nucleus - structure and function 

cytoplasmic organelles - membrane bound, nonmembrane bound 

extracellular structures - structure and function 
 
In your notes make an outline with these as your headings. 
 

Read the pages indicated by B-6 and study  behavioral objectives 7 and 8. 
 

 
 
 All cells have a nucleus. A few cells are multinucleated (cells making up the hyphae of fungi)  and some cells will lose their nucleus  at maturity (red blood cells). The figure above represents a plant cell with its nucleus. Note the nuclear membrane indicated by "4".  The nuclear membrane is a double membrane which surrounds the nuclear material inside of a nucleus called chromatin indicated by "5". 

Figure:    Eukaryote nucleus 
 

 The nucleus (eukaryote nucleus above) is the control center of the cell. All activities to maintain the cell and to perform a function for a living organism are controlled by the nucleus.  This is accomplished by  the DNA located in the nucleus which directs the syntheses of specific enzymes (protein) which will perform specific chemical reactions. This process will be examined in miniunit Delta. The nucleus also controls cell division.  When a cell is stimulated to divide the DNA  will replicate forming two nuclei which directs the cytoplasm to separate in two parts each containing one of the nuclei. This process will be examined in miniunit Gamma. In your notes draw a figure similar to the one indicated by B-8  and write paragraph describing its function and chemical make up for 
the following structures located in the nucleus of a cell: nuclear membrane (include nuclear pores), chromatin, and nucleoli. Study behavioral objective 15. 
 
 

	Nuclear Membrane	Chromatin	Nucleoli
Chemical Make-up
Function

 

 
1. Identify "A", "D" and "C" above. 

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When the nucleus of a cell prepares to divide the long slender threads of DNA (chromatin) will coil and twist back onto itself to form short thick rod shaped structures called chromosomes. This is a physical process where the DNA which makes up chromatin takes on a rod shape form called chromosomes. Examine the figures on the page indicated by B-8   to compare the differences between chromatin and chromosomes. Compare these figures with the chromatin/chromosome figure below. 
 

Figure: Chromatin Chromosomes 
 

The figure to the lefts shows the DNA molecules in the form of uncoiled, dispersed  chromatin and on the right the DNA  molecules have coiled and condensed to form chromosomes. There are six chromosomes( two short, two medium and two long length). 
 
In your notes draw a cell containing chromatin and a second cell containing chromosomes. 
 
2. Which of the following statements does not pertain to the nuclear membrane. 
     a) made up of two membrane layers 
     b) allows for only specific molecules to pass in  and out of the nucleus 
     c) contains large pores that allow large molecules pass. through 
     d) water tight membrane  which prevents chromatin from coming into contact 
         with the  cytoplasm 
     e) separates the chromatin from the cytoplasm 
 
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3. Which of the following statement does not pertain to the nucleoli? 
     a) consists of RNA which will used to form ribosomes, DNA used to direct the 
         synthesis of  RNA, protein which may form enzymes that control the 
         reactions forming RNA 
     b) separated from the chromatin by a membrane 
     c) appears as tightly condensed nucleic acids and protein 
     d) main function is to synthesize ribosomes 

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 4. Which of the following does not pertain to the chromatin? 

     a) consists of DNA which directs the synthesis of enzymes that in turn carry out 
         reactions to  maintain the cell and protein 
     b) appears as a dark stained mass because the DNA is a tangle of uncoiled 
         DNA molecules 
     c) forms a hollow outer coating which surrounds the nucleoli 
     d) separated from the cytoplasm by a double membrane 

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          Figure: Nuclear membrane. 
 
Note: The nuclear membrane in the figure above consists of a double membrane (inner and outer) and that the pores are coated with  protein. 

5. What is the function of the pore complex above? 
 
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Nonmembrane organelles can be subdivided into ribosomes and organelles consisting of  protein microtubules or protein filaments. 

 Ribosomes, like DNA,  are  present in  all cells. They are located in the cytoplasm of the cell and synthesized in the nucleoli of the nucleus. Each cell contains millions of ribosomes. Ribosomes consists of two subunits consisting of RNA (ribosomal RNA) and protein. Examine the figure of a ribosome indicated by B-7. Draw a ribosome figure in your notes. Ribosomes are the site of protein synthesis during which amino acids are condensed (synthesized into) long polymers. This concept will be explained in miniunit Delta - protein synthesis. Ribosomes  may be found free in the cytoplasm either singly or in groups called polyribosomes. These free ribosomes synthesize protein which will be used within the cell. Other ribosomes are attached to endoplasmic reticulum membranes which 
synthesize proteins that may be transported to different places within the cell or to the outside of a call. Read the pages indicated by B-7 pertaining to ribosomes and write a paragraph comparing the different types of ribosomes, location of ribosomes, and there function. 
 

    Figure: Ribosome  
 

6. The chemical make-up of  the structure above is (are) : 

    a) carbohydrates                             d) protein 
    b) lipids                                          e) both c and d 
    c) RNA 

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7. Which of the following statements is true. 

     a) Ribosomes are the site of RNA synthesis and are synthesized in the 
         chromatin of the  nucleus. 
     B) Ribosomes are the site of protein synthesis and are synthesized in the 
          cytoplasm. 
     C) Ribosomes are the site of protein synthesis and are synthesized in the 
          nucleolus 
     D) Ribosomes are site of lipid synthesis and are synthesized in the nucleolus. 
 

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8.  In a working cell protein synthesis occurs: 

     a) in the nucleus along the outer membrane. 
     b) in the cytoplasm at the ribosome. 
     c) in the nucleus at the nucleoli. 
     d) outside of the cell membrane. 
 
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9.  Ribosomes are: 

       a) free floating 
       b) attached to internal membranes within a cell 
       c) both a and b 
 
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 Read the pages indicated by B-7 pertaining to protein microfilaments and microtubules, study behavioral objective 10 and  write a paragraph comparing the structure and protein types between these two protein particles. 
 
 
Observe the cytoskeleton labeled "F" above. 
 
A cell's cytoskeleton is made up of both microfilaments and microtubules. The cytoskeleton  gives shape and organization it's  cytoplasm. In your notes write a description of a  cytoskeleton explaining how it shapes and organizes the cytoplasm. The cytoskeleton also aids in cell movement, organelle movement and cell division. In your notes draw a cell highlighting the cytoskeleton. 
 
There are several structures in a cell made only of microtubules. Study behavioral objectives  11, 12 and 13. In your notes compare the  microtubular arrangement of the centriole pair, basal bodies, cilia and flagella.  Draw in your notes, figures  representing these four structures and describe their function and location in a working cell. 
 
                          Figure: Centriole pair. 

Centriole pairs consist of microtubules in an arrangement of 9(3) +0. Nine sets of three microtubules with none in the center. (See above)  They are always located near the nucleus and are involved in spindle formation during mitosis and the formation of basal bodies. Examine figure below to locate   in an animal cell (the two solid rod structures near the nucleus). Centrioles are not found in higher plant cells. They are always present in animal cells and protista. 
  Figure: Locate centriole pair . 
 
 

Cilia and flagella are structures which enable cells to move about or cause currents to move over its surface. Flagella are usually found in unicellular organisms (Euglena) or structures (sperm) and enables  them  to move about. Flagella are usually single or present in low numbers. Cilia are present in larger numbers. They are used for locomotion by organisms (paramecium, planarian). They may also beat in a coordinated manner to force liquid currents to flow over the surfaces of  cells. Flagella are longer than cilia. Both cilia and flagella are formed from a basal body lying underneath the cell membrane. The basal bodies were in turned formed by centrioles and migrated to the outer membrane. 
 
Locate the flagella and basal body. 

The whip like tail is the flagella. It is long and flexible. The red structure beneath the cell membrane is the basal body. 
 
 

These microtubular structures have characteristic  microtubular arrangements. Read the pages and study the figures indicated by B-7 and copy the table below in you notes filling in the correct answers. 
 

                    (9(3) + 2,  9(2) + 2,  9(3) + 0,  9(3) +1) 
 

CELL STRUCTURE	MICROTUBULAR ARRANGEMENT
centriole
basal body
cilia and flagella

 

Learn more concerning the application of these organelles read the pages indicated by B-6 concerning cilia and flagella. 

Identify the following statement as pertaining to: 
         a) centriole    b) basal body    c) cilia       d) flagella   e) both c and d 

10.   Structure with 9 + 2 microtubular arrangement 

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 Identify the following statement as pertaining to: 
         a) centriole    b) basal body    c) cilia       d) flagella   e) both c and d 
 
11.  Structure with 9 + 0 microtubular arrangement . 
 
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 Identify the following statement as pertaining to: 
         a) centriole    b) basal body    c) cilia       d) flagella   e) both c and d 
 
12.  Structure with 9 + 1 microtubular arrangement 
 

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 Identify the following statement as pertaining to: 
         a) centriole    b) basal body    c) cilia       d) flagella   e) both c and d 
 
13. Found in pairs (barrel-shaped ring of microtubules)  near the nucleus of animal cells (E - below). 
 
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Identify the following statement as pertaining to: 
         a) centriole    b) basal body    c) cilia       d) flagella   e) both c and d 
 

14. Anchored beneath the plasma membrane and give rise to the microtubules of 
      the cilia or flagella. 

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 Identify the following statement as pertaining to: 
         a) centriole    b) basal body    c) cilia       d) flagella   e) both c and d 
 
15. Used by single cell organism to move about. These structures are long and 
      move in a wavelike motion. 

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 Identify the following statement as pertaining to: 
         a) centriole    b) basal body    c) cilia       d) flagella   e) both c and d 
 
16. Used by a single cell organism to move about. These structures are short and 
      move back and forth similar to oars on a boat. 
 
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 Identify the following statement as pertaining to: 
         a) centriole    b) basal body    c) cilia       d) flagella   e) both c and d 
 
17. These structures may multiply and move to the underside of the plasma 
      membrane forming basal bodies. 
 
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 18.  Which of the following structures is made up of unit membrane? 

   a) mitochondria                    d) basal bodies 
   b) ribosomes                        e) flagella 
   c) centrioles 

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This is the end of the third lesson. Click here to go back to the home page and the fourth lesson Cell Organelles - Membrane Bound.    click 
 
 
 
 
 
 
 
 
 
 
 
 
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