Cells

?

Eukaryota Cells: Ultrastructure

  • Cell surface membrane - Made up of phospholipid bi-layer (see later card) and regulates substance exchange
  • Nucleus - Contains DNA, surrounded by nucleur envelope, substances pass in and out trhough nuclear pore, contains a nucleolus
  • Mitochondrion - Structures called cristae increase surface area, contains inner matrix and outer and inner membrane. Site of respiration. 
  • Chloroplast - Contains lamallae and granum(stacked thylakoid cells), also contains stroma. Site of photosynthesis. 
  • Golgi apparatus, bounds substances into vescicles
  • Lysosome - Contains digestive enzymes
  • Ribosomes - Site of protein synthesis.
  • Rough endoplasmic reticulum - Protein synthesis
  • Smooth endoplasmic reticulum - Stores and processes lipids
  • Cell Wall - Made of cellulose (beta glucose), very strong keeps cell structure.
  • Cell Vacuole - sac filled with sap which keeps turgidity. Membrane is called the tonoplast. 
1 of 12

Prokaryotic cells: Ultrastructure

  • DNA not linear, but circular, and not asscociated with proteins (histones)
  • Some DNA loose, called plasmids
  • Sometimes have flagellum
  • No membrane bound organelles. 
  • Cell membrane/cell wall/capsid
  • Viruses are not cells
  •       They have a protein coat
  •       Attachment proteins on surface
  •       A capsid of DNA or RNA
  • Bacterium replicate by binary fission and viruses use host cells. 
2 of 12

Microscopy

  • Light microscopes use light as a source of radiation
  •     MAGNIFICATION: x1500       RESOLUTION: 0.2 Micrometers [ie. can't see ribosomes/RER/lysosomes]
  • Electron microscopes use electrons as a source of radiation
  • Electrons have a shorter wavelenght than light
  • Therefore a greater resolution can be achieved
  •        TRANSMISSION                                                       SCANNING
  •   MAG.:1000000    RES.: 0.2 nanometers                                  MAG.: 20000          RES.: 20 nanometer
  • HOWEVER, SPECIMIN MUST BE DEAD AS MUST BE IN VACUUM AND LENGTHY PREPARATION

Preparation of a microscope slide:

1) Place a drop of water on slide over 1 cell thick specimin

2) Stain it

3) Add a cover slip

3 of 12

Cell Fractionation

1) cells are broken down and homogenised in and ice cold, isotonic, buffer solution

2) Filtration must get rid of any large debris

3) Ultracentrifugation must occur to split the molecule up into supernatant and sediment.

4) Supernatant separated from sediment, and sediment centrifuged again at higher speed, for longer time

  • Heaviest organelle produced frist: Nuclei ->> Mitochondria ->> Lysosome -- > ER --> Ribosomes
4 of 12

Cell Division by Mitosis

1) INTERPHASE

  •    -->> G1 - organelle replication, cell growth
  •   --->> S Phase - DNA replication occurs
  •   -->> G2 - More organelle growth and cell growth & protein synthesis

2) MITOSIS

  •  -->> Prophase DNA condenses to chromosones, centrioles form the spindle at opposite ends of the cell, nuclear envelope breaks down
  • -->> Metaphase - Chromosones align along the equator of the cell and the spindle attaches to centromeres
  • -->> Anaphase -  The spindle retracts, pulling the chromatids apart
  • -->> Telophase - Two nuclear envelopes reform around chromosones and chromosones become DNA again.

3) CYTOKINESIS

  • -->> The cytoplasm splits, producing two, identical daughter cells. Process restarts 
5 of 12

Microscopy and Cell cycle calculations

  • Magnification = image size/object size
  • 1mm=1000 micrometers
  • To calibrate and eypiece graticule you use a stage micrometer and line it up with graticle. 5 units on stage micrometer = 10 units on graticule.
  •         Therefore, 1 unit on stage micrometer = 2 units on graticule
  •         1 unit on micrometer = 2 micrometers
  •         Therefore, 1 micrometer = 1 unit on graticule

Mitotic index = [Number of cells with condensed chromosones/total number of cells] x 100

6 of 12

The Cell Surface membrane

  • Follows fluid mosaic model and is amde up of phospholipid bi-layer = Hydrophilic heads facing outwards Hydrophobic tails facing inwards
  • Contains cholesterol molecules which keep the structure. 
  • At high temperatures phospholipid bilayer breaks down and proteins denature, meaning that it becomes more permeable
  • Intrinsic proteins = runs all the way through - E.G channel and carrier proteins
  • Extrinsic proteins = only on surface - E.G. Glycoproteins
  • Glycoprotiens = Cell recoginition
  • Glycolipids = Cell recognition and keep structure
7 of 12

Diffusion and Osmosis

  • Simple diffusion - Down concentration gradient - passive
  • Facilitated diffusion - Still passive but use of a protein
  •             Carrier proteins - Large molecules (moves through change of protein shape)
  •             Channel proteins - Charged particles (Like a pore)
  • Osmosis - Net movement of water from an area of less negative water potential to an area of more negative water potential
  •             Serial dilution to get different concentrations, place equal samples inside and leave: measure % change in mass
  • Active transport - using protein pumps, low to high concentration
  • Co transport - Sodium diffuses out of cell with potassium in sodium potassium pump. Lowers concentration of sodium ions so sodium diffuses into cell with glucose. Glucose diffuses back out by facillitaed diffusion
  •                Co transporter protein needed
8 of 12

The Primary immune Response

PHAGOCYTOSIS

  • pathogen is englufed by phagocyte, which is attracted to it by chemicals (endocytosis)
  • This forms a vescicle around phagocyte, which fuses with lysosome
  • Lysosymes break down phagocyte, and antigens presented on phagocyte surface

T Cell and B Cell Activation

  • T cell receptor proteins attach to these, which activate the T Cells. These divide by mitosis and differentiate into cytotoxic t cells, memory cells (stored in thymus gland) or T helper cells, which activate b cells or phagocytes or cytotoxic t cells

B Cells

  • Activated B cells divide into memory cells (stored in the bone marrow) or plasma cells, which release antibodies. Antibodies have light and heavy chain, variable and constant regions, and a specific structure which bind to antibodies, causing agglutination

B cells is humoral response and T cell is cell mediated response

9 of 12

The secondary immune response & active and passive

  • Due to the memory cells stored in the thymus gland and the bone marrow, when the same pathogen enters the body again, the immune system will produce a quicker, stronger immuner response, called the secondary response. 
  • Active immunity = own antibodies made Natural: Normal way  Artificial: vaccination
  • Passive immunity = Noty own antbodies made Natural: from mother in womb Artificial: actual antibodies injected
  • Herd immunity = most people have vaccination, less likelt for people who haven't had it to catch
  • Vaccination contains attenuated pathogen
  • Antigenic variation can occur to stop a.a complexes being formed
10 of 12

Monoclonal antibodies & the ELISA test

Moncolonal antibodies=antibodies produced outside of body

E.G. Mouse injected with pathogen, B cells produced and removed.

Associated with tumour to form hybridoma

Division and testing occurs

Antibodies can be used

E.G. pregnancy test

INDIRECT ELISA TEST

1) antigen bound to bottom of test plate

2) Antibody from sample passed over, then loose washed off

3) another antibody with an enzyme react passed over, and again washed

4) substrate for enzyme passed over: + result = colour produced

11 of 12

HIV and AIDS

  • Virus has capsid with reverse transcriptase, RNA, and attachment proteins, along with lipid envelope
  • Virus attaches to T helper cells, injects capsid which releases RNA. Reverse transcrioptase converts this to DNA
  • Host cells produce viral DNA from this template
  • More viruses are assembled and leave T helper cells, taking cell surface membrane
  • Goes into dormancy and comes back years later as AIDS, which attacks t helper cells again, causing immune system problems. 
  • Antibodies don't work against viruses because they stop cell wall production but viruses don't produce their own cell walls. 
12 of 12

Comments

No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Cellular processes and structure resources »