together, restricts the movement of the phospholipids, makes membrane less fluid and more rigid, it helps to maintain the shape of animal cells as they do not have cell walls, and supports cells that aren’t supported by other cells e.g. RBC
It also has hydrophobic regions so is able to create a further barrier to polar substances
Temp below 0 degrees C –> effect on membranes
phospholipids don’t have much energy, can’t move much, packed closely together, rigid membrane, channel + carrier proteins in the membrane denature thus increasing the permeability of the membrane, ice crystals may form and pierce the membrane making it highly permeable when it thaws
Temps between 0-45 –> effect on membranes
phospholipids can move around, not so tightly packed together, membrane is partially permeable, as temp increases the phospholipids move more as they have more kinetic energy –> increases the permeability of the membrane
Temps above 45 –> effect on membranes
phospholipid bilayer starts to melt/breakdown and the membrane becomes more permeable, water inside cell expands putting pressure on the membrane, channel + carrier proteins in the membrane denature so cannot control what enters/leaves –> increases permeability
what filter do you need to use for a colorimeter when testing the temp on membrane permeability?
blue filter or wavelength of 470nm
higher the absorbance reading =
greater amount of pigment released –> higher permeability of membrane
describe the investigation of solvent concs on membrane permeability
surrounding cells in increasing solvents concs increases membrane permability because the solvent dissolves the lipids in the cell membrane causing it to lose its strucutre
e.g. solvents include acetone or alcohol
5 ways substances can move across the cell-surface membrane into a cell:
simple diffusion, small non-polar molecules can diffuse down conc grad
osmosis, diffusion of water down a water potential grad
co-transport of 2 different substances using a carrier protein
active transport via a protein carrier with the use ATP aganst a conc grad
facilitated diffusion polar/larger molecule uses a channel/carrier protein to move down its conc grad
diffusion
highER to lowER conc
molecules move both ways but the NET movement is from hER –> lER
What two proteins are involved in facilitated diffusion?
channel and carrier proteins
what particles go through cell membranes via facilitated diffusion?
large or charged particles
what is a passive process?
one that doesn’t use energy e.g. diffusion or facilitated diffusion
what are carrier and channel proteins called?
transport proteins
how do carrier proteins work?
they move large molecules across the membrane
down conc grad
1) a large molecule attaches to a carrier protein
2) then the protein changes shape
3) this releases the molecule onto the opposite side of the membrane
how channel proteins work?
they form pores in the membrane for charged particles to diffuse through and go down conc grad
3 factors affecting diffusion?
surface area
thickness of the exchange surface - diffusion distance/pathway
the conc grad, the higher it is, the faster the diffusion
2 factors affecting facilitated diffusion?
Number of channel/carrier proteins
the concentration gradient, higher it is the faster the facilitated diffusion occurs
Water through cell membranes of collecting duct and DCT via aquaporins?
facilitated diffusion, aquaporins are special channel proteins
simple compared to facilitated diffusion?
simple occurs at a much slower rate
definition of water potential?
the potential of water molecules to diffuse out of or into a solution
water potential of any solution is … because?
negative because WP of pure water is always zero
adding solutes in lowers the WP
hypo hyper
water moves in swell
water moves out shrink
hand movement forming O
serial dilution
when you create a set of solutions that decrease in conc by the same factor each time
how do you determine the water potential of potato cell?
using a calibration curve
plot percentage change in mass (y) against conc of sucros solution (x)
find the point where the calibration curve crosses the x-axis (where the % change in mass is 0) this is the point when WP of sucrose solution = WP of potato cells
Check which concnetration of sucrose solution this is and look up in textbook the WP of this concentration of sucrose solution
water potential usual measurements?
kPa
what is visking tubing?
a partially permeable membrane - used a lot in osmosis + diffusion experiments
1M =
1000mM
what two proteins are involved in active transport?
carrier and co-transport
two differences two similarities between active transport and facilitated diffusion:
both transport molecules across membranes
both use carrier proteins
active transport uses ATP and usually goes against conc grad, FD doesn’t
what are co-transporters?
a type of carrier protein
used in active transport
how do co-transporters work?
the conc grad of one molecule is used to move the other molecule against its own conc grad
where is glucose co-transported?
glucose needs to move into the blood. firstly, glucose moves via co-transport with Na+ into the epithelial cell from the ileum and then moves by facilitated diffusion into the blood
Describe the co-transport of glucose using sodium ions?
Sodium ions are actively transported out of the epithelial cells into the blood to create a sodium ion conc grad
Thus the conc of Na+ is lower in the epithelial cell compared to the ileum’s lumen
Then the co-transporter carries glucose into the epithelial cell along with Na+ down the conc grad
Then glucose can move via facilitated diffusion (carrier or channel protein) into the blood from the epithelial cell
rate of active transport affected by what?
speed of individual carrier proteins - the faster they work = faster rate
number of carrier proteins present
rate of respiration thus the rate of ATP porduction and the availability of ATP –> if resp is inhibited then active transport cannot take place
definition of an antigen (2 marks)
foreign protein
stimulates an immune response/stimulates production of an antibody
definition of an antibody (2 marks)
quarternary protein/immunoglobulin that is specific to an antigen
secreted by plasma cells/produced by B cells
4 things that antigens allow the immune system to identify:
abnormal body cells
cells from another organism of the same species
toxins
pathogens
what do t cells have on their surface?
receptor proteins
what do the receptor proteins found on the surface of t cells bind to?
complementary antigens presented to it by phagocytes which are antigen-presenting cells
THIS ACTIVATES THE T CELL
What do t cells do ocne activated by an antigen?
they release chemical signals which activate cytotoxic t cells (killer t cells) which abnormal and foreign cells
and they activate b cells which produce antibodies
what do b cells have on their surface?
receptor proteins that bind to the signalling molecules released by helper t cells
what else activates a b cell, apart from the helper t cell releasing chemical signals which bind to the b cell’s receptor proteins?
when an antibody on the surface of the b cell binds to a complementary antigen forming an antigen-antibody complex - this activates the b cell and the process is called clonal selection as the activated b cells divide rapidly by mitosis to form plasma cells (which will secrete antibodies specific to that antigen)
why do b cells divide by mitosis?
so that all of the plasma cells produced are clones and they are genetically identical so they all produce identical (monoclonal) antibodies which are specific to the antigen
antibody can bind to more than one antigen at same time, pathogens become clumped together –>
agglutination
how can agglutination occur?
antibodies have two binding sites so can bind to two antigens (pathogens) at the same time
what does agglutination lead to?
phagocytes can then phagocytose multiple pathogens at once
structure of antibody
specificty of antibody relies on variable region (has its own specific 3D tertiary strucutre) which is where the antigens bind
every antibody has the same constant region – allows the rapid production of specific antibodies
look over antibody structure
pg 120
cellular response
cells that the pathogens interact with e.g. phagocytes and T-H cells
humoral response
b cells, clonal selection, production of monoclonal antibodies
primary immune response
slow
antigen enters body for first time
symtoms occur
after exposure, both t and b cells produce memory cells which remain in blood for a long time
role of memory t cells
t cells –> remember specific antigen and will recognise it thus the second-time around the memory t cells are activated and divide into the correct type of t cells to kill the cell carrying the antigen
role of memory b cells
b cells –> the record the specific antibodies needed to bind to the antigen
When the b cells come into contact a second time around clonal selection happens faster and the memory b cells are activated and divide into the plasma cells that produce the right antibody to the antigen
difference between active and passive immunity?
Active involves production of antibodies by plasma/B cells, passive doesn’t
Active is slower as it can take time to develop whereas passive is fast acting
Passive is short term as the antibody is broken down whereas active is long term because antibody produced in response to antigen –> memory cells
Passive involves antibody introduced into body from an outside/external source
active immunity
immune system makes antinodues after being stimulated by antigens
Natural –> catch a disease and become immune
Artificial –> vaccinations (containing the antigen from the pathogen) then immune
passive immunity
given antibodies made by another organism - immune system doesn’t produce any antibodies of its own
Natural –> baby becomes immune due to antibodies it receives from its mother through placenta and breast milk
Artificial –> when you become immune after injected with antibodies from someone else
attenuated viruses?
have usually been genetically/chemically modified so that they can’t produce toxins or attach to and infect host cells
herd immunity
those not vaccinated are less likely to catch the disease because there are fewer people to catch it from (those that have had their vaccinations)
antigenic variation?
pathogen can change their surface antigens
strains of a virus are…
immunologically distinct
monoclonal antibodies?
antibodies produced from a single group of genetically identical b/plasma cells so they all identical in structure
EQ what is a monoclonal antibody?
antibodies that have the same specific 3D tertiary strucutre and they are secreted from identical plasma cells/b cells
example of medical treatments that monoclonal antibodies are used in?
tagets/binds/carries used to deliver medicines/drugs to specific cells/antigens
Blocks antigens/receptors on cells
cancer cells antigens
tumour markers
why is using antibodies to deliver anti-cancer drugs good?
anti-cancer drugs are toxic chemicals that kill cells and cause side effects because they also kill normal body cells, using antibodies you can target the drugs to specific cells e.g. cancerous to reduce the number of normal body cells killled and reduce side effects
when can ELISA be used and what can it be used for?
can be used to see if a patient has any antibodies to a specific antigen or any antigens to a specific antibody
used in medical diagnosis to tes for pathogenic infections, for allergies
ELISA
enzyme-linked immunosorbent assay
when do people with HIV develop AIDS?
When no. of helper t cells in body reaches a critically low level
latency period?
the infected person (with HIV) won’t experience any symptoms as the HIV replication drops to a lower level after the person experiences severe flu-like symptoms
How does HIV replicate?
the attachment protein attaches to receptor molecules found on the cell membrane surface of host helper t cells
capsid is released into the cell where it uncoats and releases the genetic material into the cell’s cytoplasm
reverse transcriptase is used to make a complementary strand of DNA from the viral RNA template
then double stranded DNA is made and inserted into the human DNA
viral DNA then transcribed into HIV mRNA ready to be translated into viral proteins
host cell enzymes are used to make viral proteins from the viral DNA (which has been inserted into the human DNA)
the viral proteins are assembled into the new viruses which ruptures and kills the helper t cell and are then released to go on and infect other cells
How do antibiotics kill bacteria?
by interfering with their metabolic reactions
what do antibiotics target in bacteria in order to kill them?
they target the bacterial enzymes and ribosomes used in metabolic reactions
how are antibiotics only designed to target bacterial cells and not our own cells?
because bacterial enzymes and ribosomes are different to human ones so antiniotics are only designed to target the bacterial ones so that they don’t damage human cells
Why can’t antibiotics target viruses?
because viruses don’t have their own enzymes and ribosomes, as they use the host cell’s
so because antibiotics don’t target human enzymes and ribosomes, they cannot inhibit viral replication as viruses use human enzymes and ribosomes
what are antiviral drugs used to target?
designed to target the few virus-specific enzymes e.g. reverse transcriptase which HIV uses and human cells don’t
HIV is what type of virus and thus what is HIV antiviral therapy known as?
HIV is a retrovirus so it is known as antiretroviral therapy
what are antiviral drugs used to do in order to help hiv patients?
they slow down the development of aids from hiv
how can HIV spread?
hiv positive mother to baby
unprotected sex
through infected bodily fluids, blood from sharing contaminated needle
before baby is 18 months old testing for HIV can be inaccurate, why?
baby can have antibodies for HIV passed on from mother, passive immunity natural, so they have the antibodies but not because they have been infected
