Cells

• Homogenisation is the process of breaking cells open to release the organelles.
• A homogeniser is a blender that breaks the cells open.
• Ultracentrifugation is the process of spinning a homogenate at very high speeds in order to separate cell organelles.
• A homogenate is the suspension you get when you have homogenised cells.
• Densest organelles, heaviest to lightest:

  • nuclei
  • chloroplasts
  • mitochondria
  • ribosomes
• Filtration is used on a homogenate to get rid of bits of membranes and unbroken cells to provide a pure sample.
• The homogenate must be cold, isotonic and buffered.

  • isotonic:

  the solution has the same water potential as the original tissue to prevent cells from bursting/shrinking via osmotic lysis

  • cold:

  reduces enzyme activity (e.g. the hydrolytic enzymes in lysosomes) that would affect the cell samples

  • buffered:

  maintains a stable pH so that cell and enzyme activity is not altered
• A buffer is a solution which prevents a change in pH levels.
• The nucleolus is where ribosomes are assembled and where mitochondria produce ribosomal DNA.
• The RER is a membrane that is continuous with the nucleus. It has ribosomes on its surface and mRNA produces proteins here.
• The SER produces lipids and cholesterol (etc.). It has no ribosomes on its surface and also breaks down toxins.
• Ribosomes are where tRNA builds proteins out of the top of the organelle. They are different between prokaryotes (70S) and eukaryotes (80S).
• The function of the centriole is to position other organelles in the cell by imitating the formation of the spindle in cell division.
• The lysosome is a membrane-bound organelle that contains digestive/hydrolytic enzymes which break down unwanted material in a vesicle. The enzymes also assist in apoptosis by bursting and dissolving the cell.
• The centrosome is the area of cytoplasm next to the nucleus and is where the centriole is found.
• The fluid part of the cytoplasm is the cytosol, which contains dissolved material and solutes. The cytoplasm itself is the substance between a cell's membrane and its nucleus, containing and supporting the cell's organelles.
• The nuclear pores allow molecules out of the nucleus, e.g. RNA.
• The Golgi body's functions include transporting/storing lipids, producing glycoproteins, forming lysosomes, and producing secretory enzymes. It has a similar structure to the ER but is more compact, consisting of flattened sacs called cisternae.
• A typical animal cell is roughly 10-20um in diameter (0.001cm).
• How does binary fission occur?

  1. Replication of circular DNA
  2. Replication of plasmids
  3. Elongation of cell
  4. Pinches inwards
  5. Division of cytoplasm to produce daughter cells