Chapter 4 Cell Structure and Function

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Chapter 4 Cell Structure and Function
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Early Scientist

• Robert Hooke first describe the cell
• Small compartments in cells from a cork
• Van Leeuwenhoek developed the first microscope
• Observed several living cells, including sperms

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Cell Theory Scientist

• Schleiden- Botanist proposed that plants are
  made up of cells
• Schwann- zoologist proposed that animals are
  composed of cells.
• Virchow- concluded that cells come from other
  cells

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Cell Theory

• 1- All organisms are composed of one or more
  cells
• 2- Smallest unit having the properties of life
• 3- The continuity of life arises directly from
  the growth and division of single cells

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Cell Size

• atoms --gt DNA --gt virus --gt bacteria
  --gtmitochondria--gt Eukaryotic cells
• Cells must remain small in size due to the ratio
  of surface area and volume
• As the cell increases in size, its surface area
  becomes to small to support its internal
  structures. Oxygen and other important substances
  cannot diffuse fast enough. Cells that get too
  large, may divide.

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Structural Organization of Cells

• Plasma Membrane(GATEKEEPER) separates the cell
  from the environment, permits the flow of
  molecules across the membrane, and contains
  receptors that can affect the cells activities.
• Composed of lipid bilayer
• Very controlled

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Cytoplasm

• It is everything between the plasma membrane and
  nucleus
• This includes organelles, semifluid substance
  (cytosol), and filaments (cytoskeleton)

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Genetic Material

• 1. provides cellular "blueprint" that controls
  the functions of the cell2. In the form of DNA
  (Deoxyribonucleic acid)3. DNA is universal for
  all cells, and all living things - evidence of
  common ancestry4. Chromatin is the complex of
  proteins and DNA, it condenses into chromosomes
  before cell division

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Eukaryotic versus Prokaryotic

• Nucleus
• Membrane bound organelles
• Examples fungi, protist, animal, and plants

• No Nucleus Chromosomes grouped together known as
  a nucleoid
• Smaller than eukaryotes
• Bacteria

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The Nucleus

• --nuclear envelope contains pores for some things
  to enter and exit-- chromatin is DNA and
  proteins, when the cell begins to divide,
  chromatin condenses and forms chromosomes--DNA
  remains in the nucleus, it sends instructions to
  the cytoplasm via messenger RNA--RNA directs the
  synthesis of proteins on ribosome in the
  cytoplasm--Nucleolus assembles ribosome within
  the nucleus, ribosome contain the "tools" to
  construct proteins

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Endoplasmic reticulum (ER)

• Transport System (endoplasm means "within
  cytoplasm", reticulum means "little net"
• --divides cell into compartments--channels
  molecules through the cell's interior, like a
  little highway

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Smooth ER

• Smooth ER
• --mostly contains enzymes that unction in lipid
  synthesis (such as hormones like estrogen and
  testosterone)

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Rough ER

• --has ribosomes which give it its "rough"
  appearance
• --functions in protein synthesis
• --ER transports newly assembled proteins to the
  Golgi Apparatus

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Golgi Appratus

• Delivery System
• --flattened stacks of membranes
• --functions in collection, packaging and
  distribution of molecules made in the cell and
  used elsewhere
• -- front end (cis) faces the ER, and the back end
  (trans) faces the cell membrane
• --unprocessed proteins enter the Golgi apparatus,
  are processed and exit near the cell membrane for
  export
• --the folded stacks are called cisternae

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Jobs of Golgi Appratus

• 1. separates proteins according to their
  destinations2. modifies proteins (adds sugar and
  makes glycoproteins)3. packages materials into
  vesicles which are exported outside the cell

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Lysosome (Lip smacking good)

• --vesicles that are used to digest
• --contain high levels of degrading enzymes (to
  "lyse" means to dissolve)
• --recycle old and worn out cell parts
• --"suicide sac
• --digest other particles taken in by phagocytosis
• --this "food" is stored in food vacuoles, the
  lysosomes fuse with the vacuoles and release
  digestive enzymes
• --found in animal cells

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Ribosomes

• --each is composed of two subunits, one large and
  one small
• --mRNA is "read" by the ribosomes and amino acids
  are assembled into proteins
• --ribosomes are manufactured by the nuceolus
  inside the nucleus

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Mitochondria

• Powerhouse cell furance
• --contains its own DNA, support for Endosymbiosis
  Theory
• --singular is "mitochondrion
• --2 membranes, one smooth outer membrane, and an
  inner membrane folded into layers called cristae
• --Cristae has two compartments the matrix and
  the intermembrane space
• --mitochondria divide before cell division, they
  are not synthesized like other cell parts
• --function to store energy for cell use. Energy
  is stored in the form of ATP - adenosine
  triphosphate

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Mitochondria
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Chloroplast

• --only found in plant cells
• --has its own DNA, like mitochondrion
• --functions to convert light energy to ATP
• --consists of grana, closed compartments that are
  stacked
• --thylakoids are the individual disk shaped
  compartments that make up the grana
• --stroma is the fluid surrounded the thylakoids

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Cytoskeleton

• Cell is not "just a bag in a bubble". Lots of
  internal fibers internal "skeleton". Not rigid
  like bone capable of being assembled, broken
  down in minutes. Allows cell movement, cell
  division, internal motion of compartments.
• Composed of microfilaments and microtubules

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Centrioles

• --usually occur in pairs arranged at right angles
• --assemble microtubules which influence the cell
  shape and movement - part of the cytoskeleton
• --also function in cell division, mitosis
• --only found in animal cells

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Vacuoles

• --in plants the vacuoles are large and
  centralized, storage of water makes the cell
  turgid
• --in animals, they store food, water and other
  substances (much smaller)

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How Do Cells Move?

• Motor Proteins
• Through controlled assembly and disassemby of
  their subunits, microtubules, and microfilaments
  grow or diminish in length, thereby the
  structures attached to them are thereby pushed or
  dragged through the cytoplasm
• Parallel arrays of microfilaments or microtubules
  actively slide past one another to bring about
  contraction, as in muscle
• Microtubules or microfilaments shunt organelles
  from one location to another as in cytoplasmic
  streaming

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Cilia, Flagella, and False Feet

• Flagella are quite long, not usually numerous,
  and found on one-celled protistians, and animal
  sperm cells
• Cilia are shorter and more numerous and can
  provide locomotion for free-living cells may move
  surrounding water and particles if the cilated
  cells is anchored
• Pseudopods false foot temporary lobes that
  project from the cell, used in locomotion and
  food capture

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Cell Surface Specialization

• Eukaryotic Cell Walls
• Cell walls are carbohydrate frameworks for
  mechanical support in bacteria, protistans,
  fungi, and plants
• In growing plant parts, bundles of cellulose
  strands form the primary cell wall (pliable
  enough to allow for enlargement)
• Secondary walls are formed inside the primary
  walls
• 25 is composed of ligin

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Matrixes between animal cells

• The matrix between animal cells includes cell
  secretions and materials drawn from the
  surroundings between cells.
• Example Cartilage consists of scattered cells
• Collagen embedded in a ground substance of
  modified polysaccharide

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Cell Junctions

• In plants tiny channels called plasmodesmata
  cross the adjacent primary walls and connected
  the cytoplasm

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Continue

• Animal cells display three types of junction
• Tight Junctions occur between cells of
  epithelial tissues in which cytoskeletal strands
  of one cells fuse with strands of neighboring
  cells causing an effective seals
• Adhering junctions are like spot welds at the
  plasma membranes of two adjacent cells that need
  to be held together during stretching as in the
  skin and heart.
• Gap Junctions are small, open channels that
  directly link the cytoplasm of adjacent cells

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Cell Communication

• Signals and receptors allow cells to change their
  activities
• Example cell division
• Hormones- stimulators of cell activity

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Prokaryotic Cells

• Before nucleus
• Indicates existence of bacteria before evolution
  of cells with a nucleus bacterial DNA is
  clustered in a distinct region of the cytoplasm
  (nucleoid)

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• Bacteria are some of the smallest and simplest
  cell
• Bacterial flagella project from the membrane and
  permit rapid movement
• Rigid cell wall supports cell and surrounds the
  plasma membrane which regulates transport into
  and out of the cell
• Ribosomes, protein assembly sites, are dispersed
  throughout the cytoplasm