Overview of the Cellular Basis of Life
Cells and Tissues Cells: Carry out all chemical activities needed to sustain life Cells are the building blocks of all living things Tissues Cells vary in length, e.g. 2 micrometers to over a meter (nerve cells) Cells vary in function Tissues are groups of cells that are similar in structure and function
Anatomy of a Generalized Cell
Anatomy of the Cell Cells are not all the same All cells share general structures All cells have three main regions Nucleus Cytoplasm Plasma membrane Figure 3.1a
The Nucleus
The Nucleus Control center of the cell Contains genetic material, DNA, (genes) for cell reproduction Three regions Nuclear envelope (membrane) Chromatin Nucleolus
Nuclear envelope (membrane) Barrier of the nucleus Consists of a double membrane Where membrane fuses, becomes nuclear pore Contains nuclear pores that allow for exchange of material with the rest of the cell Relatively large pores allows substances to pass freely than elsewhere
Nucleoli Nucleus contains one or more nucleoli Dark staining, round bodies Sites of ribosome assembly Ribosomes migrate into the cytoplasm through nuclear pores into the cytoplasm serve as sites of protein synthesis
Chromatin When the cell is not dividing DNA combined with protein forms loose, bumpy threads called chromatin Scattered throughout the nucleus Condenses to form chromosomes when the cell divides
The Plasma Membrane
Plasma Membrane (Cell Membrane) Barrier for cell contents Plays a dynamic role cellular activities Double phospholipid layer Allows membranes to reseal quickly Hydrophilic (water loving) heads Hydrophobic tails (water hating) Impermeable to most water soluble molecules
Plasma Membrane (Cell Membrane) Proteins scattered in lipid bilayer Specialized functions include: Enzymes Receptors Anchoring the cell to fibers Protein channels Branching sugars Glycoproteins Blood type, receptors, cellto-cell interactions
Plasma Membrane Figure 3.2
Specialization of the Plasma Membrane
Plasma Membrane Specializations Microvilli Finger-like projections that increase surface area for absorption
Plasma Membrane Specializations Membrane junctions (3 types) binds cells together Tight junctions (zipperlike) Impermeable junction (e.g. in sm. Intestine keeps enzymes from bloodstream) Desmosomes (buttonlike) Anchoring junction Keeps cell from being pulled apart (e.g. skin cells)
Plasma Membrane Specializations Membrane junctions (3 types) binds cells together Continued Gap junctions Allows communication between cells (e.g. heart cells) Neighboring cells connected by connexons
Cytoplasm
Cytoplasm Cytoplasm is the material outside the nucleus and inside the plasma membrane
Cytoplasm (factory area) Site of most cellular activities Contains 3 major elements (seen by electron microscope) Cytosol Largely water fluid that suspends organelles Dissolved nutrients & solutes Organelles Metabolic machinery of the cell Little organs that perform functions for the cell
Cytoplasm (factory area) Continued Inclusions Chemical substances specific to the cell type such as stored nutrients e.g. glycogen granules in the liver Pigments in skin & hair Lipid droplets in fat cells Mucus & other secretory products
Cytoplasmic Organelles
Cytoplasmic Organelles Figure 3.4
Cytoplasmic Organelles Mitochondria Change shape continuously Consists of a double membrane Smooth outside, shelflike protrusions called cristae Enzymes inside carry out reactions where oxygen is used to break down food Most energy lost as heat but some is used to form ATP molecules ( Powerhouses of the cell) Metabolically busy cells have hundreds of mitochondria (liver and muscle)
Cytoplasmic Organelles Ribosomes (tiny, bilobed dark bodies) Made of protein and ribosomal RNA (rrna) Sites of protein synthesis Found at two locations Free in the cytoplasm As part of the rough endoplasmic reticulum
Endoplasmic reticulum (ER) fluid filled tubes Mini-circulatory system for cell Carries proteins from one to another part of cell Two types of ER Rough endoplasmic reticulum Studded with ribosomes Synthesizes proteins E.g. pancreas cells producing digestive enzymes to be delivered to sm. intestine See next slide
Rough Endoplasmic Reticulum Ribosome mrna As the protein is synthesized on the ribosome, it migrates into the rough ER cistern. Protein Rough ER In the cistern, the protein folds into its functional shape. Short sugar chains may be attached to the protein (forming a glycoprotein). Transport vesicle buds off The protein is packaged in a tiny membranous sac called a transport vesicle. Protein inside transport vesicle The transport vesicle buds from the rough ER and travels to the Golgi apparatus for further processing or goes directly to the plasma membrane where its contents are secreted. Figure 3.5
Cell Diversity Figure 3.8f
Endoplasmic reticulum (ER) fluid filled tubes Smooth endoplasmic reticulum Functions in lipid metabolism (cholesterol & fat synthesis & breakdown) and detoxification of drugs and pesticides E.g. liver cells and testes that manufacture testosterone
Cell Diversity Figure 3.8d
Golgi apparatus Traffic Director Stack of flattened membranous sacs Modifies and packages proteins sent by the rough ER via transport vesicles As the sac swells with proteins it pinches off to form Secretory vesicles 3 pathways: Vesicles fuse with plasma membrane, it ruptures, & contents ejected to outside of cell, e.g. mucus & digestive enzymes Vesicles destined to form plasma membrane Vesicles form Lysosomes that contain digestive enzymes to rid cell of worn-out structures or foreign substances
Cisterna Rough ER Proteins in cisterna Membrane Lysosome fuses with ingested substances Transport vesicle Pathway 3 Golgi vesicle containing digestive enzymes becomes a lysosome Golgi apparatus Pathway 1 Golgi vesicle containing proteins to be secreted becomes a secretory vesicle Pathway 2 Secretory vesicles Proteins Secretion by exocytosis Golgi vesicle containing membrane components fuses with the plasma membrane Plasma membrane Extracellular fluid Figure 3.6
Cell Diversity Figure 3.8e
Peroxisomes Membranous sacs of oxidase enzymes Converts free radicals to H 2 O 2 then catalase converts to H 2 O & O 2 Oxidase enzymes contain O 2 to detoxify harmful substances such as alcohol and formaldehyde Replicate by pinching in half, as do mitochondria (NOT formed by Golgi apparatus)
Cytoskeleton cell s bones & muscles Network of protein structures that extend throughout the cytoplasm Provides the cell with an internal framework Figure 3.7a
Cytoplasmic Organelles Cytoskeleton Three different types of elements Microfilaments cell motility/change shape, e.g. muscle cells Intermediate filaments resist pulling forces, e.g.from desmosomes Microtubules determine overall shape of cell Figure 3.7b d
Cell Diversity Figure 3.8c
Cell Diversity Figure 3.8b
Centrioles Rod-shaped bodies made of microtubules lie at right angles to each other Generate microtubules & mitotic spindle during cell division Centrioles make cilia (hair-like projections) & flagella (tail-like projections) Cilia move materials across the cell surface Located in the respiratory system to move mucus Flagella propel the cell The only flagellated cell in the human body is sperm
Cell Diversity Figure 3.8g
Cell Diversity Figure 3.8a
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Cell Physiology Cell Division
Events of Cell Division The cell life cycle is the series of changes a cell goes through from the time it is formed until it divides. The cycle has two major periods: Interphase: the cell grows & carries its usual metabolic activities, longer phase of cycle (metabolic phase) Cell division: the reproduction of itself Function is to produce more cells for growth and repair processes
DNA Replication Function of cell division to produce more cells for growth & repair processes All body cells have the same genetic material DNA molecules duplicate exactly before cell division Genetic material is duplicated and readies a cell for division into two cells Occurs toward the end of interphase DNA uncoils and each side serves as a template Two DNA molecules are formed that are identical to the original: one old one & one newly assembled strand
DNA Replication Figure 3.14
Events Of Cell Division
Cell Division: Consists of 2 events: Mitosis division of the nucleus Results in the formation of two daughter nuclei Cytokinesis division of the cytoplasm Begins when mitosis is near completion Results in the formation of two daughter cells with the same genetic information
Prophase (Remember, due to DNA replication, for a short time the nucleus contains a double dose of genes) First part of cell division Centrioles migrate to the poles to direct assembly of mitotic spindle fibers DNA appears as double-stranded chromosomes Nuclear envelope breaks down and disappears
Metaphase Chromosomes are aligned in the center of the cell on the metaphase plate
Anaphase Chromosomes are pulled apart and toward the opposite ends of the cell Cell begins to elongate
Telophase Chromosomes uncoil to become chromatin Nuclear envelope reforms around chromatin Spindles break down and disappear Cytokinesis Begins during late anaphase and completes during telophase A cleavage furrow forms to pinch the cells into two parts
Stages of Mitosis Cell division takes between 5 minutes-2 hours Two daughter cells exist Each is smaller with less cytoplasm than mother cell, but genetically identical The daughter cells grow & carry out normal cell activities unit it is their turn to divide for body growth in youth & repair body tissue Mitosis gone wild is the basis for tumors & cancers
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