Lecture 3A Cell Structure and Function

• Cell


  The basic structural and functional unit of living organisms
• Cell


  • Cells make up living things and carry out activities that keep a living thing alive
• Modern cell theory


  A collection of ideas and conclusions from many different scientists over time that describes cells and how cells operate
• Key ideas of modern cell theory

  • All known living things are made up of one or more cells
  • All living cells arise from preexisting cells by division
  • The cell is the basic unit of structure and function in all living organisms
  • DNA is passed between cells during cell division
  • Cells of all organisms within a similar species are mostly the same
  • Energy flow occurs within cells
• Unicellular organism


  An organism that is made up of only one cell
• Unicellular organisms


  • bacterium
  • amoeba
  • yeast
• Multicellular organism


  An organism that is made up of more than one cell
• Multicellular organisms


  • plants
  • animals
  • insects
• Micrometer


  The unit used to measure the size of a cell, 1 μm = 1/1000 millimeter
• The smallest cell is mycoplasma, size 0.1 μm
• The largest cell is the ostrich egg, size 18 cm
• The smallest human cell is the sperm cell, size 5 μm
• The largest human cell is the ovum cell, size 120 μm
• The longest cell is the nerve cell, size 1 m
• Cell shape


  • Variation depends mainly upon the function of cells
  • Human RBC's are circular and biconcave
  • Nerve cells are branched
  • Human WBC's can change their shape
• Microscopy


  • The detailed structure of a cell has been studied under compound light microscope and electron microscope
  • Certain structures can be seen only under an electron microscope
  • The structure of a cell as seen under an electron microscope is called an ultrastructure
• Compound light microscope magnification is 2000x
• Electron microscope magnification is 500000x
• Structures in an animal cell

  • Nucleus
  • Golgi body
  • Vesicle
  • Plasma membrane
  • Mitochondria
  • Cytoskeleton
  • Centriole
  • Lysosome
  • Cytoplasm
  • Rough endoplasmic reticulum
  • Smooth endoplasmic reticulum
  • Nucleolus
• Structures in a plant cell

  • Nucleus
  • Golgi body
  • Vesicle
  • Plasma membrane
  • Mitochondria
  • Chloroplast
  • Cell wall
  • Vacuole
  • Smooth endoplasmic reticulum
  • Rough endoplasmic reticulum
  • Nucleolus
• Plasma membrane


  Extremely elastic, delicate, thin, living and semi-permeable membrane made up of two layers of lipid molecules in which protein molecules are floating
• Cell wall


  Non-living and outermost covering of a cell (plants & bacteria), can be tough, rigid and sometimes flexible, made up of cellulose, hemicellulose, and protein
• Nucleus


  Dense spherical body located near the center of the cell, well developed in plant and animal cells, not present in bacteria and blue-green algae, most cells are uninucleated (having only one nucleus), few types of cells have more than one nucleus
• Cytoplasm


  Present between the plasma membrane and the nucleus, contains a clear liquid portion called cytosol and various particles, also contains many organelles with distinct structure and function
• Endoplasmic reticulum


  Network of tubular and vesicular structures which are interconnected with one another, two types: smooth (lacks ribosomes) and rough (studded with ribosomes)
• Golgi bodies


  Formed by stacks of 5-8 membranous sacs called cisternae, sacs are usually flattened
• Vacuoles


  Single membrane sac filled with liquor or sap (water, sugar, and ions), in animal cells vacuoles are temporary, small in size and few in number, in plant cells vacuoles are large and more numerous
• Mitochondria


  Small, rod shaped organelles bounded by two membranes, outer membrane is smooth and enclosed the contents of mitochondria, inner membrane is folded in the form of shelf life inward projections called cristae, contain their own DNA which are responsible for many enzymatic actions
• Lysosomes


  Small, spherical, single membrane sac filled with hydrolytic enzymes, occur in most animal cells and in few type of plant cells
• Plastids


  Double membrane-bound organelles found inside plants and some algae, responsible for activities related to making and storing food, often contain different types of pigments that can change the colour of the cell
• Chromoplasts


  Plastids that contain pigments like carotene, xanthophyll, lycopene
• Leucoplasts


  Plastids that store food like starch, protein, oil
• Chloroplasts


  Plastids that contain chlorophyll and are responsible for photosynthesis, have two distinct regions - grana and stroma
• Centrosome


  Consists of two structures called centrioles, centrioles are hollow, cylindrical structures made of microtubules
• Cytoskeleton


  Microtubules are hollow tubules made up of protein called tubulin, intermediate filaments are made up of several strands of fibrous proteins wound together, microfilaments are rod-shaped thin filaments made up of protein called actin
• Differences between prokaryotic and eukaryotic cells

  • Nucleus is absent in prokaryotic cells, only one chromosome is present in prokaryotic cells, membrane bound organelles are absent in prokaryotic cells, size ranges from 0.5-5 μm in prokaryotic cells, examples are bacteria and blue-green algae
  • Nucleus is well developed in eukaryotic cells, more than one chromosomes are present in eukaryotic cells, membrane bound organelles are present in eukaryotic cells, size ranges from 5-100 μm in eukaryotic cells, examples are all other organisms
• Differences between animal and plant cells

  • Animal cells are generally small in size, cell wall is absent in animal cells, plastids are absent in animal cells
  • Plant cells are generally large in size, cell wall is present in plant cells, plastids are present in plant cells