General Flashcards
What is a glycocalyx?
A carbohydrate rich coating that covers the outside of many eukaryotes and prokaryotes.
Compare the nucleus of prokaryotes and eukaryotes.
Prokaryotes - no nuclear membrane.
Eukaryotes - nucleus, nuclear membrane, nucleolus.
Compare whether the organelles in prokaryotes and eukaryotes are membrane bound.
Prokaryotes - no
Eukaryotes - Yes e.g lysosomes, mitochondria, chloroplasts.
Compare the flagella in prokaryotes and eukaryotes.
Prokaryotes- made with 2 proteins.
Eukaryotes - made with multiple microtubules.
Compare the Glycocalyx in prokaryotes and eukaryotes.
Pro- Present as capsule or slime layer.
Eu - Present but chemically simple - cellulose or chitin.
Compare the cytoplasm and cytoskeleton of prokaryotes and eukaryotes.
Pro- No cytoplasm and cytoskeleton
Eu- Cytoskelton and cytoplasm.
Compare the ribosomes of prokaryotes and eukaryotes.
Pro- small 70s
Eu- 80s and small 70s in organelles.
Compare the DNA of prokaryotes and eukaryotes.
Pro- single circular chromosomes with no histones.
Eu- multiple linear chromosomes with histones.
Compare the methods of cell division in prokaryotes and eukaryotes.
Pro - Binary fission
Eu- mitosis / meiosis
What are the benefits of an organism being multi-cellular (Eukaryotes).
Multi-cellular organisms are prey for fewer predators, can eat a wider variety of prey, longer life span, specialism for adaption and efficiency.
What is cytosol?
The intracellular fluid of cytoplasm. Contains dissolved ions, glucose, Aino acids, ATP, lipids and waste products.
Site of enzyme-controlled reactions.
What is the purpose of the cytoskeleton?
Provides structural support to maintain the shape and size of the cells and enable their specific function.
Provides anchorage for organelles so they don’t get moved around and damaged.
Allow cell locomotion for example in cillia and flagella.
Also important to cell communication.
What are the 3 main filament types in a cytoskeleton?
Microfilaments, intermediate filaments, microtubules.
What proteins are microfilaments in the cytoskeleton made from?
Actin and myosin.
What are the purpose of microfilaments in the cytoskeleton?
Surround the edge of the cell, help generate movement, provide mechanical support needed for cell strength and shape, create microvilli.
How do microfilaments in the cytoskeleton allow a cell to move?
Microfilaments break and reform constantly to allow the cell to move.
How do microfilaments in the cytoskeleton help when forming blood clots?
Microfilaments break and move out to form new adhesions and increase the size of platelets. This creates a large surface area and allows a blood clot to form.
What proteins are the intermediate filaments of the cytoskeleton made from?
Keratin, vimentin and lamination’s.
What are the purpose of intermediate filaments of the cytoskeleton.
They are very strong and are found in parts of the cell which are under mechanical stress such as the skin. They help stabilise the positions of the organelles within the cell.
What proteins are the microtubules in the cytoskeleton made from ?
Tubulin
What is the purpose of the microtubules in the cytoskeleton?
Help with cell strength and movement of organelles such as vesicles during cell division. Provide structure to the flagella.
Where are microtubules formed?
In the centrosome then radiate outwards.
What is the function of centrosomes?
Growth of mitotic spindles during cell division.
What do centrosomes consist of ?
2 centrioles (cylindrical structures composed of 9 clusters of microtubule triplets, both at right angles to each other. ) Pericentriola material (protein material) surrounds the centrioles.
What are cilia made of?
Microtubule core and surrounded by a membrane.
What is the function of cilia?
Transport of fluid along a cell surface.
How does smoking contribute to ectopic pregnancy in women (explain in terms of cilia).
Smoking destroys the cilia, resulting in building-up of mucus, dust and bacteria within the lungs. This build up pass the oocyte towards the uterus and so increases risk during pregnancy.
Name a human cell where a flagella is necessary
Sperm
Where does the endoplasmic reticulum extend from and too?
The nuclear envelope to the cytoplasm.
Briefly describe the structure and look of the endoplasmic reticulum.
A network of membranes in the form of flattened sacs and tubules extending from the nuclear envelope to the cytoplasm.
What is the purpose of the rough endoplasmic reticulum ? And what feature allows this?
Ribosomes are on the surface of the RER and allow protein synthesis.
What happens to proteins that have been made by the RER?
Some enter the ER space for processing and sorting - by the Golgi body.
Some enzymes may attach carbohydrate groups to the proteins or attach the proteins to phospholipids. These molecules are incorporated into membranes of organelles or the plasma membrane.
Compare the presence of ribosomes and enzymes on the smooth and rough ER.
The smooth ER contains no ribosomes but the rough ER contains Alot of ribosomes.
The smooth ER has a greater range of different enzymes.
How does the wide range of enzymes on the smooth ER aid its function ?
Allows it to synthesise fatty acids and steroids such as oestrogen and testosterones.
What is the purpose of the smooth ER in the liver?
Helps release glucose from glucose-6-pand to detoxify lipid soluble drugs such as alcohol and pesticides.
What is the purpose of the smooth ER in muscles?
Stores Ca2+
How does taking drugs such as phenobarbital cause changes in the smooth ER and what are the side effects of this ?And where in the body is the smooth ER that has these changes?
Liver cells.
The cells produce more smooth ER to counteract the poison, meaning the person has to take more of the drug to feel the effect. Causes drug addiction.
What is the genetic material of ribosomes?
Ribosomal RNA
What do ribosomes consist of structurally?
A large subunit and a small subunit which are both synthesised separately in the nucleus. Consist of about 50 different protein types.
Where are ribosomes present in the mitochondria?
Free in the cytoplasm or attached to the endoplasmic reticulum (RER).
What is the overall function of ribosomes?
Protein synthesis
What do the cis and trans faces of the Golgi body face in the cell?
Cis/ convex entry- faces the endoplasmic reticulum.
Trans / concave exit - faces the plasma membrane.
How to the Golgi complex transport and process proteins?
Proteins are surrounded by the endoplasmic reticulum membrane
Transport vesicles containing polypeptide bud off smooth endoplasmic reticulum and fuse with the cis face of the Golgi apparatus, releasing polypeptide into the lumen of the Golgi apparatus.
Proteins are modified and move into medial cistern.
Proteins then move towards the exit face where they are either formed into Golgi vesicles and then lysosomes, secretory vesicles which release polypeptide by exocytosis or membrane proteins which are inserted into the plasma membrane as a vesicle.
What is the general function of the Trans face of the Golgi apparatus?
Shipping
What is the general function of the Cis face of the Golgi apparatus?
Receiving
What are the main overall functions of lysosomes?
Digestion of substance entering the cell such as worn out organelles (Autophagy) or entire cells (Autolysis).
What is the digestion of worn out cells by lysosomes called?
Autophagy
What is the digestion of entire cells by lysosomes called?
Autolysis
Why is autophagy necessary?
Allows renewal, cellular differentiation and control of growth and tissue remodelling.
What is the cause of Tay-Sachs disease?
The absence of Hex A lysosomal enzyme.
Hex A normally breaks down the glycolipid ‘Ganglioside GM2’. Without being broken down it builds up and begins to destroy nerve cell function.
What are the symptoms of Tay Sachs disease ?
Seizures, muscle rigidity, blindness, very early death (Age 5 ish).
What is the function of peroxisomes and how do they do this?
Peroxisomes are involved with the metabolism of amino acids and fatty acids. They contain oxidases which oxidise toxic substances such as alcohol by removing a hydrogen atom.
Also contain enzymes to fight the toxic effects of hydrogen peroxide.
Where are a lot of peroxisomes found?
Liver
What is the cause of Zellweger syndrome ?
Autosomal recessive condition. Mutations in genes cause the peroxisomes to become non-functioning. This causes the myelin on neurones to breakdown and prevents the transmission of nerve impulses.
What are the symptoms of Zellweger syndrome and when is it developed?
Develop symptoms during the new-born period.
Wek muscle tone, feeding problems, hearing loss, vision loss, seizures.
What is the main function of proteosomes ?
Degrade cytosolic proteins (un-needed, damaged or faulty).
What enzymes do proteosomes contain?
Protease
How do proteosomes contribute to causing Alzheimers disease?
Caused by the build-up of misfiled proteins in brain cells.
On-going research to discover why these proteins are not degraded by Proteosomes.
What are the main functions of the mitochondria?
Aerobic respiration and ATP production.
What is the purpose of the cristae in mitochondria ?
Provide a large surface area for aerobic respiration.
Where are enzymes needed for respiration found in the mitochondria.
In the matrix and on the Cristae surface.
What might be the effect of centrosome inhibitors on cancer?
Centrosomes form the protein spindle fibres which are a necessity in cell division. They are therefore highly important when regulating cell division. If the centrosomes can’t form spindle fibres, cell division will become irregular and this can lead to the formation of some malignant tumours.
What are the functions of the plasma membrane?
Regulates what enters and exits the cell. Involved with cell recognition. Aids cell signalling. Enzymatic functions. Aids cell linking and cross-talk
Describe generally the structure of the plasma membrane.
Thin, flexible, fluid mosaic model.
How is the bi-layer able to be fluid and what is this fluidity used for?
Neighbouring phospholipids can swap places within the bi-layer. Allows movement of membrane components required for cell movement, growth, division, secretion and the formation of cellular junctions.
What is the purpose of cholesterol in the fluid mosaic model of the cell membrane?
Cholesterol immobilises the first few hydrocarbon groups of phospholipid molecules. This makes the lipid bi-layer less deformable and decreases its permeability to water soluble molecules.
What are glycoproteins used for in the phospholipid bi-layer of the cell membrane?
They contain oligosaccharides and form the glacocalyx.
How are glycoproteins helpful in red blood cells?
They help form the glacocalyx which acts as a slippery layer and helps red bloody cells move smoothly into the capillaries.
What are the purpose of transmembrane proteins?
Transport substances from outside and inside the cell.
If a membrane was depleted of cholesterol what would happen to the membrane structure?
The membrane bi-layer would be more deformable due to becoming less rigid. Permeability to water-soluble molecules would also increase.
What is the main purpose of the phospholipid bi-layer?
Separates hydrophilic and hydrophobic domains.
What type of permeability does the phospholipid bilayer have?
Selective permeability
What molecules is the phospholipid bilayer permeable and I’m-permeable to?
Permeable = non-polar, lipid soluble (oxygen and carbon dioxide) Impermeable = ions and large molecules (Glucose).
How does water pass through the phospholipid bi-layer?
Via aqua-porins.
What is the overall purpose of the phospholipid bi-layer being semi-permeable?
Allows concentration gradients to be built and pH to be regulated.
What are channel intrinsic proteins generally used for?
Used for charged ions usually.
What are carrier channel proteins generally used for and name some of their features?
Carrier proteins are specific to the substance they and transporting. They require a constant concentration gradient.
Used for larger molecules such as glucose.
What is the use of carrier proteins subject to?
Transport maximum (how many carrier proteins are actually present), saturation (the quantity of carrier proteins which are already occupied).
How many molecules can a carrier protein transport at once and why?
1 because they are gated and highly specific.
How does temperature affect the rate of diffusion?
As temperature increases, so does rate of diffusion.
How does the mass of the substance moving affect its rate of diffusion?
The greater the mass, the slower the rate of diffusion.
How does diffusion distance affect the rate of diffusion?
As diffusion distance increases, rate of diffusion decreases.
How does concentration gradient affect rate of diffusion?
As concentration gradient increases, so does rate of diffusion.
What happens to a cell when placer in a hypertonic solution and why?
The concentration of ions inside the cell is lower than outside the cell. Water moves out of the cell by osmosis. Cell shrinking.
What happens to the cell when placed in a hypotonic solution?
Concentration of ions inside the cell is higher. Water moves into the cell. Osmotic lysis.
What is an isotonic solution?
Concentration of ions inside and outside the cell is the same.
How is cerebral edema treated?
Hypertonic solution is infused to drain extra water out of the brain.
What is the energy source for active transport?
Uses energy from the hydrolysis of ADP.
Give an example of a active transport mechanism.
sodium potassium pump.
Does active transport require inter membrane proteins and if so which?
Yes - carrier proteins.
ATP changes the shape of carrier proteins and allows substances to be pumped against the concentration gradient.
What is another name for secondary active transport?
Co-transport
What is symport in secondary active transport?
Molecules travel in the same direction.
What is antiport in secondary active transport?
When molecules travel in opposite directions.
What is the positives of using secondary active transport?
More efficient than primary active transport because less ATP is required - uses alternative energy source.
How do intrinsic channel and carrier proteins differ?
Carrier proteins are gated and specific and also carry only one molecule at a time.
Channel proteins are non-specific and are constantly open.
What enzymic functions do membrane proteins have?
Act as digestive enzymes.
What will happen in receptor mediated endocytosis if no Cathrin is present?
Vesicles cant form and no LDL’s will be taken into the cell.
How do viruses often take advantage of the receptor mediated endocytosis process?
Viruses attach to the receptor proteins on the cell surface membranes and are taken into the cell by receptor mediated endocytosis. HIV attaches to CD4 receptors.
Outline the process of phagocytosis.
Chemotaxis of microbe to phagocyte.
Ingestion of microbe by phagocyte by endocytosis.
Formation of phagosome.
Fusion of phagosome with a lysosome to form a phagolysosome.
Digestion of ingested microbes by enzymes.
Formation of residual body containing indigestible material.
Discharge of waster material by exocytosis.
Which cells undergo phagocytosis?
Macrophages and neutrophils.
Outline bulk phase endocytosis.
Small droplets of extracellular fluid are taken into the cell by endocytosis.
Where does bulk phase endocytosis occur on mass?
Intestines and kidneys.
Does bulk phase endocytosis require receptors and is it selective?
No receptors required.
All solutes in the extra-cellular fluid are brought in. Non-selective.
What is the main purpose of exocytosis?
Used to transport materials out of the cell.
What are the main cells that exocytosis is exhibited by and what do they release?
Secretory cells - digestive enzymes and hormones.
Nerves - neurotransmitters.
What is transcytosis ?
A combination of endo and exocytosis used to pass substances through the cell.
Where is transcytosis common?
Endothelial cells which line blood vessels.
Describe the process of Co-transport of glucose in the small intestine.
In notebook
Describe how the second messenger model works with adrenaline.
In notebook
What is it called when Glycogen is converted to Glucose
Glycogenolysis
Describe the two possible ways vesicles can form during Receptor-mediated endocytosis.
Stimulated endocytosis- Vesicles form on the cell surface membrane when ligands bind to receptors.
Constitutive endocytosis - All receptors are taken into vesicles whether they are bound by ligands or no.
Describe how the vesicles form during receptor-mediated endocytosis.
The phospholipid PIP2 binds to AP2 adaptor proteins and allows their confirmation to change. A Cathrin coating is now able to bind to the AP2 receptors. The Cathrin buds in towards the cytosol to form a vesicle. Dynamic allows complete vesicle fusion and causes the vesicle to become un-attached from the cell surface membrane.
What is the purpose of dynamic in receptor- mediated endocytosis vesicle formation?
It allows complete vesicle fusion and allows the vesicle to become un-attached from the cell surface membrane.
What is the purpose of the Cathrin coating in receptor mediated endocytosis?
Cathrin coating buds in towards the cell cytosol to form a vesicle.
Describe the sorting process of vesicles in receptor-mediated endocytosis.
Vesicles fuse with early endoscopes. The acidic pH of the endoscopes cause AP2 receptors to release the ligands they are bound to into the endosome lumen.
Some ligands are degraded by the endosome whilst the receptors are packaged int more vesicles and returned to the plasma membrane.
However, any left over ligands and receptors form late endosomes.
Describe the maturation of the early endosomes in the receptor mediated endocytosis process.
Regions of the early endosome membrane cave into the lumen an bind off to form luminal vesicles. This creates multi vesicular bodies within the endosome. Now all of the endosome cargo (phospholipids) is contained within the lumen and is accessible to prolytic enzymes.
Describe the glycosylation of endosomes in the receptor- mediated endocytosis process and what is the purpose of this?
Transferase enzymes within the endosome covertly bond carbohydrates to proteins in the endosome membrane. This creates a thick, protective glycocalyx which cannot be degraded by lysosome enzymes.
Describe the acidification of late endosomes in receptor-mediated endocytosis.
Endosomes contain proton pumps that continually transport H+ into the endosome, making it more acidic. By the time the late endosome is formed, the endosome is highly acidic.
What happens after the late endosomes are formed in receptor-mediated endocytosis?
Late endosome fuses with a lysosomes. Lysosomal enzymes degrade proteins, lipids, DNA and RNA into smaller components. There smaller components are transferred into the cell cytosol and re-purposed. The left over lysosome can then fuse with another endosome.
Draw the Golgi packaging system.
In notes.
How is resolving power affected as frequency of light waves increases?
Resolivng power also increases
Name some types of optical microscopy.
Phase contrast, DIC, Dark field, Polarisation, UV, Fluorescent, Light field.
Describe the specimen used and images produced by phase contrast microscopy.
Living, unstained cells
Cells appear black and white
How does phase contrast microscopy happen?
2 beams of light are used - one goes through the specimen and the other doesn’t. They eventually meet. This exaggerates the difference in the refractive index of the specimens and the surroundings.
How do Normarski/ DIC microscopy images appear?
They have a high resolution and give a 3D appearance which shows the structure of the sample well.
How do Dark field microscopy images appear?
Illuminates cells and tissues against a dark background to allow for contrast.
How do polarisation microscopy images appear?
Illuminates cells and tissues against a dark background to allow for contrast.
How are Polaroid microscopy images produced?
The specimen is places between crossed polaroids. Areas where the plane of polarisation has been rotated are seen as brighter than the background. This method detects areas of highly organised rays.
How do polaroid microscopy images appear?
They detected areas of highly organised rays and illuminates cells and tissues against a dark background to allow for contrast.
What are highly organised rays in terms of sample specimen? - polarisation microsopy
X
How does UV microscopy work and what do UV images appear like?
Uses fluorescent molecules to observe structures. Certain substances within the cell strongly absorb UV and can be detected when illuminated with a UV light source.
What is needed to be able to see a UV microscope image?
UV light source
How does fluorescent microscopy work and what do the images look like?
Certain substances appear fluorescent at a particular wavelength of light or can be made fluorescent by the use of histochemical reactions. This makes the cell become visible.
What is multiple fluorescent microscopy?
Where each organelle appears a different fluorescent colour due to the wavelength of light or the use of histochemical reactions.
What is confocal fluorescent microscopy?
A method used to cleaner and resolve a fluorescent microscope image.
What is the disadvantage of using bright field microscopy?
You must stain the cells which can be damaging.
Describe how confocal microscopy works and what type of image this creates.
Lasers and optical modification are used to focus light onto a single plane. This produces a highly precise, small slice of the specimen in an image.
What 2 types of microscopy are often combines and why?
Phase contrast and fluorescent. They create a highly structured and coloured specimen image.
What is interference in terms of microscopy?
2 beams are used - one of them passes through the specimen and the other doesn’t. The light may therefore undergo phase changes due to the difference in the 2 refractive indexes that the light travels through.
What may interference in microscopy be used for?
Used to quantitatively measure. E.g find the dry mass of a sample.
What are phase changes in light?
Light waves changes by 180 degrees when they reflect from the surface of a medium with a higher refractive index than that of the medium to which they are travelling.
What type of specimen are usually stained during microscopy?
Thin specimens which are generally transparent at the visible light wavelengths.
What are vital dyes used for in microscopy?
They are used to assess culture viability by visualising how many of the cells in a culture are live and dead.
What are the 2 types of vital dye use in microscopy?
Vital dye exclusions and vital dye uptakes
What is vital dye exclusions in microscopy?
They are impermeable to live cells but permeable to dead cells. The dead cells will become visible and therefore countable
What is vital dye uptake in microscopy?
They are permeable to living cells and therefore make the living cells become visible and therefore countable. Not able to penetrate dead cells.
What is the most common type of staining used for microscopy and what does it do?
H&E staining
Haemotoxylin makes the nuclei stain blue.
Eosin stains the cytoplasm pink.
What stain is often used to stain neurones in microscopy and what colour does it go?
Golgi silver stain - black
What stain is often used to stain nucleic acids in microscopy and what colour does it go?
Nissl stain - purpose
What stain is often used to stain DNA in microscopy and what colour does it go?
Feulgen Schiff - Red
Outline the process of enzyme histochemistry.
Incubate a tissue sample with a specific substrate. The enzymes within the tissue sample react with the substrate. The complex formed has a coloured appearance and therefore identifies where enzymes are present in your sample.
What is the purpose of enzyme histochemistry?
To see the location of enzymes within a cell
What is the main purpose of autoradiography?
It uses radioactive sources to blacken desired regions of the photographic plate.
Outline the process of autoradiography.
Precursor substances containing labeled 14C or 3H are injected into the organism. The radioactive precursor substance is then used to make radioactive versions of the desired substance.
When the sections are later prepared and placed on a photographic pate or coated with photographic emulsion, black grains will appear where the radioactivity is present.
What is meant by the term ‘in vivo’?
Within a living orgaism
What is the precursor substrate for proteins during autoradiography?
Amino acids
What is the precursor substrate for DNA during autoradiography?
Thymidines
What is one of the main uses of microscopy in the clinic environment?
Immunofluorescence
What are the 2 types of immunofluorescence?
Direct and indirect
Describe direct immunofluorescence.
Specific antibodies against an antigen are labelled with fluorescent due. Antibodies then bind to the antigen and act as a labeller.
Describe indirect immunofluorescence.
Specific primary antibodies bind to the antigen. Secondary antibodies labelled with the fluorescent dye then bind to the primary antibodies.
What are the advantages of indirect immunofluorescence over direct immunobluorescnc?
Allows more binding of secondary antibodies to the primary antibodies. Therefore more fluorescent markers and present and a stronger colour image is produces.
It is a lot cheaper.
Easier process
What is tissue fixation?
The cessation of the normal life functions of the tissue and the preservation of the tissue sample.
Define resolution
The ability to distinguish between two or more objects which are close together.
What is the equation for resolution?
On laptop notes
What do the letters D, N and alpha stand for in the resolution equation?
D= resolution N = refractive index alpha = angular apeture
What is the refractive index of air?
1.0
What is the refractive index of oil?
1.5
What are arrays in terms of microscopy?
Lots of repeats of the same structure in an area of the cell
What is the purpose of the condenser in a microscope?
Focuses light onto the specimen and controls the contrast.
What is the purpose of the objective in a microscope?
Collects light from the image and focuses it to form an image within the barrel of the microscope.
Define resolution limit.
The smallest distance a which two separate items can be distinguished.
Depends on the wavelength of light used and the properties of the optical components.
What is the purpose of immersion oil in light microscopy?
Increases resolving power - most frequently used under a high magnification.
What are protozoans?
Single-celled, microscopic organisms.
What are axonemes on cilia?
A bundle of microtubules formed from tubular and their associated proteins extend from the base to the tip of the cilia.
What is meant by the “9+2” array structure in cilia?
The microtubules in the axoneme are arranged in a pattern of nine doublets in a ring around a central pair of microtubules.
What causes the cilia to be able to move and how is this triggered?
The bending of the axoneme stimulated by Calcium and ATP.
Adjacent microtubules slide with respect to each other to create a sliding activity and therefore a coordinated wave like movement.
What is the purpose of tetrahymena in relation to cilia?
It can re-generate cilia which have been gently removed.
How do Colchicine and Colcemid affect cilia?
They inhibit tubular monomers growing in microtubules.
When are membranes of adjacent cells most interactive?
During cancer cell metastasis and foetal development.
What is Metastasis?
Cancer split off from the primary tumour and travel around the body forming secondary tumours.
What controls the interactions between adjacent cell membranes?
Membrane proteins
Name some types of junctions which form between adjacent cells.
Desmosomes, Hemi-desmosomes, adherent junctions, tight junctions, gap junctions.
How many different types of gap junctions can adjacent cells have between them?
Infinite
What tissue types are desmosome gap junctions most frequently found in?
Cardiac and intestinal tissues.
Usually in epithelial cells.
Describe the structure of desmosome gap junctions.
They have a central glycoprotein core. This is then joined to connecting filaments which join to desmosomal plaques. Tonofilaments then join the desmosomal plaques to the cell’s cytoskeleton and organelles.
What type of binding do desmosome gap junctions use?
Homophillic binding
What is homophillic binding?
The binding of a receptor molecule to an identical molecule.
What type of proteins are used in desmosome gap junctions?
Cadherins
What type of adhesions do desmosome gap junctions make?
Cell-to-cell junctions.
What is the purpose of hemidesmosomal gap junctions?
Adhere cells to their basal lamina.
What is a cells basal lamina?
A layer of extracellular matrix secreted by the epithelial cells. Basement layer that the cells sit on.
How do adherent gap junctions cause cell to cell adhesion?
Adherents junctions use cadherins transmembrane proteins which are tethered via linker proteins to actin filaments. The cadherins on the plasma membranes of adjacent cells interlock and cause adhesions.
Where are adherent gap junctions most commonly used? (What tissue type?)
Epithelial tissues
What is the main importance of adherents junctions in the body?
They are used in development to form the neural tube and lens vesicles which allow round lenses to be formed in the eye.
What cell types are tight junctions found in?
Only in epithelial cells.
What are the purposes of tight gap junctions?
They prevent passage of materials between cells and therefore force materials to travel directly through cells. This tightly controls the movement of substances into and out of the blood.
Also contributes to membrane asymmetry to allow active and passive processes to be separated.
What structures do tight junctions occur at?
At intervals or encircling cells ( a cell tightly attaches to all of its neighbouring cells in a circular formation).
What would happen if tight junctions were not present in the gut?
Glucose would be lost during co-transport from the lumen of the small intestine into the capillaries. Therefore, glucose would never enter the blood capillaries.
What evidence has been found that tight junctions act as permeability barriers? Describe the experiment.
Electron-opaque tracer is added to one side of the cell layer. If tight junctions are present, the electron-opaque tracer will only travel part way between the cells and will be unable to pass through the gaps in the cells.
In what types of organisms do gap junctions occur in?
Multicellular animals
Describe the structure of gap junctions.
Connexons are hexagonal proteins that form a ring structure with a central pore. These then join each adjacent cell.
How are gap junctions controlled to control movement into and out of the adjacent cells?
Connexons can be rotated to change the size of the central pore between adjacent cells.
How are gap junctions beneficial if a neighbouring cell is undergoing apoptosis?
The connexions would rotate and make the central pore between adjacent cells close. Therefore the cell undergoing apoptosis will not pass any harmful toxins to the adjacent cells.
What is the overall purpose of gap junctions between adjacent cells?
Control cell communication
What is ionic coupling and what is its purpose in gap junctions in adjacent cells?
The movement of ions between cells via the pores produced. This allows metabolic cooperation and cellular synchornisation.
