Block one cell biology

• what is the lipid distribution in the plasma membrane ? in terms of extra cellular and intracellular regions ?


  The plasma membrane semi permeable , it has both a hydrophilic head and hydrophobic tail , its composed of phospholipids.On the extracellular surface there is phosphotydal choline and glycoproteins , cholesterol sits in the middle of the membrane , and intracellular membrane has three different variations of phosphotydal : Phosphotydal serine (PS) phosphotydial ethanol amine and phosphotydial inositol
• What is an example of the dynamic cell ?

  In membranes the lipids can renew and replaced overtime this implies lipids can be broken down
• what would happen to cell materials if there was a pure phospholipid bilayer compared to plasma membrane ?

  The pure phospholipid bilayer wouldn't contain transmembrane proteins embedded with the membrane.Hence larger polar molecules would not cross , glucose and ions. Wheres smaller non polar molecules will pass through oxygen , water , urea and glycerol . Compared to plama membrane which allows all these to pass through different methods.The active transport proteins help larger molecules necessary to pass through the membrane
• Both glucose and ions are needed for the cell give examples ?


  Ions are important , they need help from proteins in the membrane to cross especially in neurons for action potentials and the sodium and potassium channels .Glucose Is needed for oxidative metabolism
• Name the different types of proteins present in membranes ?

  1. transporters for example GLUT transporters for glucose 2. Receptors -ion gated channels ,3 enzymes , 4. Anchors - Anchor proteins important for cytoskeleton shape and stability
• Give an example of transporters in the plasma membrane ?

  Glucose must be taken in by the small intestine by the lumen of the gut .The Apical side of an intestine tissue has a transporter that only transports glucose if sodium has a concentration gradient (high to low) moving into the cell. There must be a transporter present at the Basal membrane of the cell to allow glucose into the blood stream , so it can move around the body. There are more transporters present at the apical side of the membrane as opposed to the basal membrane as glucose must be kept for the cells oxidative metabolism
• Explain in terms of protein transport how newly synthesised proteins get into the membrane of the mitochondria ?

  The protein will have a signal recognition particle on it which will bind to the matching receptor found on the outer membrane of the mitochondria. This receptor is found on the TOM complex.The protein will then be fed through the outer membrane to the TIM 23 complex , one the protein has passed this it will be inside the inner mitochondrial membrane.where it will be folded and the signal sequence will be cleaved off , producing a mature functional protein
• How does membrane proteins help E.R signalling ?

  The protein is being transcribed within the ribosomes.A Signal recognition particle binds , pausing transcription.The SRP binds to its complementary SRR (signal recognition receptor ) .When it binds the SRP will dissociate and be removed leaving the protein which will be fed through the lumen of the E.R when inside will be folded accordingly
• what are the three types of secretory vessels ?

  Membrane vesicles : secreted out of the Golgi to go to the membrane for renewal Lysosome vessicles and secretory vesicles , carry proteins out the cell
• Give an example of material released by exocytosis from cells ?

  Neurones release acetylcholine , which travels down the axon of the to the NMJ (the synapse between the motor neurone and the muscle ) causes contraction of actin and myosin through calcium mediated exocytosis. Botox prevents this process inhibiting the contraction of muscles causing relaxation.
• How does botox work ?

  V snares are found on vesicles ,T snares are found on Target membranes. Typically acetylcholine will be released in vesicles to to target membrane causing contraction of muscles.Thes v and t snares will wind around each other brining the vesicle as close to the membrane as possible until lips bilayer fuses releasing acetylcholine into the target cell (muscle). However botox cleaves these snares meaning acetylcholine can't bind causing muscle relaxation
• What are the main functions of the cytoskeleton ? Helps maintain shape , stability , strength , transport of intracellular substances in the cytoplasm : organelles or chromosomes. they help with motility : cilia and flagella are microtubules .
• What are the three main components of the cytoskeleton ?

  Microfilaments , microtubules and intermediate filaments
• Give some qualities of Micrtoubles ?

  They are the thickest of the three filaments 25 nanometers wide , they are made up of alpha and beta tubule proteins which form around a central pore making a hollow tube.
• What is some characteristics of microfilaments ?

  They are the smallest around 5 nanometers in diameter , they are associated with the plasma membrane
• Some characteristics of intermediate filaments ?

  They are in-between the other two in lengths , they are very important in the structure and stability giving the cell strength they are known as the "bones"
• How is microfilaments arranged in filopodia and skeletal muscle ?

  actin filaments are associated with myosin heads for muscle contraction.Important for movement , similarly in filopodia (plasmodium , temporary protrusion of the surface) allows cells to sense environment and move , navigate.
• What type of filament is found in neurons which help with motility and shape?

  Microtubules are heavily associated with the dendritic membrane within neurones they help with motility and shape , specifically synaptic plasticity , dendrites will alter for learning and memory.Hence actin filaments are important
• What type of intermediate filaments are associated with each cell ?

  filaments in the neurone are called neurofilaments , filaments within the epithelial cell are called keratin filaments , in connective tissue and gill they are called vimentin and vimentin associated filaments.
• What is the function of microtubules in intracellular transport ?

  Microtubules have kinesins which carry either enzymes , neurotransmitters , vesicles ore receptors from the negative end to the positive end Dyneins carry cargo from the negative end to the positive end
• Where are microtubules assembled from?

  They are assembled from the Microtubule organising centres (MTOC )
• Where are MTOC located ?

  They are located near the nucleus
• What do MTOC items of division ?

  They are the spindle fibres in mitosis helping cellular division
• What do MTOCs do ?

  These control the number, position, and orientation of microtubules in the cytoplasm