Lecture 4


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Lecture 4

  1. 1. Lecture 4: Cell Theory, Structure and Function Covers 4.1, 4.2, 4.3, 5.1
  2. 2. Cell Theory • Our current understanding of cell theory is the result of hundreds of years of research on animal and plant material. • Three basic tenets:* – Every living organism is made up of one or more cells – The smallest living organisms are single cells and cells are the functional units of multicellular organisms – All cells arise from preexisting cells (and all cells are derived from common ancestors. Ex: we come from 1 cell, but have hair cells, liver cells, heart cells, etc)
  3. 3. mitochondrion cytoplasmic fluid flagellum vesicle ribosomes on rough ER centriole intermediate filaments (cytoskeleton) Golgi apparatus cytoplasm lysosome exocytosis of material from the cell polyribosome nuclear pore basal body nuclear envelope chromatin (DNA) nucleolus nucleus plasma membrane rough endoplasmic reticulum free ribosome smooth endoplasmic reticulum micro- (cytoskeleton) tubules microfilaments Fig. 4-3
  4. 4. Fig. 4-4 central vacuole cytoplasmic fluid plastid vesicle lysosome cytoplasm plasmodesmata cell wall plasma membrane intermediate filaments (cytoskeleton) free ribosome ribosomes nucleus nucleolus nuclear pore chromatin nuclear envelope smooth endoplasmic reticulum rough endoplasmic reticulum Golgi apparatus chloroplast mitochondrion microtubules (cytoskeleton) cell walls of adjoining plant cells
  5. 5. Functions of Cells* • To survive, cells must – Obtain energy and nutrients from environment – Synthesize a variety of proteins and other molecules necessary for growth and repair – Eliminate waste – Reproduce
  6. 6. Common Features* • 1.) Plasma membrane • 2.) All cells contain cytoplasm • 3.) All cells use DNA as hereditary blueprint • 4.) All cells obtain raw materials and energy from their environment
  7. 7. 1.) PLASMA MEMBRANE* • Every cell surrounded by thin, rather fluid membrane called plasma membrane • Proteins in a “sea” of phospholipids • Functions: – Isolates inside of cell from external environment (phospholipids) – Regulates flow of material in and out of cell (proteins in the membrane allow exchange of material) – Allows communication and interaction between cells and with the external environment (proteins in the membrane allow for communication/interaction)
  8. 8. Structure of Plasma Membrane- phospholipids • Called the phospholipid bilayer, this part of the membrane is composed of 2 layers of phospholipids stacked together • Each phospholipid has a polar hydrophilic head and two non-polar, hydrophobic tails • Outside layer has heads pointing to outside of cell with tails facing inside • Inside layer has tails facing out and heads facing in • Hydrophilic heads interact with watery contents inside and outside the cell while hydrophobic tails face each other in the middle of the membrane, keeping water out • Bilayer is fluid; it can move, change shape
  9. 9. head (hydrophilic) tails (hydrophobic) A Phospholipid Fig. 5-2
  10. 10. Phospholipid Bilayer
  11. 11. Structure of Plasma Membrane- proteins • Called the “fluid mosaic” model, proteins exist in a “sea” of phospholipids • They are embedded within the phospholipid layers • There are many types of proteins embedded in the cell membrane
  12. 12. Proteins in plasma membrane •
  13. 13. Types of proteins in plasma membrane* • Receptor proteins: trigger cell response when molecules (from other cells) attach to receptor proteins ex: hormones • Recognition proteins: glycoproteins (protein with sugar component) that are identification tags on the outside of a cell • Transport proteins: allow hydrophilic molecules to move into the cell. TWO TYPES: – Channel proteins: make channels for molecules to move through the protein and into the cell – Carrier proteins: attach to molecules on outside of cell and move them through to the inside
  14. 14. Fig. 5-5 receptor hormone (cytoplasm) (extracellular fluid) A hormone binds to the receptor Hormone binding activates the receptor, changing its shape The activated receptor stimulates a response in the cell 1 2 3
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  16. 16. The whole picture •
  17. 17. Movement of material across plasma membrane • Due to phospholipids, water-soluble substances CANNOT cross the hydrophobic portion of the plasma membrane (salts, amino acids, sugars) • However, very SMALL molecules can cross (water, O2, CO2) • Hydrophobic molecules can cross
  18. 18. 2.) CYTOPLASM • All fluid and structures that lie inside plasma membrane but outside of nucleus • Contains water, salt, and organic molecules (proteins, sugars, lipids, amino acids, nucleotides)
  19. 19. 3.) DNA AS HEREDITARY BLUEPRINT • More in lecture 8 • Each cell stores all of the genetic material needed to make exact copies of itself • During cell division, DNA is copied and a complete copy of that DNA is given to the new cell.
  20. 20. 4.) OBTAIN MATERIALS AND ENERGY FROM ENVIRONMENT • More in lecture 5 • Cells must continually acquire and expend energy to live.
  21. 21. 2 types of cells* • Procaryotic (no nucleus) • Eucaryotic (have a nucleus)
  22. 22. Characteristics of eucaryotic cells* • Larger than procaryotic • Cytoplasm contains many organelles – elaborate system of membranes – membrane enclosed structures that perform specific functions • Contain cytoskeleton (protein fibers that help it maintain its shape) • Some have cell walls • Some have cilia/flagella • Nucleus is control center of cell
  23. 23. CYTOPLASM: MEMBRANE SYSTEMS • Three types of membrane systems create internal compartments housing specialized machinery. This separates different reactions that must occur. Material can be moved between these compartments via vesicles (membrane sacs) – Endoplasmic Reticulum* – Golgi Apparatus* – Lysosomes*
  24. 24. Endoplasmic Reticulum (ER) • Series of interconneted membranes that form sacs and channels in cytoplasm • PROTEINS AND PHOSPHOLIPIDS ARE MADE HERE* • Move through ER structure and are modified (folded into final protein shape, sometimes chemically modified) • Then they accumulate in pockets of ER membrane which bud off as vesicles and are carried to Golgi apparatus
  25. 25. GOLGI APPARATUS • Set of membranes derived from ER • Stack of interconnected sacs • Modify, sort and package proteins made in ER (large proteins cleaved into smaller pieces, carbohydrates added to proteins) • Modified proteins bud off golgi surface and deliver finished products to other parts of cell or to surface to leave cell.
  26. 26. Fig. 4-13 Vesicles merge with the plasma membrane and release antibodies into the extracellular fluid Vesicles fuse with the Golgi apparatus, and carbohydrates are added as the protein passes through the compartments The protein is packaged into vesicles and travels to the Golgi apparatus Antibody protein is synthesized on ribosomes and is transported into channels of the rough ER Completed glycoprotein antibodies are packaged into vesicles on the opposite side of the Golgi apparatus (extracellular fluid) (cytoplasm) vesicles Golgi apparatus forming vesicle 5 4 3 2 1
  27. 27. Lysosomes • Membrane-enclosed vesicles that contain digestive enzymes • Enzymes break food down into small molecules (amino acids, monosaccharides) that can be used by the cell for food • Lysosomes can also digest worn out organelles, recycling the basic components to be re-used
  28. 28. Fig. 4-14 Golgi apparatus digestive enzymes lysosome food vacuoles The Golgi apparatus modifies the enzymes as they pass through its compartments The enzymes are packaged into lysosomes, which bud from the Golgi apparatus food(extracellular fluid) Digestive enzymes are synthesized on ribosomes and travel through the rough ER (cytoplasm) The enzymes are packaged into vesicles and travel to the Golgi apparatus A lysosome fuses with a food vacuole, and the enzymes digest the food 5 4 3 2 1
  29. 29. CYTOPLASM-ORGANELLES • Mitochondria are double-membraned organelles that extract energy from food molecules and package it into ATP, which can be used by the cell. • Mitochondria exist in large numbers in some cells (where lots of energy needed-muscle) and smaller numbers in other cells (cartilage, for instance) – More about production of ATP in Lecture 7 – Chloroplasts are the “mitochondria” of plant cells. More in Lecture 22 • Many other organelles: – Nucleus – Nucleolus – Peroxisome – Ribosome
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  31. 31. CELL WALLS • Some eucaryotic cells have non-living, stiff coatings called cell walls • Support and protect plasma membrane • Ex: single celled marine organisms, plants
  32. 32. Fig. 4-4 central vacuole cytoplasmic fluid plastid vesicle lysosome cytoplasm plasmodesmata cell wall plasma membrane intermediate filaments (cytoskeleton) free ribosome ribosomes nucleus nucleolus nuclear pore chromatin nuclear envelope smooth endoplasmic reticulum rough endoplasmic reticulum Golgi apparatus chloroplast mitochondrion microtubules (cytoskeleton) cell walls of adjoining plant cells
  33. 33. CILIA/FLAGELLA • Extensions of plasma membrane which allow the cell to move • Ex of cilia: fallopian tubes of female mammals, respiratory tract of land mammals • Ex of flagella: sperm
  34. 34. How Cilia and Flagella Move Fig. 4-7 return stroke cilia lining trachea flagellum of human sperm surface of human egg cell (a) Cilium continuous propulsion plasma membrane direction of locomotion power stroke (b) Flagellum propulsion of fluid propulsion of fluid
  35. 35. NUCLEUS-Control Center • More in Lecture 8