Molecular Cell Biology- Cells and their Organelles: stem cells Flashcards
Single celled organisms
Bacteria, some free-living eukaryotes such as yeast and protozoa
Apical
Oriented towards the lumen
Basal/basolateral
Oriented away from lumen
What does it mean when it is said that cells are polarised?
They have apical and basal polarity
Differences between eukaryotic and prokaryotic cells
Eukaryotic cells have membrane-bound organelles in cytoplasm, eukaryotic cells are larger, eukaryotes have their DNA in the form of chromatin, eukaryotes have no cell wall and no chloroplasts (except plants)
Microtubule
Gives cell structure
Intermediate Filaments
Gives cell structure
Phospholipids. Structure of hydrocarbon tails.
Hydrophilic heads and hydrophobic tails cause them to spontaneously arrange themselves into bilayers. Tail has a bend which is important to function of lipid
Membrane lipid compositions and the importance of the effects of lipid composition
Varying lipid composition of membranes varies the physical properties of the membrane. Important because membranes fulfill many different roles in a cell so properties must vary
Flip Flop movement (transverse diffusion) and example. How fast is the process
When a lipid moves from one surface to another e.g. phospholipid changing layer it is in in the bilayer. Very slow, often needs an enzyme
Flippase
Aids Flip-Flop movement
What kinds of molecules is the membrane fully permeable and slightly permeable to? Give examples where necessary
Fully permeable to gases and small uncharged polar molecules like ethanol. Slightly permeable to small uncharged polar molecules like urea and water.
What kinds of molecules is the membrane impermeable to? Give examples
Large uncharged polar molecules like glucose/fructose. Ions like K+. Charged polar molecules like proteins and amino acids.
Cytosol
The aqueous component of the cytoplasm of a cell. Contains many metabolic pathways and is site of protein synthesis
Types of proteins in a membrane and their function
Transporters (involved in movement of molecules across membrane), Anchors (mediators of membrane associations), receptors (for recognition and receiving chemical signals) and enzymes
Use of H+ ions to provide energy
Electron transport drives pump that pumps protons across mitochondrial membrane and the proton gradient is used by ATP synthase to make ATP
Golgi apparatus
Modifies, packages and sorts proteins and lipids destined for another organelle or for secretion via exocytosis
Lysosomes, give function too
Cytoplasmic vesicles packed with degradative enzymes; the main sites of intracellular degradation/digestion
Peroxisomes, give function too
Cytoplasmic vesicles which provide a contained environment for reactive H2O2 generation. Uses oxidation reactions. The main function of oxidation reactions in peroxisomes is the breakdown of fatty acids and toxic molecules. Detoxifies toxic substances like ethanol via catalase
Endosomes
Responsible for sorting of endocytosed material
What does the cytoskeleton consist of and what does it do?
Consists of actin filaments, intermediate filaments and microtubules. Pulls chromosomes apart during mitosis, supports plasma membrane, controls cell shape, enables some cells to move and drives/guides the intracellular traffic of organelles, proteins and RNA
Actin filaments
Polymer of actin monomer,filament is 7 nm in diameter . Necessary for movement, can form contractile bundles and microvilli. May associate with myosin to form powerful contractile structures, carry cargo-bearing motor proteins e.g. myosin. Can grow, dissolve and reform.
Intermediate Filaments
10nm diameter, made of various fibrous proteins depending on cell type (keratin in epithelial, vimentin in smooth muscle cells and white blood cells, neurofilament proteins in neurones, Lamins in nucleus). Twisted into ropes, providing tensile strength. Needed to maintain cell shape
Microtubules
20nm diameter. Polymers of tubulin dimers. Organised from structures such as the centrosome. Form the spindle in mitosis. Important in cell shape and movement. Carries cargo-bearing motor proteins. They are molecular motorways, allowing proteins etc to be transported from one end of cell to the other
Name two motor proteins and discuss how they move along microtubules
Dynein and kinesin. These motor proteins walk along microtubules using energy from ATP. Dynein walks towards the negative end of the microtubule and kinesin towards the positive end.
Stem cells defining properties
It is not itself terminally differentiated. Immortal. It can divide without limit, when stem cell divides daughter cells can choose to either remain a stem cell or begin journey to terminal differentiation. Division slows as one gets older.
Where are stem cells particularly needed and how do they stay undifferentiated
Stem cells are especially needed in areas where there is a recurring need to replace differentiated cells that cannot themselves divide. To keep stem cells undifferentiated, keep the stem cells near their stem cell niche. A stem-cell niche is an area of a tissue that provides a specific microenvironment, in which stem cells are present in an undifferentiated and self-renewable state.
Pluripotent
Can differentiate into all body cells but not placental cells
Totipotent
Can differentiate into any type of body cell AND placental cells. Only embryonic cells after first few divisions are considered to be totipotent
Multipotent
Can differentiate into a few types of cell. More limited. Adult stem cells are multipotent. Multipotent cells only differentiate to make a specific specialised tissue
Stem cells in the skin
Important in skin replacement and wound healing
Haemopoietic stem cells
Differentiate into all sorts of blood cells
Induced Pluripotent Stem Cells (IPS)
Adult stem cells that have been modified to behave like embryonic pluripotent stem cells
Advantages and disadvantages of IPS
Cells taken from a patient should not elicit an immune response. Fewer ethical issues. Theoretically any cell type could be replaced. But more research needs to be done on developmental pathways. Transplanted stem cells may develop into cancer cells
Necrosis (lysis)
A form of cell death. Cells lyse (CM ruptures) and burst. CM integrity destroyed and soluble contents are released into tissue fluids. Cell components degraded by the actions of extracellular enzymes and phagocytic cells engulf fragmentary remains. Triggers immune response (inflammation)
Apoptosis
A form of cell death. The normal pathway. Signalling processes in cell activate intracellular suicide proteases which degrade intracellular structures and organelles, collapse cytoskeleton and fragment the cell into mini-cells to be engulfed by phagocytes for degradation. Apoptotic cell dies without damaging neighbours
