Chapter 4

4.1 Cell Theory

• Background

  • 1665 - Cells were first discovered by Robert Hooke using a microscope and observing cells

  • Proposed the cell Theory

    • Mathias Schleiden (1838)

    • Theodor Schwann (1839)

• Cell Theory:

  • All organisms are composed of cells

  • Cells are the smallest living things

  • Cells arise only from Pre-existing cells

  • All cell today represent a continuous line of descent from the first living cells

• Cell Size

  • Due to reliance on diffusion of substances in and out of cell

  • Rate of diffusion

    • Surface area available

    • Temperature

    • Concentration gradient

    • Distance

• Surface Area-to-Volume Ratio

  • Many cells have an advantage to organisms with fewer, larger cells

  • Cell size increase

    • Volume increases much faster than surface area

    • Overcome by being long and narrow (neurons)

• Microscope

  • Resolution: minimum distance two points can be apart and still be distinguished as two separate points

  • Light Microscope

    • Use magnifying lenses with visible light

    • Resolve structures that are 200 nm apart

    • Limit to resolution using light

  • Electron microscope

    • Use beam of electrons

    • Resolve structures that are 0.2 nm apart

    • Transmission electron microscopes transmit electrons through the material

    • Scanning electron microscopes beam electrons onto the specimen surface

• Basic Structural Similarities of Cell

  • Nucleoid or nucleus where DNA is located

    • Cytoplasm

  • Semifluid matrix of organelles and cytosol

  • Ribosomes

    • Synthesize proteins.

  • Plasma membrane

    • Phospholipid bilayer.

4.2 Prokaryotic Cells

• Components

  • Simplest organisms

  • Two domains of prokaryotes

    • Archaea 

    • Bacteria

  • Prokaryotic cells lack a membrane-bound nucleus (both arches and bacteria)

  • DNA is present in the nucleoid

    • Nucleoid - an irregularly-shaped region within the cell of a prokaryote that contains all or most of the genetic material

  • Cell wall outside of plasma membrane\

  • Also have cytoskeleton

  • Have ribosomes

• Cytoskeleton

  • Prokaryotes possess molecules related to actin and tubulin

  • HELP Influence shape of cell wall

  • The strength and shape of cell is still determined by the cell wall

• Bacterial Cell Walls

  • Most bacterial cells are encased by a strong cell wall

  • Composed of peptidoglycan

    • Cell walls of plants, fungi, and most protists different

  • Protect the cell, maintain its shape, and prevent excessive uptake or loss of water

  • Susceptibility of bacteria to antibiotics often depends on the structure of their cell walls

• Archaea

  • Cell Walls

    • Cell walls LACK Peptidoglycan

      • Greater diversity in components

    • Membrane lipid structure helps to distinguish archaea from bacteria

    • Contain saturated hydrocarbons that attach to glycerol at both ends

  • Flagella

    • Tail - may have more than 1

    • Present in some prokaryotic cells

    • May be one or more if present

    • Function: locomotion

      • Rotary motion propels the cell

4.3 Eukaryotic Cells

• Components

  • Possess a membrane-bound nucleus

  • More complex than prokaryotic cells

  • Hallmark is compartmentalization

    • Achieved through membrane-bound organelles and endomembrane system

  • Possess a cytoskeleton for support and to maintain cellular structure

• Animal VS Plant Cell

  • Heterotrophs -

  • Autotrophs - 

  • Similarities

    • Both have plasma membrane

    • Contain most of the same organelles

  • Plant cell (usually not present in eukaryotes)

    • Cell wall (outside of the plasma membrane)

      • Provide structure

      • Made of cellulose

    • Chloroplasts

    • Specialized vacuoles

  • Nucleus

    • Repository of the genetic information

      • It is important that the DNA was enclosed because it is the only things that is passed on

    • Most eukaryotic cells possess a single nucleus

      • Not ALL cells have specfic things; there will always be an exception

    • Nucleolus – region where ribosomal RNA synthesis takes place

      • Central Dogma - 

      • Different between RNA and DNA is the nucleotides

      • It is inside of the nucleus; envelopes by the nuclear envelope

    • Nuclear envelope

      • Two phospholipid bilayers.

      • Nuclear pores – control movement in and out.

        • Made by proteins

    • In eukaryotes, the DNA is divided into multiple linear chromosomes

    • Chromatin is chromosomes plus protein.

      • Can’t be accessed easily

  • Ribosomes

    • Cell’s protein synthesis machinery

      • How you make protein

    • Found in all cell types in all three domains 

      • Archaea, Bacteria, Eukarya

    • Ribosomal RNA (rRNA) - protein complex

    • Protein synthesis also requires messenger RNA (mRNA) and transfer RNA (tRNA)

      • Provides info to what amino acids goes where

    • May be free in cytoplasm or associated with the internal membranes 

    • Large and small subunit

      • Are separate in the cytoplasm but come together towards mRNA to make protein groups

      • Will come and catch mRNA and bring tRNA to slowly build polypeptide chains