Cell Structure

• Maximum resolution of a light microscope

  0.2 micrometres
• maximum useful magnification of a light microscope

  X 1500
• Max resolution of electron microscope

  0.2 nm
• max magnification of an electron microscope

  X 1000000 (sometimes more)
• How do TEM's work?

  Transmission electron microscopes use a beam of electrons to create a magnified image of a specimen. Denser parts absorb more electrons- appearing darker. For viewing internal structures (2D)
• how do SEM's work?

  They pass a beam of electrons across the surface of a specimen and detect the rate at which the electrons bounce back. They are 3D and show the surface of specimens. They have a lower maximum resolution than TEM's .
• $magnification\ =$$\frac{size\ of\ image}{size\ of\ real\ object}$
• • 1 m = 1000 mm = 1,000,000 μm = 1,000,000,000 nm
• Magnification 


  The number of times larger an image is than the actual object
• Resolution


  The ability to distinguish separate points on an image as two separate objects
• how is the resolution of a light microscope limited?

  Wavelength of light (electrons have a smaller wavelength)
• what is the diameter of the phospholipid bilayer?

  10 nm
• what is the cell wall made of in bacteria?

  Peptidoglycan
• what are the narrow threads of cytoplasm called that connect neighbouring cells?

  Plasmodesmata
• What is chromatin in the nucleus?

  A complex of DNA and histone proteins
• what are chromosomes


  Made of sections of linear DNA tightly wound around histone proteins
• where is the site of ribosome production?

  Nucleolus
• why are nuclear pores Important?

  Allows mRNA and ribosomes to travel out of the nucleus as well as allowing enzymes and signalling molecules to enter
• Where is the rough endoplasmic reticulum located?

  Surrounds the nucleus
• what is the structure of a mitochondria?

  Surrounded by a double membrane with the inner membrane folded to form cristae. This matrix contains enzymes needed for aerobic respiration, producing ATP. Small circular pieces of DNA and ribosomes are in this matrix (needed for replication)
• structure of chloroplasts 


  Larger than mitochondria. Surrounded by a double membrane. Membrane bound compartments (thylakoids) containing chlorophyll stack to form grana. These are joined by lamellae (thin and flat thylakoid membranes). Contains small circular pieces of DNA and ribosomes (for replication). Also contains starch and drops of lipids in the stroma (space enclosed by the double membrane)
• ribosome structure


  Found in all cells (part of RER in eukaryotes, free roaming in prokaryotes). Complex of rRNA and proteins (almost equal amounts). Site of translation in protein synthesis. Formed in the nucleolus. Contains a large and small subunit.
• what size ribosomes do eukaryotes contain?

  80s (60S and 40S subunits)
• what size ribosomes do prokaryotes, mitochondria and chloroplasts contain?

  70S (50S and 30S subunits)
• what is the structure and function of the rough endoplasmic reticulum?

  Structure: Continuous Membrane-bound network of flattened sacs covered in ribosomes attached to the nuclear envelope. Found in plant and animal cells Function: Protein synthesis and processing, as well as the production of membrane lipids.
• What is the structure and function of the smooth endoplasmic reticulum?

  Found in plant and animal cells. Does not have ribosomes. Involved in and production, processing and storage of lipids, carbohydrates and steroids.
• Structure and function of the golgi apparatus?

  Structure: Flattened membrane-bound sacs (cisternae) stacked on top of each other. Found in plant and animal cells Function: Modifies, sorts, and packages proteins and lipids for transport in vesicles. Usually exports substances (eg hormones), put into lysosomes (eg hydrolytic enzymes) or delivered to membrane bound organelles.
• Structure of Large permanent vacuoles

  A sac In plant cells surrounded by the tonoplast (selectively permeable membrane). Animal cells have vacuoles but they are small and not permanent.
• structure and function of vesicles

  Lipid bilayer containing internal water for transport and storage
• Structure and function of lysosomes

  Specialist forms of vesicles. Contains hydrolytic enzymes. Breaks down worn down organelles or used in the immune system for cell apoptosis.
• Structure and function of centrioles

  Hollow fibres made of microtubules. Two centrioles at right angles forms a centrosome which organises the spindle fibres during cell division. Not found in flowering plants or fungi.
• structure and function of microtubules

  Found in all eukaryotic cells. Makes up the cytoskeleton. 25nm in diameter. Made of $\alpha$ and $\beta$ tubulin combined to form Dimers which join to form protofilaments. Thirteen protofilaments can reversibly form in a cylinder to make a microtubule. The cytoskeleton provides support and movement to the cell.
• Structure and function of microvilli

  Found in specialised animal cells. Cell membrane projections which increases the surface area of the cell membrane to increase the rate of exchange of substances
• structure and function of cilia

  Hair like projections made from microtubules. Allows the movement of substances over the cell surface
• structure and function of flagella

  Found in specialised cells. Similar structure to cilia (longer microtubules). Contracts to provide cell movement (eg in sperm cells)
• What is the role of the nucleus in the production of proteins

  • DNA is stored
  • The nucleolus manufactures ribosomes
  • Transcription occurs, producing an mRNA copy of DNA
• What is the role of the ribosomes in the production of proteins

  • mRNA leaves the nucleus and attaches to a ribosome
  • Translation occurs, and a polypeptide is produced
• What is the role of the RER in the production of proteins

  • After translation, the polypeptides are folded and processed to produce protein
• What is the role of the golgi apparatus in the production of proteins

  • Proteins are modified and prepared for secretion
• What is the role of the vesicles in the production of proteins

  • Proteins are transported from the RER to the golgi apparatus to the cell surface membrane inside vesicles
  • These fuse with the cell membrane to secrete proteins via exocytosis