cytology Flashcards
What does a general cell consist of?
Outer border- PLASMA MEMBRANE which surrounds the CYTOPLASM containing ORGANELLES, the most prominent of which is NUCLEUS
What is the measurement for cm to m
cm x 10 -2m
What are the 3 main functions of a cell membrane?
Intergrity of cell- not generally permeable e.g different surfaces of epithelial cells have different permeabilities
Specific regulation of passage of molecules e.g selective and specific gates
Communication site- receptors for molecules in extracellular fluid for e.g hormones, neurotransmitters and drugs
What are the 4 elements which make up the structure of the plasma membrane?
1) bilayer of phospholipid molecules
2) protein molecules
3) cholestrol molecules
4) sugar groups attached to the surface which is - Glycocalyx
What is the phospholipid bilayer composed of?
Hydrophillic head which is polar and soluble in water- polar phosphate head
Hydrophobic tail which is non-polar and insoluble in water- 2 fatty acid tails
When both molecules hydrophillic and hydrophobic what are they known as?
Amphipathic
What are the important consequence of this amphipathic property?
IF the bilayer (membrane) has been disrupted it will automatically reform into a bilayer.
Have dual polarity
What is the main role of cholesterol?
-Stabilise the phospholipid bilayer by immoblising the first few hydrocarbon groups of the phospholipid molecules. This makes the lipid bilayer less deformable and descreases its permeability to small water soluble molecules.
What does cholesterol PREVENT from happening?
prevents the hydrocarbon chains from joining and crystalizing so it is still fluid and able to maintain its flexibility.
What are the 2 membrane proteins and what are their functions?
Integral proteins- they are span across the membrane and many act as a gate for passage of molecules
or they can be components of receptors- firmly anchroed between fatty acid tails- allows certain substance in and out
Peripheral proteins- are bound to one face or other - ‘anchors’- sit on the inner or outer surface of the plasma membrane- attached to the polar heads of phospholipid- most are glycoproteins forming glycocalyx
State the 6 functions of membrane proteins
Transport Enzymatic activity Receptors for signal transduction Intercellular joining cell-cell recognition attachment to cytoskeleton and extracellular matrix
How does a glycocalyx have a role to play in cell- cell recognition?
it enable sperm to recognise egg cell
it signals which cells should be destroyed by phagocytosis
determines ABO blood group of red blood cells
What does glycocalyx act as?
Acts as a specific marker for a cell.
What is the structure and positioning of a glycocalyx?
carbohydrate attached to a intergral protein
Explain the function of membrane proteins - Transport :
Transport- acts as a hydrophillic channel across the membrane that is selective for a particular solute.
Some ATP is hydrolysed as an energy source to actively pump molecules across the membrane
What are the 3 main junctions between cells?
- Sticky glycoproteins on cell surface
- Mechanical juncions
- specialised cell-cell junctions
What are the 2 main mechanical junctions?
Ball and socket joint between lens fibres- they lock together
Tongue and groove- they can slide across eachother as interwined
What are the 3 specialised cell-cell junctions?
Occluding (tight)
Anchoring (desmosomes)
Gap
What are occluding junctions ?
They are when adjacent protein molecules from opposing plasma membranes fuse which seal the space between cells, preventing the passage of molecules
What are anchoring junctions?
they are adhering junctions or desmosomes where adjacent cells are joined by fibres from cells of the cyoskeleton.
What are the properties of anchoring junctions?
They are very robust and are common in places with severe mechanical stress for e.g skin epithelium, cardiac muscle and uterus
What is a belt desmosome?
if the desmosome goes along way around the cell
What is a spot desmosome?
if the desmosome goes along a small area
WHat is a hemidesmosome?
when the cytoplasm is linked to the membrane
What is a gap junction and give an example of where they can be present?
adjacent cells which are joined by their membrane protein but these allow cytoplasmic contiunity between the cell. This means certain molecules/ions can pass from one cell to another directly.
An example of where they can be present is in the lens as the lens has no blood supply so it recieves its nutrients from the aqeuous humour which is stored in the anterior chamber. The cells that make up the lens are therfore gap junctions so nutrients can diffuse from the lens surface to cells in its interior.
What is the 4 things a cytoplasm is composed of?
1) Cytosol- which is viscous fluid content of the cell with other components suspened in it. It is largely made up of water but alongside sugars, proteins and salts etc
2) Cytoskeleton- which is suspended within the cytosol
3) Membrane bound organelles- individual structures which carry out specific functions e.g mitochondria for energy
4) Inclusions- substances which are found in some cells but not in others such as melanin in retinal pigment
What are the 5 things a cytoskeleton does?
Imparts shape to cell essential for cell division regulates the movement of organelles responsible for whole cell movement provides framework to organise enzyme reactions
WHat are the 3 components of cytoskeleton?
Actin filaments
mircotubules
intermediate filaments
Explain actin filaments
They consist of 2 strands of globular actin which are packed into a tight helix.
They support the cell and involve in the movement of the cell too.
Explain microtubules
They have the largest diameter
Made of alpha and beta tubulin which are arranged in long hollow tubes
They determine the cell shape and are dynamic so therefore involved in the movement within the cell
They also radiate outwards throughout cytoplasm which allow vesicles and fibres to travel through
How are microtubules organised?
By having a centrosome which consist of centrioles
WHat is the width and length of centrioles
- 2 micrometers wide
0. 4 micrometers long
How do the microtubules form the centrioles within the centrosome?
They are organised from being right angles from eachother.
There are 9 groups of microtubule triplets which form the wall of each centriole
What else do microtubules form the strcutural core of?
Cilia
What are cilia?
tiny hair like which allow fluid to move its contents over the surfaces of the cell.
What does a cilium consist of?
9 microtubule doublets
an e.g can be a flagella of a sperm
What are intermediate filaments?
They are very tough and durable and stable.
Organised like rope like polymers and are prominent to areas with mechanical stress
They form a basket aorunf the nucleus and extend outwards in curving arrays to the cells peripherey (plasma membrane)
What is the structure and components of the mitochondria?
most abundant organelle
powerhouse of cell- produces energy
abdundant in active cells for e.g cardiac
they are semi-autonomous which means they have their own DNA just like bacteria and posses own protein synthesis machinery for their own proteins
they are continuously reproducing division and growth
What is the structure of mitochondria?
Composed of 2 lipid bilyaers smooth outer membrane narrow intermembrane space crista- the more means increased surface area for e.g in more active cells containing more cristae jelly like matrix
WHat is the structure of the nucleus?
control centre - 5-10 um diameter
not present in red blood cells
regular shape but irregular in cancer cells
The nucleolus is composed of a nucleoplasm which is a membrane which surrounds it.
surrounded by a double membrane with space between (PERINUCLEAR CISTERNAE)
Inner and outer membrane fused win places producing pores (30-100nm diameter)
Allow passage of esp mRNA in and out of nucleus
What is the nucleoplasm contains?
chromatin and a nucleolus suspended in a matrix
What is the nucleolus responsible for making?
Ribsosomes as it is rich in rRNA and protein.
What does chromatin make up?
chromosomes.
What are 2 examples of cell inclusions?
Fat droplets and melanin
how thick is the plasma membrane?
5-7nm
How long is a microtubule?
25nm
How long is a cilia?
100-200um
Summarise protein synthesis in 6 steps
- DNA codes for a gene
- The DNA is transcribed onto mRNA
- mRNA leaves the nucleus and goes into the cytoplaasm attaching onto the ribsome
- the ribosome is on the E.R
- Translation
- Proteins packaged by the golgi apparatus
What is the structure of ribosomes?
very small organelles (20-30nm diameter)
What are the functions of ribosomes?
they produce protein which are exported from the cell - this is when it is attached to a E.R
free floating in the cytoplasm is when it it produces proteins for the use of that cell
What are the 2 ways a ribosome can be seen in?
Some are free in a cytoplasm producing proteins for use by the individual cells
or
others are bound to E.R- which produce proteins for cell membranes and export from cells.
What is the structure of an Endoplasmic reticulum?
series of thin membrane sacs enclosing fluid cavities known as cisternae
there is rough or smooth
What is the function of rough endoplasmic reticulum?
it makes proteins for cell membranes and for export from the cell or parcelled into vesicles by the golgi apparatus for export from cell.
What cells are the ROUGH E.R abundant in and give 3 examples?
In cells which make protein for export such as
- glandular cells
- plasma cells (antibodies)
- fibroblast (collagen)
What is the function of the SMOOTH E.R?
Produces lipids and steroid hormones
What is a sarcoplasmic reticlum and give an example?
when the smooth e.r is enlarge into some types of muscle.
for e.g - it is specialised as a calcium storage organelle - essential for muscle contraction.
What is the function of golgi complex?
it modifies and packages proteins from the rough e.r
What is the structure of the golgi complex?
- a series of flat membrane stacks
- tiny vesicles.
What are the 2 opposing faces of golgi apparatus?
CIS FACE
TRANS FACE
What is the cis and trans face of the golgi?
cis- side facing the E.R where vesicles from the E.R fuse
trans- modified and packaged proteins for transport to other parts of cell.
The protein packaged into SECERETORY VESICLES can follow a number of pathways. What are the 3 pathways they can go by?
- Be released by exocytosis
- form part of the cell membrane
- remain in the cell for later release by LYSOSYMES
What is the structure of lysosomes?
They contain hydrolytic (digestive) enzymes.
-0.05- 0.2 um diameter
What are lysosomes packaged by?
Golgi
What are the 2 functions of lysosomes?
The digestive enzyme in the lysosome:
- Digest and destroy worn out components of cells.
- Destroy bacteria and viruses via phagocytes or macrophages
What is the structure of the nucleus’ membrane?
Surrounded by a double membrane with a space inbetween called the Perinuclear cisternae
- Inner and outer membranes fused in places producing pores. (30-100nm diameter)
- There are 3000-4000 in a typical nucleus which allows easy passage of particular substances in and out of the cell.
Explain the function of membrane proteins- enzymatic activity
enzyme- a protein built into the membrane could be the enzyme with an exposed active site which can attach to a substrate and catalyse a reaction.
Explain the function of membrane proteins- receptors for signal transduction
receptors for signal transduction- a membrane protein exposed may have binding site with a specific shape which is complementary to a specific chemical messenger- initiating a chain of chemical reactions.
Explain the function of membrane proteins- intercellular joining
intercellular joining- membrane proteins of adjacent cells may be hooked together in intercellular junctions .
Explain the function of membrane proteins- cell-cell recognition
cell-cell recognition- glycoproteins serve as an identification tag
What forms gap junctions?
integral proteins as they are embedded in plasma membrane and forms channels as they fuse.
