Cell structure

• Resolution - the clarity of an image

  • the ability to be able to distinguish between two points
• Magnification - ratio of the size of an image to the size of the object
• Optical/ light microscope

  • x 1500
  • low resolution
  • 2D images
  • produce a colour image
  • examine living cells or tissues
  • cheap and easy to use
• Laser microscope

  • High resolution
  • 3D images
  • dont produce a colour image
  • observe whole living specimens and cells (e.g: cells in the retina of the eye)
• TEM - Transmission electron microscope

  
  

  • x 2,000,000
  • high resolution
  • 2D image
  • produces black and white image
  • shows cells and organelles
  • electrons pass through specimen which is stained with metal salts
• SEM - Scanning electron microscope

  • x 200,000
  • high resolution
  • 3D image
  • produces a black and white image and has false colour added
  • specimens have to be dead
  • electrons bounce off specimens surface and focused on a screen
• Why does an optical microscope have a low resolution?

  wavelength of light is greater than wavelength of electrons
• Magnification = image size/actual size
• Differential staining - multiple stains are used and each bind to a specific cell structure providing contrasts in them to make them more distinguishable
• Units

  A) x10

  B) x1000

  C) x1000

  
• • Eyepiece graticule - scale used to measure the magnification of the eyepiece
  • Stage graticule - placed on stage to calibrate value of eyepiece graticule at different lengths
• coarse focus knob - adjusts the focus of the microscope
• • methylene blue - all purpose stain
  • acetic orcein - binds to DNA and stains chromosomes dark red
  • eosin - stains cytoplasm
  • Sudan red - stains lipids
  • iodine (in potassium iodide solution) - stains cellulose in plant cell walls yellow and starch black
• • methylene blue - all purpose stain
  • acetic orcein - binds to DNA and stains chromosomes dark red
  • eosin - stains cytoplasm
  • Sudan red - stains lipids
  • iodine (in potassium iodide solution) - stains cellulose in plant cell walls yellow and starch black
• Prepared slides

  • specimens are dehydrated
  • embedded in wax to prevent distortion during slicing
  • thin sliced specimens
• describe the process that occurs in a cell during protein production

  • gene for a protein is transcribed into mRNA in the nucleus and leaves via pores in the nuclear envelope
  • mRNA attaches to a ribosome to be translated. Protein molecules pass through the cisternae in the RER
  • molecules are pinched off by the RER and travel via vesicles and motor proteins towards the Golgi apparatus until they fuse
  • Golgi apparatus modifies proteins molecules ready for release
  • molecules pinched off in vesicles from the GA and move towards plasma membrane and fuse
  • membrane releases proteins via exocytosis
• the nuclear envelope is a double membrane surrounding the nucleus with pores

  • it separates the contents of the nucleus from the cell
  • pores enable mRNA to leave nucleus and some steroid hormones from the cytoplasm to enter
• the nucleolus contains RNA and is where ribosomes are made
• the nucleus stores an organism's genome and provides instructions for protein synthesis

  • chromatin is the genetic material consisting of DNA wound around histone proteins
  • when a cell is about to divide chromatin condense, coiling into chromosomes
• The rough endoplasmic reticulum - system of membranes containing fluid filled cavities (cisternae) with ribosomes, continuous within the nuclear membrane

  • provides large SA for ribosomes which assemble proteins from amino acids which actively pass through membrane into the cisternae
  • act as an intracellular transport system
• Smooth endoplasmic reticulum - system of membranes containing fluid filled cavities without ribosomes, continuous within the nuclear membrane

  • absorb, synthesise and transport lipids
  • synthesis of cholesterol
  • synthesis of steroid hormones
• Golgi apparatus - stack of membrane bound flattened sacs

  • involved in protein modification (3D folding)
  • add sugar/lipid molecules to make glyco/lipo proteins
  • proteins are packaged into vesicles which are pinched off and stored in the cell or moved to plasma membrane
• Mitochondria

  • Cristae is folded for greater SA for enzymes in oxidative phosphorylation
  • site of ATP production during aerobic respiration
  • self-replicating to meet energy demands
  • abundant in cells where metabolic activity is high (liver and muscle cells)
• Chloroplasts

  • surrounded by a double membrane
  • abundant in leaf cells including the palisade mesophyll layer
  • site of photosynthesis
  • stroma - fluid filled matrix
  • thylakoids contain chlorophyll and ATP synthase for photophosphorylation
  • granum - their flat membrane stacks increase SA: V and small internal volumes accumulate ions quickly
  • lamella - connects and separates grana

  A) stroma

  B) thylakoid

  C) granum

  D) lamella

  E) membrane

  
• Lysosomes - small bags formed in the Golgi apparatus surrounded by one membrane

  • contain hydrolytic enzymes
  • abundant in phagocytic cells
  • keep hydrolytic enzymes separate from rest of cell
  • digest old organelles and forgein matter and reuse them in the cytoplasm
  • exoctyosis is used to secrete old organelles and enzymes
• vacuoles

  • tonoplast - vacuole membrane
  • contains cell sap, dissolved sugars, minerals, amino acids and waste
  • cell sap has a low water potential helping plants remain turgid and stable
• Cilia

  • cells lining the trachea
  • cells lining the fallopian tubes
  • sense chemicals around the cell (e.g cells in the nose)
  • contain microtubules
  • formed from centrioles
  • undulipodia - a long cilia
  • both flagella and cilia arranged in 9+2 microtubule pair structure
  • using energy from ATP pairs of microtubules can move relative to pairs next to them creating bending motion of organelles
• Ribosomes

  • made of ribosomal RNA
  • made in the nucleolus
  • those bound to the exterior of the RER - synthesising proteins to be exported outside the cell
  • those free in the cytoplasm - site of assembly for proteins used inside cell
• Centrioles

  • made of microtubules and tubulin protein subunits arranged in a cylinder
  • before a cell divides the spindle(of tubulin) forms centrioles
  • chromosomes attach to middle part of spindle and motor proteins walk along tubulin threads moving them across the cell
  • before cilia form: centrioles multiply and line up beneath cell surface membrane where microtubules sprout outwards forming cilium
• Cell wall

  • outside plasma membrane
  • bound by bundles of cellulose fibres
  • prevent cell bursting when turgid
  • provide strength and support
  • maintain cell shape
  • permeable for solutions, solute and solvents
• Cytoskeleton

  network of protein structures increasing in size

  (microtubules, actin filaments and intermediate filaments)

  • provide mechanical strength in cells e.g; stress on skin
  • movement - vesicles, cilia, flagellum
  • form spindle fibres involved in movement of chromosomes during mitosis and meiosis
  • form network in cytoplasm - providing cell shape and structure
  • involved in cell transport:
  • > WBCs diffuse out blood stream to infected tissue
  • > cell division - in cytokinesis cell membrane is moved inwards dividing cytoplasm in two
• The endosymbiosis theory - suggests that eukaryotic cells evolved from bacteria (prokaryotic) cells that were taken inside other cells

  >Support -

  Mitochondria and chloroplasts evolved from a bacteria taken inside other cells as:

  • it contains its own (circular) DNA
  • is the same size as bacteria
  • has a double membrane
  • divide by binary fission
• How are prokaryotic cells similar to eukaryotic cells?

  • consist of a plasma membrane
  • cytoplasm
  • ribosomes and DNA/RNA
• How are prokaryotic cells different to eukaryotic cells?

  • they are much smaller
  • smaller ribosomes
  • have a less well developed cytoskeleton with no centrioles
  • don't have a nucleus - have naked DNA
  • don't have membrane bound organelles
  • wall is made of peptidoglycan not cellulose
  • have Pili which adhere to host cells and a waxy, protective capsule
• Binary fission - division of a single cell into two identical daughter cells
• Viruses

  DNA surrounded by a protein cover

  Can only reproduce inside a host cell

  
• prepared slides - improvements

  place water drop at edge of base not middle

  place cover slip at an angle

  apply a stain