L2 - movement and stability in cells

• Vacuole: a membrane bound vehicle found in the cytoplasm of a cell whose function includes intracellular secretion, excretion, storage, and digestion
• Intermediate fibres: cytoplasmic filaments intermediate in diameter (about 10nm) between micro filaments and micro tubules. They may be composed of a number of different proteins and form a ring around the cell nucleus
• Cytoskeleton: the network of proteins fibres and micro tubules found within the cell that gives structure and shape to the cell and is responsible for movement of many materials within it
• Murein: peptidoglycan that usually makes up the cell walls of prokaryotic cells
• Actin: the protein that makes up microfilaments
• Prokaryote: an organism with cells that do not contain a true nucleus
• Microfilament: smallest of the protein filaments (7nm diameter) that make up the cytoskeleton, involved in cell division and muscle contraction, cell shape and motility (white blood cells)
• Endosymbiosis: a type of symbiosis in which one organism lives inside the other, the two typically behaving as a single organism. It is believed to be the means by which such organelles as mitochondria and chloroplasts arose within eukaryotic cells
• Peptidoglycan: a substance forming the cell walls of many bacteria, consisting of glycosaminoglycan chains interlinked with short peptides
• Murein serves a structural role in the cell wall of bacteria, giving structural strength and rigidity
• Division of labour: any system where different parts perform specialised functions, each contributing to the functionping of the whole
• Basal body: a cylindrical organelle, within the cytoplasm of flagellated and ciliated cells, that contains micro tubules and forms the base of a flagellum or cilium
• Tubulin: a protein that is the main constituent of the micro tubules of living cells
• ATP: a molecule used to store energy temporarily in organisms
• Ultrastructure: the detailed structure of the internal components of cells as revealed by electron microscope
• ATP stands for adenosine triphosphate and temporarily stores energy in organisms. It is broken down into ADP and phosphate to release energy to drive metabolic processes
• ATP is an organic compound composed of adenosine (an adenine ring and a ribose sugar) and three phosphate groups, hence, the name
• Cell fractionation is the process used to separate cellular components while preserving individual functions of each component

  -this is achieved through a process called differential centrifugation
• Differential centrifugation: the sequential increase in gravitational force results in the sequential separation of organelles according to their density
• The cell cytoskeleton: a complex network of protein filaments that extends throughout the cytoplasm

  -provided structure and motility allowing the cell to move or allowing “cargo” to be transported from one part of the cell to another

  -cellular scaffolding upon which cellular organisation is arranged

  -has “free” ribosomes attached to it
• Three different filaments make up the cytoskeleton:

  -actin filament/microfilaments

  -intermediate fibres

  -microtubules
• Microfilaments:

  -7nm wide contractile protein fibres, made up of actin in the cytoplasm of the cell

  -they are found in muscle fibres

  -involved in cytokinesis during the process of cell division

  -help white blood cells engulf foreign bodies
• Microfilaments:

  -cell motility depends on the reorganisation of the actin cytoskeleton

  -the actin filaments change length with the addition and removal of monomer subunits

  -the rate at which these subunits are added is different at each end of the filament

  -the increase in length of the filaments at one edge of the cell, the leading edge, results in cells such as phagocytes moving in a particular direction
• Intermediate fibres:

  -found in most, but not all, animal cells

  -made of highly elongated fibrous proteins like keratin

  -give mechanical strength to the cells

  -surround the nucleus and extend to the periphery of the cell where they interact with the plasma membrane

  -there is also an extensive network under the nuclear envelope

  -anchor nucleus and organelles in the cytosol
• Microtubules:

  -cylinders of molecules of a protein called tubulin

  -diameter of 25nm

  -proteins attached to them which are known as microtubule motors

  -these are involved in moving objects around the cell

  -they require ATP
• Functions of microtubules:

  -scaffold structure that determines shape of cell

  -moving chromosomes around during cell division

  -moving vesicles around (eg. from the ER to the Golgi apparatus)
• How is insulin made and secreted from the cell (1-3):

  -mRNA copy of the instructions (gene) for insulin is made in the nucleus

  -mRNA leaves the nucleus through a nuclear pore

  -mRNA attaches to a ribosome (sometimes attached to ER). Ribosome reads rags instructions to assemble the protein (insulin)
• How is insulin made and secreted from the cell (4-6):

  -insulin molecules are “pinched off” in vesicles and travel towards Golgi apparatus

  -vesicle fuses with Golgi apparatus

  -Golgi apparatus processes and packages insulin molecules ready for release
• How is insulin made and secreted from the cell (7-9):

  -packaged insulin molecules are “pinched off” in vesicles from Golgi apparatus and move towards cell surface membrane

  -vesicles fuses with the cell surface membrane

  -cell surface membrane opens to release insulin molecules outside
• Plant vacuole function:

  -large permanent vacuole

  -a sac filled with cell sap (water and solutes) and is surrounded by a membrane called a tonoplant

  -pushes the cytoplasm against the cell wall

  -makes the plant cell turgid and maintains cell stability

  -helps support the plant (especially non woody plants) by applying pressure to the rigid cellulose wall

  -vacuoles in animal cells are small and transient
• Cell motility (cilia and undilipodia):

  -cilia and undilipodia are extensions of the plasma membrane, they are used for movement

  -many and short (3-4um in length) are cilia

  -few and long are undilipodia (sometimes also called flagella)

  -each cilium and flagellum has a basal body at its base, embedded into the cytoplasm of the cell
• Cilia and undilipodia have a 9+2 microtubule arrangement. This means there are 9 outer doublet microtubules and 2 central microtubules

  
• The cylinder of microtubules is called the axoneme. The protein motors are molecules of dyenin. These dyenin molecules cause the microtubules to slide over each other, which causes the undilipodium to bend. Undilipodia and cilia in eukaryotes use ATP

  
• When there is a group of cilia, they all work together in a coordinated manner to move. Each cilium slightly out of phase with its neighbour to produce a wave like motion across the surface of the cell
• Function of undilipodia and cilia:

  -undilipodia enable cell motility, eg. sperm cells

  -can be used as a sensory organelle in some cells, detecting chemical changes

  -cilia can be mobile or stationary
• Mobile or stationary cilia:

  -stationary used in sensory organs like the nose

  -mobile can be used to move material across tissue in multicellular organisms (eg. in the trachea they move mucus/in oviducts they move the egg)

  -mobile are also used to move single celled organisms such as paramecium
• Bacteria have flagella but with a different structure. The flagellum is made of a spiral protein (flagellin) attached to a hook. The hook connects to a molecular motor. It does NOT use ATP
• 2 levels of cellular organisation:

  -biologists recognise a major distinction between two major cell types

  -eukaryotic cell, typical of most organisms including animals and plants

  -prokaryotic cell, found in prokaryote kingdom which includes bacteria
• Prokaryotes do not have a nucleus but a long strand of dna in the middle of the cell
• Eukaryotic cells:

  -have a clearly distinctive nucleus

  -full complement of membrane bound organelles in their cytoplasm

  -can be unicellular or multicellular