Clarification: Events at the rER (synthesized protein will end up in the rER lumen and later bud off in an ER vesicle)

- protein synthesis
- folding of protein
- chemical modification of protein (FURTHER chemical modification will occur in the GA later)

Lysosome vs Peroxisome

http://sln.fi.edu/qa97/biology/cells/cell7.html

"Peroxisomes contain oxidative enzymes. They are similar to lysosomes. Their enzymes have two functions; to convert fats to carbohydrates and to detoxify potentially harmful molecules which form in the cell.

Peroxisomes, in contrast to lysosomes, are produced only on the smooth ER system. They are found in the cytoplasm of many eukaryotic cells as well as prokaryotic cells, microorganisms, and plant cells.

The enzymes of peroxisomes remove hydrogen atoms from small molecules and joins them to oxygen creating hydrogen peroxide (toxic), which is later neutralised by a peroxisomal enzyme, catalase. In the liver this method is used to break down molecules of alcohol into substances that can be eliminated from the body. "

Clarification - primary vs secondary lysosomes

1) Origin of Primary lysosomes (page 17 of your notes I believe)

In your cell structure and function lecture notes, under the section on Lysosomes, it states that primary lysosomes bud off from the Golgi Apparatus OR Endoplasmic Reticulum.

Note that primary lysosomes largely originate from the GA, that is why we have emphasized this during the lecture/tutorial. In some cases, primary lysosomes can bud off the ER but you do not need to know this in detail.

Even if you mention just GA alone, it is still correct. :)

2) Primary vs Secondary lysosomes (tutorial structured Q1d)

- Primary lysosome are formed from the GA while the secondary lysosome is formed by the fusion of the primary lysosome and an endocytotic/phagocytotic vesicle.

- The primary lysosome does not release its contents out of the cell but the secondary lysosome may release useful products (which will serve as building blocks of new materials) into the cytoplasm of the cell via facilitated diffusion, or release waste products/products that cannot be digested out of the cell via exocytosis.

You can view a good diagram of primary and secondary lysosomes here: http://biology.kenyon.edu/HHMI/Biol113/lysosomes.htm

Cell structure and function (cell membrane) - SDL Wksheet A

Video of facilitated diffusion:
http://www.youtube.com/watch?v=I4123hUU8xo&list=FL-cFTJ8NxBjonnjuwSQgSsw&index=26&feature=plpp_video

Video of active transport:
http://www.youtube.com/watch?v=yz7EHJFDEJs&feature=autoplay&list=FL-cFTJ8NxBjonnjuwSQgSsw&lf=plpp_video&playnext=1

Query about cell membranes: Can water diffuse through the lipid bilayer?

Water, though small, is a hydrophilic molecule. Hence it cannot diffuse through the hydrophobic interior of the lipid bilayer. Aquaporin channels are required for water to pass through the lipid bilayer.

FYI: You can read about the experimental discovery of aquaporin in the links below:

http://www.ncbi.nlm.nih.gov/pubmed/11773613

http://www.bing.com/images/search?q=aquaporin+oocyte&view=detail&id=2BE08C8AEE232A3B3F05FE97719A64215101C3BE&first=0&FORM=IDFRIR

Reminder

HOMEWORK this weekend (besides studying VERY HARD for your lecture test on Monday :p):

1) For the current tutorial worksheet on Cell Structure, please copy out (since you should have already done it) your essay question (there's only one essay question, on the last page) onto a piece of foolscap for me to mark. Hand it in to your Bio reps and Bio reps, please put it in my *new* pigeonhole (labelled with my name) by 5pm the coming Monday.

I believe this is crucial as alot of students do badly in essays as they not know how to phrase their answers. As such, all essays (in future) must be done on a piece of foolscap and handed in for me to mark.

2) After the lecture test on Monday, I will be collecting your tutorial worksheets on Biological Molecules (carbo, lipids, protein tutorial worksheet + SDL worksheet B on nucleic acids) during our tutorial class next week. So please remember to bring them to school.

This is because all of you are new to the rigours of JC life, so I want to check that you are keeping up well with the course (and understand what is expected of you). :)

Good luck for your test!

Cell structure and function tutorial - origin of mitochondria and chloroplasts

Q1) How does the presence of double-membranes in these two organelles serve as evidence that these two organelles actually existed as free -living bacteria centuries ago?

A1) - The ancestor eukoryotic cells engulfed bacteria by phagocytosis/endocytosis, and the bacteria eventually became the mitochondria or chloroplast.
- Hence, the outer membrane is derived from the eukaryotic cell and the inner membrane is derived from the bacteria.

FYI only: This theory is actually named the "endosymbiotic theory", but you are not required to know it. You can watch an animation of the theory here: http://www.youtube.com/watch?v=EgaGh9-mFnQ

Note: Please do not be confused, prokaryotes (i.e. bacteria) have only one cell membrane. You will learn more about its structure in the later topics.


Q2) How does linear DNA (in eukaryotes) and circular DNA (in prokaryotes, mitochondria, and chloroplasts) look like under the electron microscope (EM)?

A2) Linear DNA (above) and circular DNA (below), in a relaxed state.