3.2 Cells Flashcards
3.2.1.1 Structure of eukaryotic cells
What organelles do eukaryotic cellls contain?
Hint: contains 10 organelles.
- CSM
- Nucleus
- Mitrochondira
- Chloroplasts (in plants and algae)
- Golgi apparatus and Golgi vesicles.
- Lysosomes
- Ribosomes
- Rough endoplasmic reticulum and smooth endoplasmic reticulum.
- Cell wall (in plants, algae and fungi)
- Cell vacuole. (in plants)
3.2.1.1 Structure of eukaryotic cells
Structure and function of CSM.
STRUCTURE
Found in all cells.
Phospholipid bilayer: molecules embedded within and attached on outside (proteins, carbohydrates, cholesterol.)
FUNCTION
controls what enters and exits the molecule.
3.2.1.1 Structure of eukaryotic cells
Structure and function of nucleus.
STRUCTURE
1. Nuclear envelope: double membrane surrounding the nucleus. Controls entry and exits of materials in and out of nucleus.
2. Nuclear pores: allows passage of large molecules out of nucelus i.e. mRNA.
3. Nucleoplasm: Granular jelly-like material.
4. Chromosome: protein-bound linear DNA.
5. Nuceolous: Smaller sphere inside which is a site of rRNA production and makes ribosomes.
FUNCTION
Site of DNA replication and transcription (making mRNA)
Contains genetic code for each cell.
Manufactures rRNA and ribosomes.
3.2.1.1 Structure of eukaryotic cells
Structure and function of mitrochondria.
STRUCTURE
Double membrane.
Inner membrane called cristae.
Fluid centre called mitrochondrial matrix.
Loop of mitrochondira DNA.
FUNCTION
Site of aerobic respiration.
Site of ATP production.
DNA to code for enzymes needed in respiration.
3.2.1.1 Structure of eukaryotic cells
Structure and function of chloroplast.
STRUCTURE
1. Chloroplast envelope: double plasma membrane. Controls entry and exit of substane within chloroplast.
2. Grana: stacks of 100 disc-like called thylakoid } contains chlorophyll. 1st stage of photosythesis (light absorption)
3. Stroma: fluid-filled matrix. 2nd stage of photosynthesis. contains starch grains.
FUNCTION
1. Site of photosynthesis.
2. Granal membrane: provide large surface area for attachement of chlorophyll, electron carriers and enzymes in first stage of photosynthesis.
3. Fluid of stroma: posseses enzymes needed to make sugars in 2nd stage of photosynthesis.
3.2.1.1 Structure of eukaryotic cells
Structure and function of golgi apparatus and golgi vesicle.
STRUCTURE
1. Folded membranes making cisternae.
2. Secretary vesicles pinch off from the cisternae.
3. More curved in apperance but may look like SER.
FUNCTION
1. Add carbs to proteins to form glycoprotein.
2. Produce secretory enzymes.
3. Secrete carbs
4. Transport, modify and store lipids.
5. Form lysosomes.
6. Molecules “labelled” with their destination.
7. Finished products are transported to cell surface in golgi vesicles where they fuse with membrane and contents in released.
3.2.1.1 Structure of eukaryotic cells
Structure and function of lysosomes.
STRUCTURE
1. Bags of digestive enzymes.
2. Membrane bound organelle that releases hydrolytic enzymes.
FUNCTION
1. Hydrolyse phagocytic cells.
2. Completely break down dead cells
3. Exocytosis - release enzymes to outside of cell to destory material.
4. Digest worn out organelles for reuse of materials.
3.2.1.1 Structure of eukaryotic cells
Structure and function of ribosomes.
STRUCTURE
1. Small, made up of two sub-units of protein and rRNA.
2. **80s ** large ribosome found it eukaryotic cells
3. 70s smallers ribosome found in prokaryotic cells, mitochondria and chloroplasts.
FUNCTION
site of protein synthesis.
3.2.1.1 Structure of eukaryotic cells
Structure and function of RER.
STRUCTURE
Series of flattened sacs enclosed by a membrane with ribosomes on surface.
FUNCTION
1. Provides large SA for synthesis of proteins / glycoproteins.
2. provides pathway for transport of materials through cells especially proteins.
3.2.1.1 Structure of eukaryotic cells
Structure and function of SER.
STRUCTURE
1. system of membrane bound sacs.
2. doesn’t contain ribosomes on its surface
FUNCTION
1. sythesis, store and transport lipids and carbs.
3.2.1.1 Structure of eukaryotic cells
Structure and function of cell wall.
(inside plant cells not animal)
STRUCTURE
1. Consist of number of polysaccharides i.e. cellulose embedded in matrix.
2. Thin layer } middle lamellae.
FUNCTION
1. Provides mechanical strength in order to prevent cell from bursting under osmotic pressure by the entry of water.
2. provides strength to plant as a whole.
3. allows water to pass along it.
3.2.1.1 Structure of eukaryotic cells
Structure and function of cell wall in algae.
STRUCTURE
made up of cellulose or glycoproteins or both.
FUNCTION
same as plant cell wall function.
3.2.1.1 Structure of eukaryotic cells
Structure and function of cell wall in fungi.
STRUCTURE
do not contain cellulose, instead contain chitin, glycan (polysaccharide) and glycoproteins.
FUNCTION
3.2.1.1 Structure of eukaryotic cells
Structure and function of cell vacuole.
STRUCTURE
1. fluid filled sac bound by a single membrane.
2. Plant vacuoles may contain: solution of mineral salt, sugars, amino acids, wastes and pigments.
FUNCTION
1. Supports herbaceous plants by making cells turgid.
2. Sugars and amino acids may act as temporary food stores.
3. Pigment can colour petals, attracting pollinating insects.
3.2.1.1 Structure of eukaryotic cells
How are specialised cells organised into?
C lark
T ripped
O ver
O llies
O bjects
Cells, tissues, organs, organ system, organisms.
3.2.1.2 Structure of prokaryotic cells and of viruses
How do prokaryotic cells differ from eukaryotic cells?
- Cytoplasm lacks membrane bound organelles.
- Smaller ribosomes (70s).
- No nucleus ; single circular DNA molecule free in cytoplasm not associated with proteins / histones
- Cell wall contains murein, a glycoprotein.
- No chloroplast
- Contains capsule surrounding the cell.
- +1 plasmids
- +1 flagella
3.2.1.2 Structure of prokaryotic cells and of viruses
Function of capsule.
protects bacterium from other cells and helps groups of bacteria to stick together for further protection.
3.2.1.2 Structure of prokaryotic cells and of viruses
Function of circular DNA.
Posseses genetic info. for replication of bacterial cells.
3.2.1.2 Structure of prokaryotic cells and of viruses
Function of plasmids.
Posseses genes that may aid survival of bacteira in harmful conditions i.e. producing enzymes that can break down antibiotics.
3.2.1.2 Structure of prokaryotic cells and of viruses
Structure and function of a virus.
STRUCTURE
1. acellular and non-living particles.
2. Smaller than bacteria
3. Contain nucleic acids } DNA or RNA but can only multiply inside living host cells.
4. Capsid: nucleic enclosed within protein.
5. Attachment proteins: Lipid envelope or capsid have AP, allow virus to identify and attach to a host cell.
HIV further surrounded by lipid envelope.
3.2.1.3 Methods of studying cells
Define magnification.
how many times bigger the image produced by the microscope is than the real-life object you are viewing
3.2.1.3 Methods of studying cells
Define resolution.
ability to distinguish between objects that are close together.
(i.e. the ability to see two structures that are very close together as two separate structures)
3.2.1.3 Methods of studying cells
What are the two main types of microscopes?
- Optical microscope (Light)
- Electron microscope.
3.2.1.3 Methods of studying cells
Describe an optical (light) microscope.
Use light to form an image.
Light microscopes use a pair of convex glass lenses that can resolve images that are 0.2um apart.
3.2.1.3 Methods of studying cells
Strengths and limitations of optical microscopes.
STRENGTHS
1. Cheap to purchase.
2. Easy to use.
3. Small & portable.
4. Vaccum not required.
5. Natural colour of sample is maintained.
6. Can observe eukaryotic cells, their nuceli and maybe mitrochondria and chloroplast.
LIMITATIONS
1. Magnifies objects up to 2000x only.
2. Because optical uses light, it limits the resolution as it’s impossible to resolve two objects that are close together.
3. Have low resolution } 0.2 micrometers
3.2.1.3 Methods of studying cells
Describe an electron microscope.
Use beams of electrons to form an image inside vaccum environment.
Vaccum environment needed so particles in air do not deflect electrons out of beam aligment.
Two types TEM and SEM.
3.2.1.3 Methods of studying cells
Strengths and limitations of electron microscopes.
STRENGTHS
* High resolution
* High magnification
* 3D images with SEM
LIMITATIONS
* Expensive
* Large and not portable
* Only dead specimens can be used
* Training is required in order to use them
3.2.1.3 Methods of studying cells
Describe transmission electron microscope.
Electron gun that produces beams of electrons that is focused onto the specimen by condenser electromagnet.
Beam passes through thin section of specimen. Parts absorb electrons therefore appear dark.
Other parts of specimen allows electrons to pass through therefore appear bright.
3.2.1.3 Methods of studying cells
Strengths and limitations of TEM.
STRENGTHS
* High resolution images produced.
* Internal structures within cells or organelles can be seen.
LIMITATIONS
* Can only be used when very thin specimens or thin sections of the object are being used.
* They cannot be used to observe live specimens (vaccum inside a TEM and all the water must be removed from the specimen)
* Artefacts can be produced.
* Do not produce a coloured image.
3.2.1.3 Methods of studying cells
Describe the scanning electron microscope.
Directs beam of electrons onto the surface of the specimen from above.
Beam bounces off the surface of the specimen and electrons are detected forming an image.
} they can produce 3D images
3.2.1.3 Methods of studying cells
Strengths and limitations of SEM.
STRENGTHS
* Can be used on thick or 3D specimens.
* allow external 3D structure of specimens to be observed.
LIMITATIONS
* Give lower resolution images than TEM.
* Cannot be used to observe live specimens (unlike optical microscopes)
* They do not produce a colour image.
3.2.1.3 Methods of studying cells
How do you measure the size of an object viewed with an optical / light microscope?
Using an eye piece graticule
3.2.1.3 Methods of studying cells
Magnification formula
I = AM
or
I
A M
3.2.1.3 Methods of studying cells
Magnification conversion
/1000,/100,/10,/1000,/1000
<–
Km, m, cm, mm, micrometres, nm
–>
x1000,x100,x10,x1000,x1000
3.2.1.3 Methods of studying cells
Why can’t the eyepiece graticule be used to directly measure the size of the object under the microscope’s obbtained under the objective lens?
- The objective lens will magnify to a different degree.
- Graticule must be first calibirated for a particular objective lens
3.2.1.3 Methods of studying cells
What object do you use to calibrate the eyepiece graticule?
- Stage micrometre - has scale etched onto it.
- Scale is usually 2mm long.
3.2.1.3 Methods of studying cells
What are the steps for calibrating the eyepiece graticule?
- Line up stage micrometre and eyepiece graticule whilst looking through the eye piece.
- Count how many divisions fit onto the eyepiece graticule fit into one division on the micrometre scale.
- Each division on the micrometre is 10 micrometres, this can be used to calculate what one division on the eye piece graticule is at the current magnification.
3.2.1.3 Methods of studying cells
what is cell fractionation?
Process where the cells are broken up and they different organelles they contain are seperated out.
3.2.1.3 Methods of studying cells
Before cell fractionation can begin the tissue must be placed in what type of solution and why?
- COLD - reduce enzyme activity that might break down the organelles.
- SAME WATER POTENTIAL - prevent organelles bursting or shrinking as a result of osmotic gain or loss of water.
- BUFFERED - so that the pH does not fluctuate. Any change in the pH may alter the structure of the organelles or affect the functioning of enzymes.
3.2.1.3 Methods of studying cells
What are the two stages of cell fractionation?
- Homogenation
- Ultracentrifugation.
3.2.1.3 Methods of studying cells
What is homogenation?
- Cells are broken up by a homogeniser.
- Releases organelles from the cell.
- Homogenate (resultant fluid) is filtered to remove any complete cells or large debris.
3.2.1.3 Methods of studying cells
What is ultracentrifugation?
- The process where the fragments in the filtered homogenate (resultant fluid) is seperated in a machine called a centrifuge.
- The tube is spun at very high speed in order to create a centrifugal force.
3.2.1.3 Methods of studying cells
Outline the steps for cell fractionation.
REMEMBER cell fractionation contains two steps: homogenisation and ultracentrifugation.
- Tissue is cut up and kept in a cold, buffered solution of the same water potential as the tissue.
- Cut-up tissue is further broken up in a homogeniser.
- Homogeniser is spun in an ultracentrifuge at low speed for 10 mins.
- Pellet is formed at the bottom with the heaviest organelles and supernatant is formed at the top of the tube and is removed.
- Supernatant is transferred to another tube and is spun in the centrifuge at a faster speed.
- step 4-5 continues until desired organelle is removed.
3.2.1.3 Methods of studying cells
What is the speed of centrifugation of nuclei, mitrochondria, and lysosomes?
NUCLEI 1000 min-1
MITROCHONDRIA 3500 min-1
LYSOSOMES 16500 min-1
3.2.1.3 Methods of studying cells
What are artefacts?
Give some examples of artefacts.
When looking at a prepared sample under a microscope, you can sometimes see things that aren’t actually part of the specimen.
FOR EXAMPLE
Dust, air bubbles, fingerprints
3.2.1.3 Methods of studying cells
How do artefacts occur?
During preparation, a sample is often squashed or stained, which can generate artefacts.
Occurence of artefacts can be decreased by more careful preparation of samples.
3.2.1.3 Methods of studying cells
In which microscopes are artefacts common in?
electron microscopes especially when using TEM due to the lengthy treatment required to prepare samples.
3.2.1.3 Methods of studying cells
There was a considerable period of time during which the scientific community distingushed between artefacts and cell organelles. Describe what happened in this period of time.
- To distinguish between artefacts and the cell organelles the scientific community had to repeatedly prepare specimens in different ways, using different techniques.
- If they saw a particular object in a specimen prepared using one preparation technique, but not another, the object was more likely to be an artefact than an organelle.
- This continued until preparation techniques and knowledge of organelles improved.
3.2.1.3 Methods of studying cells
Where are starch grains usually found in?
Practical Skills: Using iodine to detect starch.
- Stroma of the chloroplast
- Storage organs such as potato tubers.
- seeds of cereal and legumes.
3.2.1.3 Methods of studying cells
Are starch seen with optical or electron microscopes and why?
Practical Skills: Using iodine to detect starch.
Optical (light) microscope as they are large enough but first require staining in order to be seen easily
3.2.1.3 Methods of studying cells
Practical Skills: Using iodine to detect starch.
Practical Skills: Using iodine to detect starch.
Iodine (I2) in potassium iodide (KI) can be used to stain starch grains.
This is done by adding a drop of KI onto specimen before placing the coverslip on top of it.
KI makes the starch grains darker in colour, making it easier to see them.
REMEMBER iodine solution has a orange-brown colour but turns blue-black in the prescence of starch.
3.2.1.3 Methods of studying cells
After staining the starch grains with KI, why should you slowly lower the coverslip onto the specimen and at an angle?
To avoid any air bubbles getting trapped } may create artefacts.
3.2.2 All cells arise from other cells
What organims do retain the ability to divide and show a cell cycle?
Within multicellular organisms,not all cells retain the ability to divide.
Eukaryotic cells.
3.2.2 All cells arise from other cells
What does the cell cycle consist of?
- Interphase
- Nuclear division (mitosis)
- Cell division (cytokenisis)
3.2.2 All cells arise from other cells
What happens during interphase?
- DNA REPLICATION
- Organelles doubles, cell grows and DNA replicates
- longest stage in the cell cycle
3.2.2 All cells arise from other cells
What are the 3 stages of interphase and outline what they do?
G1 phase: growth } all the organelles in the cell would double and cell would grow in size.
S phase: DNA synthesis } DNA replication.
G2 phase: Growth and preparation for mitosis } Error checking stage. DNA replicated is checked for any mutations. If mutation is detected cell is destroyed at that stage to prevent harm.
3.2.2 All cells arise from other cells
What is mitosis?
- Part of cell cycle in which a eukaryotic cell divides to produce two daughter cells, each with genetically identical DNA by the parent cell during DNA replication.
- a controlled process
3.2.2 All cells arise from other cells
What are the four stages of mitosis?
- Prophase
- Metaphase
- Anaphase
- Telophase
3.2.2 All cells arise from other cells
Prophase:
- Chromosomes condense and become visible.
- Chromosomes = 2 sister chromatids joined by centromere.
- Centrioles seperate and move to opposite poles of the cell.
- Centrioles create spindle fibres.
- Collectively, spindle fibres called spindle apparatus. PLANTS DO NOT HAVE CENTRIOLES BUT DO DEVELOP SPINDLE APPARATUS
- Nuceolous dissappears.
3.2.2 All cells arise from other cells
Metaphase:
- The chromosomes align along the equator of the cell
- Spindle fibres released from the poles and now attach to the centromere and chromatid
in exam must mention that the spindle fibres attach to the centromere and chromatid and NOT the chromosome.
3.2.2 All cells arise from other cells
Anaphase:
- Spindle fibres pulls centromere and chromatids they are bound to, to opposite poles.
- Sister chromatids seperate at centromere
- Centromere is divided into 2
- Spindle fibres = shorten
- Seperated sister chromatids = chromosomes pulled to opposite poles by spindle fibres.
ATP required } respiration } mitrochondria.
3.2.2 All cells arise from other cells
Telophase:
- Chromosomes are at opposite ends of the poles and begin to decondense.
- Nuclear envelopes being to reform around each chromosome.
- Spindle fibres break down.
3.2.2 All cells arise from other cells
Cytokenisis:
Cytoplasm splits into two to create the 2 new genetically identical cells.
3.2.2 All cells arise from other cells
Mitotic index calculation:
MI = (Number of cells in mitosis / total number of cells ) x 100
Number of cells in mitosis when counting = count the number of chromosomes you can see.
3.2.2 All cells arise from other cells
Mitosis is important in organisms as it produces daughter cells that are gentically identical to the parent cells.
Why is it essential to make exact copies of the existing cells? (3 reasons)
1.GROWTH: 2 haploid cells (sperm and ovum) fuse together to form a diploid cell, it has all the genetic info needed to form new organism. If new organism is to resemble parent, all cells that grow from this orginal cell must be gentically identical. Mitosis ensures that this happens.
2.REPAIR: Cells damaged or have died, it is important new cells have an identical structure and function to the ones that were lost.
3.ASEXUAL REPRODUCTION: single-celled organisms divide by mitosis to give 2 new genetically identical organisms
3.2.2 All cells arise from other cells
The apperance of cells in each stage of mitosis: PROPHASE
- Chromosomes are visible.
- The nuclear envelope breaks down.
3.2.2 All cells arise from other cells
The apperance of cells in each stage of mitosis: METAPHASE
- Chromosomes line up along the middle of the cell (equator)
3.2.2 All cells arise from other cells
The apperance of cells in each stage of mitosis: ANAPHASE
- Sister Chromatids / chromosomes move away from the middle of the cell towards opposite poles
3.2.2 All cells arise from other cells
The apperance of cells in each stage of mitosis: TELOPHASE
- Sister chromatids / chromosomes have arrived at opposite poles of cell.
- Chromosomes begin to decondense
- Nuclear envelope reforms.
- Spindle fibres disappear
3.2.2 All cells arise from other cells
The apperance of cells in each stage of mitosis: CYTOKINESIS
- Cytoplasm divides
- Parent cell becomes 2 daughter cells with identical genetic information.
3.2.2 All cells arise from other cells
What can uncontrolled cell division lead to?
- Formation of tumors and cancers.
- } cancerous cells divide repeatedly and uncontrollably, forming a tumour (irregular mass of cells).
3.2.2 All cells arise from other cells
What is an oncogene?
When cancer occurs changes within the gene that control cell division is a mutated gene.
3.2.2 All cells arise from other cells
What does a mutation often result in?
- Early cell death
- Cells being destroyed by the body immune system.
3.2.2 All cells arise from other cells
What happens when cancerous cells are mutated?
- do not results in early cell death
- cells are not destroyed by the body’s immune system.
- harmful mutation can be passed on to cell’s descendants.
3.2.2 All cells arise from other cells
What treatment is used for cancer to control the rate of cell division?
- Disrupt the cell cycle.
- Kills the tumour cells. } divides more frequently than body cells.
- Though will also kill normal body cells, treatment won’t distinguish between tumour and normal body cells.
3.2.2 All cells arise from other cells
Cell cycle target of cancer treatment: G1 (cell growth and protein production)
- Chemotherapy prevents synthesis of enzymes needed for DNA replication.
- prevent cell from entering synthesis phase.
- disrupts cell cycle.
- Cell kills itself.
3.2.2 All cells arise from other cells
Cell cycle target of cancer treatments: S phase (DNA replication):
- Radiation and other drugs damage DNA.
- DNA is checked for damage before and during S phase.
- Damage detected, cell kills itself.
- Prevents more tumour from growing.
3.2.2 All cells arise from other cells
Binary fission in prokaryotic cells involves:
- Circular DNA replicates and both copies are attached to the CSM.
- Palsmids replicate in the cell
- CSM grows between the 2 circular DNA molecules and pinches inwards, dividing the cytoplasm into 2.
- New cell wall formed between 2 DNA molecules.
- Identical copies of daughter cells have single copy of circular DNA and variable number of plasmids.
3.2.2 All cells arise from other cells
Do viruses undergo cell divison?
- NO
- They are accelluar and non-living.
- Their attachement protein binds to a complementary receptor on a host cell.
- Inject nucleic acid.
- The infected host cells replicates the viruses particles.
HIV protein is complementary to the receptor on the surface of T cells.
* 3.2.2 All cells arise from other cells
Why is HCL used?
PREPARE STAINED SQUASHED CELLS FROM A ROOT TIP: REQUIRED PRACTICAL 2
- to soften and loosen the tissues.
3.2.2 All cells arise from other cells
Why is a stain used?
PREPARE STAINED SQUASHED CELLS FROM A ROOT TIP: REQUIRED PRACTICAL 2
- to stain the chromosomes in the nucleus so they become visible under the microscope.
3.2.2 All cells arise from other cells
Why is a mounted needle used when lowering down your cover slip?
PREPARE STAINED SQUASHED CELLS FROM A ROOT TIP: REQUIRED PRACTICAL 2
- prevents any air bubbles coming under the coverslip.
3.2.2 All cells arise from other cells
Why is the root tip of a garlic or onion used?
PREPARE STAINED SQUASHED CELLS FROM A ROOT TIP: REQUIRED PRACTICAL 2
- Root tip = growing region of the root.
- Mitosis occurs here.
3.2.2 All cells arise from other cells
Why do you gently press down on the cover slip?
PREPARE STAINED SQUASHED CELLS FROM A ROOT TIP: REQUIRED PRACTICAL 2
- Spreads out the cells to get a single layer so light can pass through when using a microscope.
3.2.2 All cells arise from other cells
Steps of preparing stained squashed cell.
PREPARE STAINED SQUASHED CELLS FROM A ROOT TIP: REQUIRED PRACTICAL 2
- Grow garlic in dark over beakerfor a few days until roots are formed.
- Cut 5mm of the root tip from the end.
- Place root tip in HCL and into water bath at 60°C, leave for 10 mins.
- Pour acid out of test tube. Place root tip of watch glass. Rinse with distilled water.
- Place root tip on microscope slide, use filter paper to soak up any excess water.
- Add stain to root tip.
- Use mounted needle to lower on coverslip and leave for 10 mins.
- Place filter paper ontop of the slide and gently press down, do not turn coverslip sidewards.
3.2.3 Transport across cell membranes
What does the CSM contain?
- Phospholipids : hydrophillic head points outwards and hydrophobic tails points inwards.
- allows lipid-soluble molecules to pass through membrane not water-soluble molecules.
- Allows membrane to be flexible and self-sealing.
3.2.3 Transport across cell membranes
Outline the components the fluid-mosaic model contains.
- PROTEINS : instrinsic and extrinsic
- CHOLESTRAL
- PHOSPHOLIPIDS
- GLYCOPROTEINS
- GLYCOLIPIDS
3.2.3 Transport across cell membranes
Explain the role of PROTEINS in the fluid mosaic model.
INTRINSIC
* electron carriers (photosynthesis, respiration)
- CHANNEL PROTEINS:
- facillitated diffusion } ↓ conc. gradient
- transport charged or polar molecules
- act as pore, can be gated, open or close.
- CARRIER PROTEINS:
- active transport } against conc. gradient
- facillitated diffusion } ↓ conc. gradient
- transports large molecules and protein changes shape when molecule attaches.
EXTRINSIC
* binding sites / receptors e.g hormones
* antigens (glycoproteins)
* bind cells together
* involved in cell signaling.
3.2.3 Transport across cell membranes
Explain the role of CHOLESTRAL in the fluid mosaic model.
- restricts lateral movement of other molecules making up the membrane.
- steriod molecule in some plasma membrane.
- Connects phospholipids (fatty acid tails) and reduces fludity to make bilayer more stable, packs them more closely together.
3.2.3 Transport across cell membranes
Explain the role of PHOSPHOLIPIDS in the fluid mosaic model.
- allows the transport of small non-polar, lipid-soluble molecules.
- i.e. oxygen, water. = ↓ conc. gradient = simple diffusion.
- Restricts movement of large / polar molecules.
3.2.3 Transport across cell membranes
Explain the role of GLYCOPROTEINS in the fluid mosaic model.
- They are CARBS that attach to extrinsic protein and acts as cell surface receptors and neurotransmitters.
- allow cells to recognise each other and attach to form tissues
3.2.3 Transport across cell membranes
Explain the role of GLYCOLIPIDS in the fluid mosaic model.
- Made up of carbs bound to a lipid
- act as cell surface receptors.
- allow cells to adhere to each other to form tissues.
3.2.3 Transport across cell membranes
What is passive transport?
- doesn’t require energy from ATP as they utilize the conc. gradient or water potential gradient.
- Simple diffusion, facilitated diffusion, Osmosis.
3.2.3 Transport across cell membranes
Simple diffusion
- Net movement of small, lipid-soluble molecules through the bilyaer from area of high to low concentration. (down conc. gradient)
3.2.3 Transport across cell membranes
Facilitated diffusion:
- specific channel or carrier proteins with complementary binding sites transport large or polar molecules down a concentration gradient.
3.2.3 Transport across cell membranes
Osmosis:
- diffusion of water molecules from an area of high water potential to an area to low water potential through a partially permeable membrane.
3.2.3 Transport across cell membranes
What is active transport?
- requires energy from ATP.
- Against a conc. gradient (low to high)
- transports molecules through a carrier protein
} ATP is hydrolysed to release energy, changes shape of tetiary structure of carrier protein to push substances through.
3.2.3 Transport across cell membranes
Co-transport
- transports 2 molecules through a carrier protein (co-transporter protein.)
- i.e. absorption of glucose lining the ileum.
3.2.3 Transport across cell membranes
Absorption of glucose lining the ileum:
- AIM: glucose transported from lumen -> epithelial cell -> capillary
- Na+ / glucose co transporter protein (carrier protein) } Low conc of glucose in lumen than in epithelial cell. High conc of glucose in lumen that epithelial cell.
- Na+ moves down conc. gradient into epithelial cell, glucose binds to Na+ and goes through too.
- Na+ actively transported out of epithelial cell and into capillary transporting K+ inside (Na+ / K+ pump) } creates conc. gradient of glucose.
- Glucose moves down conc. gradient from epithelial cell to capillary via a glucose channel protein (specific to movement of glucose.)
3.2.3 Transport across cell membranes
The rate of gas exchange by diffusion becomes more rapid as:
- Conc. or water potential gradient becomes more steep.
- The diffusion distance decreases : one cell thick, thin capillaries.
- Surface area increases i.e: microvilli epithelial cell.
- Temperature increases.
3.2.3 Transport across cell membranes
Increase in channel or carrier proteins in the membrane?
FACILITATED DIFFUSION:
Channel and carrier proteins
ACTIVE TRANSPORT
Carrier proteins.
- Movement is limited by the number of channel or carrier proteins } once proteins become saturated
(in use) the increase in rate will stop. - speed, temperature and pH affect the tetiary structure and FD and AT as they rely on carrier and channel proteins.
- amount of ATP only affects AT. ATP produce by respiration so rate of respiration would also affect AT.
3.2.3 Transport across cell membranes
How to work out dilution series?
PRACTICAL SKILLS
- (Required conc. / conc. of solution)
- Vol / ANS = amount transferred to a new test tube
- Vol - amount transferred to a new test tube = amount of distilled water.
i.e If you want to make 15cm3 of 0.4M sucrose solution:
Start with know concentration, 1M.
1. 1 / 0.4 = 2.5 } want the solution you make to be 2.5 x weaker than the one you have.
2. 15 / 2.5 = 6cm3 } transferred to a new test tube
3. 15 - 6 = 9 cm3 } amount of distilled water added.
3.2.3 Transport across cell membranes
What happens when a plant tissue is placed in hypotonic solution?
HypOtonic solution: the cell to expand and eventually burst. Lower solute concentration than plant tissue.
- Water moves into the plant tissue by osmosis
- Plant tissue increases in mass.
3.2.3 Transport across cell membranes
What happens when a plant tissue is placed in hypertonic solution?
HypErtonic solution: cell shrinks. Higher solute concentration than plant tissue.
- Water particles move out of plant tissue.
- Plant tissue decreases in mass.
3.2.3 Transport across cell membranes
What happens when a plant is placed in isotonic solution?
Isotonic solution: same solute concentration as plant tissue.
- No net movement of osmosis / water particles.
- Solution has same water potential as plant tissue.
3.2.3 Transport across cell membranes
Why are the plant tissues left in the solution for a long time?
- To allow time for osmosis to occur until the plant reaches equilibrium with its surrounding solution.
3.2.3 Transport across cell membranes
Why is the percentage change used instead of actual change in mass?
- Plant tissue may not have the same starting mass.
- % change allows for comparisons.
3.2.3 Transport across cell membranes
Why are the potato tubes dabbed dry after removing it from the sucrose solution?
- To remove any excess water on its surface.
3.2.3 Transport across cell membranes
Why is the temperature kept constant when measuring the effect on mass of plant tissue?
- will affect rate of movement
} water bath at constant temperature i.e. 30°C
3.2.3 Transport across cell membranes
Why is a calibaration curve used?
They determine the concentration of an unknown sample by comparing it to a set of standard values with known concentrations.
3.2.3 Transport across cell membranes
What are two factors that affect the permeability of cell membranes?
- Temperature
- Concentration of solvents (ethanol)
3.2.3 Transport across cell membranes
How is beetroot used to measure the permeability of cell membranes?
- Higher permeability = more red pigment leaks out of beetroot within a given time.
- Colorimeter = used to measure the absorbance / concentration of pigment. } more light that passes through = less permeable = less concentrated.
3.2.3 Transport across cell membranes
What is the effect of temperature on membrane permeabilty?
- Increase temperature = increase in membrane permeability = increase in fluidity of phospholipid bilayer / denature transport proteins above certain temp.
3.2.3 Transport across cell membranes
What is the effect of ethanol concentration on membrane permeability?
Increase in ethanol concentration = increase in membrane permeability = dissolve bilayer / denature proteins above certain temp.
3.2.4 Cell recognition and the immune system
Define an antigen.
- A foreign protein that stimulates an immune response
3.2.4 Cell recognition and the immune system
Describe how antigen variability effects disease and disease prevention.
- Antigen variability means that antigens on the surface of the virus for example are changing all the time so each time you’re infected by a new virus, you won’t have immune cells with complementary receptors.
- no rapid response to an infection like you would if you was vaccinated.
3.2.4 Cell recognition and the immune system
What are two defence mechanisms?
Non-Specific:
- Physical Barrier (i.e. skin)
- Phagocytes (phagocytosis)
- Same for all pathogens
Specific:
- Cell mediated response (T Cells)
- Humoral response (B Cells)
- Slower but longer lasting
- Specific to particular pathogens/antigens
3.2.4 Cell recognition and the immune system
What is the process of phagocytosis?
-
CHEMOTAXIS: Phagocyte is attracted to a pathogen by the chemical products of the pathogen.
* moves towards pathogen along a conc. gradient. - Phagocyte has many receptors on its CSM that attach to chemicals on the surface of the pathogen.
- Pathogen is now engulfed and forms a vesicle. Lysosomes move towards the vesicle and fuse with it.
- Lysosomes contain hydrolytic enzymes } lysozymes released into phagosome. Lysozymes destroy ingested bacteria by hydrolysis of cell wall.
- Hydrolysis products of pathogen are absorbed by the phagocyte.
3.2.4 Cell recognition and the immune system
What are two types of lymphocytes and how are they different?
B lymphocytes:
* mature in bone marrow
* associated with humoral immunity, involving antibodies that are present in bodily fluids.
T lymphocytes:
* mature in thymus gland
* associated with cell-mediated immunity
3.2.4 Cell recognition and the immune system
Describe the response of T lymphocytes to a forgein antigen.
- Pathogens are engulfed by phagocytes.
- Phagocyte places antigens on the CSM. } APC (antigen presenting cell)
- Receptors on Helper T-cell can attach to the antigens on the CSM.
- Attachment activates T cells to divide rapidly by mitosis and form clone of genetically identical cells.
CLONED CELLS:
a) develop into memory cells: enable a rapid response to future infection by the same pathogen.
b) macrophages: perform more phagocytosis.
c) stimulate B cells to divide and secrete their antibodies.
d) activate cytotxic T cells.
3.2.4 Cell recognition and the immune system
How do cytotoxic T cells kill infected cells?
- produce protein called perforin makes holes in CSM.
- Holes = CSM becomes freely permeable to all substances and cell dies.
3.2.4 Cell recognition and the immune system
What is the role of APC?
antigen presenting cell
- APC presents antigens to helper T cells to activate the T cells during cellular response.
3.2.4 Cell recognition and the immune system
Describe role of helper T cell.
- Stimulates B cells and cause cytotoxic cells to divide.
3.2.4 Cell recognition and the immune system
Describe the response of B lymphocytes to a forgein antigen.
- The antigens on the surface of the invading pathogen is taken up by B cells.
- B cell processes antigens and presents it on its surface.
- Helper T cell attaches to processed anitgens on B cell. } activates B cell.
- B cell is activated and divides by mitosis to give plasma cells or memory cells.
- Plasma cells produce and secrete antibodies that exactly fit the antigen on the pathgogen’s surface.
- Antibody attaches to antigens on the pathogen and destroys them.
3.2.4 Cell recognition and the immune system
Define an antibody.
- A protein specific to an antigen and is produced by b cells
3.2.4 Cell recognition and the immune system
Describe the antibody’s structure.
- Constant region made up of 2 heavy polypeptide chains and 2 light polypeptitde chains.
- Chains held by disulfide bridges
- Variable region provides a binding site to form antigen-antibody complexes.
3.2.4 Cell recognition and the immune system
How does an antigen-antibody complex form?
- each antibody has a specific binding site which fits exactly onto the antigen.
- binding site is different on different antibodies } variable region.
- each binding site consists of sequence of amino acids that form a specific 3D shape that binds to the specific antigen.
- rest of the antibody is called constant region
3.2.4 Cell recognition and the immune system
Destruction of an antigen (of bacterial cells).
(advantage of agglutination as well)
- Antibodies don’t destroy antigens but prepares them for destruction.
- Antibodies are flexible } can bind to multiple antigens to clump together = agglutination
ADVANTAGE OF AGGLUTINATION
* makes it easier for phagocytes to locate and destroy pathogens as they are less spread out.
3.2.4 Cell recognition and the immune system
What is the role of plasma cells in producing the primary immune response?
- secrete antibodies usually in blood plasma
- antibodies lead to destruction of antigens
- responsible for the immediate defence of the body against infection.
3.2.4 Cell recognition and the immune system
What is the role of memory cells in producing the secondary immune response?
- Live longer than plasma cells and circulate in the tissue and blood fluid.
- when they encounter the same pathogen later, they divide rapidly to produce plasma and memory cells
- provide long term immunity and an increase amount of antibodies is secreted at a faster rate than in primary immune response.
3.2.4 Cell recognition and the immune system
Why are vaccines used?
- introduces appropiate disease antigens into the body to stimulate an immune response against a particular disease.
- Memory cells are produced and remain in the blood and allow a greater and immediate response.
- results in rapid production of antibodies
- new infection is overcome before it can cause harm.
3.2.4 Cell recognition and the immune system
Explain the concept of herd immunity.
- when enough people are vaccinated, the disease cannot spread.
- Certain people can’t be vaccinated so rely on herd immunity.
- transmission of pathogen is interrupted.
3.2.4 Cell recognition and the immune system
What is the passive immunity? Give an example.
- introduction of antibodies from an outside source.
- no direct contact with the pathogen or its’ antigens. Immunity is immediate.
- No lasting immunity as memory cells are not produced e.g: immunity acquired by a foetus when antidbodies pass across the placenta from the mother.
3.2.4 Cell recognition and the immune system
What is natural active immunity? Give an example
- results from indivdual becoming infected with disease under normal circumstances
- body produces its own antibodies
3.2.4 Cell recognition and the immune system
What is artificial active immunity? Give an example
- Vaccination
- introduce immune response in an indivdual without them suffering the symptoms of the disease.
3.2.4 Cell recognition and the immune system
Describe the structure of HIV.
- Lipid envelope, embedded with attachment proteins.
- Inside envelope is protein layer called capsid encloses two single strands of RNA and some enzymes.
- Reverse transcriptase catalyses the production of DNA from RNA.
3.2.4 Cell recognition and the immune system
Explain the replication of HIV in helper T cells.
- HIV enters the bloodstream and circulates the body.
- CD4 (a protein) binds to HIV.
- Protein capsid fuses with the CSM. RNA and enzymes of HIV enter the helper T cell.
- HIV reverse transcriptase converts virus’s RNA to DNA.
- DNA moves into the helper T cell’s nucleus which is inserted into cells DNA.
- HIV DNA in nucleus creates mRNA using cell’s enzymes.
- mRNA leaves the nucleus through the nuclear pores, using the cell’s protein synthesis to make HIV particles.
- HIV particles break away from the helper T cell with piece of CSM surrounding them forming a lipid envelope.
3.2.4 Cell recognition and the immune system
How does HIV cause the symptoms of AIDS?
- HIV particles kill / interfere with helper T cells, reducing their number in the blood.
- without T cells, the immune system cannot stimulate B cells to produce antibodies or cytotoxic cells or memory cells that kill infected cells.
- Body is unable to produce enough immue response becoming vunerable to infections + cancers
- Secondary diseases can kill the patient ; infections of organs, weight loss, diarrohea developed.
3.2.4 Cell recognition and the immune system
Why are antibiotics ineffective against viruses?
- Viruses rely on host cells to carry out their metabolic activities and thus lack in their own metabolic pathways and cell structure.
- antibiotics are ineffective as there are no metabolic mechanisms or cell structures for them to disrupt.
3.2.4 Cell recognition and the immune system
Describe monoclonal antibody therapy to treat cancer.
- Monoclonal antibodies are produced that are specific to antigens on cancer cells.
- Antibodies are given to patients and attach themselves onto receptors on their cancer cells.
- Attach to the surface of their cancer cells and block chemical signals that stimulate uncontrolled growth.
3.2.4 Cell recognition and the immune system
Give 3 examples of ethical issues of monoclonal antibodies.
- Uses mice in production
- have been some deaths associated with the use (important the patient has full knowledge of the risks and benefits involved before giving permission.)
- testing for safety of new drugs presents certain dangers.
3.2.4 Cell recognition and the immune system
What are the ethical issues with using vaccines?
- Animal testing.
- Side-effects.
- How should trials be carried out?
- Is it acceptable to try a new vaccine with unknown health risks?
- Should the vaccine be compulsory?
3.2.4 Cell recognition and the immune system
Explain how the ELISA test works.
- Apply the sample to a surface (slide) where antigens in the sample will attach.
- Wash the surface many times to remove any unattached antigens.
- Add the antibody that is specific to the antigen leaving them to bind.
- Wash the surface to remove any excess antibodies.
- Add a second antibody, that has an enzyme attached to it, that binds with the first antibody.
- Add colourless substrate of the enzyme. The enzyme acts on the substrate changing it into a coloured product.
- The amount of antigen present is relative to the intensity of the colour that develops.
3.2.4 Cell recognition and the immune system
Describe how giving a vaccine leads to the production of antibodies against a particular disease.
- Vaccine contains antigen of disease.
- Specific helper T cells stimulate B cells.
- B cells divide to produce plasma cells.
- Plasma cells secrete antibodies.
3.2.4 Cell recognition and the immune system
In ELISA test why is it important to wash the well?
- to remove any unbound second antibodies otherwise enzymes may be present.
3.2.4 Cell recognition and the immune system
The number of people diagnosed with AIDS is always lower than the number of people diagnosed with HIV. Suggest why.
- AIDS sufferers have to be infected with HIV.
- Not all people with HIV will develop AIDS.
3.2.4 Cell recognition and the immune system
Number of people diagnosed with HIV rose dramatically between 1998 and 2004. Suggest why.
- More testing for HIV.
- Increase in heterosexual transmission.
