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1. All organisms are composed of cells.
- 2. Cells are the smallest living things.
- 3. Cells arise only from pre-existing cells.
- All cells today represent a continuous line of descent from the first living cells.
- Cell size is limited.
- -As cell size increases, it takes longer for material to diffuse from the cell membrane to the interior of the cell.
- Surface area-to-volume ratio: as a cell increases in size, the volume increases 10x faster than the surface area
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can resolve structures that are 200nm apart.
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can resolve structures that are 0.2nm apart
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All cells have certain structures in common.
- 1. genetic material – in a nucleoid or nucleus
- 2. cytoplasm – a semifluid matrix
- 3. plasma membrane – a phospholipid bilayer
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Prokaryotic cells lack a membrane-bound nucleus.
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Two types of prokaryotes:
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Prokaryotic cells possess
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-genetic material in the nucleoid
- -cytoplasm
- -plasma membrane
- -cell wall
- -ribosomes
- -no membrane-bound organelles
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Prokaryotic cell walls
Bacterial cell walls
Archaean cell walls
-protect the cell and maintain cell shape
- -may be composed of peptidoglycan
- -may be Gram positive or Gram negative
-lack peptidoglycan.
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-present in some prokaryotic cells
- -used for locomotion
- -rotary motion propels the cell
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-possess a membrane-bound nucleus
- -are more complex than prokaryotic cells
- -compartmentalize many cellular functions within organelles and the endomembrane system
- -possess a cytoskeleton for support and to maintain cellular structure
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-stores the genetic material of the cell in the form of multiple, linear chromosomes
- -surrounded by a nuclear envelope composed of 2 phospholipid bilayers
- -in chromosomes – DNA is organized with proteins to form chromatin
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-the site of protein synthesis in the cell
- -composed of ribosomal RNA and proteins
- -found within the cytosol of the cytoplasm and attached to internal membranes
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Endomembrane system
- -a series of membranes throughout the cytoplasm
- -divides cell into compartments where different cellular functions occur
- 1. endoplasmic reticulum
- 2. Golgi apparatus
- 3. lysosomes
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Rough endoplasmic reticulum (RER)
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-membranes that create a network of channels throughout the cytoplasm
- -attachment of ribosomes to the membrane gives a rough appearance
- -synthesis of proteins to be secreted, sent to lysosomes or plasma membrane
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Smooth endoplasmic reticulum (SER)
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-relatively few ribosomes attached
- -functions:
- -synthesis of membrane lipids
- -calcium storage
- -detoxification of foreign substances
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-flattened stacks of interconnected membranes
- -packaging and distribution of materials to different parts of the cell
- -synthesis of cell wall components
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-membrane bound vesicles containing digestive enzymes to break down macromolecules
-destroy cells or foreign matter that the cell has engulfed by phagocytosis
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Microbodies
- -membrane bound vesicles
- -contain enzymes
- -not part of the endomembrane system
- -glyoxysomes in plants contain enzymes for converting fats to carbohydrates
- -peroxisomes contain oxidative enzymes and catalase
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-membrane-bound structures with various functions depending on the cell type
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There are different types of vacuoles:
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-central vacuole in plant cells
- -contractile vacuole of some protists
- -vacuoles for storage
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Mitochondria
- -organelles present in all types of eukaryotic cells
- -contain oxidative metabolism enzymes for transferring the energy within macromolecules to ATP
- -found in all types of eukaryotic cells
- -surrounded by 2 membranes
- -smooth outer membrane
- -folded inner membrane with layers called cristae
- -matrix is within the inner membrane
- -intermembrane space is located between the two membranes-contain their own DNA
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Chloroplasts
- -organelles present in cells of plants and some other eukaryotes
- -contain chlorophyll for photosynthesis
- -surrounded by 2 membranes
- -thylakoids are membranous sacs within the inner membrane
- -grana are stacks of thylakoids
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Endosymbiosis
- -proposal that eukaryotic organelles evolved through a symbiotic relationship
- -one cell engulfed a second cell and a symbiotic relationship developed
- -mitochondria and chloroplasts are thought to have evolved this way
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Mitochondria and chloroplasts:
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-have 2 membranes
- -possess DNA and ribosomes
- -are about the size of a prokaryotic cell
- -divide by a process similar to bacteria
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Cytoskeleton
- -network of protein fibers found in all eukaryotic cells
- -supports the shape of the cell
- -keeps organelles in fixed locations
- -helps move materials within the cell
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Cytoskeleton fibers include
- -actin filaments – responsible for cellular contractions, crawling, "pinching"
- -microtubules – provide organization to the cell and move materials within the cell
- -intermediate filaments – provide structural stability
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Cell movement takes different forms.
- -Crawling is accomplished via actin filaments and the protein myosin.
- -Flagella undulate to move a cell.
- -Cilia can be arranged in rows on the surface of a eukaryotic cell to propel a cell forward.
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The cilia and flagella of eukaryotic cells have a similar structure:
- -9-2 structure: 9 pairs of microtubules surrounded by a 2 central microtubules
- -Cilia are usually more numerous than flagella on a cell.
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Extracellular structures include:
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-cell walls of plants, fungi, some protists
-extracellular matrix surrounding animal cells
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Cell walls
- -present surrounding the cells of plants, fungi, and some protists
- -the carbohydrates present in the cell wall vary depending on the cell type:
- -plant and protist cell walls - cellulose
- -fungal cell walls - chitin
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Extracellular matrix (ECM)
- -surrounds animal cells
- -composed of glycoproteins and fibrous proteins such as collagen
- -may be connected to the cytoplasm via integrin proteins present in the plasma membrane
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