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Cytology & Cell Facts Concepts Insights Questions Answers

© Donald Reinhardt,2011
 
 Cytology is the study of  the structures and functions of cells. Cells can be viewed and photographed while alive, or cells may be fixed, stained, sectioned or even broken open and analyzed and studied in many different ways. 

The Universal Code of Life for All Prokaryotes and Eukaryotes

From the smallest of bacteria to mammals, prokaryote and eukaryote cells work similarly:

DNA —> RNA (mRNA, tRNA, rRNA) —> Proteins.

DNA makes three types of RNA and these RNA molecules then help to produce proteins such as enzymes. Enzymes are protein catalysts which generate chemical energy and enzymes are involved in the production of other cell biochemicals such as other proteins, lipoproteins, polysaccharides.

 

 

 
The nucleus of a cell contains the DNA which is the full code and instructions for each cell. The DNA is arranged in discrete sequences of DNA with a beginning and an end. Each specific and different DNA code in a cell is called a gene. The gene code specifies a unique messenger RNA (m-RNA) which migrates from the DNA to the cytoplasm and attaches to organelles termed ribosomes (rRNA + ribosomal protein). Next, by a series of enzymatic reactions and tRNAs that carry amino acids, this m-RNA directs the instructions for a protein to be made.
Escherichia coli 
is a very simple bacterium and each small bacterium contains about 1,000 genes inside that prokaryote nucleus (nucleoid). Each human, eukaryotic cell has about 25,000 genes and each gene carries information for one, specific product. All genes are not turned on or working at the same time. In any living cell, some genes are turned on and some are turned off depending upon the needs of that cells.

The universal code of life carries us to the next question: what are the minimum requirements for a functional cell?

Cell Essentials and Basics: Parts and Features of Cells

All cells
 are structured as follows:

  • Cell membrane (plasmalemma) is the phospholipid diffusion barrier with selective permeability.
  • Nucleic acids are DNA and RNA (3 types of RNA: messenger (mRNA), transfer(tRNA), ribosomal (rRNA).
  • Ribosomes are organelles for protein synthesis. Ribosomes are chemical complexes of rRNA and protein.
  • Enzymes are protein catalysts that speed up chemical reactions and change molecules. Enzymes of different kinds are found in the cell membrane, cytoplasm and nucleus.
  • Cytoplasm or protoplasm is the "plasma"  of the cell which is bounded by the plasmalemma (cell membrane) and plasma forms an internal sol-gel mix of proteins with abundant water and dissolved and suspended compounds, ions.


Cell Biology of Eukaryotes and Prokaryotes Compared

All cells, in summary, use the universal code of life and contain common cell parts. Eukaryotes and prokaryotes differ from each other based on generally larger size and the greater complexity of eukaryotes when compared to the simplicity of prokaryotes. Prokaryotes are simpler cells when analyzed and compared to eukaryotes. Simple, prokaryotic cells (prokaryotes) are successful cells. Bacteria which are prokaryotic cells are very abundant and common. Therefore, prokaryotes such as Escherichia coli grow, survive and multiply very well despite their simple and basic structure. Eukaryotes such as human cells, although larger and more complicated, grow and survive well also.

Eukaryote organelles and functions of organelles:

Double-membraned organelles of eukaryotes:

  • Nucleus contains DNA and RNA and has a nuclear membrane with pores. Prokaryotic DNA lacks a membrane. DNA and m-RNA contain the code and instruction sheet, respectively, for protein manufacture.
  • Mitochondria (sing. mitochondrion) are oxidative organelles with distinctive cristae (folded inner membranes). Mitochondria contain Kreb's cycle enzymes and produce much ATP by oxidative phosphorylation.
  • Chloroplasts are found in plants, have stacked, thylakoid disks (grana) with chlorophyll a and b. Photosynthesis captures light energy, produces ATP and uses CO2 and H2O, to produce sugar and oxygen.


Single-Membrane Organelles:


  • Endoplasmic Reticulum (ER) is a folded membrane system in the cytoplasm and the site of protein, hormone synthesis. The rough ER has ribosomes attached to the ER membrane and this is an active place for protein synthesis. The smooth ER appears smooth because it has no  attached ribosomes and it is the region where synthesized materials are prepared for export via the Golgi  body or apparatus.
  • Golgi Body is a distinctive membrane system that packages synthesized compounds produced at the endoplasmic reticulum by ribosomes and enzymes, and then transports or exports them via vesicles.
  • Vesicles are membranous packages produced by the Golgi body (e.g., lysosomes, peroxisomes, et al.)
  • Vacuoles are found in plants, contain dissolved sugars, amino acids, calcium oxalate crystals or gas.
  • Leucoplasts are special vacuoles in plants which are storage sites for starch
  • Chromoplasts are vesicles of plants which contain pigment. These pigment-containing vesicles give distinctive colors to flowers.


Other organelles of importance
:

  • Nucleolus is composed of clusters of rRNA and protein within the eukaryotic nucleus. rRNA passes across the nuclear membrane via nuclear pores and into the cytoplasm and to the ER where protein synthesis occurs.
  • Microtubules and microtubular structures are 25 nm diameter. Tubulin proteins are found in eukaryotic flagella, cilia, centrioles, the mitotic spindle apparatus and kinetochores.
  • Flagellum (pl. flagella) and Cilium (pl. cilia) are involved in cell movement. Sperm cells typically move by means of a flagellum. Cilia are also important in the respiratory tract and oviducts of humans. In the respiratory tract cilia move mucus, dust, particulates, allergens, bacteria, viruses upward and outward for expulsion via sneezes and coughs.
  • Centrioles are tubular structures, arranged in pairs, that direct and make possible chromosome movement and separation at mitosis and meiosis.
  • Kinetochores are sites on chromosomes for attachment to the spindle during mitosis and meiosis.
  • Microfilaments are extremely thin (5-7 nm) actin proteins that interact with myosin to form contractile bodies and these are characteristic muscle fibers or muscle filaments.
  • Intermediate filaments are of 8-12 nm diameter and are stabilizing cytoskeletal proteins that strengthen, shape animals cells. Intermediate filaments include: keratins (protein of hair, skin, nails), desmins (cell adhesins), vimentins (membrane support protein and positional proteins), and lamins (fibrous network on inner surface of the nuclear envelope).
  • Kinesin and Dynein are ATP- powered, motor proteins, that move in opposite directions (toward + and - poles, respectively) on the spindle or microtubule. These proteins join and separate as needed by breaking and forming new bonds and as they do this they help push and pull chromosomes. Kinesin and dynein each also are involved in the transport vesicles.

Cells are interesting and wonderful structures to know and understand. A test of your knowledge on cells and cell struture will appear here soon.
 


Animal and Plant Cells and Structures Compared. Photo Credit: rst.gsfc.nasa.gov
 
This article is modified from an original article prepared, published, copyrighted by the author and linked to here.

Source and Reference

Lodish, H. et al. 2000. Molecular Cell Biology. Fourth Ed., W. H. Freeman and Co., New York, N.Y.

All the Written Material within Site is Copyrighted 2011 and Owned by Dr. Donald Reinhardt, and this original material is protected legally by this copyright notice and by the Digital Millennium Act. None of this original material may be copied or reproduced without the expressed written consent of the author. 

The author is a Freelance Science writer, and is available for specific assignments. For those who are interested other questions related to this teaching site should be directed to sciencesuperschool@gmail.com.
 

Important Cell Biology & Cell Questions for Review

Listed are 50 cell questions for thinking and review. Study about the cell and its organelles and functions and then take the test to see what you remembered and what you need to review further. 

Each question contains an important concept or word which relates best to one organelle in the key. Choose the letter or letters of the organelle that best matches the term or concept in the numbered question.

KEY for questions 1 to 15: 
A. ribosome  B. centriole  C. chloroplast  D. nucleus  E. mitochondria  AB. cilia  AC flagellum  AD. Golgi body  AE. vesicle 

1. cristae  
2. granum  
3. thylakoid disks would be found here  
4. the motility structure of sperm  
5. a respiratory tract filament that moves on the surface of a cell  
6. the site of oxidative phosphorylation
7. generates ATP by light-driven reactions
8. involved in the structuring and coordination of the spindle apparatus
9. contains a full set of chromosomes and instructions for a cell's activities
10. responsible for the rough appearance of the endoplamic reticulum
11. characteristically has 70S and 80 S molecular weight characteristics
12. responsible for  the packaging and export of materials to the outside of the cell
13. among all the listed organelles in the key above, these are the only ones that exist as a paired set in the cell
14. able to split water and reduce carbon dioxide
15. a sac-like structure that contains enzymes, hormones or cell-synthesized products

16. to 22. If the structure listed is a single-membraned structure mark A.; if double-membraned, mark B.

16. nuclear membrane
17. vesicle
18. chloroplast
19. endoplasmic reticulum
20. mitochondrion
21. chromoplasts
22. leucoplasts

23. to 27. For these numbered items indicate if the structure noted contains 
A. DNA only  B. RNA only  C. both DNA & RNA are present D. neither DNA or RNA is present in the organelle

23. nucleus
24. ribosome
25. chloroplast
26. mitochondria
27. messenger (m-) and transfer (t-) types of this molecular type are designated

28. to 35. Indicate if the numbered statement is characteristic of:
A. prokaryotes only  B. eukaryotes only  C. common to both pro- and eu- karyotes  D. not present in either cell type

28. presence of a nuclear membrane
29. have mitochondria
30. ribosomes are present in
31. DNA can be detected in
32. protein synthesis occurs in
33. cell membrane is present in
34. can produce cellular energy
35. human cells are characterized as

36. to 42. Indicate whether the structure is A. microfilament type  B. microtubule type  C. intermediate fiber type

36. flagellar protein
37. vimentins
38. actin
39. lamin
39. keratin
40. tubulin protein
41. cilia
42. myosin

43. to 50. Indicate the structure that best fits and matches the numbered term.
KEY: A. kinetochore  B. nucleus  C. nucleolus  D. spindle  E. endoplasmic reticulum

43. The place where three types of RNA are produced.
44. This organelle is used to move chromosomes to opposite poles.
45. Specific site on chromosomes used for attachment and migration purposes.
46. Organelle with a membrane that has actual "pores"
47. Site inside the nucleus rich in rRNA.
48. This organelle is composed of tubulin proteins.
49. that part of the cell that connects to the Golgi apparatus.
50. The instruction manual for the life and activities of the cell resides here.

All the Written Material within Site is Copyrighted 2011 and Owned by Dr. Donald Reinhardt, and this original material is protected legally by this copyright notice and by the Digital Millennium Act. None of this original material may be copied or reproduced without the expressed written consent of the author. 

The author is a Freelance Science writer, and is available for specific assignments for those who are interested – by contacting adminstrator@sciencesuperchool.com. Other questions related to this teaching site should be directed to teacher@sciencesuperschool.com.
 

Cell Biology & Cell Answers to Questions for Review

 
KEY for questions 1 to 15: 
A. ribosome  B. centriole  C. chloroplast  D. nucleus  E. mitochondrium  AB. ciliium  AC flagellum  AD. Golgi body  AE. vesicle 

1. A. Cristae are membrane folds are found in mitochondria.  
2. C. A granum is a stack of thylakoid disks of the choloroplast.  
3. C. The thylakoid disks are chlorophyll-containing membranes of the chloroplast.  
4. AC. A flagellum is the motility structure of sperm.  
5. AB. Cilium is a respiratory tract filament that functions by a sweeping and wavy motion on the surface of a cell.  
6. E. Mitochondrium is the site of oxidative phosphorylation.
7. C. Chloroplast generates ATP by light-driven reactions.
8. B. Centriole is involved in the structuring and coordination of the spindle apparatus.
9. D. The nucleus contains a full set of chromosomes and instructions for a cell's activities.
10. A. Ribosomes are responsible for the rough appearance of the endoplamic reticulum.
11. A. Ribosome characteristically has 70S and 80 S molecular weight characteristics.
12. AD. The Golgi body is responsible for  the packaging and export of materials to the outside of the cell
13. B. Centrioles are the only organelles that exist as a paired set in the cell.
14. C. Chloroplast is able to split water and reduce carbon dioxide.
15. AE. Vesicle is a sac-like structure that contains enzymes, hormones or cell-synthesized products

16. to 22. If the structure listed is a single-membraned structure mark A.; if double-membraned, mark B.

16. B. double-membraned nuclear membrane
17. A. single-membrane vesicle
18. B. double-membraned chloroplast
19. A. single membrane endoplasmic reticulum
20. B. double-membraned mitochondrion
21. A. single-membrane chromoplasts
22. A. single-membrane leucoplasts

23. to 27. For these numbered items indicate if the structure noted contains 
A. DNA only  B. RNA only  C. both DNA & RNA are present D. neither DNA or RNA is present in the organelle

23. C. The eukaryotic nucleus has DNA chromosomes and produces three kinds of RNA which migrates from the nucleus to the cytoplasm.
24. B. The ribosome is an rRNA and protein structure.
25. C. The chloroplast contains both DNA and RNA.
26. C. Mitochondria contain both DNA and RNA.
27. B. RNA only is charactereristic for messenger (m-) and transfer (t-) types of this molecular type are designated

28. to 35. Indicate if the numbered statement is characteristic of:
A. prokaryotes only  B. eukaryotes only  C. common to both pro- and eu- karyotes  D. not present in either cell type

28. B. Eukaryotes alone have nuclear membranes. Prokaryotes do not.
29. B. Eukaryotes have mitochondria.
30. C. Ribosomes are present in both types of cell.
31. C. DNA can be detected in both types of cell.
32. C. Protein synthesis occurs in both cell types.
33. C. Cell membrane is present in both cell types.
34. C. Both cell types can produce cellular energy.
35. B. Human cells are characterized as eukaryotes.

36. to 42. Indicate whether the structure is A. microfilament type  B. microtubule type  C. intermediate fiber type

36. B. Flagellar protein is tubulin.
37. C. Vimentins are intermediate-sized fibers.
38. A. actin is a microfilament. Both actin and myosin are the only 2 microfilaments.
39. C. Lamin is an intermediate filament.
39. C. Keratin is another type of intermediate filament of skin, hair and nails.
40. B. Tubulin protein is found in spindles, flagella. cilia and microtubules.
41. B. Cilia are composed of microtubules.
42. C. Myosin is a microfilament. Myosin and actin are the only two types of microfilaments.

43. to 50. Indicate the structure that best fits and matches the numbered term.
KEY: A. kinetochore  B. nucleus  C. nucleolus  D. spindle  E. endoplasmic reticulum

43. B. Nucleus. The place where three types of RNA are produced.
44. D. Spindle. This organelle is used to move chromosomes to opposite poles.
45. A. Kinetochore. Specific site on chromosomes used for attachment and migration purposes.
46. B. Nucleus. Organelle with a membrane that has actual "pores"
47. C. Nucleolus. Site inside the nucleus rich in rRNA.
48. D, Spindle. This organelle is composed of tubulin proteins.
49. E. Endoplasmic reticulum. That part of the cell that connects to the Golgi apparatus.
50. B. Nucleus. The instruction manual for the life and activities of the cell resides here.

All the Written Material within Site is Copyrighted 2010 and Owned by Dr. Donald Reinhardt, and this original material is protected legally by this copyright notice and by theDigital Millennium Act. None of this original material may be copied or reproduced without the expressed written consent of the author. 

Donald Reinhardt is a Consultant in Medical and Industrial Microbiology and a Freelance Science writer. He is available for specific assignments for those who are interested – by contacting sciencesuperschool@gmail.com. Other questions related to this teaching site should be directed to sciencesuperschool@gmail.com.