CELL STRUCTURE AND FUNCTION

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CHAPTER 4

• CELL STRUCTURE AND FUNCTION

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Introduction

• CELL
• Smallest unit of life
• Leeuwenhoek (1632-1723)
• first described cells as animalcules
• Robert Hooke (1635-1703)
• Creator of term cell

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The cell theory -

• Schwann Schleiden (1839)
• all living things contain cells
• all cells come from existing cells

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two cell types - starting point in organism
classification

• prokaryotic cell
• No nucleus
• Bacteria 2 domains
• eukaryotic cell
• true nucleus and membrane bound organelles
• animal cells, plant cells, fungal cells, algae
  and protozoa

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eubacteria - true bacteria

• Unicellular cell wall
• Streptococcus pyogenes
• Clostridium botulinum

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archaea extreme environments

• Examples
• halophiles
• thermococcus

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Similarity Prokaryotes Eukaryotes

• Cell membrane
• Enzymes
• DNA RNA
• Energy molecules
• Cytosol

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Components of cells
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cell wall -

• In plant cells prokaryotes

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CELL MEMBRANE or PLASMA MEMBRANE

• Outer cell boundary of all cells
• Contains proteins and Lipids
• Phospholipid bilayer (2 layers)
• Two ends of phospholipid
• Hydrophilic water soluble
• Hydrophobic water insoluble

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CELL MEMBRANE FUNCTION

• Encloses the cytoplasm
• Transportation of molecules
• Attachment site for other molecules
• Senses stimuli

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MEMBRANE BOUND ORGANELLES

• ENDOPLASMIC RETICULULUM
• Network of folded membranes/canals
• Rough endoplasmic reticulum (RER)
• Ribosomes attached to their membranes
• Protein synthesis
• Smooth endoplasmic reticulum (SER)
• Lipid synthesis

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GOLGI APPARATUS

• Flattened sacs, stacked-membrane bound
• Functions
• Synthesis of phospholipids
• Packaging of materials for transport
• Production of lysosomes

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LYSOSOMES

• Bubbles contain digestive enzymes
• Function
• Destruction of damaged cells (suicide bags)
• Development of organs
• Digestion of food particles, or bacteria

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PEROXISOMES

• Small vesicles produced by the GA
• Contain hydrogen peroxide
• Destroys invading microbes

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VACUOLES

• Food vacuole
• Hold food
• Water vacuole
• Eliminate excess water from cytoplasm
• Plants one central vacuole for food, water,
  minerals and waste storage.

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NUCLEUS

• Only in eukaryotes
• Nuclear membrane has pores
• Nucleoplasm inside nuclear membrane
• Contains DNA, RNA, Protein, etc

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MITOCHONDRION

• Has 2 membranes
• cristae folds in inner membrane
• Site of energy production
• Has its OWN DNA!!

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Fig. 4.14a
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CHLOROPLASTS

• 2 membranes own DNA
• Only in plants algae
• Contains
• Chlorophyll green photosynthetic pigment
• Green thykaloid membranes discs (dinner plates)
• Grana stacked thykaloids (singular granum)
• Stroma space between the grana with no
  chlorophyll

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ORGANELLES with no membranes

• RIBOSOMES
• CENTRIOLES
• CYTOSKELETON
• CILIA AND FLAGELLA
• INCLUSION BODIES
• NUCLEAR COMPONENTS

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NUCLEAR COMPONENTS

• Chromatin
• DNA molecules plus proteins
• Histone proteins in Eukaryotic cells
• Loosely organized DNA
• Chromosomes
• Tightly coiled chromatin
• Short and dense
• Nucleolus
• Site of ribosome manufacture
• Nucleoplasm
• Liquid matrix of the nucleus Water, ribosomes,
  nucleic acids , etc.

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TRANSPORT ACROSS THE CELL MEMBRANE

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DIFFUSION

• Net movement of molecules from areas of high
  concentration to areas where they are low in
  concentration
• high-to-low
• Passive process

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DIFFUSION

• OXYGEN
• Cellular O2
• CARBON DIOXIDE
• Cellular CO2 outside cell

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OSMOSIS

• Diffusion of water from a region of high water
  concentration through a semi-permeable membrane
  to a region of low water concentration
• From a dilute to a concentrated solution
• 90 H20, 10 sugar ? 80 H20, 20 sugar

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Osmosis Osmosis is the net diffusion of water
down its own concentration gradient (to the area
of higher solute concentration).
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OSMOSIS

• 3 different kinds of environments /solutions
• Isotonic
• Hypertonic
• Hypotonic

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ISOTONIC Solution

• Equal solute conc. In cell and solution
• diffusion of water into cell diffusion out of
  cell

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HYPERTONIC SOLUTION

• Has a higher solute conc. than cell
• Water diffuses out of the cell
• cell shrivels or dries

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HYPERTONIC SOLUTION -

• RBCs
• crenation - cell shrivels
• Bacteria
• plasmolysis - cell wall and cell membrane
  separate
• used as a method of food preservation - salty
  foods
• Plants
• central vacuole losses water
• plasmolysis - wilted lettuce

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HYPOTONIC SOLUTION

• Has a lower solute concentration than cell
• Net flow of water into the cell
• Cell swells and possibly explode

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Hypotonic solution

• RBCs
• hemolysis burst
• Plants
• central vacuole gains water
• Cells become turgid turgor pressure crisp lettuce
• Bacteria
• cell wall helps, eventually will burst

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FACILITATED DIFFUSION

• movement of molecules from a region of higher
  concentration to a region of lower concentration
• requiring the assistance of a carrier protein
• passive process
• example glucose

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ACTIVE TRANSPORT

• Movement of molecules across the membrane from
  areas of low conc. to an area of high conc.
• Movement against the conc. gradient
• Requires energy (ATP) a carrier protein
• Movement of Na and K (pumped)
• Na pumped out of the cells
• K pumped into the cell

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ENDOCYTOSIS

• ENDOCYTOSIS
• Bulk passage into the cell
• Includes Phagocytosis and Pinocytosis
• Phagocytosis
• Cell eating of large solids
• E.g. WBC engulf bacteria, viruses

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ENDOCYTOSIS

• PINOCYTOSIS
• Cell drinking of liquids or dissolved materials
• Sacs formed are small vs phagocytosis
• Sacs called vesicles

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EXOCYTOSIS

• Cell secretion reverse of endocytosis
• Important in plants
• For exporting cell wall materials through plasma
  membrane
• In animal cells
• hormone secretion, digestive enzymes, and other
  substances.

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SUMMARY

• Cell is the common unit of life
• Prokaryotic
• Eukaryotic
• True membrane, membrane-bound organelles
• Plants, Animals, Algae, Fungi and Protozoa
• Cell membranes semi-permeable
• Mechanisms of transport
• Simple diffusion, Facilitated diffusion, Osmosis,
  Active Transport
• Endocytosis and exocytosis