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
What are intermediate filaments?
- 8-12nm diameter
-Organised like rope like polymers and are prominent to areas with mechanical stress
-acts as anchor
-attached to desmosome - very tough and durable and stable.
Organised like rope like polymers and are prominent to areas with mechanical stress
-They form a basket around the nucleus (holding it in place) and extend outwards in curving arrays to the cells peripherey (plasma membrane).
What are actin filaments?
- They consist of 2 strands of globular actin which are packed into a tight helix.
- They support/maintain the cell shape and involve in the movement of the cell too.
- Found inside plasma membrane and form a sheet- can extend across cell
- Help the passage of quantities out of the cell via endocytosis
- essential for vesicles via exocytosis
What are microtubules?
-Coiled shape
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.
What is the organsining centre that microtubules have?
centrosome- located to one side of the nucleus
What is centrosome made up of?
2 centrioles- aligned 90 degrees to each other
What else does the microtubules form?
structural core of cilia
What is a cilia?
-tiny hair like appendages on the surface of many cells
allows fluid to move its contents across the surface of cell. i.e. move/beat
What does a cilium consist of?
9 pairs of microtubules doublets
What is mitochondria?
- powerhouse of cell- produces energy
- site of aerobic respiration
- energy harnessed in ATP to use in other reactions
How does mitochondria harness energy using ATP?
- Anareboic respiration in gluycolysis - no oxygen used- turns glucose into pyruvate
- krebs cylce- harness electrons in other molecules NADH and FADH2
- Electron Transport chain - harnesses electrons from bonds within the NADH and FADH2 in ATP.
- Produces lots of ATP
What are ribosomes?
20-30nm in diameter Very small -Contain nucleic acids (RNA) -made from RNA and protein -Found either free floating the cytoplasm producing proteins for use by cells or others are bound to endoplasmic reticulum - produce proteins for cell membranes and for export from the cell.
What is an endoplasmic reticulum?
- series of thin membrane sacs enclosing fluid cavities known as cisternae
- membranes are continuous with plasma membrane and nuclear membrane
- there are 2 types : rough and smooth
What is Rough E.R?
- surface studded with ribosomes
- makes proteins for membranes of cell or parcelled into vesicles by Golgi for subsequent export from the cell
- Thus abundant in cells that make protein for export e.e glandular cells, plasma cells (antibodies), fibroblasts (collagen)
What do fibroblasts do?
essential in wound repair
- make lots of c.t
- when activated release lots of proteins such as collagen
What is smooth e.r?
- no ribosomes attached
- produce lipids, steroid hormones
- Enlarged in some types of muscle - Sarcoplasmic reticulum
- in this case it is specialised as a calcium storage organelle - essential for muscle contraction.
What are the cell inclusions?
- fat droplets- full of triglycerides- expand/increase size of the cell
- Melanin- retinal pigment epithelium contains these granules- retina harnesses the light energy.
What is nucleus?
control centre
- present in virtually all cells expect RBC
- Some cells e.g muscle cells have several
- Have a regular shape in normal cells
When are nucleus irregular shape?
in cancer cells
What is the nucleus composed of?
a membrane surrounding the nuceloplasm
What does the nucleoplasm contain?
chromatin and the nucleolus within a matrix.
What is the structure of the nucleoplasm?
-composed of chromatin and nucleolus suspended in a matrix
-
What is nucleolus for?
-responsible for making ribosomes.
Rich in rRNA and protien
What is chromatin?
makes up our chromosome
- It is intertwined DNA and histone proteins
- DNA wraps around histones and makes the chromatin- stabilised
What does DNA store?
genetic information for e.g controls what a proteins a cell makes and when
Where are our genetic info stored?
chromosomes- composed of DNA double helix
What does DNA exist as?
2 complimentary chains of nucleotides
What do nucleotides consist of ?
- Phosphate group
- Pentose sugar- deoxyribose sugar ( 5carbons)
- Base- variable- A,C,G,T
What are the 4 DNA bases?
Adenine
Guanine
Cytosine
Thymine
What are pyrimidines?
T, C double ring
What are purines?
A, G single ring
How do they form the DNA double helix?
Pentose sugar and phosphate group make up the backbone of the DNA
-Complimentary base pairs are linked by hydrogen bonds (A,T AND C,G)
What are the hydrogen bonds between A and T and C and G?
A and T= 2 h bonds
C and G = 3 h bonds
What is a gene?
a piece of DNA that codes for the production of a particular protein shape and function etc
Each gene makes a different protein
How do we get from bases to the genetic code?
- proteins made from amino acids
- chain of a.a forms a larger protein molecule
- Each a.a coded for by a triplet ‘codon’ of 3 adjacent nucleotides.
What codes for one amino acid?
a codon (triplet)
How does each gene get translated into a protein molecule ?
Transcription
Translation
Brief summary of transcription and translation
-Triplet codes of a gene are copied into a molecule of mRNA (transcription)
This leaves the nucleus and combines on ribosomes &the mRNA combines with complementary tRNA molecules (translation).
-The amino acids on the adjacent tRNA molecules join to form the protein.
Summary of protein synthesis?
- DNA codes for a gene for a protein
- The genes DNA is transcribed onto mRNA
- mRNA leaves the nucleus and goes into the cytoplasm attaching onto the ribsome (located in the cytosol or E.R)
- the ribosome is on the E.R
- Translation- PROTEINS ARE MADE by the mRNA and tRNA together
- synthesised proteins packaged by the golgi apparatus
What are junk DNA?
introns- does not code for PROTEINS
What are coding portions of DNA?
Exons
How much chromosomes do humans have?
46
How many homologous pairs ?
23
What is the total amount of genes we have?
21 000
How many pairs of autosomes are there?
22 autosome pairs- carries same gene - e.g 2 gene coding for hair (same function)
How many sex chromosomes?
1 pair
how much of junk DNA do we have ?
97% is introns
How much DNA codes for proteins?
3% are exons
how many genes do we have for most traits ?
we have 2 genes for most traits located at the same locus on homolgous chromosomes
what are the 2 genes located at the same locus called ?
alleles
what is homozygous ?
if the 2 alleles are the same the individual is homozygous
what is heterozygous ?
if the 2 alleles are different the individual is heterozygous
what is genotype?
a person’s genetic makeup is their geneotype
what is phenotype?
the expression of genotype is the phenotype
why do most cells in the body need to be replaced ?
because they have a limited lifespan
e.g. red blood cells=120 days
what are some examples of cells that do not get replaced ?
CNS neurons
cardiac muscle
corneal endothelial cells
how do most cells replicate ?
most cells replicate by division when a parent cell divides it must pass on all its DNA to the 2 daughter cells
this is achieved by the process of mitosis
what are labile cells ?
these are cells that are continuously replicating
e.g corneal epithelial cells as they are constantly abraded
what are stable cells ?
stable cells are cells that multiply only when needed
e.g fibroblast
what is the cell cycle ?
the life of a cell can be divided into various phases
what is the cell cycle divided into ?
interphase and the mitotic phase
what happens in the interphase of the cell cycle ?
- in G0 - normal cell metabolism occurs - duration is variable
- in G1 - prepares the cell for replication by the multiplication of organelles
take 8 hours or more
e.g. centrioles replicate during this phase of the cell cycle - in S phase DNA replicates
the 2 stands of DNA unwind and DNA polymerase moves along the exposed chains adding complimentary nucleotides from a pool within the nucleoplasm , forming 2 identical strands of DNA, histone synthesis also occurs
- takes about 6-8 hrs - in G2 the enzymes needed for cell division are synthesised
. division of nucleus
the cell is ready for mitosis
what are the stages of mitosis ?
. early prophase . late prophase . metaphase . anaphase . telophase and cytokinesis
what happens in the early and late prophase of mitosis ?
early prophase
. cell sets stage for division of chromosomes
. centrosomes replicate to make 2 centrosomes that are made of centrioles
. chromatin condenses to form chromosomes inside the nucleus
. formation of mitotic spindles - this forms as microtubules span from centrioles
. microtubules elongate and push centrioles to each end of cell
. nucleolus disappears during early prophase
late prophase
. mitotic spindle attaches to chromosomes and starts to align them
. microtubules bind to condensed chromosomes at kinetochore - now called kinetochore microtubules
. kinetochore are patch of proteins attached to centrosome of chromosomes
what happens during metaphase of mitosis ?
. microtubules are dynamic and span from one centriole to other and start pushing cell to make it longer
.kinetochore microtubules align chromosomes up along equator of cell through metaphase
. each kinetochore in middle of chromosome which has been doubled as DNA has been copied must be split with each portion going to each end of cell
what happens during anaphase of mitosis ?
. sister chromatid separate as they are pulled to each end of cell
. cell’s axial length increases because microtubules are expanding cell’s length
. half DNA complement is in each side of cell
… note that DNA was doubled so in essence you get full DNA complement in each side
what happens during telophase and cytokinesis of mitosis ?
. formation of nuclear envelope to package chromosomes which then goes to form nucleus
. contractile ring at cleavage furrow
. cleavage furrow pinches cell into two separate cells
. 2 identical daughter cells each with a diploid complement of DNA
