Cell Structure Chapter 4. 2 Cell Theory 1.All organisms are composed of cells 2.Cells are the...
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Transcript of Cell Structure Chapter 4. 2 Cell Theory 1.All organisms are composed of cells 2.Cells are the...
Cell StructureChapter 4
2
Cell Theory
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
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Cell size is limited
• Most cells are relatively small due reliance on diffusion of substances in and out of cells
• Rate of diffusion affected by– Surface area available– Temperature– Concentration gradient– Distance
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Surface area-to-volume ratio
• Organism made of many small cells has an advantage over an organism composed of fewer, larger cells
• As a cell’s size increases, its volume increases much more rapidly than its surface area
• Some cells overcome limitation by being long and skinny – like neurons
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What do all cells do?
• Make more cells/DNA
• Make energy
• Make proteins
• Transport materials into and out of cell
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What part of the cell does this?
• Make more cells
• Energy • Proteins
• Transport into and out of cells
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Basic structural similarities
1. Nucleoid or nucleus where DNA is located
2. Cytoplasm– Semifluid matrix of enzymes/organelles – Cytosol
3. Ribosomes– Synthesize proteins
4. Plasma membrane– Phospholipid bilayer
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Prokaryotic Cells
• (Simplest organisms)
• Lack a membrane-bound nucleus– DNA is present in the nucleoid (“cluster”)
• Enzymes
• Do contain ribosomes (not membrane-bound organelles)
• Cell membrane
• Cell wall outside of plasma membrane
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Two Domains of Prokaryotes
• Two domains of prokaryotes– Archaea
• Extremophiles
– Bacteria• “Bacteria”
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Prokaryotic cell walls
• Archaea lack peptidoglycan• Most bacterial cells are encased by a strong cell
wall– composed of peptidoglycan– Cell walls of plants, fungi, and most protists different
• Protect the cell, maintain its shape, and prevent excessive uptake or loss of water
• Susceptibility of bacteria to antibiotics often depends on the structure of their cell walls
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EUKARYOTIC CELLS
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What do all cells do?
• Make more cells/DNA
• Make energy
• Make proteins
• Transport materials into and out of cell
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BUT…
• Now these have specialized membrane-bound organelles!
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Eukaryotic Cells
• Possess a membrane-bound nucleus
• More complex than prokaryotic cells
• Compartmentalization– Achieved through use of membrane-bound
organelles and endomembrane system
• Possess a cytoskeleton for support and to maintain cellular structure
What do all cells do?
• Make more cells/DNA – Nucleus
• Make energy– Mitochondria
• Make proteins – Ribosomes
• Transport materials into and out of cell– SER, RER, Golgi, Cell Membrane
AND other specialized organelles19
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Nucleus
• Repository of the genetic information• Most eukaryotic cells possess a single nucleus• Nucleolus – region where ribosomal RNA
synthesis takes place• Nuclear envelope
– 2 phospholipid bilayers– Nuclear pores – control passage in and out
• In eukaryotes, the DNA is divided into multiple linear chromosomes– Chromatin is chromosomes plus protein
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Ribosomes
• * Ribosomes do NOT have a membrane
• Cell’s protein synthesis machinery
• Found in all cell types in all 3 domains
• Ribosomal RNA (rRNA)-protein complex
• Protein synthesis also requires messenger RNA (mRNA) and transfer RNA (tRNA)
• Ribosomes may be free in cytoplasm or associated with internal membranes
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Endomembrane System
• Series of membranes throughout the cytoplasm
• Divides cell into compartments where different cellular functions occur
• One of the fundamental distinctions between eukaryotes and prokaryotes
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Endoplasmic reticulum
• Rough endoplasmic reticulum (RER)– Attachment of ribosomes to the membrane gives a
rough appearance– Synthesis of proteins to be secreted, sent to
lysosomes or plasma membrane
• Smooth endoplasmic reticulum (SER)– Relatively few bound ribosomes– Variety of functions – synthesis, store Ca2+ ,
detoxification
• Ratio of RER to SER depends on cell’s function
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Golgi apparatus
• Flattened stacks of interconnected membranes (Golgi bodies)
• Functions in packaging and distribution of molecules synthesized at one location and used at another within the cell or even outside of it
• Cis and trans faces
• Vesicles transport molecules to destination
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Lysosomes
• Membrane-bounded digestive vesicles
• Arise from Golgi apparatus
• Enzymes catalyze breakdown of macromolecules
• Destroy cells or foreign matter that the cell has engulfed by phagocytosis
• Involved in apoptosis (cell death)
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Peroxisomes
• Variety of enzyme-bearing, membrane-enclosed vesicles
• Peroxisomes– Contain enzymes
involved in the oxidation of fatty acids
– H2O2 produced as by-product – rendered harmless by catalase
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Vacuoles
• Membrane-bounded structures in plants• Various functions depending on the cell
type
• There are different types of vacuoles:– Central vacuole in plant cells– Contractile vacuole of some protists– Storage vacuoles
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Mitochondria
• Found in all types of eukaryotic cells• Bound by membranes
– Outer membrane– Intermembrane space– Inner membrane has cristae– Matrix
• On the surface of the inner membrane, and also embedded within it, are proteins that carry out oxidative metabolism
• Have 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
• Have their own DNA
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Endosymbiosis
• Proposes that some of today’s eukaryotic organelles evolved by a symbiosis arising between two cells that were each free-living
• One cell, a prokaryote, was engulfed by and became part of another cell, which was the precursor of modern eukaryotes
• Mitochondria and chloroplasts
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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
• Dynamic system – constantly forming and disassembling
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3 types of fibers
• Microfilaments (actin filaments)– Two protein chains loosely twined together– Movements like contraction, crawling, “pinching”
• Microtubules– Largest of the cytoskeletal elements– Dimers of α- and β-tubulin subunits– Facilitate movement of cell and materials within cell
• Intermediate filaments– Between the size of actin filaments and microtubules– Very stable – usually not broken down
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Centrosomes
• Region surrounding centrioles in almost all animal cells
• Microtubule-organizing center– Can nucleate the assembly of microtubules
• Animal cells and most protists have centrioles – pair of organelles
• Plants and fungi lack centrioles
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• Eukaryotic cell walls– Plants, fungi, and
many protists– Different from
prokaryote– Plants and protists
– cellulose– Fungi – chitin– Plants – primary
and secondary cell walls
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Extracellular matrix (ECM)
• Animal cells lack cell walls
• Secrete an elaborate mixture of glycoproteins into the space around them
• Collagen may be abundant
• Form a protective layer over the cell surface
• Integrins link ECM to cell’s cytoskeleton– Influence cell behavior
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Cell-to-cell interactions
• Surface proteins give cells identity– Cells make contact, “read” each other, and
react– Glycolipids – most tissue-specific cell surface
markers– MHC proteins – recognition of “self” and
“nonself” cells by the immune system
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Cell connections
• 3 categories based on function
1.Tight junction– Connect the plasma membranes of adjacent cells in a
sheet – no leakage
2.Anchoring junction– Mechanically attaches cytoskeletons of neighboring
cells (desmosomes)
3.Communicating junction– Chemical or electrical signal passes directly from one
cell to an adjacent one (gap junction, plasmodesmata)
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Cell Movement
Prokaryotes and Eukaryotes can BOTH have flagella and cilia…
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Prokaryotes Eukaryotes
Smaller and Simpler Larger and more complex
Protein flagellin Tubulin (9+ 2 microtubule arrangement)
Rotary Motion Bending movement
Proton driven ATP driven
Prokaryotic Flagella
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Eukaryotic Flagella
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