physio cell (3) - mt. san antonio college physio lectures... · • sites of protein synthesis •...
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The CellThe CellThe Cell
ByDr. Carmen Rexach
PhysiologyMt San Antonio College
ChocWalk 2006
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Size ranges
0.1nm - 1nm atoms, small molecules
1nm-10nm proteins, lipids
1μm to 10μm nucleus, most bacteria, mitochondria
10μm to 100μm plant and animal cells
1mm to 1cm frog egg
1m - 2m human height
10nm to 100nm viruses, ribosomes
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Prokaryotic vs. eukaryotic
• Prokaryotic• <5μm• simple internal
structure• homogenous cytoplasm• secreted cell wall• some with glycocalyx• single, circular DNA
• Eukaryotic• >10μm• membrane-bound
organelles• cytoplasm: cytosol +
organelles• cytoskeleton• more complex
By definition, all living things are made up of cells.Cells are the structural and functional unit of life.
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eukaryotic prokaryotic
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Human Cells
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Eukaryotic cell structure
• 3 principal parts:– Plasma membrane– Cytoplasm and
organelles– Nucleus
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Organelles
• nucleus• ribosomes• endomembrane system
– ER– Golgi– lysosomes
• mitochondria• peroxisomes
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Nucleus = “control center”
Nuclearpore
Doublemembrane
nucleolusNuclearpore
Nucleoplasm with DNA
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Nucleolus
• Nucleolus– Most prominent structure within nucleus– Contains genes that code for ribosomal RNA
(rRNA)– Site of rRNA transcription and processing– Site of ribosome assembly
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Nuclear envelope• Separates nuclear compartment from
cytoplasm• Provides structural framework for nucleus• Composed of two nuclear membranes
– Outer membrane continuous with endoplasmic reticulum
– Inner membrane unique proteins found only in nucleus
• Nuclear pores– Regulate which molecules enter and leave
nucleus– Important role in regulating gene expression
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Ribosomes
• Sites of protein synthesis
• Composed of protein and rRNA
• Found free in the cytoplasm and associated with endoplasmic reticulum
• Eukaryotic cells contain about 10 million ribosomes each!
Large subunit
Small subunit
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Endomembrane system
• Series of organelles connected by vesicular transport
• Include three structures– Endoplasmic reticulum– Golgi apparatus– lysosomes
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Endomembrane system: Endoplasmic reticulum
• Series of intracellular channels• Two types
– smooth• lipid synthesis• Ca++ storage in muscle cells
– rough• “sprinkled” with ribosomes• proteins processing & sorting
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Endomembrane system: Golgi apparatus
• Stack of flattened sacks• three functions
– protein modification• ex) add carbohydrates to
produce glycoproteins– separation of products based
on function and destination– packaging and shipping
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Golgi apparatus
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Lysosomes• Membrane bound
sacks of digestive enzymes
• Work at low pH• three functions
– breakdown of food particles in the cell
– destroys invaders in phagocytic cells of the immune system
– autophagy
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Mitochondria: the powerhouse
Outer membrane
Inner membrane
matrixcrista
Inner membranousspace
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Peroxisomes• Single membrane vesicles • Contain approximately 50
different enzymes depending on cell
• Produce and degrade hydrogen peroxide, (H2O2) which is toxic to cells– Contain catalase
• Decomposes H2O2 to water and oxygen, or
• Utilizes H2O2 to oxidize other compounds
• Also involved in biosynthesis of certain lipids
• They are not part of the endomembrane system
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The cytoskeleton• Function
– structural support– motility– regulation
• Components – microtubules– microfilaments– intermediate filaments– muscle thick filaments
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Cytoskeletal filaments
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Microtubules
• Structure– hollow tubes
• diameter– 25nm
• Subunits– Composed of α & β tubulin
• function– cell shape– motility– spindle fibers– organelle movement
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Centrosomes
• Region containing the centrioles and the microtubule organizing center (MTOC)
• centrioles– bundles of microtubules
involved in cell division– replicate during S phase
of interphase• MTOC
– origin of the cytoskeleton
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Cilia and flagella• cilia:
– 10-25μm, move parallel to plasma membrane
– moves fluid over the surface– examples
• respiratory epithelium• fallopian tubes
• flagella:– 15-25μm, move perpendicular to
plasma membrane– human sperm is the only flagellated
cell in human body
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Microfilaments• Structure
– two intertwined actin strands• diameter
– 7nm• subunits
– actin• functions
– cell shape & shape changes– muscle contraction– cell motility = pseudopodia– cell division = cleavage furrow
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Intermediate filaments• Structure
– super-coiled fibrous proteins• Diameter
– 8-12nm• subunits
– various proteins of the keratin family• Functions
– Provide mechanical strength to cells and tissues– cell shape– anchorage of nucleus and other organelles– formation of nuclear lamina
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Muscle thick filaments
• Structure– myosin filaments
• Diameter– 15nm
• Function– muscle contraction
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Plasma membrane structure: Fluid Mosaic Model
• Phospholipidbilayer
• Associated protein• Cholesterol
• stronger• more flexibility• less permeable to
polar substances
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Plasma membrane functions
• Isolate cell cytoplasm from external environment
• Regulate exchange of essential substances
• Communicate with other cells• Bear markers that identify cell
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Functions of proteins associated with the plasma
membrane• Transport• enzymatic activity• signal transduction• intercellular joining• cell to cell recognition• attachment of cytoskeleton and
extracellular matrix (ECM)
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Membrane proteins• Integral
– Integral part of membrane structure– Amphipathic– Can move laterally, like phospholipids– Most transmembrane
• Peripheral– Not amphipathic– Predominately located in cytosolic
surface of plasma membrane– Function
• Associated with cytoskeleton• Influence cell shape and motility
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Types of membrane proteins
• Three major categories– transport proteins
• channel proteins• carrier proteins
– receptor proteins• signal transduction• protein channel regulation
– recognition proteins and glycoproteins• antigens
Cytosolic side
Extracellular side
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Fluidity
• Lateral movement = 2μm per second• Flip flops• Unsaturated phospholipids
– kinked tails = enhanced fluidity• Saturated phospholipids
– straight tails = increased viscosity• Cholesterol
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Microvilli• Purpose: to increase the surface area• Examples
– small intestines• increased absorption
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Endocytosis
• Phagocytosis: “cell eating”– only in cells capable of forming pseudopods
• Pinocytosis: “cell drinking”– uptake of smaller molecules and liquids
• Receptor mediated endocytosis– coated pits– binding to receptor triggers endocytosis
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Endocytosis
Exocytosis is the opposite!
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Extracellular matrix: cell surface
• Composition– Fibrous structural and adhesion proteins
embedded in gelatinous polysaccharide ground substance
• Function– Binds cells and tissues together
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Extracellular matrix: cell surface
proteoglycan complex Collagen fiber
PhospholipidbilayerMicrofilaments
(cytoskeleton)integrinfibronectin
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Cell Junctions
tight junction
Intermediatefilaments
desmosomes
Gap junctions
Adjacent cells
Intercellular space
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Cell junctions
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Bullous pemphigoid
disease resulting from defective or absent desmosomes