Cells and organelles Flashcards
Cell polarity, using nerve cells and ciliated epithelial cells as an example
This is when cells have an apical and basal end.
The apical end is usually where secretion happens, and usually faces a lumen.
The basal end faces the inside of the body.
E.g in nerve cells:
The axon and nerve terminal is the apical end.
The cell body and dendrite is the basolateral domain.
In ciliated epithelial cells:
The cilia membrane is the apical domain of the cell.
The parts of the cell that attach to other cell or the basement membrane is the basolateral domain.
Differences between bacteria and animal cells.
- Animal cells are eukaryotic, contains membrane bound organelles, including nucleus.
Bacteria cell only have plasmid and free DNA. - Eukaryotic cells are usually larger, 5 micrometers or more.
Prokaryotes are 1-5 micrometers - Eukaryotic cells have membrane bound organelles whereas prokaryotes don’t.
- Eukaryotic cells do not have a cell wall (except plants and fungi) whereas prokaryotes do.
Main components of the cell membrane
Cell membrane is selectively permeable:
Phospholipid bilayer, composed of phospholipid lining up with their hydrophilic heads outwards.
Cholesterol: maintains fluidity of the membrane, especially in changes to temperature.
Plasma membrane proteins: Can be integral or peripheral. Involved in cell signalling and transport of substances across the membrane.
Functions of the cell membrane.
Regulates transportation of solutes.
Cell communication
Defines the limits of a cell and its organelles.
Phosphatidylcholine
Major lipid component of the membrane.
Composed of four groups:
Choline —> Phosphate –> Glycerol –> 2 hydrophobic tails.
The head is hydrophilic, composed of the choline, phosphate and glycerol groups
The hydrophobic tails have kinkds when it is unsaturated. This causes the membrane to be more permeable.
Fluidity of the lipid bilayer
The fatty acid tails move to help push molecules across:
Flex
Rotate
Flip flop (rarely)
The head is very hydrophilic so attracts water, but cannot pass through with channels due to the hydrophobic tail.
The fluidity of the membrane is managed by cholesterol.
What type of functional protein is the Na+ pump?
Transporter: actively pumps Na+ out of cells and K+ into cells.
What type of functional protein are integrins?
Anchors: links actin filaments in cells to ECM proteins.
Used in wound contraction
Four types of functional proteins in membranes
Transporters: pump of channel.
Anchors: binding to ECM components
Receptors: binding of a specific molecule triggers an intracellular response.
Enzymes: Catalyses the production of specific molecules.
What types of molecules is the membrane impermeable to?
Charged polar molecules.
Ions
Large unchaged polar molecules
What types of molecules is the membrane permeable to?
Gases
Small uncharged molecules
Small polar molecules (slightly), like water.
Structure and function of mitochondria
Double membrane:
outer- very permeable
inner- forms cristae, very selective in permeability
Contains matrix, fluid filled space.
Function:
Site of ATP generation to provide energy
How does mitochondria produce ATP for energy?
Electrochemical gradient produced by protons and a proton pump, in the inner membrane
- Energy from the electron transport chain supplies energy for pump to push protons across membrane. This forms proton gradient
- Protons diffuse down gradient across ATPase which uses that energy to produce ATP.
Lysosomes
Irregular cytoplasmic vesicles that contain hydrolytic enzymes.
Site for intracellular digestion and are involved in the immune defence.
Peroxisomes
Cytoplasmic vesicles which mainly breaks down fatty acids using oxidation.
Provides optimum conditions for hydrogen peroxide
Detoxification through oxidation: i.e ethanol.
Functions of the cytokeleton
In cell division: pulls chromosomes apart.
Supports the plasma membrane
Enables cell movement
Controls the cell shape
Drives intracellular movement: organelles, proteins, RNA
Components of the cytoskeleton
Thin actin filaments: 7nm
- Necessary for movement.
- Can form contractile bundles and microvilli.
- Carry cargo-bearing proteins, like myosin
Thick microtubules: 20nm
- In mitosis, mainly forms spindle
- Composed of tubulin dimers
- Cell shape maintenance and movement
- Carry cargo-bearing motor proteins
- Originate from centrosome
Intermediate filament- intermediate thickness: 10nm
- Mainly fibrous proteins like: keratin, vimentin, lamins, neurofilmaents.
- Maintains cell shape and provides tensile strength.
These components bind with motor proteins to enable various functions.
Motor proteins
ATP dependant proteins that pull along filaments like microtubules.
The ‘walk’ along microtubule with their heads and pull along the tubules.
Examples: dynein and kinesin
Properties of stem cells
Is not terminally differentiated.
Unlimited cell division. The daughter cells either differentiate or stay stem cells.
Are important in replacing damaged tissue or cells that cannot divide.
Stem cells can be:
Embryonic
Adult
Embryonic stem cells
Totipotent cells from the morula of the embryo- can differentiate into anything.
Cells from the inner mass of the blastocyst are pluripotent- can differentiate into many cells but not all
Adult stem cells
Multipotent cells produced in the bone marrow.
Can divide to replace certain cells types:
Like intestinal stem cells replace gut tissue.
They could be used to replace defective tissue- prevents rejection of tisse
Stem cells in the skin
Can be found associated with hair appendages and are the bottom of of the epidermis, near the basement membrane
Helps to replace damaged tissue in wound healing
Also replaces the skin due to epithelial high cell turnover.
Haemopoietic stem cells
Found in the bone marrow- multipotent stem cells.
Differentiates into all the different types of blood cells:
Lymphocytes
Granuloytes
Red blood cells
Induced pluripotent stem cells (IPS)
Adult stem cells are taken from a patient and induced to produce specific cells to form a tissue- i.e for transplants or grafts.
Advantages:
No immune response as cells are ‘self’
Fewer ethical issues regarding embryos
Disadvantages:
More research needs to be done
Stem cells could develop into cancer
Compare necrosis and apoptosis
Apoptosis- programmed cell death
Necrosis- cell lyses or burst, Usually due to pathological reasons.
Apoptosis involves the cell degrading its own structures and organelles. Sectioned into blebs engulfed by phagocytes.
Necrosis- cell components destroyed by extracellular enzymes, then a phagocyte.
