Chapter 4 Organization of the Cell

Recall: Cell Theory: All living things are made up of one or more cells Cells are the basic unit of organization and function in all organisms All cells come from other cells

Cells Maintain Homeostasis Homeostasis - process of maintaining constant internal environment Due to organization and size

Organization Similar in all cells Due to plasma membrane Surrounds cells Selective barrier Cells have internal structures called organelles Important activities

Cell Size Most are microscopic Micrometer (1/1000) of a millimeter Ratio of surface area to volume Upper limit on cell size As the cell increases in size, its surface area becomes too small to support its internal structures. Oxygen and other important substances cannot diffuse fast enough.

Cell Shape Variation in cell shape To increase the ratio of surface area to volume Plant cells often long and thin Microvilli - finger-like projections of the plasma membrane

Microvilli

Cell Size and Shape are Related to Function Examples: Amoeba - can change shape to move Sperm - have flagella Nerve cells - long, thin extensions to transmit messages

Nerve Cells

Prokaryotes vs. Eukaryotes Prokaryotic cells – without nucleus Lacks other membrane-bound organelles Bacteria and Archaea Small Eukaryotic cells – nucleus Organelles All other cells (animals, plants, protists, fungi)

Prokaryotes DNA is located in nuclear area/ nucleoid Plasma membrane Cell walls Flagella Ribosomes RNA and protein

Eukaryotes Cytoplasm – contains fluid (cytosol) and organelles Nucleoplasm – inside nucleus Membrane-bound organelles

Membranes Membranes divide cell into compartments Sites of chemical reactions Enzymes embedded in membranes Part of endomembrane system Organelles connect directly or indirectly ER, nucleus, Golgi complex, lysosomes, vacuoles, plasma membrane Vesicles – membrane-bound transport sacs Carry materials from one organelle to another

Plasma Membrane Surrounds cell Regulates what enters/exits the cell Maintains structure of cell Separates internal structures of cell from outside cell

Cell Wall Prokaryotic cells & Plant cells Support Protection Surrounds plasma membrane

Cell Nucleus Control center of cell Most cells have only one Nuclear Envelope – controls what enters/exits nucleus Nuclear pores – allow materials to pass in/out of nucleus

Cell Nucleus Contains majority of cell’s DNA Genes – segments of DNA that code for proteins Takes form of chromosomes during cell division Not dividing – chromatin (DNA loosely arranged)

Ribosomes Manufacture proteins Composed of RNA and protein Free or attached to ER Assembled in the nucleolus

Endoplasmic Reticulum Network of internal membranes Synthesizes lipids and modifies many proteins Origin of intracellular transport vesicles that carry proteins Smooth – lack ribosomes Rough – ribosomes on outer surface

Rough ER Studded with ribosomes Connect directly ER modifies the proteins with enzymes Proteins transferred to other sites within cell or outside the cell Via transport vesicles

Smooth ER No ribosomes Site of phospholipid, steroid, and fatty acid metabolism Some types of cells have extensive amounts Liver cells – synthesizes/processes cholesterol and other lipids Enzymes that break down toxins such as carcinogens

Golgi Complex Stacks of flattened membranous sacs Cisternae Not all connected Processes, sorts and packages proteins Products are then passed to other organelles or to plasma membrane Manufactures lysosomes (animal cells)

Lysosomes Small sacs of digestive enzymes Break down: Lipids, proteins, carbohydrates, and nucleic acids Cytoplasm Rarely, tissue can be damaged from “leaky” lysosomes

Peroxisomes Contain enzymes, catalase, that split hydrogen peroxide H 2 O 2 is toxic to the cell Most common in cells that synthesize, store, or break down lipids

Vacuoles Large, fluid-filled sacs Mostly in plants, fungi, algae May be up to 90% of the volume of a plant cell

Vacuoles - Functions Store wastes, water, and materials such as sugars and ions Maintain hydrostatic pressure Applies pressure to the cell membrane, causing it to expand and stick close to the cell wall

Vacuoles Unique functions: Contain compounds poisonous to herbivores Food vacuoles – found in protists Fuse with lysosomes so their food can be digested Contractile Vacuoles – also in protists Remove excess water from the cell

Mitochondria Sacs consisting of 2 membranes Membranes form 2 compartments: Intermembrane space – between 2 membranes Matrix – enclosed by inner membrane Inner membrane is folded to form cristae Increase surface area of the inner membrane

Mitochondria Site of most reactions of cellular respiration Transformation of energy originating from glucose or lipids Convert ->ATP Numerous in cells with high energy requirements Ex. Liver cells – more than 1000 in a single cell!

Mitochondria Contains circular molecules of DNA 1% of total DNA Mutations more frequent Mutations linked to certain diseases Ex. Young adult blindness, muscle degeneration

Mitochondria Involved in apoptosis Programmed cell death Inappropriate apoptosis may be involved in cancer, AIDS, and Alzheimer’s Disease Involved in the metamorphosis of amphibians Responsible for human diseases: Tay-Sachs disease – lipid can not be broken down, accumulates in brain cells

Chloroplasts Convert light energy to chemical energy -> Photosynthesis Contain chlorophyll – green pigment that traps light energy for photosynthesis Also contain carotenoids Yellow and orange light-absorbing pigments

Chloroplasts Larger than mitochondria Leaf cell may contain Disc-shaped

Chloroplast Structure Complex system of folded membranes 2 membranes Inner space – stroma Disclike sacs in stroma called thylakoids Arranged in stacks called grana Thylakoid membranes – where chlorophyll is found Thylakoid lumen – third, innermost compartment within chlorplast

Cytoskeleton Eukaryotic cells Dense network of protein fibers Functions: Mechanical support Cell movement Transport of materials within the cell Cell division

Cytoskeleton Made of 3 types of protein filaments: Microtubules Hollow cylinders Cilia and flagella Cell division Microfilaments Intermediate filaments Centrioles – cell division

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