cytology Flashcards
what is the average cell diameter?
5-10 um
what does a general cell consist off ?
- outer border - plasma membrane which surrounds cytoplasm
- cytoplasm- which contains organelles
- organelles
- nucleus - which is most prominent organelle
what is the function of plasma membrane ?
- integrity of cell - keeps inside of cell from outside
not generally permeable but a simple barrier, there is selective barrier which allows small uncharged molecules to pass through such as CO2 , O2 - specific regulation of passage of molecules inwards and outwards
- communication site - receptors for molecules in extracellular fluid
e.g. hormones , neurotransmitters and drugs
what is the size of plasma membrane ?
. 5-7nm
what is the structure of plasma membrane ?
. not a solid/rigid structure but a FLUID MOSAIC
— fluid structure allows cells to move and change shape
composed of :
1. bilayer of phospholipid molecules which are dispersed
2. protein molecules -
3. cholesterol molecules
4. there are also sugar groups attached to the surface - glycocalyx
what is the structure of phospholipid bilayer ?
- polar - HYDROPHILIC head - attracted / soluble in water
2. non-polar - HYDROPHOBIC tail - repelled/insoluble in water
what are molecules that are hydrophobic at one end and hydrophilic at other end known as ?
AMPHIPATHIC
what happens to phospholipids in water ?
. in water phospholipids will automatically form bilayers, the hydrophilic heads contacting the water , and the hydrophobic tail hiding in between , facing one another
what happens if the membrane becomes disrupted ?
it will automatically reform into a bilayer
where is cholesterol located in the membrane ?
cholesterol sits in between fatty acid tail
what is the function of cholesterol ?
. it immobilises the first few hydrocarbon groups of the phospholipid molecules . this makes the lipid bilayer less deformable and decreases its permeability to small-water soluble molecules
. it also prevents the hydrocarbons from joining and crystallizing
what are the two types of membrane proteins ?
- integral proteins - which span the membrane and act as gates for passage of molecules in or out cell
. they can be components of receptors - peripheral proteins - bound to face one another
. they help in opening and closing of gates
what is the function of membrane proteins ?
- transport
- enzymatic activity
- receptors for signal transduction
- intercellular joining
- cell-cell recognition
- attachment to cytoskeleton and extracellular matrix
how do proteins help in transport ?
protein spans membrane and provides a hydrophilic channel across membrane that is particular for certain solute
. some transport proteins hydrolyze ATP as an energy source to actively pump substances across membrane
how do proteins aid in enzymatic activity ?
. protein built into a membrane may be an enzyme with its active site exposed to substances in adjacent solution
how do proteins act as receptors ?
a membrane protein exposed to the outside of cell may have a binding site with shape that fits shape of chemical messenger such as hormone
how do proteins aid in intercellular joining ?
membrane proteins of adjacent cells may be hooked together in various intercellular joining that can help with cell migration
how do proteins aid in cell- cell recognition ?
some glycoproteins serve as identification tags that are specifically recognised by other cells
how do proteins aid in attachment to cytoskeleton and extracellular matrix ECM ?
elements of cytoskeleton and ECM are anchored to membrane proteins which help maintain cell shape and fix location of certain membrane proteins , others play role in cell movement or bind adjacent cells together
what is glycocalyx ?
glycocalyx is sugar coating of cell which can be pound to lipid or protein
. it is sugary cell coat which acts as specific marker for that cell
. all cells of multicellular organisms have carbohydrates on outer surface attached mainly to integral proteins
what is the function of glycocalyx ?
. plays a role in cell-cell recognition
- enables sperm to recognise egg cell
- signals which cells should be destroyed by phagocytosis
- determines the ABO blood group of red blood cells
what are the type of junctions you can find between cells ?
- sticky glycoproteins on surface of cell
- mechanical junctions
- specialised cell-cell junctions
what are mechanical junction ?
cause deformation and changes in shape of plasma membrane
what are examples of mechanical junctions ?
- ball and socket joint between lens fibres
- tongue and groove
mostly found between cells within the lens
what are the 3 examples of specialised cell-cell junction ?
. occluding ( tight )
. anchoring
. gap
what is occluding junction ?
adjacent proteins of opposing plasma membranes fuse together sealing the space between cells . this prevents passage of molecules between cells creating an
impermeable barrier
. main function is to limit flow
where occluding junctions found ?
in epithelial cell in skin to prevent water inside skin leaking out
what are anchoring junctions ?
adhering junctions or desmosomes are where adjacent cells are joined by fibres from the cells cytoskeleton
. the membranes of adjacent cells thicken into plaques
. plaques are anchored to the inside of cell by intermediate filaments
. they are very robust
what are plaques of adjacent cells linked by ?
cadherins which are integral proteins
where are desmosomes mostly found ?
found in tissues subject to severe mechanical stress
e.g. skin epithelium , cardiac muscle , uterus
what are desmosomes known as if they go along way ?
belt desmosome
what are desmosomes known as if it is a small area ?
belt desmosome
what is a hemidesmosome ?
desmosome links membrane to cytoplasm
what is a gap junction ?
adjacent cells are joined by membrane proteins but these proteins allow cytoplasmic continuity between cells. this means that molecules/ ions can pass directly from one cell to next
what are connexons ?
the junctions between membrane proteins in gap junctions
where are gap junctions found ?
the lens has no blood supply it receives nutrients from aqueous humour
the cells that make up lens are joined by gap junctions so nutrients can diffuse from lens surface to cells in its interior
What is the cytoplasm composed of?
1) Cytosol
2) Cytoskeleton
3) Membrane-bound organelles
4) Inclusions
What is cytosol?
viscous fluid content of the cell with other components suspended in it.
-mostly water, but also sugars, proteins, salts
What is cytoskeleton?
- suspended in cytosol
- cells skeleton
- strings of proteins which help cells make it shape etc (Architecture of cell)
What are membrane bound organelles?
- each organelle bound to a membrane.
- Individual structure with a specific function to play in a cell
e.g mitochondria - harness energy
ribosome- make protein
What are inclusions?
- Various substances found in some cells but not others
e. g melanin granules - brown pigment - found in epidermis of skin, in retinal pigment epithelium, in melanocytes scattered throughout choroid and ciliary body and iris
e. g lipid store- massive triglyceride stored in adipocytes - store for lipids (for thermal insulation in skin) or energy store - break down
Why do we have a cytoskeleton?
- Imparts shape to cell
- Mediates cytoplasmic movements of organelles
- crucial role of cell division
- responsible for whole cell movement- migrate around body
- provides framework to organise enzymatic reactions
What are the 3 main types of protein filament?
- Intermediate filaments
- microfilaments
- Microtubules