BSCI 124 Lecture Notes

Undergraduate Program in Plant Biology, University of Maryland


Part 1: The Cell

    I. Function of the cell
        A. Serves as the structural building block to form tissues and organs
        B. Each cell is functionally independent- it can live on its own under the right
            1. it can define its boundaries and protect itself from external changes causing internal
            2. it can use sugars to derive energy for different processes which keep it alive
            3. it contains all the information required for replicating itself and interacting with other cells
            in order to produce a multicellular organism
            4. It is even possible to reproduce the entire plant from almost any single cell of the plant

    II. Types of cells
        A. Prokaryotic cells- eg. bacteria
            1. very simple-there are no organelles and most everything functions in the cytoplasm
        B. Eukaryotic cells
            1. all contain the organelles that subcompartmentalize the cell
            2. includes unicellular algae and protists (e.g. ameba) that live alone or in colonies
            3. includes multicellular organisms - animals, plants, fungi - where cells work together
                a. plant cells are unlike animal cells in that plant cells have chloroplasts and cell walls.
                Animal cells have neither of these. Plant cells also have relatively large vacuoles.

    III. Parts of the eukaryotic cell and their function- See this fully annotated and useful diagram of a
    plant cell. dissect a cell online
        A. Outside (boundary) of the cell
            1. cell wall
                a. protects and supports cell
                b. made from carbohydrates- cellulose and pectin- polysaccharides
                c. strong but leaky- lets water and chemicals pass through- analogous to a cardboard
            2. cell membrane
                a. membrane is made up from lipids - made from fatty acids
                b. water-repelling nature of fatty acids makes the diglycerides form a sheet or film which
                keeps water from moving past sheet (think of a film of oil on water)
                c. membrane is analogous to a balloon- the spherical sheet wraps around the cell and
                prevents water from the outside from mixing with water on the inside
                d. membrane is not strong, but is water-tight- lets things happen inside the cell that are
                different than what is happening outside the cell and so defines its boundaries. Certain
                gatekeeping proteins in the cell membrane will let things in and out.
        B. Inside the cell
            1. cytosol - watery inside of cell composed of salts, proteins which act as enzymes
            2. microtubules and microfilaments - cables made out of protein which stretch around the
                a. provide structure to the cell, like cables and posts on a suspension bridge
                b. provide a structure for moving cell components around the cell -sort of like a moving
                conveyer belt.- see also this site
            3. organelles - sub-compartments within the cell which provide different functions. Each
            organelle is surrounded by a membrane that makes it separate from the cytosol
                a. nucleus- contains the genetic information which tells the cell machinery which proteins,
                carbohydrates and lipids to make and how they are assembled.
                    i. this genetic information is coded in DNA (deoxyribonucleic acid)
                    ii. the DNA is seen packaged up into Chromatin/chromosomes
                b. mitochondrion - Cell powerhouse. Converts sugars into energy through aerobic
                respiration. (up to 100 per cell)
                c. chloroplast (50-100 per cell) - site of photosynthesis.
                    i. allows production of sugars from sunlight and carbon dioxide
                    ii. only found in plants and algae- other cells have to find sugar from outside the cell
                d. vacuole or tonoplast- stores compounds that may interfere with other things in the cell.
                Dominates the inside of a plant cell.
                    i. sugars, salts, pigments (e.g. red pigment in beets and purple onions, acids (lemon
                e. ribosomes - site of protein synthesis- see also this site
                    i. many different proteins have to be made by the cell- the proteins that a cell makes
                    directs the cell's function and identity
                    ii. ribosomes use the information coded in the DNA of the nucleus to produce
                f. endoplasmic reticulum (ER) - a network of folded membranes throughout the cytoplasm
                    i. rough ER has attached ribosomes, active in protein synthesis
                    ii. smooth ER lacks ribosomes and functions in the transport and packaging of proteins
                    as well as the synthesis of lipids
                g. golgi apparatus - membranous hollow sacs arranged in a stack
                    i. modifies proteins, lipids, and other substances from the ER
                    ii. packets of these materials move to the edge of the golgi where the golgi membrane
                    is pinched off to make vesicle (package); this new vesicle moves to the plasma
                    membrane where it leaves the cell, or it goes to other sites within the cell
                    iii. builds primary cell walls between newly divided nuclei

Part 2: What is a cell made from?

Four groups of biologically important molecules: lipids, carbohydrates, nucleic acids, proteins

    I. Lipids
        A. Composed of Carbon, Oxygen, Hydrogen atoms (COH) in building blocks of Fatty acids (see different fatty acids here)
        B. Fats (solid) and oils (liquid at room temperature)
            1. fats associated with animals - butter, lard
            2. oils associated with plants - corn oil, olive oil
        C. Main characteristic of lipids - won't dissolve in water and is repelled from water (e.g. Corn
        oil in water- the oil droplets separate from the water and float to the top to try and avoid the
        water) and form self-associating packages to exclude water.  A membrane is one such
        self-associating structure.
        D. Roles of lipids
            1. food- high energy (many C-H bonds), has more energy than any other molecule
            2. part of cell membranes
            3. also- waxes (cutin, suberin), hormones (testosterone, estrogen), certain vitamins, certain
            pigments (chlorophyll)
            4. basic form for energy storage- monoglycerides, diglycerides, triglycerides
                a. glycerol + 1 fatty acid -> monoglyceride + water (ex- butyric acid w/4C; 14-20 C
                most common)
                b. monoglyceride + 2nd fatty acid -> diglyceride
                c. diglyceride + 3rd fatty acid -> triglyceride

    II. Carbohydrates
        A. Composed of COH
            -makes building blocks of monosaccharides (see different structures here)
        B. Roles
            1. energy storage (many C-H bonds) - sugar/starch energy source
            2. structural (especially in plants- cellulose)
                Note: most important structural component in animals - protein
            3. carbon sources for making other building blocks (such as ribose and deoxyribose for
            nucleic acids, amino acids)
        C. 3 main types
            1. monosaccharides
                a. simple sugars
                    i. example- glucose C6H12O6, energy storage - blood sugar very different structure
                    ii. example- fructose C6H12O6, energy storage - fruit sugar
                    iii. example- ribose C5H10O5, nucleic acids
            2. disaccharides
                a. example- sucrose (transport form for plants)
                        Glucose + Fructose -> Sucrose + Water
                b. C12H22O11
                c. sugar cane, sugar beet --> sucrose (table sugar)
            3. polysaccharides (poly = many)
                a. polymers- composed of repeating subunits of monosaccharides -
                b. eg. all these are repeating units of glucose
                    i. starch-energy storage (plants store glucose in a compact, insoluble form)
                    ii. cellulose- cell walls in plants- component of cardboard
                    iii. glycogen- energy storage in animals

    III. Nucleic acids- DNA (deoxyribonucleic acid; master information carrying molecule for the
    cell), RNA (ribonucleic acid; Copy of DNA molecule)
        A. Function- Contains the information for entire cell-expressed through protein
        B. Polymers of nucleotides- composed of:
            1. base- organic molecule with nitrogen- cytosine, guanine, thymine, adenine, and uracil
            (uracil is in RNA only)
            2. sugar- ribose, deoxyribose
            3. phosphate
        C. Shape of DNA molecule- double helix (DNA
        D. Other important nucleotide compounds- example- ATP (universal in organisms; role-
        energy transfer or exchange)
            1. Recall ATP <->ADP + P + energy

    IV. Proteins
        A. Composed of COH and Nitrogen (four main elements) -building block is amino acids (20 different) (see structures here)
        B. Large molecular weight (10,000 - 1,000,000) - note: hydrogen atom = 1
        C. Roles
            1. basic building blocks of cell - much of cell structure
            2. part of cell membranes (help control entrance and exit of materials through
            3. important in animal structure: hair, nails, connective tissue (tendons, cartilage),
            4. enzymes- facilitate chemical reactions -see this avi file of enzyme (thin lines) and substrates (thick spheres)
        D. Composed of amino acids
            1. repeating amino acids joined by the peptide bond forms a protein
            2. 20 of them in proteins
            3. 2 functional groups:-NH2 (amino group) & -COOH (acid group)
            4. order of amino acids is important- order determines the 3-dimensional shape of the
            molecule. This is significant because the function follows form: the biological activity of a
            protein depends largely on its 3-dimensional structure.
            Click here to see a folded protein move.

Link to other sites
A beginner's guide to molecular biology: A scary title but really filled with wonderful stuff on cells!
Facts about cells: And other neat stuff
Another summary: But with all of the serious stuff
A solid discussion of organelles, great diagrams The Cell: Excellent review
An imaginary trip through a piece of a cell: In wonderful color as well!
A review of basic chemistry
Introduction to lipids and carbohydrates
Introduction to nucleic acid
CyberDiet (Commercial site)- shows the nutritional content of specific foods

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Last revised:Feb2, 1999, Browning