Cellular Level of Organization Chapter 3 Lecture Notes

1
Cellular Level of OrganizationChapter 3
Lecture Notes

• to accompany
• Anatomy and Physiology From Science to Life
• textbook by
• Gail Jenkins, Christopher Kemnitz, Gerard Tortora

2
Chapter Overview

• 3.1 Principle Parts of a Cell
• 3.2 Plasma Membrane
• 3.3 Transport Across the Membrane
• 3.4 Cytoplasm
• 3.5 Nucleus
• 3.6 Transcription and Translation
• 3.6 Cell Division

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Essential Terms

• cell biology
• study of cellular structure
• plasma membrane
• cell membrane
• transcription
• making RNA from DNA
• translation
• making protein from RNA
• mitosis
• nuclear division

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Introduction

• Cells
• are the basic, living, structural and functional
  units of the body
• are composed of characteristic parts
• the coordinated function of which allows each
  cell type to fulfill a unique biochemical or
  structural role
• Cell structure and function are intimately related

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Concept 3.1Principal Parts of a Cell
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Three Principal Parts of a Cell

• plasma membrane
• separates the inside of cell from outside
• cytoplasm
• all cellular contents between plasma membrane and
  nucleus
• two major components
• cytosol
• organelles
• nucleus
• large organelle that houses the cells DNA

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Figure 3.1
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Concept 3.2 Plasma Membrane
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Plasma Membrane

• surrounds and contains cytoplasm of cell
• fluid mosaic model
• ever-moving sea of fluid lipids with a mosaic of
  many different proteins
• lipids allow passage of hydrophobic substances
• protein channels

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Figure 3.2
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Lipid Bilayer

• bilayer
• bi two
• two back-to-back layers of lipids
• lipids
• three types
• phospholipids (75)
• lipid with phosphate attached
• cholesterol (20)
• steroid with attached hydroxyl group
• glycolipids (5)
• lipid with carbohydrate attached

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Phospholipid Portion

• phospholipids have both polar and nonpolar parts
• phosphate head is polar (hydrophillic)
• lipid tails are nonpolar (hydrophobic)
• lipid tails orient toward one another
• away from water
• phosphate heads orient toward membrane surfaces
• near water

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Cholesterol Portion

• only hydroxyl group is polar
• forms hydrogen bonds with head of phospholipids
  and glycolipids
• majority of molecule is nonpolar
• steroid rings
• hydrocarbon tail
• nonpolar regions fit among fatty acids of
  phospholipids
• away from water

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Glycolipid Portion

• carbohydrate group is hydrophillic
• lipid portion hydrophobic
• appear only in the layer that faces extracellular
  fluid
• one reason two layers are asymmetric

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Membrane Proteins

• Categorized as integral or peripheral
• integral proteins are firmly embedded
• most are transmembrane
• span the entire bilayer
• peripheral proteins are more loosely associated
  with membrane
• with polar heads of membrane lipids
• or with transmembrane proteins
• can be at inner or outer layer

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Glycoproteins

• membrane protein with a carbohydrate group
  attached
• carbohydrate part on extracellular surface only
• part of the surface coating of cells called the
  glycocalyx
• sugar portion of glycolipids and glycoprotein
• acts like molecular signature for cell-to-cell
  recognition
• also enables cell attachment

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Figure 3.2
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Membrane Protein Functions

• Integral proteins
• Ion channels
• transporters
• receptors
• enzymes
• linkers (anchors)
• cell-identity markers
• Peripheral Proteins
• help support plasma membrane
• anchor integral proteins
• participate in mechanical activities of cells

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Figure 3.3 pt 1
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Figure 3.3 pt 2
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Figure 3.3 pt 3
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Figure 3.3 pt 4
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Figure 3.3 pt 5
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Figure 3.3 pt 6
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Membrane Fluidity

• Fluids move
• most membrane lipids and many proteins easily
  rotate and move sideways in bilayer
• do not confuse with flip-flopping sides
• lipids may wander completely around a cell in
  only a few minutes
• fluidity is increased by
• increased number of double bonds in fatty acid
  tails of lipids
• increased amount of cholesterol in membrane

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Figure 2.18
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Membrane Fluidity

• Rigid membrane lacks mobility
• Some fluidity needed for
• interactions of membrane proteins
• movement of membrane components responsible for
• cell movement
• growth
• division
• secretion
• formation of cellular junctions
• But complete fluidity would lack structural
  organization and mechanical abilities

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Membrane Permeability

• permeable
• substances can pass through
• impermeable
• substances cannot pass through
• selectively permeable
• some substances get through while others do not

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Membrane Permeability

• permeablilty of lipid portion
• nonpolar substances can easily pass
• polar, charged, large cannot pass
• only slightly permeable to
• small uncharged polar molecules such as water and
  urea
• as lipids randomly move these molecules are
  thought to sneak through gaps

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Membrane Permeability

• transmembrane proteins
• can act as channels and transporters
• increase permeability
• are very selective with each being specific to
  particular particles
• transport of very large particles discussed in
  3.3

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Gradients Across Membrane

• living cells maintain different concentrations of
  certain substances on each side of membrane
• concentration gradient
• a difference between concentrations on each side
  of membrane
• can be chemical
• can be electric (difference between charges on
  each side of membrane)
• electrochemical gradients
• created by different concentrations of chemicals
  and charges across membrane

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Concept 3.3 Transport Across the Plasma Membrane
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Transport Across Membrane

• essential to the life of cell
• classified active or passive
• passive process require no cellular energy
• examples include diffusion and osmosis
• active processes require cellular energy (ATP)
• substances generally move uphill against
  gradient
• examples include using transporter proteins,
  endocytosis, and exocytosis,

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Diffusion

• random mixing of particles in solution
• substances move down concentration gradient
• particles eventually become evenly distributed
• kinetic energy is driving force
• can occur across a membrane given there is no
  barrier to movement of the substance

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Figure 3.4
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Factors that Influence Diffusion

• steepness of the gradient
• steeper faster
• temperature
• hotter more kinetic energy
• mass of diffusing substance
• larger particles move slower
• surface area
• more area faster diffusion
• diffusion distance
• longer distances slower diffusion

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Diffusion Through Lipid Bilayer

• nonpolar, hydrophobic molecules move freely
  through bilayer
• oxygen, carbon dioxide, nitrogen gases, fatty
  acids, steroids, fat soluble vitamins (A, E, D,
  K), small alcohols, ammonia
• recall that very small charged particles can also
  move
• water and urea
• important for life processes such as nutrient,
  waste, and gas exchange

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Figure 3.5a
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Diffusion Through Ion Channels

• integral transmembrane proteins
• allow passage of
• small inorganic ions too hydrophillic to pass
  lipid portion of bilayer
• specific ions
• generally slower than diffusion across lipid
  portion
• less opportunity
• some channels are gated and open and close in
  regulated processes

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Figure 3.5b
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Osmosis

• passive process
• diffusion of water across a selectively permeable
  membrane
• from high concentration of WATER to lower
  concentration of WATER
• moves toward higher solute concentration

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Osmosis

• Hydrostatic pressure
• force of pressure against membrane
• opposes osmosis forcing water back toward higher
  concentration of water
• Osmotic pressure
• pressure of a solution proportional to
  concentration gradient of solute particles on
  side of membrane with more solutes
• more solutes on opposite side increased osmotic
  pressure

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Figure 3.6
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Tonicity

• Describes relationship of solutions on each side
  of membrane
• hypertonic
• solution with more solutes
• water moves toward
• hypotonic
• solution with less solutes
• water moves away from
• isotonic
• both solutions have similar concentrations of
  solutes

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Figure 3.7
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Transporter Proteins

• Facilitated Diffusion
• solute binds to specific transporter on one side
  of and released on other side
• solutes are too big or too polar or too highly
  charged
• Active Transport
• solutes moving against concentration gradient
• can be driven by ATP use or via energy stored in
  ionic concentration
• Primary Active Transport uses ATP
• sodium potassium pump

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Figure 3.8
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Transporter Proteins

• Secondary Active Transport
• no ATP use needed
• energy stored in ion concentrations used to drive
  other substances across membrane against
  concentrations
• usually sodium or hydrogen ions
• symporters
• both substances move same direction
• antiporters
• each substance moves a different direction

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Figure 3.9
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Transport in Vesicles

• Endocytosis
• receptor mediated
• phagocytosis
• bulk-phase

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Figure 3.10
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Receptor Mediated Endocytosis

• Steps
• binding
• vesicle formation
• uncoating
• fusion with endosome
• recycling of receptors to plasma membrane
• degradation in lysosomes

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Phagocytosis

• only a few body cells are capable
• two main types
• macrophages
• neutrophils
• particle binds to plasma membrane receptor on
  phagocyte
• pseudopods extend and surround particle forming
  phagosome
• phagosome fuses with lysosomes which destroy
  invader

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Figure 3.11a
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Figure 3.11b
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Figure 3.11c
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Bulk-phase Endocytosis

• most body cells carry out process
• especially absorptive cells in intestines and
  kidneys
• also called pinocytosis
• tiny droplets of extracellular fluid taken into
  cell
• no receptor proteins are involved
• lysosomes fuse and degrade particles into smaller
  useable particles

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Figure 3.12
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Exocytosis

• releases materials form a cell
• all cells carry out process
• especially important in
• secretory cells
• release digestive enzymes, hormones, mucus, or
  other secretions
• nerve cells
• release neurotransmitters
• vesicles fuse with plasma membrane and release
  contents into extracellular fluid
• balanced with endocytosis

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Figure 12.17
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Transcytosis

• active process
• vesicles undergo endocytosis followed by
  exocytosis
• occurs most often across endothelial cells that
  line blood vessels
• pregnancy antibodies pass from mother to fetus
  through this process

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Table 3.1 pt 1
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Table 3.1 pt 2
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Table 3.1 pt 3
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Concept 3.4 Cytoplasm
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Cytoplasm

• all cellular contents between plasma membrane and
  nucleus
• two components
• cytosol
• various organelles

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Cytosol

• intracellular fluid
• fluid portion that surrounds organelles
• 55 of total cell volume
• varies in composition and consistancy
• 75-90 water
• 10-25 dissolved and suspended ions, glucose,
  amino acids, fatty acids, proteins, lipids, ATP,
  waste products, and some various aggregations of
  organic molecules

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Figure 3.1
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Cytosol

• intracellular fluid
• fluid portion that surrounds organelles
• 55 of total cell volume
• varies in composition and consistency
• 75-90 water
• 10-25 dissolved and suspended ions, glucose,
  amino acids, fatty acids, proteins, lipids, ATP,
  waste products, and some various aggregations of
  organic molecules

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Organelles

• specialized structures within the cell
• have characteristic shapes
• perform specific functions
• cellular growth
• cellular maintenance
• cellular reproduction
• each organelle has its own set of enzymes
• numbers and types vary in different cells,
  depending on function
• all organelles cooperate to maintain homeostasis

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Organelles

• cytoskeleton
• microfilaments
• intermediate filaments
• microtubules
• centrosome
• two centrioles
• cilia
• flagella
• ribosomes

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Organelles

• endoplasmic reticulum (ER)
• rough ER
• smooth ER
• Golgi complex
• lysosomes
• peroxisomes
• proteosomes
• mitochondria
• nucleus

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Cytoskeleton

• network of protein filaments that extends
  throughout cytosol
• provides structural framework for cell
• determining cell shape
• organizes cellular contents
• aids movement of organelles within cell during
  cell division
• aids movement of whole cells such as phagocytes
• continually reorganizes as changes shape