3.2 Cells Flashcards
what is a prokaryotic cell? give examples (3)
an organism whose cell generally lacks a true nucleus and no membrane bound organelles e.g bacteria, archaea
what is eukaryotic cell? give examples (3)
organism that possesses a membrane bound nucleus e.g plant and animal cells
how are prokaryotic cells made?
by binary fission?
how are eukaryotic cells made?
by mitosis or meiosis
name the organelle for the following letters
A= mitochondria
B= Golgi Apparatus
C= cytoplasm
F= nucleus membrane
G= Cell membrane (cell plasma)
D= nucleolous
E= nucleus
H= Rough Endoplasmic recticulum
I= centrioles
J= smooth endoplasmic reticulum
K= vessicle
L=ribosomes
no label (TLC)= lysosome
no label (BRC)= free ribosomes
name the organelle for the following letters
A. Cell Wall | B. Cell Membrane | C. Golgi Apparatus | D. Chloroplasts | E. Vacuole | AB. Mitochondria | AC. Cytoplasm AD. Ribosome | AE. Smooth Endoplasmic Reticulum | BD. Nucleolus | BC. Chromosomes | BE. Rough ER
what is the Golgi body and what does it do? (5)
the Golgi body is made up of golgi apparatus and goli vesicles.
It is a system of membranes forming flattened sacs (called cisternae)
It is responsible for forming lysosomes, glycoproteins and enzymes as well as transporting, modifying and storing lipids
modified proteins and lipids are then transported around or out of the cell in the golgi vesicles
what is the cell surface membrane and what does it do?
the cell surface membrane is formed by a double layer of phospholipids
responsible for cell recognition, communicstion and entry and exist of substances
what are mitochondria and what does it do?
referred to as the powerhouse of the cell,
surrounded by a double membrane folded into cristae to provide a large surface area for respiratory enzymed
also surrounded by a fluid called the matrix which contains enzymes, lipids, proteins, DNA and ribosomes
it is also the site of respiration and where ATP is produced
what are lysosomes and what do they do?
they are membrane bound sacs produced by the golgi
they contain digestive enzymes
they are used to digest foreign material that has been ingested by a phagocytic cell ( eg white blood cells)
they also release enzymes outside of the cell
and break down cells and organelles
what are ribosomes? and what do they do?
tiny organelle found in the cytoplasm or Rough endoplasmic reticulum
type 80S found in eukaryotes
type 70S found in the prokaryotes
site of protein synthesis
what is the nucleus and what does it do?
the brain/headquarters of the cell
controls protein synthesis
made up of the nuclear envelope, nuclear pores, nucleoplasm and nucleolus
nucleus is surrounded by a double membrane called the nuclear envelope which controls the entry and exist of substances via nuclear pores
the nucleoplasm contains chromatin and genetic information in the form of chromosomes
nucleolus is in the centre reponsible for making ribosomes and RNA
what is the rough and smooth endoplasmic reticulum and what does they do?
it is a system of membranes which form flattened sacs called cisternae,
some have surface ribosomes and is responsible for producing and transporting proteins (RER)
the other lacks ribosomes and is responsible for synthesising, storing and transpoting lipids and carbohydrates (SER)
what is the cell vacuole and what does it do?
it is a fluid filled sac
surrounded by a single membrane called a tonoplast,
found in plant cells.
provides support by making cells trugid and a food store
what are chloroplasts and what do they do?
they have a double membrane responsible for the entry and exist of materials
site of photosynthesis
within chloroplast are stacks of thykaloid membranes (called grana) which provide a large surface area, and are surrounded by matrix fluid and stoma
marix fluid and stoma contain starch grains and photosynthetic enzymes
chlorophyll is found in the thykaloid membranes and responsible for light absorption
what is the cell wall and what does it do?
it is made up of microfibrils of polysacchride,
also made up of cellulose which provides high tensile strenght and support for the plant
and made up of a middle lamella which cements adjacent walls together
prevents lysis (rupture of the cell membrane
it allows water to pass through
in algae cell wal can be from cellulose and/or glycoproteins & in fungi it is made from chitin
which organelles are involved in protein synthesis?
- Nucleus
- ribosomes
- RER
- golgi apparatus
- golgi vesicles
whta causes cells to become specialised?
- genes
- every diploid cell has an indenticqal set of genes but it is the switching on and off of particular genes that result in cell differentation
- the genes that are switched on, controls what proteins are produced and what role and fuchntion the cell will have.
what is meant by tissue? give examples of tissues for plant and animal
-a collection of similar cells which peform a specific function
animal= epithelial tissues: line the surface of organs and usually have a protective or secretory function
plant= xylem: made up of a number of similar cell types, it is used to transport water and mineral ions throughout the plant and also gives mechanical support.
give examples of a organ for a plant and animal
a combination of tissues that are coordinated to perform a variety of functions
animal= stomach made from muscle tissiue, epithelial tissue and connective tissue
plant= palisade mesophyll: made up of leaf palisade cells that carry out photosynthesis
spongy mesophyll: adapted for gaseous diffusion
eperdermis to protect the leaf and allow gaseous diffusion
phleom: transport organic materials away from the leaf
xylem: to transport water and ions into the leaf
why is artery described as an organ where as a blood capillary is not?
an artery is a combination of tissues that are coordinated to perform a function which is to to carry oxygenated blood away from the heart to the tissues (except for the pulmonary arteries)
what is meant by organ system?
organs that work together as a single unit
give examples of a organ system
- digestive system: digests and processes food. It is made up of organs that include the salivary glands, oesophagus, stomach, duodenum, ileum, pranceas and liver
- the respiratory system: is used for breathing and gas exchange. It is made up of organs such as the trachea, bronchi and lungs
what is the role of the capsule?
it protects bacterium from other cells and helps group of bateria stick together for protection
what is the role of the cell wall?
it is a physical barrier that exclude certain substances and protects against mechanical damage and lysis by osmosis
what is the role of cicular DNA?
it possesses the genetic information for the replication of bacterial cells
what is the role of the cell surface membrane?
it acts as a selectively permeable layer which controls the entry and exist of substances
what is the role of the plasmid?
it possessed genes that may aid the survival of bacteria e.g produce enzymes that can break down antibiotics
what are the properties of viruses?
- they are acellular and non living particles
- they are 20-300nm (much smaller than bacteria)
- they contain strands of DNA and RNA (but dont have a nuclues)
- they can only produce inside a living cell
- they are enclosed by a protein coat (A CAPSID) and sometimes a lipid envelope
- the attachment proteins on the capsule are used by the virus to identify and attach to a host cell
what is cell fractionation and what are the steps involved?
this is the process which is used to seperate organelles from the rest of the cell so it can be studied in a electron microscope.
the three steps that are involved are;
- homogenisation
- filtration
- ultracentrifugation
what happens in homogenisation and what conditions must there be for the process to occur?
- in homogenisation the plasma membrane is broken up releasing the organelles
- this can be done by virbating the cells or grinding in a blender
- this must occur in an ice cold, isotonic buffer solution
in homogenisation why must one of the conditions be ice cold?
to reduce enzyme activity
in homogenisation why must one of the conditions be isotonic?
to create same water potential which prevents water moving in and out of organelles distorting the shape. (prevents the osmosis effect)
in homogenisation why must one of the conditions be a buffered solution?
so the solution has a constant pH
in stage 2 of cell fractionation (Filtration) what happens?
a gauze is used to filter and remove unbroken cells or tissues as organelles are much smaller so pass through the gauze
in stage 3 of cell fractionation (ultracentriguation) what happens?
- the filtrate is centrifguged at a low speed to remove partially opened cells and small pieces of debris
- the supernatant containing the organelles is carefully decanted off for the next sample
- the sample is then centrifuged at 500-600 g for 5-10 mins, the supernatent is then decanted ready for the next round of centrifuging. at this stage the pellet may be enriched in nuclei
- the sample is centrifuged at 10 000-20 000 g for 15-20 mins then decanted again ready for the last round of centrifuging. at this stage the pellet may be enriched in mitochondria (or chloroplast from plants)
- the sample is centrifuged at 100 000 g for 60 minutes then decanted. at this stage the pellet may be enriched in ribosomes
-
what are the different types of microsopes?
- light microscope
- electron microscope
what is magnification and how is usually expressed?
it is the ratio of enlargement (or resolution) of an image (drawing or photomicrograph)
-it is usally expressed as x1/2, x1/0 x430, x1000
how do you calculate the magnification?
magnification= size of image/ actaul size of the object
- how many nanometers in a micrometer?
- how many micrometeres in a millimetre
- how many milimetres in a metre?
- how many metres in kilometre
- 1000 nanometres in a micrometer
- 1000 icrometre in a millimetre
- 1000 milimetre in a metre
- 1000 metres in a kilometre
what does resolution mean?
how well a microscope can distonguish between two seperate points that are close together
what resolution does a light microscope have and what magnification are they limited to and what by?
- a light microscope has a resolution of 0.2 micrometre and uses a beam of light with a relatively long wavelenght
- light microscopes are limited to a magnification of 1500 x by their resolving power (they have lower resolution)
for a light microscope object that are _____ micrometres or more apart can be seen _________, if objects are less than this they will be seen as ____ object
object that are 0.2 micrometres or more apart can be seen seperately, if objects are less than this they will be seen as one object
talk about TEM (transmission electron microscope)
- a beam of electrons is passed through the specimen
- the elctrons that passed through the specimen are detected on a flourecent screen on which the image is displayed
- ultrathin sections are needed for transmission electron microscopy, as elctrons have to pass through the specimen for the image to be produced
- this is the most common form of electron microscope
- it has the
talk about SEM (scanning electron microscope)
- pass a beam of electrons over the surface of the specimen in the form of a ‘scanning beam’
- Electrons are reflected of the surface of the specimen as it has been previously coated in heavy metals, and then focussed on a flourescent screen to make a visible image
- larger, larger thicker structures can thus be seen under the SEM, as the electrons do not have to pass through the sample in order to form the image
- this gives excellent 3-dimensional images of surface but the resolution is lower than that of the TEM
state the differences betwee Light microscopes and electron microscopes.
- Vacuum is not required for a light microscope whilst it is needed for an electron microscope
- the light microscope maintains the natural colour of the sample, whilst all images are black and white in an electron microscope
- light microscopes magnifies object only up to 2000 time whlist electron microscopes can magnify up to 500, 000 times
- in a light microscope, the specimens can be living or dead but in an electron microscope the specimens have to be dead, in a fixed plastic view in a vacuum
- A light microscope had a limites resolution 0.2 nanometres (200 nanometres whilst Transmission E-M has excellent resolution (about 1nm) so you can see the most minute cell details.
what does mitosis produce?
two genetically identical daughter cells which have the same amount of chromosomes as the parent cell
which cells in multicellular organisms do not retain the ability to divide?
- nerve cells
- brain cells
- liver cells
- kidney cells
- heart muscle cells
- egg cells
- sperm cells
why is mitosis important?
- replace cells during tissue repair
- increase cell number during growth
- reproduction in single celled organisms
what are stages in the cell cycle
- Interphase covers; Gap Phase 1, Synthesis, Gap Phase 2
- Mitosis
- Cytokinesis comes at the end
what happens in Gap phase 1 of the cell cycle in interphase?
the cells grows and new organelles and proteins are made
what happes in Synthesis of the cell cycle interphase?
cell replicates its DNA ready to divide by mitosis (so mass doubles)
what happens in Gap phase 2 of the cell cycle in interphase?
the cell keeps growing and proteins needed for cell devision are made
what process happens at the end of mitosis in the cell cycle?
-cytokinesis
this is where the cyoplasm of a cell divides in two to make the two genetically identical daughter cells
In the cell cycle there are points at which checks take place. State at which point the checks are at and what they check for
- Halfway through Gap phase 1= check to see if the cell is big enough or if the environment is suitable for mitosis
- at the end of Gap phase 2= check to see if there are errors in duplicated chromosomes making any needed repairs.
what are the four divisions of mitosis?
- prophase
- metaphase
- Anaphase
- Telophase
what are chromosomes made up of? and what is that middle of their structure?
- two sister chromatids
- centromere
what happens overall in interphase?
- the cell is actively sythesising
- the DNA is being replicated as well as organelles
- ATP content is increased (energy for division)
- chromosomes are not visibe
*DNA that is spread out in the this phase is called chromatin
what happens in prophase of mitosis?
- replicated chromsomes condense and become visible
- centrioles move to opposite poles of the cell
- spindle fibres are formed from the centrioles to create the spindle apparatus
- nuclear envelope (membrane) breaks down and nucleolus dissapears
- chromosomes lie free in the cytoplasm
what happens in metaphase of mitosis?
- the spindle apparatus has formed across the cell
- chromosomes (made up of two sister chromatids) line up along the equator and become attached to spindle fibres by their centromeres
what happens in anaphase of mitosis?
- the centromere divide, seperating each pair of sister chromatids
- the spindle contract, pulling chromatids to opposite poles of the cell, centromere first
- this process needs respiration from ATP
(*chromatids appear v shaped)
what happens in telophase of mitosis?
- the chromatids are now at opposite poles of the cell, they uncoil and become long and thin again ( wide spread chromatin), so they are now called chromosomes again
- a nuclear envelope forms around each group of chromosomes so there are two nuclei
- cytokinesis divides the cell into two genetically identical daughter cells
what is the advantage of chromatids not contracting independantly during prophase?
the chromosomes can later be pulled apart without getting tangled
why is it important that the chromatids remain attached at the centromere until prophase?
so that members of each pair are pulled to the opposite ends
what is an advantage of being genetically identical?
- cells are more likely to survive and reproduce (as they have already been successful at dividing)
- limited genetic variation. This means that if the environment changes, the individual may not have the genes necessary to survive in a new environment
describe the process of binary fission
- circular DNA replicates and each attaches to a cell membrane on the opposite sides of the cell
- plasmids replicate
- cell membrane grows between the two DNA molecules and divides cytoplasm (cytokinesis)
- New cell wall forms to make two identical daughter cells
- each daughter cell contains one copy of the original circular DNA and a variable number of plasmids
describe the process in which a virus replicates
- attach to a host cell via attachment proteins
- inject their nucleic acid into the host cell
- genetic information on the nucleic acid provides instructions for the host cell to synthesise viral components, nucleic acid, enzymes and stuctural proteins all which can be assembled into the new virus
what is cancer and what is it caused by?
- it is a disease caused by a growth disorder of cells
- it is the rapid and uncontrolled growth and division of cells
- as a result a group of abnormal cells will develop ( this is what you call a tumour )
what is mutation?
changes im the base sequence of an organisms DNA
which parts of the cell cycle are targeted by cancer treatment?
Gap phase 1 (cell growth and protein production)- some chemical drugs (chemotherapy) prevent the synthesis of enzymes need for DNa replication. If these arent produce the cell is unable to reach the synthesis phase, disrupting the cell cycle and forcing the cell to kill itself.
S Phase (DNA replication) radiation and some drugs damage DNA. In the cell cycle the cell is checked for damage to the DNA. If severe damage is detected the cell will kill itself -preventing further tumour growth
vincristine (cancer treatment drug type of vinca alkaloids) prevents spindle formation during mitosis. how will this drug affect the behaviour of chromosomes during mitosis?
- if the spindle fibres dont form then the attachment of the chromosomes can not occur.
- Therfore the centromere will not divide so the chromosomes will not seperate to form two chromatids
cytarabine (cancer treatment drug) inhibits an enzyme needed to synthesis new DNA. explain why this is an effective drug in treating cancer
-it means that in the S phase new DNA can not be synthesised so replication is less likely to take place, which means mitosis is affected and therefore slowing the formation of a new cancer.
how can you observe mitosis in a cell?
what is the eqaution for mitotic index?
mitotic index= number of cells with visible chromosomes/ total number of cells observed
how can you use a eyepiece and graticule to calculate the size of the cell?
actual size= size of image/ magnification
what are artefacts?
-
what is the role of cell surface membrane?
-control the entry and exit of substances out of the cell and organelles e.g
surface memrane of mitochondria controls the entry and exist of substances used for respiration
- isolate digestive enzymes e.g
the cell surface membranes isolate tne lysosomes in the golgi body that digest organelles and cells
-Seperate organelles from cytoplasm so metabolic reactions are contained e.g
cell surface mebrane of mitchondria
-provide an internal transport system e.g cell surface membrane for the golgi apparatus
what are phospholipids made up of? and how do they act as barrier to water soluble substancees
- phosopholipids have a head and a tail
- they are made up of two fatty acids (tail), glycerol and a phosphate group (head)
- head is hydrophllic (attracts water)
tail is hydrophillic (repells water)
- they arrange themselves into a bilayer
- they can act as a barrier because molecules automatically arrange themselves with heads facing outwards towards the water on either side of the membrane and tails facing inwards away from the water
- centre of the bilayer is hydrophobic so no water soluble substances is allowed through
what is the importance of the phospholipid bilayer?
- allows lipid soluble and non polar substances to enter or leave the cell
- hyrdophobic tail prevents water soluble and polar substances entering and leaving the cell
- makes membrane flexible
what are extrinsic proteins
-proteins that appear on the surface or partly embedded and act as support and as hormone receptors
what are instrinsic proteins?
- proteins that span the entire bilayer
- some are enzymes or protein carriers or channels for molecules that cannont diffuse directly through the bilayer such as those that are not lipid soluble or dissolved in water.
what are functions of proteins in the membrane?
- they provide structural support
- transportt water soluble substances through the membrane
- allow active transport through carrier proteins
- help cell adhere (stick) together
- act as receptor for homons or cell recognition
where do you find Cholesterol, what does it do?
- they are by the hydrophobic tail, so are repelled by water and therefore prevent water loss of dissolved ions from the cell.
- restricts movment of the phospholipid by binding to them which gives the membrane strenght
- therefore making the membrane less fluid and and more rigid.
what are glycoproteins?
- carbohydrate chain attached to extrinsic protein
- act as a recognition site for chemicals e.g hormones
what are glycolipids
carbohydrate chain attached to a lipid
-recognition site e.g cholera toxins
Why is the cell surface membrane described as a fluid mosaic model
- fluid because phospholipids are constantly moving giving a membrane a flexible structure
- mosaic because proteins are scattered through the bilayer like tiles in a mosaic
why will some substances not freely diffuse through the layer?
- because they’re too big to pass through channel proteins
- they are electrically charges so they are replled by fatty acid tails
- not lipid soluble
the protein content of a typical cell membrane is around 50%. In energy releasing organelles, such as mitochondria, the amount rises to around 75%. suggest a reason for the difference
- energy releasing organelles need more substances such as ATP to travel across their membrane
- therefore these substances will need more carrier proteins to help get across the membrane
a person removes some raspberries from the freezer that have frozen solid and leaves them on a plate to defrost. when he returns, there’s a red puddle on the plate around the fruit. Use your knowledge of membranes to explain what has happened.
- freezing the raspberries would have caused ice crystals to form and pierce the cell membranes
- this will make the membranes highly permeable when they became thawed
- which will then cause the red pigment to leak out of the raspberry
what is the fluid mosaic model?
a model to describe the arrangementof molecules in the membrane
why is the bilayer fluid in the fluid mosaic model?
it is fluid because individual phospholipid molecules can move relative to one another. this gives the membrane a flexible structure that is constantly changing in shape
why is the bilayer described as mosaic?
it is described as mosaic because the proteins that are embedded in the phospholipid bilayer cary in shape, size and pattern in the same way as the stones or tiles of a mosaic
what are glycoproteins and what do they do?
they are a branching carbohydrate portion of a protein which acts as a recognition site for chemicals e.g hormones
what are glycolipids and what do they do?
- they are a branching carbohydrate portion of a lipid
- they act as a recognition site for chemicals such as cholera
how can you investigate the permeability of the cell membrane in the lab
-
what experiment could you do to test how temperature increases membrane permeability
-
what is diffusion?
diffusion is the net passive movement of particles (molecules or ions) from an areas of higher concentration to an area of lower concentration across a partially permeable plamsa membrane
what are the factors that affect diffusion?
- concentration gradient: the greater the difference in concentration gradient on each side of the excange surface the faster the rate of diffusion
- thickness of exchange surface: the thinner the exchange surface, the faster the rate of diffusion
- surface area of exchange surface: the larger the surface area the faster the rate of diffusion
what are the factors that affect diffusion across a membrane?
- number of channel/carrier proteins in membranes
- size and nature of diffusing particles
e. g lipid soluble/non polar molecules diffuse quickly through the phospholipid bilayer (they dissolve in the hydrophobic bilayer)
but water soluble/polar ones diffuse slower through the protein channels/ carriers
-temperature
what is facilitated diffusion?
the passive movement of larger molecules and charged particles through the cell surface membrane by carrier proteins or channel proteins.
why is facilitated diffusion needed?
because;
- some larger molecule (e.g amino acids, glucose) would diffuse extremely slowly through the phospholipid bilayer because they’re so big
AND
- charged particles (e.g ions and polar molecules) would diffuse slowly because they’re water soluble and the centre of the bilayer is hydrophobic
- so to speed things up, large or charged particles diffuse through carrier proteins or channel proteins in the membrane instead
in facilated diffusion which way does the concentration gradient move?
- down the concentration gradient
- from a area of higher concentration gradient to an area of a lower concentration
what do carrier proteins do and how do they do this?
-carrier proteins move large molecules across membrane, down their concentration gradient
it works when;
- a molecule which is specific to the protein present binds with the carrier protein
- this causes the carrier protein to open
- then the protein changes shape
- this releases the molecule on the opposite side of the membrane (inside of the membrane)
what do channel proteins do?
channel proteins form pores in the membrane for charged particle to diffuse through (down their cocentration gradient)
-different channgel proteins facilitae the diffusion of different charged particles.
what are the factors that increase the rate of diffusion by facilitated diffusion?
- the concentration gradient; the higher the concentration gradient the faster the rate of facilitated diffusion until the it reaches equillibrium
- the number of channel or carrier proteins; the greater the number of channel or carrier proteins in the cell membrane, the faster the rate of facilitated diffusion
how do microvilli increase the surface area for faster diffusion?
microvilli are projections formed the cell-surface membrane folding up on itself
- microvili give the cell a larger surface area
- a larger surface area mean that more particles can be exchanged in the same amount of time (increasing the rate of diffusion)
what is osmosis?
the diffusion of water molecules acrossa a partially permeable membrane, from an area of higher water potential to an area of lower water potential
what is meant by water potential?
the potential (likelihood) of water molecules to diffuse out of or into a solution
does pure water have the lowest or highest water potential?
highest water potential
if two solutions have the same water potential what are they said to be?
isotonic
what will the addition of solute to pure water do to its water potential?
it will lower the water potential
what factors affect the rate of osmosis?
how can you test for the factors that affect the rate of osmosis?
- you can do a simple experiment using potato cylinders to find out water potenial of plant tissue
- make several dilutions of dfferent known concentrations to test the cylinder in
- line up five test tubes in a rack
- add 10cm3 of the intitial 2 M succrase solution to first tube and % cm3 of distilled water to the other four test tubes
- then draw 5cm3 of the solution from the first test tube, add it to the distilled warer in the secon test tube and mix the solution thoroughly.
- you now have 10cm3 of a solutoon thats half as concentrated as the solution in the first test tube
- repeat this process three more time to create solutions with 0.5 M, 0.25 M, 0.125 M
when a higher water potential enters plant cells what happens to the protoplast and the condition of the cell?
the protoplast swells and is pushed against the cell wall and the cell becomes turgid.
when the same water potential inside plant cells and outside plant cells what happens to the protoplast and the condition of the cell?
- there is no change in the protoplast
- the cell is said to be in incipient plasmolysis
when there is a lower water potential in plant cells (water is being moved out) what happens to the protoplast and the condition of the cell?
the protoplast shrinks
-the cell becomes plasmolysed
-explain why an aimal cell placed in pure water bursts while an plant cell in pure water does nit
- both cells have a lower water potential than the pure water
- so water enters into the cells by osmosis from an area of low water potential to an area of high
- the animal cell does not have a cell wall
- so when then water potential is too much in the cell its eventually burst (lysis) because it has no cell wall tp resist the entry of further water
what is Active Transport?
the movement of molecules or ions into or out of the cell from a region of high concentration to a region of lower concentration using energy in the form of ATP and carrier proteins
give the eqaution for the hydrolysis of ATP
ATP -H2O–> ADP + Pi
describe the active transport of a single molecule or ion
- the carrier proteins on the cell surface membrane binds to the molecule or ion to be transported
- the molecule or ion bids to the receptor sites on the carrier protein
- on the inside of the cell/organelle ATP binds to the protein causing it to split into ADP and a phophate molecule
- as a result the protein molecule changed shape and opens to the opposite side of the membrane
- the molecule or ion is then released to the other side fo the membrane
- the phosphate molecule is released from the protein which causes the proteins to revert to its original shape
- ADP combines with the phosphate molecule to form ATP
what are co-transporters and how do they work?
co-transporters are a type of carrier protein
they work by;
- binding two molecules at the same time
- the concentration gradient of one of the molecule is used to move the other molecule against its own concentration gradient
what are the differences between facilitated diffusion and Active transport?
- active transport usually moves solutes from a low to high concentration (in facilitated diffusion they move from a high to low)
- active transport requires energy (facilitated diffusion does not)
what are the factors affecting the rate of active transport?
- the speed of the individual carrier protein: the faster they work, the faster the rate of active transport
- the number of carrier proteins present- the more proteins there are, the faster the rate of active transport
- the rare of respiration in the cell and the availibility of ATP (if the respitation in inhibited, active transport cant take place.
in the ileum (the final part of the intestine) the concentration of glucose is too low for glucose to diffuse out into the blood.
so glucose is absorbed from the lumen (middle) of the ileum by co-transport.
describe this process
- sodium ions are actively transported out of thr ileum epithelial cells, into the blood by the sodium potassium pump.
- This creates a mcuh higher concentration gradient of Sodium ions in the lumen of the intestine than inside the epithelial cells
- sodium ions diffuse into the epithelial cells down the concentration gradient through a different type of carrier protein (co-transport protein) in the cell surface membrane
- as the sodium diffuse in through this second carrier protein they carry either amino acid molecule or glucose molecule into the cell with them
what are the two types of responses the human body has to protect itself from pathogens and what type of lympocytes do they involve?
- ) cell mediated response involving T lymphocytes
- ) humoral responses involving B lymphocytes
for non specific defence mechanism state what the repsonse is like and defences/reponse is used
- in non specific the response is immediate and the same for all pathoges
- this is your physical barrier e.g skin OR phagocytosis
for specific defence mechanism state what the repsonse is like and defences/reponse is used
- in specific the repsonse is slower and specific to each pathogen
- so this includes cell-mediated reponse (T lymphocytes) OR humoral response (B lymphocytes)
what help cells to be identified by lymphocytes so as to stop them destroying the organism’s own tissues?
specific molecues e.g proteins
each type of cell has specific molecules on its surface that identify it, these molecules include proteins and enable the immune system to identify certain things.
what are these ‘things’?
- pathogens e.g HIV
- non-self material e.g cells from other organisms of the same species (organ transplant)
- abnormal body cells e.g cancer cells
- toxins e.g thos produced by pathogens like the bacterium that causes cholera
what is an antigen?
antigens are molecules (usually proteins) on the cell surface membrane which are responsible for self and nonself cell recoginition, that can generate an immune response when detected by the body
how does antigenic variation affect disease and disease prevention
Some pathogens can change surface antigens to bypass the secondary response
The memory cells from the first infection won’t recognise the different antigens
The immune system must carry out a primary response against the new antigens
Different antigens are formed due to gene changes in the pathogen
AV can make it difficult to develop vaccines against some pathogens (HIV, Flu)
in brief what is phagocytosis?
where large particles e.g bacteria can be engulfed by the cells in vesicles formed by the cell surface membrane.
in the blood, what do you call the types of white blood cells that carry out phagocyosis?
phagocytes
what is a phagocyte? where are they found? and what do they do?
a phahocyte e.g macrophage is a type of white blood cell that carries out phagocytosis (engulfement of pathogens).
they are found in the blood and in the tissues
they are the first cells to respond to an immune system trigger inside the body
describe the process of phagocytosis
- a phagocyte have serveral receptors on their cell surface membrane that recognises the foreign antigen on a pathogen
- the cytoplasm of the phagocyte moves round the pathogen, engulfing it to form a vesicle known as a phagosome
- the pathogen is now contained in a phagocytic vacuole (a bubble) in the cytoplasm of the phagocyte
- a lysosome (an organelle that can contain enzymes called lysoszymes) fuses with the phagocytic vacuole. The lysosozymes break down the pathogen by hydrolysis of their wall.
- the phagocyte then presents the pathogen’s antigens
- it sticks the antigens on it surface to activate other immune system cells (e.g T cells)
immune responses such as phagocytosis specific or non specific?
non-specific
after phagocytosis what cells are then activated?
T-cells
“after a pathogen gains entry to the body it is often a number of days before the body’s immune system begins to control it. suggest a possible reasin why this is so.”
in the above case suggest why it would be inaccurate to say that the body takes days to respond to the pathogen?
the body repsonds immediately by ‘recoginising’ the pathogen and by phagocytosis;
the delay is the building up numbers of lymphocytes and therefore controlling the pathogen
after a pathogen gains entry to the body it is often a number of days before the body’s immune system begins to control it. suggest a possible reasin why this is so.
-the lymphocytes that will finally control the pathogen need to buid up their numbers and this takes time
among other places, lysozymes are found in tears. suggest a reason why this is so.
the protective covering of the eye, especially the tear ducts, are potential entry points for pathogens
the eyes are vulnerable to infection because the covering are thin to allow light through
lysozymes will break down the cell walls of any bacterial pathogens and so destroy the before they cause harm.
what are the two types of lymphocytes, where are they made and what sort of repsonse are they associated with?
- you have T-lymphocytes and B-lymphocytes
- T lymphocytes (T cells) mature in the thymus gland and are associated with cell-mediated immunity (immunity involving body cells)
- B lymphocytes (B Cells) mature in the bone marrow and are associated with humoral immunity (immunity involving atibodies that are present in body fluids or ‘humour’ such as blood plasma
what is a T-cell?
what are antigen presenting cells?
- antigen presenting cells are cells that display foreign antigens on their surface
- they can present antigens of other cells on their own cell surface membrane
what will T cells only respond to?
T cells will only respond to antigens that are presented on a body cell
describe the cell-mediated response (T cells)
- pathogens invade body cells or are taken in by phagocytes
- the phagocyte places antigens from the pathogen on its cell-surface membrane
- receptors on a specific helper Tcell (TH) fit exactly onto these antigens
- this attachment activated the T cell to divide rapidly by mitosis and form a clone of genetically identical cells
- The clones T cells:
a. develop into memory cells that enable a rapid response to future infections by the same pathogen
b. stimulate phagocytes to engulf pathogens by phagocytosis
c. stimulate B cells to divide and secrete their antibody
d. activate cytotoxic T cells (TC) (killer t cells)
after the T cells ddivide by mitosis what do they form?
The clones T cells:
a. develop into memory cells that enable a rapid response to future infections by the same pathogen
b. stimulate phagocytes to engulf pathogens by phagocytosis
c. stimulate B cells to divide and secrete their antibody
d. activate cytotoxic T cells (TC) (killer t cells that kill abnormal and foreign cells)
how do cytotoxic t cells kill infected cells?
cytotoxic t cells kill abornal cells and bofy cells that are infected by pathogen;
by producing a protein called perforin that makes holes in the cell surface membrane
these holes mean the cell membrane becomes freely peermeable to all substances and the cell dies as a result
is cell-mediated immunity specific or non-specific? why?
cell mediated repsonse is specific, since only the T cells that have complementary shaped receptors to the pathogen’s antigens will be stimulated
from your knowledge of cell-mediated immunity and lung structyre suggest why humans infected with the H5N1 virus may sometimes die from suffocation.
- H5N1 infects the lungs
- leading to a massive production of T cells
- accumulation of these cells may block the airways/fill the alveoli and cause suffocation
what is a B cell?
another type of white blood cell
they’re covered with antibodies
each B-cell has a specific shaped antibody on its membrane so specific antibodys bind to specific shaped antigens
describe the process of humoral immunity (b cells)
- the b cell is attracted to the anitgens on the pathogen (due to recognition of the foreign antigens)
- when the anitbody on the surface of a B-cells meets a complementary shaped antigen, it binds to it
- the antigen enters the B cell by endocytosis and gets presented on its surface of the B-cell (processed)
- T helper cells bind to these processed antigens and stimulate this B cell to divide by mitosis to form a clone of identical b cells all of which produce the antibody that is specific to the foreign antigen (clonal selection).
what is clonal selection?
where the B cells with the processed antigens are activated by T helper cells to divide by mitosis to produce a clone of identical B cells, all of which produce the antibody that is specific to the foreign antigen
how do monoclonal anitbodies arise?
- a typical pathogen has many different proteins on it’s surface, all of which act as antigens
- some pathogens, such as the bacterium that cause cholera, also produce toxins.
- each toxin mlecule also acts as an antigen
- therefore many different b cells make clones, each of which produces its own type of antibody
- as each clone produces one specific antibody, these anitbodies are referred to as monoclonal antibodies
when a B cells divide by mitosis to form a clone of identical b cells, the cells produced develop into type of cells. what are these cells?
-plasma cells and memory cells
what is a plasma cell? and what do they do?
a cloned B- cells which secrete loads of anitbodies specific to the antigen (monoclonal antibodies)
they bind to the antigens on the surface of the pathogen to form lots of antigen-antibody complexes
how are antibodies used for the destruction of the antigen?
- an antibody has two binding sites, so can bind to two pathogens at the smae time
- this means pathogens can be clumped together (this is called agglutination)
- phagocytes then bind to the antibodies and phagocytose many pathogens at once
- this leads to the destruction of the pathogens carrying this antigen in the body
what is an anitbody and what are they made up off?
antibodies are protiens
they’re made up of chains of amino acid
what does the specificity of an antibody depend on?
its variable regions which form the antigen binding sites
what structure is the variable region made up from?
a unique tertiary structure (due to different amino acid sequences) thats complementary to another specific antigen.
label this antibody
a= variable regions
b= hinge (*like hinge joint) protein
c= heavy chain
d= contant regions
e=disulphide bridge
f= light chain
what is a memory cell? what do they do?
cells that remain in the blood and tissue fluid (humoral fluid) so that when they encounter the same anitgen at a later date, they divide rapidly and develop into plasma cells and more memory xells
what is the primary immune response?
the production of anitbodies and memory cells (the pathogen first enters the body)
what is the secondary immune response?
where memory cells circulate in the blood in readiness to repsond fluid in readiness to respond to a future infection by the same pathogen by dividing and developing into plasma cells that produce antibodies
what is the difference in antibody production between the primary and the secondary repsonse
an increased quantity of antibodies is secreted at a faster rate than in the primary immune repsonse
describe and explain what is happening in this graph
- in the primary response there is less anitbodies in the blood when exposed to the antigen compared to the secondary reponse
- the primary response involves the intial and slow production of anitbodies and memory cells.
- there is an increased number of antibodies released after the sencond response due to large numbers of memory cells that divide rapidly and priduce many antibodies.
- more memory cells remain in the blood
- rate of production is quicker (steeper curve)
state two similarities between T-cells and B-cells
- both produced by stem cells
- both are types of white blood cells
-
state two differences between B cells and T cells
- T cells mature in the thymus gland, B cells mature in the bone marrow
- T cells are involved in cell immunity, B cells are involved in humoral immunity
compare cell mediated immunity compared to humoral immunity
- cell med involves T-cells whlist humoral involves B-cells
- there is no antibodies are produced in cell med but are produced in humoral
- cell med is effective through cells, humoral is effective through body fluids
what is passive immunity?
this is produced by the introduction of antibodies into individuals from an outside source
- the immunity is aquired immediately as the antibodies are not been produced by the individuals themselves
- there is no long lasting immunity as the anitbodies are not replaced when they are broken down, and no memory cells are formed
what is active immunity?
- is produced by stimulating the production of antibodies by the individuals’ own immune system
- the body produces its own antibodies and may continue to do so for many years
what is artificial active immunity?
- forms the basis of vaccination (immunisation)
- it involves inducing an immune resposne in an individual, without them suffering the symptoms of the disease
what is natural active immunity?
- results form an individual becoming infected with a disease under normal circumstances
- the body produces its own antibodies and may continue to do so for many years
what is the difference between active and passive immunity?
passive: antibodies from an outside source are produced active: antibodies are produced by the body
passive: no contact with pathogen/antigen active: contact with a pathogen or antigenms is via a vaccine (artificial active immunity) or natural (natural active immunity)
passive: no memory cells are formed (short term immunity) acive:memory cells are formed (long term immunity)
passive: e.g breats milk, anti-venom and across placenta active: infection, oral vaccines or injected vaccines
what do vaccines do?
- contains antigens for a particular pathogen
- stimulate the primary repsonse and large numbers of B memory cells are made against a particular pathogen without the pathogen causing disease- this means you become immune without having any symptoms
(you are now immune)
-antigens in vaccines are free or attached to dead or attenuated (weakened) pathogens
how are pathogens taken?
- taken orally or by injection
- oral: can be broken down by enzyme or be too large to be absorbed into the blood
what is a BOOSTER?n
makes sure that more memory cells are made
how are vaccines made harmless?
- KILLING: the pathogen leaving it’s antigens unaffected
- WEAKENING the pathogen
- REMOVING: the antigens from the surface of the pathogen and injecting them alone into the blood
what are the pros of vaccination?
- eradicates harmful diseases permanently
- saves lives and money
what are the cons of vaccinations?
- side effects
- tested on animals
- need to be trailled
- espensive
- not always very (so boosters are needed)
what are the points that make for a successful vaccination?
- affordable
- have few side effects
- easy to transport and store
- adminstering the vaccine correctly and in the right time frame
- must be able to establish herd community by vaccinating the majority of the population
what is herd immunity?
- vaccinating a large number of the population and establishing herd immunity
- you are reducing the chances of a susceptible (non-vaccinated) person coming into contact with an infected person
- the result; disease elimanted from the population
why would vaccines fail to elimante a disease?
- weakened immune systems
- antigenic variation due to mutation
- pathogen hides from the immune system
- people can be carriers of a disease but not show systems
- unvaccinated due to religous/ethical reasons
- unvaccinated due to concerns from media
what is an antigen?
a molecule (usually a protein) that triggers an immune response by lymphocytes
how does antigenic variation affect the production of vaccines to help prevent people catching influenza:
- the influenza (flu vaccine) changes every year. that because the antigens on the surface of the influenze virus change reguarly forming new strains of the virus
- memory cells produced from the vaccination with one strain of the flu will not recognise other strains with diffferent antigens. The strains are immunologically distinct
- every year there are different strains of the influenza virus circulating in the poplulation, so a different vaccine has to be made
- new vaccines are developed and one is chosen every year that is the most effective against the recently circulating infulenza viruses
- governments and health authorities then implement a programme of vaccination using the most suitable vaccine
why is it important that scientific evidence is treated with caution?
- to be universallu accepted must be first critcally appraised and confrimed by other people or oganisations who are anticipatin a particular outcome from the research
- some scientists may not be acting totally independently but may be funded by other people or other organisations who are anticipating a particular outcome of the research
- scientist’ personal beliefs, views and opinions may infuence the way they approach or represent their research
- the fact, as presenetd by the media headline writers companies, governments and other organisations may have been biased or disorted to suit their own interest
- new knowledge may challenge accepted scientific beliefs; theories are being modified all the time
how can monoclonal antibodies be used to treat cancer?
- different cells in the body have different surface antigens
- cancer cells have antigens called tumour markers that are not found on normal body cells
- monoclonal antibodies can be made that will bind to the tumour markers
- you can also attach anti-cancer drugs to the anitbodies
- when the antibodies come into contact with the cancer cells they will bind to the tumour markers
- this means the drug will only accumulate in the body where there are cancer cells
- so the side effects of an antibody-based drug are lower than other drugs because they accumalate near specific cells
describe how monoclonal antibodies are used for pregancy testing
- pregancy tests detect the hormone human chorionic gonadotropin (hCG)
- the applicaion area contains antibodies for hcG bound to a coloured bead (blue)
- when the urins is applied to the application area any hCG will bind to the antibody on the beads, forming an antigen-antibody complex
- the urine moves up the stick to the test strip, carrying any beads with it
- the test strip contans antibodies to hCG that are stuck in place (immobilised)
- if there is hCH present the test strip turns blue because the immobilised antibody binds to any hCG - concentrating the hCG antibody compex with the blue beads attached.
- if no hCG is present, the beads will pass through the test area without binding to anything and so it wont go blue
what does ELISA stand for?
enzyme linked immunosorbant assay
what is the use of ELISA test?
-it is used to identify the presence of certain anitbodies or antigens
how the products produced from ELISA testing be analysed?
- qualitatively (observing coulour change)
- quantitavely (from working out intensity of the colour change by using a colorimeter to see how much antibody there is
what are the two types of ELISA test?
direct and indirect
what is direct ELISA test used for?
used if you want to find out if a patient has a certain antigen
describe the process of direct ELISA testing
- antigens from a patien’s blood sample are extracted and bound to a well plate
- the complementary antibody with attached enzyme is added (detection antibody)
- if complementary antigen is present an antigen-antibody compex will form and the complex will become immobilised (stuck permanently)
- any unbound antibody is washed away
- a substrate is added that will bind to the enzyme on the antibody
- the enzyme-substrate complex will produce a colour change as it breaks the substrate down
what is indirect ELISA test
this is when two different antibodies are used to detect an antigen
describe what happens in indirect ELISA test for HIV
- HIV antigen is bound to the bottom of a well in a well plate
- a sample of the patient’s blood plasma, which might contain several different anitbodies is added to the well
- if there are any HIV-specific antibodies these will bidn to the HIV antigen stuck to the bottom of the well
- the well is then washed out to remove any unbound antibodies
- the secondary antibody, that has a specific enzyme is added to the well. the secondary antibody can bind to the HIV specific antibody (which is also called the primary antibody)
- the well is washed out again to remove any unbound secondary antibody. if there is no primary antibody in the sameple all the secondary antibody will be washed away
- a solution is added to the well. this solution contains a subrate which is able to react with the enzyme attached to the secondary antibody and produce a coloured product
- if the solution changes colour it indicates that the pateint has HIV-specific antibodies in their blood and is infected with HIV
in the ELISA test, why is washing out important?
- it makes sure that any unbound anitbodies are not left in the well which could affect the results
e. g unbound antibodies could cause the test to appear positive when there is no antibodies present
what does HIV stand for?
human immunodeficiency virus
what does the disease HIV cause?
aquired immune deficiency syndrom (AIDS)
label the HIV virus
how does the HIV virus replicate?
being a virus HIV cannot replicate itseld so it uses genetic material to instruct the host cell’s biochemial mechanisms to produce componenet required to make new HIV
- HIV enters the blood stream and circulates around the body
- a protein on the HIV readily binds to a protein call CD4, most frequently on a helper T cell
- the protein capsid fuses with the cell-surface membrane. the rna and enzymes of HIV are released into the helper T cell’s cytoplasm
- the HIV reverse transcripase converts the virus’s RNA to DNA
- newly made DNA is moved into the helper T cell’s nucleus where it is inserted into the cell’s DNA, here mRNA using cell’s enzymes
- mRN has instructions for making new viral proteins and the RNA to go ingot the new HIV
- mRNA passes out of nucleus through a nuclear pore and uses the cell’s protein synthesis mechanisms to make particles
- the HIV particles break away from the T helper cells with a piece of its cell-surface membrane surrounding them which forms their lipid envelope
what is the name given for the period of time where HIV replication drops to a lower level?
-latency period
what are the symptoms of someone who develops AIDS
symptoms:
- minor infection of mucous membranes
- recurring respiraatory infections
to
- chronic diarrhoea
- severe bacterial infection
- tuberculosis
to
- toxoplasmosis of the brain
- candidiasis of the respiratory system (fungal infection)
why do antibiotics not work against HIV?
- ) anitbiotics kill bacteria by interfering with their metabolic rections, they target bacterial enzymes and ribosomes used in these reactions
- ) viruses dont have their own enzymes and ribosomes - they use the one’s in the host’s cells. so the human viruses uses human enzymes and ribosomes to replicate, anitbiotics can not inhibit them because they dont target human process
describe the structure of HIV
HIV has a core that contains the genetic material (RNA) and some proteins
it has an outer layer called the capside, which is made of protein surrounded by an lipid envelope that is made from the membrane of the host cells
There are attachement proteins sticking out from the envelope
End of Topic
