cell structure jaime

• What is Magnification?

  how much bigger a sample appears to be under the microscope than in real life
• What is Resolution?

  the ability to distinguish between two points on an image - how much detail
• What affects resolution?

  light wavelength and objective lens - if organelles overlap light may be diffracted making it blurry
• Equation for magnification


  I A M
• Light Microscope - info?

  x1500 to x2000

  Res = 200 nm

  uses visible light

  • cheap

  • easy to use and portable

  • study live specimens

  • requires stains
• How are samples prepared for light microscopy?

  Dry mounts - solid or sliced specimens placed directly onto slide

  Wet Mounts - specimen suspended within liquid

  Smears - edge of slide smears the liquid to create an even coat

  Squash - specimen is squashed by lens tissue
• transmission electron microscope - Info?

  x 2 million

  Res = 0.2 nm

  beam of electrons passes through specimen

  • dead specimens ( chemically fixed / dehydrated )

  • stained with heavy metal salts

  • grey scale image
• scanning electron microscope - Info?

  x 200,000

  Res = 10 nm

  electrons bounce off specimen

  • 3D image

  • dead specimens

  • specimens coated with thin layer of heavy metal and placed in a vaccum ( often gold )
• Laser scanning microscope - Info?

  uses laser light - resolution better than LM

  • uses depth selectivity

  • specimens can be living

  • moving parts of cells visible

  • can be 3D

  • medical and biological research
• What is sectioning?

  - specimens are dehydrated with alcohols and then placed in a mould with wax or resin to form a hard block

  - this can be sliced thinly with a knife called a microtome
• What is staining?

  coloring microorganisms with chemicals that binds to certain structures
• What is an artefact?

  processing may cause damage so abnormal structures may be seen eg mesosomes
• Why are stains used in microscopy?

  Most cells are colourless. Stains are used to add contrast. Certain stains are also used to stain specific cell structures ( differential staining ) or cell products.
• What are examples of some stains?

  Methylene blue - all purpose positive charge attracted to negative charges

  eosin - cytoplasm

  sudan red - lipids

  iodine - cellulose and starch

  acrtic orcein - DNA
• What is an eyepiece graticule?

  a glass disc that fits on top of the eyepiece lens that is marked with a fine scale from 1 to 100

  
  

  (arbitrary scale)
• What is a stage micrometer?


  A millimeter long ruler etched onto a slide. it has 100 divisions, each of 0.01mm or 10 micrometers. It is used to calibrate the eyepiece graticule
• What are two types of staining?

  positive and negative
• What is a gram stain?

  It is a test to determine if a bacteria is gram positive or gram negative.

  Gram positive bacteria keep the stain while gram negative have thinner walls and dont
• What is the acid fast stain?

  differential stain used to detect cells capable of retaining a primary stain when treated with an acid alcohol ( mycobacterium species )
• What is fixing?

  Chemicals like formaldehyde are used to preserve specimens in as near-natural a state as possible.
• What does membrane bound mean?

  surrounded by a membrane - keeps contents separate
• What do eukaryotic cells have?

  nucleus surrounded by an envelope, membrane bound organelles, jelly like cytoplasm and a cytoskeleton
• What is the cytoskeleton?

  a network of protein ( actin and microtubules ) fibres extending throughout the cytoplasm allowing organelles to move and contraction
• What do organelles within a cell provide?

  Division of labour
• Recall the diagram of a cell and organelle positing!
• What is the nucleus structure?

  The nucleus is surrounded by a double membrane ( envelope ) that contains pores. Within the nucleus is the nucleolus. Chromatin is wound around histone proteins in the nucleus forming chromosomes.
• What is the function of the nucleus?


  The envelope separates the cell contents and some areas fuse to allow movement of substances

  
  

  pores allow larger substances such as mRNA to leave

  
  

  the nucleolus is where ribosomes are made

  
  

  it controls cell and stores the genome where information is transmit for protein synthesis
• What is the structure of RER?

  A system of membranes enclosing a fluid-filled cavities that are continuous with the nuclear membrane. The surface is covered with ribosomes.
• What is the function of RER?

  Folds and processes proteins that have been made at the ribosomes.

  The cisternae form channels where assembled proteins pass through from the ribosomes
• What is the structure of SER?


  Similar to RER but with no ribosomes
• What is the function of SER?

  Synthesises, stores and transports lipids and carbohydrates

  
  

  contains enzymes for lipid metabolism

  •synthesis of cholesterol

  •synthesis of lipids/phospholipids

  •synthesis of steroid hormones
• What is the structure of the Golgi apparatus?


  A stack of membrane bound flattened sacs - secretory vesicles bring material to and from the golgi
• What is the function of the golgi?

  Modifies, sorts, and packages proteins and lipids for storage or transport out of the cell

  
  

  It modifies proteins by:

  •adding sugars ( glycoproteins )

  •adding lipids ( glycolipids )

  •folding into 3D shape
• What is the structure of mitochondria?

  two membranes with a fluid filled space with the inner membrane folding to form a cristae
• What is the function of the mitochondria?

  It is the site of cellular respiration and it contains enzymes which are needed for chemical reactions and DNA for self replication.

  
  

  They are abundant in high metabolically active cells
• Organelles Plant (some protoctists) - Structure of Chloroplasts


  double membrane, inner membrane continuous stacks of thylakoids containing chlorophyll ( stack = granum )

  
  

  fluid filled matrix = stroma

  
  

  they are connected by the lamallae
• What are the functions of chloroplasts?

  Chloroplasts capture the energy from sunlight and convert it into food that contains chemical energy in a process called photosynthesis.

  
  

  Light E is trapped in the grana. H20 is split to supply H+ ions

  H recudes CO2
• structure of lysosomes and peroxisomes?


  small bags formed from the golgi in a single membrane. Lysosomes contain powerful hydrolytic enzymes

  
  

  •vesicles have storage and transportation roles
• What is the function of lysosomes?


  - Keep powerful hydrolytic digestive enzymes separate from the rest of the cell, compartmentalisation

  
  

  - Engulf and destroy old organelles

  
  

  - Destroy foreign bodies (such as pathogens)
• What is the structure of cilia and undulipodia?

  - These are protrusions from the cell and are surrounded by cell-surface membranes.

  - Each contains microtubules.

  - They are formed from centrioles and are surrounded by a plasma membrane.