Cells- Biology

• Eukaryotic cell- DNA is contained in a nucleus + contains membrane bound specialised organelles

  Prokaryotic cell- DNA is free in cytoplasm + no organelles
• Specialised cells make up tissues that perform specific functions

  Organ systems -> organs made up of several tissue types
• Structure of cell surface membrane

  • Fluid mosaic model
  • Phospholipid bilayer
  • Embedded proteins
• Function of cell surface membrane

  • Isolates cytoplasm from environment outside the cell
  • Selectively permeable to regulate transport of substances
  • Involved in cell recognition
• Cholesterol: connects phospholipids + reduces fluidity

  Glycoproteins: Cell signalling + recognition, binding cells together

  Glycolipids: cell signalling + recognition
• Structure of the nucleus

  Nuclear envelope - semi permeable double membrane

  Nuclear pores - allows substances to enter/ exit

  Nucleolus - dense + made out of RNA and proteins- assembles ribosomes
• Function of the nucleus

  DNA coiled around chromatin into chromosomes

  Controls cellular processes
• Structure of mitochondrion

  • Surrounded by double membrane
  • Inner membrane forms cristae (site of ETC)
  • Fluid matrix - contains mitochondrial DNA, respiratory enzymes, lipids, proteins
• Structure of chloroplast

  • Thylakoids - flat discs stack forming grana- contains photosystems with chlorophyll
  • Interganal lamellae - tubes attach thylakoids in agjacent grana
  • Stroma - fluid filled matrix
• Function of mitochondria

  Site of aerobic respiration to produce ATP which releases energy
• Function of chloroplast

  Site of photosynthesis to convert solar energy to chemical energy
• Structure + function of golgi body

  Planar stack of membrane bound flattened sacs

  Molecules are processed in cisternae vesicles bud off via exocytosis:

  • Modifies + packages proteins for export
  • Synthesises glycoproteins
• Structure + function of lysosomes

  Sac surrounded by single membrane embedded H+ pump maintaining acidic conditions

  Contains digestive hydrolytic enzymes

  • Digests contents of phagosome
  • Exocytosis of digestive enzymes
• Structure + function of ribosome

  Formed of protien and rRNA

  free in cytoplasm + attached to ER

  • Site of protein synthesis (translation)
  • Large subunit - joins amino acid
  • Small subunit - contains mRNA binding site
• Structure + function of endoplasmic reticulum

  Cisternae: tubule network + flattened sacs that extend from cell membrane through cytoplasm + connects to nuclear envelope

  • Rough ER - many ribosomes attached for protein synthesis + trabsport
  • Smooth ER - lipid synthesis
• Structure of cell wall

  • Bacteria - made of murein
  • Plants - made of cellulose
• Function of cell wall

  • Mechanical strength and support
  • Physical barrier against pathogens
  • Enable easy diffusion of water (apoplast pathway)
• Structure + function of permanent vacuole

  Surrounded by single membrane (tonoplast), contains cell sap: mineral ions, water, enzymes, soluble pigments

  • Controls turgor pressure
  • Absorbs and hydrolyses potentially harmful substances to detoxify cytoplasm
• Common cell adaptations

  • Folded membrane / microvilli increase surface area
  • Many mitochondria- large amounts of ATP which releases energy
  • Walls - one cell thick to reduce distance of diffusion pathway
• Role of plasmids

  • Small ring of DNA that carries non-essential genes
  • Can be exchanged between bacterial cells via conjugation
• Role of flagella in prokaryotes- rotating tail propels organism
• Role of flagella in prokaryotes- rotating tail propels organism
• Role of capsule in prokaryotes

  • Prevents desiccation
  • Food reserve
  • Mechanical protection against phagocytosis + chemicals
  • Sticks cells together
• Similarities of eukaryotic + prokaryotic cells

  • Cell membrane
  • Cytoplasm
  • Ribosomes
• What does prokaryotic have that eukaryotic don't

  • Small cells
  • Unicellular
  • No membrane bound organelles + no nucleus
  • Circular DNA not associated with proteins
  • Small ribosomes
  • Binary fission
  • Murein cell walls
  • Capsule, sometimes plasmids + cytoskeleton
• What do eukaryotes have that prokaryotes don't

  • Larger cells
  • Multicellular
  • Contains membrane bound organelles + nucleus
  • Linear chromosomes associated with histones
  • Larger ribosomes
  • Mitosis + meiosis
  • Cellulose wall (plants) / chitin cell wall (fungi)
  • No capsule + plamsids , sometimes cytoskeleton
• Why are viruses particles not cells?

  Acelllular + non living

  No cytoplasm

  Cannot self reproduce

  No metabolism
• Structure of a viral particle

  • Linear genetic material + viral enzymes
  • Surrounded by capsid
  • No cytoplasm
• Structure of enveloped virus

  • Simple virus surrounded by matrix protein
  • Surrounded by envelope from cell membrane of host cell
  • Attachment proteins
• What is the role of capsids on viruses?

  Protect nucleic acid from degradation

  Surface sites enable viral particle to bind to and enter host cells / inject genetic material
• What is the role of attachment proteins on viral particles?

  Enables viral particles to bind to complementary sites on host cells
• How do optical microscopes work?

  1. Lenses focus rays of light + magnify the view of specimen
  2. Different structures absorb different amounts and wavelengths of light
  3. Reflected light is transmitted to the observer via objective lens and eyepiece
• How to prepare sample for optical microscope

  • Obtain think section of tissue
  • Place tissue in a drop of water
  • Stain tissue on a slide- make structures visible
  • Add coverslip using mounted needle at 45 degrees to avoid air bubbles
• Advantages of optical microscope

  • colour image
  • Shows living structures
  • Affordable apparatus
• Disadvantages of optical microscope

  • 2D image
  • Lower resolution than electron microscope - larger wavelength
• How does a TEM work?

  1. Pass high energy beam of electrons through thin slice of specimen
  2. Denser structures appear darker- absorbs more electrons
  3. Focus image on fluorescent screen/ photographic plate using magnetic lenses
• Advantages of TEM

  • electrons have shorter wavelength- high resolution
  • High magnification
• Disadvantages of TEM

  • 2D image
  • Requires a vacuum- no living structures
  • Extensive preparation may produce artefacts
  • No colour image
• How does SEM work?

  1. Focus beam of electrons onto specimen surface using EM lenses
  2. Reflected electrons hit a collecting device and are amplified to produce image on photgraphic plate
• Advantages of SEM

  • 3D image
  • Electrons have shorter wavelength- higher resolution