cell structure and function

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Biologists use microscopes and the tools of biochemistry to study cells © 2011 Pearson Education, Inc.

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Microscopy : Use microscopes to visualize cells too small to see with the naked eye Light microscope (LM) - visible light is passed through a specimen and then through glass lenses Lenses refract (bend) the light, so that the image is magnified © 2011 Pearson Education, Inc.


Ocular lens Objective lens Platform/stage w/ slide/specimen Light (diaphragm) Focus


Magnification - the ratio of an object’s image size to its real size Resolution - the measure of the clarity of the image, or the minimum distance of two distinguishable points Contrast - visible differences in parts of the sample © 2011 Pearson Education, Inc.

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2 basic types of electron microscopes (EMs) used to study subcellular structures - by focusing beam of electrons on specimen Scanning electron microscopes (SEMs) - providing images that look 3-D of cell surface Transmission electron microscopes (TEMs) - used mainly to study the internal structure of cells © 2011 Pearson Education, Inc.


Light Micrograph (LM) (living cells) Light micrograph of a protist, Paramecium LM Colorized SEM Scanning Electron (SEM) surface features) Scanning electron micrograph of Paramecium Transmission Electron (TEM) (internal structures) Transmission electron micrograph of Paramecium Colorized TEM Figure 4.1

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Figure 6.2 10 m 1 m 0.1 m 1 cm 1 mm 100  m 10  m 1  m 100 n m 10 n m 1 n m 0.1 n m Atoms Small molecules Lipids Proteins Ribosomes Viruses Smallest bacteria Mitochondrion Most bacteria Nucleus Most plant and animal cells Human egg Frog egg Chicken egg Length of some nerve and muscle cells Human height Unaided eye Light microscopy Electron microscopy Super- resolution microscopy

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Cells: The Fundamental Units of Life All organisms are made of cells The cell is the simplest collection of matter that is alive Cell structure is correlated to cellular function All cells are related by their descent from earlier cells © 2011 Pearson Education, Inc.

Biologists use microscopes and the tools of biochemistry to study cells:

Two types of cells Prokaryotic and Eukaryotic Basic features of all cells ……. Plasma membrane Semifluid substance called cytosol Chromosomes (carry genes) - DNA Ribosomes (make proteins) © 2011 Pearson Education, Inc.

Microscopy: Use microscopes to visualize cells too small to see with the naked eye :

Prokaryotic cell Nucleoid region Organelles Nucleus Colorized TEM • Simpler structure • • • Smaller DNA concentrated in nucleoid region, which is not enclosed by membrane Lacks most organelles • Eukaryotic cell Larger More complex structure Nucleus enclosed by membrane Contains many • • • • types of organelles Eukaryotic cells have internal membranes that compartmentalize their functions

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ENDOPLASMIC RETICULUM (ER) Rough ER Smooth ER Nuclear envelope Nucleolus Chromatin Plasma membrane Ribosomes Golgi apparatus Lysosome Mitochondrion Peroxisome Microvilli Microtubules Intermediate filaments Microfilaments Centrosome CYTOSKELETON: Flagellum NUCLEUS Animal Cell

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NUCLEUS Nuclear envelope Nucleolus Chromatin Golgi apparatus Mitochondrion Peroxisome Plasma membrane Cell wall Wall of adjacent cell Plasmodesmata Chloroplast Microtubules Intermediate filaments Microfilaments CYTOSKELETON Central vacuole Ribosomes Smooth endoplasmic reticulum Rough endoplasmic reticulum Plant Cell

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Hydrophobic region Hydrophilic region selective barrier that allows sufficient passage of oxygen, nutrients, and waste to service the volume of every cell Structure is a Bilayer of phospholipids PLASMA MEMBRANE:

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Plasma membrane NUCLEUS Animal Cell Cytoplasm (cytosol): fluid, gel-like matrix with suspended organelles and cytoskeleton Interior to plasma membrane and outside nucleus

Figure 6.2:

Nucleus: House the DNA Nucleolus Chromatin Nuclear envelope: Nuclear pore Chromatin Close-up of nuclear envelope The DNA and proteins of chromosomes together

Cells: The Fundamental Units of Life:

Ribosomes: Protein Factories © 2011 Pearson Education, Inc. Conduct protein synthesis in two locations In the cytosol ( free ribosomes ) On the surface of endoplasmic reticulum or nuclear envelope ( bound ribosomes )

Two types of cells Prokaryotic and Eukaryotic:

Synthesis of mRNA in the nucleus Nucleus DNA mRNA Cytoplasm mRNA Movement of mRNA into cytoplasm via nuclear pore Ribosome Protein Synthesis of protein in the cytoplasm Figure 4.12-3

Eukaryotic cells have internal membranes that compartmentalize their functions:

In Eukaryotic cells the endomembrane system regulates protein traffic and performs metabolic functions in the cell Components of the endomembrane system Plasma membrane Nuclear envelope Endoplasmic reticulums Golgi apparatus Lysosomes Vacuoles These components are either continuous or connected via transfer by vesicles © 2011 Pearson Education, Inc.

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Smooth ER Rough ER Ribosomes Transport vesicle Transitional ER Nuclear envelope Endoplasmic R eticulum (ER) is continuous with nuclear envelope Rough ER - surface is studded with ribosomes Smooth ER - lacks ribosomes

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Smooth ER Rough ER Ribosomes Transport vesicle Functions of smooth ER ……. Synthesizes lipids Metabolizes carbohydrates Detoxifies drugs and poisons Stores calcium ions Functions of rough ER ………. bound ribosomes secrete glycoproteins (proteins bonded to carbohydrates) Distributes transport vesicles

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Proteins are often modified in the ER. Secretory proteins depart in transport vesicles. Vesicles bud off from the ER. A ribosome links amino acids into a polypeptide. Ribosome Transport vesicle Polypeptide Protein Rough ER Figure 4.14

Cytoplasm (cytosol): fluid, gel-like matrix with suspended organelles and cytoskeleton:

cis face (“receiving” side of Golgi apparatus) Modifies products of the ER Manufactures certain macromolecules Sorts and packages materials into transport vesicles The Golgi Apparatus : Shipping and Receiving Center trans face (“shipping” side of Golgi apparatus)

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Smooth ER Nucleus Rough ER Plasma membrane cis Golgi trans Golgi The endomembrane system is a complex and dynamic player in the cell’s compartmental organization

Ribosomes: Protein Factories:

Digestive enzymes Digestion Food vacuole Lysosome Plasma membrane Phagocytosis Autophagy Peroxisome Vesicle Mitochondrion Lysosome Digestion membranous sac of hydrolytic enzymes hydrolyze proteins, fats, polysaccharides, and nucleic acids Lysosomal enzymes work best in the acidic environment inside the lysosome Lysosomes : digest macromolecules

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Vacuoles : Diverse Maintenance Compartments © 2011 Pearson Education, Inc. Plants may have one or several vacuoles for various storage uses, Central Vacuole is one type Protists use contractile vacuoles for osmoregulation Food vacuole Animal cells form food vacuoles by phagocytosis

In Eukaryotic cells the endomembrane system regulates protein traffic and performs metabolic functions in the cell:

Vacuole filling with water Vacuole contracting TEM Contractile vacuoles of protists pump excess water out of cell

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Central vacuole Cytosol Nucleus Cell wall Chloroplast Central vacuole Central vacuoles in plants hold organic compounds like food, pigments, poisons and water

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Light energy Chloroplast Mitochondrion Chemical energy (food) ATP PHOTOSYNTHESIS CELLULAR RESPIRATION CHLOROPLASTS AND MITOCHONDRIA : ENERGY CONVERSION Cells require a constant energy supply to perform the work of life. Chloroplasts - in plants and algae, perform photosynthesis Mitochondria – in plants and animals , perform cellular respiration

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Ribosomes Stroma Inner and outer membranes Granum Intermembrane space Thylakoid DNA The chloroplast is one of a group of plant organelles, called plastids Chloroplast  use CO 2 and sunlight to do Photosynthesis and synthesize glucose

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Intermembrane space Outer DNA Inner membrane Cristae Matrix Free ribosomes membrane Mitochondria  use organic compounds and Oxygen to do Cellular Respiration and generate ATP Plants and animals both use mitochondria

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Mitochondria and chloroplasts have similarities with bacteria…. Enveloped by a double membrane Contain free ribosomes and circular DNA molecules Grow and reproduce somewhat independently in cells © 2011 Pearson Education, Inc. Evolutionary Origins of Mitochondria and Chloroplasts

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Nucleus Ancestral prokaryote (host cell) Engulfing of oxygen- using nonphotosynthetic prokaryote, which becomes a mitochondrion Mitochondrion Nonphotosynthetic eukaryote Mitochondrion Photosynthetic eukaryote Engulfing of photosynthetic prokaryote Chloroplast Endosymbiosis Theory

Vacuoles: Diverse Maintenance Compartments:

Chloroplast Peroxisome Mitochondrion Break down fatty acids for mitochondria or detoxify alcohol remove H+ and transfer to O 2 produces hydrogen peroxide contains an enzyme to convert toxic H 2 O 2 into water Peroxisomes : still not well understood

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Cytoskeleton : network of fibers that provides structure/support and motiliy and organizes activities in the cell a network of fibers extending throughout the cytoplasm helps to support the cell and maintain its shape

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Figure 6.21 ATP Vesicle Motor protein (ATP powered) Microtubule of cytoskeleton Receptor for motor protein Vesicles Microtubule Interacts with motor proteins to produce motility vesicles and organelles can travel along “monorails” provided by the cytoskeleton


Components of the Cytoskeleton 3 main types of fibers……. Microtubules – thickest, hollow tube Microfilaments (actin filaments) – thinnest, two intertwined strands Intermediate filaments - middle range, fibrous and coiled © 2011 Pearson Education, Inc.

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Tubulin dimer 25 nm   Column of tubulin dimers 10 m Table 6.1a

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10 m Actin subunit 7 nm Table 6.1b

Evolutionary Origins of Mitochondria and Chloroplasts:

5 m Keratin proteins Fibrous subunit (keratins coiled together) 8 12 nm Table 6.1c

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Figure 12.7a Centrosomes (with centriole pairs) Nucleolus Nuclear envelope Mitotic spindle Chromosome, consisting of two sister chromatids Kinetochore Kinetochore microtubule In many cells, microtubules grow out from a centrosome near the nucleus The centrosome is a “microtubule-organizing center” In animal cells, the centrosome has a pair of centrioles

Peroxisomes: still not well understood:

Centrioles Microtubules Microtubules centriole Centrosome each with nine triplets of microtubules arranged in a ring

Cytoskeleton: network of fibers that provides structure/support and motiliy and organizes activities in the cell:

Direction of swimming Direction of organism’s movement Power stroke Recovery stroke Cilia and flagella = locomotor appendages made of microtubules Flagella Cilia

Figure 6.21:

Cross section of motile cilium Microtubule doublet Dynein proteins Central microtubule Cross-linking dynein between microtuble doublets Plasma membrane core of microtubules (9 + 2) sheathed by the plasma membrane ( motor protein) dynein - drives the bending movements Cilia and flagella share a common structure

Components of the Cytoskeleton:

Figure 6.27b Cortex (outer cytoplasm): gel with actin network Inner cytoplasm: sol with actin subunits Extending pseudopodium Pseudopodia (cellular extensions) in amoeba extend and contract through the reversible assembly and contraction of actin subunits into microfilaments

Table 6.1a:

Intermediate filaments….. support cell shape and fix organelles in place © 2011 Pearson Education, Inc.

Table 6.1b:

Extracellular components and connections between cells help coordinate cellular activities materials external to the plasma membrane = extracellular matrix extracellular structures include……… Cell walls of plants The extracellular matrix (ECM) of animal cells Intercellular junctions © 2011 Pearson Education, Inc. Intermediate filaments

Table 6.1c:

Cell Walls of Plants found in plants cells ….. not in animal cells The cell wall protects the plant cell, maintains its shape, and prevents excessive uptake of water Plant cell walls are made of cellulose fibers embedded in other polysaccharides and protein © 2011 Pearson Education, Inc. (Prokaryotes, fungi, and some protists also have cell walls)

Figure 12.7a:

Secondary cell wall Primary cell wall Middle lamella Central vacuole Cytosol Plasma membrane Plant cell walls Plasmodesmata = cytosol connections 1 m channels between adjacent plant cells Cell Walls of Plants

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Figure 6.31 Interior of cell Interior of cell Plasmodesmata Plasma membranes Cell walls channels that perforate plant cell walls water and small solutes, proteins can pass from cell to cell Plasmodesmata in Plant Cells

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EXTRACELLULAR FLUID Collagen Fibronectin Plasma membrane Micro- filaments CYTOPLASM Integrins Proteoglycan complex Polysaccharide molecule Carbo- hydrates Core protein Proteoglycan molecule Proteoglycan complex made of glycoproteins such as collagen , proteoglycans , and fibronectin Extracellular Matrix (ECM) of Animal Cells

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Figure 6.30a EXTRACELLULAR FLUID Collagen Fibronectin Plasma membrane Micro- filaments CYTOPLASM Proteoglycan complex Functions of the ECM….. Support Adhesion Movement Regulation

Figure 6.27b:

Neighboring cells in tissues, organs, and systems …… adhere, interact, and communicate via direct physical contact Intercellular junctions facilitate this contact Types of intercellular junctions………. Plasmodesmata Tight junctions Desmosomes Gap junctions © 2011 Pearson Education, Inc.

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Tight junctions prevent fluid from moving across a layer of cells Extracellular matrix Plasma membranes of adjacent cells Space between cells Ions or small molecules Desmosome Intermediate filaments Tight junction Gap junction Tight junctions membranes of neighboring cells bound together by proteins- seal prevents leakage of extracellular fluid Desmosomes (anchoring junctions) fasten cells together into strong sheets Gap junctions (communicating junctions) provide cytoplasmic channels between adjacent cells Animal Cells:

Extracellular components and connections between cells help coordinate cellular activities:

The Cell is a Living Unit Greater Than the Sum of Its Parts

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