Cells and organelles Flashcards
Cell discovered in 1665 by robert hooke, not much known about him as isaac newton stole his thunder
1839 Cell theory
All organisms consist of one or more cells • The cell is the basic unit of structure for all organisms (Thought cells originated “spontaneously”)
- theodor schwaan
1855 cell theory and human mechanisms ( pathology )
The cell was the basic unit of the body that had to be studied to understand disease • Cells originate from preexisting cells - start of thoery of mitsosi and meoisis
Rudolf Virchow
The size of cells ensure that they can have adequate diffusion and be able to move around the body freely , also ensures that if damage occurs it is not the end of the world. All cells are smaller than the eye . Some cells can be much smaller ( eg bacteria ) or larger ( human eggs )
Properties of cells
Microscopic packages tha ac as independent units
cells originate from preexisting cells - grow and reproduce
cells have a finite lifetime - they do die - by deisng, age , disease
Cells internal processes allow them to change / adapt / respond
Different jobs for diff cells/ parts of the body
Membranes enclose the cell space
The plasma membrane encloses the cell
as packages of life cells can function as ind units because they are enclosed by a semipermeable membrane ( flexible, continous bag - a barrier to water )
The plasma membrane encloses the cell as an independent reaction container ( contains salty, protein rich solution )
The membrane is composed of a bilayer of phospholipid molecules with added protein molecules
The lipid bilayer is 5nm long
The protein molecules are typically 50% of the mass
Reading
- all proteins are funadmentally the same in overall structure
the membranes differ because of protein/lipid types
1/3 of all cell proteins are membrane proteins
Proteins define function - receptors, transporters, signalling,adhesion etc
There are two different types of cells
Prokaryotes - before a nucleus - only one outer membrane
the simplest and smallest prokrayotes are bacteria ( all processes in cytosol , no internal membranes, nucleus absent )
Up to few thousands of a mm ( few microns ) in size
Amongst “ oldest “ and most abundant type of life of earth ( preceded complex cells )
Eukaryotes
some cells have internal membranes and are bigger
more complex eukaryotes are found in human, animal and plants
( cytoplasm divided by membrane to enclose compartments/organelles )
Up to a 10 thousandths of a mm in size ( 10 microns or much more )
Amongst more recent in evolution representing complex cells in multicellular organisms
eukarytes are much bigger than prokaryotes
a skin cell infected with bacteria
Eukaryote protein expression
• DNA (with its genes) packaged in a central store called a nucleus. Specifically in EUKARYOTIC CELLS: (human, animal, plant cells) • Nucleus is enclosed by a double membrane the nuclear envelope (nucleus is one of a number of cell compartments) • mRNA (message) passes from the nucleoplasm to the cytoplasm via holes called nuclear pores Protein expression – the organelles • mRNA is decoded and proteins made (translation) on specialised factories ribosomes • DNA (with its genes) transcribed to produce mRNA (transcription)
DNA is packaged with proteins called histones – forming a complex called chromatin
Chromatin is packaged in two main ways – euchromatin and more dense heterochromatin
Most of the active genes are found in the euchromatin, inactive ones in heterochromatin
Nuclear pores are selective aqueous channels for transport between nucleus and cytosol (mRNA passage but also proteins in both directions)
nuclear pores - openings in the nucleus for mrna
euchromatin - lighter
heterochromatin - darker
mRNA and translation machinery - ribosomes in the cytoplasm in eukaryotes
Proteins are made on specialised organelles called Ribosomes Many ribosomes remain “free” during protein translation Ribosomes have two subunits Ribosomes decode mRNA message and convert it to linear polypeptides (protein)
Big decisions are made for ribosomes as they start protein synthesis - they basically have to determine what that protein is destined to be , whether its a cytoplasm or nuclear protein or destined to have further werk done in the rer and golgi
All protein synthesis starts in the cytosol
First stretches of any proteins destined for ER/ golgi processing are recognised and then bound to ER to generate ER coated with ribosomes - RER
Free ribsomes
Free ribosomes (translating proteins destined for cytosol, nucleus, mitochondria
Bound ribosomes
Bound ribosomes (these ribosomes are translating proteins with signal sequences destined for RER and other membranes and secretion)
Eukaryote secretion
Pathway for secretion
synthesis modification secretion delivery
RER -> Golgi -> secretion/plasma membrane
Vesicles vesicles
Vesicles carry cargo from RER to the golgi
cargo processed and sorted in the golgi
vesicles bud from the golgi with membrane for the PM ( constitutive vesicles )
Different vesicles can bud from the golgi containing packaged secretion
RER function
(1) Site of membrane synthesis (lipids and proteins) (2) Modifies proteins – adds sugar chains, trims them (3) Quality control – e.g. monitors correct folding (4) Signals stress - e.g. when secretion is blocked/poorly folded proteins
The rer to the golgi in eukaryote secretion
• RER makes membrane and is widely spread through most cells • Cargo packaged into vesicles sent along tracks to the central Golgi complex • Golgi complex stacks of flattened sacs (found close to the nucleus). • Golgi receives these membrane vesicles + their content (cargo) from RER.
Golgi
All membrane exported from the ER goes through a processing factory called the golgi
Processes and sorts cargo into vesicles specific for the target organelle (cell membrane, lysosome, outside of the cell (secretion))
Golgis function
(1) Receives output of RER (2) Modifies lipids/proteins – grows sugar chains on proteins/adds phosphate to some proteins (1) Sorts and packages cargo into distinct vesicles for export to other organelles (this happens at the exit face of the Golgi)
How is vesicle content released and membrane added to the plasma membrane ?
Secretory vesicles - release content via exocytosis at the plasma membrane
The vesicles move toward and way from the golgi through slight polarisation on microtubules that are 25 nm thick , they ahve a motor protein on them That has the vesicle cargo on top
Most of the microtuules emanate from the centrosome,which the golig is normally close to int he cell centre, and other organelles may move or be positioned on the microtubules
the centrosome is the centre for organising microtubules and it usually contains two centrioles and 0 array of microtubules
Uptake and degradation in eukaryotes
Lyosomes are low ph degenerative bodies that contain hydrolytic enzymes which degredate the material.
Uptake is by endocytosis ( large particles by phagocytosis and molcules by pinocytosis )
membrane/ cargo internalised delivered to endosomes and then passed to lyosomes for degradation. Some membrane is reycled back to the cell surface
portions of the cell itself can be walled off and digested in lyosomes ( autphagy ).
Phagocytosis ( big chonks ) , pino cytosis ( cell drinking )
receptor mediated endocytosis is very effective bc it has selective uptake
Endocytosis ( uptake for degradation to lyosomes; uptake for recycling )
Membrane and functional components of lyosomes and endosomes are also made on RER
- proteins must be diverted by special sequences ( sorted from secretory pathway) in the golgi
SO membane of RER, golgi , secretory vesicles , PM, lyosomes and endosomes all made in the RER
Degradation can happen in the cytosol without mebranes ( lyosomes )
Degradation by a proteosome
• “Junk” protein is tagged (with ubiquitin) • No membrane involved • Macromolecular complex • In the cytoplasm not in lysosomes - turns it into fragments
kind of like a bin bag
Two great steps in eukaryote cell evolution
compartmenalization and mitochondria
Compartmentalization
internal membrane compartments with a range of specilaised functions
this means that specialised rwactions that can sometimes be harmful can be seperated and concentrated and optimised while not damaging other parts of the cell
vesicle transport is a consequence of cargo between compartments - selective transport maintains composition of membrane compartments - vesicle budding - one type of scaffold coat is called clathrin
Mitochondria (Produce most of ATP supply Enabled cells to grow bigger Present in all eukaryotic cells Two membranes - inner membrane folded into interior Contain their own DNA - reproduce by dividing in two All your mitochondria come from your mothers egg (cell nucleus makes most but not all mitochondria proteins))
the best idea -
About 2 billion years ago large non-nucleated cell (archaea) engulfs a bacterium. • Bacterium provides energy (ATP) + multiplies to provide energy boost for growth (bigger cells become viable). • During further evolution cell membrane invaginates to form internal membranes – segregation of protein synthesis on ER. ER coats nucleoid to form nuclear envelope.
Cytoskeleton
provides framework for cells and organelles
moving/positionng, supproting , protecting
Microtubules
- thickness of a ribosome (25nm), vesicle tracks, position/move organelles (cell division), dynamic - subunits tubulins
Microfilaments
- thinner than microtubules (7nm), generates contractile forces enabling cells to move, parts of cells to move, cells to contract subunits actin + myosin (motility)
Intermediate filaments
- middle thickness (10nm), strength, support Some in cytoplasm (keratins) some support nuclear envelope (lamins) - keratins, lamins
There is two organelles prominent in a few specialised cell types
smooth er
peroxiomes
Smooth ER - connected domain of the RER membrane with no ribosomes and involved in lipid, steroid production and detoxification.
Peroxisomes – break down some fatty acids, synthesis some specialised lipids (e.g. in nervous system). Peroxisomes do oxidative reactions using molecular oxygen. These generate hydrogen peroxide, and excess is broken down with catalase.
Prokaryotes summarised
Small, simple cells (relative to eukaryotes) • Size: about 1 µm • No internal membrane-enclosed organelles* • No nucleus • Simple cell division
Eukaryotes summarised
• Larger cellular dimensions 5-20 µm diameter (1000x bigger than bacteria) • Internal membranes with specialisation and vesicular transport • Packaged DNA in a nucleus • Contain endosymbiont organelles (mitochondria/chloroplasts)
Birth and death of cells
chromatin condenses all together as chromosomes during cell division - packaging protects the genes
it is paritioned by microtubule based movementws by the phase metaphase - the microtubules moves and organises the chromosomes into daughter cells
phases in order - prophase - metaphase - anaphase - telophase - cytokinesis
Cells can die on command - programmed cell death - apoptosis - cell deah between digits
Multicelluarity
(1) cell specialisation
(2) adaptations for living together
(1) cell specialisation
DIversity - more than 200 cell types identified in human body - arranged into tissues - 4 basic tissue types - eptihelia - connective tissue - muscle - nervous tissue
Protein expression profile defines the type of cell
- Surrounded by an enclosing membrane (reaction containers)
- Cells are protein factories 20,000 different proteins can be coded from an identical set of genes Patterns of protein expression determine each of 200+ cell types
- Grow (increase in size)
- Divide
- Die (disease (age), design)
All cells are derived from a totipotent stem cell
(2) living together
cell communication
static cells can adhere to each other thru junctions
Tight junctions - seals neughbouring cells together in an epithelial sheet to prvent leakage of molecules between them
adherens junction - joins in actin bundle in one cell to a similar bundle in a neighbouring cell
desmosome - joins the intermediate filaments in one cell to those in a neighbour
gap junction - forms channels that allow small water-soluble molecules , including ions, to pass from cell to cell
hemidesmosome - anchors intermediate filaments in a cell to the basal lamina
selective cell-cell adhesion
familial hyperchlosterolemia ( defective uptake of lipoproteins )
• LDL receptors bind LDL (“bad cholesterol”) for uptake – 3 causes for defective uptake of LDL • LDLR is not properly transported from RER to Golgi for expression on cell surface (X) • LDLR bound to LDL does not cluster in endocytic vesicles on plasma membrane (X) • LDLR is not recycled back to the cell surface (X)
Examples of mistakes and mishaps in cell biology
All diseases are caused by mistakes at cellular level
Hypercholesterolemia (defective uptake of lipoproteins) • Cystic fibrosis (misfolding of key protein) • Hypertension (defective cell-cell adhesion in the kidney) • Congenital heart defects (errors in cell migration during development) • Muscular dystrophy (defective attachment of the plasma membrane to the cytoskeleton) • Lysosomal storage disease (defective intracellular transport of enzymes) • Food-borne illness (Salmonella, E. coli) • Cancer (errors in cell division, migration, cell polarity, growth, etc) • Ageing
