Biology 2.1.1- Cell structure

• 3 ideas about cell theory (in 1855)

  All plant and animal tissue is composed of cells

  Cells are the basic unit of all life

  Cells only develop from existing cells
• Why are microscopes important? (3)

  Most cells are too small to see

  Without them we would have mo idea that cells are the unit of life

  We need to see organelles to determine their function
• What is contrast and how do you improve it?

  Contrast is the difference in colour and light between the image and its background. Stains improve contrast
• Light microscope:

  Max resolution, Max magnification, Pros and cons

  200nm, x1500, can see living things, low res- low mag.- no detail of internal structure
• Confocal laser scanning microscope:

  Max resolution, Max magnification, Pros and cons

  180 laterally- 800 axially, x400, non-invasive- 2D and 3D- Living things, Low mag- Low res- No natural colour
• Scanning electron microscope:

  Max resolution, Max magnification, Pros and cons

  3-10nm, x100,000, High mag- High res- 3D, No living things- Monochrome- Samples in vacuum- only the surface
• Transmission electron microscope:

  Max resolution, Max magnification, Pros and cons

  0.5nm, x500,000, Highest and best mag and res, Must be in vacuum- non-living things- 2D and monochrome
• Magnification definition

  How much bigger an image is compared to the object
• Resolution definition

  The shortest distance between two points on a specimen that can still be told apart
• What are artefacts?

  Visible structural detail caused by processing a specimen, but not a feature of the specimen
• Describe the cytoskeleton (4)

  Network of fibres present throughout the cytoplasm

  Necessary for the shape and stability of a cell

  Controls cell movement and movement of organelles within a cell

  Holds organelles in place
• Describe microfilaments (2)


  Contractile fibres formed from the protein actin

  Responsible for cell movements and cell contraction, during cytokenesis
• What do microtubules do?

  Act as tracks for movement of oranelles around the cell

  Form scaffold like structure that determines cell shape

  Form spindle fibres
• What do intermediate fibres do?

  Give mechanical strength to cells to help maintain integrity
• Describe the cell surface membrane's function

  Selectively permiable- Controls the movement of substances into and out of the cell/ organelles
• Describe the nucleus and its contents

  Nucleus- Contains DNA, wound around histone proteins to form chromatin and chromosomes

  Nucleolus- Area within nucleus, produces ribosomes

  Nuclear envelope- A double membrane containing nuclear pores that allow molecules in and out

  
• Describe mitochondria's functions (2)

  The cristae (folds) contain the enzymes used in aerobic respiration

  Site of final stages of cellulose aerobic respiration, producin ATP for the cell

  (very active cells have a lot of mitochondria)

  
• Describe vesicles and lysosomes (structure and function)

  Single membrane with fluid inside

  Vesicles transport materials inside the cell

  Lysosomes are specialed vesicles that contain hydrolic enzyme called lysozyme, which breaks down waste materiales, old organelles, pathogens

  
• Describe the structure, location and role of ribosomes

  Made of rRNA and proteins

  Can be free-floating in the cytoplasm or attached to endoplasmic reticulum (forming rogh ER)

  Site of protein synthesis
• Describe the roguh and smooth ER- Function

  A network of plasma membranes enclosing flattened sacs call listernae

  Roguh ER- ribosomes bound to the surface -synthesis and transport of proteins

  Smooth ER- No ribosomes bound to the surface -Synthesis and storage of lipid and carbohydrates
• Describe the structure and function of the golgi apparatus

  Similar in structure to the smooth endoplasmic reticulum

  Modifies proteins and 'packages' them into vesicles:

  - Secretory vesicles (proteins that leave cells)

  - Lysosomes (proteins that stay in cell)
• Describe the structure and function of centrioles

  Composed of microtubules

  2 associated centrioles form the centrosome

  Involved in the assembly and organisation of spindle fibres during cell division
• Describe the structure and function of flagella

  Tail like structures that protrude from some cells

  Enables mobility, whip like

  Sensory organelle, detecting chemical changes, in some cells
• Describe the structure and function of cilia

  Hair like and can be mobile or stationary

  Mobile cilia beat in a rhythmic manner, creating a current that causes fluid to move
• What is the size and age comparison of prokaryotic vs eukaryotic cells

  Prokaryotic- older and smaller, 3.5 billion years old and 0.1-10µm

  Eukaryotic- younger and bigger, 1.5 billion years old and 10-100 µm
• Compare where DNA is located and how it is organised, in prokaryotic vs eukaryotic cells

  Prokaryotic- in nucleoid (no nucleus) and organised in circular DNA chromosome called genophore and circular plasmids in cytoplasm

  Eukaryotic- in nucleus and organised as linear DNA, wound around histone proteins and condensed into chromosomes
• Compare the cell wall and membrane bound organisms (yes or no) in prokaryotic vs eukaryotic cells

  Prokaryotic- cell wall made from peptidoglycan and no membrane bound organisms

  Eukaryotic- cell wall made from cellulose in plans, chitin in fungi but there are none in protoctista or animal cells. membrane bound organisms are present
• Describe the structure and function of chloroplasts

  Double membrane enclosing stroma, with a network of membranes with form thylakoids (which stack to form granum, which are joined by lamellae)

  Responsible for photosynthesis (found in the leaf and stem but not the leaf)
• Describe the function and structure of cell walls

  Rigid structure made from cellulose that gives the plant cell shape

  Freely permiable
• Describe the structure and function of plasmodesmata

  Membrane lined cytoplasmic nanopores witch bridge adjacent plant cells and enable direct communication between cells
• Describe the sturcture and function of vacuoles

  Important in the maintenance of cell tugor

  Contains cell sap, surrounded by a semi-permiable membrane called the tonoplast