Topic Cell Organelle Essay - Main Points!

Q) Describe the roles of the rough endoplasmic reticulum, mitochondria and ribosomes

Main points
Key idea:	Functions of rough endoplasmic reticulum (rER)
Fn : Transport of protein  synthesized by ribosomes attached to its surface · Proteins leave ER throu transport vesicles that pinched off fr membr, to various destinations within cell or exported out (exocytosis) · Proteins may be transported to Golgi body, modified before reaching their final destinations
Key idea:	Functions of mitochondria
Fn : Syn of ATP · Pyruvate (fr glycolysis) enters mitoch, form acetyl CoA + NADH · Acetyl CoA enters Krebs cycle, form more NADH + FADH2 + ATP (substrate level phosphorylation) · NADH + FADH2 transported to inner mitoch membr, form most ATP (via oxidative phosphorylation) per glucose during cellular resp
Key idea:	Functions of ribosomes
Fn : Syn of polypep using mRNA as template · Ribo positions mRNA, tRNA, other protein factors to form complex for translation · Peptidyl transferase (of large ribo subunit) form peptide bonds b/w adj aa
Comments: (i) Visualize the answer with the aid of labelled pictures of the organelles (refer to URL provided) (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min)

Topic Cell Organelle Essay - Main Points!

Q) Describe the structure and function of Golgi body

Main points
Key idea:	Structural features of Golgi body
· Stack (of flattened sacs) + sys (of assoc vesicles) · Made fr vesicles derived fr rER · Ref to ‘forming’ or cis face + ’maturing’ or trans face
Key idea:	Functions of Golgi body
i) Chemically modifies proteins (e.g. attach carbo chain to protein - glycoprotein) ii) Sorts, packages proteins into (transport or secretory) vesicles for transport w/n or out of cell via exocytosis iii) Forms lysosome iv) Lipid synthesis + transportation v) Forms cell plate which becomes cell wall
Comments: (i) Visualize the answer with the aid of a labelled picture of the organelle (refer to earlier post for URL) (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min) (iv) sER is the primary site of lipid synthesis (e.g. cholesterol, phospholipids, steroid, fatty acid, etc) + drug detoxification

Topic Cell Organelle Essay - Main Points!

Q) Describe the differences between lysosome and ribosome

Key ideas	Main points
1) Memorize the 6 features for comparison first : · Size · No. of subunits · Content within · Origin · Location in cell ·  Function 2) Then memorize specific features for each organelle	Lysosome · 0.1-0.5μm · made up of single unit, bound by single membrane · Consists of hydrolytic enz (e.g...) · Originate fr Golgi body · Exist freely in cytoplasm  · Fn : i) Fuse w endocytic vesicles + digestion + absorbed + assimilate into cell ii) Autophagy ... iii) Autolysis  ...	Ribosome · 20-30nm (smaller) · 2 subunits (large, small), not membrane bound, large subunit contains peptidyl transferase · Each subunit  consists of rRNA + protein in about equal quantities · Origin: rRNA component fr nucleus, protein component fr cytoplasm -  subunits form in nucleus but assemble to ribosome in cytoplasm · Exist freely or attached to ER · Fn : i) Protein syn, peptide bond form b/w aa
Comments: (i) Visualize the answer with the aid of a labelled picture of both organelles (refer to earlier post for URL) (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min) (iv) Typo error in the book – ‘each subunit....in roughly equal quantities’

Topic Cell Organelle Essay - Main Points!

Q) Distinguish between plant and animal cells in terms of their structural features

Key ideas	Main points
1) Memorize 6 features for comparison first – · Cell wall · Middle lamella · Chloroplast · Vacuole · Lysosome · Centriole 2) Then specific features for each type of cell	Plant cell · Possess cellulose cell wall w plasmodesmata · Middle lamella join walls of adjacent cell · Chloroplasts · Large central vacuole surrounded by tonaplast - ·  Absent in higher plants	Animal cell - - - · Small scattered vacuoles · Possess lysosomes · Centrioles
Comments: (i) Visualize the answer with the aid of a labelled picture of both cells (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min)

Topic Cell Organelle Essay - Main Points!

Q) Describe rough endoplasmic reticulum, mitochondria and ribosomes in terms of their structural features

Main points
Key idea:	Structural features of rough endoplasmic reticulum (rER)
· Complex network of membranous tubules + sacs (cisternae) · Ribosomes attached to outer surf of membrane · which is continous w outer membr of nucleus
Key idea:	Structural features of mitochondria
· Cylindrical or rod-shaped · Double membrane-bound: outer + inner membr sep by inter-membrane space  · (i) outer membrane - smooth cont layer + (ii) inner membrane - folded inward, form cristae, project into semi-fluid matrix · Matrix contains circular DNA + 70S ribo. · Stalked particles containing ATP synthase (or ATPase) embedded w/n inner membr, for ATP syn
Key idea:	Structural features of ribosomes
· Made up of proteins + ribosomal RNA (rRNA) · One small + one large subunit (contains peptidyl transferase) · Euk cell - 40S & 60S subunits ; Prok cell - 30S & 50S subunits · Exist suspended in cytosol or attached to outer surf of ER · Has specific sites : (i) Aminoacyl-tRNA binding site (A site) which bind to tRNA w aa (ii) Peptidyl-tRNA binding site (P site) which bind to tRNA w growing polypep
Comments: (i) Visualize the answer with the aid of labelled pictures of the organelles (refer to URL provided) (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min) (iv) Ribosomes also contains the E site where the uncharged tRNA exits

Topic Cell Organelle: URL links to electron micrographs and drawings

For this topic, you should be able to identify the organelles based on their characteristic features. Since students tend to be confused over the following organelles, visit the URLs at least once and remember. 

Look out for the following in the organelles:
Nucleus - black spot(s) (nucleolus/nucleoli), (nuclear) pores may be visible at times 
rER - lots of black dots (ribosomes) on the surface of the organelle
sER- numerous tubular sacs
GA - a stack of flattened sacs with vesicles
Mitochondrion - infolding of membrane (cristae) w/n organelle
Chloroplast - stacks of membranes (grana) w/n organelle
Ribosomes - small dots suspended in the cytosol or attached to the ER (as rER)
(P.S. The above descriptions are for you to recognize and identify the organelles, and may not be suitable as exam answers. Refer to your notes for the correct descriptions of the characteristic structural features.)

Nucleus (including nucleolus and nuclear pore)

1) http://en.wikipedia.org/wiki/File:Micrograph_of_a_cell_nucleus.png (nice electron micrograph showing at least one distinct nucleolus, you can also see a nuclear pore on the right; it is not a cell as the rER are clearly present)

2)https://www.biomedia.cellbiology.ubc.ca/cellbiol/user/scripts/qry_media_id.php?media_id=152 (electron micrograph of labelled nucleus and other organelles)

3) http://www.etap.org/demo/grade7_science/Image32.gif (a labelled diagram showing how the outer membrane of the nucleus continues to becomes the membrane of ER)

4)http://kentsimmons.uwinnipeg.ca/cm1504/nucleus.htm (nice drawing; scroll down to view other organelles)

Mitochondrion

1)http://microbewiki.kenyon.edu/index.php/File:Mito_pic_diagram.gif (nice electron micrograph and drawing)

(nice picture of drawing and electron micrograph)

2)http://www.bmb.leeds.ac.uk/illingworth/dance/mito.gif (nice labelled electron micrograph)

3)http://kvhs.nbed.nb.ca/gallant/biology/mitochondrion.jpg (note that circular DNA and 70S ribosomes are found in the matrix!)

Chloroplast

1)http://www.agri.huji.ac.il/~zacha/images/chloroplast.jpg (v clear and labelled electron micrograph)

2)http://media.photobucket.com/image/chloroplast+/akucic_biology/chloroplast.jpg

(close up of characteristic feature - grana linked by intergranal lamellae)

3)http://www.biology.iupui.edu/biocourses/N100/images/ch9chloroplast.jpg (remember that chloroplasts are organelles in plant cells!)

4) http://www.biology-innovation.co.uk/pages/plant-biology-ecology/photosynthesis/

(a simple drawing but that site has a nice overview of the light and dark rx and animation)

http://year12biologyatsmc.wikispaces.com/Chloroplast

(chloroplasts in a plant specimen slide seen under a light microscope)

Rough and smooth endoplasmic reticulum

1) http://www.tutorvista.com/content/biology/biology-iii/cell-organization/membranous-cell-organelles.php#smooth-endoplasmic-reticulum

(a nice picture showing the characteristic numerous sac-like structures of sER; scroll down to view rER - note the difference!)

2) http://www.cytochemistry.net/cell-biology/ser.htm

(beautiful electron micrograph showing sER, rER and mitochondrion; by now you should be able to recognize the diff organelles!)

3)http://www.visualphotos.com/image/1x8466949/smooth_endoplasmic_reticulum_tem (a nice electron micrograph of sER beside a mitochondrion)

4) http://kentsimmons.uwinnipeg.ca/cm1504/nucleus.htm

(scroll down - close up of rER and sER next to each other)

Golgi body (or apparatus)

1)http://www.google.com.sg/imgres?q=golgi+body&um=1&hl=en&tbm=isch&tbnid=HXxFrPH2ehvSPM:&imgrefurl=http://herricks.org/webpages/sglasser/resources.cfm%3Fsubpage%3D7140&docid=07_zhmab89m0eM&w=350&h=233&ei=zPxyTqycGc6JrAezz-2zCg&zoom=1&iact=hc&vpx=519&vpy=86&dur=2157&hovh=183&hovw=275&tx=178&ty=130&page=7&tbnh=165&tbnw=220&start=48&ndsp=8&ved=1t:429,r:2,s:48&biw=1024&bih=571

(electron micrograph of the characteristic GA; view the site once for other organelles)
2) http://www.cytochemistry.net/cell-biology/golgi.htm (drawing showing cis face of GA receiving vesicles pinched off from ER)

3)http://kentsimmons.uwinnipeg.ca/cm1504/nucleus.htm (scroll down to see Golgi apparatus)

4) http://creationrevolution.com/2010/11/golgi-apparatus-steel-industry-of-the-simple-cell-%E2%80%93-part-6/ (shows the transport of a secretory protein from the rER to the Golgi body and secretion out of cell via exocytosis - good for revising the membrane system)

5) http://www.cytochemistry.net/cell-biology/golgi.htm

(nice drawing showing the fusion of vesicles to cis face and the forming of vesicles from the trans face of GA)

Lysosome

1)http://www.google.com.sg/imgres?q=Lysosome&um=1&hl=en&sa=N&tbm=isch&tbnid=zz5hhbHr82ntOM:&imgrefurl=http://www.stolaf.edu/people/giannini/cell/lys.htm&docid=O0i-Gy6I_gpU0M&w=500&h=479&ei=ggJzToXbFoWzrAeElO3WCg&zoom=1&biw=1024&bih=571&iact=rc&dur=328&page=4&tbnh=165&tbnw=172&start=24&ndsp=8&ved=1t:429,r:4,s:24&tx=152&ty=75

(nice electron micrograph of a lysosome breaking down a mitochondrion)

2) http://apbio-werle.wikispaces.com/Cell+and+Cell+Transport+%28Ch+6-7%29 (scroll down to see the lysosome in action - digesting phagocytic vesicle and worn out organelle)
3) http://faculty.une.edu/com/abell/histo/Histolab4a.htm (scroll down to see lysosome; remember lysosome is made from GA)

Ribosome

1)http://bass.bio.uci.edu/~hudel/bs99a/lecture22/index.html (polyribosome / polysome; good to read the info once)

2) http://www.uni-mainz.de/FB/Medizin/Anatomie/workshop/EM/EMRibosomE.html (confusing? just know that ribosomes are so small they appear as dots on electron micrographs)

3)http://kentsimmons.uwinnipeg.ca/cm1504/nucleus.htm (scroll down to view free and bound ribosomes)
4) http://sandwalk.blogspot.com/2007/10/compositon-of-ribosomes.html?showComment=1192732380000

(shows composition of 70S and 80S ribosome; fyi only)

5)http://bass.bio.uci.edu/~hudel/bs99a/lecture21/index.html (polyribosome electron micrograph + diagram)

6)http://micro.magnet.fsu.edu/cells/ribosomes/ribosomes.html

(computer model showing the 3 binding sties of ribosome; good to use it when revising translation!)

Centriole

1) http://mvc.bioweb.dcccd.edu/weblinks/cilia.htm (scroll down to view electron micrograph)

2)http://sciencyscience.tumblr.com/post/130146054/biology-textbook-treasures (note the "centrosome" where centrioles are found; some cells do not have centrioles but spindles can still be formed)

3)http://www.nature.com/nrm/journal/v8/n6/fig_tab/nrm2180_F2.html (shows the duplication of centrioles during interphase)

Others

1) http://www.anatomybox.com/tag/tem/

(nice photo of myelinated neurone and node of Ranvier)

2) http://apbrwww5.apsu.edu/thompsonj/Anatomy%20&%20Physiology/2010/2010%20Exam%20Reviews/Exam%201%20Review/Ch03%20Cell%20Organelles%20&%20Cytoskeleton.htm (great picture of a typical eukaryotic cell with description of various organelles but some organelles are not in the A level syllabus; refer to the syllabus).

Select some of the pictures and use them during your revision. This will help you remember the features of the organelles and processes in other topics! Remember - study smart!

Topic Cell Organelle: Q) Besides the transcription of rRNA genes, what is the other role of nucleolus?

Ans: Nucleolus is also the site where proteins imported from the cytoplasm are assembled with rRNA into the large and small ribosomal subunits. These subunits then exit the nucleus through the nuclear pores to the cytoplasm where they assemble into a ribosome.